Patel Narayan Prasad, Majumdar Bishnu, Vijiyan V, Hota Pradeep K
Department of Medical Physics A. H. Regional Cancer Centre Cuttack-753 007, India.
J Cancer Res Ther. 2005 Oct-Dec;1(4):213-20. doi: 10.4103/0973-1482.19590.
The Gammamed Plus 192Ir high dose rate brachytherapy sources were calibrated using the therapy level ionization chambers (0.1 and 0.6 cc) and the well-type chamber. The aim of the present study was to assess the accuracy and suitability of use of the therapy level chambers for in-air calibration of brachytherapy sources in routine clinical practice. In a calibration procedure using therapy ion chambers, the air kerma was measured at several distances from the source in a specially designed jig. The room scatter correction factor was determined by superimposition method based on the inverse square law. Various other correction factors were applied on measured air kerma values at multiple distances and mean value was taken to determine the air kerma strength of the source. The results from four sources, the overall mean deviation between measured and quoted source strength by manufacturers was found -2.04% (N = 18) for well-type chamber. The mean deviation for the 0.6 cc chamber with buildup cap was found -1.48 % (N = 19) and without buildup cap was 0.11% (N = 22). The mean deviation for the 0.1 cc chamber was found -0.24% (N = 27). Result shows that probably the excess ionization in case of 0.6 cc therapy ion chamber without buildup cap was estimated about 2.74% and 1.99% at 10 and 20 cm from the source respectively. Scattered radiation measured by the 0.1 cc and 0.6 cc chamber at 10 cm measurement distance was about 1.1% and 0.33% of the primary radiation respectively. The study concludes that the results obtained with therapy level ionization chambers were extremely reproducible and in good agreement with the results of the well-type ionization chamber and source supplier quoted value. The calibration procedure with therapy ionization chambers is equally competent and suitable for routine calibration of the brachytherapy sources.
使用治疗级电离室（0.1立方厘米和0.6立方厘米）和井型电离室对伽马美Plus 192铱高剂量率近距离放射治疗源进行校准。本研究的目的是评估在常规临床实践中使用治疗级电离室对近距离放射治疗源进行空气中校准的准确性和适用性。在使用治疗电离室的校准程序中，在一个专门设计的夹具中，在距源的几个距离处测量空气比释动能。基于平方反比定律，通过叠加法确定房间散射校正因子。对在多个距离处测量的空气比释动能值应用各种其他校正因子，并取平均值以确定源的空气比释动能强度。对于四个源的结果，发现井型电离室测量值与制造商公布的源强度之间的总体平均偏差为-2.04%（N = 18）。发现带建成帽的0.6立方厘米电离室的平均偏差为-1.48%（N = 19），不带建成帽的平均偏差为0.11%（N = 22）。发现0.1立方厘米电离室的平均偏差为-0.24%（N = 27）。结果表明，对于不带建成帽的0.6立方厘米治疗电离室，在距源10厘米和20厘米处，估计过量电离分别约为2.74%和1.99%。在10厘米测量距离处，0.1立方厘米和0.6立方厘米电离室测量的散射辐射分别约为初级辐射的1.1%和0.33%。该研究得出结论，使用治疗级电离室获得的结果具有极高的可重复性，并且与井型电离室的结果以及源供应商公布的值非常一致。使用治疗电离室的校准程序同样适用于近距离放射治疗源的常规校准。
