Three Year Outcomes of Breast Intensity Modulated Radiation Therapy with Simultaneous Integrated Boost

Abstract

To report acute toxicity, late cosmesis, normal tissue dose, risk of locoregional recurrence (LRR), and overall survival (OS) using breast intensity modulated radiation therapy (IMRT) with simultaneous integrated boost (SIB) to the resection cavity. In other reports, breast SIB achieved superior dosimetry to sequential boost techniques with equivalent radiobiologic effects while shortening treatment duration up to 10 fractions. Our breast SIB technique has been presented previously. Published clinical experience with breast SIB remains sparse. Retrospective review identified 353 patients with Stage 0-III breast cancer treated with IMRT + SIB following conservative surgery between 2003 and 2006. An institutional inverse-planned IMRT technique with dynamic multileaf collimators was developed using Eclipse software (Varian Medical Systems). The planning target volume was ipsilateral breast tissue, clinically demarcated with radiopaque wire placed at simulation and contoured with adjustments in CT window level. The boost targeted the CT-defined resection cavity and surgical clips. Four tangential fields encompassed the entire breast while two customized fields delivered the SIB. The most common fractionation (89%) was 1.8 Gy to the breast with concomitant 2.14 Gy to the cavity yielding a breast dose of 45 Gy (25 fxs) and cavity dose 59.92 Gy (28 fxs). For tumor control, this was biologically equivalent to 45 Gy to the breast with sequential 16 Gy boost. Acute toxicity was graded according to CTC v3 criteria. Cosmesis was scored according to the Harvard criteria. OS and risk of LRR were determined by the Kaplan Meier method. 355 breasts in 353 pts were treated with IMRT + SIB: 281 had infiltrating breast cancer (IBC), stage I 61%, II 34%, III 5%, while 74 had DCIS. The median breast volume was 736 cc, cavity volume 23 cc. The median ipsilateral lung V20 was 10.6%. For left breast radiation, the median cardiac V15 was 2.9%, left ventricle V15 1.7%. Median follow-up was 33 months (range: 4-73 mo). Acute toxicity was Grade 1 in 57%, G2 43%, G3 <1%. For IBC, 3 yr OS (SE) was 97.6% (0.011), and risk of LRR 2.8% (0.012). For DCIS, 3 yr OS was 98% (0.02), and risk of LRR 1.4% (0.014). Assessment of breast cosmesis at a minimum of 3 yrs follow-up was available in 40% of cases, of which 96.5% were judged good or excellent, while 3.5% had fair cosmesis. Breast IMRT + SIB reduced treatment duration by 5 fxs while maintaining acceptable ipsilateral lung dose. For left breast tumors, cardiac volume receiving high dose was minimal. Our clinical experience with breast IMRT + SIB confirmed a favorable acute toxicity profile and excellent OS and local control at 3 years. Assessment of late toxicity at 3 years showed a high percentage with good or excellent cosmesis.