JP2001137370A - Radiation dosage measuring method and radiation dosage measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure the irradiation field for X-rays. SOLUTION: This dosage measuring device 1 is constituted of a density data converting means 62, an information processing means 63 and a display means 72. The density data converting means 62 scans a film 35 for measurement, which is irradiated with rays, and converts the radiation field image to density data. The information processing means 63 processes two-dimensional information and three-dimensional information based on the density information. The display means 72 displays a density image based on the processed density information. The film for measurement is irradiated with the rays, and variable density information (radiation field variable density image) is obtained. Then, the variable density information is converted into density data, and the radiation field and the flatness are projected on the display means and measured. Since the radiation field is obtained from the density data, the size and the shape of the radiation field can be accurately measured. The flatness can be easily calculated as well. By this constitution, the adjustment of the radiation field or a replacement timing for a target which is built in the radiation device can be accurately grasped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation dose measuring device and a measuring method for a radiation irradiation device applicable to radiation therapy and the like.

[0002]

2. Description of the Related Art In a therapeutic radiation irradiating apparatus for treating an affected part by irradiating the affected part with radiation, for example, X-rays, it is necessary to intensively irradiate a predetermined dose to only the affected part. The X-ray irradiation field and dose flatness are periodically verified. FIG. 15 shows an outline of a radiation dose measuring device used in such a case.

[0005] In FIG. 15, a radiation irradiation apparatus 10 has an acceleration tube 12 inside which an electron gun 14 is arranged. A plurality of focusing coils 1 are arranged on the electron traveling direction side of the electron gun 14.
6 and a high-frequency source 18 such as a magnetron or a klystron is mounted outside the accelerating tube 12.

The electron gun 14 has an energy of 4 MV to 20 M.
V, an accelerating voltage for V
, The electrons emitted from the electron gun 14 are accelerated when passing through the acceleration tube 12. Then, the electrons emitted from the acceleration tube 12 are caused to collide with a flat target 22 using tungsten W or the like. Radiation such as X-rays is generated by the collision with the target 22.
This radiation is emitted from the inside of the housing 26 to the outside after its irradiation field (size and shape) is restricted by the collimator (mask) 24. Irradiation field is 800-1 from case 26
It is determined by the spread of the irradiation beam and the radiation dose at a position separated by 000 mm.

A light source 28 for an optical crosshair is provided in connection with the target 22, and a cross plate 29 for obtaining an optical crosshair is provided below the collimator.
3 causes an optical crosshair to be projected. This optical crosshair is also emitted to the outside of the housing 26 similarly to the X-ray.
The optical crosshair is used when verifying the X-ray irradiation position, and the relationship between the optical crosshair and the X-ray irradiation position is set so that the intersection of the optical crosshair becomes the X-ray irradiation center. Has been adjusted in advance.

[0006] When radiation is used for treatment, the radiation irradiating device is used to remove the radiation from the patient, more specifically, from the affected area.
X-rays will be applied to the affected area by setting it at a distance of 0 to 1000 mm, but in the same way when measuring the dose, it is necessary to measure the radiation dose at the melter 800 to 1000 mm away. Become.

Conventionally, when measuring radiation dose, a chamber is used and a water tank or the like is filled with water.
This water is regarded as the patient's equivalent tissue, and the dose in the water is measured. Actually, as shown in FIG. 15, the water tank 3 for dose measurement is located on the X-ray beam travel path at a predetermined distance.
0 is placed. The water tank 30 is filled with water 32,
And just 800-1000m from the radiation irradiation device 10
A dosimetry chamber 34 is arranged at a reference depth in water at a distance of m.

[0008] The chamber 34 is a scanning body containing a detection element sensitive to X-rays, and is mounted in a moving device (not shown) so that it can scan underwater two-dimensionally. By scanning the chamber 34 two-dimensionally, a dose distribution (intensity distribution) as shown in FIG. 16 is obtained. Although the example in the figure shows a case where the irradiation field is circular for convenience, a rectangular (10 × 10 cm) irradiation field is actually used as a dose measurement shape. FIG. 17 shows the dose distribution on the scanning line n in FIG.

