CN101199425B - Three-dimensional conformal irradiation device for heavy ion beam to tumor target area - Google Patents

Abstract

The invention relates to a device for performing three-dimensional conformal irradiation therapy on a tumor target area with a heavy ion beam, which includes a scanning magnet system, a beam current monitoring system, a miniature ridge filter, a range shifter, a multi-leaf collimator and The patient's body surface compensators are placed in front of the patient's body surface in sequence, and the centers of the above-mentioned devices and the center of the tumor target area are on the beam axis. The present invention overcomes the disadvantages of the current two-dimensional conformal irradiation treatment method based on the heavy ion beam of the passive beam distribution system, such as the low degree of conformity, the scatterers reducing the quality of the beam, etc., without using the existing two-dimensional conformal irradiation method Under the condition of scatterers in the medium, the conformity of the heavy ion beam to the tumor target area is improved through three-dimensional conformal irradiation, and the high-dose Bragg peak area of the heavy ion beam is used to efficiently kill the tumor cells in the target area without reducing the high-efficiency. It can maximize the protection of healthy tissues around the tumor target area, reduce the chance of complications in normal tissues, and improve the therapeutic effect of heavy ion beams.

Description

Three-dimensional conformal irradiation device for heavy ion beam to tumor target area

technical field

The invention relates to a device for irradiating heavy ion beams in the field of biomedicine, in particular to a device for performing three-dimensional conformal radiation therapy on tumor target areas by heavy ion beams.

Background technique

Heavy ion beams are known as the most ideal rays for radiotherapy in the 21st century. The device can realize the three-dimensional conformal irradiation of the heavy ion beam on the tumor target area. The three-dimensional conformal irradiation technology can give full play to the advantages of heavy ion beams in cancer treatment, kill tumor cells in the target area to the greatest extent, and at the same time protect the healthy tissues around the tumor target area from damage to the greatest extent, and reduce the complications of normal tissues. It can improve the conformity degree of heavy ion beam therapy, thereby improving the curative effect of heavy ion beam radiation therapy.

Due to its reversed depth dose distribution and high relative biological effect (RBE), heavy ion beams have become the most advanced and effective radiation therapy in the world today. At present, only the United States, Japan and Germany, three developed countries, have successively realized the clinical trials of heavy ion beam therapy for tumor patients, and the clinical treatment results show that heavy ion beam therapy has a very significant curative effect. The heavy ion beam therapy equipment in the United States and Japan adopts a passive beam distribution system, that is, a large irradiation field is formed through the swinging magnet and the scatterer in cooperation with the horizontal expansion of the cancer treatment beam, and the irradiation is intercepted laterally by a multi-leaf collimator. field, the shape of the obtained irradiation field is consistent with the maximum projection shape of the tumor in the beam direction, and the Bragg peak of the heavy ion beam is broadened longitudinally through the ridge filter, so that the width of the Bragg peak after broadening is the same as that of the tumor target area in the beam direction. The thickness of the high-dose area on the widened Bragg peak is adjusted by the tissue compensator placed on the patient's body surface, which can avoid the high-dose area from irradiating important organs behind the tumor target area, and can realize heavy ion beam Two-dimensional conformal irradiation of tumor targets. Germany has adopted an active beam distribution system, and the method of realizing conformal irradiation therapy is completely different from that under the passive beam distribution system. In my country, the Institute of Modern Physics of the Chinese Academy of Sciences, based on the medium-energy heavy ion beam provided by the Lanzhou Heavy Ion Research Facility (HIRFL), has carried out basic research on heavy ion beam cancer treatment technology, conducted radiation physics, radiation biology experiments and some treatments. Preliminary research on cancer technology has accumulated some necessary basic data for heavy ion beam clinical treatment, made preliminary technical preparations, and built a shallow tumor heavy ion beam therapy equipped with a passive beam delivery system on HIRFL. device. However, from the above-mentioned heavy ion beam therapy equipment in the United States and Japan that uses a passive beam distribution system, it can be seen that the heavy ion beam therapy under the passive beam distribution system can only achieve two-dimensional conformal irradiation. When expanding the beam laterally, it is necessary to use scatterers, which reduces the quality of the beam, so the degree of conformity of the treatment is not high. There are still a large number of healthy tissues in front of the tumor target area in the high-dose region of the broadened Bragg peak, which will affect the quality of the beam. Healthy tissue is more severely damaged and is the source of a higher rate of normal tissue complications after treatment.

