以Plexiglass假體校正Ir-192近接治療射源活度

Calibration of IR-192 Hdr Brachytherapy Source Using Plexiglass Phantom

黃英明(Ing-Ming Hwang) ； 李必忍(James C. Li) ； 賴耿光(Paul Kun-Goung Lai) ； 顏溫榕(Wen-Long Yean)

《放射治療與腫瘤學》 5卷3期 (1998/09) Pp. 201-206

https://doi.org/10.6316/TRO/199805(3)201

摘要

本文以PTW N23333游離腔在空氣中測得Ir-192射源的曝露率為基準，探討Gammamed後荷近接治療機組提供的有限體積圓柱型plexiglass假體用於校正Ir-192射源活度時應修正的參數及此假體的臨床應用上的優點。
材料與方法：先以PTW N23333游離腔，根據AAPM Report 41的報告所敘述的參數修正後，測得距射源8公分處之空氣中曝露率，加入研究中額外參數的修正後，求得介質內之劑量率；再測量位於Piexiglass假體內，有無附加回散射水假體之曝露率，求得此假體之回散射因子，以探計在plexiglass假體內測量應做的修正。
結果：使用Plexiglass假體時，其回散射修正因子(BSF)經測呈應為1.081。劑呈梯度校正因子(Cgrad)在射源至游離腔的距離(SCD)等於8公分處之修正值為1.158。
結論：使用Plexiglass假體校正Ir-192射源活度，在臨床應用上比在空氣中測量有較高的穩定性，重現性及方便性，然而在使用前需先與其他測量方法相互印證，求得其回散射等因子才能準确用於定期射源活度之檢測。

關鍵字

近接治療 ； Ir-192射源活度 ； 固態假體

並列摘要

Purpose: In this paper, the PTW N23333 ionization chamber was used to calibrate the in air exposure rate of IR-192 HDR brachytherapy source in a Gammamed 12I remote afterloading machine. The exposure rate of the source in finite cylinder plexiglass phantom that was equipped with the system was measured. The calibration factor of the plexiglass phantom for IR-192 source activity calibration is discussed and the clinical advantages of the phantom is summarized.
Materials and Methods: The in air exposure rate of the source was measured with the PTW N2333 ionization chamber connected to the Capintec electrometer at SCD equal to 8 cm. Source activity was calculated from the measured exposure according to the suggested parameters of AAPM Report 41. The in phantom exposure rate were measured with and without water phantom to calculated the back-scatter-factor of the plexiglass phantom.
Results: The back-scatter-factor is equal to 1.081 and the factor Cgrad=1.158 should be considered to calibrate the scatter from the upper and button side of the phantom which was less due to the lack of scatter and dose gradient correction.
Conclusion: Calibrations in plexiglass phantom of Ir-192 HDR brachy-therapy source allow more stability and reproducibility. The calibration factors of the plexiglass phantom needs to be considered in routine source calibration.

並列關鍵字

Brachytherapy ； Ir-192 source activity ； Plexiglass phantom