JPS6220814B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for so-called radiotherapy, which uses a radiotherapy machine such as a medical linear therapy to irradiate a patient with a lesion in the body with radiation to treat cancer. Among them, anatomical diagrams of the patient's body necessary for accurate treatment,
So-called CT (computerized tomography)
This relates to a device for obtaining computed tomography images, using them for radiation treatment planning, and for accurate positioning during treatment.

Conventionally, in this type of technology, a radiation therapy machine such as a medical linear scanner and a CT were separate, separate devices that were operated separately from each other. Therefore, it had the following drawbacks.

1 Since CT is used for diagnostic purposes, the operating rate for diagnostic purposes is high, making it difficult to find time to use it for treatment.

2 Conventional CT is a CT image obtained as a distribution of X-ray absorption coefficients obtained from a low-energy X-ray source with an energy of 120 KV class, so
It lacked accuracy in direct use for treatment planning (particularly dose distribution calculations) in treatments using MV class high-energy X-ray sources.

3. It was extremely difficult to position the patient using the radiation therapy machine while maintaining the same body position and anatomy that was used to position the patient using CT. In particular, since CT is made for diagnostic use, it cannot be operated as if it had the same structure as a treatment machine, and even if a patient's photograph is taken with CT, it cannot be used for treatment as is. There were often cases where this was not possible.

In addition, a device for positioning that operates as if it had the same structure as a conventional radiation therapy machine,
A so-called simulator was used, but this device cannot obtain a cross-sectional image of the patient like CT, and cannot grasp the anatomical structure inside the body in three dimensions, so it is difficult to accurately position the lesion. The drawback was that it was not possible. Japanese Patent Application No. 53-28515 (publication No. 56-8623) was made in order to solve the above-mentioned drawbacks 1 and 3. however,
The drawbacks of No. 2 still exist, and in addition, two sets of radiation sources and detectors are required, resulting in a complex and expensive device, which creates new drawbacks in that it is complicated to operate and difficult to maintain.

The purpose of the present invention is to solve the above-mentioned drawbacks, to facilitate radiation treatment planning (dose distribution calculation and positioning), and to reproduce the same body position and anatomical structure during treatment as at the time of planning. To provide a device which can easily and accurately absorb radiation to a lesion of a patient, minimize radiation damage to other healthy tissues, and improve the clinical results of treatment.

In order to achieve the above object, the high-energy CT for radiation therapy according to the present invention shares the same radiation source as the radiation source of the radiation therapy machine, and both radiation therapy and CT imaging use radiation of the same energy or the same quality as this radiation source. a first means for emitting a constant electron beam pulse into an accelerator tube of a radiation source in response to rotational displacement of a gantry; and a second means for reducing a current value per pulse of the electron beam. , a third means for reducing the microwave power supplied to the accelerator tube according to the current value of the electron beam, and by sharing the same patient positioning geometry and mechanism, it can be used as a normal whole-body CT. In addition to the same functions as a regular radiotherapy machine, it also enables scanning scanography from any angle.
During CT imaging, the dose rate is reduced by the first, second, and third means while keeping the beam energy the same, and during CT imaging, an X-ray beam of the required shape is emitted by a collimator and the CT scanner It is configured to be able to operate as

That is, in the present invention, the treatment radiation source and CT radiation source of the radiation therapy machine are the same, they share exactly the same patient positioning mechanism, and the CT detector is embedded in the conventional beam stopper of the treatment machine. Alternatively, by having a new structure, the treatment machine and CT can be integrated, so to speak. For this purpose, while keeping the energy of the radiation from the source the same,
A means for reducing the dose rate only during CT imaging and making effective use of the linear range of sensitivity of the CT detector is added or newly provided to the functions of conventional treatment machines. In addition, if we focus on the functions of conventional treatment machines, we can add the so-called CT function to obtain the transmitted X that has passed through the patient's body from the detector.
It is equipped with a function to reorganize and display images from line data. Furthermore, one of the functions of CT is so-called scanography (a bed with a patient placed on it moves at a constant speed while emitting X-rays in the form of a thin slit to obtain a projected image, making it easy to reproduce the patient's positioning). It goes without saying that the simulator has the same function as the above-mentioned simulator. The present invention utilizes the same principle as rotational therapy such as linear therapy in radiotherapy and CT, in which a radiation source is rotated around the patient and radiation is irradiated. In addition to the original operation of a radiation therapy machine, the present invention also performs an operation as a CT, but it is not a mere combination or combination of these two operations, but also an operation as a simulator for treatment planning and a radiation dose X that can be used directly for distribution calculations
Not only does it create a new working behavior that describes the anatomical structure as the X-ray absorption coefficient in the radiation energy range or the distribution of electron density, but it also maintains exact reproducibility of the setup for each treatment of the patient. This action is performed.

