JP6384713B2 - Radiation shielding wall - Google Patents

Description

  The present invention relates to a radiation shielding wall provided around a radiation generating apparatus such as a medical linac.

  As a medical device for cancer treatment, a medical linac used to irradiate an affected area with radiation is known. For example, Patent Document 1 (Japanese Patent No. 5334582) discloses a linac (linear accelerator) capable of generating a radiation beam containing X-rays, gamma rays, electrons, protons, helium ions, carbon ions, other heavy ions, or neutrons. ) Is disclosed.

In an irradiation room where a medical linac for irradiating radiation is installed, a radiation shielding wall is provided to shield the radiation. For example, in Patent Document 2 (Japanese Patent Laid-Open No. 2010-151617), in a radiation shielding structure for an irradiation chamber that houses a radiation source, a wall shielding member that stands on the indoor side of a reinforced concrete wall structure housing and shields radiation. And a ceiling shielding member that shields radiation and is laid on a reinforced concrete ceiling structure housing that is structurally integrally formed on the top of the wall structure housing, and protrudes indoors at the upper end of the wall shielding member The point which forms the protrusion part which does is disclosed.
Japanese Patent No. 5334582 JP 2010-151617 A

  The structure of the radiation shielding wall 5 forming the medical linac installation chamber 1 will be described. FIG. 6 is a perspective view of the structure of the conventional radiation shielding wall 5 as seen through. In FIG. 6, the configuration related to entering and leaving the medical linac installation chamber 1 is not shown.

  A target T (not shown) is provided in the medical linac head section 50 of a medical linac (not shown in its entirety) installed in the medical linac installation chamber 1. By causing particles accelerated by an energy of 10 MeV (or 15 MeV) by an accelerator (not shown) to collide with the target T, radiation such as a photon or an electron beam is generated.

  The radiation generated at the target T is narrowed down by a metal collimator (not shown) or the like and used for treatment at an isocenter (IC) position. It is assumed that the patient is laid on the treatment table 3 so that the affected part of the patient overlaps with the isocenter IC.

  The medical linac head unit 50 is configured to be able to rotate 360 ° in the A direction or the B direction around the isocenter IC, and is isocentered from any position on the rotation trajectory of the medical linac head unit 50. The IC can be irradiated with radiation.

  In the medical linac installation room, a radiation shielding wall 5 is provided to shield the radiation radiated from the medical linac head unit 50 as described above. The radiation shielding wall 5 is made of metal such as iron. The metal shielding part 30 is composed of a concrete shielding part 40 made of concrete so as to cover the metal shielding part 30.

This invention solves the above problems, and the invention according to claim 1 is a radiation shielding wall provided around a medical linac, and has a rectangular cross section. A metal shielding portion comprising: a body, and two second metal shields provided at both ends of the first metal shield and having a rectangular cross-sectional area smaller than that of the first metal shield; A radiation shielding wall comprising: a concrete shielding portion made of concrete covering the metal shielding portion. However, the cross-section in the cross-sectional shape of the metal shielding part is a cross-section when the metal shielding part is cut horizontally with respect to what is provided on the side wall part of the medical linac installation chamber where the medical linac is installed. The metal shielding portion can be provided on a ceiling or floor portion of the medical linac installation room so that the metal shielding portion can be perpendicular to the plane including the rotation path of the head portion of the medical linac. It is a cross section when.

FIG. 7 is a horizontal cross-sectional view including the XX ′ line in the conventional radiation shielding wall 5. In the medical linac, the maximum size of the therapeutic irradiation field at the isocenter IC position is determined to be 40 × 40 cm ² . The linac is a metal collimator for medical linacs (not shown) so that radiation such as photons and electron beams generated as a point source at the position of the metal target T has a maximum irradiation field of 40 × 40 cm ^{2 in} an isocenter IC that is 100 cm away. (The angle θ at half the opening of the collimator is tan ⁻¹ (20/100) = 11.31 °).

