Kamst Onno, Desai P
ICON Cancer Care, Gold Coast University Hospital, Southport, Australia.
Phys Eng Sci Med. 2023 Mar;46(1):57-66. doi: 10.1007/s13246-022-01197-1. Epub 2022 Dec 1.
HyperArc™ is a stereotactic radiotherapy modality designed for targeting multiple brain metastases using a single isocenter with multiple non-coplanar arcs. This study aimed to assess the efficacy of two patient-specific quality assurance methods, film and the Varian Portal Dosimetry System with Varian's HyperArc™ technique and raise important considerations in the customisation of patient-specific quality assurance to accommodate HyperArc™ delivery. Assessment criteria included gamma analysis and mean dose at full width half maximum. The minimum metastasis size, maximum off-axis distance and suitable energy were identified and validated. Patient-specific quality assurance procedures were applied to a range of clinically relevant brain metastasis plans. Initial investigation into energy selection showed no significant differences in gamma pass rates using 6MV, 6MV FFF, or 10MV FFF for metastasis sizes greater than 15 mm diameter at the isocenter. Gamma pass rates (2%/2mm) for 15 mm metastases at the isocenter for all energies were greater than 96.0% for portal dosimetry and greater than 98.7% for film. Fields of size 15 mm placed at various distances (10-70 mm) from the isocenter resulted in a maximum mean dose difference of 1.5% between film and planned. Clinically relevant plans resulted in a maximum mean dose difference for selected metastases of 1.0% between film and plan and a maximum point dose difference of 2.9% between portal dose and plan. Portal dose image prediction was a quick and convenient quality assurance tool for metastases larger than 15 mm near the isocenter but provided diminished geometrical relevance for off-axis metastases. Film QA required exacting procedures but offered the ability to assess the accuracy of geometrical targeting for off-axis metastases and provided dosimetric accuracy for metastases to well below 15 mm diameter.
HyperArc™是一种立体定向放射治疗方式，旨在使用单个等中心和多条非共面弧来靶向多个脑转移瘤。本研究旨在评估两种针对患者的质量保证方法（胶片和带有Varian公司HyperArc™技术的Varian门静脉剂量测定系统）的疗效，并提出在定制针对患者的质量保证以适应HyperArc™治疗时的重要考虑因素。评估标准包括伽马分析和半高宽处的平均剂量。确定并验证了最小转移瘤大小、最大离轴距离和合适的能量。针对一系列临床相关的脑转移瘤计划应用了针对患者的质量保证程序。对能量选择的初步研究表明，对于等中心处直径大于15毫米的转移瘤，使用6MV、6MV FFF或10MV FFF时，伽马通过率无显著差异。等中心处15毫米转移瘤在所有能量下的伽马通过率（2%/2毫米），门静脉剂量测定法大于96.0%，胶片法大于98.7%。将15毫米大小的射野放置在距等中心不同距离（10 - 70毫米）处，胶片与计划之间的最大平均剂量差异为1.5%。临床相关计划中，所选转移瘤的胶片与计划之间的最大平均剂量差异为1.0%，门静脉剂量与计划之间的最大点剂量差异为2.9%。门静脉剂量图像预测对于等中心附近大于15毫米的转移瘤是一种快速便捷的质量保证工具，但对于离轴转移瘤，其几何相关性降低。胶片质量保证需要严格的程序，但能够评估离轴转移瘤几何靶向的准确性，并为直径远低于15毫米的转移瘤提供剂量测定准确性。
