JP2893512B2 - Multi-ring range modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-ring type range modulator used for a proton beam therapy system.

[0002]

2. Description of the Related Art When a proton beam enters a substance, it proceeds while gradually losing energy, and emits maximum energy immediately before stopping. Such a feature of the proton beam is generally called a black peak, and a proton beam therapy device is known as a device that uses this black peak to irradiate a lesion in the body with a high dose.

[0003] Here, with reference to FIG. 5, a proton beam therapy system will be outlined.

A proton beam therapy system (irradiation field forming device) includes a first scatterer 12, a double ring second scatterer 13, a lip filter 14, a binary energy fine adjuster 15, an irradiation dose monitor 15a, an X-ray tube. 16, light field device 17,
It comprises a block collimator 18, a bolus 19, and a final collimator 20, and as shown, a first scatterer 12, a double ring second scatterer 13, a lip filter 1
4, a binary energy fine adjuster 15, an irradiation dose monitor 15a, an X-ray tube 16, a light irradiation field device 17, and a block collimator 18 are arranged in a cylindrical body 21. The proton beam is provided to a lip filter 14 via a first scatterer 12 and a double ring second scatterer 13, where the monoenergetic proton beam has an energy distribution to generate an expanded black peak. Lip filter 1
4 passes through the binary energy fine-tuner 15
, The energy distribution is adjusted, and the patient 22 is irradiated. Note that an image intensifier 24 is arranged to face the patient bed 23. As described above, in the irradiation field forming apparatus, the proton beam extracted from the accelerator is shaped according to the size of the affected part. In the irradiation field forming apparatus, various range modulators may be used instead of the lip filter.

In the above-described irradiation field forming apparatus, the scatterer is used for expanding the beam diameter of the proton beam, and the range modulator is used for expanding the proton beam in the depth direction of the affected part. Here, the spread of the proton beam by the scatterer and the range modulator will be outlined with reference to FIG.

[0006] The proton beam supplied from the accelerator has a beam diameter of about 5 mm, and has a Gaussian beam distribution. The beam diameter of the proton beam incident on the first scatterer 12 increases due to multiple Coulomb scattering (the beam distribution of the proton beam after passing through the first scatterer is a Gaussian distribution). The second scatterer 13 shapes the Gaussian proton beam after passing through the first scatterer into a flat beam distribution at the position of the patient. That is, the second scatterer 13 is made of two or more materials having different atomic numbers near the center and outside.
Utilizing the property that the scattering angle of the proton beam differs depending on the atomic number of the material, the beam distribution of the proton beam is flattened. For example, the proton beam near the central axis having a high beam distribution is largely scattered to the outside with lead, and the proton beam outside the low beam distribution is allowed to pass through aluminum with low scattering, and the beam distribution after passing through the second scatterer is determined by the patient. It is flat at the position.

[0007] The energy of the proton beam that has passed through the second scatterer 13 is constant.
Has a structure with a different thickness depending on the passage position of the proton beam, as will be described later, and the energy (range) of the proton beam after passing is different according to this thickness. As a result, the black peak has a width in the depth direction, and can correspond to an affected part having a thickness.

[0008]

Here, FIG. 7 and FIG.
, A conventional range modulator will be outlined.

The range modulator shown in FIG. 7 is of a rotary type (hereinafter referred to as a rotary range modulator), and the rotary range modulator rotates around a central axis, thereby mixing beams having different energies in time. . When such a rotary range modulator is used, a motor drive system for driving the rotary range modulator is required, and the irradiation field forming apparatus becomes large.

On the other hand, the range modulator shown in FIG. 8 is called a ridge filter. In this ridge filter, a plurality of wedge-shaped ridges are arranged, and beams having different energies are spatially mixed by utilizing a scattering effect. The illustrated ridge filter generally has a size of about 150 mm × 150 mm. As described above, the size of the ridge filter is not small, and as a result, there is a limitation in downsizing the irradiation field forming apparatus.

Further, it is necessary to arrange both the above-mentioned rotary range modulator and ridge filter on the downstream side of the second scatterer. However, at this position, it is necessary to enlarge the range modulator because the beam diameter is large and spread.

In addition, the above-described irradiation field forming apparatus requires the first and second scatterers in addition to the range modulator. As a result, it is difficult to reduce the size of the irradiation field forming apparatus. .

