Li X A, Ma C M, Salhani D, Agboola O
Department of Medical Physics, Ottawa Regional Cancer Centre, Canada.
Med Phys. 1998 Aug;25(8):1464-71. doi: 10.1118/1.598320.
In this paper we present the dosimetric data of a Therapax DTX300 kilovoltage x-ray unit for endocavitary rectal irradiation. The unit if operated at tube voltage of 40-60 kVp (30 mA) with an added filtration of 0.2-0.4 mm Al generates acceptable beam qualities comparable to those of the original Papillon technique. Relative dosimetric measurements were performed at the cone end (37.2 cm SSD) of a 3 cm diameter rectal cone using various detectors to ensure the accuracy. A Monte Carlo method was used to calculate correction factors for the diode used in the percentage depth-dose (PDD) measurement, and to study the effect of the detector size on the beam profile. The PDD data were determined using the diode measurement corrected for its energy and angular response. It was found that the PTW N23342 and Markus parallel-plate chamber can be used directly to measure the PDD for this beam quality with 2% uncertainty. Measurement and Monte Carlo results have shown that the detector size has a significant effect on the penumbral profile. Film and diode detectors have a better spatial resolution compared to ionization chambers, but they may give an incorrect profile tail due to either nonlinear response at low energy or angular dependence. This can be corrected using the ionization-chamber measurement, based on the Monte Carlo analysis. The isodose distributions for this x-ray unit are presented.
在本文中，我们展示了用于腔内直肠照射的Therapax DTX300千伏X射线装置的剂量学数据。该装置在管电压为40 - 60 kVp（30 mA）且添加0.2 - 0.4 mm铝滤过的条件下运行，可产生与原始帕皮永技术相当的可接受射束质量。在一个直径3 cm的直肠锥形模体的锥形端（源皮距37.2 cm）使用各种探测器进行相对剂量测量，以确保准确性。采用蒙特卡罗方法计算用于百分深度剂量（PDD）测量的二极管的校正因子，并研究探测器尺寸对射束剖面的影响。PDD数据是使用针对其能量和角度响应进行校正的二极管测量确定的。结果发现，PTW N23342和马库斯平行板电离室可直接用于测量该射束质量的PDD，不确定度为2%。测量结果和蒙特卡罗结果表明，探测器尺寸对半值层剖面有显著影响。与电离室相比，胶片和二极管探测器具有更好的空间分辨率，但由于低能量下的非线性响应或角度依赖性，它们可能给出不正确的剖面尾部。基于蒙特卡罗分析，可使用电离室测量对此进行校正。本文还给出了该X射线装置的等剂量分布。