Hereinafter, the apparatus according to the present invention will be explained in more detail with reference to the drawings and the like.

FIG. 1 is a side view of an apparatus according to an embodiment of the present invention;
and a simple internal structural diagram, and Figure 2 is the first
They are a side view seen from the right side to the left side of the side view in the figure, and a simple structural diagram of the inside. Figure 3 is
FIG. 2 is a front view of a CT image display device.

Most of the external appearance and structure shown in Figures 1 and 2 are the same as conventional or current radiation therapy machines (medical linear accelerators in this figure); The only difference is that an X-ray detector 11 is included.
Although not shown in the figure, circuits related to the X-ray detector 11 and other related devices are attached to the medical linear rack. The microwave oscillated by the klystron 1 passes through the circulator 2 and reaches the acceleration tube 4, where it accelerates the electron beam as a pulse emitted from the electron mirror 3 to an energy of several MeV. (In this example, it is 10 MeV.) Then, the X-ray source 5 collides with the target 5 and emits X-rays from the X-ray source 5 having that energy to the patient 2.
Irradiate towards 1. At this time, the X to be irradiated to the patient
In order to obtain a line radiation field of arbitrary size and shape, the length in the axial direction of the patient's body is adjusted by the collimator 6, and the width in the lateral direction of the patient's body is adjusted by the collimator 61. The collimator 6 is adjusted to obtain a slice width with a constant thickness when this device is used as a CT. Although this is not shown in this figure, when you press the switch button from the treatment machine to the CT function on the console, it is set so that the slice thickness (for example, 10 mm) at the patient's irradiation area is automatically obtained. Ru. At the same time, the collimator 61 is fully opened to cover the entire width of the patient (for example, 42 cm).
be done. As a result, a normal linear system that obtains the X-ray fan beam 9 has a field of about 32 cm when fully opened, so this device can obtain a wide irradiation field (42 cm) even after being modified. When setting up the patient 21 on the treatment bed 7 at a predetermined position, the patient 21 is moved vertically, horizontally, and vertically using the functions of the treatment bed as a normal treatment machine.
When acquiring a CT image (this point is one of the most important points in the present invention), the same patient is set up at the same position that would be set up during treatment. Therefore,
The operation of the treatment table may be exactly the same as in conventional linear therapy. However, the top of the bed on which the patient rests and the frame on which the top is placed do not use the metal frames used in conventional treatment machines.
Artifacts occur in CT images and must be avoided. As shown in the figure, in the case of a single-support bed, materials other than metal that have sufficient strength include carbon graphite and others. For example, in the US
Such a material is used in the single support top plate of the Varian CT V-360-3. X-ray detector 11
is a detector based on the so-called third generation CT principle. An ion chamber system may be used, a scintillation crystal and photomal, a scintillation crystal and a semiconductor amplification device, etc. may be used. However, it is most ideal to use a semiconductor detector of the SURF S-barrier type that directly converts X-rays into electrical signals using high-purity silicon crystals. In this case, when using this device as a CT, there is an advantage that it can be used without significantly reducing the dose rate while maintaining the same high energy as in the case of treatment, because the X-ray irradiation dose This is because the ratio can be detected while maintaining linearity from a small amount to a large amount.

