S26
Brachytherapy - Gastro-intestinal, paediatric brachytherapy, miscellaneous
ESTRO 2026
Proffered Paper 4142
area of the targeting window applicator (Fig 1).Dwell positions for all five source channels showed positional accuracy within 0.5 mm compared to the source positions from the TPS. At a depth of 2 mm, we observed a 2 mm shift in the isodose lines between the planned and measured dose distributions (Fig 2). However, the absolute dose at the center of the treatment area agreed within 1%. Outside the proctoscope’s shielding, the planned and measured isodose lines aligned closely, indicating effective shielding.
HDR Brachytherapy for Organ Preservation in locally advanced Rectal Cancers (DEROP-RC) : Prospective Phase II study Reena Engineer 1 , Ashwin DeSouza 2 , Rahul Krishnatry 1 , Mufaddal Kazi 2 , Shivkumar Gudi 1 , Akshay Baheti 3 , Purvi Haria 3 , Shridhar Sundaram 4 1 Radiation Oncology, Tata Memorial Centre, Mumbai, India. 2 Surgical Oncology, Tata Memorial Centre, Mumbai, India. 3 Radiology, Tata Memorial Centre, Mumbai, India. 4 Gastroenterology, Tata Memorial Centre, Mumbai, India Purpose/Objective: Increasing the dose of radiotherapy to primary rectal tumor is associated with increase in complete response and is recommended for patients enrolled for NOM of rectal cancersThis phase II trial was designed to test the hypothesis that, additional brachytherapy boost will lead to a better complete clinical response without increasing toxicity resulting in a higher proportion of patients being managed nonoperatively Material/Methods: Patients diagnosed with T2-T3, N0-N2 distal rectal cancer treated from July 2022 to May 2023 were accrued. Patient and tumor characteristics are described in Table no.1All were treated with radiation dose of 50Gy in 25 fractions( #) with concurrent capecitabine. All patients received escalated dose of radiation by MR guided high dose rate endorectal brachytherapy of 7 Gy in 3 #s within 2 to 3 weeks post CTRT. Two inflatable balloons were used to push the rectal mucosa (Fig 2). The brachytherapy dose of 7 Gy was prescribed to the periphery of the residual tumor seen on MRI with the applicator in situ Results: 70 patients were accrued. Majority 52(74%) had T3 Node positive disease. Of these 62 (88%) completed CTRT and brachytherapy (2 patients died on CTRT, in 2 brachytherapy was technically not feasible and 4 refused brachytherapy and further treatment). Post RT at a median follow-up of 33 months (8-39 months), 41/62 (66.1%) patients achieved cCR and nCR. All the 21 patients with partial response underwent salvage surgeries (1- TEMS and 20 – TME). Of the 41 patients with cCR/nCR, 10 underwent TME, 5 due to persistent nCR (>12 weeks) and 2 opted for surgery. Six of these 7 had pathological complete response. 3 patients had regrowth (2 – rectal wall 1- mesorectal node) all were salvaged. Rest 32 patients continue to be on observation. Hence organ preservation rate without TME was achieved in 32( 51.4%)of the patients at 3years. The OAS and DFS for the whole cohort was 84.1% and 80.6%On multivariate analysis, Tumors involving less than half of circumference, T2 and Node
Conclusion: This work describes the development of CXB
equivalent treatment plans for the MRA which were used in the clinical feasibility trial, as well as a practical workflow for successful commissioning of this applicator.The applicators met the predefined commissioning targets. Keywords: dosimetry, 3D printing References: 1. Gerard JP, Barbet N, Schiappa R, Magne N, Martel I, Mineur L, et al. Neoadjuvant chemoradiotherapy with radiation dose escalation with contact x-ray brachytherapy boost or external beam radiotherapy boost for organ preservation in early cT2-cT3 rectal adenocarcinoma (OPERA): a phase 3, randomised controlled trial. Lancet Gastroenterol Hepatol. 2023;8(4):356-67.2. Bellezzo M, Fonseca GP, Voncken R, Verrijssen AS, Van Beveren C, Roelofs E, et al. Advanced design, simulation, and dosimetry of a novel rectal applicator for contact brachytherapy with a conventional HDR (192)Ir source. Brachytherapy. 2020;19(4):544-53.
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