Robust optimization in lung treatment plans accounting for geometric uncertainty

摘要

Robust optimization generates scenario‐based plans by a minimax optimization method to find optimal scenario for the trade‐off between target coverage robustness and organ‐at‐risk (OAR) sparing. In this study, 20 lung cancer patients with tumors located at various anatomical regions within the lungs were selected and robust optimization photon treatment plans including intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) plans were generated. The plan robustness was analyzed using perturbed doses with setup error boundary of ±3 mm in anterior/posterior (AP), ±3 mm in left/right (LR), and ±5 mm in inferior/superior (IS) directions from isocenter. Perturbed doses for D99, D98, and D95 were computed from six shifted isocenter plans to evaluate plan robustness. Dosimetric study was performed to compare the internal target volume‐based robust optimization plans (ITV‐IMRT and ITV‐VMAT) and conventional PTV margin‐based plans (PTV‐IMRT and PTV‐VMAT). The dosimetric comparison parameters were: ITV target mean dose (Dmean), R95(D95/Dprescription), Paddick's conformity index ( style="fixed-case">CI), homogeneity index ( style="fixed-case">HI), monitor unit ( style="fixed-case">MU), and style="fixed-case">OAR doses including lung (Dmean, V20 Gy and V15 Gy), chest wall, heart, esophagus, and maximum cord doses. A comparison of optimization results showed the robust optimization plan had better style="fixed-case">ITV dose coverage, better style="fixed-case">CI, worse style="fixed-case">HI, and lower style="fixed-case">OAR doses than conventional style="fixed-case">PTV margin‐based plans. Plan robustness evaluation showed that the perturbed doses of D99, D98, and D95 were all satisfied at least 99% of the style="fixed-case">ITV to received 95% of prescription doses. It was also observed that style="fixed-case">PTV margin‐based plans had higher style="fixed-case">MU than robust optimization plans. The results also showed robust optimization can generate plans that offer increased style="fixed-case">OAR sparing, especially for normal lungs and style="fixed-case">OARs near or abutting the target. Weak correlation was found between normal lung dose and target size, and no other correlation was observed in this study.