Can the Choice of Radiotherapy Delivery Technique Influence Which Target Delineation Protocol to Use? A Plan-Quality-Based Analysis in Left Breast Cancer

Introduction This study investigates the optimal target delineation protocol stratified by treatment planning technique in patients undergoing whole breast radiotherapy after breast conservation surgery. Materials and Methods Target delineation using Tangent (RTOG 0413 Whole Breast Irradiation Protocol), European SocieTy for Radiotherapy and Oncology (ESTRO), and Radiation Therapy & Oncology Group (RTOG) guidelines was performed on 10 randomly selected treatment planning computed tomography datasets of patients with left-sided breast cancer. An objective plan quality metric (PQM) scoring schema was defined and communicated to the medical physicist prior to commencement of treatment planning. Treatment planning was performed using field-in-field (FiF) intensity modulated radiotherapy technique (IMRT), inverse IMRT, and volumetric modulated arc therapy (VMAT), for each type of target. Two-way repeated measures, analysis of variance was utilized to compare the total PQM scores and dosimetric variables, stratified by treatment planning method. Results Total PQM score of plans for FiF, IMRT, and VMAT revealed that Tangent and ESTRO delineations were equivalent regardless of planning technique (Tangent vs. ESTRO for FiF, p = 0.099; Tangent vs. ESTRO for IMRT, p = 0.029; Tangent vs. ESTRO for VMAT, p = 0.438). Both delineation protocols were significantly superior to RTOG for all treatment planning techniques. Conclusion For all treatment planning techniques, ESTRO and Tangent delineation were equivalent and both achieved significantly higher scores than RTOG delineation