Comparing simultaneous integrated boost vs sequential boost in anal cancer patients: results of a retrospective observational study

BACKGROUND: To evaluate clinical outcomes of simultaneous integrated boost (SIB) - intensity modulated radiotherapy (RT) in patients with non metastatic anal cancer compared to those of a set of patients treated with 3-dimensional conformal RT and sequential boost (SeqB). METHODS: A retrospective cohort of 190 anal cancer patients treated at 3 academic centers with concurrent chemo-RT employing either SIB or SeqB was analysed. The SIB-group consisted of 87 patients, treated with 2 cycles of Mitomycin (MMC) and 5-Fluorouracil (5FU) using SIB-IMRT delivering 42-45Gy/28-30 fractions to the elective pelvic lymph nodes and 50.4-54Gy/28-30fractions to the primary tumor and involved nodes, based on pre-treatment staging. The SeqB group comprised 103 patients, treated with MMC associated to either 5FU or Capecitabine concurrent to RT with 36 Gy/20 fractions to a single volume including gross tumor, clinical nodes and elective nodal volumes and a SeqB to primary tumor and involved nodes of 23.4 Gy/13 fractions. We compared colostomy-free survival (CFS), overall survival (OS) and the cumulative incidence of colostomy for each radiation modality. Cox proportional-hazards model addressed factors influencing OS and CFS. RESULTS: Median follow up was 34 (range 9-102) and 31 months (range 2-101) in the SIB and SeqB groups. The 1- and 2-year cumulative incidences of colostomy were 8.2% (95%CI:3.6-15.2) and 15.0% (95%CI:8.1-23.9) in the SIB group and 13.9% (95%CI: 7.8-21.8) and 18.1% (95%CI:10.8-27.0) in the SeqB group. Two-year CFS and OS were 78.1% (95%CI:67.0-85.8) and 87.5% (95%CI:77.3-93.3) in the SIB group and 73.5% (95%CI:62.6-81.7) and 85.4% (95%CI:75.5-91.6) in the SeqB, respectively. A Cox proportional hazards regression model highlighted an adjusted hazard ratio (AdjHR) of 1.18 (95%CI: 0.67-2.09;p = 0.560), although AdjHR for the first 24 months was 0.95 (95%CI: 0.49-1.84;p = 0.877) for the SIB approach. CONCLUSIONS: SIB-based RT provides similar clinical outcomes compared to SeqB-based in the treatment of patients affected with non metastatic anal cancer.