JP2012161662A - Radiotherapy apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiotherapy apparatus controlled by therapy control computer.SOLUTION: A therapy plan device for a radiotherapy apparatus is the apparatus of a type including: a radiation source which is capable of emitting a beam of radiation for therapy along a beam axis, is rotatable around a rotation axis practically matching the beam axis, and thereby drawing an arc with the axis as the center; a multileaf collimator configured to collimate the beam into a desired shape; and a control means capable of controlling the rate of the dose of the radiation source, the rotation of the radiation source, and the multileaf collimator.

Description

  The radiotherapy apparatus is typically controlled by a treatment control computer. When equipped with a multi-segment collimator (“MLC”), the treatment control computer is a radiation control computer that controls the generation of radiation, an MLC control computer that controls the shape of the MLC, and a gantry It can be considered that a gantry control computer for controlling the position is provided. These computers may physically be one or more computers, but are considered herein as separate functional elements of the system.

  “Mu” is an abbreviation for “monitor units”. This is the term used for the unit of radiation from the radiotherapy device. mu is equivalent to the unit of dose delivered to the patient under good calibration conditions. The relationship between mu and dose is modeled with a treatment planning computer. While the user interacts with the patient's dose prescription, the treatment plan computer defines the treatment plan in units of mu. One of the tasks of the treatment planning computer is to achieve a specific dose in the patient's body, both with a sufficiently high dose in the tumor and with a sufficiently low dose in other parts of the patient. It is to confirm the mu that the device needs to send. Although informal, the use of the term “dose rate (dose rate)” means “mu rate”.

  Intensity modulated radiotherapy is a generic term for many radiotherapy techniques. This essentially changes the beam directed at the patient. This change is spatial, temporal, or both.

  Known linac delivery techniques include the techniques listed below.

  Segmental or static multi-leaf collimator— “SMLC” —is a technique in which a multi-segment collimator (“MLC”) is static during irradiation. The MLC moves (changes) from one shape (mode) to the next shape (mode) during irradiation. In one structure, the point in time when irradiation is stopped and the MLC is moved is controlled by dosimetry hardware and a radiation control computer. Thereby, the dose is delivered very accurately for each MLC shape. The modified system uses a DMLC structure to achieve the same effect. The MLC control computer monitors the delivered dose and stops radiation when it detects that it must move (change) from one shape (aspect) to another. Due to the inevitable delay of the control system associated with this structure, the dose for each MLC shape is indeterminate and, in some cases, the shape is incorrect.

  Dynamic MLC-DMLC- is a technique in which the MLC moves during irradiation while the gantry remains stationary. The MLC moves linearly as a function of the delivered dose from one shape to the next. The MLC control system must monitor the delivered dose, which inevitably causes a delay. In older systems this delay was 200 ms to 300 ms, but in relatively modern systems it is about 40 ms to 50 ms. This delay, coupled with the MLC response, introduces a shape lag in the dose. This has been reported exclusively in the literature, but is widely considered not clinically important.

  Rotating DMLC-RDMLC- is a technique in which the MLC moves during irradiation during a constant rotation of the gantry. The gantry moves at a constant mu / degree. The MLC moves linearly as a function of the delivered dose from one shape to the next. The shape is usually defined at equal intervals over the arc, but this is not necessarily so. This can be done by a substantially independent MLC control computer, radiation control computer, and gantry control computer.

  Sensitized rotation DMLC-ERDMLC- is a technique in which the MLC moves during irradiation while the gantry moves at a variable mu / degree. The gantry moves with variable mu / degree. The following effects can be obtained with variable gantry speed or variable dose rate (or both): When using only variable dose rates, it was analyzed by Gent University as a preferred option. This is to increase the transmission time. The MLC moves linearly as a function of the delivered dose from one shape to the next. The shape and dose are usually defined at equal intervals over the arc, but this is not necessarily so. This technology requires a very high degree of integration between the MLC control computer, the radiation control computer, and the gantry control computer, and there is currently no one that can deliver ERDMLC except for the linac. Therefore, only linac is theoretically possible.

