ESTRO 2022 - Abstract Book

S562

Abstract book

ESTRO 2022

Conclusion The EMT based implant reconstruction was found to be geometrically accurate within the intrinsic limits of the EMT system and did not deteriorate the dosimetric implant quality in 17 of 20 patients. In the three cases in which the implant quality decreased, only small manual adjustments of some of the reconstruction points were sufficient to meet the clinical dose requirements again. Therefore strategies to further refine the EMT based reconstruction are currently being explored.

OC-0632 Endorectal brachytherapy to enhance complete response receiving neoadjuvant CTRT in rectal cancers

R. Engineer 1 , D. Dutta 1 , A. Saklani 2 , A. D'Souza 2 , L. Scaria 3 , S. Ankathi 4 , A. Baheti 5 , J. Poddar 6 , M. Patil 6

1 Tata Memorial Hospital, Radiation Oncology, Mumbai, India; 2 Tata Memorial Centre, GI Surgical Oncology, Mumbai, India; 3 Tata Memorial Centre, Radiation Physics, Mumbai, India; 4 Tata Memorial Centre, Radioldiagosis, Mumbai, India; 5 Tata Memorial Centre, Radiodiagnosis, Mumbai, India; 6 Tata Memorial Centre, Radiation Oncology, Mumbai, India Purpose or Objective Purpose: Patients achieving complete response post NACTRT can be managed using watch and wait (W&W) approach. We aimed to study whether additional boost with endorectal brachytherapy (ERBT) increases complete response as well as reduces local regrowth rates. Materials and Methods Materials and Methods : Patients diagnosed with distal rectal cancers (T2-T4/N0-N+) were treated with concurrent chemoradiotherapy. Post EBRT a select group of patients having residual non circumferential lesions <7cm in length were given additional boost of ERBT using multi-channel surface loader with Ir192 HDR source. The brachytherapy application and planning was done using MRI guidance. All were reassessed 6-8 weeks post ERBT and patients with near complete/complete clinical response (nCR/cCR) were followed up with wait and watch strategy. The nCR/cCR rate, local regrowth rate and organ preservation rate were estimated. Patients with partial or no response were advised standard total mesorectal surgery. Results Results : One hundred patients treated between December 2017 to April 2021receiving endorectal brachytherapy post NACTRT were identified. External beam radiotherapy was given to a dose of 45-55Gy (median 50Gy) in conventional fractionation with concurrent Capecitabine, followed by endorectal brachytherapy 8-12Gy in 2-3 (median 12Gy/3) fractions. Brachytherapy was performed at a median time of 2 (range 1-4) weeks post last fraction of EBRT. The overall nCR/cCR rate was 50% (20 nCR, 30 cCR and 50 PR). Of the 50 patients with cCR/nCR, 7 were unwilling for W&W and underwent surgical resection (5 had pCR, 1 pN1, 1-pT3N0) and the rest 43 patients were kept on observation. Fifty patients having partial response underwent TME