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.