JP5379580B2 - Dose distribution measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dose distribution measurement device measuring, with high accuracy, the dose distribution by a small number of measurements. <P>SOLUTION: In the dose distribution measurement device for measuring the dose distribution to the depth direction of a particle beam 13 irradiating in a water tank 14, a plurality of sensors 1-10 are disposed around an underwater virtual cylindrical form 11 at the positions with equiangular intervals and equidistant depth, and the measurement points obtained by one measurement are set in accordance with the number of the sensors. The distance between the sensors is kept at a predetermined value or above in the plane vertical to the direction of the irradiation in accordance with the depth of the sensor so that the scattering of the particle beam 13 irradiating along the central axis 12 of the virtual cylindrical form 11 incident to one sensor do not influence the other sensors. When calibrating the sensors, a first dose measurement is performed under a predetermined condition after the sensor group 20 is moved to the same depth, and then a second measurement is performed at the sensor configuration by turning around by 1 interval in the round direction centered around the Z axis 12, and the sensor is calibrated by comparing the two measurement results. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a dose distribution measuring apparatus that measures a dose distribution in water in order to confirm the actual dose distribution of the charged particle beam before treatment with the charged particle beam, and further constitutes the dose distribution measuring apparatus. The present invention relates to a sensor calibration method.

  A conventional dose distribution measurement device consists of a water tank that simulates a patient, an ionization chamber that is a single dose measurement sensor installed in the water tank, and a drive motor that changes the depth position of the ionization chamber in the water tank. Thus, a radiation such as a particle beam is incident on the water surface perpendicularly, and a predetermined three-dimensional dose distribution is formed in the water tank. According to this prior art, the dose distribution in the depth (deep part) direction in water is measured while scanning the position of one ionization chamber. In addition to the ionization chamber, various sensors such as a semiconductor detector, a scintillator detector, and a film are disclosed as sensors for measuring the underwater dose (for example, Patent Document 1).

  In the conventional multi-sensor sensitivity calibration method, a sensor array arranged on a straight line is used for distribution measurement. When calibrating the relative sensitivity of the sensor array, place the sensor array in a predetermined position, measure the output of the sensor array using a predetermined calibration field, and then record it in the next step after the first measurement. Then, the sensor array is moved linearly by one sensor, and the second measurement is performed. Thus, a calibration method is disclosed in which relative sensitivity calibration between sensors is performed based on the first and second measurement results before and after linear movement of the sensor (for example, Patent Document 2).

Japanese Patent No. 3203211 Japanese Patent No. 3317178

  In an irradiation apparatus using a particle beam, a high-dose region can be formed in water over a depth range of up to 30 cm. In a conventional distribution measurement device, for prior verification, the dose distribution in the depth direction of the dose distribution formed by radiation irradiation is measured using a single ionization chamber while scanning the position in the depth direction. It was. Here, when measuring a 30 cm range with a measurement pitch of 2 mm, a maximum of 150 measurement points are required. Therefore, when a conventional distribution measurement device is used, one ionization chamber has a depth. It was necessary to repeat the measurement as many as 150 times with 150 rotations in the direction. For this reason, the time required for distribution measurement may require several tens of minutes, and since the same amount of radiation is irradiated in each measurement, the total amount of radiation required for measurement increases in proportion to the number of irradiations. There was also a problem of end up. Such a problem becomes more conspicuous when the so-called three-dimensional irradiation method in the particle beam irradiation apparatus is used.

  In addition, with a conventional sensor array arranged on a straight line, it is possible to measure a lateral dose distribution in a plane perpendicular to the radiation irradiation direction, such as a particle beam, but the depth in the same direction as the radiation irradiation direction can be measured. When measuring the lateral dose distribution, the presence of the sensor may disturb the original dose distribution. In particular, in the case of an irradiation apparatus using a particle beam, the kinetic energy and direction of the particle beam that has passed through the sensor are greatly affected. Therefore, the sensor array distribution measuring apparatus and its calibration method arranged on a straight line in the prior art cannot be used for measuring the dose distribution in the depth direction with high accuracy in an irradiation apparatus such as a particle beam.

  The present invention has been made to solve the above-described problems, and in a particle beam irradiation apparatus or the like, the dose distribution in the depth direction can be measured in a short time without disturbing the original dose distribution. Another object of the present invention is to provide a dose distribution measuring apparatus capable of measuring with high accuracy, and to provide an efficient calibration method for sensors constituting the dose distribution measuring apparatus.

The dose distribution measuring apparatus according to the present invention includes a plurality of sensors respectively arranged at different heights on the outer periphery of a virtual cylindrical shape extending about an irradiation direction of the radiation, and the plurality of sensors are formed of the virtual cylindrical shape. A first sensor disposed at a different height at a predetermined position outside the outer periphery, and a second sensor disposed at a position where the rotation angle from the predetermined position is a value closest to 180 degrees. The second sensor and the second sensor are arranged at positions farthest in the axial direction, and among the plurality of sensors, the sensors other than the first sensor and the second sensor are different in the axial direction. The spiral is arranged at a height and extends in the clockwise direction from the first sensor toward the second sensor along the axial direction on the outer periphery of the virtual cylindrical shape, and counterclockwise. On another spiral extending in the direction, the sensors are alternately and sequentially arranged so that the relative angle with the first sensor gradually increases, and the plurality of sensors are respectively arranged in a direction perpendicular to the axis. The radiation dose is measured at different positions on the axis, and the number of measurement points corresponding to the number of sensors is obtained by one measurement .

  According to the dose distribution measuring apparatus of the present invention, since the plurality of sensors are arranged around the virtual cylinder having the radiation irradiation direction as an axis, the original radiation dose distribution is not disturbed by the presence of the sensors. In addition, since the dose is measured by a plurality of sensors at different positions on the axis, a plurality of measurement points can be obtained in a single measurement, so that the axial dose distribution in the water tank Can be measured accurately and efficiently.

It is a composition conceptual diagram of the dose distribution measuring device of the depth direction in Embodiment 1 of the present invention. It is the perspective view and virtual cylinder deployment sensor arrangement | positioning figure which show that the some sensor of Embodiment 1 of this invention was arrange | positioned in the shape of two spirals. It is a perspective view which shows arrangement | positioning of the some sensor of Embodiment 1 of this invention. It is a projection top view which shows arrangement | positioning of the some sensor of Embodiment 1 of this invention. It is a figure which shows the scattering state of a particle beam required for description of Embodiment 1 of this invention. It is the perspective view and virtual cylinder deployment sensor arrangement | positioning figure which show that the several sensor of Embodiment 2 of this invention was arrange | positioned at one spiral shape. It is a projection top view of a plurality of sensors of Embodiment 2 of the present invention. It is a structure conceptual diagram containing the sensor moving apparatus and sensor rotation apparatus of Embodiment 3 of this invention.

It is a perspective view which shows sensor calibration arrangement | positioning of Embodiment 3 of this invention. It is principal part sectional drawing which shows the structure of the sensor moving apparatus of Embodiment 3 of this invention. It is a figure which shows the underwater depth dependence of the dose required for description of Embodiment 3 of this invention. It is a figure which shows the underwater depth dependence of the dose required for description of Embodiment 3 of this invention. It is a principal part side view which shows the structure of the dose distribution measuring apparatus containing the sensor moving apparatus of Embodiment 4 of this invention. It is a principal part side view of the dose distribution measuring apparatus at the time of sensor calibration arrangement | positioning of Embodiment 4 of this invention. It is a schematic plan view of the sensor rotation apparatus of Embodiment 4 of this invention. It is a figure which shows the flowchart of the sensor calibration method of Embodiment 5 of this invention.

