3484 - Surgical Outcomes in Locally Advanced Rectal Cancer Following Preoperative Chemoradiation with Simultaneous Integrated Boost (SIB-CRT)
Presenter(s)
M. Loi1, F. Passagnoli2,3, L. Fortuna2,3, F. Coratti3, P. Bonomo4, M. Valzano5, M. Aquilano6, A. Galardi7, D. Greto1, G. Francolini1, G. Simontacchi1, C. Becherini1, V. Salvestrini5, I. Desideri1,8, M. Mangoni9,10, M. Zani11, M. Casati11, S. Calusi11, F. Cianchi2,3, and L. Livi1; 1Radiation Oncology Unit, Azienda Ospedaliero Universitaria Careggi, University of Florence, Florence, Italy, 2Department of Experimental and Clinical Biomedical Sciences, University of Florence, Firenze, Italy, 3Unit of Digestive Surgery, Azienda Ospedaliero Universitaria Careggi, Firenze, Italy, 4Radiation Oncology Unit, Azienda Ospedaliero-Universitaria Careggi, University of Florence, Florence, Italy, 5Radiation Oncology Unit, Careggi University Hospital, University of Florence, Florence, Italy, 6Cyberknife Unit, Istituto Fiorentino di Cura ed Assistenza, IFCA, Florence, Italy, 7Radiation Oncology, Careggi University Hospital, University of Florence, Firenze, Italy, 8Department of Experimental Clinical and Biomedical Sciences “Mario Serio”, University of Florence, Florence, Italy, 9Department of Biomedical, Experimental and Clinical Sciences, University of Florence, Firenze, Italy, 10Radiation Oncology Unit, Azienda Ospedaliero Universitaria Careggi, University of Florence, Firenze, Italy, 11Medical Physics, Careggi University Hospital, University of Florence, Florence, Italy
Purpose/Objective(s):
In patients affected by locally advanced rectal cancer (LARC), intensification of preoperative chemoradiation (CRT) with use of radiation boost (>50 Gy) has been proposed to increase response to treatment. However, a potential detrimental effect on subsequent surgical management has been hypothesized in relation to radiation-related fibrosis, particularly with the use of hypofractionated simultaneous-integrated boost (SIB). The aim of our study is to compare the surgical outcomes of SIB-CRT versus conventional CRT in LARC patients.Materials/Methods: Data from a consecutive cohort of LARC patients treated with Total Mesorectal Excision (TME) by the same surgical team following CRT between June 2019 and June 2024 were retrospectively reviewed. All patients received conventionally fractionated VMAT pelvic irradiation in 25 fractions to mesorectum (50 Gy, 2Gy/fraction) and sacral, internal iliac and obturator nodes (45 Gy, 1.8 Gy/fraction) in association with capecitabine and daily CBCT imaging. SIB-CRT was performed to total dose of 53 Gy boost (2.12 Gy/fraction) to the high risk volume (primary tumor with 1 cm craniocaudal expansion along the rectum and 0.5 cm radial expansion in involved mesorectum and pathological lymphnodes, plus 0.5 cm expansion to PTV). Coverage of at least 95% of the PTV receiving 53 Gy with the prescription dose was obtained in all SIB-CRT plans. Clinical, pathological and treatment-related data were collected.
Results: Seventy-four patients (median age: 69 years, range 37-83) were included: 25% (n=19) had a history of prior abdominal surgery. At baseline MRI, stage T4 and/or N2, mesorectal fascia (MRF) involvement and extramural venous invasion (EMVI) were detected in respectively 15(20%), 39 (52%), 22 (30%) and 14 (19%) patients, with no significant difference between the conventional (n=52, 70%) and SIB-CRT (n=22, 30%) group. Grade 3 acute toxicity was reported in 5 patients (6%), consisting of diarrhea (n=3), obstructive dysuria (n=1) and anemia (n=1). All patients completed the intended preoperative CRT course and underwent TME following restaging MRI after a median time interval of 11 (range 7-18 ) weeks. Median operating time was 255 (range 200-455) minutes. Clavien-Dindo =3 complication rate was 12% (n=9). Intact mesorectum (Quirke= 3) was found in 67 (93%) patients. Pathological complete response (pCR) rate was 27% (n=20). Despite longer median time to surgery (12 vs 10 weeks, p<0.001) no significant difference was found between SIB-CRT and conventional CRT patients in terms of operating time, mesorectum integrity, Clavien-Dindo=3 complication and pCR rate.
Conclusion: SIB-CRT with VMAT was technically feasible in LARC patients without increased incidence of severe acute toxicity or impaired surgical outcomes compared to conventional CRT. Due to relatively high incidence of pCR in both groups, larger cohorts are needed to assess potential clinical benefit of this strategy.