Connor Michael, Wei Randy L, Yu Suhong, Sehgal Varun, Klempner Samuel J, Daroui Parima
Department of Radiation Oncology, University of California, Irvine Medical Center, Orange, CA.
Department of Medicine, Division of Hematology/Oncology, University of California, Orange, CA.
Med Dosim. 2016 Autumn;41(3):221-4. doi: 10.1016/j.meddos.2016.02.003. Epub 2016 Jun 2.
American Association of Physicists in Medicine (AAPM) Task Group 176 evaluated the dosimetric effects caused by couch tops and immobilization devices. The report analyzed the extensive physics-based literature on couch tops, stereotactic body radiation therapy (SBRT) frames, and body immobilization bags, while noting the scarcity of clinical reports of skin toxicity because of external devices. Here, we present a clinical case report of grade 1 abdominal skin toxicity owing to an abdominal compression device. We discuss the dosimetric implications of the utilized treatment plan as well as post hoc alternative plans and quantify differences in attenuation and skin dose/build-up between the device, a lower-density alternative device, and an open field. The description of the case includes a 66-year-old male with HER2 amplified poorly differentiated distal esophageal adenocarcinoma treated with neoadjuvant chemo-radiation and the use of an abdominal compression device. Radiation was delivered using volumetric modulated arc therapy (VMAT) with 2 arcs using abdominal compression and image guidance. The total dose was 50.4Gy delivered over 40 elapsed days. With 2 fractions remaining, the patient developed dermatitis in the area of the compression device. The original treatment plan did not include a contour of the device. Alternative post hoc treatment plans were generated, one to contour the device and a second with anterior avoidance. In conclusion, replanning with the device contoured revealed the bolus effect. The skin dose increased from 27 to 36Gy. planned target volume (PTV) coverage at 45Gy was reduced to 76.5% from 95.8%. The second VMAT treatment plan with an anterior avoidance sector and more oblique beam angles maintained PTV coverage and spared the anterior wall, however at the expense of substantially increased dose to lung. This case report provides an important reminder of the bolus effect from external devices such as abdominal compression. Special consideration must be given to contour and/or avoiding beam entrance to the device, and to the use of such devices in patients who may have heightened radiosensitivity, such as those who are human immunodeficiency virus (HIV)-positive.
美国医学物理学家协会（AAPM）第176任务组评估了治疗床面和固定装置所引起的剂量学效应。该报告分析了大量基于物理学的关于治疗床面、立体定向体部放射治疗（SBRT）框架和身体固定袋的文献，同时指出因外部装置导致皮肤毒性的临床报告较少。在此，我们呈现一例因腹部压迫装置导致1级腹部皮肤毒性的临床病例报告。我们讨论了所采用治疗计划的剂量学影响以及事后替代计划，并量化了该装置、低密度替代装置和开放野之间在衰减和皮肤剂量积累方面的差异。病例描述包括一名66岁男性，患有HER2扩增的低分化远端食管腺癌，接受了新辅助放化疗，并使用了腹部压迫装置。采用容积调强弧形放疗（VMAT），使用2个弧形野并结合腹部压迫和图像引导进行放疗。总剂量为50.4Gy，在40个疗程内给予。还剩2次分割放疗时，患者在压迫装置覆盖区域出现了皮炎。原治疗计划未包括该装置的轮廓。生成了事后替代治疗计划，一个是勾勒出该装置的轮廓，另一个是在前部避开该装置。总之，对该装置进行轮廓勾勒后重新规划显示出了剂量增强效应。皮肤剂量从27Gy增加到36Gy。在45Gy时计划靶体积（PTV）的覆盖率从95.8%降至76.5%。第二个VMAT治疗计划采用前部避开扇形区和更倾斜的射束角度，维持了PTV的覆盖率并使前壁免受照射，然而代价是肺部剂量大幅增加。本病例报告重要地提醒了人们注意腹部压迫等外部装置的剂量增强效应。必须特别考虑勾勒出装置轮廓和/或避免射束进入装置，以及在可能具有较高放射敏感性的患者（如人类免疫缺陷病毒（HIV）阳性患者）中使用此类装置的情况。