Embodiment 1 FIG.
Next, the configuration and operation of the dose distribution measuring apparatus according to Embodiment 1 of the present invention will be described with reference to FIGS.
FIG. 1 is a conceptual diagram showing the configuration of a dose distribution measuring apparatus according to the present invention. As shown in FIG. 1, a particle beam 13 is used as radiation for treatment or the like. The particle beam 13 is irradiated downward from the irradiation head (not shown) onto a water tank 14 simulating a human body arranged below the irradiation head. Note that the particle beam 13 is not a completely parallel beam (uniform in the horizontal direction) but a beam that spreads radially (because of emittance> 0).

  In this dose distribution measuring apparatus, a sensor group 20 consisting of a plurality of sensors (dose distribution measuring sensors, including ionization chamber sensors) 1 to 10 is disposed under the water surface 14a in the water tank 14 in which water is stored. The sensors 1 to 10 are arranged at different heights around the virtual cylindrical shape 11 (outside of the outer periphery) around the sensor arrangement center axis (Z axis or center axis) 12 so as to be along the Z axis 12. The dose of the irradiated particle beam 13 can be measured at different positions on the Z-axis 12 only at measurement points corresponding to the number of sensors at a time.

  The sensor group 20 is a first sensor 1 disposed at a predetermined position outside the outer periphery of the virtual cylinder 11 and a second sensor disposed at a position where the rotation angle from the predetermined position is closest to 180 degrees. The first sensor 1 and the second sensor 10 include the sensor 10, and the first sensor 1 is placed on the upper end of the virtual cylinder 11 so that the measurement is performed at a position farthest in the Z-axis 12 direction. The second sensor 10 is disposed at the lower end of the virtual cylinder 11.

  Further, FIG. 2A is a perspective view showing the sensor arrangement, and FIG. 2B is a sensor arrangement diagram when the virtual cylinder 11 is developed. The plurality of sensors 1 to 10 are clockwise and counterclockwise on the outer circumference of the virtual cylinder 11 and along the Z-axis 12 direction from the first sensor 1 toward the second sensor 10. The numbers are arranged in two spirals, and the numbers are large so that the depth on the Z-axis 12 gradually increases from the first sensor 1 toward the second sensor 10. It is arranged so deep.

In the virtual cylinder deployment sensor arrangement diagram of FIG. 2B, the arrangement of each sensor is indicated by a black circle, the first helix is indicated by a one-dot chain line, and the second helix is indicated by a broken line. In the example of FIG. 2, it is assumed that the sensor arrangement angle increases in the direction of the sensor 2 (counterclockwise direction) with the sensor 1 as a reference. Here, the first spiral is a path (arrangement angle 0) from the first sensor 1 to the second sensor 10 via the sensor 2, the sensor 4, the sensor 6, and the sensor 8 counterclockwise in the cylindrical coordinate system. The sensors with even numbers are arranged on the first helix. The second helix is a path from the first sensor 1 to the second sensor 10 via the sensor 3, the sensor 5, the sensor 7, and the sensor 9 in the cylindrical coordinate system (arrangement angle 360 to 180 degrees). On the second spiral, sensors with odd numbers are arranged.
In addition, the head (sensing part) of each sensor is provided toward the Z-axis 12 and is arranged so as to measure the dose on the Z-axis 12 from a direction perpendicular to the Z-axis 12.

As shown in FIG. 1 and FIG. 2, the first sensor 1 disposed at the shallowest position in the depth direction in the water tank 14 among the plurality of sensors 1 to 10 on the Z axis 12, The other sensors 2 to 9 are sequentially arranged from a shallow position to a deep position so that the second sensors 10 are arranged at deep positions at equal intervals in different positions in the depth direction, thereby providing a depth. The dose distribution of the particle beam 13 can be measured at equal intervals in the direction. In addition to arranging the sensor arrangement in the depth direction at equal intervals, there is also a method of arranging it at arbitrary intervals, and it is possible to use properly depending on the type of radiation to be measured, sensor installation conditions, etc. Needless to say.
In addition, the sensors 1 to 10 are arranged around the virtual cylinder 11 at equal angular intervals toward the Z-axis 12, and when the sensor group 20 includes ten sensors, the Z-axis 12 is the center. One sensor is arranged for every rotation of 36 degrees at this angle. In addition, the angle said here is a relative angle on the basis of the predetermined position where the 1st sensor 1 is arrange | positioned.

  When the number n of installed sensors is an even number, the n-th sensor (second sensor) is arranged at a position 180 degrees away from the first sensor 1 (the opposite side), and on the circumference. The number of sensors (the same applies to the angle of arrangement) on the left and right of the line connecting the sensor 1 and the sensor n can be made the same. On the other hand, if the number n of installed sensors is an odd number, if the n-th sensor is arranged at a position 180 degrees away from the sensor 1, the sensor is located on the left and right of the line connecting the sensor 1 and the sensor n. The number of arrangements cannot be the same as each other, and the number of arrangements differs by one. If all the sensors are arranged at the same angle, the n-th sensor is slightly deviated from the position 180 degrees away from the sensor 1 (the angle at which the sensor is arranged is 180 degrees). It will be placed at the closest position.) In any case, the nth sensor is arranged at a position 180 degrees away from the sensor 1 or at a position close thereto, and either arrangement is acceptable.

  Further, as shown in FIG. 1, in the sensor group 20 constituting the dose distribution measuring apparatus, all the sensors are integrally held by the sensor holding member 16, and along the sensor moving direction (the same as the Z-axis 12 direction) 24. The sensor holding member 16 is moved along the guide member 17 that extends downward from the upper end of the water tank 14 into the water tank 14, and the depth of the sensor group 20 in the water tank 14 is changed. ing. Here, the sensor holding member 16 is driven by the sensor moving device 40, and the sensor moving device 40 includes a driving device made of a motor or the like. Further, the sensors 1 to 10, the sensor moving device 40, the radiation irradiation device, and the like are comprehensively controlled by the control device 41. The control device 41 may be installed at a plurality of locations so as to share the function for each device or sensor, and if the control device 41 is configured to communicate data between the control devices divided into a plurality, There are no restrictions on the number of installations.

  FIG. 3 shows a sensor arrangement example of the dose distribution measuring apparatus of the present invention. In FIG. 3, the distance in the depth direction (Z-axis 12 direction) between the first sensor 1 at the shallowest position and the second sensor 10 at the deepest position (depth direction measurement range, virtual (Corresponding to the length of the cylinder 11) is indicated by reference numeral 11a, and the diameter of the virtual cylinder 11 surrounded by the plurality of sensors 1 to 10 is indicated by reference numeral 11b. The size of the depth direction measurement range 11a is determined by the range of the depth direction distribution to be measured or the required measurement distance pitch, but is several millimeters to several tens of centimeters in the distribution measurement related to the particle beam therapy system. For example, when 10 sensors are used to measure at a pitch of 1 mm, the depth direction measurement range 11a is about 9 mm in the arrangement of FIG. In the dose distribution measurement of the Bragg peak of carbon beam particles, the pitch may be about 0.2 mm, and the depth direction measurement range 11a of the sensor group 20 at that time is less than about 2 mm.