  Listed below are treatment techniques that have both a treatment planning function and a linac delivery function, and known techniques.

  Intensity Modulated Radiation Therapy-IMRT- is a series of MLC shapes, and related doses can be delivered using SMLC and DMLC. These shapes are defined by a limited number of stationary gantry positions, typically 5-9. The shape and dose are determined by the optimizer trying to meet the user determined goal. The treatment planning function is generally specific to the MLC restriction-delivery technique.

  Rotational Conformal Arc Treatment-RCAT-is a technique that rotates the gantry constantly while dynamically adjusting the leaf to the projection of the target volume. This technology has been used in Japan for many years. The transmission technique is RDMLC, which uses only one pendulum.

  Intensity Modulated Arc Therapy-IMAT-is an optimization that attempts to deliver the required dose distribution to the critical target structure, rather than the pendulum and leaf positions being determined by target volume projection It is a treatment planning function determined by a routine. In general, many pendulums are used over various gantry angle ranges. Optimization is done in the same way as IMRT, but includes the additional flexibility of a rotating gantry. IMAT can be sent via RDMLC, but this limits the optimization to keep mu / degree constant. For this reason, this is a non-optimal plan. More ideally, optimization is possible by using full freedom and ERDMLC techniques. The delivery time is very short, typically completing the plan in 3 minutes. Apparently, this technique looks similar to RCAT, but the method for determining the shape of the MLC is different.

  The IMAT, for example, described in chapter 3 of the International Society of Oncology, Volume 60, pages 794-806, dated 1 November 2004, “The great potential for improving both planning and delivery levels. One of the most important technological improvements for IMAT is to make the gantry speed variable, ”Dusoi et al.,“ Intensity-Modulated Pendulum Irradiation Therapy for Rectal Cancer (IMAT) Clinical Are discussed in the section "Implementation" That is, the device can perform ERDMLC.

Optimal segment-aperture mono-arc therapy -OSMAT- is a special grade of IMAT that uses only one pendulum. This is suitable for some clinical indications. It can also be considered an improvement of RCAT. Similar to IMAT, the delivery technique may be just RDMLC, but more ideally ERDMLC.
The delivery time is very fast, typically one minute.

  Arc Modulation Optimization Algorithm -AMOA- is a technology used by 3D Line Medical Systems. The leaf shape is determined by anatomy (as in RCAT), then the pendulum is divided into approximately 20 ° sub-pendulums, the weight or mu / degree of these sub-pendulums optimized, and the best dose distribution Provided (similar to IMAT or IMRT). Thus, this is a form of IMAT or OSAMAT and does not use the option of changing leaf positions. This can be planned and delivered very quickly, especially using ERDMIC delivery technology.

  Helical intensity modulated arc therapy -HIMAT- is a technique developed from IMAT technology, which translates the patient in the length direction and simultaneously rotates the gantry. Thereby, the lengthwise length of the field where the treatment can be performed is practically not limited and is practically comparable to the tomotherapy delivery technology. This is described in detail in US Pat. No. 5,818,902 and WO 97/13552. This typically has an MLC with a fixed orientation and the leaf moving laterally relative to the patient. The MLC has a high resolution leaf and has a limited field size. This is because the field size can be extended by using helical technology.

  The transmission technology for HIMAT may be just RDMLC. This is because various high doses can be delivered from a predetermined angle by many rotations. Delivery time is extremely fast, typically completing a plan in 3 minutes.

  ERDMLC delivery technology may be advantageous over IMAT and HIMAT treatment plans. However, I did not know that ERDMLC was actually sent. Therefore, although the performance is almost the same as that of ERDMLC, a transmission technique that is technically easy to perform transmission has great value.

