Nara Tetsuzo, Iwasaki Akira, Komai Fumio, Sato Kazuhiko, Fukushi Hideto, Horanai Yoshiaki
Department of Radiation Oncology, Aomori Prefectural Center Hospital.
Nihon Hoshasen Gijutsu Gakkai Zasshi. 2004 Nov;60(11):1592-603. doi: 10.6009/jjrt.kj00003326584.
Calculation of in-air or in-water dose for 4 MV X-ray irregular fields could be accurately performed using the collimator scatter factor (S(c)) and phantom scatter factor (S(p)) concepts. It has been revealed that the equivalent square field for a multi-leaf collimator (MLC) irregular field can be evaluated accurately by using the S(p)-Clarkson or S(c)-Clarkson integration method; however, the S(c)-Clarkson integration method is more straightforward because the S(c) factor expresses the in-air X-ray output factor. It has been found that when the MLC field is relatively much smaller than the main collimator field, the Sc factor can be accurately evaluated by introducing the small segment correction (SSC) factor (except for the case in which the MLC field is less than 1 x 1 cm(2)). It has also been found that both the S(p) factor and the tissue-phantom ratio (TPR) can be precisely evaluated by introducing the F(MLC) factor in cases in which the ratio of the MLC equivalent square field side to the main collimator equivalent square field side is less than about 0.7.
利用准直器散射因子（S(c)）和模体散射因子（S(p)）的概念，可以准确计算4兆伏X射线不规则射野在空气中或水中的剂量。研究表明，通过使用S(p)-克拉克森或S(c)-克拉克森积分法，可以准确评估多叶准直器（MLC）不规则射野的等效方野；然而，S(c)-克拉克森积分法更直接，因为S(c)因子表示空气中的X射线输出因子。研究发现，当MLC射野相对主准直器射野小得多时，通过引入小射野校正（SSC）因子可以准确评估Sc因子（MLC射野小于1×1平方厘米的情况除外）。还发现，在MLC等效方野边长与主准直器等效方野边长之比小于约0.7的情况下，通过引入F(MLC)因子可以精确评估S(p)因子和组织-模体比（TPR）。