FIG. 16 shows the size and shape of the irradiation field.
FIG. 17 shows the intensity distribution (flatness distribution) in the irradiation field.
Also, by scanning the chamber 34 in the depth direction from the position (water surface) at the point c in FIG. 15, a dose distribution as shown in FIG. 18 is obtained. Since the dose (intensity) at the reference depth below the water surface is known from FIG. 18, it can be determined whether the dose matches the target dose at the depth of the reference depth. Although the reference depth changes depending on the energy of the X-rays,
It is 5 cm in MV.

The above-mentioned water tank 30 is 48 × 48 × 4
It is a relatively large water tank of 0 cm or more, and it is necessary to scan the water with the chamber 34 after filling it with water. Therefore, the dosimeter becomes large and the measurement involves underwater scanning. is there. In addition, since the chamber 34 must be scanned two-dimensionally, the measurement time takes more than 30 minutes even for a veteran worker.

[0011]

In order to solve such a problem, an apparatus for measuring the degree of blackening of the X-ray dose instead of directly detecting the X-ray dose as in the chamber 34 is considered. Have been. In this case, a photosensitive film is used, and when the film is developed, X transmitted through the film is used.
Since the film is blackened according to the dose, an irradiation field image (X-ray image) similar to that in FIG. 16 is obtained.

The size of the irradiation field is checked by measuring the extent of the blackened contour with a ruler. The shape of the irradiation field can be seen from the blackened contour. Further, by visually examining the degree of blackening, the dose distribution, that is, the state of flatness in the irradiation field can be examined.

However, the determination based on the blackened image using the film is performed by visual observation of a measurer or by using a ruler or the like. In particular, the irradiation field and flatness measure the size and density of the contour of the blackened image. When the half-value width at which the dose is reduced to 1/2 is used as the irradiation field size, only the density information of the blackened image is used. It is almost impossible to measure this field accurately.

It is conceivable to use a micro-density meter or a fine concentration detecting element instead of these measuring devices. In this case, however, it is impossible to obtain information on the entire irradiation field two-dimensionally (as a surface). No, the operator must manually set the location to scan. Therefore, it is impossible to measure the entire information (rotation, size, etc.). In view of the above, the present invention has solved such a conventional problem, and proposes a radiation dose measuring method and a measuring device capable of accurately measuring a dose in a short time.

[0015]

According to a first aspect of the present invention, there is provided a radiation dose measuring method for irradiating a radiation having a radiation field serving as a measurement reference from a radiation source. It is characterized in that the irradiation field of the radiation is measured by converting the blackened irradiation field image into density data using the obtained measurement film and displaying the converted density information as a digital image. It is.

According to a fifth aspect of the present invention, there is provided a radiation dose measuring apparatus which scans a measuring film for irradiating radiation and converts an irradiation field image into density data. 2D information based on 3
It is characterized by comprising information processing means for processing into dimensional information and display means for displaying this density image based on the processed density information.

In the present invention, the measurement film is irradiated with radiation to obtain density information (irradiation field density image), which is converted into density data to measure the irradiation field and flatness. Since the irradiation field is obtained from the concentration data, the size and shape of the irradiation field can be accurately measured. Flatness can also be easily calculated.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the radiation dose measuring method and the measuring device according to the present invention will be described in detail with reference to the drawings. FIG. 1 shows the concept of measuring a radiation dose using a film instead of a chamber. The radiation dose measuring device 1 includes a radiation irradiating device 10 to be measured and a measuring film 35 to be irradiated with radiation.
And a data processing device 60 that takes in and processes a blackened image (shadow dose image) of the film 35 as density data. The film 35 is placed on the film mounting device 40 and irradiated with radiation after adjusting the relative positional relationship with the radiation irradiation device 10. The data processing device 60
It is composed of a scanner 62 for converting the density image of the film 35 into density data, and a data processing unit 63.

