Surface Dose and Skin Toxicity Analysis in Breast Cancer Radiotherapy after Conserving Surgery with Five Treatment Modalities

Abstract

The present study aimed to evaluate surface dose and skin toxicity in breast cancer after breast-conserving surgery with five treatment modalities: flattening filter mode of intensity modulated radiation therapy (IMRT-FF,6MV), flattening filter-free mode of intensity modulated radiation therapy (IMRT-FFF,6MV), direct mode of TOMO (TOMO-direct, FFF, 6MV), helical mode of TOMO (TOMO-helical, FFF, 6MV), intensity modulated proton therapy (IMPT, spot scanning). Ten patients with breast cancer treated at our institution after breast-conserving surgery were randomly selected for this study. Five plans were designed for each patient with the same target coverage and the prescription of 50Gy/25f, IMRT-6FF, IMRT-6FFF, TOMO-direct, TOMO-helical, and IMPT. Based on CT datasets, IMRT-6FFF, TOMO-direct, TOMO-helical, and IMPT were compared to IMRT-6FF with skin dose and skin toxicity. Among the five plannings, the angles of the IMRT-6FF vs. IMRT-6FFF and TOMO-direct were the same. We extracted the relative complement in the Body of its 3Derosion defined by a spherical structuring element of radius r = 3 mm and r = 5mm (skin3 and skin5). To calculate the relative Dose-surface histograms (DSH), we used the surface of patients receiving at least 5Gy to delimit the breast region's skin area and normalize the absolute DSH. Skin dose were assessed with V5Gy, V10Gy, V15Gy, V20Gy, V25Gy, V30Gy, V40Gy, V45Gy, V50Gy of the structure of skin3 and skin5. The published NTCP LKB (normal tissue complication probability, Lyman-Kutcher-Burman) model (TD50 = 39 Gy,m = 0.14,n = 0.38) was employed to evaluate severe acute radiation-induced skin toxicity. There was no statistically significant difference between the structure of skin3 and skin5 between IMRT-6FF and IMRT-6FFF. For the same PTV coverage, the TOMO-helical plans had significantly higher surface dose in terms of V5Gy, V10Gy, and V15Gy than the IMRT plans (p <0.005). For structure of skin3, mean V30Gy, V35Gy, V40Gy, V45Gy, V50Gy were (64.0%,65.8%,79.0%,70.0%,64.6%), (51.3%,55.4%,74.3%,61.7%,59.5%), (32.4%,36.6%,65.2%,53.0%,53.0%), (13.7%,14.1%,45.8%,35.7%,37.6%), (1.6%/0.8%/12.2%,6.6%,1.0%). For the structure of skin5, mean V30Gy, V35Gy, V40Gy, V45Gy, V50Gy were (66.1%,67.1%,76.4%,68.6%,62.6%), (57.9%,60.4%,72.3%,61.2%,57.7%), (45.5%,48.4%,65.2%,53.9%,51.8%), (28.4%,30.8%,51.2%,42.0%,40.0%), (6.8%,6.3%,22.6%,17.9%,8.0%).Compared to IMRT-6FF, TOMO-direct and TOMO-helical had higher surface dose(p<0.05). For IMRT-6FF/IMRT-6FFF/TOMO-direct/TOMO-helical/IMPT, the mean ratio of severe acute radiational skin toxicity were14.7%,17.1%,46.3%,29.4%, and 24.1%. For TOMO-direct and TOMO-helical planning, the skin dose and toxicity ratio were higher than IMRT-6FF. Compared to IMRT-6FF, V45Gy of skin3 and V40Gy of skin5 of IMPT were higher than IMRT-6FF, while the skin toxicity ratio was no significant difference.