Medical Physics Division, Candiolo Cancer Institute - FPO, IRCCS, Strada Provinciale 142 km 3.95, 10060 Candiolo (TO), Italy.
Medical Physics Division, Candiolo Cancer Institute - FPO, IRCCS, Strada Provinciale 142 km 3.95, 10060 Candiolo (TO), Italy.
Phys Med. 2018 Aug;52:65-71. doi: 10.1016/j.ejmp.2018.06.005. Epub 2018 Jun 26.
The aim of this paper is to characterize two different EPID-based solutions for pre-treatment VMAT quality assurance, the 2D portal dosimetry and the 3D projection technique. Their ability to catch the main critical delivery errors was studied.
Measurements were performed with a linac accelerator equipped with EPID aSi1000, Portal Dose Image Prediction (PDIP), and PerFRACTION softwares. Their performances were studied simulating perturbations of a reference plan through systematic variations in dose values and micromultileaf collimator position. The performance of PDIP, based on 2D forward method, was evaluated calculating gamma passing rate (%GP) between no-error and error-simulated measurements. The impact of errors with PerFRACTION, based on 3D projection technique, was analyzed by calculating the difference between reference and perturbed DVH (%ΔD). Subsequently pre-treatment verification with PerFRACTION was done for 27 patients of different pathologies.
The sensitivity of PerFRACTION was slightly higher than sensitivity of PDIP, reaching a maximum of 0.9. Specificity was 1 for PerFRACTION and 0.6 for PDIP. The analysis of patients' DVHs indicated that the mean %ΔD was (1.2 ± 1.9)% for D2%, (0.6 ± 1.7)% for D95% and (-0.0 ± 1.2)% for Dmean of PTV. Regarding OARs, we observed important discrepancies on DVH but that the higher dose variations were in low dose area (<10 Gy).
This study supports the introduction of the new 3D forward projection method for pretreatment QA raising the claim that the visualization of the delivered dose distribution on patient anatomy has major advantages over traditional portal dosimetry QA systems.
本文旨在描述两种不同的基于 EPID 的 VMAT 预治疗质量保证解决方案，即 2D 端口剂量测定和 3D 投影技术。研究了它们捕捉主要关键交付误差的能力。
使用配备 EPID aSi1000、Portal Dose Image Prediction (PDIP) 和 PerFRACTION 软件的直线加速器进行测量。通过系统地改变剂量值和微多叶准直器位置来模拟参考计划的扰动，研究了它们的性能。基于 2D 正向方法的 PDIP 的性能通过计算无误差和误差模拟测量之间的伽马通过率（%GP）来评估。基于 3D 投影技术的 PerFRACTION 的误差影响通过计算参考和扰动 DVH 之间的差异（%ΔD）进行分析。随后，对 27 名不同病理的患者进行了 PerFRACTION 预治疗验证。
PerFRACTION 的灵敏度略高于 PDIP 的灵敏度，最高可达 0.9。特异性为 1 对于 PerFRACTION 和 0.6 对于 PDIP。对患者的 DVHs 分析表明，PTV 的 D2%、D95%和 Dmean 的平均%ΔD 分别为（1.2±1.9）%、（0.6±1.7）%和（-0.0±1.2）%。对于 OARs，我们观察到 DVH 上的重要差异，但高剂量变化在低剂量区域（<10Gy）。
本研究支持引入新的 3D 正向投影方法进行预治疗 QA，并提出了在患者解剖结构上可视化交付剂量分布相对于传统端口剂量测定 QA 系统具有主要优势的观点。
