基于 EPID 的 3D 剂量学在使用剂量 Check 进行 FFF VMAT 立体定向体部放疗计划预验证中的应用。

EPID-based 3D dosimetry for pre-treatment FFF VMAT stereotactic body radiotherapy plan verification using dosimetry Check.

机构信息

Medical Physics Unit, Azienda USL-IRCCS di Reggio Emilia, Reggio Emilia, Italy; Postgraduate School in Medical Physics, University of Bologna, Bologna, Italy.

Medical Physics Unit, Azienda USL-IRCCS di Reggio Emilia, Reggio Emilia, Italy.

出版信息

Phys Med. 2021 Jan;81:227-236. doi: 10.1016/j.ejmp.2020.12.014. Epub 2021 Jan 20.

DOI:10.1016/j.ejmp.2020.12.014

PMID:33485140

Abstract

PURPOSE

The software Dosimetry Check (DC) reconstructs the 3D dose distribution on CT images data set by using EPID measured signal. This study aimed to evaluate DC for stereotactic body radiotherapy (SBRT) with unflattened photon beams (FFF) for dosimetric independent plan verification in pre-treatment modality.

METHODS

DC v.4.1 was configured for Varian TrueBeam STx FFF beams equipped with EPID aS-1200. The DC FFF models were tested using arc open fields (from 1×1 cm to 15×15 cm) and VMAT (Volumetric Modulated Arc Therapy) SBRT plans on phantom and patient CTs. DC dose distributions (D) were compared with that calculated by Eclipse with Acuros XB algorithm (D) and one measured by Octavius 1000 SRS detector (D). All differences were quantified in terms of the local 3D gamma passing rate (%GP), DVH and point dose differences.

RESULTS

DC was configured for FFF VMAT using an appropriate correction procedure. %GP (mean±standard deviation) of D-D was 96.3±2.7% for open fields whereas it was 90.1±5.9% for plans on homogeneous phantom CT. However, average %GP of D-D was 95.0±4.1 for treatments on patient CT. The fraction of plans passing the %GP DQA tolerance level [10% (50%) of maximum dose threshold] were 20/20 (14/20) and 18/20 (16/20) for OCT on phantom CT and DC on patient CT, respectively.

CONCLUSIONS

DC characterization for FFF beams was performed. For stereotactic VMAT plan verifications DC showed good agreement with TPS whereas underlined discrepancies with Octavius in the high dose regions. A customized tolerance level is required for EPID-based VMAT FFF pre-treatment verification when DC system is applied.

摘要

目的

Dosimetry Check（DC）软件通过使用 EPID 测量的信号在 CT 图像数据集上重建 3D 剂量分布。本研究旨在评估用于立体定向体放射治疗（SBRT）的 DC，以在治疗前模式下进行剂量独立计划验证。

方法

为配备 EPID aS-1200 的瓦里安 TrueBeam STx FFF 射线束配置了 DC v.4.1。使用弧开野（从 1×1cm 到 15×15cm）和 VMAT（容积调制弧形治疗）SBRT 计划在体模和患者 CT 上测试了 DC FFF 模型。将 DC 剂量分布（D）与 Eclipse 结合 Acuros XB 算法（D）和 Octavius 1000 SRS 探测器（D）测量的剂量分布进行比较。所有差异均以局部 3D 伽马通过率（%GP）、DVH 和点剂量差异进行量化。

结果

为 FFF VMAT 配置了适当的校正程序。开野的 D-D %GP（平均值±标准差）为 96.3±2.7%，而均匀体模 CT 上的计划为 90.1±5.9%。然而，患者 CT 上治疗的平均 D-D %GP 为 95.0±4.1。通过 OCT 在体模 CT 和 DC 在患者 CT 上分别通过 10%（50%）最大剂量阈值的 %GP DQA 容限水平的计划分数分别为 20/20（14/20）和 18/20（16/20）。