When the depth direction measurement range 11a is small, depending on the size of the housing of the sensors 1 to 10, the distance between adjacent sensors cannot be secured and interference may be considered, so that the sensors do not interfere with each other. There is a need to. FIG. 4 shows a projection plan view in a plane perpendicular to the Z-axis 12 direction of the sensors 1 to 10. In the example of FIG. 4, the number of sensors is 10, and the angle step 26 between the sensors arranged at equal angular intervals in the cylindrical coordinate system is about 36 degrees. Here, conditions for eliminating interference between sensors will be described. Assume that each sensor (considering the outer shape is cylindrical) has the same diameter D0, and the diameter 11b of the virtual cylinder 11 is D1. And let the distance between the front-end | tips of the adjacent sensor (side near the virtual cylindrical form 11) shown in FIG. 4 be s (s> 0). Then, the following relationship (Formula 1) is established. Since FIG. 4 is a plan view, in the drawing, the component s1 in the plane direction of the distance s is shown, and the component in the depth direction is not shown.
π * D1> n * (D0 + s) (Formula 1)

If the diameter D1 of the virtual cylinder 11 is selected according to the above inequality (formula 1), the sensor as described above can be used without any problem even when the depth direction measurement range 11a shown in FIG. 3 is as small as about 2 mm. 1-10 can be arranged.
In FIG. 4, reference numeral 25 denotes the rotation direction of the sensor group (rotation direction about the axis of the virtual cylinder 11) during sensor calibration, which will be described later.

  In actual depth direction dosimetry, it is necessary to make D1 (the diameter 11b of the virtual cylinder 11) as small as possible. The reason is that the dose is not necessarily uniform in the lateral direction, and the influence of the dose non-uniformity in the lateral direction is minimized. However, if the value of D1 becomes too small, an overlapping portion is generated when viewed in the axial projection view of the sensor. Even if there is this overlapping part or there is no overlapping part, if the gap between the sensors is too small, the downstream sensor in the irradiation direction will affect the influence of disturbance of the dose field by the upstream sensor, as will be described later. D1 which is too small also has a problem because it is directly covered according to the degree of overlap, and the evaluation accuracy of the dose distribution deteriorates. Since an appropriate value of D1 depends on the type, size, particle beam energy, etc. of the sensor, it must be evaluated from time to time.

  As described above, if D1 is made too small, the particle beam that has passed through the sensor 1 reenters the sensitive region of the sensor 10 due to scattering received while reaching the depth position of the sensor 10, and the sensor 10 There is a possibility that an accurate dose cannot be measured. The reason will be described with reference to the particle beam scattering model diagram of FIG. FIG. 5 shows a state in which the particle beam 13 is vertically incident on the sensor 1 in the water tank 14 and scattered when the particle beam 13 passes through the sensor 1. The relationship between the expanding horizontal direction (direction perpendicular to the depth direction) distance 30a and the depth direction distance 30b is shown.

  As shown in FIG. 5, the particle beam 13 hitting the sensor 1 is scattered, and the scattered particle beam 30 moves in the direction of the arrow in a direction different from the direction until it enters the sensor 1. Further, after the particle beam 13 passes through the sensor 1, the distance deviated from the original lateral position before reaching the sensor n disposed on the downstream side corresponds to the horizontal distance 30b. As can be seen from FIG. 5, the deviating distance 30b increases in proportion to the depth distance 30a between the sensors. Therefore, in order to prevent the sensors 2 to n arranged at positions deeper than the sensor 1 from being affected by the scattered particle beam 30 passing through the sensor 1, it is proportional to the distance from the sensor 1 in the depth direction. Thus, an interval for avoiding interference with the scattered particle beam 30 should be provided in the lateral (horizontal) direction from the sensor 1.

  Accordingly, the diameter D1 of the virtual cylinder 11 that has been assumed as a reference for the sensor arrangement is the depth direction measurement range 11a between the sensor 1 and the sensor n (n = 10 in this example) and the direction of the scattered particle beam 30 ( The degree of scattering angle or angle deviation). Here, when the particle beam is a proton beam, the average angular deviation when traveling 20 cm in water is about 1 degree. This angle is even smaller when the particle beam is a carbon beam. However, in an irradiation apparatus using an actual particle beam, the particle beam 13 may enter the sensor 1 obliquely, and a typical scattering angle is about 4 degrees or less. When the one with the larger angle is used, when the particle beam advances 30 cm in water, the deviation of the position in the lateral direction is about 2 mm. Therefore, if the diameter D1 of the virtual cylinder 11 is about 3 mm or more, it is considered that the particle beam 30 that has passed through the sensor 1 will not pass through the sensitive region of the sensor n again.

In fact, in case 1, if the sensor arrangement pitch in the depth direction is larger than the diameter D0 of the sensor casing (cylindrical approximation), the diameter D1 of the virtual cylindrical shape 11 can be calculated to be 3 mm or 4 mm. . However, in this case, when the sensor group 20 is projected onto a plane, the distance between the sensor projection images is not separated (s1 <0). However, since it can be sufficiently arranged in three dimensions, there is no problem in arrangement if the pitch condition in the depth direction is satisfied. Further, as the case 2, when the sensor arrangement pitch in the depth direction is made smaller than the diameter D0 of the sensor casing, the diameter D1 of the virtual cylindrical shape 11 may be determined according to the above (Formula 1).
Further, as a generally used irradiation field forming method, there are a broad beam irradiation method and a scanning irradiation method. Even when a plurality of sensors are arranged in a spiral shape as in the present application, the virtual cylindrical shape 11 If the diameter D1 is set to a value of several millimeters or less, there is no problem in accuracy in performing dose distribution measurement.

  As described above, in the dose distribution measuring apparatus of the present invention, the particle beam 13 is used as the radiation to be measured, and the particle beam 13 is directed from the upper side to the lower side of the water tank 14 in the Z axis. The plurality of sensors 1 to n (10) are irradiated along 12 directions, and are arranged at substantially equal intervals (every predetermined depth) within a predetermined range in the Z-axis 12 direction. In the direction perpendicular to the Z-axis direction, each sensor is disposed along a virtual cylindrical shape 11 having a predetermined diameter at a substantially same predetermined distance from the central axis. The sensors are arranged around the virtual cylinder 11 so that the angles in the cylindrical coordinate system are spaced apart from each other by substantially the same angle and are equiangularly spaced with respect to the position coordinates of the sensor. Among the sensors, two sensors (first sensor 1 and second sensor 10) whose positions in the Z-axis 12 direction are farthest from each other are arranged on substantially opposite sides of each other with the virtual cylinder 11 interposed therebetween, For the sensors 2 to 9 other than the two most distant sensors, the angles in the cylindrical coordinate system alternate in the clockwise and counterclockwise order in the order of increasing coordinate values on the Z axis 12 toward the Z axis 12 direction. Are arranged so as to increase.

  The operation of the dose distribution measuring apparatus according to Embodiment 1 of the present invention will be described below. In the dose distribution measurement in the depth direction using the dose distribution measurement device, first, the sensor group 20 held integrally by the sensor holding member 16 is moved to a predetermined underwater depth position by the sensor moving device 40. At that time, the sensor holding member 16 is moved by driving of the driving device in a state of being engaged with the guide member 17 extending along the sensor moving direction (depth direction) 24. These commands are issued from the control device 41. The arrangement of the sensors 1 to n (10) is stored in a sensor arrangement storage unit (not shown) in the control device 41. The sensor arrangement storage unit records arrangement angle information on the outer circumference of the virtual cylinder 11 of the sensors 1 to 10, position information in the Z axis 12 direction in the water tank 14, and the like.

