Impact of breathing on post-mastectomy radiotherapy: a dosimetric comparison between intensity-modulated radiotherapy and 3D tangential radiotherapy

Abstract

AbstractPurposeTo quantify the effect of breathing motion on post-mastectomy radiotherapy with three-dimensional (3D) tangents and intensity-modulated radiotherapy (IMRT)Materials and methodsPatients trained for breath-hold underwent routine free breathing (FB) computed tomography (CT) simulation for radiotherapy as well as additional CT scans with breath held at the end of normal inspiration (NI scan) and expiration (NE scan) for study. The FB scan was used to develop both tangents and IMRT plans. To simulate breathing, each plan was copied and applied on NI and NE scans. The respiratory parameters of the patients as well as the dosimetric data with both the plans were analysed.ResultsBreathing motion resulted in mean fall in target coverage (V95) with IMRT by more than 5% when compared with tangents, and this effect significantly correlated with higher tidal volume. There was also a decrease in the mean target minimal dose by 20–25% with IMRT when compared with 10–12% with tangents, attributable to breathing motion. However, the cardiac dose crossed the limit (V25<10%) with breathing in the 3D tangents plan.ConclusionsDosimetric coverage of the chest wall is sensitive to breathing motion for the IMRT technique when compared with standard tangents, especially in patients with large tidal volume.