Evaluation and Correlation of Radiological and Pathological Response Following Neoadjuvant Short-course Radiotherapy Followed by Chemotherapy Followed by Surgery in Resectable Locally Advanced Adenocarcinoma of the Rectum.

Background: The aim of this article is to evaluate radiological and pathological response rates and correlate them after neoadjuvant short-course radiotherapy (SCRT) followed by chemotherapy in resectable locally advanced adenocarcinoma of the rectum (LARC). Materials and Methods: It is a single institutional, prospective observational study from January 2021 to March 2022 including 45 patients with resectable adenocarcinoma of the rectum. Radiotherapy was delivered to a dose of 25 Gy in 5 Gy per fraction using image-guided radiotherapy followed by mFOLFOX-based chemotherapy. After completion of 4–8 cycles of chemotherapy, tumor regression grade (TRG) was evaluated using magnetic resonance imaging and whole-body positron emission tomography. In case of a satisfactory response on imaging (mrTRG), patients underwent appropriate locoregional surgery. Histopathological examination of the surgical specimen was carried out and response to neoadjuvant treatment was assessed (pTRG). Results: A significant downstaging of T and N stages (60% and 72%, respectively, p <.0001) was observed after neoadjuvant therapy with a pathological complete response rate of 16%. Conversion of positive circumferential resection margin (CRM) to negative CRM was observed in 71.4% patients. A poor agreement between mrTRG and pTRG (k 0.133, p.16) was noted. Conclusion: Preoperative SCRT in LARC is feasible and well-tolerated with encouraging radiological and pathological response rates. A significant number of patients achieve negative CRM, thereby improving the chances of R0 resection. Significant relief in pain and bleeding can be achieved rapidly leading to an improved quality of life. [ABSTRACT FROM AUTHOR]