ESTRO 2024 - Abstract Book

S6012

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

2648

Digital Poster

Plan Robustness Evaluation for Breast VMAT: Robust Optimization Versus Manual Flash

Ray C. K. Chan 1 , Curtise K. C. Ng 2,3 , Rico H. M. Hung 4 , Yoyo T. Y. Li 1 , Yuki T. Y. Tam 1 , Blossom Y. L. Wong 1 , Jacky C. K. Yu 1 , Vincent W. S. Leung 1 1 The Hong Kong Polytechnic University, Department of Health Technology and Informatics, Hong Kong, Hong Kong. 2 Curtin University, Curtin Medical School, Perth, Australia. 3 Curtin University, Curtin Health Innovation Research Institute, Perth, Australia. 4 Pamela Youde Nethersole Eastern Hospital, Department of Clinical Oncology, Hong Kong, Hong Kong

Purpose/Objective:

Volumetric modulated arc therapy (VMAT) offers improved treatment options for breast cancer, providing better conformity, homogeneity of target dose, and reduced treatment time [1-7]. However, uncertainties in VMAT such as dosimetric variations caused by chest wall motion are noted in the literature [8-10]. Plan robustness which refers to the ability of a radiotherapy plan to maintain the desired dose under uncertainties has become a crucial element for addressing this issue [11-13]. Manual flash (MF) is the current standard robust planning technique in breast VMAT which involves expanding the planning target volume (PTV) and optimizing plans by treating a pseudo-structure as part of the body external contour [2,14]. Robust optimization (RO) is an alternative approach for defining uncertainties and generating plans based on worst-case scenarios to minimize objective functions, aiming at achieving desired skin flashing effect [15-19]. Previous studies have compared RO planning with free-breathing VMAT, deep-inspiration breath-hold (DIBH) conformal radiotherapy, and addressed organ deformation issues [20,21]. Besides, there was a previous study with five patients compared the RO and MF approaches and reported that RO planning able to achieve greater robustness when compared to MF [19]. This study aims to compare the plan robustness of RO and MF approaches in terms of dose variation to the clinical target volume (CTV) and organs at risk (OARs) with a greater sample size.

Material/Methods:

This retrospective study included 34 female patients from Pamela Youde Nethersole Eastern Hospital in Hong Kong who underwent VMAT for breast cancer between January 2020 and December 2021. The study focused on patients who had breast-conserving surgery or total mastectomy for unilateral breast cancer, received whole breast or chest wall and regional lymph node irradiation, and underwent DIBH VMAT [16,19]. Exclusion criteria were incomplete medical records and inadequate imaging data for VMAT planning. Institutional review board approvals were obtained for this study. The CTV, PTV, and OARs were segmented using the Eclipse treatment planning system (Varian Medical Systems, Palo Alto, CA, USA). The CTV and PTV were contoured based on international guidelines, while the OARs included heart, ipsilateral lung, contralateral lung, and spinal cord [22,23].

For each patient, one MF plan and one RO plan were generated using the RayStation 12A treatment planning system (RaySearch Laboratories AB, Stockholm, Sweden). The plans were optimized to deliver a standardized prescription of