  Therefore, if the distance from the isocenter IC to the side wall of the medical linac installation chamber 1 is 300 cm, radiation such as photons and electron beams is about 80 cm on one side in the direction perpendicular to the radiation incident direction. If the distance to the side wall of 1 is 400 cm, it will enter the wall with a spread of about 100 cm on one side in the direction perpendicular to the radiation incident direction.

  Radiation such as actual photons and electron beams spreads a little more and enters the shielding wall due to the influence of scattering in the air and collimator and the precision of narrowing the irradiation field. Considering these points, the width of the metal shielding part 30 such as iron in the concrete shielding part 40 is generally set to 400 cm in total of ± 200 cm on both sides as shown in FIG. is there.

  By the way, according to laws and regulations such as the Radiation Hazard Prevention Law and the Medical Law, the leakage dose at the boundary of the management area (the outer periphery of the concrete shielding part 40) is determined to be 1300 μSv / 3 months. For example, when the operation time of a medical linac is set to 133 hours in 3 months, the dose rate that can be cleared with a tolerance of 20% with respect to the reference dose of 1300 [μSv / 3 months] at the boundary of the management area is 7 .8 [μSv / h]. This can be obtained by 1300/133 × 0.8 = 7.82.

FIG. 8 is a simulation diagram for explaining the problems of the conventional radiation shielding wall 5. In addition, the simulation calculation of the radiation in a medical linac and the radiation shielding wall 5 was implemented on condition of the following.
Calculation code: 3D Monte Carlo calculation code MCNP5
Cross-sectional area library: Photon-electron interaction library (MCPLIB04, EL03) Transport calculation target particle: Photon and electron beam source: 10 MeV electron beam target: Copper (1.5 cm thick)
Collimator: Tungsten shielding wall: concrete thickness 150 cm (density 2.1 g / cm ³ ) (= concrete shielding part 4
0), iron plate thickness 40 cm (density 7.8 g / cm ³ ) (= metal shielding part 30)
According to the simulation as described above, the exposure dose at the management area boundary (the outer periphery of the concrete shielding portion 40) is 0.74 μSv / h at the position a, 2.35 μSv / h at the position b, and c It can be seen that the position is 7.81 μSv / h.

  According to such a simulation result, there is a possibility that the operation time of the medical linac has to be limited depending on the case, for example, the exposure dose at the position c is 7.81 μSv / h. In this way, it is found from the simulation results that the higher exposure dose in some places is due to the influence of radiation that wraps around and leaks at the end E of the metal shielding part 30, It was a problem.

  On the other hand, there is a solution for setting the width of the metal shielding part 30 to 400 cm or more. However, increasing the width of the metal shielding part 30 increases the weight and cost of the radiation shielding wall 5. Problems occur.

  This invention solves the above problems, and the invention according to claim 1 is a radiation shielding wall provided around a medical linac, and has a rectangular cross section. A metal shielding portion comprising: a body, and two second metal shields provided at both ends of the first metal shield and having a rectangular cross-sectional area smaller than that of the first metal shield; And a concrete shielding part made of concrete covering the metal shielding part.

  The invention according to claim 2 is characterized in that, in the radiation shielding wall according to claim 1, the metal shielding part is arranged in a square shape.

According to a third aspect of the present invention, in the radiation shielding wall according to the first or second aspect, the distance from the isocenter formed by the medical linac to the metal shielding portion is L [cm], and the medical linac When the irradiation angle is 2θ, the length W [cm] in the longitudinal direction of the metal shielding portion is W = C × (100 + L) × tan θ, where C is a constant.
It is characterized by setting by.

  The invention according to claim 4 is characterized in that in the radiation shielding wall according to claim 3, C = 4.

  The radiation shielding wall according to the present invention is provided with a first metal shield having a rectangular cross-sectional shape, and a rectangular cross-sectional shape provided at both ends of the first metal shield and having a cross-sectional area smaller than that of the first metal shield. A second metal shield having a metal shielding portion, and the radiation shielding wall according to the present invention, the two second metal shields wrap around the end portion. It becomes possible to reduce the influence of the radiation leaking out. In addition, since it is not necessary to increase the width of the entire metal shielding part, it is possible to reduce the weight and cost of the entire radiation shielding wall.

