Long-term clinical outcomes of IMRT with simultaneous integrated boost for breast cancer

[[abstract]]Purpose or Objective: To report the long-term survival outcomes and late toxicities resulted from intensity modulated radiotherapy (IMRT) with simultaneous integrated boost (SIB) for breast cancer patients after breast conserving surgery (BCS). Material and Methods: The study included 216 patients with pathologically proven breast cancer who underwent BCS between 2010 and 2013. The median age was 52 years (Range: 21 to 81). All patients received IMRT-SIB to 2 dose levels simultaneously. They received 50.4 Gy at 1.8 Gy per fraction to the whole breast and 60.2 Gy at 2.15 Gy per fraction to the tumor bed by integral boost. The fractionation scheme was biologically equivalent to the sequential boost-technique comprising 25 fractions of 2 Gy to the whole breast PTV followed by a boost irradiation in 6 fractions, using an alpha/beta ratio of 4 Gy for tumor response, based on the linear-quadratic cell survival model. Dermatological toxicities were assessed and documented in agreement with the Common Toxicity Criteria Adverse Events version 3 (CTCAE v.3.0). Cox regression model and Kaplan-Meier curves were calculated, and the log-rank test was used to evaluate the differences of overall (OS) and disease free (DFS) survival rates between two different modalities of radiotherapy. Results : Among 216 patients, 174 received post-operative radiotherapy with Rapid-Arc and 42 patients had Tomotherapy after BCS. All patients tolerated IMRT-SIB without any interruption. The median follow-up was 6.4 years. Four patients (1.85%) in the entire cohort developed late skin complication after IMRT-SIB. For the entire cohort, the 5-year and 7-year OS rates were 94.4% and 93.1% respectively. The 5-year and 7-year DFS rates were 94.9% and 94.0 % respectively. Conclusion: There exists no statistically significant difference in the rates of locoregional recurrence and overall survival when comparing RapidArc with Tomotherapy. IMRT-SIB was well tolerated with small late skin complication and good survival rates