Plan Quality Variability in Radiotherapy of Whole Breast and Regional Lymph Nodes: An Intra-institutional Analysis.

[BACKGROUND/AIM] Adjuvant radiotherapy is a key component in breast cancer treatment, improving local control. Three-dimensional conformal radiotherapy (3D-CRT) remains widely used owing to its robustness; however, treatment planning for whole-breast (WB) irradiation including regional lymph nodes (RLN) and internal mammary nodes (IMN) is challenging. Planner-dependent variability may affect plan quality and organ-at-risk (OAR) sparing. The aim of this study was to evaluate intra-institutional variability in 3D-CRT plan quality for locoregional breast radiotherapy.

[PATIENTS AND METHODS] Seven anonymized copies of the planning computed tomography (CT) of a representative patient with left-sided breast cancer treated with WB, RLN, and IMN were created. The clinical target volume (CTV) for the WB, RNL and IMN and OARs were delineated according to institutional guidelines. The planning target volumes (PTVs) were generated using a 5-mm isotropic margin and cropped 5 mm from the skin. Seven treatment planners with varying experience independently generated 3D-CRT plans following institutional guidelines. Plan quality was evaluated using target coverage and dose-volume metrics for OARs according to Swedish national guidelines and compared with the clinically delivered plan.

[RESULTS] All plans fulfilled dose objectives for the PTVs (D98% >93%, V105% <20%) and CTVs (D98%>95%), for WB and RLN. Two plans failed to meet coverage criteria for the IMN CTV (D98% >90%). Mean heart dose was consistent across plans (1.3-1.5 Gy). In contrast, substantial variability was observed for the ipsilateral lung, with mean dose ranging from 11.5 to 13.2 Gy and V16Gy from 29.8% to 34.8%.

[CONCLUSION] Although acceptable target coverage was generally achieved, clinically relevant variability in lung dose metrics was observed. These findings highlight the need for further standardization of 3D-CRT planning to improve consistency and optimize plan quality in WB radiotherapy with nodal involvement.