It is the perspective view which looked at the structure of the radiation shielding wall 5 which concerns on embodiment of this invention transparently. It is sectional drawing of the horizontal surface containing the X-X 'line | wire in the radiation shielding wall 5 which concerns on embodiment of this invention. It is a figure used as the premise at the time of calculating the dose rate with respect to the distance from the edge part E of the metal shielding part 30 of the radiation shielding wall 5. FIG. It is a figure which shows the dose rate with respect to the distance from the edge part E of the metal shielding part 30 of the conventional radiation shielding wall 5. FIG. It is a simulation figure explaining the effect of the radiation shielding wall 5 which concerns on embodiment of this invention. It is the perspective view which looked at the structure of the conventional radiation shielding wall 5 transparently. It is sectional drawing of the horizontal surface containing the X-X 'line | wire in the conventional radiation shielding wall 5. FIG. It is a simulation figure explaining the problem of the conventional radiation shielding wall 5. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of the structure of the radiation shielding wall 5 according to the embodiment of the present invention as seen transparently. Moreover, FIG. 2 is sectional drawing of the horizontal surface containing the XX 'line | wire in the radiation shielding wall 5 which concerns on embodiment of this invention.

  The configuration of the medical linac installed in the medical linac installation chamber 1 is the same as that described in the column “Problems to be solved by the invention”, and thus the description thereof is omitted.

  In the radiation shielding wall 5 according to the present invention, as shown in FIG. 2, the metal shielding part 30 is provided at the first metal shielding body 10 having a rectangular cross-sectional shape and at both ends of the first metal shielding body 10. The second metal shield 20 has a rectangular cross-sectional shape smaller than that of the first metal shield 10.

  In addition, a cross section obtained by cutting the metal shielding portion 30 on a plane perpendicular to the X-X ′ line has a mouth shape.

  This is the same as the conventional metal shielding part 30. Moreover, the concrete shielding part 40 is the structure made from concrete which covers the above metal shielding parts 30. FIG.

  In addition, the cross section in defining the rectangular cross-sectional shape of the 1st metal shield 10 or the 2nd metal shield 20 in the above is a metal shield part with respect to what is provided in the side wall part of a medical linac installation room. It is a cross section when 30 is cut in the horizontal direction.

  In addition, for those provided on the ceiling and floor of the medical linac installation room, the metal shielding unit 30 is made of a plane perpendicular to the plane including the rotation trajectory of the medical linac head unit 50. FIG.

  In the radiation shielding wall 5 according to the present invention, since the two second metal shields 20 are provided at both ends of the first metal shield 10, the ends of the first metal shield 10 are provided as in the conventional example. It is possible to suppress a phenomenon in which radiation wraps around and leaks at the portion.

Here, as shown in FIG. 2, when the distance from the isocenter IC formed by the medical linac to the metal shield 30 is L [cm] and the irradiation angle of the medical linac is 2θ, C is a constant. The length W [cm] in the longitudinal direction of the metal shielding part (the width of the first metal shield 10 and the two second metal shields 20 combined) is W = C × (100 + L) × tan θ.
It is preferable to set by. Furthermore, it is preferable to set C = 4.

Is the spread angle from the target T point formed by the irradiation field at the isocenter IC position, and 11.3 in the case of a 40 × 40 [cm ² ] irradiation field size at the isocenter IC position.
1 °.

  The reason why such a setting is preferable will be described. FIG. 3 is a precondition for calculating the dose rate with respect to the distance from the end E of the metal shielding part 30 of the radiation shielding wall 5. FIG. 4 is a diagram showing the dose rate with respect to the distance from the end E of the metal shielding part 30 of the conventional radiation shielding wall 5.

  Since the constant C is 215 × 2 = 430 [cm], the width (W) of the metal shielding part 30 that can be 7.8 [mSv / h] or less even when the dose rate is highest from FIG. , So that this W can be satisfied. At this time, L = 445 [cm] and θ = 11.31 [degrees] were set based on the calculation conditions of FIG. Thereby, a suitable value can be calculated as the constant C as follows.

