Pierce Greg, Balogh Alex, Frederick Rebecca, Gordon Deborah, Yarschenko Adam, Hudson Alana
Department of Medical Physics, Tom Baker Cancer Centre, Calgary, AB, Canada.
Department of Physics & Astronomy, University of Calgary, Calgary, AB, Canada.
J Appl Clin Med Phys. 2019 Jan;20(1):200-211. doi: 10.1002/acm2.12519. Epub 2018 Dec 27.
In this work, we develop a total body irradiation technique that utilizes arc delivery, a buildup spoiler, and inverse optimized multileaf collimator (MLC) motion to shield organs at risk. The current treatment beam model is verified to confirm its applicability at extended source-to-surface distance (SSD). The delivery involves 7-8 volumetric modulated arc therapy arcs delivered to the patient in the supine and prone positions. The patient is positioned at a 90° couch angle on a custom bed with a 1 cm acrylic spoiler to increase surface dose. Single-step optimization using a patient CT scan provides enhanced dose homogeneity and limits organ at risk dose. Dosimetric data of 109 TBI patients treated with this technique is presented along with the clinical workflow. Treatment planning system (TPS) verification measurements were performed at an extended SSD of 175 cm. Measurements included: a 4-point absolute depth-dose curve, profiles at 1.5, 5, and 10 cm depth, absolute point-dose measurements of an treatment field, 2D Gafchromic films at four locations, and measurements of surface dose at multiple locations of a Alderson phantom. The results of the patient DVH parameters were: Body-5 mm D98 95.3 ± 1.5%, Body-5 mm D2 114.0 ± 3.6%, MLD 102.8 ± 2.1%. Differences between measured and calculated absolute depth-dose values were all <2%. Profiles at extended SSD had a maximum point difference of 1.3%. Gamma pass rates of 2D films were greater than 90% at 5%/1 mm. Surface dose measurements with film confirmed surface dose values of >90% of the prescription dose. In conclusion, the inverse optimized delivery method presented in the paper has been used to deliver homogenous dose to over 100 patients. The method provides superior patient comfort utilizing a commercial TPS. In addition, the ability to easily shield organs at risk is available through the use of MLCs.
在这项工作中，我们开发了一种全身照射技术，该技术利用弧形射束传输、剂量建成补偿器和逆向优化多叶准直器（MLC）运动来保护危及器官。验证了当前的治疗射束模型，以确认其在延长源皮距（SSD）时的适用性。治疗过程包括向仰卧位和俯卧位的患者递送7 - 8个容积调强弧形治疗射束。患者以90°的治疗床角度置于配备1厘米丙烯酸剂量建成补偿器的定制床上，以增加表面剂量。使用患者CT扫描进行单步优化可提高剂量均匀性并限制危及器官的剂量。展示了109例采用该技术治疗的全身照射患者的剂量学数据以及临床工作流程。在175厘米的延长SSD下进行了治疗计划系统（TPS）验证测量。测量内容包括：一条4点绝对深度剂量曲线、在1.5厘米、5厘米和10厘米深度处的剂量分布曲线、一个治疗野的绝对点剂量测量、四个位置的二维Gafchromic胶片以及在Alderson体模多个位置的表面剂量测量。患者剂量体积直方图（DVH）参数的结果为：体部 - 5毫米D98为95.3 ± 1.5%，体部 - 5毫米D2为114.0 ± 3.6%，平均剂量（MLD）为102.8 ± 2.1%。测量的和计算的绝对深度剂量值之间的差异均<2%。延长SSD时的剂量分布曲线的最大点差异为1.3%。二维胶片的伽马通过率在5%/1毫米时大于90%。胶片表面剂量测量证实表面剂量值大于处方剂量的90%。总之，本文中提出的逆向优化递送方法已用于向100多名患者递送均匀剂量。该方法利用商业TPS可提供卓越的患者舒适度。此外，通过使用MLC能够轻松保护危及器官。