FIG. 2 shows an embodiment of the film placing apparatus 40. At the center of the flat base 32, two columns 3 are provided.
4, 36 were planted and these two pillars 3 were planted.
The mounting table 42 is rotatably attached to the mounting tables 4 and 36. For this purpose, rotating shafts 38 for rotatably supporting the mounting table 42 are provided at the distal ends of the columns 34, 36, respectively. A mounting table 42 is provided near the rotation shaft 38.
Fixing pin (not shown) for fixing the rotational position of
Are inserted, and three insertion holes 39 are provided concentrically in the example of the figure.

An opening / closing lid 50 is provided on the upper surface side of the mounting table 42, and a rectangular recess 44 which is slightly concave as shown in the figure is provided on the upper surface of the mounting table 42. A measuring film 35 for measuring a radiation dose is placed in the concave portion 44. Therefore, the concave portion 44 has a shape substantially corresponding to the size and thickness of the film 35. In this embodiment, the concave portion 44 has a depth and a width that allow the film 35 to be placed even in a wrapper. By the way, the size is A
The size is about four plates, and the depth is 1.5 to 2 mm. In the illustrated example, the right side of the concave portion 44 is released,
This is to make it easy to place the film 35 and make it easy to grasp.

The opening / closing lid 50 comprises a frame 52 and a pressing member 54 mounted inside the frame 52.
Is partially fitted into the concave portion 44. In this example, a transparent or translucent acrylic plate or the like can be used as the pressing body 54. The lower surface of the acrylic plate 54 is attached and fixed to the frame 52 in a slightly protruding state as described above. In the example shown in the figure, a transparent acrylic plate is used to make it easy to confirm the position of the film 35 placed.

A reference crosshair 56 is engraved (marked) on the lower surface of the transparent acrylic plate 54 at a predetermined position, in this example, substantially at the center, and at a predetermined position on an extension of the reference crosshair 56. As shown in FIG. 3, four reference pins 58 are embedded as shown in the sectional view of FIG.

The reference crosshair 56 is used for adjusting the radiation irradiation position of the radiation irradiation device 10. The radiation irradiating apparatus 10 is configured to be capable of irradiating an optical crosshair for allowing the radiation emission position to be visually observed instead of the radiation as described above. The irradiation position of the radiation irradiation device 10 is adjusted such that the light crosshairs match the reference crosshairs 56. The plurality of reference pins 58 are used as pointers indicating reference positions when converted into density (dose) data. This is because the reference crosshair 56 is not formed into a latent image on the film 35 even when the X-ray is irradiated.

On the side surface of the mounting table 42 on which the rotating shaft 38 is provided, and at positions corresponding to the above-described insertion holes 39, insertion holes for insertion pins (both not shown) are provided. A hook 60 for fixing the opening / closing lid 50 to the mounting table 42 is provided in a part of the opening / closing lid frame 52.

The mounting table 42 is configured to be rotatable with respect to the base 32 because the radiation irradiating apparatus 10 used for radiation therapy is of a fixed type that irradiates radiation from directly above (vertical axis). This is because there is a rotary type whose irradiation position can be rotated. In order to be able to measure the radiation dose from any type of device, the mounting table 42 is configured to be freely rotatable.

FIG. 4 shows a case where the mounting table 42 is fixed at a horizontal position, and FIG.
This is the case where the camera is rotated and fixed so that 4 faces right.
FIG. 6 shows the same vertical position, but the case where the transparent acrylic plate 54 is fixed so as to face the left side.