The above-mentioned 7.8 [μSv / h] is 20% more than the reference dose of 1300 [μSv / 3 months] at the boundary of the management area when the operation time of the medical linac is 133 hours in 3 months. It is a dose rate that can be cleared with a degree (1300/133 × 0.8 = 7.82).

  Next, the effect of the radiation shielding wall 5 according to the present invention configured as described above will be described. FIG. 5 is a simulation diagram for explaining the effect of the radiation shielding wall 5 according to the embodiment of the present invention.

In addition, the simulation calculation of the radiation in a medical linac and the radiation shielding wall 5 was implemented on condition of the following.
Calculation code: 3D Monte Carlo calculation code MCNP5
Cross-sectional area library: Photon-electron interaction library (MCPLIB04, EL03) Particles for transport calculation: Photon and electron beam source: 10 MeV electron beam target: Copper (1.5 cm thickness)
Collimator: Tungsten shielding wall: concrete thickness 150 cm (density 2.1 g / cm ³ ) (= concrete shielding part 40), iron plate thickness 40 cm (density 7.8 g / cm ³ ) (= first metal shielding 10)
Shield to be added: Iron plate thickness 5 cm (density 7.8 g / cm ³ ) (= second metal shield 20)
According to the above simulation, the exposure dose at the boundary of the management area (the outer periphery of the concrete shielding part 40) is 0.53 μSv / h at the position a, 1.46 μSv / h at the position b, 4.83 μSv / h at the position, and at any position, the dose rate that can be cleared with a tolerance of 20% with respect to the reference dose of 1300 [μSv / 3 months] at the boundary of the management area is 7.8 [μSv / H].

  Thus, the radiation shielding wall 5 according to the present invention is provided at the first metal shield having a rectangular cross-sectional shape and at both ends of the first metal shield, and the cross-sectional area of the first metal shield is The metal shielding part which has two 2nd metal shields which have a smaller rectangular cross-sectional shape, and according to the radiation shielding wall 5 concerning the present invention, it is two 2nd metal shields However, it becomes possible to reduce the influence of the radiation leaking around the end portion. In addition, since it is not necessary to increase the width of the entire metal shielding portion, it is possible to reduce the weight and cost of the radiation shielding wall 5 as a whole.

DESCRIPTION OF SYMBOLS 1 ... Medical linac installation room 3 ... Treatment table 5 ... Radiation shielding wall 10 ... 1st metal shielding body 20 ... 2nd metal shielding body 30 ... Metal shielding part 40 ...・ Concrete shield 50 ... Medical linac head E ... End T ... Target IC ... Isocenter

Claims (4)

A radiation shielding wall provided around a medical linac,
A first metal shield having a rectangular cross-sectional shape;
A metal shield part, which is provided at both ends of the first metal shield, and includes two second metal shields having a cross-sectional area smaller than the first metal shield and having a rectangular cross-sectional shape;
A concrete shielding portion made of concrete covering the metal shielding portion;
A radiation shielding wall comprising:
However,
The cross-section in the cross-sectional shape of the metal shielding part is
The cross section when the metal shielding part is cut in the horizontal direction with respect to what is provided in the side wall part of the medical linac installation room where the medical linac is installed,
When the metal shielding portion is provided on the ceiling or floor of the medical linac installation room, the plane is perpendicular to the plane including the rotation trajectory of the head portion of the medical linac. It is a cross section. The radiation shielding wall according to claim 1, wherein the metal shielding portion is arranged in a square shape. When the distance from the isocenter formed by the medical linac to the metal shield is L [cm] and the irradiation angle of the medical linac is 2θ, the length W in the longitudinal direction of the metal shield is defined as C as a constant. [Cm] is W = C × (100 + L) × tan θ
The radiation shielding wall according to claim 1, wherein the radiation shielding wall is set according to claim 1. The radiation shielding wall according to claim 3, wherein C = 4.