By the way, in order to use this device as both a treatment machine and a CT, the dose rate for use as a treatment machine must be several hundred.
rads/min and dose rate rads/min used as CT
The gantry 8 housing the radiation source 5 is rotated to perform CT imaging or treatment by rotating irradiation while maintaining the energy at a predetermined stable high energy level at considerably different dose rates and irradiating the patient. It is also necessary to obtain stable output without time-varying changes in dose rate. The reason for this is that during CT imaging, the radiation exposure dose to the patient must be minimized as much as possible, and as mentioned above, the X-ray detector becomes saturated with radiation at a high dose rate, causing linear distortion. There is a technical reason why the intensity of X-rays cannot be detected. To this end, when using this device as a CT, perform the following operations.

First, when the gantry 8 holding the X-ray source 5 and the detector 11 is rotated 360 degrees around the patient while emitting X-rays in pulse form, an electron beam pulse is transmitted to the acceleration tube for each degree of gantry rotation. It must be possible to fire inside. To this end, the gantry rotation speed can be precisely controlled at a constant speed of one rotation per minute.
This is possible with the existing technology of conventional medical linear axes. In addition, the electron beam pulses emitted from the electron mirror 3 are precisely controlled to be 360 pulses/min, that is, an integral multiple of 60 pps, and a steering coil is installed at the connection between the accelerator tube and the electron mirror. The pulses of the electron beam incident on the accelerating tube are thinned out so that the electron beam can be accelerated to exactly 60pps. This is done by controlling the oscillator of the pulse voltage generator applied to the cathode of the electronic mirror and the circuit that drives the steering coil.

Second, one of the electron beams emitted from the electronic mirror 3
The current value per pulse must be reduced. This is done by controlling the bias voltage applied to the grid provided on the electronic mirror 3. Exactly the same measures are used as are taken to make the energy of the linear strike variable.

Thirdly, the microwave power supplied to the accelerator tube is reduced in accordance with the electron beam current value reduced by the second means, and a predetermined energy (e.g.
10 MV), and must be controlled so that it can be accelerated stably. To this end, the klystron 1 and its control device are controlled to oscillate microwave power of a predetermined value obtained through calculations and experiments in advance. This is exactly the same means used to vary the energy of the linear electron beam.

Next, a method of using the present device will be explained for a patient 21 (an example to be treated). First, this device uses the scanography function of CT to clarify the location of the patient's lesion and the irradiation range. That is, the target volume is determined. To this end, this device makes effective use of scanography photography. Unlike general CT, this device can obtain scanography from any gantry angle (i.e., irradiation angle from any direction), so you can effectively utilize this advantage to determine the target volume and at the same time improve treatment. It is possible to take photographs at the appropriate irradiation angle and determine the irradiation field range, etc. In the example shown in FIG. 3, the gantry angle is set slightly to the upper right (that is, the radiation source position is set slightly to the upper right), and scanography is taken. By viewing the scanographic image 33 on the CT image display device 31, a graphical display 34 indicating the irradiation range is obtained while determining the target volume. The size, position, and shape can be arbitrarily determined by operating levers and knobs attached to the CT image display device 31. When performing multi-field irradiation, scanographic imaging is performed at the gantry angle of each gate, and sets of images 33 and 34 are obtained as many as the number of gates. The usage described above is almost the same as that of conventional therapeutic simulators.

Second, this device uses the CT cross-sectional imaging function to confirm the location of the patient's lesion and clarify the irradiation range. That is, the target volume in the cross-sectional image is determined. At this time, the normal
Of course, it is possible to use the photographs obtained with scanography and the scale contained therein to calculate and confirm slice positions, just as with CT. The embodiment shown in FIG. 3 shows an example in which the gantry angle is set slightly to the upper right (the radiation source position is set slightly to the upper right), and the irradiation direction and irradiation range are set. While looking at the CT image 32 on the CT image display device 31, by operating the levers and knobs attached to the CT image display device 31, the irradiation angle and irradiation field width are determined while freely moving the graphic display 35 indicating the irradiation field range.
At this time, the irradiation angle and irradiation field width must be consistent with those determined in the scanographic image 33 and the graphic display 34 showing the irradiation field range above it, so an automatic check is performed by the software. , so that the operator can understand. When performing multi-field irradiation, the irradiation field width is determined based on the gantry angle of each gate.

