Prospective study on dose escalation using intensity modulated radiotherapy (IMRT) with simultaneous integrated boost (SIB) and concurrent chemotherapy in preoperative locally advanced rectal cancer.

Background: Neoadjuvant chemoradiotherapy (NACTRT) with 45-50.4 Gy in 25-28 fractions, followed by total mesorectal excision and adjuvant chemotherapy is a standard treatment option for locally advanced rectal cancers (LARC). Literature has showed benefit in terms of tumour downstaging and pathological complete response (pCR) rates with radiotherapy dose escalation. The aim of our prospective single-arm study was to analyse the role of this dose escalation, using intensity modulated radiation therapy (IMRT) with simultaneous integrated boost (SIB) in LARC. Materials and methods: Fifty-two patients of LARC included in the study were treated with NACTRT. Pelvic nodes and primary disease received 45 Gy/25 fractions along with SIB to the gross disease, to a total dose of 52 Gy, along with concurrent capecitabine. Six weeks post-NACTRT, patients underwent pelvic magnetic resonance imaging (MRI) for response assessment and were sent for surgery six-eight weeks after completion of NACTRT, followed by Adjuvant chemotherapy after surgery. Post-op histopathological report was analysed and patients underwent 3-monthly follow up to further ascertain any local recurrences or distant metastasis, disease free survival (DFS) and dose-escalation related toxicities. Results: Post-NACTRT response evaluation done with Pelvic MRI suggested a complete response or near complete response in 36.54% patients, while sphincter preservation surgery was feasible in 42.30% patients. R0 resection, T and N downstaging, pCR was observed in 94%, 68%, 36% and 26% patients, respectively. The Grade-3 toxicity rates were acceptable. One-year-DFS was 91.84%. Conclusions: It may be safely concluded that dose-escalated NACRT delivered using IMRT-SIB technique in LARC patients offers decent rates of pCR with acceptable toxicity rates.