Contents of the invention

In order to give full play to the advantages of heavy ion beams in radiotherapy, the purpose of this invention is to overcome the shortcomings of the current two-dimensional conformal irradiation therapy, such as the low degree of conformation and the reduction of beam quality by scatterers. We based on passive beam distribution The system provides a device for performing three-dimensional conformal irradiation therapy on the tumor target area with heavy ion beams, so that the high-dose Bragg peak area of the heavy ion beam completely falls on the tumor target area, and the proportion of healthy tissues irradiated by the high-dose area greatly reduced. As a result, the conformity and beam quality of heavy ion beam therapy with many advantages are improved, the tumor cells in the target area can be killed to the greatest extent, and the healthy tissues around the tumor target area can be protected to the greatest extent, reducing the chance of complications in normal tissues , improve the curative effect of heavy ion beam therapy, and lay a solid foundation for the development of the most advanced and effective radiotherapy technology in our country.

The purpose of the present invention is achieved through the following technical solutions:

A device for performing three-dimensional conformal irradiation therapy on a tumor target area with a heavy ion beam, including a scanning magnet system, a beam current monitoring system, a miniature ridge filter, a range shifter, a multi-leaf collimator, and patient surface compensation The devices are respectively placed in front of the patient's body surface in sequence. The centers of the above devices and the center of the tumor target area are on the beam axis. The scanning magnet system consists of two sets of mutually perpendicular secondary magnets in the x and y directions. The beam monitoring system It consists of an ionization chamber and a position sensitive detector. The scanning frequency of the scanning magnet system in the x direction is 50-150 Hz, the scanning frequency in the y direction is 15-50 Hz, the distance from the scanning magnet to the patient in the y direction is 3-10 m; the position sensitive detector has a position resolution of at least 1 mm, and the ionization chamber monitors the ion beam The intensity is 10 ⁶ ~ 10 ⁸ pps; the mini ridge filter is an energy-reducing material of plexiglass PMMA, polystyrene, or aluminum in the shape of a ridge, and the distance between the peaks of the energy-degrading material ≤ 1.5mm, ion beam The broadened Bragg peak after passing through the mini ridge filter showed a Gaussian distribution, and the half-maximum width of the broadened peak was 2-3 mm, and the mini ridge filter was placed at a distance of 65-100 cm from the beam axis to the center of the tumor target area. .

Based on the passive beam distribution system, the principle of the present invention to realize the three-dimensional conformal irradiation of heavy ion beam therapy is shown in Figure 1, that is, the scanning magnet is used to laterally expand the beam current to obtain a wide heavy ion beam irradiation field. The flow direction is divided into different slices, and the beam Bragg peak is broadened to a width suitable for the thickness of the tumor slice by using a mini-ridge filter, and the slices are irradiated one by one. When treating a slice, use a multi-leaf collimator to intercept the irradiation field to obtain an irradiation field consistent with the projection shape of the tumor slice in the beam direction, and adjust the beam energy through the range shifter so that the broadened Bragg peak falls on this fault.

Specifically, the cancer treatment beam is adjusted to a beam spot with a relatively small lateral diameter before entering the scanning magnet system, and the beam intensity in the cross section of the beam spot presents a Gaussian or near-Gaussian distribution. After the beam is output, two sets of mutually perpendicular secondary magnets in the x and y directions scan the beam in the lateral direction to obtain a wide heavy ion beam irradiation field, so that the beam can evenly irradiate the entire tumor target area in the lateral direction. The uniform irradiation field is realized by the sawtooth raster scanning method, that is, the secondary magnet in the x direction guides the beam current to periodically shift at a faster speed with the change of the sawtooth wave magnetic field strength with a higher frequency, while the secondary magnet in the y direction changes the frequency The lower sawtooth magnetic field intensity changes guide the beam current to periodically shift at a slower speed, and finally form a wide and uniform irradiation field. Figure 2 is a schematic diagram of a uniform irradiation field obtained by sawtooth raster scanning. As shown in the figure, two sets of secondary magnets perpendicular to each other can scan the beam current to form a horizontally uniform irradiation field that meets the treatment requirements. The change of the sawtooth wave magnetic field strength of the secondary magnet is realized by the current that changes the sawtooth wave input to it. Under the passive beam distribution system, obtaining a horizontally uniform irradiation field is a prerequisite for realizing the conformal irradiation of the heavy ion beam on the tumor in the lateral direction.