Third, dose distribution calculations are performed using the CT images obtained with this device. It is well known that dose distribution calculations can be performed using conventional CT images, so we will not discuss them in detail, but the CT images obtained with this device calculate the absorption coefficient distribution of X-rays with the same energy as that used for treatment. Because it represents the electron density distribution in the body as it is, it has the characteristic that there is no need to incorporate uncertain elements such as approximate conversion from low-energy absorption coefficient (CT number) to electron density as in conventional methods. ing. Further, it is not necessary to use a method such as approximation by extrapolation of electron density using the dual energy method. This device has the advantage of being able to obtain CT images with the same radiation quality as those used for such treatments and to calculate dose distribution accurately and with theoretical consistency. It is something. An optimal treatment plan for a given patient can be obtained by comparing the results of the dose distribution calculation thus performed with the results of the aforementioned determination of the irradiation direction and irradiation field size. The optimized plan includes information such as the gantry angle, irradiation field size, dose, wedge filter, and other treatment parameters at each gate, as well as the position of the movement of the treatment table with the patient on it. It is.

Fourthly, this device is used as a radiation therapy machine to perform treatment. At this time, it goes without saying that when setting up the patient 21 on the treatment table 7, the patient 21 is placed in the same position and posture as when the device is used as a CT. CT scan the device again just before treatment to ensure
A major feature of this device is that it can be used as a As a result, patient set-up and treatment can be performed so that a graphical display 34 showing the irradiation field range on the scanography image 33 and a graphical display 35 showing the irradiation field range on the CT image 32 and above are obtained, which are the same as those taken at the time of treatment planning. Set up the machine
CT images are taken and compared with the treatment plan. Radiotherapy for the same patient is often divided into dozens of sessions over dozens of days and repeated using the same setup to maintain accurate reproducibility. has important effects that have not been achieved before. That is,
It is possible not only to accurately match the treatment plan in setting up the patient and setting up the radiation therapy machine, but also to maintain accurate reproducibility in each treatment.

As explained above, the present invention allows for the same patient setup and treatment machine setup as during treatment by configuring a CT that has the same energy radiation source and patient setup geometry and mechanism as the radiation therapy machine. It has the effect that treatment planning can be carried out,
It has the effect of supplying an X-ray absorption coefficient distribution using high-energy X-rays that was previously unobtainable in order to accurately calculate the dose distribution, and it also has the effect of providing an accurate comparison with the aforementioned treatment plan for each divided radiation treatment. , which has the effect of maintaining reproducibility accuracy. The synergistic effect of these three effects contributes to improving the accuracy of radiation therapy that was previously unobtainable.
It will produce new effects that will help improve the clinical results of cancer treatment.

[Brief explanation of the drawing]

FIG. 1 is a side view and a simple internal structural diagram of a device according to an embodiment of the present invention, and FIG. 2 is a side view and a simple internal structural diagram when viewed from the right side to the left side of FIG. FIG. FIG. 3 is a front view of the CT image display device. 1... Klystron, 2... Circulator, 3... Electronic mirror, 4... Accelerator tube, 5... X-ray source, 6... Collimator, 7... Treatment bed, 8...
Gantry, 9...X-ray fan beam, 61...collimator, 11...X-ray detector, 21...patient,
31...CT image display device, 32...CT image, 3
3... Scanographic image, 34... Graphical display showing the irradiation range, 35... Graphical display showing the irradiation range.

Claims (1)

[Claims] 1 In high-energy CT for radiation therapy, the same radiation source as that of the radiation therapy machine is shared, radiation of the same energy or the same radiation quality is obtained from this radiation source for both radiation therapy and CT imaging, and the rotational displacement of the gantry is a first means for injecting a correspondingly constant electron beam pulse into the accelerator tube of the source; and a second means for reducing the current value per pulse of the electron beam.
and a third means for reducing the microwave power supplied to the accelerator tube in accordance with the current value of the electron beam, and by sharing the same patient positioning geometry and mechanism, CT for
In addition to the same functions as those of a normal radiation therapy machine, it also enables scanning scanography from any angle. 1. A high-energy CT for radiation therapy, characterized in that it is configured to reduce the dose rate and operate as a CT scanner by emitting an X-ray beam with a required shape during CT imaging using a collimator.