  Next, in accordance with a command from a dose distribution measurement control unit (not shown) in the control device 41, the particle beam 13 is irradiated under the planned conditions, and the water volume region stored in the water tank 14 has a predetermined three-dimensional size. Form a dose distribution. When the irradiation is performed, measurement by the sensor group 20 is performed, and each sensor output value of the sensor group 20 (when the sensor is an ionization chamber or the like) is transmitted to the control device 41 via the measurement circuit. Is recorded in the sensor output recording section. After the irradiation, the dose values (recorded in the sensor output recording unit) measured by the sensors 1 to 10 arranged at different depth positions are stored in the sensor arrangement storage unit in the control device 41. Is obtained as a function of the depth position and stored in a predetermined storage unit in the control device 41.

  In this way, among the three-dimensional dose distributions formed by the irradiation of the particle beam 13, the depth direction distribution D (z) in the vicinity of the Z-axis 12 is n in a predetermined depth pitch over the depth range 11a. (10) Measurement points can be obtained collectively. Then, after moving the entire sensor group 20 by a necessary distance in the depth direction, the dose distribution measurement as described above is repeated in different depth ranges. In this way, a dose distribution in the depth direction at the required pitch within the required depth range can be obtained.

  At the time of the measurement, the sensor 1 arranged at the shallowest position and the sensor 10 arranged at the deepest position are arranged so that the respective plane projection images are most distant from each other as shown in FIGS. The passed particle beam hardly enters the sensor 10 again, and the dose value measured by the sensor 10 is measured as a value that is almost the same as the dose value measured when the other sensors 1 to 9 are not arranged. It becomes possible. In addition, since the sensors from the sensor 2 to the sensor 9 are arranged so that the relative angle to the sensor 1 gradually increases in the depth order, the measured values of each sensor are hardly affected by other sensors, and the accuracy is high. It is possible to obtain a good dose distribution in the depth direction.

In addition, since the dose values at 10 depth positions can be measured in one measurement, the time required for distribution measurement can be greatly reduced. Furthermore, the total amount of irradiation of the particle beam required for confirming the dose distribution can be significantly reduced as compared with the measurement using a single ionization chamber. This is a great advantage in terms of satisfying the limit of the maximum amount of particle beam that can be irradiated in a week at a particle beam therapy facility.
The deep dose distribution measuring apparatus of the present invention is particularly effective when an advanced three-dimensional irradiation method such as scanning irradiation or multilayer body irradiation that takes several minutes is used to form one stable distribution.

  In the first embodiment, the case where the sensor is an ionization chamber has been described. However, in practice, the present invention is not limited to this, and the basic effect is the same even with other dose sensors. Differences in sensor materials, and more specifically, differences in absorption and average scattering angle due to differences in human body constituent materials, atomic numbers, and densities, so the mutual arrangement of sensors must be different accordingly. However, it is common in that the sensor arrangement is a three-dimensional arrangement that minimizes the influence of each other, and the basic effects can be said to be the same in that sense. In short, if the sensor is made of human body equivalent material, such a problem (the problem that the sensor creates a situation that deviates from the Bragg cavity principle) does not occur, so the sensor is, for example, a plastic scintillator It can be said that the adoption of is suitable from the viewpoint of measuring the absorbed dose of the human body. Further, in the present invention, it is effective to employ a sensor system (semiconductor, polymer gel, etc.) as well as the sensor electrode and wall material (housing) that is suitable for measuring the absorbed dose of the human body. is there.

In the first embodiment, the case where the sensor group 20 is placed in water (water phantom) has been described. However, the sensor group 20 is not limited to the water phantom. A similar effect can be obtained by measuring the vertical dose distribution.
In addition, although the example in which the particle beam 13 is incident perpendicularly to the water surface 14a has been shown, since the beam may be irradiated obliquely to the patient, the particle beam 13 may be obliquely applied to the water surface 14a. In some cases, the dose distribution is measured by irradiation. In that case, the distance traveled along the irradiation direction from the incident position on the water is taken as the depth of the water, and a dose distribution can be obtained in the same manner as in the case where the beam is incident perpendicular to the water surface 14a (sensor group 20). Needless to say, the arrangement center axis 12 is set obliquely. As an extreme example, the particle beam 13 may be incident from the side. At that time, the particle beam 13 is incident from the side surface of the water tank, and a three-dimensional dose distribution is formed in water.

  In the above example, the sensors 1 to 10 are arranged at equal angular intervals in the cylindrical coordinate system and at equal intervals in the depth direction. However, arrangements other than equal intervals are possible. Needless to say, for example, some sensors are arranged with a small pitch, and others are arranged with a large pitch, and adjusted according to the location and characteristics of the beam to be measured. It can also be used. Even in that case, dose distributions at a plurality of positions in different depth directions can be obtained by a single measurement by the sensor group arranged around the virtual cylinder 11, and particles scattered by the presence of other sensors can be obtained. Accurate dose measurement is possible without being affected by the line.

Embodiment 2. FIG.
In the above-described first embodiment, the example in which the sensors 1 to 10 are arranged so as to form two spirals is shown. However, in this second embodiment, the sensor arrangement is shown in FIGS. 6 and 7. FIG. 6 (a) shows a sensor arrangement perspective view and FIG. 6 (b) shows a virtual cylindrical deployment sensor arrangement diagram for an example in which a plurality of sensors 1 to 10 are arranged in a spiral shape. I will explain. Note that the sensor arrangement angle is assumed to increase by 36 degrees in the direction from sensor 1 to sensor 2 (clockwise direction). Further, the sensor arrangement angle increases with the depth. As shown in the sensor arrangement projection plan view of FIG. 7, the sensor 10 at the deepest position, that is, the position farthest from the sensor 1 in the depth direction, 1 is adjacent to one another. Therefore, when the sensors are arranged so as to form a single spiral, the diameter of the virtual cylinder 11 is made relatively large compared to the double spiral arrangement shown in FIGS. Measures should be taken to eliminate the impact. When the sensor diameter D0 is sufficiently small, a certain merit can be obtained even if this arrangement is adopted.

Embodiment 3 FIG.
Next, the dose distribution measuring apparatus according to the third embodiment of the present invention will be described with reference to FIGS. In the first embodiment described above, the sensor group 20 composed of a plurality of sensors is integrated and supported by one sensor holding member 16, and the sensor holding member 16 moves in the depth direction. Although an example of changing the arrangement has been shown, in the third embodiment, a configuration in which a plurality of sensors can individually change the arrangement in the depth direction will be described.

  FIG. 8 shows a conceptual diagram of a main part configuration of the dose distribution measuring apparatus with a focus on some sensors (sensor 5 and sensor 10) (the description of other sensors is omitted). As illustrated in FIG. 8, the sensor 5 is attached to the sensor holding member 16a, and the other sensors are similarly attached to individual holding members. Each of the sensor holding members 16a is individually attached to a guide member 17a that guides movement of the sensor arrangement in the depth direction. Further, a guide member 17 a and the like are fixed on a support base 21 that supports the sensor group 20. A sensor depth switching device (corresponding to one of the sensor moving devices) 50a, which is a mechanism for moving the sensor holding member 16a along the guide member 17a, is in response to a command from a pitch change control unit in a control device (not shown). The sensor 5 can be switched (changed) to one of two different arrangements on the Z-axis 12. The upper and lower limits of the sensor movement range 19a (19b) in the depth direction of the sensor 5 (10) are regulated by the positioning stoppers 15a and 18a.

