Deng Jun, Ma C M, Hai Jenny, Nath Ravinder
Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
Med Phys. 2003 Dec;30(12):3124-34. doi: 10.1118/1.1624753.
The goal of this work is to implement a beam commissioning procedure to generate a multiple source model using a set of standard measurement data for possible Monte Carlo treatment planning in the clinic for a Cyberknife stereotactic radiosurgery system. The required measurement data include the central axis depth dose curve (PDD), the dose profile at dmax(= 1.5 cm) of 60 mm cone at 80 cm source-to-surface distance (SSD), and the cone output factors for cones of 5 mm to 60 mm at 80 cm source-to-axis distance (SAD). The employed dual source model has the same structure as the one that has been studied in our previous work while most of the parameters of each source are extracted from the measurement data rather than the beam phase space. The energy spectra will be extracted from the central axis PDD, the fluence distributions will be deconvoluted from the dose profile at dmax, and the source distributions will be determined from the measured cone output factors. Monte Carlo dose calculations in various water phantoms have been performed to verify the beam commissioning procedure. The agreement between the measurements and the commissioning results was within 2%/1 mm for the central axis PDDs and the dose profiles at various depths when an IC-3 chamber was used and within 2% for the cone output factors for various collimator sizes of 5 to 60 mm. Largest difference (9.5%) was observed for the 7.5 mm cone when an IC-10 chamber was used. The large differences can be attributed to the volumetric averaging effect of the IC-10 chamber, whose dimension is comparable to the field of the small cones. The overall agreement between the measurements and the commissioning results is clinically acceptable, which implies that our commissioning tool is adequate for clinical applications of Monte Carlo dose calculations for the Cyberknife stereotactic radiosurgery system.
这项工作的目标是实施一个射束调试程序，利用一组标准测量数据生成多源模型，以便在临床中为射波刀立体定向放射治疗系统进行可能的蒙特卡罗治疗计划。所需的测量数据包括中心轴深度剂量曲线（PDD）、源皮距（SSD）为80 cm时60 mm准直器在最大剂量深度（dmax = 1.5 cm）处的剂量分布，以及源轴距（SAD）为80 cm时5 mm至60 mm准直器的准直器输出因子。所采用的双源模型与我们之前工作中研究的模型结构相同，而每个源的大多数参数是从测量数据中提取的，而非射束相空间。能谱将从中心轴PDD中提取，注量分布将从dmax处的剂量分布中解卷积得到，源分布将根据测量的准直器输出因子确定。已在各种水模体中进行蒙特卡罗剂量计算，以验证射束调试程序。当使用IC - 3电离室时，中心轴PDD和不同深度处的剂量分布测量值与调试结果之间的一致性在2%/1 mm以内，对于5至60 mm不同准直器尺寸的准直器输出因子，一致性在2%以内。当使用IC - 10电离室时，7.5 mm准直器观察到的最大差异为9.5%。这些较大差异可归因于IC - 10电离室的体积平均效应，其尺寸与小准直器的射野相当。测量值与调试结果之间的总体一致性在临床上是可接受的，这意味着我们的调试工具足以用于射波刀立体定向放射治疗系统蒙特卡罗剂量计算的临床应用。
