Inui Shoki, Ueda Yoshihiro, Ono Shunsuke, Ohira Shingo, Isono Masaru, Nitta Yuya, Ueda Hikari, Miyazaki Masayoshi, Koizumi Masahiko, Teshima Teruki
Department of Radiation Oncology, Osaka International Cancer Institute, Osaka, Japan.
Department of Medical Physics and Engineering, Osaka University Graduate School of Medicine, Suita, Japan.
Rep Pract Oncol Radiother. 2021 Apr 14;26(2):281-290. doi: 10.5603/RPOR.a2021.0041. eCollection 2021.
The aim of the study was to evaluate analysis criteria for the identification of the presence of rectal gas during volumetric modulated arc therapy (VMAT) for prostate cancer patients by using electronic portal imaging device (EPID)-based dosimetry (IVD).
All measurements were performed by determining the cumulative EPID images in an integrated acquisition mode and analyzed using PerFRACTION commercial software. Systematic setup errors were simulated by moving the anthropomorphic phantom in each translational and rotational direction. The inhomogeneity regions were also simulated by the I'mRT phantom attached to the Quasar phantom. The presence of small and large air cavities (12 and 48 cm) was controlled by moving the Quasar phantom in several timings during VMAT. Sixteen prostate cancer patients received EPID-based IVD during VMAT.
In the phantom study, no systematic setup error was detected in the range that can happen in clinical (< 5-mm and < 3 degree). The pass rate of 2% dose difference (DD2%) in small and large air cavities was 98.74% and 79.05%, respectively, in the appearance of the air cavity after irradiation three quarter times. In the clinical study, some fractions caused a sharp decline in the DD2% pass rate. The proportion for DD2% < 90% was 13.4% of all fractions. Rectal gas was confirmed in 11.0% of fractions by acquiring kilo-voltage X-ray images after the treatment.
Our results suggest that analysis criteria of 2% dose difference in EPID-based IVD was a suitable method for identification of rectal gas during VMAT for prostate cancer patients.
本研究旨在评估通过基于电子射野影像装置（EPID）的剂量测定法（IVD），在前列腺癌患者容积调强弧形治疗（VMAT）期间识别直肠气体存在的分析标准。
所有测量均通过在集成采集模式下确定累积EPID图像来进行，并使用PerFRACTION商业软件进行分析。通过在每个平移和旋转方向移动人体模型来模拟系统设置误差。不均匀性区域也通过连接到类星体模型的I'mRT模型进行模拟。在VMAT期间，通过在几个时间点移动类星体模型来控制大小气腔（12和48厘米）的存在。16名前列腺癌患者在VMAT期间接受了基于EPID的IVD。
在模型研究中，在临床可能出现的范围内（<5毫米和<3度）未检测到系统设置误差。在照射四分之三次后气腔出现时，小大气腔中2%剂量差异（DD2%）的通过率分别为98.74%和79.05%。在临床研究中，一些分次导致DD2%通过率急剧下降。DD2%<90%的比例占所有分次的13.4%。治疗后通过采集千伏X射线图像，在11.0%的分次中确认存在直肠气体。
我们的结果表明，基于EPID的IVD中2%剂量差异的分析标准是在前列腺癌患者VMAT期间识别直肠气体的合适方法。
