# US 10,500,419 B2 · Radiation shields for LINAC head and system

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- Number: US 10,500,419 B2
- Document ID: US10500419B2
- Status: Granted
- Kind: B2
- Application number: 16/401,061
- Filed: 2019-05-01
- Published: 2019-08-22
- Granted: 2019-12-10
- Earliest claimed: 2015-09-11
- Assignees: Varian Medical Systems, Inc.
- Applicants: Varian Medical Systems, Inc.
- Inventors: HsinLu Hsu; Magdalena Constantin; Stuart Scollay
- Web page: https://patentgrep.com/patent/US10500419B2

## CPC

- A61N 5/1077: {Beam delivery systems}
- G21F 3/00: Shielding characterised by its physical form, e.g. granules, or shape of the material
- G21G 4/08: specially adapted for medical application (radiation therapy using radioactive sources A61N5/10)
- A61N 2005/1094: {Shielding, protecting against radiation}
- G06F 30/00: Computer-aided design [CAD]
- A61N: ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY (measurement of bioelectric currents A61B; surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body A61B18/00; anaesthetic apparatus in general A61M; incandescent lamps H01K; infrared radiators for heating H05B)
- G21F: PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR (radiation protection by pharmaceutical means A61K8/00, A61Q17/04; in cosmonautic vehicles B64G1/54; combined with a reactor G21C11/00; combined with X-ray tubes H01J35/16; combined with X-ray apparatus H05G1/02)
- G21G: CONVERSION OF CHEMICAL ELEMENTS; RADIOACTIVE SOURCES (applications of radiation in general G21H5/00; handling particles, e.g. neutrons, or electromagnetic radiation not otherwise provided for G21K)
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)

## Abstract

In a method of constructing a head shield for a radiation machine, the angular distribution of radiation propagating from a source and the angular function of thickness of a material in attenuating the radiation to a certain level of its original value are determined. Based on the angular distribution of radiation from the source and the angular function of thickness of the material, the thicknesses of the material at a plurality of angular locations around the source and distances from the source can be calculated for attenuating the radiation to or less than a predetermined threshold value. A shield around the source is constructed based on the calculated thicknesses of the material through iterative steps to ensure a cost-saving, weight-efficient, optimal solution. A method of designing a local radiation shield for a point of interest in a radiation system is also described to improve the machine reliability, regardless of the motion component of the POI with respect to the main radiation source and the secondary radiation source created by the patient scatter.

## Claims

### Claim 1

A method of designing a radiation shield for a point of interest (POI) at a location in a radiation system, where the POI is a component of the radiation system that is sensitive to radiation, the radiation system comprising a movable source configured to generate radiation to be delivered to an isocenter in a patient, the POI being movable with the source, the method comprising:
determining a first portion of radiation intensity reaching the location of the POI originated from the source;
determining a second portion of radiation reaching the location of the POI due to patient scatter originated from the isocenter;
calculating accumulated radiation at the location of the POI by at least summing the first and the second portions of radiation; and
constructing a shield for the POI based on the accumulated radiation at the location of the POI.

### Claim 2 (depends on 1)

The method of claim 1 wherein the source is rotatable about the isocenter and the POI is rotatable with the source.

### Claim 3 (depends on 2)

The method of claim 2 wherein the step of determining the first portion of radiation reaching at the POI comprises determining an angular distribution of radiation propagating from the source.

### Claim 4 (depends on 3)

The method of claim 3 wherein the angular distribution of radiation from the source comprises an angular distribution of radiation dose.

### Claim 5 (depends on 3)

The method of claim 3 wherein the angular distribution of radiation from the source is determined using a Monte Carlo method.

### Claim 6 (depends on 3)

The method of claim 3 wherein the first portion of the radiation reaching at the location of the POI is determined according to the following equation:
LTAR(θ)/d2
where d represents a distance from the POI to the source, θ represents a spatial angle of the POI with respect to the source, and LTAR(θ) represents a value of the angular distribution of radiation from the source.

### Claim 7 (depends on 1)

The method of claim 1 wherein the determining of the second portion of radiation reaching at the location of the POI comprises determining an angular distribution of radiation of patient scatter propagating from the isocenter.

### Claim 8 (depends on 7)

The method of claim 7 wherein the angular distribution of radiation of patient scatter comprises an angular distribution of radiation dose.

### Claim 9 (depends on 7)

The method of claim 7 wherein the angular distribution of radiation of patient scatter is determined using a Monte Carlo method.

### Claim 10 (depends on 7)

The method of claim 7 wherein the second portion of radiation is determined according to the following equation:
LPS(α)/d′2
where d′ represents a distance from the POI to the isocenter, α represents a spatial angle of the POI with respect to the isocenter, and LPS(α) represents a value of the angular distribution of radiation of patient scatter when irradiated with an unblocked beam.

### Claim 11 (depends on 10)

The method of claim 10 further comprising determining a modulation factor (MF) of the unblocked beam, and determining the second portion of radiation according to the following equation:
LPS(α)/d′2/MF.

