Department of Radiation Oncology, University of Virginia, Charlottesville VA, United States of America.
Phys Med Biol. 2018 Jul 16;63(14):14NT02. doi: 10.1088/1361-6560/aacebb.
A clinical case of delivery dose deviations on a TomoTherapy treatment was discovered during a patient specific treatment quality assurance (QA) verification. An in-house developed QA system, MCLogQA, for TomoTherapy has been implemented in our clinic for patient specific treatment QA. The MCLogQA system utilizes the log file and detector-based multileaf collimator (MLC) leaf opening time (LOT) to assess accuracy of treatment plan delivery. Recently, the MCLogQA system discovered >10% dose deviation for a low dose/fraction treatment plan. To verify the adequacy of the MCLogQA result, a delivery quality assurance (DQA) plan was created and performed. The treatment plan was also transferred to a second TomoTherapy unit and planning system to investigate if the plan-delivery deviation was unit dependent. Further testing was carried out in phantom plans. MCLogQA showed MLC LOT was on average 2.4% higher than the planned LOT, resulting in 3.5% increase in mean dose, and 14% increase in dose to 1 cc volume of max dose in PTV. Independent DQA verification confirmed the MCLogQA result. For the transferred treatment plan delivery, the MCLogQA also showed an average increase of 6.6% in MLC LOT, resulting in increases in mean dose by 9.3% and dose to 1 cc volume of max dose in PTV by 16%. The inaccurate MLC LOT was a result of a poor latency model at very small LOT. Phantom testing confirmed low LOT will result in relatively large dosimetric variation, and detector-based MCLogQA will detect differences in planned and measured LOT. Accuracy in TomoTherapy treatment delivery can be susceptible to LOT uncertainty. Using MCLogQA for QA verification not only validates the treatment delivery, but also provides information on LOT variation and comprehensive dose distribution. This information can help decision making when large plan-delivery deviation occurs.
在患者特定的治疗质量保证（QA）验证过程中，发现了 TomoTherapy 治疗中的交付剂量偏差的临床病例。为了进行患者特定的治疗 QA，我们的诊所已经实施了一种内部开发的 TomoTherapy QA 系统，即 MCLogQA。该 MCLogQA 系统利用日志文件和基于探测器的多叶准直器（MLC）叶片开启时间（LOT）来评估治疗计划交付的准确性。最近，MCLogQA 系统发现低剂量/分次治疗计划的剂量偏差超过 10%。为了验证 MCLogQA 结果的充分性，创建并执行了交付质量保证（DQA）计划。还将治疗计划转移到第二台 TomoTherapy 设备和计划系统，以研究计划-交付偏差是否与设备相关。在体模计划中进行了进一步的测试。MCLogQA 显示 MLC LOT 平均比计划 LOT 高 2.4%，导致平均剂量增加 3.5%，PTV 中最大剂量的 1cc 体积剂量增加 14%。独立的 DQA 验证证实了 MCLogQA 的结果。对于转移的治疗计划交付，MCLogQA 还显示 MLC LOT 平均增加了 6.6%，导致平均剂量增加了 9.3%，PTV 中最大剂量的 1cc 体积剂量增加了 16%。不准确的 MLC LOT 是由于非常小的 LOT 时滞后模型不佳造成的。体模测试证实，低 LOT 将导致相对较大的剂量学变化，并且基于探测器的 MCLogQA 将检测计划 LOT 和测量 LOT 之间的差异。TomoTherapy 治疗交付的准确性可能容易受到 LOT 不确定性的影响。使用 MCLogQA 进行 QA 验证不仅验证了治疗交付，还提供了 LOT 变化和全面剂量分布的信息。当出现大的计划-交付偏差时，此信息有助于决策。