In addition, the support base 21 that supports the sensor group 20 can be rotated with the support shaft 22 extending along the Z axis 12 as a rotation axis, and the support shaft 22 is moved along the depth direction 24. The sensor group 20 can be moved in the depth direction. The support shaft 22 can be rotated and moved in the depth direction by the driving device 23.
Here, for example, a position corresponding to the upper end portion of the sensor movement range 19a (19b) can be a position at the time of dose distribution measurement, and a lower end portion can be a position at the time of sensor calibration described later. FIG. 9 shows a perspective view of the arrangement state of the sensors 1 to 10 at the time of calibration.

  In addition, the sensor depth switching device 50a of FIG. 8 is an image diagram expressing that each sensor can take two arrangements in the depth direction. An example of a switching mechanism of two types of sensor arrangement pitches of the specific sensor depth switching device 50a is shown in the cross-sectional views of the main part in FIGS. 10 (a) and 10 (b). FIG. 10A shows a state in which the sensor 5 is arranged at the lower end portion of the sensor movement range 19a, and FIG. 10B shows a state in which the sensor 5 is arranged at the upper end portion of the range 19a. Is shown.

  As shown in FIGS. 10A and 10B, the sensor holding member 60 (corresponding to the above-described reference numeral 16 a) that holds the sensor 5 protrudes in the lateral direction and supports the sensor 5. A portion 61, a trunk body 62 movably held in a cylinder (case) 39 (corresponding to 17a) arranged to extend in the depth direction, and provided so as to protrude to the lower end side. The protrusion 63 is a member formed by coupling, and the trunk body 62 is configured to move in the depth direction in the cylindrical body 39 so that the position of the sensor 5 can be moved. A positioning stopper 15a that is in contact with the upper end of the trunk body 62 of the sensor holding member 60 at the time of dose measurement (first arrangement) is provided at the upper part in the cylinder 39, and at the lower part in the cylinder 39 at the time of calibration or first arrangement. The positioning stopper 18a is arranged so that the stepped portion of the lower part of the trunk 62 of the sensor holding member 60 contacts when measuring doses at different pitches (second arrangement).

  In addition, a spring 36 is disposed in the upper part of the cylindrical body 39, and a balloon 37 described later is disposed in the lower part, and the trunk body 62 of the sensor holding member 60 is sandwiched between the spring 36 and the balloon 37. Thus, the position of the sensor holding member 60 in the depth direction is adjusted by the elastic force of the spring 36 and the expansion of the balloon 37. The spring 36 may use another elastic body, and the balloon 37 may be another structure whose external dimensions can be adjusted from the outside. Further, the spring 36 and the balloon 37 can be arranged upside down, and the structure is not limited to that shown in FIG. 10 as long as the sensor holding member 60 can be changed to two arrangements in the depth direction.

  Here, the lower part of the trunk body 62 of the sensor holding member 60 is formed with the outer peripheral part contacting the positioning stopper 18a as a crank, and the axial center portion of the trunk body 62 is below the positioning stopper 18a in the second arrangement. A protruding portion 63 is formed in contact with the balloon 37 accommodated in the bottom of the cylindrical body 39. A pipe 38 is connected to the balloon 37, and fluid is drawn into and out of the balloon 37 through the pipe 38. The positioning stoppers 15a and 18a can also be formed by providing a partial protrusion on the inner wall of the cylinder 39.

As shown in FIG. 10A, when the sensor 5 takes the second arrangement, the fluid in the balloon 37 is discharged to the outside, the balloon 37 is deflated, and the sensor holding member 60 contacts the positioning stopper 18a in the lower part. The sensor 5 is held at the position where it is to be moved.
Also, as shown in FIG. 10B, when the sensor 5 takes the first arrangement, fluid is sent into the balloon 37 from the outside, the balloon 37 expands, and the trunk 62 of the sensor holding member 60 is pushed up. The upper end of the trunk 62 moves to a position where it contacts the positioning stopper 15a in the cylinder 39, and the sensor 5 is held. In the drawing, the position of the sensor 5 in the second arrangement is indicated by a broken line.
In the sensor capable of switching between the first and second arrangements as described above, the second arrangement may be a sensor measurement arrangement with a pitch different from the first arrangement, instead of the arrangement at the time of sensor calibration. Is possible.

  Next, FIG. 11 shows an example of the dose distribution in the depth direction of water by the carbon beam particles used in the particle beam therapy system. As shown in FIG. 11, in the dose distribution by the carbon beam, a flat region portion 70 where the dose becomes a constant value at a predetermined depth in water is formed, and a peak region portion 71 where the dose changes sharply at a predetermined depth is formed. . FIG. 12 shows an example of a dose distribution in the depth direction by an enlarged Bragg peak formed in accordance with the shape of the affected part during particle beam therapy. In FIG. 12, the flat region portion 70a continues to a predetermined depth in water, the dose increases sharply in the peak region portion 71a, the dose is held in the depth range of the flat region portion 70b, and the peak region at a deeper position. It is exemplified that the dose decreases sharply in the portion 71b.

  In the third embodiment, as shown in FIG. 8, each sensor can be switched to one of two arrangement positions separated by a depth distance 19a (or 19b or the like). The switching of the arrangement is performed by, for example, a sensor depth switching device (one of sensor moving devices) 50a (50b, etc.) shown in FIGS. 10 (a) and 10 (b). The two arrangements are caused by the difference in arrangement pitch in the depth direction of the sensors 1 to 10 and are restricted by the relative arrangement between the sensors. In addition, the two sensor arrangements are the first and second arrangements in which the first and second arrangements are spirally arranged as in the first or second embodiment at the first and second depth pitches. As shown in FIG. 9, only the case and the second arrangement include a second case which is a sensor calibration arrangement in which all sensors are arranged at the same depth.

First, the operation of the dose distribution measuring apparatus in the first case will be described.
As shown in FIG. 8, each of the sensor 5 or the sensor 10 or another sensor can take two depth pitches (arrangement pitches). And when there is a sensor in the first arrangement, for example, the position of each sensor is determined so that the sensor has the same arrangement as in the first embodiment and the depth pitch is 5 mm. In the second arrangement, the sensor arrangement form is spiral, and only the arrangement pitch in the depth direction is different from the first arrangement, and is arranged at a pitch of 0.2 mm, for example. The switching between the two types of depth pitches can be realized, for example, by the mechanism shown in FIGS. 10 (a) and 10 (b).

When measuring the dose distribution in the depth direction, first, the position of the sensor group 20 is moved to the depth position shown in the flat region portion 70 shown in FIG. In the flat region 70, the dose hardly depends on the depth of water, and the fluctuation amount is small. Therefore, the arrangement of the sensor group 20 is set to the first arrangement having a large pitch. In this state, the particle beam 13 is irradiated according to a predetermined plan, and the dose is measured.
In this first arrangement, the measured point pitch is 5 mm.

  Next, the sensor group 20 is moved to the depth position of the peak region 71 shown in FIG. In the peak region portion 71, there is a peak portion where the dose changes sharply, and the change of the dose depending on the depth in water is large. At this position, the balloon 37 is filled with pressurized air via the pipe 38 shown in FIG. 10A, the spring 36 contracts, the sensor holding member 60 rises, and comes into contact with the positioning stopper 15a. It stops in the state shown in FIG. This switching is performed for all sensors other than the sensor (5) that does not move in the first and second arrangements. Thereby, the arrangement of the sensor group 20 is switched to the second arrangement. In this second arrangement, the pitch in the depth direction is 0.2 mm, for example, which is smaller than the first arrangement. In this sensor arrangement, the depth position of the sensor group 20 is scanned so as to match the peak region portion 71 shown in FIG. 11, and the dose distribution in the depth direction is measured. In the case of the dose distribution of FIG. 12, the flat region portions 70a and 70b are measured with a first arrangement with a large pitch, and the peak region portions 71a and 71b are measured with a second arrangement with a small pitch.

