- 學位論文
利用EBT2進行腔內近接放射治療之體內直腸劑量計校正因子分析
Calibration factor analysis in vivo rectal dosimetry of brachytherapy using EBT2 film technique
摘要
EBT2自顯影底片的有效原子序與水接近所以在臨床放射線劑量的測量上有低的能量依持特性,這種特性使得使用不同能量之劑量轉換曲線來做劑量轉換時之誤差降低。本實驗所使用之EBT2底片為ISP公司所開發展之免顯影定影底片及EPSON Expression 1680平台式全彩影像掃描器,利用近接治療射源Ir-192照射EBT2底片取得Ir-192之特性曲線，比較與6 MV直線加速器照射底片所得特性曲線。利用EBT2底片低能量依存性特性，在Ir-192射源照射下，配合自製矽膠條夾EBT2底片直接套用6 MV特性曲線校正PTW T9112直腸劑量偵檢器，最後取得其校正因子。研究結果發現， 在EBT2底片低能量依存性特性之下6 MV光子能量與Ir-192近接治療射源其底片特性曲線非常相近，利用EBT2配合自製矽膠條可以取得EBT2底片中軸線上之劑量分佈，藉此校正PTW T9112直腸偵檢器內5個二極體偵檢器，取得其在固態水假體中校正因子為2.98×10^7cGy/C至3.99×10^7cGy/C，在壓克力假體中為2.98×10^7cGy/C至3.2×10^7cGy/C。本研究建立將EBT2底片用於對近接治療之絕對劑量測量流程，並用於對其他劑量計做校正因子測量。除此之外也設計並製作可用於測量體內直腸劑量之裝置，進一步分析其劑量特性做為下階段用於臨床測量之準備。
並列摘要
EBT2 Gafchromic film is tissue equivalence and energy independence, this characteristic can makes dose conversion and decrease error in different energy by using calibration curve. This study use EBT2 Gafchromic film manufactured by ISP and Epson 1680 flatbed scanner. Using Ir-192 source to irradiated EBT2 film and obtained the calibration curve, compare the calibration curve of Ir-192 with 6 MV photon beam. Dose calculation can be used silicon rod and EBT2 film to corrected PTW T9112 rectal detector and to acquired the correction factor. Result show that two different calibration curves of Ir-192 source and 6 MV photon beam are not significant different. Applying EBT2 film combine with silicon rod can achieved the axial flat dose to corrected PTW T9112 rectal detector. The correction factor is 2.98×10^7cGy/C to 3.99×10^7cGy/C in solidwater phantom and 2.98×10^7cGy/C to 3.2×10^7cGy/C in acrylic phantom. This study provided procedures for measure treatment dose and calibrate the other detector by EBT2 film.