Cardiac Substructure Dose in Patients Undergoing Cardiac-Sparing Techniques for Whole Breast Radiotherapy or Partial Breast Irradiation: A Dosimetric Follow-Up to IMPORT LOW.

Abstract

PURPOSE/OBJECTIVE(S)\nThis dosimetric analysis evaluates the impact on dose to cardiac substructures using the cardiac-sparing techniques prone positioning and deep inspiratory breath hold (DIBH) with either whole breast radiotherapy (WBRT) or partial breast irradiation (PBI) using the field designs employed by the IMPORT LOW trial.\n\n\nMATERIALS/METHODS\nPaired planning CT scans from women with left (n\u202f=\u202f10) or right (n\u202f=\u202f10) breast cancer (BC) each simulated in the prone vs. supine positions as well as 10 women with left BC simulated at free breathing (FB) vs. DIBH were contoured using target volumes as defined by IMPORT LOW. The right ventricle (RV) and right coronary artery (RCA) were delineated for right BC patients; the left ventricle (LV) and left anterior descending artery (LAD) were delineated for left BC patients. Maximum (max) and mean doses were compared using two-way repeated measures analysis of variance (ANOVA) with Bonferroni adjustment.\n\n\nRESULTS\nIn each cohort, PBI was associated with decreased cardiac substructure dose (Table 1). For patients with right BC, PBI in the supine position was associated with decreased RV max/mean doses compared to PBI in the prone position. For patients with left BC, lower LV max/mean and LAD mean doses were associated with use of PBI for treatment in the supine position and with WBRT for treatment in the prone position. For patients with left BC treated supine at FB vs. DIBH, lower LV max/mean and LAD max/mean doses were achieved using PBI and DIBH; the lowest doses among all left BC patients were found using PBI and DIBH in combination.\n\n\nCONCLUSION\nPBI is associated with significantly lower cardiac substructure dose. When using PBI for treatment of right BC, supine positioning is associated with decreased RV dose for right-sided BC compared to prone positioning. Prone positioning is associated with decreased LV/LAD dose for left-sided BC when delivering WBRT, and supine positioning is associated with decreased LV/LAD dose for administration of PBI. The lowest left-sided cardiac substructure doses were found using PBI with DIBH.