Chest wall radiotherapy with volumetric modulated arcs and the potential role of flattening filter free photon beams.

PURPOSE: The goal of the work was to assess the role of RapidArc treatments in chest wall irradiation after mastectomy and determine the potential benefit of flattening filter free beams.

METHODS AND MATERIAL: Planning CT scans of 10 women requiring post-mastectomy chest wall radiotherapy were included in the study. A dose of 50 Gy in 2 Gy fractions was prescribed. Organs at risk (OARs) delineated were heart, lungs, contralateral breast, and spinal cord. Dose-volume metrics were defined to quantify the quality of concurrent treatment plans assessing target coverage and sparing of OARs. Plans were designed for conformal 3D therapy (3DCRT) or for RapidArc with double partial arcs (RA). RapidArc plans were optimized for both conventional beams as well as for unflattened beams (RAF). The goal for this planning effort was to cover 100% of the planning target volume (PTV) with ≥ 90% of the prescribed dose and to minimize the volume inside the PTV receiving > 105% of the dose. The mean ipsilateral lung dose was required to be lower than 15 Gy and V(20 Gy) < 22%. Contralateral organ irradiation was required to be kept as low as possible.

RESULTS: All techniques met planning objectives for PTV and for lung (3DCRT marginally failed for V(20 Gy)). RA plans showed superiority compared to 3DCRT in the medium to high dose region for the ipsilateral lung. Heart irradiation was minimized by RAF plans with ~4.5 Gy and ~15 Gy reduction in maximum dose compared to RA and 3DCRT, respectively. RAF resulted in superior plans compared to RA with respect to contralateral breast and lung with a reduction of ~1.7 Gy and 1.0 Gy in the respective mean doses.

CONCLUSION: RapidArc treatment resulted in acceptable plan quality with superior ipsilateral tissue sparing compared to traditional techniques. Flattening filter free beams, recently made available for clinical use, might provide further healthy tissue sparing, particularly in contralateral organs, suggesting their applicability for large and complex targets.