### Claim 12 (depends on 11)

The method of claim 11 wherein the modulation factor is determined by dividing a total dose generated by the radiation system with a delivered dose to the isocenter.

### Claim 13 (depends on 1)

The method of claim 1 wherein the accumulated radiation is determined according to the following equation using an averaged modulated field size:
L(x, y, z) =L_TAR(d, θ) +L_PS(d′, α)
wherein L (x, y, z) represents the accumulated leakage, L_TAR(d, θ) represents the first portion of radiation, L_PS(d′, α) represents the second portion of radiation, d represents a distance from the POI to the source, θ represents a spatial angle of the POI with respect to the source, d′ represents a distance from the POI to the isocenter, α represents a spatial angle of the POI with respect to the isocenter; and
wherein the averaged modulated field size is determined by a field size area divided by a modulation factor.

### Claim 14

A method of constructing a radiation shield for a point of interest (POI) at a location in a radiation system, where the POI is a component of the radiation system that is sensitive to radiation, the radiation system comprising a movable source configured to generate radiation to be delivered to an isocenter in a patient, the POI being non-movable with the source, the method comprising:
selecting a plurality of locations of the source with respect to the location of the POI, and at each of the plurality of locations of the source:
determining a first portion of radiation reaching the location of the POI originated from the source;
determining a second portion of radiation reaching the location of the POI due to patient scatter originated from the isocenter;
calculating an average first portion of radiation;
calculating an average second portion of radiation;
calculating accumulated radiation reaching at the location of the POI by at least summing the average first portion and the average second portion of radiation;
constructing a shield for the POI based on the accumulated radiation at the location of the POI.

### Claim 15 (depends on 14)

The method of claim 14 wherein the source is rotatable about the isocenter in the patient and the POI is stationary relative to the isocenter.

### Claim 16 (depends on 15)

The method of claim 15 wherein the plurality of locations of the source are spaced apart in substantially equal angular increments along a circular orbit.

### Claim 17 (depends on 16)

The method of claim 16 wherein the plurality of locations of the source include 12 locations substantially equally spaced apart in 30 degrees in a circular orbit.

### Claim 18 (depends on 16)

The method of claim 16 wherein the step of determining the first portion of radiation at the POI comprises determining an angular distribution of radiation propagating from the source.

### Claim 19 (depends on 18)

The method of claim 18 wherein the angular distribution of radiation from the source comprises an angular distribution of radiation dose.

### Claim 20 (depends on 18)

The method of claim 18 wherein the angular distribution of radiation from the source is determined using a Monte Carlo method.

### Claim 21 (depends on 18)

The method of claim 18 wherein the first portion of the radiation is determined according to the following equation:
LTAR(θ)/d2
where d represents a distance from the POI to the source at one of the plurality of locations, θ represents a spatial angle of the POI with respect to the source at the one of the plurality of locations, and LTAR(θ) represents a value of the angular distribution of radiation from the source at the one of the plurality of locations.

### Claim 22 (depends on 14)

The method of claim 14 wherein the determining of the second portion of radiation comprises determining an angular distribution of radiation scattered from the isocenter.

### Claim 23 (depends on 22)

The method of claim 22 wherein the angular distribution of radiation from the isocenter comprises an angular distribution of radiation dose.

### Claim 24 (depends on 22)

The method of claim 22 wherein the angular distribution of radiation from the isocenter is determined using a Monte Carlo method.

### Claim 25 (depends on 22)

The method of claim 22 wherein the second portion of radiation is determined according to the following equation:
LPS(α)/d′2
where d′ represents a distance from the POI to the isocenter, α represents a spatial angle of the POI with respect to the isocenter when the source is at one of the plurality of location, and LPS(α) represents a value of the angular distribution of radiation from the isocenter when irradiated with an unblocked beam from the source at the one of the plurality of locations.

### Claim 26 (depends on 25)

The method of claim 25 further comprising determining a modulation factor (MF) of the unblocked beam, and determining the second portion of radiation according to the following equation:
LPS(α)/(d′2*MF).

### Claim 27 (depends on 26)

The method of claim 26 wherein the modulation factor is determined by dividing a total dose generated by the radiation system with a delivered dose to the isocenter.

### Claim 28 (depends on 14)

The method of claim 14 wherein the accumulated radiation is determined according to the following equation using an averaged modulated field size:
L(x, y, z)=L_TAR(d, θ) +L_PS(d′, α)
wherein L (x, y, z) represents the accumulated leakage, L_TAR(d, θ) represents the first portion of radiation, L_PS(d′, α) represents the second portion of radiation, d represents a distance from the POI to the source, θ represents a spatial angle of the POI with respect to the source, d′ represents a distance from the POI to the isocenter, α represents a spatial angle of the POI with respect to the isocenter; and
wherein the averaged modulated field size is determined by a field size area divided by a modulation factor.