The choice of IMRT for early-stage right breast cancer.

Abstract

81 Background: The benefit of Intensity Modulated Radiation Therapy (IMRT) has been established for left breast cancer. However, IMRT is not routinely employed for right breast cancer. The purpose of this study is to (1) compare dosimetric parameters in women with early stage right breast cancer undergoing whole breast radiation therapy using 3-dimensional conformal radiation (3DCRT) versus intensity modulated radiation therapy (IMRT) (2) determine treatment planning and/or anatomical correlates for patients who may benefit from IMRT. Methods: IMRT versus 3DCRT treatment plans were compared for 20 consecutive female patients with early stage (T1-T2 N0M0 ) right breast cancer treated at our center from 1/2012 to 12/2012. The planned target volume (PTV), contoured according to the RTOG atlas guidelines, was prescribed to 46-8-50.4 Gy in 26-28 fractions with PTV coverage goal of ≥ 95 % receiving the prescription dose. Dosimetric and anatomic parameters: % right lung receiving 20 Gy (lung V20), maximum breast dose (Dmax), maximum skin dose (Dmax skin), chest wall separation (CWS) and medial gantry angle (MGA) were determined for each paired treatment plan. Wilcoxon-signed rank test was utilized to compare IMRT and 3DCRT dosimetric parameters. Univariate analysis was used to identify planning or anatomic correlates associated with favorable dosimetric outcomes. Results: The lung V20Gy for IMRT ( 10.86±2.81%) was significantly lower than for 3DCRT (12.92±3.45 %, p < 0.043). IMRT significantly reduced Dmax to 53.79 ± 2.17 Gy from 56.7 ± 2.24 Gy with 3DCRT (p 0.001). 3DCRT yielded significantly higher Dmax skin (33.47±3.21 Gy) than IMRT (24.16 ±2.65 Gy, p< 0.0001). Mean CWS and MGA were 22.4 ± 2.6 cm and 126 ± 5.1° respectively. There was a significant association between CWS and Dmax for 3DCRT (p < 0.026). Conclusions: The most significant impact of IMRT for right breast cancer was the reduction of Dmax and Dmax skin, with a more tempered advantage in the reduction of lung V20. Reduction of maximum breast and skin dose harbors clinical relevance as it relates to acute skin toxicity, long- term fibrosis and adverse cosmetic outcomes. Chest wall separation may be a potential planning surrogate marker to determine which right-sided breast cancer patients may benefit from IMRT.