Centro Médico Paitilla, Calle 53 y ave. Balboa, Panama City, Panama.
Instituto de Investigaciones Científicas y de Alta Tecnología, INDICASAT-AIP, City of Knowledge, Building 219, Panama City, Panama.
Radiat Oncol. 2019 Apr 23;14(1):67. doi: 10.1186/s13014-019-1269-1.
The PRIMO system is a computer software that allows the Monte Carlo simulation of linear accelerators and the estimation of the subsequent absorbed dose distributions in phantoms and computed tomographies. The aim of this work is to validate the methods incorporated in PRIMO to evaluate the deviations introduced in the dose distributions by errors in the positioning of the leaves of the multileaf collimator recorded in the dynalog files during patient treatment.
The reconstruction of treatment plans from Varian's dynalog files was implemented in the PRIMO system. Dose distributions were estimated for volumetric-modulated arc therapy clinical cases of prostate and head&neck using the PRIMO fast Monte Carlo engine DPM. Accuracy of the implemented reconstruction methods was evaluated by comparing dose distributions obtained from the simulations of the plans imported from the treatment planning system with those obtained from the simulations of the plans reconstructed from the expected leaves positions recorded in the dynalog files. The impact on the dose of errors in the positions of the leaves was evaluated by comparing dose distributions estimated for plans reconstructed from expected leaves positions with dose distributions estimated from actual leaves positions. Gamma pass rate (GPR), a hereby introduced quantity named percentage of agreement (PA) and the percentage of voxels with a given systematic difference (α/Δ) were the quantities used for the comparisons. Errors were introduced in leaves positions in order to study the sensitivity of these quantities.
A good agreement of the dose distributions obtained from the plan imported from the TPS and from the plan reconstructed from expected leaves positions was obtained. Not a significantly better agreement was obtained for an imported plan with an increased number of control points such as to approximately match the number of records in the dynalogs. When introduced errors were predominantly in one direction, the methods employed in this work were sensitive to dynalogs with root-mean-square errors (RMS) ≥0.2 mm. Nevertheless, when errors were in both directions, only RMS >1.2 mm produced detectable deviations in the dose. The PA and the α/Δ showed more sensitive to errors in the leaves positions than the GPR.
Methods to verify the accuracy of the radiotherapy treatment from the information recorded in the Varian's dynalog files were implemented and verified in this work for the PRIMO system. Tolerance limits could be established based on the values of PA and α/Δ. GPR is not recommended as a solely evaluator of deviations introduced in the dose by errors captured in the dynalog files.
PRIMO 系统是一款计算机软件，可用于对线性加速器进行蒙特卡罗模拟，并估算体模和计算机断层扫描中的后续吸收剂量分布。本工作旨在验证 PRIMO 中纳入的方法，以评估在患者治疗过程中记录在 dynalog 文件中的多叶准直器叶片位置误差对剂量分布造成的偏差。
在 PRIMO 系统中实现了从瓦里安 dynalog 文件重建治疗计划。使用 PRIMO 快速蒙特卡罗引擎 DPM 估算前列腺和头颈部容积调强弧形治疗临床病例的剂量分布。通过比较从治疗计划系统导入的计划的模拟获得的剂量分布与从记录在 dynalog 文件中的预期叶片位置重建的计划的模拟获得的剂量分布，评估所实现的重建方法的准确性。通过比较从预期叶片位置重建的计划的估计剂量分布与从实际叶片位置重建的计划的估计剂量分布，评估叶片位置误差对剂量的影响。本文引入了一个名为百分比一致性（PA）的量和一个给定系统差异（α/Δ）的百分比的量（简称百分比一致性），用于比较。引入叶片位置误差以研究这些量的敏感性。
从 TPS 导入的计划和从预期叶片位置重建的计划的剂量分布具有良好的一致性。对于增加了控制点数量的导入计划（例如，大致匹配 dynalogs 中的记录数量），并未获得更好的一致性。当引入的误差主要在一个方向上时，本文所采用的方法对 RMS≥0.2mm 的 dynalogs 较为敏感。然而，当误差在两个方向上时，只有 RMS＞1.2mm 的误差才会导致剂量出现可检测的偏差。PA 和 α/Δ 比 GPR 对叶片位置误差更敏感。
本文为 PRIMO 系统实施并验证了从瓦里安 dynalog 文件中记录的信息验证放射治疗准确性的方法。可以基于 PA 和α/Δ 的值建立容限。不建议仅使用 GPR 评估 dynalog 文件中捕获的误差引入的剂量偏差。
