Free Breathing versus Breath-Hold Scanning Beam Proton Therapy and Cardiac Sparing in Breast Cancer

Abstract Purpose: To assess dose errors caused by the interplay effects of free-breathing (FB) motion and to assess the value of breath-hold (BH) in terms of cardiac dose reduction for scanning beam proton therapy (SBPT). Materials and Methods: Three patients with left-sided breast cancer previously treated with photon therapy were included in this dosimetric study: 2 following breast-conserving surgery with 2 hypothetical target volumes (whole breast alone and whole breast plus regional nodes, including supraclavicular, axillary, and internal mammary lymph nodes); and 1 postmastectomy, with the target volume including the chest wall plus regional nodes. SBPT plans were generated with various beam angles that ranged between 2 tangential directions. For treatment with FB, nominal dose and dose with interplay effects considered were calculated based on FB 4-dimensional computed tomography scans. SBPT plans on the BH computed tomography were also calculated for one of the patients, who was selected to be tre...