Fluence to Dose Conversion Coefficients for Nuclear eat Radiations in Localized Exposure and for Risk
Grant-in-Aid for Scientific Research (B)
|Allocation Type||Single-year Grants |
|Research Institution||Hokkaido University |
SAWAMURA Sadashi Hokkaido University, Graduate School of Engineering, Professor, 大学院・工学研究科, 教授 (70002011)
FUJIYOSHI Ryoko Hokkaido University, Graduate School of Engineering, Instructor, 大学院・工学研究科, 助手 (70229061)
高橋 憲司 北海道大学, 大学院・工学研究科, 助手 (00216714)
|Project Period (FY)
2002 – 2003
Completed (Fiscal Year 2003)
|Budget Amount *help
¥6,700,000 (Direct Cost: ¥6,700,000)
Fiscal Year 2003: ¥2,400,000 (Direct Cost: ¥2,400,000)
Fiscal Year 2002: ¥4,300,000 (Direct Cost: ¥4,300,000)
|Keywords||Radiation Protection / Effective Dose / External Exdposure / Partial Exposure / onversion Coefficient / 外部被曝 / 非均質被曝|
Progress us accelerator engineering has offered beams of various sizes, energies, and pulse widths. When using such beams, the exposure is not always to the whole human body but it may be only to certain parts of a body in which the size of the exposed area is smaller than a whole human body.
For such localized exposure of the AP and PA geometry. we have calculated the conversion coefficients from fluence to organ dose and to effective dose for electrons. photons sad positrons op 200 MeV using EGS4 Monde Carlo code and the MIRD-5 human phantom.
Calculations were carried out for whole body as well as partial (localized) beam exposure with mono-energetic radiations The phantom is placed in a vacuum in both types of exposure. In the calculations, the incident beam is parallel and rectangular, and the sizes are 1(whole body exposure), 1/2(half body exposure). 1/5, or 1/10 of the area of the MIRD phantom. To investigate the beam size effects on the effective doses, calculations are carried ou
t for 5 different beam sizes of isocenter irradiation. The results as follows
1.Effective dose per unit fluence for 1/2 size exposure (half body exposure)
In general, the energy dependence of the effective dose for half body exposure is very similar to that the whole body exposure. The value of the effective dose at any half body exposure is smaller than that of the whole body exposure in the energy region studied. At energies lower than about 1 MeV the skin is the main contributor to the effective dose at any irradiation geometry so the ratio between the effective dose value of the half body and whole body exposure is about 1/2 which is the same ratio as the source size. However, at energies higher than 0 MeV the differences in the effective dose in half and whole body exposures become large. This is because of the locations of organs which mainly contribute to the effective dose with respect to the radiation source plane.
2. 1/10 size exposure
The conversion factors defined as H_T E per unit particle fluence have been obtained. The calculated results shows that with uniform exposure the effective dose increases gradually with increasing electron energy while in partial exposure it increase rapidly from the energy depending on the exposure position. for example from 7 MeV in the exposure of the abdomen. This is because the effective dose depends on what the organs are irradiated by the beam and also where they located in the body and what values of the tissue weighting factors they have.
3.Dependence on the beam size
Effective doses per fluence when the is irradiated by rectangular isocentered beams of different sizes are calculated. The result show that the effective dose increases with increasing beam sizes but at energies higher than 1MeV the dose curve indicates the saturation. Effective doses at the energies lower than 1 MeV are almost proportional to the beam size. This is because at these energies the skin is the largest contributor to the effective dose and the irradiated-skin area increased in proportion to the beam size. At energies higher than 10 Me V, electrons reach the main organs in the chest and abdomen. Among the irradiated organs the lungs show the same size dependence above 10 MeV. In the 1MeV to 5 MeV energy region the effective dose curves show a rather sleep increase at low irradiations due to the contribution of the breasts and thyroid which electrons reach at around 1MeV. Less
Report (3 results)
Research Products (15 results)