A Treatment Planning Study for Bilateral Breast Irradiation Comparing Intensity-Modulated Proton Therapy to Single Isocenter Bilateral Tangential Fields Conformal Irradiation Combined with Intensive Modulated Radiation and Volumetric Modulated Arc Therapy

Abstract

Delivery of irradiation in women with bilateral breast conserving surgery(BCS) represents a technical challenge. Currently intensity modulated proton therapy (IMPT) holds the potential to improve dose delivery and spare nontarget tissues. The purpose of this study was to compare IMPT to a single isocenter bilateral tangential fields (IBTF) combined with intensive modulated radiation (IMRT) (3D/IMRT) and Volumetric modulated arc therapy(VMAT) in bilateral breast radiotherapy that are commonly used for breast cancer. IMPT plans, 3D/IMRT and VMAT photon plans were created for 5 patients with synchronous bilateral breast cancer who underwent bilateral BCS. The conventional dose (50Gy/25f to whole breast and 60Gy/25f to tumor bed) was delivered. The 3D/IMRT plans used 8-11 fields, including 4 tangential ones; Only one field was used for delivering the dose in VMAT plans; For IMPT, 2 fields for each side were chosen: 5/20°for left breast and 340/355° for right breast so as to avoid motion uncertainties and to maximize robustness for improving plan quality. IMPT and VMAT plans conferred higher target volume coverage as compared with 3D/IMRT. V107 were 13.7±11.7, 0.4±1.3 and 0.03±0.05% for tumor bed and 25.0±5.9, 22.7±7.1 and 22.0±2.8% for the breast subtract tumor bed using 3D/IMRT, VMAT and IMPT. The results of Dmean and V20Gy of lungs using 3D/IMRT(5.0±1.9Gy and17.2±1.6%) and VMAT(7.6±1.3Gy and 15.9±4.1%) were comparable, while it was lower in IMPT plan(0.6±0.8Gy and 5.2±3.2 %). The mean V5Gy in VMAT plans(44.9±7.7%) were the highest while it was still the lowest in IMPT plans(13.2±4.2%). Also, VMAT resulted in highest Dmean to heart(7.6±1.3Gy) than 3D/IMRT(5.0±1.9Gy) and IMPT(0.6±0.8Gy).Dose for left anterior descending coronary artery were significantly decreased as well using IMPT(Table 1). IMPT provides improved homogeneity with excellent sparing of surrounding normal structures. Lower doses for lungs and heart were higher using VMAT compared to either IMPT or 3D/IMRTAbstract 3649; Table 1Comparison of the plans by 3D/IMRT, VMAT and IMPTTarget/OARParameters3D/IMRTVMATIMPTPTumorbedCoverage%91.7±5.996.7±1.595.6±0.80.01Whole breast95.4±1.097.4±1.495.3±0.5<0.01TumorbedV107%13.7±11.70.4±1.30.03±0.05<0.01Rest breast25.0±5.922.7±7.122.0±2.8nsLungsDmean/Gy9.3±0.410.3±1.73.0±1.4<0.01V5%35.0±0.944.9±7.713.2±4.2<0.01V20%17.2±1/615.9±4.15.2±3.2<0.01HeartDmean/Gy5.0±1.97.6±1.30.6±0.8<0.01V5%20.2±8.442.2±10.02.8±2.4<0.01V30%4.8±3.62.4±1.80.8±1.10.07LADDmax/Gy46.5±3.547.4±5.247.5±9.10.97Dmean/Gy20.2±3.420.3±4.76.9±4.60.001Spinal CordDmax/Gy0.8±0.11.9±0.10<0.01 Open table in a new tab