Abstract P2-11-07: Evaluation of lung and heart dose in patients treated with radiation for breast cancer

Abstract

Abstract BACKGROUND: A recent systematic review of women receiving radiation therapy (RT) for breast cancer combined with modeled estimated risks of mortality from heart disease and lung cancer found that the mean heart dose (MHD) was 4.4 Gy (5.2 Gy for left-sided, 3.7Gy for right-sided) and the mean total lung dose (TLD) was 5.7 Gy. Estimated excess cardiac mortality ranged from 0.3-1.2% and lung cancer mortality ranged from 0.2-4.4% with modern RT. Using these data as a benchmark, we set to review the MHD and mean TLD for our patients receiving adjuvant breast RT in a modern era when RT planning includes meeting normal tissue constraints. METHODS: We evaluated the MHD and mean TLD for patients with unilateral breast cancer treated with curative intent between January 2012 and May 2017 at our institution. Dosimetric data was complete for 793 patients. During this time period the MHD constraint was 4 Gy and lung V20 was 20% for breast only and 35% for regional nodal irradiation (RNI). RNI included the axillary, supraclavicular and internal mammary nodes.. Patients were evaluated by laterality (right vs. left), prone vs. supine position, breast only whole breast irradiation (WBI) and RNI with intact breast or chestwall post-mastectomy. The RNI group was examined by treatment technique, intensity modulated radiation therapy (IMRT) vs. 3D conformal (3DCRT). We compared differences in the MHD and mean TLD within those groups using the Student's t-test. RESULTS: We identified 651 patients: 481 WBI only and 170 RNI. In the RNI group, 77 (45.3%) received IMRT. Of the WBI only group, 229 (47.6%) were right-sided and 313 (65.1%) were treated prone. The mean TLD for the WBI only group was significantly lower in the prone vs. supine position (0.62 Gy vs. 3.90 Gy, p<0.0001). The prone position resulted in lower MHD for both left-sided WBI (1.17 Gy vs. 1.67 Gy, p<0.0001) and right-sided WBI (0.51 Gy vs. 0.64 Gy, p=0.1067). In patients that received RNI, the mean TLD was 8.20 Gy (SD 1.03) and the MHD was 2.67 Gy (3.25 Gy for left-sided vs. 1.83 Gy for right-sided, p=0.0001). Compared to 3DCRT, IMRT increased the MHD (2.46 Gy vs. 4.23 Gy for left-sided, p<0.0001; 0.94 Gy vs. 2.85 Gy, p<0.0001 for right-sided) and mean TLD (8.50 Gy vs. 7.95 Gy, p=0.0005). CONCLUSIONS: In the era of RT treatment planning that incorporates normal tissue constraints, very low MHD and lower TLD are achievable in prone or supine position patients receiving WBI only for breast conserving treatment. This means lower late cardiac and lung cancer mortality risks from RT. Women that receive RNI also have acceptably low MHD but high mean TLD. Node positive breast cancer patients derive a disease free survival benefit from RNI, which must be balanced against potential late risk for lung cancer, especially in smokers. More attention should be focused on identifying lung cancer risk, smoking cessation and screening efforts in node positive breast cancer patients with indications for RNI to minimize late radiation risks. Citation Format: Healy EH, Pratt DN, DiCostanzo D, Bazan JG, White J. Evaluation of lung and heart dose in patients treated with radiation for breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-11-07.