  Traditionally, all pendulum irradiation has been delivered at a constant nominal rotational speed and a constant dose rate. This made the rotation mu / degree constant. This requires limiting treatment plan optimization. This reduces the clinical quality of the plan. Furthermore, the leaves of a multi-segment collimator have a maximum moving speed, and therefore there is a maximum distance that these leaves can move at a given dose rate and dose for a given pendulum segment. This is also a limitation in the plan and limits the quality of the plan.

  If mu / degree can be changed by optimization in the treatment planning computer, the number of important organs in the path of radiation is reduced by putting more doses into the gantry angle. For example, when treating the prostate, the bladder and rectum enter and exit the path of radiation as the gantry rotates. It is impossible to prevent these organs from being irradiated at all, and it is desirable (otherwise the dose delivered to the prostate is insufficient), but the dose delivered to these important organs by optimization If it can be controlled relatively freely, undesired exposure can be reduced.

  If the dose rate for pendulum irradiation can be reduced, this can make planning more flexible, but delivery is time consuming, which is undesirable. The object of the present invention is to eliminate such limitations from the treatment planning process, thus maximizing the quality of the plan and at the same time speeding up the delivery time. Rapid delivery time is important for departmental efficiency and precision image-guided radiotherapy, and is important to keep the organ from moving between imaging and completion of irradiation.

  Accordingly, the desired treatment according to the present invention will be described by the treatment planning computer in terms of "control point" order. Each “control point” determines the position of the gantry, the dose to be delivered between this control point and the next (previous) control point, and the MLC at the control point. Each successive pair of control points (in between) determines an arc segment (arc-segment).

  This treatment is performed between the nth control point and the (n + 1) th control point, and the necessary dose is delivered from the position of the nth control point to the position of the (n + 1) th control point. Therefore, it is moved at a predetermined rotation speed and dose rate combined. At this time, when the gantry is at the (n + 1) th control point, the MLC leaf is moved so that the leaf is in a correct position with respect to that point. Typically, the travel distance of the MLC leaf moves the MLC leaf at a speed that is always linearly related to the dose delivered by the arc segment. The process is then repeated for the arc segment between the (n + 1) th control point and the (n + 2) th control point, which is performed until the treatment is complete.

  Thus, the following radiotherapy apparatus is proposed. A radiotherapy apparatus is a radiation source capable of emitting a beam of therapeutic radiation along a beam axis, and is rotatable about a rotation axis substantially orthogonal to the beam axis, thereby causing the axis to be rotated. A source that draws a central arc, a multi-segment collimator configured to collimate the beam to the desired shape (to collimate the beam to the desired shape), and the dose / time rate of the source And a control means capable of controlling the rotational speed of the radiation source and the position of the multi-division collimator. The control means is a treatment plan in which the arc is divided into a plurality of conceptual arc segments, receives a treatment plan that identifies the total dose for the arc segment and the start and end positions of the MLC, and according to the plan The radiation source is configured to be controlled. During the first arc segment, at least one of the rotational speed and the dose rate is constant and the multi-segment collimator changes shape. Also, during the second arc segment, at least one of rotational speed and dose rate will be constant at a level different from the constant level employed in the first arc segment. MLC leaf travel at maximum leaf speed from the arc segment's predetermined start position to the arc segment's predetermined end position, and the total time required for the arc segment, from the start to the end of the arc segment Calculate multiple factors including source rotation at maximum source rotation speed and dose delivery at maximum dose rate per hour, and select and select the factor that indicates the longest time By controlling the device to operate at its maximum speed for a given factor and to operate at a reduced pace (rate, speed) selected to fit the longest time for the remaining factors, It is configured to control the source.

  The control means typically includes a therapy control computer and an actuator.

  The radiotherapy device preferably monitors the actual delivered dose during treatment and the actual location of the source and / or MLC, and compares this to the treatment plan to determine the source location and / or MLC. And / or the dose rate is configured so that the actual relationship between the delivered dose and the source position substantially corresponds to the treatment plan.

  Similarly, the radiotherapy device preferably monitors the actual delivered dose during the treatment and the actual position of the patient localization system (patient placement system), compares this with the treatment plan, and The position and / or dose rate is controlled so that the actual relationship between the delivered dose and the patient positioning system position substantially corresponds to the treatment plan.

