Department of Radiation Oncology, University of Virginia, Charlottesville, VA 22908, USA.
Int J Radiat Oncol Biol Phys. 2012 Feb 1;82(2):1013-20. doi: 10.1016/j.ijrobp.2010.12.043. Epub 2011 Feb 28.
To evaluate a three-dimensional dose verification method based on the exit dose using the onboard detector of tomotherapy.
The study included 347 treatment fractions from 24 patients, including 10 prostate, 5 head and neck (HN), and 9 spinal stereotactic body radiation therapy (SBRT) cases. Detector sonograms were retrieved and back-projected to calculate entrance fluence, which was then forward-projected on the CT images to calculate the verification dose, which was compared with ion chamber and film measurement in the QA plans and with the planning dose in patient plans.
Root mean square (RMS) errors of 2.0%, 2.2%, and 2.0% were observed comparing the dose verification (DV) and the ion chamber measured point dose in the phantom plans for HN, prostate, and spinal SBRT patients, respectively. When cumulative dose in the entire treatment is considered, for HN patients, the error of the mean dose to the planning target volume (PTV) varied from 1.47% to 5.62% with a RMS error of 3.55%. For prostate patients, the error of the mean dose to the prostate target volume varied from -5.11% to 3.29%, with a RMS error of 2.49%. The RMS error of maximum doses to the bladder and the rectum were 2.34% (-4.17% to 2.61%) and 2.64% (-4.54% to 3.94%), respectively. For the nine spinal SBRT patients, the RMS error of the minimum dose to the PTV was 2.43% (-5.39% to 2.48%). The RMS error of maximum dose to the spinal cord was 1.05% (-2.86% to 0.89%).
An excellent agreement was observed between the measurement and the verification dose. In the patient treatments, the agreement in doses to the majority of PTVs and organs at risk is within 5% for the cumulative treatment course doses. The dosimetric error strongly depends on the error in multileaf collimator leaf opening time with a sensitivity correlating to the gantry rotation period.
评估一种基于 Tomotherapy 机载探测器的出口剂量的三维剂量验证方法。
该研究纳入了 24 名患者的 347 个分次治疗，包括 10 例前列腺、5 例头颈部（HN）和 9 例脊柱立体定向体部放疗（SBRT）病例。检索探测器声谱并进行反向投影以计算入射通量，然后将其正向投影到 CT 图像上以计算验证剂量，并与 QA 计划中的电离室和胶片测量以及患者计划中的计划剂量进行比较。
在 HN、前列腺和脊柱 SBRT 患者的体模计划中，DV 与电离室测量点剂量的 RMS 误差分别为 2.0%、2.2%和 2.0%。当考虑整个治疗过程中的累积剂量时，对于 HN 患者，计划靶区（PTV）的平均剂量误差从 1.47%到 5.62%不等，RMS 误差为 3.55%。对于前列腺患者，前列腺靶区体积的平均剂量误差从-5.11%到 3.29%不等，RMS 误差为 2.49%。膀胱和直肠的最大剂量 RMS 误差分别为 2.34%（-4.17%至 2.61%）和 2.64%（-4.54%至 3.94%）。对于 9 例脊柱 SBRT 患者，PTV 的最小剂量 RMS 误差为 2.43%（-5.39%至 2.48%）。脊髓的最大剂量 RMS 误差为 1.05%（-2.86%至 0.89%）。
测量值与验证剂量之间存在极好的一致性。在患者治疗中，对于累积治疗过程剂量，大多数 PTV 和危及器官的剂量一致性在 5%以内。剂量误差强烈依赖于多叶准直器叶片开启时间的误差，其灵敏度与机架旋转周期相关。