Different from the practice of using a ridge filter in the two-dimensional conformal irradiation method to broaden the beam Bragg peak to be consistent with the thickness of the tumor target area in the beam direction, the present invention uses a miniature The ridge filter only slightly broadens the Bragg peak of the beam, so that the broadened Bragg peak has a Gaussian distribution, and the half-maximum width of the broadened peak is 2-3 mm, which is consistent with the divided tumor slice thickness. The mini ridge filter is composed of energy-reducing materials in the shape of ridges (usually organic glass PMMA, polystyrene and other tissue equivalent materials or aluminum), and the ridge-shaped energy-reducing materials are periodically distributed. The beam passing through different parts of the ridge-shaped energy-degrading material has different degrees of energy reduction, so the proportion of each energy component in the mixed energy beam is determined by the shape of the ridge, so the shape of the broadened Bragg peak is determined by the shape of the ridge. Fig. 3 is a partial cross-sectional schematic diagram of a miniature ridge filter, the miniature ridge filter is made of aluminum material, and the water equivalent length coefficient of the thickness of the aluminum material under ion beam irradiation is 2.08, one cycle The shape of the inner ridge is described by the following function:

y=0.16268+0.17224x+6.83184x ² +129.20854x ³ -1413.52359x ⁴ +5520.70736x ⁵ -9669.93909x ⁶ +6402.03492x ⁷ ----------------- x∈[ 0mm, 0.5mm]

y＝975.65678-9145.53211x+36514.11121x ² -80354.79601x ³ +105212.37231x ⁴ -81943.98216x ⁵ +35144.38156x ⁶ -6402.04891x ⁷ ]------x∈[0.5mm，1.0

It can broaden the Bragg peak of the 90MeV/u carbon ion beam into a Gaussian distribution with a half-maximum width of 2mm. Figure 4 shows the effect of the mini ridge filter on the broadening of the Bragg peak of the 90MeV/u carbon ion beam. 1 in the middle is the Bragg curve of the 90MeV/u monoenergetic carbon ion beam, and 2 in the figure is the depth dose distribution after the Bragg peak is broadened by the mini ridge filter. In order to ensure that the multiple scattering effect of the beam passing through the mini-ridge filter makes the irradiation field achieve a uniform dose distribution in the lateral direction, it is required that the distance between the ridge peaks of the periodically distributed ridge-shaped energy-degrading material be small, and the mini-ridge The distance between the shaped filter and the isocenter of the treatment device is relatively large. Within the energy range of the cancer treatment beam (carbon ion beam energy 80-400 MeV/u), this distance is 65-100 cm.

When irradiating a tumor tomography, use a multi-leaf collimator to make the shape of the irradiation field consistent with the projected shape of the tomography in the beam direction of the tumor target area to be irradiated, and adjust the range shifter to make the above-mentioned broadened Bragg peak Irradiate on the slice of the tumor target area. Finally, according to the shape of the trailing edge of the tumor target area in the patient's body in the beam direction, the patient's body surface compensator is designed using tissue equivalent materials, so that the shape of the trailing edge of the broadened Bragg peak high-dose area is consistent with the trailing edge of the tumor target area in the beam direction. Consistent shape. In this way, the three-dimensional conformal radiation therapy of the heavy ion beam to the tumor target area is realized.

Advantage of the present invention and the beneficial effect that produce are:

Three-dimensional conformal irradiation improves the conformity of the heavy ion beam to the tumor target area, and can maximize the protection of the tumor target area without reducing the high-dose Bragg peak area of the heavy ion beam to effectively kill the tumor cells in the target area Surrounding healthy tissues, reducing the chance of normal tissue complications, thereby improving the therapeutic effect of heavy ion beams. In addition, in the present invention, the method of zigzag raster scanning is used to expand the beam laterally to obtain a wide irradiation field, which does not require the use of scatterers in the existing two-dimensional irradiation method, and the quality of the beam is improved; tumor targets can be differentiated more Layer fine conformal irradiation, the conformal degree of irradiation therapy is higher, the damage to the normal tissue in front of the tumor target area is small, which is beneficial to reduce the complications of normal tissue and improve the curative effect of heavy ion beam therapy.