  The radiation is preferably not interrupted between the first arc segment and the second arc segment.

  In this way, a system that is practically close enough to an ERDMLC is produced in the sense that it can be handled by an ERDMLC system for many purposes. Thereby, (i) a radiation source, (a) a beam of therapeutic radiation can be emitted along the beam axis, and (b) about a rotational axis substantially coincident with the beam axis. A source capable of rotating and thereby arcing about the axis; (ii) a multi-segment collimator configured to collimate the beam into a desired shape; and (iii) of the source Further proposed is a treatment planning device for a type of radiotherapy device having a dose rate, a rotation of the radiation source, and a control means capable of controlling the multi-segment collimator. The treatment planning apparatus is configured to send a first specific dose by sending a predetermined number of mu, and a second arc designed to send a second specific dose. Includes arc segments. During the first arc segment, the source rotates by a first specific angle that is a predetermined degree (°), and the multi-segment collimator changes shape at a rate (pace, speed) per first specific angle. During the second arc segment, the source rotates at a second specific angle and the multi-segment collimator changes shape at a rate (pace, speed) per second specific angle. First and second specific doses, the first and second specific angles, the rate (pace, speed) per the first and second specific angles, the mu per angular rotation (°), and , At least one of the mu per MLC leaf movement (mm) is different between the first arc segment and the second arc segment.

  The beam axis and the rotation axis of the source are preferably substantially orthogonal for geometric simplicity.

  As is apparent from the above, it is preferred that both the rotational speed and the dose rate are constant in the arc segment, but at least one of these is different between the first arc segment and the second arc segment.

  In general, the first arc segment and the second arc segment are continuous. However, individual successive arc segments may in fact be the same specific rotation speed and dose rate. However, in the treatment plan according to the present invention, at least one of the paired arc segments is different.

  The treatment planning device, of course, includes some form of output means for communicating the treatment plan to the radiation treatment device.

  The treatment planning device further prescribes a treatment plan that includes movement of the patient localization system during treatment. This movement of the system takes place in a manner that correlates with the source and / or dose delivery. This can provide (in itself) HIMAT therapy.

  Next, an embodiment of the present invention will be described by way of example with reference to the accompanying drawings.

FIG. 1 is a graph showing optimization control points for leaf position and dose from a treatment planning computer. FIG. 2 is a graph showing optimization control points for the dose delivered according to the gantry position and treatment progress from the treatment planning computer, with approximations under the condition that mu per constant angle is constant. . FIG. 3 is a graph showing the effect of the control points of FIG. 2 on the dose rate, along with similar approximations. FIG. 4 is a graph showing ideal calculations of dose rate (solid line) and rotational speed (dashed line). FIG. 5 is a graph showing the actual calculation of dose rate (solid line) and rotational speed (dashed line) for a system without a continuously variable dose rate. FIG. 6 shows the relationship between computers.

  The desired treatment is described in relation to a series of “control points” by the treatment planning computer. Each “control point” describes the position of the gantry, the dose to be delivered between this control point and the next control point (or previous control point), and the shape (mode) of the MLC at that control point. Define. Each control point in consecutive pairs forms an arc segment (between those control points).

  The control points (in theory) may be strategically spaced across the entire arc. However, if the available computing power is relatively low, there is little advantage in trying to do this. Therefore, the control points are typically spaced at equal intervals across the arc every degree (°), every few degrees, or every few minutes.

  By moving the gantry from the position of the nth control point to the position of the (n + 1) th control point position at a predetermined rotational speed and a dose rate associated with delivery of the required dose, this treatment is made n It implements between the 1st control point and the (n + 1) th control point. At this time, when the gantry is at the position of the (n + 1) th control point, the MLC leaf is moved at a substantially constant speed so that the MLC leaf is at a correct position with respect to that point. The process starts at n = 1 and then repeats for the arc segment between the (n + 1) th control point and the (n + 2) th control point, which is performed until the treatment is complete.

