Xie Kai, Sun Hongfei, Gao Liugang, Sui Jianfeng, Lin Tao, Ni Xinye
Department of Radiation Oncology, Changzhou No. 2 People's Hospital, Nanjing Medical University.
The Center for Medical Physics of Nanjing Medical University, Changzhou, China.
Medicine (Baltimore). 2019 Jul;98(30):e16536. doi: 10.1097/MD.0000000000016536.
This study aimed to analyze the influence of the radiation field size on the passing rate of the treatment planning system using MatriXX if the field irradiated the circuit.Two sets of static fields which were 10 cm and 30 cm in the left-right direction (X), and was 31 cm to 40 cm in gun-target direction (Y) were designed. In these fields, the gantry was 0 and the monitor units were 200 MU. Two plans from an esophagus carcinoma patient with a planning target volume of 86.4 cm and a cervical carcinoma patient with a planning target volume (PTV) of 2094.1 cm were chosen. The passing rates of these plans were gained without and with protecting the circuit area from lead alloys. The gamma analysis was used and the standard was set to 3%/3 mm.The verification passing rate decreased from 95.0% to 69.2% when X was 10 cm while Y increased from 31 cm to 40 cm. With the protection from low melting point lead alloys, the passing rate was from 96.2% to 89.6%. The results of the second set of plans without lead alloys were similar but the passing rate decreased more sharply. The passing rates of the 2 patients were 99.5% and 57.1%. With the protection of the lead alloys, their passing rates were 99.8% and 72.1%, respectively.The results showed that with the increase of the radiation field size in the Y direction, more areas were irradiated in the circuit, and the passing rate gradually decreases and dropped sharply at a certain threshold. After putting lead alloys above the circuit, the passing rate was much better in the static field but was still less than 90% in the second patient volumetric modulated arc therapy (VMAT) because the circuit was irradiate in other directions. In daily QA, we should pay attention to these patients with long size tumor.
本研究旨在分析当射野照射到电路时，射野大小对使用MatriXX的治疗计划系统通过率的影响。设计了两组静态射野，其左右方向（X）分别为10 cm和30 cm，靶区方向（Y）为31 cm至40 cm。在这些射野中，机架角度为0，监测单位为200 MU。选取了一名计划靶体积为86.4 cm³的食管癌患者和一名计划靶体积（PTV）为2094.1 cm³的宫颈癌患者的两个计划。分别在不保护和保护电路区域免受铅合金影响的情况下获得这些计划的通过率。采用伽马分析，标准设定为3%/3 mm。当X为10 cm且Y从31 cm增加到40 cm时，验证通过率从95.0%降至69.2%。在低熔点铅合金的保护下，通过率从96.2%降至89.6%。第二组无铅合金计划的结果相似，但通过率下降得更急剧。两名患者的通过率分别为99.5%和57.1%。在铅合金的保护下，其通过率分别为99.8%和72.1%。结果表明，随着Y方向射野尺寸的增加，电路中被照射的区域更多，通过率逐渐降低，并在一定阈值处急剧下降。在电路上方放置铅合金后，静态射野中的通过率要好得多，但在第二名患者的容积调强弧形治疗（VMAT）中仍低于90%，因为电路在其他方向受到照射。在日常质量保证中，我们应关注这些肿瘤尺寸较长的患者。