As described above, in the film mounting device 40, the reference cross line 56 for determining the reference irradiation position when irradiating the radiation to the predetermined position of the pressing plate 54 is engraved, and the reference cross line 56 is extended. A reference pin 58 indicating the position of the reference crosshair is provided on the line. Accordingly, when an optical crosshair 80 (see FIG. 8), which will be described later, radiated from the radiation irradiating apparatus 10 is aligned with the reference crosshair 56,
The center of the reference crosshair 56 is the reference point (center point) of the radiation irradiation device.

Since there is a reference pin 58, when the film 34 is developed, this portion is blackened. Therefore, the horizontal blackened portion and the vertical blackened portion are defined by the X-axis and the Y-axis on the density information capturing side. (Monitor-side reference axis), the X-ray reference axis 80 and the monitor-side reference axis (XY axis) can be completely matched. It can be easily understood that the analysis of the distribution state and the intensity distribution of the X-ray dose can be accurately performed by the coincidence of the reference axes.

FIG. 7 shows an embodiment of the data processing device 60. The data processing device 60 includes a scanner 62 and a data processing unit 63 that processes density data read from the scanner 62. The scanner 62 is used as density data conversion means for converting a blackened image (shadow dose image) formed on the film 35 into digital density data. The scanner 62 is of a transmission type. It is enough that the resolution (resolution) is 200 dpi or more,
In this embodiment, a case where a transmission scanner of 600 dpi is used is shown.

In the case of a 200 dpi scanner, the resolution is about 0.12 mm, whereas the resolution is about 0.12 mm.
The resolution of the dpi scanner is 0.047 mm, and the performance is remarkably improved. Because of this resolution,
Even if the irradiation field of the radiation is 5 mm or less, the density information can be detected reliably. When the conventional chamber 34 is used, an irradiation field of 5 mm or less cannot be detected because the chamber itself has a size of about 6 × 23 mm. According to the present invention, even if the irradiation area is smaller than 1/10 of the chamber 34, the irradiation field can be reliably detected. If the X-ray dose can be measured in a state where the irradiation field is reduced to a fraction of the conventional value, X-rays can be accurately irradiated only to the affected area even if the affected area is 5 mm or less. Treatment is possible.

The data processing section 63 has a computer configuration and includes a CPU (64) as a central processing section and a memory (for example, a ROM) in which various processing programs are built.
66, a working memory (eg, RAM) 68 for processing density data into two-dimensional information or three-dimensional information;
A memory 72 for storing processed data, a monitor 72 for displaying a density image, a printer 74 for outputting processed two-dimensional information and three-dimensional information,
It comprises an external input device 76 such as a keyboard and a mouse, and an interface 78 for the scanner 62.

Now, an example of the measurement processing of the radiation dose measuring device 1 configured as described above will be described below. The X-ray is exemplified as the radiation as described above.

Before irradiating the film 34 with X-rays, the film 34 or a package containing the film is set in the concave portion 44 and the opening / closing lid 50 is closed (see FIG. 8). Open / close lid 5
By closing 0, the film 35 is pressed against the main body side, so that the film 35 is securely fixed.
Thereafter, the mounting table 42 is rotated to a horizontal position or a vertical position (see FIG. 4 or FIG. 5, FIG. 6), and the mounting table 42 is fixed at that position using an insertion pin at that position. At this time, the distance from the radiation irradiation device 10 to the opening / closing lid 50 of the mounting table 42 is 800 to 1000 as described above.
mm, the radiation irradiation device 10 and the mounting device 40
Relative distance is adjusted.

After the mounting table 42 is fixed, an optical crosshair 80 is irradiated on the upper surface of the opening / closing lid 50 as shown in FIG. At this time, the adjustment is performed so that the optical crosshair 80 matches the reference crosshair 56 formed on the upper surface of the opening / closing lid 50 (see FIG. 9). This completes the preparation stage of X-ray irradiation, and then irradiates the film 34 with a predetermined dose of X-rays in place of the optical crosshairs 80 for a predetermined time.