  1 and 2 show control point patterns for treatment. FIG. 1 graphically shows details of control points according to treatment progress for a particular MLC leaf position. During treatment, the total mu dose delivered is tracked, the leaf is first extended, retracted and then extended again. The dashed line indicates the instantaneous position of the leaf when the controller moves the leaf between the control points at a constant speed so that the leaf is in the desired position when the next control point is reached. A similar graph exists for each of the 80 (typically) leaves. Each of these graphs typically has 6 or more control points, with 45 °, 90 °, or 180 ° control points.

  FIG. 2 shows the details of the control points for the total dose delivered during the gantry rotation. Thus, these control points are marked on a monotonic ascending scale. However, the amount of increase between successive control points varies correspondingly with the gantry angle at which a relatively large amount of radiation is delivered and in some cases a relatively small amount of radiation is delivered. The gantry angle at which a relatively small amount of radiation is delivered corresponds to the angle at which the target structure is hidden by important structures. The delivered dose can be changed by changing either the dose rate per hour or the gantry rotation speed or both. Obviously, the cumulative dose delivered between a given range of positions can be reduced by increasing the rotational speed or by reducing the dose rate. FIG. 2 shows the approximation given by the dashed line, provided that the mu rate per angle is constant. This reduces flexibility and requires either suboptimal dose distribution or absorption of changes due to MLC position, which increases treatment time.

  FIG. 3 shows the results of FIG. 2 for the dose rate at each gantry angle. At some gantry angles, the dose rate is high, indicating that a clear image of the target structure is obtained. At other gantry angles, the dose rate is greatly reduced. This indicates that the target is hidden by important structures.

  Thus, FIGS. 1, 2 and 3 show a treatment plan developed by a treatment plan computer without the limitations imposed by previously known devices. Again, the treatment control computer of the radiotherapy device converts the treatment plan into a set consisting of gantry movement, dose rate and MLC movement (deformation).

In this case, the minimum time that each arc segment can be delivered may be determined by the dose, gantry, or any one of the leaves of the MLC. Thus,
Minimum dose time = dose between control points / maximum dose rate Minimum gantry time = gantry travel distance / maximum gantry speed Minimum leaf time = leaf travel distance / maximum leaf speed
(Think about each moving leaf)

  In this case, the minimum time for the arc segment is the highest value of all these minimum values. This determines a time limiting parameter that can be any of the gantry, dose, or 80 leaves.

If the dose is not a time limiting parameter, the desired dose rate can be selected and the calculation is performed as follows.
Desired dose rate = control point dose / minimum time

  If the dose is a time limiting parameter, the selected dose rate is of course the maximum dose rate.

The expected gantry and leaf speed can then be calculated from the selected dose rate as follows.
Expected arc segment time = control point dose / selected dose rate Expected gantry speed = gantry travel distance / expected arc segment time And for each leaf of MLC,
Expected leaf speed = leaf travel distance / expected arc segment time

  FIG. 4 shows a choice between dose rate and gantry speed, ignoring the effect of MLC leaf speed for illustrative purposes. The x-axis is the dose rate per angle realized, which corresponds to the cumulative dose delivered between the two control points. The solid line is the dose rate and the broken line is the gantry rotation speed. Both are given maximum pace (rate and speed) due to the limitations of the particular device used. Thus, a dose D per unit revolution is achieved by a device operating at maximum rotational speed and maximum dose rate (per unit time).

  In order to achieve a dose per unit revolution higher than D, the rotational speed must be increased inversely, so the rotational speed in this region (see dashed line) exhibits a 1 / x profile, where The dose rate (see solid line) is constant. In order to make the dose per unit rotation smaller than D, the dose rate must be reduced proportionally as shown.

  Therefore, FIG. 4 shows the above calculation in the form of a graph.

  It should be noted that some radiation therapy devices do not actually produce a continuously variable dose rate. Instead, the dose rate can only adopt one of many preset levels. In such cases, the highest available dose rate that is lower than the desired dose rate must be selected. The other factor is determined as described above.

