| Project/Area Number |
16591182
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Radiation science
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| Research Institution | University of Tsukuba |
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Principal Investigator |
TAKADA Yoshihisa University of Tsukuba, Graduate School of Pure and Apphed Sciences, Associate Professor, 大学院数理物質科学研究科, 助教授 (00134205)
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| Project Period (FY) |
2004 – 2005
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| Project Status |
Completed (Fiscal Year 2005)
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| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2005: ¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 2004: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Keywords | Heavy-charged particles / Bi-material bolus / Flattening of dose distribution / Ridge filter / 2-dimensional cone filter / SOBP / Proton beam / Carbon ion beam / Bi-material bolus / 2次元コーンフィルタ / 2次元コーンフィルター |
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| Research Abstract |
In cancer therapy using heavy-charged particles, uniform dose is expected to impart to the target volume while minimizing the dose to the surrounding healthy tissues. For the broad-beam delivery system, a range-compensating bolus is used to conform the dose distribution to the distal boundary of the target volume. However, insertion of the bolus deteriorates the dose distribution and induces the dose inhomogeneity as large as 15-20%p-p in some cases. Using a bi-material bolus made from low-Z material and high-Z material, we improved the dose distribution. Combination of two materials makes it possible to equalize the lateral spread of dose distributions of pencil beams traversing different parts of the bolus at the same water-equivalent depth, which results in the smooth lateral distribution. We manufactured a 4x4 matrix shaped bi-material bolus with different base thicknesses made from Cycowood (main component is ABS resin) and brass based on our dose calculation model. Dose distributions of 160 MeV proton beam passing through the HIMAC wobbling system with a ridge filter (60mm SOBP width) and the bolus, was measured using an array of 96-channel parallel-plate ionization chambers (the lateral size of each channel is 1.7mm x 1.7mm) at different depths in water. Uniform dose distribution was obtained as expected by the dose calculation model.
A ridge filter is used to form a uniform dose distribution covering the target thickness. Insertion of the ridge filter deteriorates the dose inhomogeneity due to the scattering. We designed a two-dimensional array of cone filters made from Lucite instead of the ridge filter made from aluminum alloy to reduce the scattering effect. The structure of cone filter is required to reduce the extremity of the ridge filter. We verified that the dose distribution is improved by use of the cone filter by calculations using the GEANT4 Monte Carlo code.
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