An object of the present invention is to provide a range modulator which can reduce the size of an irradiation field forming apparatus.

[0014]

According to the present invention, there is provided a range modulator for use in an apparatus for irradiating a proton beam for treatment, wherein the range modulator is arranged on a trajectory of the proton beam and has the orbit axis as a center axis. A plurality of block bodies arranged in a core shape, each of the block bodies having a different scattering angle of the proton beam, and a height defined in the orbit axis direction in each of the block bodies; A multi-ring range modulator characterized by varying along a direction perpendicular to the axis is obtained.

[0015]

In the present invention, a plurality of blocks are arranged concentrically around the orbit of the proton beam with the orbit axis as the center axis, and the scattering angle of the proton beam is made different in each of the blocks, and in each of the blocks, Since the height defined in the orbital axis direction is changed along the direction orthogonal to the orbital axis, when used in the irradiation field forming apparatus, it can also serve as the second scatterer and has a flat beam distribution. Proton beam can be obtained. As a result, the irradiation field forming apparatus can be downsized.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

Referring to FIG. 1, the illustrated multi-ring type range modulator 30 includes a disc-shaped base plate 31 on which a first block 32 is disposed. The first block 32 includes a plurality of cylindrical portions (in the illustrated example, the first block 32 includes three cylindrical portions 32a, 32b, and 32c). These cylindrical portions 32a, 32b and 32c are connected to the base plate 31.
Are arranged concentrically with respect to the central axis of
The inner wall surfaces of 2a, 32b and 32c form the same plane. The outer diameters of the cylindrical portions 32a, 32b, and 32c are different from each other, where the outer diameter of the cylindrical portion 32a> the outer diameter of the cylindrical portion 32b> the outer diameter of the cylindrical portion 32c. Therefore, a step-like step 32c is formed on the outer surface of the first block 32. The first block 32 is formed of a low atomic number material (for example, aluminum).

Further, a second block 33 is provided on the base plate 31 in the first block 32. The second block 33 is formed by a plurality of column portions. In the illustrated example, the three columnar portions 33a to 33a
3c. These cylindrical portions 33a to 33c
Is a cylindrical portion 3 with the central axis of the base plate 31 as the central axis.
3a, 33b, and 33c are arranged in this order. As a result, a step-like step 33 is formed on the outer surface of the second block 33.
d will be formed. The second block 33 is formed of a material having a high atomic number (for example, lead). In addition,
The outside diameter of the illustrated range modulator is about φ50 mm.

Here, the operation of the multi-ring type range modulator according to the present invention will be described with reference to FIG.

As shown in FIG. 2A, the first scatterer 12 was arranged along the proton beam path, and the range modulator 30 was arranged downstream of the first scatterer 12. Further, a collimator 40 was arranged downstream of the range modulator 30, and the beam distribution was examined.

The proton beam is incident on the first scatterer 12. Then, the proton beam is scattered by the first scatterer 12 as described above. Then, the proton beam that has passed through the first scatterer 12 is incident on the range modulator 30.

As described above, since the second block 33 is formed of lead, the proton beam incident near the center of the range modulator 30 spreads greatly after passing through the second block 33 (ie, theta ₁ as shown in FIG. 2 (a) becomes larger). On the other hand, since the first block 32 is made of aluminum, the range modulator 30
Are hardly spread after passing through the first block 32 (that is, θ ₂ as shown in FIG. 2).
Becomes smaller). As a result, the center portion of the Gaussian distribution of the proton beam after passing through the range modulator 30 moves outward, and the beam intensity becomes flat.

Further, in the range modulator 30, since the first and second blocks have the step-like steps as described above, the proton beam has a range corresponding to the height of the steps, and the irradiation position is different at the irradiation position. The different beams are mixed and ultimately modulated to the range required for treatment.
The dose distribution was measured at the irradiation position. When the beam distribution of the proton beam output at the irradiation position was examined using a silicon semiconductor detector as a dose distribution measurement sensor, FIG. 2
(B) The beam distribution shown in (c) was obtained (FIG. 2 (b)
Fig. 2 shows the lateral beam distribution at the irradiation position.
(C) shows the beam distribution in the same vertical (depth) direction.)

The proton beam emitted from the range modulator 30 is cut off an unnecessary beam by the collimator 40 and guided to the irradiation position.