  This is shown in FIG. This corresponds to FIG. 4 except that in the region of FIG. 4 where the dose rate is linear, the dose rate is forcibly increased stepwise to the maximum dose rate. This is compensated not only for the maximum dose rate but by a rotational speed profile employing a series of 1 / x curves for each stage. Thus, by using a device that does not continuously change the dose rate per unit time, there is a problem with respect to the required treatment time, but there is no problem with the dose distribution.

  Ideally, the actual position is controlled to match the actual delivered dose, so that the actual speed varies slightly from the expected speed. However, the expected speed is a very useful parameter in ensuring optimal operation of the servo device.

  In this way, a system that is practically close enough to an ERDMLC can be produced in the sense that it can be treated as an ERDMLC system for many purposes.

  FIG. 6 shows the relationship between the various computers included in the system. The treatment plan computer generates a treatment plan that determines the treatment and sends it to the treatment control computer. As a result, for each arc segment (each pendulum irradiation), it is confirmed which factor is a factor that limits time. As a result, each of the MLC control computer, the gantry control computer, and the radiation control computer can be instructed about the operation of those particular items in the arc segment.

  In practice, it may be determined whether each of the exemplary computers should be on a separate computer, or whether some or all of the exemplary computers should be incorporated into a single processor. Needed. This determination is made based on the expected computational load and the pattern of available computing power.

  Such a treatment plan can be implemented on a radiation treatment machine substantially similar to that currently used. The physical difference from the present invention is the control device and treatment planning device, ie the actual radiation head and its driving means. The MLC and other systems may be those currently in use. However, the device has certain useful changes relating to the operation of the machine in this way.

  First, the radiating head reel system has the advantage of being able to move two or three revolutions or more over 360 °. This allows the operator to treat with IMAT pendulum irradiation three or more times without stopping, and further, the patient can be imaged and treated from below with continuous pendulum irradiation.

  Secondly, it is proposed to fit the entire machine in a set of covers, similar to a CT or MR machine, preferably closed at the inner end of the bore. By encircling the moving parts, the possibility of dangerous collisions is eliminated and thus the speed of the gantry can be increased fairly easily from 1 RPM to at least 2 RPM, and in some cases 5 RPM or 6 RPM. Thereby, treatment time can be reduced significantly. In addition, increasing speed provides new options for cone beam image acquisition. For example, an image can be captured while holding a single breath, thereby eliminating artifacts due to breathing motion.

  Finally, in order to further shorten the treatment time at high rotational speeds, it is proposed to eliminate the flattening filter normally placed in the beam path. This is to further equalize the intensity of the radiation across the device hole. These filters, of course, act to reduce the intensity of the beam in the central region of the hole, thus making a compromise between uniformity and overall dose. Alternatively, non-flat or uneven beams may be characterized and compensated for treatment planning. This eliminates the difficulties associated with uneven beam intensity. This is because adjustments are made with other treatment parameters, which can reduce the treatment time in proportion to the “recovery” of the radiation. This is removed in other aspects by a flattening filter.

  Of course, it will be understood that many modifications can be made to the embodiments described above without departing from the scope of the present invention.

Claims (15)