The effect of the invention is illustrated with a specific example. Assuming that there is a spherical tumor target area with a diameter of 4cm in the patient, if the existing two-dimensional conformal irradiation method is used for treatment, there will be a healthy tissue with a volume of about ^30.5cm3 in front of the tumor target area at 100% of the prescribed dose It is almost equivalent to the volume of the tumor target area itself, which is 33.5cm ³ , and the degree of conformity at this time is 52.3%. If the three-dimensional conformal irradiation method of the present invention is used for treatment, only healthy tissues not exceeding 3 cm ³ in front of the tumor target area will be within 100% of the prescribed dose, and the degree of conformity at this time is 91.8%. As far as radiation therapy is concerned, reducing the radiation dose received by healthy tissues during radiation therapy is of great significance for maximally protecting normal tissues. The three-dimensional conformal irradiation method of the present invention improves the conformity degree of heavy ion beam therapy, and can protect normal tissues to the greatest extent on the premise that high-dose Bragg peak area of heavy ion beam is used to efficiently kill tumor cells in the target area. In addition, in the present invention, the method of zigzag raster scanning is used to expand the beam laterally to obtain a wide irradiation field, and there is no need to use the scatterers in the existing two-dimensional irradiation method, thus eliminating the reduction in cancer treatment due to the use of scatterers. The unfavorable factor of beam quality.

Description of drawings

Figure 1 is a schematic diagram of the three-dimensional conformal irradiation method for heavy ion beam therapy of the present invention, in which 1: scanning magnet, 2: beam current and dose monitoring system, 3: mini ridge filter, 4: range shifter, 5: Multi-leaf collimator, 6: patient body surface compensator, 7: patient body surface, 8: tumor target area.

Fig. 2 is the schematic diagram of the zigzag raster scanning of the present invention,

Fig. 3 is a partial cross-sectional schematic view of the miniature ridge filter of the present invention

Fig. 4 is the broadening effect diagram of the miniature ridge filter of the present invention on carbon ion beam Bragg peak

Figure 5 is a circular carbon ion beam uniform irradiation field with a diameter of 5 cm obtained by scanning the horizontally expanded beam with a zigzag raster and collimating it.

Fig. 6 is the theoretical design (solid line) and experimental measurement (hollow circle symbols) of the broadening of the Bragg peak of the 80.55 MeV/u carbon ion beam by the mini ridge filter of the present invention.

Fig. 7 is a simulation experiment diagram (left side) of the present invention implementing three-dimensional conformal irradiation therapy on the tumor target area and the measurement results of dose distribution on different slices of the tumor target area (right side).

Detailed ways

Below, the present invention will be further described in conjunction with accompanying drawing:

Example 1

The present invention takes the chemically etched solid nuclear track detector CR39 sheet as an example to illustrate the three-dimensional conformal irradiation of the heavy ion beam on the target area composed of the CR39 sheet.

Utilize the 80.55MeV/u carbon ion beam provided by Lanzhou Heavy Ion Research Facility (HIRFL) of Institute of Modern Physics, Chinese Academy of Sciences, we scan the magnet in the present invention at the HIRFL shallow layer tumor heavy ion therapy terminal equipped with passive beam distribution system The uniform irradiation field formed by the system and the mini ridge filter were used to test the broadening of the beam Bragg.

As shown in Figure 1, the device for performing three-dimensional conformal irradiation therapy on the tumor target area with heavy ion beams includes a scanning magnet system 1, a beam current monitoring system 2, a mini ridge filter 3, a range shifter 4, a multi-leaf The collimator 5 and the patient's body surface compensator 6 are respectively placed in front of the patient's body surface 7 in sequence, and the centers of the above devices and the center of the tumor target area 8 are on the beam axis. The scanning magnet system 1 is composed of two sets of mutually perpendicular secondary magnets in the x and y directions. The beam monitoring system 2 consists of an ionization chamber and a position sensitive detector.

Place the solid nuclear track detector CR39 sheet at the center of the target area 8, and when the scanning magnet system expands the beam laterally in a sawtooth raster scanning manner, the scanning frequency of the scanning magnet system in the 1x direction is 75 Hz, and the scanning frequency in the y direction is 45 Hz. The distance from the scanning magnet to the CR39 sheet in the y direction is 3m; the position sensitive detector has a position resolution of 1mm, and the ion beam intensity is 107pps; the mini ridge filter 3 is made of aluminum material, and the distance between the ridge peaks is 1.0mm, the beam current The Bragg peak after passing through the mini ridge filter 3 has a Gaussian distribution, the half maximum width of the broadened peak is 2 mm, and the distance from the center of the target area is 65 cm.

Under the above conditions, a carbon ion beam irradiation field with a uniformity of 93% is obtained through the measurement of the position-sensitive detector multi-wire proportional chamber, which meets the needs of clinical tumor treatment. Fig. 5 is a uniform irradiation field of a circular carbon ion beam with a diameter of 5 cm obtained by scanning the horizontally expanded beam with a zigzag raster and collimating it. It shows that the material of the irradiation field is a solid nuclear track detector CR39 sheet.

