超薄型熱發光劑量計經外加磁鐵評估放射治療中電子污染量

放射治療爲治療癌症的主要方法之一在控制癌症及治癒率上，一直有極大的貢獻。目前執行放射治療最常使用的儀器爲直線加速器(linear accelerators)，此儀器能產生高能量的光子射束來治療癌症。但在放射治療過程中，直線加速器所產生的光子射束與機頭內的裝置及射程中的空氣發生相互作用產生電子污染(electron contamination)。本文將測量Elekta Precise SLi直線加速器6MV及15MV光子射束開啓照野分別爲5×5cm、10×10cm、15×15cm及20×20cm照野內、外的污染電子劑量。利用外加磁鐵將電子污染偏離光子射束，搭配GR-200F超薄型熱發光劑量計(Ultra-thin thermo luminescent detector, TLD)比較架設磁鐵前後電子污染量。結果顯示，6MV光子射束在照野內最多可減少37.03%，照野外則最多可減少60.28%；而15MV在照野內最多可減少37.72%之電子污染劑量，照野外更減少72.64%。因此，在放射治療過程中搭配外加磁鐵可明顯減少照野內及照野外的電子污染量，降低病人的皮膚劑量。

關鍵字

電子污染；磁鐵；超薄型熱發光劑量計； GR-200F ；皮膚劑量

並列摘要

The radiotherapy is dominantly used for the cancer therapy at present. In the control and cure rate of cancers, radiotherapy by high-energy photon beams provided by linear accelerators already gives a read contribution. As high-energy of x-ray beams used in radiation therapy treatment, however, it always combines with production of electron contaminations. In this study, measured electron contamination dose of 6 MV and 15 MV x-ray beams were investigated for several clinical field sizes that ranging from 5×5 cm up to 20×20 cm. To inside a magnetic deflector in the path of photon beams with various field sizes, the percentage of electron contamination beam swept away were measured by using ultra-thin thermo luminescent dosimeter (TLD) of GR-200F. The results showed that the percentage reduction of electron contamination dose up to 37.03% and 37.72% for 6MV and 15 MV inside of field sizes, respectively, and 60.28% and 72.64% for 6MV and 15 MV outside of field sizes, respectively, were achieved with the installation of magnetic deflector. Therefore, in the course of treatment, use of magnetic fields can reduce the electron contamination doses inside and outside of field size significantly.

並列關鍵字

electron contamination ； magnet ； ultra-thin thermo luminescent dosimeter ； GR-200F ； skin dose

國際替代計量

超薄型熱發光劑量計經外加磁鐵評估放射治療中電子污染量

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