Taasti Vicki T, Bäumer Christian, Dahlgren Christina V, Deisher Amanda J, Ellerbrock Malte, Free Jeffrey, Gora Joanna, Kozera Anna, Lomax Antony J, De Marzi Ludovic, Molinelli Silvia, Kevin Teo Boon-Keng, Wohlfahrt Patrick, Petersen Jørgen B B, Muren Ludvig P, Hansen David C, Richter Christian
Department of Medical Physics, Aarhus University Hospital, Aarhus, Denmark.
Westdeutsches Protonentherapiezentrum, Essen gGmbH, Essen, Germany.
Phys Imaging Radiat Oncol. 2018 Apr 30;6:25-30. doi: 10.1016/j.phro.2018.04.006. eCollection 2018 Apr.
Stopping-power ratios (SPRs) are used in particle therapy to calculate particle range in patients. The heuristic CT-to-SPR conversion (Hounsfield Look-Up-Table, HLUT), needed for treatment planning, depends on CT-scan and reconstruction parameters as well as the specific HLUT definition. To assess inter-centre differences in these parameters, we performed a survey-based qualitative evaluation, as a first step towards better standardisation of CT-based SPR derivation.
A questionnaire was sent to twelve particle therapy centres (ten from Europe and two from USA). It asked for details on CT scanners, image acquisition and reconstruction, definition of the HLUT, body-region specific HLUT selection, investigations of beam-hardening and experimental validations of the HLUT. Technological improvements were rated regarding their potential to improve SPR accuracy.
Scan parameters and HLUT definition varied widely. Either the stoichiometric method (eight centres) or a tissue-substitute-only HLUT definition (three centres) was used. One centre combined both methods. The number of HLUT line segments varied widely between two and eleven. Nine centres had investigated influence of beam-hardening, often including patient-size dependence. Ten centres had validated their HLUT experimentally, with very different validation schemes. Most centres deemed dual-energy CT promising for improving SPR accuracy.
Large inter-centre variability was found in implementation of CT scans, image reconstruction and especially in specification of the CT-to-SPR conversion. A future standardisation would reduce time-intensive institution-specific efforts and variations in treatment quality. Due to the interdependency of multiple parameters, no conclusion can be drawn on the derived SPR accuracy and its inter-centre variability.
在粒子治疗中，阻止本领比（SPRs）用于计算患者体内的粒子射程。治疗计划所需的启发式CT到SPRs转换（Hounsfield查找表，HLUT）取决于CT扫描和重建参数以及特定的HLUT定义。为了评估这些参数在不同中心之间的差异，我们进行了一项基于调查的定性评估，作为朝着基于CT的SPRs推导更好地标准化迈出的第一步。
向12个粒子治疗中心（10个来自欧洲，2个来自美国）发送了一份问卷。问卷询问了CT扫描仪、图像采集和重建、HLUT的定义、身体区域特定HLUT的选择、束硬化研究以及HLUT的实验验证等详细信息。对技术改进对提高SPRs准确性的潜力进行了评分。
扫描参数和HLUT定义差异很大。使用化学计量法的有8个中心，仅使用组织替代物HLUT定义的有3个中心。1个中心将两种方法结合使用。HLUT线段的数量在2到11之间差异很大。9个中心研究了束硬化的影响，通常包括对患者体型的依赖性。10个中心对其HLUT进行了实验验证，验证方案差异很大。大多数中心认为双能CT有望提高SPRs的准确性。
在CT扫描的实施、图像重建，尤其是CT到SPRs转换的规范方面，发现各中心之间存在很大差异。未来的标准化将减少特定机构的耗时工作以及治疗质量的差异。由于多个参数的相互依赖性，无法得出关于推导的SPRs准确性及其中心间变异性的结论。