After the mini ridge filter, the experimental measurement of the broadened Bragg peak of the carbon ion beam has the characteristics of a Gaussian distribution. Figure 6 is the theoretical design of the mini ridge filter for the broadening of the 80.55MeV/u carbon ion beam Bragg peak (solid line ) and experimental measurements (open circle symbols) graphs. As can be seen from Figure 6, the FWHM of the broadening peak is 1.94 mm (experimental measurement (open circle symbol)) and the Gaussian peak of the miniature ridge filter theoretical design (solid line) broadening the Bragg peak has a width at half maximum of 2.0 mm distribution fits well. The experiment confirmed that the mini ridge filter properly broadens the sharp Bragg peak of the 80.55 MeV/u carbon ion beam into a Gaussian distribution, which meets the needs of three-dimensional conformal irradiation.

Example 2

Using the device described in Example 1 to implement three-dimensional conformal radiation therapy on the tumor target area, the present invention is a phantom stacked with tissue-equivalent material CR39 thin slices (thickness 0.66mm, water equivalent length coefficient 1.061) As an example, to illustrate the three-dimensional conformal irradiation of a carbon ion beam to a target area composed of CR39 flakes.

Integrating all the devices in the present invention, a three-dimensional conformal irradiation is performed on a phantom made of tissue-equivalent material CR39 thin slices, and the tumor slice is seven of them, as shown in the left figure in Fig. 7, along the beam current The tumor slices in the penetrating direction are circles with diameters of 10mm, 20mm, 30mm, 40mm, 30mm, 20mm and 10mm. In the irradiation, the scanning frequency of the scanning magnet system in 1x direction is 75Hz, the scanning frequency in the y direction is 45Hz, the distance from the scanning magnet in the y direction to the center of the CR39 sheet stack is 3m; the position sensitive detector has a position resolution of 1mm, and the ion beam intensity is 107pps The miniature ridge filter 3 is an aluminum material, and the distance between the ridge peaks is 1.0mm. The Bragg peak after the beam flows through the miniature ridge filter 3 is a Gaussian distribution, and the FWHM of the broadened peak is 2mm. The distance from the center of the target area is 65cm. Use the mini ridge filter to broaden the Bragg peak of the beam, adjust the range shifter to make the broadened Bragg peak of the beam fall on the corresponding tumor slice, and adjust the multi-leaf collimator to make the shape of the irradiation field match the corresponding slice of the tumor of the same shape. After irradiation, all CR39 flakes were chemically etched, and the ion tracks and dose distribution of the tumor target area were visualized, as shown in the right panel of Figure 7. Each CR39 slice reflects each slice of the tumor target area, and the dose distribution uniformity reflected on each CR39 slice is better than 93%, and the size of the dose distribution area is consistent with the diameter of the tumor slice. Through this experiment, it can be seen that we have implemented very good conformal irradiation on the simulated tumor target area by using the three-dimensional conformal irradiation method of the present invention, which proves that the technical solution of the present invention is feasible.

Claims (1)

1. a HIB is implemented the device of three-dimensional conformal irradiation treatment to the tumor target area, comprise sweeping magnet system (1), beam monitoring system (2), miniature ridged filter (3), range shift unit (4), multi-diaphragm collimator (5) and patient's body surface compensator (6), place patient's body surface (7) preceding respectively in regular turn, sweeping magnet system (1), beam monitoring system (2), miniature ridged filter (3), range shift unit (4), the center of the center of multi-diaphragm collimator (5) and patient's body surface compensator (6) and tumor target area (8) is on the beam axis, sweeping magnet system (1) is made up of x and two groups of orthogonal secondary Magnet of y direction, beam monitoring system (2) is made of ionization chamber and position sensitive detector, it is characterized in that sweeping magnet system (1) x scanning direction frequency is 50～150Hz, y scanning direction frequency is 15～50Hz, and y scanning direction Magnet is to distance 3～10m of patient; Position sensitive detector has the position resolution of 1mm at least, and ionization chamber monitoring ion beam intensity is 10 ⁶～10 ⁸Pps; Miniature ridged filter (3) be shaped as falling of the lucite PMMA of ridge or polystyrene or aluminum can material, peak-to-peak distance≤the 1.5mm of energy material ridge falls, spread-out Bragg peak behind the ion beam miniature ridged filter of process (3) is gaussian shaped profile, the halfwidth at broadening peak is 2～3mm, and miniature ridged filter (3) to place beam axis be 65～100cm place apart from center, tumor target area (8).

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