  According to the third embodiment, the arrangement pitch of the sensors can be easily switched according to the steepness of the distribution, and the dose distribution measurement is performed, so that the measurement accuracy is efficiently maintained in a shorter time. The effect that the dose distribution in the complex depth direction can be measured is obtained.

  Next, the operation of the dose distribution measuring apparatus will be described for the second case of the third embodiment according to the present invention. In the first arrangement of the second case, the depth direction dose distribution at a predetermined arrangement pitch can be measured as in the first case. On the other hand, the second arrangement of the second case is a sensor calibration arrangement in which all the sensors have the same depth, and the arrangement pitch in the depth direction between the sensors is 0 mm. At the time of sensor calibration, a sensor depth switching device 50a (50b, etc.) as shown in FIGS. 10A and 10B is used, and the sensor group 20 is switched to the second arrangement, that is, the sensor calibration arrangement, and the particle beam is changed. Irradiate a predetermined condition and a predetermined amount, and record the output of each sensor.

Subsequently, all sensors are rotated about the Z axis 12 by a predetermined angle (an angle corresponding to an angle step indicated by reference numeral 26 in FIG. 9) using the sensor rotating device (sensor group rotating means) 23. Is arranged so as to overlap with the position of the adjacent sensor before rotation. In this state, the second measurement is performed. This second measurement is desirably performed under exactly the same conditions as the irradiation performed before rotation. Even if the dose distribution formed by irradiation is not uniform, it can be calibrated later. Then, the second sensor output is recorded. Thus, the relative calibration of each sensor sensitivity can be obtained by simple proportional calculation from the two measurement results performed in the sensor calibration arrangement.
As described above, by performing the measurement as shown in the second case of the third embodiment according to the present invention, an effect that the relative sensitivity of the dosimetry sensor can be easily calibrated is obtained.

Embodiment 4 FIG.
Next, regarding the fourth embodiment of the present invention, the configuration and operation of a dose distribution measuring apparatus will be described with reference to FIGS. In the above-described third embodiment, the example in which the plurality of sensors are fitted and held on the guide member 17a protruding upward from the support base 21 in the lower part of the water tank 14 has been shown, but in this fourth embodiment, The case where the sensor 1 (-n) is hold | maintained at the guide member 17b sunk from the upper part of the water tank 14 to the downward direction in the water tank 14 is demonstrated.

  In the dose distribution measuring apparatus according to the fourth embodiment, the arrangement of the sensor group 20 including the plurality of sensors 1 to n (10) is the same helical arrangement as that of the first and second embodiments. 13 and 14 exemplify only the first sensor 1 and the second sensor 10. The sensor 1 is fixed to the sensor holding member 16b, and the sensor holding member 16b is supported by a guide member 17b that guides the movement of the sensor 1 along the depth direction. As described above, the guide member 17b is fixed to the upper part of the water tank 14, and the lower end is submerged in water. For each sensor, a sensor moving device 40 for moving the sensor in the depth direction is provided at the upper edge of the water tank 14, and an arbitrary depth within the sensor moving range 19a (corresponding to the sensor 10 is 19c). It can be placed in a stopped position. In the above-described third embodiment, it has been shown that one sensor can be changed to one of two depths by switching the arrangement pitch. However, in this fourth embodiment, a predetermined sensor movement range 19a (19c, etc.) It is possible to arrange the sensor at an arbitrary depth within ().

  The plurality of sensors are arranged around the Z axis 12 at substantially equal circumferential angle intervals. For example, when the number of sensors is 10, the adjacent sensors are arranged apart by about 36 degrees. Further, the dose distribution measuring apparatus of FIG. 13 is provided with a rotation mechanism (not shown) that rotates the sensor group 20 around the Z axis 12 by an angle corresponding to one interval.

  When taking the measurement arrangement, as shown in FIG. 13, the first sensor 1 is set to the shallowest position and the second sensor 10 is set to the deepest position by the sensor moving device 40. The sensor 1 and the sensor 10 have an arrangement angle of about 180 degrees different. As shown in FIG. 2 and the like, the sensors other than the sensor 1 and the sensor 10 are arranged so that the relative angle with the sensor 1 gradually increases in the depth order. Corresponding to this measurement arrangement, sensor depth position information and arrangement angle information are stored in a sensor arrangement storage section provided in the control device 41. In FIGS. 13 and 14, a driving device for moving the sensor is abbreviated. When the sensor calibration arrangement is adopted, as shown in FIG. 14, the sensor moving device 40 moves all the sensors to the same depth. Similarly to the measurement, depth position information corresponding to the sensor calibration arrangement is stored in the sensor arrangement storage unit of the control device.

  Next, the operation of the dose distribution measuring apparatus according to the fourth embodiment of the present invention will be described. Before starting the measurement, as shown in FIG. 13, the control device according to the sensor measurement placement information (including the Z-axis 12-direction pitch and the Z-axis placement information) recorded in the sensor storage unit of the control device 40. A command is issued from the pitch change control unit in 40, and all the sensors 1 to n (10) are moved by the respective sensor moving devices 40 and set to the measurement arrangement. Next, a command is issued from the control device 41, and the particle beam 13 is irradiated according to the planned conditions. Each sensor output value is stored in a predetermined storage device of the control device 41. Thus, the dose at 10 depth positions within the predetermined depth range is measured. Subsequently, as necessary, the control device 41 controls the sensor moving device 40 to move the depth positions of all the sensors in the direction of increasing or decreasing by the same amount, and measures dose distributions in different depth regions. To do. By repeating this, a dose distribution in the necessary depth range can be obtained.

  Alternatively, a plurality of measurement position arrangement information with different numbers of measurement points or measurement pitches may be stored in a predetermined storage medium of the control device 41 and selectively recalled during measurement to measure the depth direction dose distribution. As a result, when measuring the dose distribution as illustrated in FIG. 11 and FIG. 12, there is an effect that the measurement pitch can be freely adjusted and changed according to the degree of dose change, and more accurate measurement is possible. The result can be obtained.

  Next, a sensor calibration method according to the fourth embodiment will be described with reference to FIG. Based on the sensor calibration arrangement information stored in a predetermined storage medium in the control device 41, all the sensors are set to the same depth as shown in FIG. Then, the particle beam 13 is irradiated according to the planned condition (referred to as condition A). Then, the output {Ci, i = 1, 2,..., N; n = 10} of each sensor is recorded in the storage device.

Subsequently, all the sensors are rotated about the Z axis 12 by about 36 degrees (one interval) using a sensor rotating device described later. In this state, the particle beam 13 is irradiated under the same condition as the condition A. The output {Di, i = 1, 2,..., N; n = 10} of each sensor obtained by the second irradiation is stored in the storage medium of the control device 41. Thus, for example, the sensor 10 and the sensor 9 measure the dose under the same irradiation condition A at the same depth position and the same angular position. When the rotation direction is opposite, the measured values of the sensor 10 and the sensor 1 are compared. If the output values (C ₁₀ and D ₉ ) are used under the condition that the measured values measured at the same position should be the same, the relative sensitivity coefficients of the sensors 10 and 9 can be obtained. Similarly, the same can be said for other adjacent sensors. In this way, the relative sensitivity coefficients of the sensors 1 to 10 can be obtained by two measurements as necessary, and the time required for sensor calibration is greatly increased compared to the case where calibration is performed for each individual sensor. The effect that it can be shortened is obtained.