A radiation source capable of emitting a beam of therapeutic radiation along a beam axis, and is rotatable about a rotation axis substantially orthogonal to the beam axis, thereby centering on the axis An arc source,
A multi-segment collimator configured to collimate the beam into a desired shape;
Control means capable of controlling the dose / time rate of the source, the rotational speed of the source, and the position of the multi-segment collimator,
The control means includes
A treatment plan in which the arc is divided into a plurality of conceptual arc segments, receiving a treatment plan identifying an overall dose for the arc segment and the start and end positions of the MLC; and
Configured to control the source according to the plan over an arc segment;
The control means includes
The total time required for the one arc segment,
i. Movement of the MLC leaf at maximum leaf speed from a predetermined start position of the arc segment to a predetermined end position of the arc segment;
ii. Rotation of the source at the maximum source rotation speed from the start to the end of the arc segment; and
iii. Calculating for multiple factors including delivery of said dose at a maximum dose rate per hour, and
Select a factor indicating the longest time, and
Control the source according to the plan by operating at its maximum speed for the selected factor and controlling the device to operate at a reduced pace selected to fit the longest time for the remaining factors A radiotherapy apparatus characterized by: The radiotherapy apparatus according to claim 1, wherein the control means includes a treatment control computer and an actuator. The radiotherapy apparatus according to claim 1 or 2, wherein the radiation is not interrupted between the first arc segment and the second arc segment. Monitor the actual dose delivered during treatment and the actual position of the source,
Compare this with the treatment plan, and
Controlling the position of the source and / or the rate of the dose so that the actual relationship between the delivered dose and the source position substantially corresponds to the treatment plan. The radiotherapy apparatus as described in any one of Claims 1-3 characterized by the above-mentioned. Monitor the actual delivered dose during treatment and the actual location of the MLC;
Compare this to the treatment plan and control the position of the MLC and / or the dose rate so that the actual relationship between the delivered dose and the MLC position substantially corresponds to the treatment plan. The radiotherapy apparatus according to any one of claims 1 to 3, wherein the radiotherapy apparatus is configured as described above. Monitor the actual dose delivered during treatment and the actual position of the patient localization system,
Compare this to the treatment plan and control the position of the patient localization system and / or the rate of the dose so that the actual relationship between the delivered dose and the patient localization system position is substantially equal to the treatment plan. The radiotherapy apparatus according to any one of claims 1 to 3, wherein the radiotherapy apparatus is configured so as to correspond to each other. (I) a radiation source, (a) capable of emitting a therapeutic beam of radiation along the beam axis, and (b) rotating about a rotational axis substantially coincident with said beam axis. A line source that draws an arc about the axis; and
(Ii) a multi-segment collimator configured to collimate the beam into a desired shape;
(Iii) a treatment planning apparatus for a radiation therapy apparatus of a type having a dose rate of the radiation source, rotation of the radiation source, and control means capable of controlling the multi-segment collimator,
The treatment planning device is configured to divide the arc into a plurality of conceptual arc segments and deliver a first arc segment and a second particular dose adapted to deliver a first particular dose. Configured to prepare a treatment plan having a second arc segment,
During the first arc segment, the source rotates at a first specific angle, and the multi-segment collimator changes shape at a rate per first specific angle;
During the second arc segment, the source rotates at a second specific angle, and the multi-segment collimator changes shape at a rate per second specific angle;
At least one of the first and second specific doses, the first and second specific angles, and the rate per the first and second specific angles are determined by the first arc segment and the second A treatment planning device characterized in that it becomes different between arc segments. During one arc segment, both the rotational speed and the dose rate are constant,
The treatment planning apparatus according to claim 7, wherein at least one of these is different between the first arc segment and the second arc segment. The treatment planning apparatus according to claim 7 or 8, wherein the first arc segment and the second arc segment are continuous. The treatment planning apparatus according to any one of claims 7 to 9, further comprising output means for transmitting the treatment plan to the radiotherapy apparatus. The irradiation time for each arc segment adapted to deliver a necessary dose is calculated, and the rotation speed is estimated from the irradiation time. The treatment planning device according to Item. 12. The treatment according to any one of claims 7 to 11, characterized in that it is configured to define a treatment plan including the operation of a patient localization system during treatment in relation to the movement of the source. Planning equipment. 12. The treatment plan according to any one of claims 7 to 11, characterized in that it is configured to define a treatment plan including the operation of a patient localization system during treatment in relation to the delivery of the dose. apparatus. The treatment planning apparatus according to any one of claims 7 to 13, wherein the beam axis and the rotation axis of the radiation source are substantially orthogonal to each other.   A radiation therapy apparatus substantially as herein described with reference to and / or shown in the accompanying drawings.

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