Dosimetric and workflow comparison of inverse-planned breast radiotherapy techniques on a Halcyon FFF platform in a low-resource setting

Introduction Breast radiotherapy in low-and-middle-income countries (LMICs) must balance target coverage, organ-at-risk (OAR) sparing, and workflow efficiency in resource-limited environments. This is pronounced in large or pendulous breasts treated on flattening-filter-free (FFF) linear accelerators (LINACs), where beam characteristics and larger fields can complicate dose homogeneity. This study compared the dosimetric performance and planning efficiency of breast radiotherapy techniques on a Halcyon platform. Materials and methods Thirty patients with large breast anatomy (separation >25 cm) were replanned using 3D conformal radiotherapy (3DCRT), intensity modulated radiotherapy (IMRT) with two- and four fields (IMRT4F), volumetric modulated arc therapy (VMAT), and VMAT with butterfly fields (VMATBF). Corresponding AutoPTV-based plans, generated from 3DCRT isodose contours, were also evaluated. Plans were generated in Eclipse v15.6 using Anisotropic Analytical Algorithm for delivery on a Halcyon 2.0 LINAC (40.05 Gy in 15 fractions). Target coverage, homogeneity, conformity, near-maximum dose and heart and lung OAR metrics were assessed. Planning efficiency and learning effects were evaluated using recorded planning times. Statistical analysis used one-way ANOVA with Tukey post-hoc testing (p < 0.05). Results Meaningful differences in target coverage and dose homogeneity were observed between techniques (p < 0.05). IMRT4F achieved the highest and most consistent target coverage (median V95% approximately 95% for both cohorts), most closely approaching the V95% ≥ 97% goal, with acceptable hotspot control, while 3DCRT frequently failed to meet coverage criteria. VMAT improved conformity (p < 0.05) but increased low-dose spread and planning time. Planning time was influenced by technique (p < 0.0001) and training (p = 0.0065), with IMRT options showing the greatest improvement (∼53% reduction). AutoPTV produced dosimetric outcomes comparable to manually contoured PTVs (p > 0.05). Conclusion AutoPTV IMRT4F represents a clinically feasible and resource-appropriate approach for large-breasted patients treated on Halcyon systems in LMIC settings, providing robust dosimetric performance with improved workflow efficiency.