  In the sensor calibration, as a means for rotating the sensor around the Z axis 12, the sensor moving device 40 and the guide member 17b attached to each sensor are integrated, and a plurality of sensor moving devices 40 are individually connected to the Z axis. In addition to providing a rotating device that rotates at an arbitrary angle around twelve, a rotating device that rotates all sensors with a single rotation drive mechanism may be provided. In addition, when rotating a sensor group with one rotation apparatus, it can be set as a rotation apparatus cheaper than the case where a rotation apparatus is provided for each sensor.

Further, as another rotating device, as shown in a schematic plan view of the sensor and the water tank 14 in FIG. 15, a plurality of sensor moving devices 40 (a sensor unit 42 including a sensor and its support moving mechanism is fixed). May be fixed to the water tank 14 and integrated, and a tank rotating device 43 for rotating the water tank 14 itself may be provided around the Z axis 12. In addition, when rotating the water tank 14, it is possible to reduce the load generated during the rotation by storing the water in the water tank 14 again and storing necessary water again after the rotation. By configuring in this way, the sensor rotating device has an effect that a low torque is sufficient.
In the case of a particle beam therapy system, since a treatment table for placing a patient is provided, the sensor can be rotated using a rotation mechanism attached to the treatment table. In this case, there is an advantage that the dose distribution measuring device in the depth direction can be configured at low cost.

Embodiment 5 FIG.
Next, a sensor calibration method of the dose distribution measuring apparatus according to the present invention will be described with reference to the flowchart of FIG.
First, in the first step 51, the sensor group 20 is moved to the sensor calibration arrangement using the sensor moving device 40 shown in the first, second, and fourth embodiments. In this sensor calibration arrangement, all sensors are arranged at the same depth position. The control device 41 for controlling the sensor group 20 records the arrangement angle information on the outer periphery of the virtual cylinder 11 of the sensor and the position (depth) information in the direction of the Z axis 12 in the water tank 14. A sensor arrangement storage unit is provided, and is configured to process sensor arrangement information in correspondence with sensor measurement results described later.

  Next, in the second step 52, a command is issued from the control device 41 and the particle beam 13 is irradiated. The irradiation condition at this time is defined as condition A. The irradiation condition A includes, for example, the beam energy of the particle beam, the current value, the irradiation field forming condition, and the like. Furthermore, it is desirable that the irradiation condition A includes the total number of particles to be irradiated. Further, it is desirable that the conditions allow the formation of almost the same dose distribution within 2 percent in water when irradiation is repeated under the same conditions.

  Next, in the third step 53, the particle beam 13 irradiated in the second step 52 is measured by the sensor group 20, and a measurement result is obtained. Here, for example, the sensor group 20 includes ten sensors 1 to 10, and sensor outputs {Ci, i = 1, 2,... N; n = 10} (corresponding to the first measurement value) as measurement results. ) Is recorded in the measured value recording unit in the control device 41.

  Next, in the fourth step 54, when the third step 53 is completed, the sensor group 20 is moved to about 36 degrees around the Z axis 12 by using sensor group rotating means (for example, the sensor rotating device 43 in FIG. 15). The angle corresponding to one interval when the sensors are arranged at equal angular intervals). The sensor group rotating means is controlled by a rotation angle control unit in the control device. Here, since the ten sensors are arranged at substantially equal angular intervals, after rotation, all the sensors are moved to the pre-rotation angular position of the adjacent sensor. In the case of the double spiral arrangement of the sensor shown in the first embodiment, in the sensor calibration arrangement of FIG. 9, the rotation in the fourth step 54 causes the sensor 10 to the sensor 9, the sensor 9 to the sensor 7, and the sensor 7 to To sensor 5, sensor 5 to sensor 3, sensor 3 to sensor 1, sensor 1 to sensor 2, sensor 2 to sensor 4, sensor 4 to sensor 6, sensor 6 to sensor 8, sensor 8 to sensor 10 Rotate to.

Next, in the fifth step 55, the particle beam 13 is irradiated under the same irradiation condition (condition A) as in the second step 52 (second time). A dose distribution formed in water by the particle beam 13 is measured by the sensors 1 to 10.
Next, in the sixth step 56, the output {Di, i = 1, 2,... N} of each sensor obtained by the measurement in the fifth step 55 is recorded in the measurement value recording unit of the control device 41.

Next, in the seventh step 57, the sensor outputs {Ci, i = 1, 2,..., N} and {Di, i = 1, 2,... Recorded in the third step 53 and the sixth step 56, respectively. n} is used to calculate the relative sensitivity coefficients {Gij, i = 1, 2,..., n, j = 1, 2,. When the gain of each sensor is {Gi, i = 1, 2,..., N} and the dose value formed at each sensor position before rotation is {Si, i = 1, 2,. Since 10 is in the same position as the sensor 9 before rotation after rotating, the following equations (Equation 2 and Equation 3) hold.
D ₁₀ = G ₁₀ * S ₉ (Formula 2)
C ₉ = G ₉ * S ₉ (Formula 3)

Therefore, G ₁₀ / G ₉ = D ₁₀ / C ₉ or Gij (i = 10, j = 9) = D ₁₀ / C ₉ , and the relationship of Gij = Di / Cj is similarly applied to other sensors. can get.
Where j is the sensor next to i in the sensor calibration arrangement.
In this way, the relative sensitivity coefficient between all sensors can be obtained. Si represents the dose distribution in the plane where the sensor in the sensor calibration arrangement is located. In the sensor calibration method of the dose distribution measuring apparatus according to the present invention, this {Si} does not necessarily have a uniform distribution and has a large tolerance in beam formation. Therefore, it becomes possible to easily perform relative calibration of a plurality of sensors of the dose distribution measuring apparatus in the depth direction.

  Although not shown in FIG. 16, in order to confirm the accuracy of the relative calibration coefficient obtained in the seventh step 57, finally, after each sensor is calibrated using the obtained calibration coefficient Gij, Check whether the sensor outputs Ci and Dj (j indicates the sensor next to i in the sensor calibration arrangement) recorded in the third step 53 and the sixth step 56 are equal within a predetermined accuracy (for example, 1% to 2%). It is effective to provide a step to perform. By providing such steps, it can be confirmed that substantially the same dose distribution is formed in the two irradiations, which is the premise of the sensor calibration method of the dose distribution measuring apparatus according to the present invention. Then, an effect is obtained that it is easy to ensure that the sensor calibration constant, which is very important in the distribution measurement, is always obtained correctly.

  In addition, as shown in Embodiment 1, 2, and 4 mentioned above, the method of arrange | positioning the sensor group 20 which consists of several sensors 1-10 in various sensor calibration positions is various, and in the depth direction of each sensor. Change the placement pitch, determine the position in the depth direction, and set the pitch between sensors to 0 mm (same depth placement) for calibration placement, or set each sensor to an intermediate depth of the entire sensor group In some cases, the arrangement (see FIG. 14) is used as a calibration arrangement.

  Needless to say, the above-described sensor calibration method can also be applied to the dose distribution measuring apparatus of the third embodiment that switches the arrangement pitch in the depth direction. In this case, the sensor is moved in the depth direction by the sensor depth switching device 50a (50b). Further, the rotation of the sensor is performed by rotating the support base 21 around the rotation shaft 22. As described above, the calibration flow shown in FIG. 16 can be applied to the sensor calibration of the dose distribution measuring apparatus of the present invention regardless of the sensor moving means and the rotating means.

