Post-mastectomy radiation therapy technique and cardiopulmonary sparing: a dosimetric comparative analysis between photons and protons with free breathing versus deep inspiration breath hold

Publication date: Available online 21 June 2017
Source:Practical Radiation Oncology
Author(s): Sagar A. Patel, Hsiao-Ming Lu, Jacqueline A. Nyamwanda, Rachel B. Jimenez, Alphonse G. Taghian, Shannon M. MacDonald, Nicolas Depauw
PurposeDosimetric studies have suggested greater cardiopulmonary sparing with protons over photons for left-sided post-mastectomy radiation (PMRT). Modern techniques such as deep inspiration breath hold (DIBH) can help spare the heart. This analysis compares photon and proton delivery with and without DIBH.Methods and MaterialsTen women with left breast cancer referred for PMRT on a prospective clinical trial with unfavorable cardiac anatomy underwent free breathing (FB) and DIBH CT simulation. A partially wide tangent photon (PWTF) during DIBH, passively scattered proton during FB, pencil-beam scanning (PBS) proton during FB, and PBS proton during DIBH plan was completed for each patient. Plans were designed to achieve 95% prescription dose coverage to 95% of chest wall and regional lymphatics while maximally sparing heart and lungs.ResultsAll techniques resulted in similar target coverage, though protons improved homogeneity indices (HI) and cardiopulmonary sparing (omnibus p<0.0001 for each metric). Heart/lung metrics for PWTF with DIBH, scattered protons with FB, PBS protons with FB, and PBS protons with DIBH, respectively, were as follows: mean heart dose (2.09, 0.39, 0.98, 0.71 GyRBE), mean left ventricle dose (3.72, 0.08, 0.19, 0.21 GyRBE), V20 left ventricle (2.73, 0.03, 0, 0%), maximum LAD artery dose (46.14, 8.28, 4.58, 4.63 GyRBE), mean lung dose (13.30, 5.74, 7.63, 7.49 GyRBE), V20 lung (26.04, 12.04, 15.18, 14.43%). Pairwise testing confirmed an improvement in each metric with all proton plans compared to PWTF with DIBH; there were no differences in HI or cardiopulmonary sparing between passively scattered and PBS protons, regardless of addition of DIBH.ConclusionFor left-sided PMRT, passively scattered or PBS protons with or without DIBH improves homogeneity and cardiopulmonary sparing without compromise in target coverage compared to PWTF photons with DIBH. Furthermore, the addition of DIBH to proton therapy did not provide a significant dosimetric benefit.



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