Megias Daniel, Phillips Mark, Clifton-Hadley Laura, Harron Elizabeth, Eaton David J, Sanghera Paul, Whitfield Gillian
1 National Radiotherapy Trials Quality Assurance Group (RTTQA), Mount Vernon Hospital, London, UK.
2 Cancer Research UK and University College London Cancer Trials Centre, London, UK.
Br J Radiol. 2017 Mar;90(1071):20160829. doi: 10.1259/bjr.20160829. Epub 2017 Jan 6.
The HIPPO trial is a UK randomized Phase II trial of hippocampal sparing (HS) vs conventional whole-brain radiotherapy after surgical resection or radiosurgery in patients with favourable prognosis with 1-4 brain metastases. Each participating centre completed a planning benchmark case as part of the dedicated radiotherapy trials quality assurance programme (RTQA), promoting the safe and effective delivery of HS intensity-modulated radiotherapy (IMRT) in a multicentre trial setting.
Submitted planning benchmark cases were reviewed using visualization for radiotherapy software (VODCA) evaluating plan quality and compliance in relation to the HIPPO radiotherapy planning and delivery guidelines.
Comparison of the planning benchmark data highlighted a plan specified using dose to medium as an outlier by comparison with those specified using dose to water. Further evaluation identified that the reported plan statistics for dose to medium were lower as a result of the dose calculated at regions of PTV inclusive of bony cranium being lower relative to brain.
Specification of dose to water or medium remains a source of potential ambiguity and it is essential that as part of a multicentre trial, consideration is given to reported differences, particularly in the presence of bone. Evaluation of planning benchmark data as part of an RTQA programme has highlighted an important feature of HS IMRT dosimetry dependent on dose being specified to water or medium, informing the development and undertaking of HS IMRT as part of the HIPPO trial. Advances in knowledge: The potential clinical impact of differences between dose to medium and dose to water are demonstrated for the first time, in the setting of HS whole-brain radiotherapy.
HIPPO试验是一项英国的随机II期试验，针对预后良好、有1 - 4个脑转移瘤的患者，在手术切除或立体定向放射治疗后，比较海马区保留（HS）放疗与传统全脑放疗的效果。每个参与中心完成了一个计划基准病例，作为专门的放射治疗试验质量保证计划（RTQA）的一部分，以促进在多中心试验环境中安全有效地实施HS调强放射治疗（IMRT）。
使用放射治疗可视化软件（VODCA）对提交的计划基准病例进行审查，评估计划质量以及与HIPPO放射治疗计划和实施指南的合规情况。
计划基准数据的比较突出显示，与使用水的剂量指定的计划相比，使用中等剂量指定的计划为异常值。进一步评估发现，报告的中等剂量计划统计数据较低，原因是在包含颅骨的计划靶体积（PTV）区域计算的剂量相对于脑较低。
水或中等剂量的指定仍然是潜在歧义的一个来源，作为多中心试验的一部分，必须考虑报告的差异，特别是在存在骨骼的情况下。作为RTQA计划的一部分对计划基准数据进行评估，突出了HS IMRT剂量测定的一个重要特征，即取决于水或中等剂量的指定，为作为HIPPO试验一部分的HS IMRT的开发和实施提供了信息。知识进展：首次在HS全脑放疗的背景下证明了中等剂量与水剂量之间差异的潜在临床影响。
