Simultaneous integrated boost vs sequential boost chemoradiotherapy in anal squamous cell carcinoma: Association with improved disease-free survival and the role of treatment delivery parameters.

UNLABELLED: Background and purpose.The optimal radiotherapy delivery strategy for anal canal cancer remains debated. We compared outcomes between simultaneous integrated boost (SIB) and sequential boost approaches in patients treated with chemoradiotherapy.

MATERIALS AND

METHODS

This single-centre retrospective study included consecutive patients with localised or locally advanced anal canal squamous cell carcinoma treated with volumetric modulated arc therapy between June 2019 and July 2024. All patients received 60 Gy to the primary tumour and involved lymph nodes. Prophylactic nodal irradiation was delivered either sequentially (44 Gy in 22 fractions) or with SIB (45 Gy in 30 fractions). The primary endpoint was disease-free survival (DFS). Secondary endpoints included overall survival (OS) and treatment-related adverse events (CTCAE v5.0). Survival was estimated using the Kaplan-Meier method and compared with the log-rank test. Cox models were used for multivariable analysis.

RESULTS

Eighty-four patients were included: 50 treated with SIB and 34 with a sequential approach.Median follow-up from the end of radiotherapy was 21 and 48 months in the SIB and sequential groups, respectively. The 24-month DFS rate was 96% in the SIB group versus 70% in the sequential group. SIB was independently associated with improved DFS (HR 0.12, 95% CI 0.03-0.53; p = 0.006). OS at 24 months was 98% with SIB and 85% with sequential treatment, without statistical significance after adjustment. Acute grade ≥ 2 adverse events tended to be lower with SIB, without significant differences. No grade > 3 adverse event was observed. Post-treatment lymphocyte counts were higher in the SIB group (p = 0.029).

CONCLUSION

SIB-based radiotherapy was associated with improved DFS without increasing the rate of treatment-related adverse events. This benefit may be partly related to shorter overall treatment time and potential immune-sparing effects. Longer follow-up and prospective studies are warranted.