JP4402851B2 - Particle beam therapy device with separate snout - Google Patents

Description

[0001]
[Prior art]
Radiation therapy for cancer with charged particle beams such as protons and carbon ions greatly improves the commonly used radiotherapy with gamma rays, X-rays or electron beams. Because gamma rays, X-rays, or electron beams decay exponentially as they travel through a medium containing the human body, treatment of deep cancers is possible due to the acceptable dose limit of normal tissue near the body surface. While the necessary dose cannot be given, charged particle beams such as protons and carbon ions have a range determined by energy in the medium, giving a dose almost uniformly from the incident, just before the end of the range. Since the maximum of dose application called the Bragg peak occurs, it is possible to improve the therapeutic effect by matching this with cancer.
[0002]
This means, however, that if the Bragg peak is not exactly matched to the cancer, not only cancer treatment will not be performed, but normal tissue will be damaged and rather harmful. Therefore, an irradiation field forming device that is not used in conventional radiotherapy is required for accurate irradiation.
[0003]
The charged particle beam necessary for the treatment is supplied by a particle accelerator. In general, the particle beam supplied from an accelerator is a thin beam, and its cross section is much smaller than cancer. Therefore, in order to irradiate the entire cancer surface, the particle beam is expanded three-dimensionally by an irradiation field forming device. As a method of expanding the beam in a two-dimensional direction perpendicular to the direction of particle movement, there are a scanning method in which the beam is deflected by a magnetic field and a scatterer method in which the beam is incident on a thin metal plate having a large atomic number and is expanded by Coulomb multiple scattering. . The former is a situation where a lot of technological development is still needed for practical use, despite the fact that it has been attempted for more than 20 years, because of technical problems and related safety. Almost all treatments are basically performed using the latter scatterer method.
[0004]
The beam spread by the scatterer is axisymmetric, its intensity decays away from the central axis, and its intensity distribution can be approximated by a Gaussian distribution curve. In order to cut this according to the cross-sectional shape of the cancer, first, the beam is allowed to pass through a metal slit called a block collimator having a simple shape such as a rectangle or a circle, thereby stopping a low-strength component widely spread around the periphery. Next, a patient collimator (hereinafter referred to as a collimator) having an opening machined based on the cross-sectional shape of the cancer measured by X-ray CT is used to match the cross-sectional shape of the beam with the cross-sectional shape of the cancer. Irradiate cancer. The collimator needs to have a thickness corresponding to its energy in order to block the incident beam other than the aperture that matches the shape of the cancer. For example, in the case of a 200 MeV proton beam, if the collimator material uses brass, its thickness Is 7 cm.
[0005]
In general, the width of the Bragg peak of a single-energy charged particle beam is narrower than the size in the depth direction of the cancer. Therefore, in order to widen the width of the Bragg peak so as to correspond to the size in the deep direction of the cancer, the incident energy is spread by a ridge filter or a range modulator. Depending on the shape of the cancer, a beam with a different energy distribution must be incident in each direction. For this purpose, an energy absorber called a bolus based on the shape of the cancer is made of a plastic that has little function to scatter protons and used together with a collimator. This collimator bolus part is called a snout.
[0006]
In analogy with optics, the part corresponding to the light source of the beam is not a point but a surface with a certain spread. Therefore, a portion called penumbra is generated around the beam cut by the collimator. The snout is placed close to the patient in order to reduce the penumbra of the collimator, accurately irradiate the cancer, and reduce normal tissue exposure from the penumbra.
[0007]
The scatterer is installed at the end of the beam transport for transporting the beam from the accelerator to the irradiation device, and devices necessary for treatment such as a dosimeter are arranged near the scatterer. The conventional snout is fixed on the beam ridge like the beam transport, scatterer, dosimeter, etc., and has no freedom of movement other than being slightly movable in the direction of the patient. Therefore, the patient positioning work, that is, the approximate position is determined by moving the bed with a laser pointer and a handwritten mark on the skin or a bed mark, the simple X-ray device is moved on the beam axis, and the collimator is moved by X-ray imaging. The operation of finely moving the bed so that the cancer matches and then removing the simple X-ray device and mounting the collimator / bolus takes much longer than the particle beam irradiation. In a typical example, although the actual irradiation time of the beam is about 2 minutes, it is not easy to perform one irradiation within 30 minutes, and the utilization efficiency of the particle beam irradiation apparatus is significantly reduced. .
[0008]
In addition, the collimator cannot be easily installed depending on the irradiation angle. This is because there is no space in the irradiation position, and the collimator must be manually attached regardless of the weight of the dozen. For some cancers, the position / shape cannot be identified by simple X-rays, and the position / shape can be recognized only by X-ray CT. However, it is impossible to arrange a horizontal general X-ray CT apparatus at the irradiation position of particle beam therapy because of the size of the apparatus.
[0009]
[Problems to be solved by the invention]
Therefore, in particle beam therapy that requires much higher precision than conventional X-ray therapy, it is possible to perform alignment with a much more accurate X-ray CT apparatus, and at the same time occupy the irradiation position for alignment Therefore, it has been required to significantly improve the operation efficiency of the particle beam therapy apparatus which is much larger and more expensive than the X-ray therapy apparatus, and to improve workability and safety.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a particle beam therapy system according to the present invention provides a patient collimator / bolus portion (snaught) constituting a radiation field forming apparatus in a cancer treatment apparatus using a charged particle beam. Means for separate and independent movement from other components and beam transport system, and the same shape as the opening of the patient collimator bolus part (snoot) or the distance between the light source and the patient in the opening (SSD ) With the shape of the corrected template, and means for aligning the template with respect to the cancer other than the irradiation position by the X-ray imaging apparatus, while maintaining the relative position of the patient and the template constant, Means for moving the patient to the irradiation position; and means for matching the template with the patient collimator / bolus part.
