eP508 - Organ Preservation in Low Lying Rectal Adenocarcinoma Using Dose Escalated Radiotherapy for Locally Advanced Rectal Cancers

Purpose/Background: Locally advanced rectal cancers undergoing neoadjuvant chemoradiation having complete or near complete or near complete clinicoradiological response are offered nonoperative management leading to organ preservation in these patients. Efforts like radiotherapy boost to the primary tumor using Endorectal HDR brachytherapy can increase organ preservation rates in these payients.Methods/Interventions: Patients with rectal cancers (T2-T4/N0-N+) treated with concurrent chemoradiotherapy(50Gy/25# with Capecitabine) between June-2017 to April-2022. Post external radiation, patients having residual non-circumferential lesions < 8cm in length were administered escalated-dose MRI guided brachytherapy to a dose of 12Gy (8-15Gy) in 3 (2-3) fractions at 3-5 day intervals. Patients having near complete/complete clinical response (nCR/cCR) were advised observation as per watch and wait policy whereas patients with residual disease were offered surgery.Results/Outcomes: 145 patients registered from June 2017 to April 2022 were included in the study. All patients received concurrent chemoradiotherapy followed by brachytherapy boost. Commonly used boost dose regimen for brachytherapy was 12Gy/3# once weekly for 3 weeks-59% while in 39% of patients a boost dose of 8Gy in 2# was given; once weekly.Patient and disease characteristics of these 145 patients are illustrated in table.At a median follow up of 40 months (IQR 29-53 months), 81 (56%) patients achieved nCR/cCR (34 had cCR while 19 had nCR) while 64 (46%) had either partial response or no response . Of the 78 patients achieving cCR or nCR 4 opted for surgical resection and 13 patients were operated by surgeons due to persistent nCR beyond 12 weeks. Of these 17 patients with cCR/nCR undergoing resection 14 (82%) had pCR. No patient with complete primary tumour response had positive tests for lymph nodes on MRI at the time of response assessment. 9 (20%) in PR group undergoing resection.Of the 64 patients kept on obsevation, 8(12.5%) (7 endoluminal and 1 mesorectal node) had local regrowth. 2 had local regrowth with synchronous distant metastasis, while 1 had mesorectal nodal recurrence. All of the 8 patients with local regrowth were surgically salvaged.Of the 67(46%) patients with partial response 56 underwent resection whereas 9 refused surgery. 9 (20%) of these had pCR.Thus the overall organ preservation rate in whole cohort of 145 patients is 39%. The overall organ and sphincter preservation rate was 68%/On univariate analysis factors affecting cCR /nCR were T size ( < 5cm) at presentation, T stage, N stage and presence of EMVI (Table 3). On multivariate analysis the only factors affecting were the tumor size and presence of EMVI. 19(36.5%) patients kept on WWS developed late rectal toxicity, 7 had grade 1 while another 12 had grade 2 toxicity. Only 1 patient had late urinary toxicity.Conclusion/

Discussion: Dose Escalated MR-EBRT is an effective and safe method to enhance complete clinical response, thus improving the rate of organ preservation for locally advanced, distal rectal cancers."CONSORT: Organ Preservation in low lying Rectal Adenocarcinoma using dose escalated Radiotherapy for advanced rectal cancers

Organ preservation in rectal cancer
MRI guided Brachytherapy

Brachy Procedure
Factors affecting response to Radiotherapy
"