A Simple Cardiac Sparing Strategy for Left Breast Radiation Therapy Using Right Semi-Decubitus Positioning

Abstract

Radiotherapy for left-sided breast cancer is associated with increased risk of heart disease. Prone, lateral decubitus, and deep inspiration breath hold (DIBH) treatments can reduce the heart dose. However, use of these techniques may be limited by requirements for specialized equipment, patients’ intolerance or inability to comply, and the need for nodal irradiation. Notably, 65% of U.S. radiation oncologists offered DIBH in the 2017 ASTRO Workforce Survey. We examined the right semi-decubitus position as a strategy to reduce heart dose in breast radiotherapy and compared cardiac and lung exposure for treatment in the supine (S) and right semi-decubitus (SD) positions. Left breast patients undergoing CT simulation who had unfavorable cardiac dosimetry in the S position were rescanned in either prone (favored for large breast size) or SD position. For the SD position, the patient is rolled up on the right side with the entire left torso from shoulder to hip elevated 25-35 degrees by a foam wedge. SD was well tolerated, and set up reproducibility and treatment time equaled those of S treatment. Whole breast plans (40.05 Gy, 2.67 Gy per fraction) were created on the S and SD scans using segmented tangents with no blocking. Target and OAR delineations followed the RTOG Breast Atlas and Feng's heart atlas. Concordance in breast and lumpectomy cavity V90% across the 2 plans was assessed with Pearson correlation coefficients. Heart and lung dosimetric parameters were compared using the Wilcoxon signed rank test. Paired analysis was performed for 31 patients treated between March 2016 and February 2018. Breast and lumpectomy cavity V90% were concordant across S and SD plans (correlation coefficients 0.860 and 1.000 respectively.) SD was associated with significantly lower median cardiac dosimetry parameters (Table). Mean heart dose in SD was lower by >15 cGy in 20 (65%) patients, lower by <15 cGy in 6 (19%), unchanged in 3 (10%), and higher in 2 (6%). Lung dosimetry parameters were similar in the two positions (Table). The SD position was associated with reduced cardiac exposure. The effect was seen in most though not all patients. It is easily performed, stable, and well tolerated. Further study of this approach is warranted.Abstract TU_11_3424: mTable 1Supine median (range)Right Semi-Decubitus median (range)p-valueHeart mean dose (cGy)168.75 (95.7-436.5)135.1 (82.4-274.0)<0.0001Heart V5 (%)3.3 (0.1-14.5)2.0 (0.0-7.9)<0.0001Heart V20 (%)0.5 (0.0-6.2)0.0 (0.0-2.9)<0.0001Lung mean dose (cGy)469.5 (136.2-864.1)426.8 (156.8-804.1)0.288Lung V5 (%)18.4 (4.9-31.7)17.3 (5.7-32.5)0.477Lung V20 (%)7.7 (0.3-18.9)6.5 (0.7-16.8)0.165 Open table in a new tab