[0011]
Here, a proton beam, a helium ion beam, or a carbon ion beam is used as the charged particle beam, and an X-ray CT apparatus, a simple X-ray apparatus, or an X-ray simulator is used as the X-ray imaging apparatus.
[0012]
[Action]
The present invention improves the workability by making it possible to move the patient collimator / bolus part (snaught) separately from the other components of the irradiation field forming device and to attach the collimator at a place away from the irradiation position. And ensure patient safety when wearing a collimator. In order to accurately irradiate cancer, it is indispensable to accurately position the collimator with respect to the cancer. For this reason, the patient and the template are placed by a horizontal general X-ray CT apparatus or X-ray simulator. Simultaneous imaging improves the patient positioning accuracy, shortens the time required for positioning, and remarkably improves the operation efficiency of the particle beam irradiation apparatus. Here, the template is used because it is impossible to simultaneously photograph the patient and the collimator using the X-ray CT apparatus.
[0013]
【Example】
A configuration of a particle beam therapy system according to an embodiment of the present invention and an operation method thereof will be described with reference to the drawings.
FIG. 1 shows the arrangement of the devices of the particle beam therapy system. FIG. 2 shows an example of the components in the present invention and their arrangement during irradiation.
First, the position and shape of cancer are measured by X-ray CT, and the irradiation direction and irradiation range are specified. The collimator 6 and bolus 5 are designed and manufactured based on the treatment plan. When processing the collimator 6, a template 7 having an opening having the same shape as the opening of the collimator 6 is manufactured on a thin plate of metal or plastic.
[0014]
A patient fixture and a support for the template 7 are fixed to the bed top plate 8 of the X-ray CT apparatus. For patient positioning, the patient and the template 7 are simultaneously imaged on the 2 or 3 slice plane by an X-ray CT apparatus, and the relative position between the cancer and the template 7 viewed from the irradiation direction is measured. Based on the result, the position of the template is corrected, and it is confirmed again by simultaneous shooting that the two match. If possible, the bolus 5 is simultaneously photographed to confirm the dose distribution in the depth direction.
[0015]
The rotating base 11 on which the snout 4 is mounted has a structure that can be rotated around the horizontal axis by the roller 10 so that the snout 4 is directed in the beam direction, and the snout 4 is set in the beam direction from the irradiation field forming device 3 in advance. . Then, after the collimator 6 is mounted on the snout 4, the snowt stand is moved to place the snout 4 at the irradiation position.
[0016]
After matching the cancer with the template 7 as seen from the beam irradiation direction by X-ray CT, the bed top plate 8 is moved while keeping the relative position of the patient and the template constant, and the patient is X-ray CT scanned. Move from position. Then, the bed is moved horizontally, the bed top plate 8 is returned to the same position with respect to the bed at the time of X-ray CT imaging, the bed is moved again, and the patient is moved to the irradiation position in the rotary mount 11 on which the snout 4 is mounted. move. Then, the snout collimator 6 and the template 7 are accurately matched by moving the bed up and down and finely adjusting the top plate.
[0017]
Then, based on the treatment plan after mounting the bolus 5, the beam from the particle accelerator 1 is irradiated with the particle beam through the beam transport system 2 and the irradiation field forming device. Since the bolus 5 is lightweight, it can be easily mounted at the irradiation position. Also, the reason why the bed top plate is substantially equal to the bed at the time of X-ray CT imaging and particle beam irradiation is to avoid errors due to the bending of the bed top plate.
[0018]
【The invention's effect】
As is clear from the above description, according to the present invention, in particle beam therapy that requires much higher accuracy than conventional X-ray therapy, a handwritten mark on the skin and a beam by a simple X-ray apparatus are generated. It is much larger than the X-ray treatment device because it is possible to align with the X-ray CT device, which is much more accurate than the conventional alignment, and at the same time the time to occupy the irradiation position for alignment is reduced. The operating efficiency of expensive particle beam therapy equipment will be greatly improved, and workability and safety will be improved.
[Brief description of the drawings]
FIG. 1 shows an arrangement of devices of a particle beam therapy system.
FIG. 2 shows an example of components in the present invention and their arrangement during irradiation.
[Explanation of symbols]
1: Particle accelerator, 2: Beam transport system, 3: Irradiation field forming device, 4: Snout, 5: Bolus, 6: Collimator, 7: Template, 8: Bed top plate, 9: Snowboard, 10: Roller, 11 : Rotating mount.

Claims (3)

In cancer treatment equipment using charged particle beams,
Means for allowing the patient collimator bolus part (snaught) constituting the irradiation field forming device to be moved independently from other components of the irradiation field forming device and the beam transport system;
A template having the same shape as the opening of the patient collimator bolus part (Snoot), or a shape obtained by correcting the distance between the light source and the patient (SSD) in the opening;
Means for aligning the template other than the irradiation position by an X-ray imaging apparatus;
Means for moving the patient to the irradiation position while keeping the relative position of the patient and the template constant;
A particle beam therapy system comprising: the template and means for matching the patient collimator / bolus part. The particle beam therapy system according to claim 1, wherein the charged particle beam is a proton beam, a helium ion beam, or a carbon ion beam. The particle beam therapy system according to claim 1 or 2, wherein the X-ray imaging apparatus is an X-ray CT apparatus, a simple X-ray apparatus, or an X-ray simulator.

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