(P020) 3D Conformal External Beam Radiation Therapy May Result in Lower Heart Dose and Risk of Radiation-Induced Major Coronary Events Compared With Multicatheter Balloon High-Dose-Rate Brachytherapy for Left-Sided Breast Cancer Patients

Jason C. Ye, MD, Brittney Wilson, BS, CMD, Igor Shuryak, MD, Jenghwa Chang, PhD, Samuel Trichter, MSc, David Brenner, MD, DSc, Dattatreyudu Nori, MD, John Ng, MD; Department of Radiation Oncology, Weill Cornell Medical College; Center for Radiologic Research, Columbia University Medical Center

PURPOSE: To determine and compare the heart dose and potential increased risks in long-term cardiac toxicity from three-dimensional conformal external beam radiation therapy (3DCRT) and multicatheter balloon high-dose-rate (HDR) brachytherapy treatments for left-sided breast cancer patients.

METHODS: Fifteen consecutive patients who were treated with balloon HDR (3,400 cGy in 10 fractions, twice daily) after lumpectomy for left-sided breast cancer between 2011 and 2014 were included in this study. Target volumes drawn for HDR brachytherapy. Left breast, heart, and left anterior descending artery (LAD) were contoured by a physician in the brachytherapy treatment planning system and independently confirmed by another physician. 3DCRT plans (5,040 cGy in 28 fractions using opposed tangential beams) were developed using the same computed tomography (CT) scans and contours by the same team by transferring the image and structure sets to the external beam planning system. Appropriate target coverage, dose distribution, and dose homogeneity (± 7%) were confirmed independently. Cardiac blocks were allowed, as long as they did not significantly affect the breast and lumpectomy cavity coverage. The radiation doses to the heart and LAD using 3DCRT and HDR techniques were recorded. The risk of long-term additional cardiac toxicity was estimated by calculating the 10-year radiation-induced estimated actual risk (EAR) for major coronary events using a previously published cardiac risk model.

RESULTS: The 15 women (median age: 65 yr, range: 59–86 yr) all had early-stage localized disease that fit the American Society for Radiation Oncology (ASTRO) guidelines for accelerated partial breast irradiation. Average of the mean heat doses (MHDs) delivered using HDR was 251.6 cGy (range: 137–427 cGy), while the average MHD that they would have received using 3DCRT was 128.99 cGy (range: 90–236.4 cGy) (Student’s t-test: P < .001). The mean dose to the LAD was not statistically significant (551 cGy for HDR vs 814 cGy for 3DCRT; P = .11 by Student’s t-test). After factoring in MHD, age, smoking status, history of hyperlipidemia, hypertension, and diabetic history, the mean 10-year radiation-induced EAR for 3DCRT and HDR for the 15 women was 0.51% (range: 0.17%–1.51%) and 1.01% (range: 0.31%–3.5%), respectively (Student’s t-test: P = .0064).

CONCLUSIONS: Both 3DCRT and balloon HDR can achieve relatively low MHDs and result in minimal increases in the risk of additional major coronary events. In certain cases, compared with HDR brachytherapy, 3DCRT may result in lower MHDs and a lower risk of long-term cardiac toxicity.

Proceedings of the 97th Annual Meeting of the American Radium Society - americanradiumsociety.org