医療被曝の解析に関する研究第1報;モンテカルロ計算による直方体水ファントム内の利用線錘外線量分布

概要

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It is necessary to know the dose distributions not only inside but also outside the region exposed by the useful X-ray beam, to evaluate doses in a patient during the radiographic procedures.In this paper, we calculated systematically three dimensional absorbed dose distributions outside the useful beam of diagnostic X-rays in a rectangular prism water phantom using the Monte Carlo method.The isodose curves, which showed the scattered dose distribution, were in turn moved further away from the useful field as simultaneously increasing the X-ray tube voltage and/or the field size. But, this movement of isodose curves in the low dose rates tends to gradually decrease with the increase of the tube voltage as a result of the probability density of photon scattering angle dependence on the photon energy. When the width of the X-ray field is larger than the free path length in the water of the scattered photons, the distance of the isodose curves from the edge of the field is almost constant.This systematic data of dose distributions is very useful to estimate doses at various locations when patients undergo radiologic examinations.
日本保健物理学会の論文