When the film 34 is irradiated with the X-rays, the film 34 is exposed to the X-rays. The exposed film 34 is developed. The portion irradiated with the X-rays by the development is blackened according to the dose. The film 34 is placed on the scanner 62 shown in FIG. 1 to scan a blackened image. As a result, the blackened grayscale image formed on the film 34 is converted into density data (digital grayscale data), which is taken into the data processing unit 63.

Since the grayscale image includes an image of the reference pin 58 struck on an extension of the reference crosshair 56, when the grayscale data captured by the data processing section 63 is displayed on the monitor 72, The reference cross line 56 of the grayscale data is made to coincide with the monitor display axis so that the reference axis 72 (X, Y coordinate axes) passes on the image 58S (see FIG. 11) indicating the reference pin. By using the information of the reference pins, display processing for performing rotation correction and the like of the entire image is also possible.

Since the monitor image XS (see FIG. 11) in which the dose is converted into the density information is obtained by the above processing, the irradiation field is obtained from the density area of the monitor image XS. As described above, since the irradiation field is defined by a half width at which the dose value is １ ／, the half width is calculated. The value of the irradiation field can be displayed on a monitor screen. The shape of the irradiation field is not limited to a circle. Even when a rectangular irradiation field of 10 × 10 cm is used, the irradiation field can be determined from the half width. When displaying on two dimensions, the X,
Since a scale is also displayed on the Y-axis at the same time, the irradiation field can be measured from this scale.

The irradiation field can be calculated from the half width on a specific scanning line. For example, if the light and shade information only on the horizontal crosshair is picked up and displayed, the result is as shown in FIG. 12, so that the irradiation field can be obtained from this. When displayed on the monitor screen, the irradiation field can also be obtained visually from the scale on the horizontal axis.

Of course, the dose distribution can be displayed from the two-dimensional information as shown in FIG. The example in FIG. 13 is a dose distribution obtained when the same dose value is connected by a line. It is also possible to convert the two-dimensional information into three-dimensional information and display it as a three-dimensional dose distribution as shown in FIG. Since digital density data is used, data processing becomes easy,
It is also possible to display the two-dimensional variation of the dose intensity in the irradiation field in color. By displaying these dose distributions, the state of flatness of the entire irradiation field can be visually and immediately determined.

When the irradiation field can be accurately grasped as described above,
The determination as to whether the irradiation field is appropriate is accurate. As a result, it is possible to accurately determine the irradiation field when used for treatment. It can solve problems such as not being able to provide a significant therapeutic effect.

Further, the flatness of the dose in the irradiation field can be determined from the image data representing the density shown in FIG. 8 of the irradiation field
The flatness variation can be known from the maximum density value max and the minimum density value min within 0%. When the variation ΔX is such that ΔX = {(max−min) / max} ≧ 5 (%), it is recommended that the irradiation output be adjusted. This determination can be made based on the converted density data as well as the prediction of the measurer, so that the fluctuation of the irradiation output can be grasped more accurately.

[0042]

As described above, according to the present invention, a radiation image latent on a film is developed, and a gradation image corresponding to the dose is converted into density information to determine a radiation irradiation field and the like. It was done. The use of such a radiation dose measuring method and measuring device has the following features.

(1) Since a gray-scale radiation image obtained by irradiating radiation is converted into density data (gray-scale data), an irradiation field defined by 1/2 (half width) of the dose is electronically converted. Can be determined. As a result, the size and shape of the irradiation field in the radiation irradiation device, which is the device to be measured, can be accurately compared with those of the standard, and the radiation irradiation device can be accurately adjusted.

(2) The flatness of the irradiation field can be measured from the maximum and minimum density data within the range of 80% of the irradiation field among the density data. When the flatness becomes 5% or more, it is recommended that the apparatus be adjusted, so that the timing of these adjustments can be accurately grasped.

