比較聚合底片和傳統感光驗證片於立體定位放射手術之劑量分佈

Comparison of Dose Distribution and Sensitivity with Radiochromic and Silver Halide Films for Stereotactic Radiosurgery

孫崇騰(Tchung-Ten Sun) ； 朱唯勤(Wei-Chin Chu) ； 羅濟慶(Chi-Ching Lo) ； 葉健一(Jami Yeh) ； 李俊信(Jason J. S. Lee)

《放射治療與腫瘤學》 3卷2期 (1996/06) Pp. 121-127

https://doi.org/10.6316/TRO/199603(2)121

摘要

目的：利用聚合底片和感光驗證底片來探討在立體定位放射手術的劑量分佈情形及其對放射線的靈敏度。
材料與方法：一種新且具有高度均勻度的直接造影底片radiochromic film,其感應層的厚度為7μm。經放射線照射後，聚合作用會使其片子由無色變為深藍色而無需額外處理。利用模機立體定位放射手術的四個多弧非共平面之照射，分析其在劑量反應曲線與照射後劑量分佈的結果，並與僅需250 cGy劑量大小的傳統感光膠片做一比較。
結果：我們發現聚合底片不會有傳統感光驗證片需要後處理的誤差產生，如光害、顯影和定影過程及其濃度無法保持一定等因素，因此是可以用來做為不錯的劑量量測材質。然而為了達到合理的光度值，所用的立體定位放射手術模擬總劑量高達10Gy，而在臨床上是很少用到如此高劑量。在劑量分佈的比較上，可以得到與傳統感光驗證片的平均偏差不大於0.5mm。
結論：可以得知聚合底片能提供臨床的精確度在1mm以內。對於放射手術的品質確認和治療時的劑量輸出提供了另一精確的量測工具。

關鍵字

立體定位放射手術 ； 聚合底片 ； 劑量分佈 ； 劑量反應曲線

並列摘要

Purpose: To study the dose distribution and sensitivity with radiochromic (Gafchromic) film and silver halide (Kodak X-Omat V-film) on stereotactic radiosurgery.
Material and Method: A new radiochromic film, with highly uniform, thin and sensitive layer (7μm thick), is employed in the study. The film changes from colorless to blue by dye polymerization without processing, upon exposure to ionization from 0-50 Gy. The dose distribution patterns of 4 non-coplanar irradiation with the Gafchromic film were compared with the ones from the verification film which was only exposed with 250 cGy.
Result: The Gafchromic film appears to be a better choice for actual dose measurement in the medium with avoiding potential uncertainties found in most of silver halide films such as light exposure, processing time, developer concentration etc. However, to obtain reasonable good optical densities in the Gafchromic film, there is a need to offer irradiation about 10 Gy that is not practically achievable in the clinical settings. The accuracy study of the chromic film was found to be less 0.5% in error comparing with the one from the verification film.
Conclusion: It is clinically possible to obtain an accuracy of 1mm on determining the physical center in the linac-based radiosurgery. For actual dose measurement in the body, the chromic film offers a good test tool for dosimetry and quality assurance.

並列關鍵字

Stereotactic radiosurgery ； Radiochromic film ； Dose distribution ； Dose response curve