  In any case, a sensor of a dose distribution measuring device that measures the dose distribution of radiation irradiated into the water tank 14 in which water is stored at a plurality of different positions on the axis along the radiation irradiation direction. In the calibration method, a step of arranging the plurality of sensors arranged at equiangular intervals around a virtual cylinder extending around the axis at the same position on the axis, and a predetermined amount of the radiation along the axis Irradiating only A and measuring the radiation dose of the predetermined amount A by the plurality of sensors to obtain a first measurement value, rotating the plurality of sensors around the virtual cylindrical axis, A step of disposing the sensor by one interval in the circumferential direction of the virtual cylindrical shape, irradiating the radiation by a predetermined amount B along the axis, and using a plurality of the sensors The radiation dose of a predetermined amount B (in the above description, exemplified as the same condition as A, but it is also possible to select a different dose, in which case correction based on the difference in dose is required) is measured. A step of obtaining a second measured value, and calculating a relative sensitivity of the plurality of sensors using the first and second measured values. It is possible to easily perform relative calibration of the sensor.

Embodiment 6 FIG.
In the first embodiment and the like described above, an example has been described in which a large number of sensors (for example, 10 sensors) are arranged in a predetermined method with respect to a virtual cylindrical shape having a diameter of 3 mm or more to configure a dose distribution apparatus in the depth direction. The sixth embodiment shows a case where the diameter (diameter) of the virtual cylinder is zero (D1 = 0) when the number of sensors is further reduced.
The number of sensors is two, and the angle and depth are distributed on the outer circumference of a virtual cylinder (that is, the axis on which radiation is irradiated) with a diameter of 0 so that the sensors are spiral. The inventors were able to confirm by experiment that the original deep dose distribution to be measured may be measured with an accuracy of about 1% error when measuring the dose distribution in the depth direction. . When the number of sensors is as large as 10 and the error becomes large in the sensor arrangement in the vicinity of the diameter 0 of the virtual cylindrical diameter, there is a problem, but if the number of sensors is small, the error is suppressed to 1% or less. It becomes possible. At this time, since all sensors at different depth positions can measure the dose at D1 = 0, there is an effect that a measurement result closer to the deep dose distribution on the axis of D1 = 0 can be obtained.

  In addition, when the members around the sensitive part of the dosimetry sensor to be constructed are made of a material called a solid phantom that is close to water, such as carbon, the sensitive part of the sensor is placed in the same lateral direction (perpendicular to the depth direction Even in the case where the sensor is not disposed, it is possible to obtain a distribution that is almost the same as the dose distribution when the sensor is not disposed. In this case, by adopting the helical sensor arrangement of the present invention, the lead wire, high voltage cable, sensor support part, etc. connected to the sensor sensitive part are in a sufficiently separated state when viewed from the beam irradiation direction. Interference with the dose distribution of the part to be measured by the sensitive part can be suppressed. Therefore, the effect of measuring the deep dose distribution with high accuracy can be expected.

  In the first embodiment and the like described above, the invention has been described on the assumption that the sensor is disposed in a container storing water. However, the present invention is not limited to this, and the sensor is not limited to the above-described solid state. Even in the phantom, the depth dose distribution can be measured with high accuracy in the same manner. In this case, as for the rotation operation of the sensor, if the solid phantom and the sensors arranged in the solid phantom are integrally rotated about the beam incident direction axis (D1 = 0 axis), the above-described embodiment is performed. Needless to say, the same effect can be obtained.

1 to 10 sensors (1: first sensor, 10: second sensor),
11 Virtual cylinder 11a Depth direction measurement range,
11b Virtual cylinder diameter 12 Sensor arrangement center axis (Z axis),
13 Particle beam 14 Water tank,
14a Water surface 15a, 18a Positioning stopper,
16, 16a, 16b, 60 sensor holding member,
17, 17a, 17b Guide member 19a, 19b, 19c Sensor movement range, 20 Sensor group 21 Support base,
22 Rotating shaft 23 Drive device,
24 Sensor moving direction 25 Sensor rotating direction,
26 Angular step 30 Scattered particle beam,
30a Depth direction distance 30b Horizontal direction distance,
36 Spring 37 Balloon,
38 pipes 39 cylinders,
40 sensor movement device 41 control device,
42 sensor part 43 tank rotation device,
50a, 50b Sensor depth switching device 61 Branch body,
62 trunk 63 projection,
70, 70a, 70b Flat region portion 71, 71a, 71b Peak region portion.

Claims (11)

A plurality of sensors arranged at different heights on the outer periphery of the virtual cylinder extending about the radiation direction, and the plurality of sensors are arranged at predetermined positions on the outer periphery of the virtual cylinder. One sensor, a second sensor disposed at a position where the rotation angle from the predetermined position is closest to 180 degrees, and the first sensor and the second sensor are the most in the axial direction. is remotely located, the plurality of the sensors, the first sensor and the second sensor other than the sensors are respectively disposed at different heights above axial direction and the virtual cylindrical outer periphery on the in along the axial direction, the direction from the first sensor to the second sensor, the helix extending clockwise, and another on the spiral extending in the counterclockwise direction, and the first sensor Relative angle of As but gradually increased, they are arranged sequentially distributed alternately, a plurality of the sensors, the direction perpendicular to the axis, respectively to measure the dose of the radiation at different positions on the shaft, one measurement A dose distribution measuring apparatus characterized by obtaining a number of measurement points corresponding to the number of sensors .   The dose distribution measuring apparatus according to claim 1, wherein the plurality of sensors measure the dose distribution of the radiation at equal intervals in the axial direction.   The dose distribution measuring apparatus according to claim 1, wherein the plurality of sensors are arranged at equiangular intervals with the virtual cylindrical axis as a center.   The dose distribution measuring apparatus according to any one of claims 1 to 3, further comprising a sensor moving device for moving the sensor along the axial direction.   A pitch change control unit that controls the sensor moving device so as to change the arrangement pitch of the plurality of sensors arranged at equal pitches in the axial direction. The dose distribution measuring apparatus according to claim 4, wherein:   6. The dose distribution measuring device according to claim 1, further comprising a sensor rotating device for rotating the plurality of sensors around the axis of the virtual cylindrical shape. A control device for controlling the sensor, wherein the control device has a plurality of sensors when the plurality of sensors arranged at equiangular intervals around the virtual cylindrical axis are arranged at the same position on the axis. 7. The dose distribution measuring device according to claim 6, further comprising a rotation angle control unit that controls the sensor rotation device so that the sensor rotates by an angle corresponding to one interval.   The apparatus includes a control device that controls the sensor, and the control device includes a sensor arrangement storage unit that records arrangement angle information on the outer circumference of the virtual cylinder and position information on the axis of the sensor. The dose distribution measuring apparatus as described in any one of Claims 1-4.   9. The dose distribution measuring apparatus according to claim 1, wherein the sensor is disposed in a water tank in which water is stored.   The irradiation direction of the radiation is downward in the vertical direction, and the radiation is irradiated into a water tank in which water is stored along the axis of the virtual cylindrical shape, and the sensor is connected to the water tank of the radiation. The dose distribution measuring apparatus according to claim 1 or 2, wherein a dose distribution in a depth direction in the inside is measured.   The dose distribution measuring apparatus according to claim 1, wherein the sensor is arranged so that the diameter of the virtual cylindrical shape is zero.

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