Using flattening filter free beams in electronic tissue compensation whole breast irradiation with deep inspiration breath hold

Purpose In order to reduce heart dose, DIBH has become a common practice in left‐sided whole breast irradiation. This technique involves a significant strain on patients due to the breath‐hold requirements. We hereby investigate the dosimetric and delivery feasibility of using flattening filter free (FFF) energies with electronic tissue compensation (ECOMP) planning technique to reduce the required breath‐hold lengths and increase patient compatibility. Methods Fifteen left‐sided, postlumpectomy patients previously receiving DIBH whole‐breast radiotherapy (266cGy x 16fx) were retrospectively planned using ECOMP for both 6X and 6X‐FFF. A dosimetric comparison was made between the two plans for each patient using various dosimetric constraints. Delivery feasibility was analyzed by recalculating the 6X ECOMP plan with 6X‐FFF without replanning (6X‐FFF QA) and delivering both plans for a one‐to‐one comparison using Gamma analysis. Beam‐on times for the 6X and 6X‐FFF plans were measured. For all tests, Wilcoxon signed‐rank test was used with P  < 0.05 as significant. Results No statistical difference was observed between 6X and 6X‐FFF plans for most dosimetric endpoints except contralateral breast D max ( P  = 0.0008) and skin D max (p = 0.03) and D min ( P  = 0.01) for which 6X‐FFF showed favorable results when compared with 6X. 6X‐FFF significantly reduced beam‐on times for all patients by 22%–42% (average 32%). All plan QAs passed departmental gamma criteria (10% low‐dose threshold, 3%/3mm, >95% passing). Conclusion ECOMP planning with FFF was found feasible for left‐sided breast patients with DIBH. Plan quality is comparable, if not better, than plans using flattened beams. FFF ECOMP could significantly reduce beam‐on time and required breath‐hold lengths thereby increasing patient compatibility for this treatment while offering satisfactory plan quality and delivery accuracy.