Ohira Shingo, Ueda Yoshihiro, Isono Masaru, Masaoka Akira, Hashimoto Misaki, Miyazaki Masayoshi, Takashina Masaaki, Koizumi Masahiko, Teshima Teruki
Department of Radiation Oncology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Nakamichi 1-3-3, Higashinari-ku, Osaka, 537-8511, Japan.
Department of Medical Physics and Engineering, Osaka University Graduate School of Medicine, Suita, Japan.
J Radiat Res. 2017 Sep 1;58(5):685-692. doi: 10.1093/jrr/rrx006.
We investigated whether methods conventionally used to evaluate patient-specific QA in volumetric-modulated arc therapy (VMAT) for intracranial tumors detect clinically relevant dosimetric errors. VMAT plans with coplanar arcs were designed for 37 intracranial tumors. Dosimetric accuracy was validated by using a 3D array detector. Dose deviations between the measured and planned doses were evaluated by gamma analysis. In addition, modulation complexity score for VMAT (MCSv) for each plan was calculated. Three-dimensional dose distributions in patient anatomy were reconstructed using 3DVH software, and clinical deviations in dosimetric parameters between the 3DVH doses and planned doses were calculated. The gamma passing rate (GPR)/MCSv and the clinical dose deviation were evaluated using Pearson's correlation coefficient. Significant correlation (P < 0.05) between the clinical dose deviation and GPR was observed with both the 3%/3 mm and 2%/2 mm criteria in clinical target volume (D99), brain (D2), brainstem (D2) and chiasm (D2), albeit that the correlations were not 'strong' (0.38 < |r| < 0.54). The maximum dose deviations of brainstem were up to 4.9 Gy and 2.9 Gy for Dmax and D%, respectively in the case of high GPR (98.2% with 3%/3 mm criteria). Regarding MCSv, none of the evaluated organs showed a significant correlation with clinical dose deviation, and correlations were 'weak' or absent (0.01 < |r| < 0.21). The use of high GPR and MCSv values does not always detect dosimetric errors in a patient. Therefore, in-depth analysis with the DVH for patient-specific QA is considered to be preferable for guaranteeing safe dose delivery.
我们研究了在颅内肿瘤容积调强弧形放疗（VMAT）中，常规用于评估患者特异性质量保证（QA）的方法是否能检测出临床相关的剂量学误差。为37例颅内肿瘤设计了具有共面弧形的VMAT计划。使用三维阵列探测器验证剂量准确性。通过伽马分析评估测量剂量与计划剂量之间的剂量偏差。此外，计算每个计划的VMAT调制复杂性评分（MCSv）。使用3DVH软件重建患者解剖结构中的三维剂量分布，并计算3DVH剂量与计划剂量之间剂量学参数的临床偏差。使用Pearson相关系数评估伽马通过率（GPR）/MCSv与临床剂量偏差。在临床靶体积（D99）、脑（D2）、脑干（D2）和视交叉（D2）中，采用3%/3 mm和2%/2 mm标准时，临床剂量偏差与GPR之间均观察到显著相关性（P < 0.05），尽管相关性并不“强”（0.38 < |r| < 0.54）。在高GPR（3%/3 mm标准下为98.2%）的情况下，脑干的最大剂量偏差在Dmax和D%时分别高达4.9 Gy和2.9 Gy。关于MCSv，所评估的器官均未显示与临床剂量偏差有显著相关性，相关性为“弱”或无相关性（0.01 < |r| < 0.21）。使用高GPR和MCSv值并不总能检测出患者的剂量学误差。因此，对于保证安全的剂量输送，认为对患者特异性QA进行深度剂量体积直方图（DVH）分析更为可取。
