Held Mareike, Kirby Neil, Morin Olivier, Pouliot Jean
Department of Radiation Oncology, University of California San Francisco, California 94143-1708, USA.
Med Phys. 2012 Aug;39(8):5263-71. doi: 10.1118/1.4739250.
To develop optimal beam parameters and to verify the dosimetric aspects of the recently developed modulated-arc total-body irradiation (MATBI) technique, which delivers an inverse-planned dose to the entire body using gantry rotation.
The patient is positioned prone and supine underneath the gantry at about 2 m source-to-surface distance (SSD). Then, up to 28 beams irradiate the patient from different gantry angles. Based on full-body computed-tomography (CT) images of the patient, the weight of each beam is optimized, using inverse planning, to create a uniform body dose. This study investigates how to best simulate patients and the ideal beam setup parameters, such as field size, number of beams, and beam geometry, for treatment time and dose homogeneity. In addition, three anthropomorphic water phantoms were constructed and utilized to verify the accuracy of dose delivery, with both diode array and ion chamber measurements. Furthermore, to improve the accuracy of the new technique, a beam model is created specifically for the extended-SSD positioning for MATBI.
Low dose CT scans can be utilized for dose calculations without affecting the accuracy. The largest field size of 40 × 40 cm(2) was found to deliver the most uniform dose in the least amount of time. Moreover, a higher number of beams improves dose homogeneity. The average dose discrepancy between ion chamber measurements and extended-SSD beam model calculations was 1.2%, with the largest discrepancy being 3.2%. This average dose discrepancy was 1.4% with the standard beam model for delivery at isocenter.
The optimum beam setup parameters, regarding dose uniformity and treatment duration, are laid out for modulated-arc TBI. In addition, the presented dose measurements show that these treatments can be delivered accurately. These measurements also indicated that a new beam model did not significantly improve the accuracy of dose calculations. The optimum beam setup parameters along with the measurements performed to ensure accurate dose delivery serve as a useful guide for the clinical implementation of MATBI.
制定最佳射束参数，并验证最近开发的调制弧形全身照射（MATBI）技术的剂量学方面，该技术利用机架旋转为全身提供逆向计划剂量。
患者俯卧和平卧于机架下方，源皮距（SSD）约为2 m。然后，多达28束射束从不同的机架角度照射患者。基于患者的全身计算机断层扫描（CT）图像，使用逆向计划优化每束射束的权重，以创建均匀的身体剂量。本研究探讨如何最佳模拟患者以及理想的射束设置参数，如射野大小、射束数量和射束几何形状，以实现治疗时间和剂量均匀性。此外，构建了三个拟人化水模体并用于验证剂量传递的准确性，采用二极管阵列和电离室测量。此外，为提高新技术的准确性，专门为MATBI的扩展SSD定位创建了一个射束模型。
低剂量CT扫描可用于剂量计算而不影响准确性。发现最大射野大小为40×40 cm²时，能在最短时间内提供最均匀的剂量。此外，更多的射束数量可提高剂量均匀性。电离室测量与扩展SSD射束模型计算之间的平均剂量差异为1.2%，最大差异为3.2%。在等中心进行传递时，使用标准射束模型的平均剂量差异为1.4%。
针对调制弧形全身照射，制定了关于剂量均匀性和治疗持续时间的最佳射束设置参数。此外，所呈现的剂量测量结果表明这些治疗可以准确实施。这些测量还表明，新的射束模型并未显著提高剂量计算的准确性。最佳射束设置参数以及为确保准确剂量传递而进行的测量，为MATBI的临床应用提供了有用的指导。
