改良式軟片劑量驗證應用於強度調控放射線治療之先期研究

A Prelimnary Study of Improved Film Dosimetry for Imrt

蔡忠宏(Chung-Hung Tsai) ； 莊克士(Keh-Shih Chuang) ； 戴宏旗(Hung-Chi Tai) ； 周志成(Chih-Cheng Chou) ； 蕭安成(An-Cheng Shiau) ； 林芳仁(Fang-Jen Lin)

《放射治療與腫瘤學》 10卷1期 (2003/03) Pp. 53-62

https://doi.org/10.6316/TRO/200310(1)53

摘要

”目的：為了使軟片適用於強度調控放射治療(IMRT)多重角度入射，及動態性照野變化的劑量驗證特性，本研究針對射束與軟片平行排列時，照野與深度改變的情況下，如何正確將軟片光密度值正確轉換劑量，提供一套可行的辦法。
材料與方法：利用數種材質的濾片與軟片之組合接受X光的照射，再以類神經網路將不同能譜與劑量之間的關係找出來，可以得到實際的劑量。
結果：經本系統轉換的劑量值，在深度及照野變化的情況下，仍能有效轉換劑量至最大誤差小於±4%，平均誤差2%左右，此為臨床上可接受之誤差範圍。
結論：本實驗所提出之劑量轉換方式，已能正確轉換劑量於射束和軟片平行排列及照野變化的情況，進一步將實際評估本系統在臨床應用及多重照野(multiple field)下的表現。”

關鍵字

強度調控放射治療,劑量驗證,類神經網路,軟片劑量量測

並列摘要

”Purpose: Intensity Modulation Radiation Therapy (IMRT) is implemented using multiple beam orientations and varius field sizes, X-ray film can't be used as a dosimetry tool in such situation because of its serious energy dependent problem. We present and develop an improved method to overcome the circumstances.
Materials and Methods: We used the combination of film with various filters (None, Pb, Cu, and AI) so that each film is irradiated to different energy spectrum. A neural-network is employed to relate the actual dose and energy spectra. After calibration and training, the optical densities of the four films can be input to the network to yield the actual dose at any location.
Results: The PDD of a 20 x 20 field size and the dose distribution of an off-axis location at 5cm are estimated using this trained neural network. The maximum differences between the measurements of this film system and ionization chamber were less than ±4%, and less than 2% for the mean error in our investigation.
Conclusion: Optical density and dose relationship can be found and converted by our neural-net system. For the future studies, we will focus on clinical application of these experimental results and extend the concept to multiple beam orientations.”

並列關鍵字

IMRT, Dose verification, Neural-net, Film dosimetry