Medical Physics Department, IRCCS San Raffaele, Milano, Italy.
Radiat Oncol. 2011 Feb 9;6:14. doi: 10.1186/1748-717X-6-14.
To analyse limits and capabilities in dose calculation of collapsed-cone-convolution (CCC) algorithm implemented in helical tomotherapy (HT) treatment planning system for thorax lesions.
The agreement between measured and calculated dose was verified both in homogeneous (Cheese Phantom) and in a custom-made inhomogeneous phantom. The inhomogeneous phantom was employed to mimic a patient's thorax region with lung density encountered in extreme cases and acrylic inserts of various dimensions and positions inside the lung cavity. For both phantoms, different lung treatment plans (single or multiple metastases and targets in the mediastinum) using HT technique were simulated and verified. Point and planar dose measurements, both with radiographic extended-dose-range (EDR2) and radiochromic external-beam-therapy (EBT2) films, were performed. Absolute point dose measurements, dose profile comparisons and quantitative analysis of gamma function distributions were analyzed.
An excellent agreement between measured and calculated dose distributions was found in homogeneous media, both for point and planar dose measurements. Absolute dose deviations <3% were found for all considered measurement points, both inside the PTV and in critical structures. Very good results were also found for planar dose distribution comparisons, where at least 96% of all points satisfied the gamma acceptance criteria (3%-3 mm), both for EDR2 and for EBT2 films. Acceptable results were also reported for the inhomogeneous phantom. Similar point dose deviations were found with slightly worse agreement for the planar dose distribution comparison: 96% of all points passed the gamma analysis test with acceptable levels of 4%-4 mm and 5%-4 mm, for EDR2 and EBT2 films respectively. Lower accuracy was observed in high dose/low density regions, where CCC seems to overestimate the measured dose around 4-5%.
Very acceptable accuracy was found for complex lung treatment plans calculated with CCC algorithm implemented in the tomotherapy TPS even in the heterogeneous phantom with very low lung-density.
分析在螺旋断层调强放疗（HT）治疗计划系统中实施的坍塌锥卷积（CCC）算法在胸部病变剂量计算中的局限性和能力。
在均匀（奶酪体模）和定制的不均匀体模中验证了测量剂量与计算剂量之间的一致性。不均匀体模用于模拟患者胸部区域，其中包含在极端情况下遇到的肺密度以及肺腔内部各种尺寸和位置的丙烯酸插入物。对于这两种体模，使用 HT 技术模拟并验证了不同的肺部治疗计划（单个或多个转移灶和纵隔中的靶区）。进行了点和平面剂量测量，均使用放射照相扩展剂量范围（EDR2）和放射化学外照射治疗（EBT2）胶片。分析了绝对点剂量测量，剂量分布比较和伽马函数分布的定量分析。
在均匀介质中，无论是点剂量测量还是平面剂量测量，都发现测量和计算的剂量分布之间具有极好的一致性。对于所有考虑的测量点，绝对剂量偏差均<3％，包括 PTV 内部和关键结构内部。平面剂量分布比较的结果也非常好，至少 96％的点满足伽马接受标准（3％-3mm），无论是 EDR2 还是 EBT2 胶片。不均匀体模的结果也可以接受。点剂量偏差相似，但是平面剂量分布比较的一致性稍差：EDR2 和 EBT2 胶片的伽马分析测试分别有 96％的点通过了可接受的 4％-4mm 和 5％-4mm 标准。在高剂量/低密度区域观察到较低的准确性，其中 CCC 似乎高估了测量剂量约 4-5％。
即使在具有极低肺密度的不均匀体模中，使用 CCC 算法在 Tomotherapy TPS 中计算复杂的肺部治疗计划也具有非常可接受的准确性。
