- 著者
-
足立 宏美
稲越 英機
早川 岳英
井上 富夫
笠原 敏文
五十嵐 智
早川 英樹
棚邊 哲史
- 出版者
- 公益社団法人日本放射線技術学会
- 雑誌
- 日本放射線技術學會雜誌 (ISSN:03694305)
- 巻号頁・発行日
- vol.64, no.3, pp.306-315, 2008-03-20
- 被引用文献数
-
2
2
To estimate the collimator scatter factor, <i>S</i><sub>c</sub> of small field sizes in which a mini-phantom cannot be fully included at the nominal treatment distance (NTD=100 cm), we measured the in-air output of 4 MV and 10 MV X-rays of a Varian's Clinac 2100 C/D using a mini-phantom at NTD and at a long source-to-chamber distance (SCD=200 cm) with field-size defined at the isocenter down to 4.6×4.6cm<sup>2</sup> and 2.3×2.3cm<sup>2</sup>, respectively. We then compared the fitted curve to the NTD dataset by a cumulative exponential distribution model with that by a cumulative Gaussian distribution (error function) model containing a zero-field extrapolated term derived from the long SCD dataset. The results showed that the zero-field extensions of two fitted curves coincided for a 4 MV X-ray, but a large discrepancy was seen between them for a 10 MV X-ray. Therefore, the <i>S</i><sub>c</sub> of small field sizes not measurable using a mini-phantom at the NTD can be well estimated by applying the cumulative exponential model to the NTD dataset in the case of a 4 MV X-ray beam filtrated with a cone-shaped flattener. However, to estimate the <i>S</i><sub>c</sub> of such small field sizes in the case of a 10 MV X-ray beam filtrated with a bell-shaped flattener, we consider it preferable to also measure in-air output at a long SCD and to apply the cumulative Gaussian model as described here.