Department of Oncology, Division of Radiation Physics, Clínica Universidad de Navarra, Avda. Pío XII, 36 Pamplona, Navarra 31008, Spain.
Med Phys. 2010 Sep;37(9):4634-42. doi: 10.1118/1.3476467.
This article presents an improved pencil-beam dose calculation formalism based on an experimental kernel obtained by deconvolution. The new algorithm makes it possible to calculate the absorbed dose for all field sizes.
The authors have enhanced their previous work [J. D. Azcona and J. Burguete, Med. Phys. 35, 248-259 (2008)] by correcting the kernel tail representing the contribution to the absorbed dose far from the photon interaction point. The correction was performed by comparing the calculated and measured output factors. Dose distributions and absolute dose values calculated using the new formalism have been compared to measurements. The agreement between calculated and measured dose distributions was evaluated according to the gamma-index criteria. In addition, 35 individual intensity-modulated radiation therapy (IMRT) fields were calculated and measured in polystyrene using an ionization chamber. Furthermore, a series of 541 IMRT fields was calculated using the algorithm proposed here and using a commercial IMRT optimization and calculation software package. Comparisons were made between the calculations at single points located at the isocenter for all the beams, as well as between beams grouped by anatomic location.
The percentage of points passing the gamma-index criteria (3%, 3 mm) when comparing calculated and measured dose distributions is generally greater than 99% for the cases studied. The agreement between the calculations and the experimental measurements generally lies in the +/- 2% interval for single points, with a mean value of 0.2%. The agreement between calculations using the proposed algorithm and using a commercial treatment planning system is also between +/- 5%.
An improved algorithm based on an experimental pencil-beam kernel obtained by deconvolution has been developed. It has been validated clinically and promises to be a valuable tool for IMRT quality assurance as an independent calculation system for monitor units and dose distributions. An important point is that the algorithm presented here uses an experimental kernel, which is therefore independent of Monte-Carlo-calculated kernels.
本文提出了一种基于反卷积获得的实验内核的改进铅笔束剂量计算形式。新算法使得计算所有射野大小的吸收剂量成为可能。
作者通过比较计算出的和测量出的输出因子，改进了他们之前的工作[J. D. Azcona 和 J. Burguete，《医学物理学》35，248-259（2008）]，纠正了表示远在光子相互作用点的吸收剂量贡献的核尾部。使用新形式计算的剂量分布和绝对剂量值与测量值进行了比较。根据伽马指数标准评估计算出的和测量出的剂量分布之间的一致性。此外，使用电离室在聚苯乙烯中计算并测量了 35 个单独的强度调制放射治疗（IMRT）场。此外，使用本文提出的算法和商业的 IMRT 优化和计算软件包计算了一系列 541 个 IMRT 场。在所有射束的等中心处对单个点进行了计算和测量的比较，以及按解剖位置分组的射束之间进行了比较。
在研究的情况下，比较计算出的和测量出的剂量分布时，通过伽马指数标准（3%，3 毫米）的点的百分比通常大于 99%。计算和实验测量之间的一致性通常在单点的+/- 2%范围内，平均值为 0.2%。使用所提出的算法和使用商业治疗计划系统的计算之间的一致性也在+/- 5%之间。
已经开发了一种基于通过反卷积获得的实验铅笔束核的改进算法。它已经在临床上得到验证，并有望成为 IMRT 质量保证的有价值工具，作为独立的监测单位和剂量分布计算系统。一个重要的观点是，这里提出的算法使用了实验核，因此它独立于蒙特卡罗计算的核。