(3) The measurement time of the radiation dose can be shortened. In the case of using a chamber as in the related art, it takes time to install the chamber and the like.
Often, more than a minute of measurement time is spent. In the present invention, the time required for setting the film, adjusting the irradiation position, loading the grayscale image into the computer, analyzing and displaying the monitor is completed within 10 minutes even for a measurer who is not familiar with the handling of the apparatus. Therefore, according to the present invention, the efficiency of the measurement operation can be improved.

(4) Since digital density data is used, it is easy to process the data, and it is possible to display the two-dimensional variation of the dose intensity in the irradiation field in color and display the intensity distribution. It can be grasped visually.
This makes it possible to know the uniformity of the irradiation field. By processing the two-dimensional data, three-dimensional display of the irradiation field becomes possible, and detection from various directions becomes possible.

Therefore, the present invention is very suitable for application to dose measurement of a radiation irradiation apparatus used for treatment.

[Brief description of the drawings]

FIG. 1 is a system diagram of a main part showing an embodiment of a radiation dose measuring device according to the present invention.

FIG. 2 is a perspective view of a main part showing an embodiment of the film mounting device.

FIG. 3 is a partial sectional view thereof.

FIG. 4 is a perspective view of a use state in a horizontal position.

FIG. 5 is a sectional view of a use state in a vertical position (part 1).

FIG. 6 is a sectional view of a used state in a vertical position (part 2).

FIG. 7 is a system diagram of a main part showing one embodiment of a data processing device.

FIG. 8 is a diagram showing a relationship between a reference cross hair and an optical cross hair (No. 1).

FIG. 9 is a diagram illustrating a relationship between a reference cross hair and an optical cross hair (part 2).

FIG. 10 is a partial cross-sectional view of the film loading device showing a film insertion state.

FIG. 11 is a diagram of a density image.

FIG. 12 is a density distribution diagram on a horizontal crosshair.

FIG. 13 is a two-dimensional dose distribution diagram.

FIG. 14 is a three-dimensional dose distribution diagram.

FIG. 15 is a system diagram of a conventional radiation dose measuring device.

FIG. 16 is a diagram showing the obtained shading information.

FIG. 17 is a dose distribution diagram on a scanning line n.

FIG. 18 is a dose depth distribution diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Radiation irradiation apparatus 22 Target 28 Light source for light crosshairs 30 Water tank 35 Film 40 Film mounting device 42 Mounting table 44 Depression 60 Data processing device 62 Transmission scanner 63 Data processing unit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshio Matsuda 1763 Shimonuma, Nakahara-ku, Kawasaki-shi, Kanagawa F-term in UI Engineering Co., Ltd. 4C082 AA01 AC02 AE01 AN02 AN10 AP03

Claims (7)

[Claims] An image of a blackened irradiation field is converted into density data using a measurement film obtained by irradiating a radiation having an irradiation field serving as a measurement reference from a radiation source, and the converted density information is digitally converted. A radiation dose measuring method, wherein an irradiation field of radiation is measured by displaying it as an image. 2. The radiation dose measuring method according to claim 1, wherein the flatness of the radiation dose on the irradiation surface is measured from the digital image. 3. The radiation dose measuring method according to claim 2, wherein the flatness of the radiation dose is measured from a maximum density and a minimum density of the digital image in the irradiation field. 4. The radiation dose measuring method according to claim 1, wherein the radiation is irradiated after the optical crosshair on the radiation source side is aligned with the reference crosshair on the measurement frame side. 5. Density data conversion means for scanning a measurement film for irradiating radiation to convert an irradiation field image into density data, and information processing means for processing into two-dimensional information and three-dimensional information based on the density information. And a display unit for displaying the density image based on the processed density information. 6. The radiation dose measuring device according to claim 5, wherein said density data converting means is a transmission type scanner. 7. The radiation dose measuring apparatus according to claim 5, wherein the information processing means performs processing for measuring a radiation irradiation field and flatness.