Krithivas G, Rao S N
Med Phys. 1987 Mar-Apr;14(2):274-81. doi: 10.1118/1.596138.
Dosimetric characteristics of a 24-MV photon beam produced by a Varian Clinac 2500 linear accelerator are presented. Particular attention is paid to measurements and applications relating to depth of maximum dose and scatter correction factors. New experimental methods were adopted to investigate scatter factors for field sizes ranging from 5 X 5 to 40 X 40 cm. For the largest field investigated, a 3% phantom scatter factor relative to a 10 X 10 cm field was determined. From the study, clinically useful scatter-phantom ratios were generated. The study also demonstrated that the estimated correction factors for scatter in a medium caused negligible changes (approximately equal to 0.1%) on the percent depth-dose values derived from the measured tissue-phantom ratio (TPR) data. The paper also quantitatively compares results obtained for dosimetric parameters like scatter output, tissue-phantom ratio, and percent depth-dose with those obtained from similar machines used for radiotherapy. Measured data relating to these parameters are expressed by taking a reference depth of 8 g/cm2 in a medium for normalization purposes and its importance discussed. Additional measurements presented in this work include beam quality and collimator effect on dose rate. Phantoms of various sizes and materials and a variety of detectors were used throughout the investigation.
介绍了Varian Clinac 2500直线加速器产生的24兆伏光子束的剂量学特征。特别关注与最大剂量深度和散射校正因子相关的测量及应用。采用了新的实验方法来研究5×5至40×40厘米射野大小的散射因子。对于所研究的最大射野，确定了相对于10×10厘米射野的3%体模散射因子。通过该研究，得出了临床上有用的散射-体模比。该研究还表明，介质中散射的估计校正因子对由测量的组织-体模比（TPR）数据得出的百分深度剂量值产生的变化可忽略不计（约等于0.1%）。本文还定量比较了散射输出、组织-体模比和百分深度剂量等剂量学参数的结果与用于放射治疗的类似机器所获得的结果。为归一化目的，以介质中8克/平方厘米的参考深度来表示与这些参数相关的测量数据，并讨论了其重要性。这项工作中给出的其他测量包括射束质量和准直器对剂量率的影响。在整个研究过程中使用了各种尺寸和材料的体模以及多种探测器。