First block 32 and second block 33
When the height (H) is increased, the flat portion becomes wider in the longitudinal (depth) beam distribution. That is, the first block 3
The height (H) of the second and second blocks 33 is changed from H-2 to H-1.
, The flat portion in the vertical (depth) beam distribution expands from H-2 to H-1.

As described above, by using the multi-ring type range modulator according to the present invention, a proton beam having a desired (ie, flat) beam distribution can be obtained without the second scatterer. That is, since the multi-ring type range modulator of the present invention substantially also has the function of the second scatterer, the use of the multi-ring type range modulator can reduce the size of the irradiation field forming apparatus. .

In the above-described embodiment, aluminum is used as a material having a low atomic number and lead is used as a material having a high atomic number. However, acrylic and polyethylene can be used as a material having a low atomic number. Also, tungsten and tantalum can be cited as high atomic number materials.

Further, various types of structures of the range modulator can be considered. For example, those having the structures shown in FIGS. 3 and 4 may be used. In the range modulator shown in FIG. 3, a slope-shaped inclined surface is formed on the outer surface of the first block 32, while the outer surface of the second block 33 is curved.

The range modulator shown in FIG. 4 is provided with first to third blocks. The third block surrounds the center member and has a lower height as it surrounds the center member.
The second block and the first block are arranged so as to surround the third block.

The range modulator having the structure shown in FIGS. 3 and 4 has the same effect as the range modulator described with reference to FIG.

In any case, the range modulator is
It has a plurality of blocks arranged on the orbit of the proton beam and arranged concentrically with the orbit axis as a central axis, and each of these blocks has a different scattering angle of the proton beam and each of the blocks has In this case, any structure may be used as long as the height defined in the orbit axis direction changes along a direction orthogonal to the orbit axis.

[0032]

As described above, when the multi-ring type range modulator according to the present invention is used, a proton beam having a flat beam distribution can be obtained without using a second scatterer. There is an effect that the field forming device can be reduced in size.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an embodiment of a multi-ring type range modulator according to the present invention.

FIG. 2 is a diagram for explaining a beam distribution when a multi-ring type range modulator according to the present invention is used.

FIG. 3 is a sectional view showing another embodiment of the multi-ring type range modulator according to the present invention.

FIG. 4 is a sectional view showing another embodiment of the multi-ring type range modulator according to the present invention.

FIG. 5 is a view schematically showing an irradiation field forming apparatus.

FIG. 6 is a diagram for explaining the spread of a proton beam when a conventional range modulator is used.

FIG. 7 is a perspective view showing an appearance of an example of a conventional range modulator.

FIG. 8 is a perspective view showing the appearance of another example of the conventional range modulator.

[Explanation of symbols]

 12 First scatterer 13 Second scatterer 14 Ripple filter 15 Binary energy fine adjuster 15a Irradiation dose monitor 16 X-ray tube 17 Light irradiation device 18 Block collimator 19 Bolus 20 Final collimator 21 Cylindrical body 22 Patient 23 Patient bed 24 Image intensifier 30 Range modulator 31 Base plate 32 First block 33 Second block 40 Collimator

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Toshiyuki Okumura 1-1-1, Tennodai, Tsukuba-city, Ibaraki Pref. (72) Inventor Hiroshi Tsuji 1-1-1-1, Tennodai, Tsukuba-shi, Ibaraki Pref. 72) Inventor Yoshinori Hayakawa 1-1-1, Tennodai, Tsukuba, Ibaraki Pref. University of Tsukuba (56) References JP-A-4-197273 (JP, A) JP-A-4-132567 (JP, A) 1-1131675 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) A61N 5/10

Claims (2)

(57) [Claims] 1. A range modulator used in an apparatus for performing treatment by irradiating a proton beam, comprising a plurality of blocks arranged on a trajectory of the proton beam and arranged concentrically with the trajectory axis as a center axis. And each of the block bodies has a different scattering angle of the proton beam, and the height defined in the orbit axis direction in each of the block bodies changes along a direction orthogonal to the orbit axis. A multi-ring type range modulator characterized by the above-mentioned. 2. The multi-ring type range modulator according to claim 1, wherein a scattering angle with respect to the proton beam is smaller in a block located outside the concentric arrangement.