Abstract Book

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ESTRO 37

EP-2232 Feasibility of dose escalation with individualised bladder filling for intrauterine brachytherapy J. Turner 1 , M. Dillon 1 , A. Taylor 1 1 The Royal Marsden Hospital, Clinical Oncology, London, United Kingdom Purpose or Objective With image-guided intrauterine brachytherapy (IGBT) the tumour dose is limited by the pelvic organs at risk (OAR) tolerances. Our current standard of care is to treat all patients with an empty bladder. Bladder filling is used in external beam radiotherapy to displace small bowel, however some studies have demonstrated higher bladder doses when this technique is employed with IGBT. This study aims to evaluate how bladder filling can be assessed on an individual basis to allow for variations in anatomy, thus allowing a customised optimal strategy for each patient. Material and Methods Patients receiving IGBT had planning CT and MRI scans, with a full (clamped after instilling 100mls water) and empty catheterised bladder. OARs were outlined and doses calculated with a full bladder (bladder-f) and empty bladder (bladder-e) for bladder, rectum, sigmoid and bowel 2cc and 10cc dose. Brachytherapy plans were optimised using GEC-ESTRO guidelines, selecting either bladder-e or bladder-f to deliver maximal dose to HR-CTV within OAR 2cc cumulative dose constraints. Results Twenty-eight patients (26-84 years) were treated between November 2015 and September 2017. The majority had FIGO stage 2B tumours (57%); 71% cervical squamous cell carcinoma, 7% cervical adenocarcinoma, 22% other pathologies. Median HR-CTV volume was 20cm 3 , range 7.1-82.4 cm 3 with median D90 83.6 Gy. The median difference in bladder volume was 113mls, range 58-178mls. In 24 cases (85.7%) bowel doses were improved with bladder filling. The median bowel D2cc reduced from 70.2% to 49.9% with median difference 15% (range 9.8% increase to 52.7% reduction). Median bladder D2cc dose increased with bladder filling from 101.3% to 112.1% with median difference 11.8% (34% increase to 16.4% reduction). Cumulative D2cc EQD2 for bowel were bladder-e: 64.5 Gy (48.0 – 90.3), reduced to bladder-f: 56.8 Gy (47.5 – 84.7) with difference -5.5 Gy (-20.0 to +6.1). Cumulative bladder D2cc EQD2 were bladder-e: 78.3 Gy (58.4 – 103.4) and bladder-f 84.3 Gy (63.4 – 107.4) with difference 7.1 Gy (-8.2 – 17.1 Gy). In 19 cases at least one OAR dose constraint on either bladder-e or bladder-f were exceeded; bladder 8, sigmoid 5, bowel 4, rectum 2. With individualised assessment of bladder filling 9 patients had potential for dose escalation: 7 with bladder-f and 2 with bladder-e.

filling provides the opportunity for dose escalation in IGBT.

Electronic Poster: Brachytherapy: Head and neck

EP-2233 Treatment of Squamous Cell Carcinoma by Alpha-radiation based Brachytherapy (Alpha DaRT) A. Popovitzer 1 , R. Ran Ben Hur 1 , R. Elli 2 , D. Dimirti Bragilovski 1 , D. David Silvern 1 , I. Itzhak Kelson2 3 , Y. Yona Keisari3 4 1 Rabin Med. Ctr. Beilinson Campus, Department of Radiation Oncology, Petah-Tikva, Israel 2 Rabin Med. Ctr. Beilinson Campus, Department of oral Maxiofacial Surgery, Petah-Tikva, Israel 3 Tel Aviv university, PHYSICS, Tel Aviv, Israel 4 Tel Aviv university, Department of Clinical Microbiology and Immunology, Tel Aviv, Israel Purpose or Objective Diffusing Alpha emitters Radiation Therapy (DaRT) is a unique intra-tumoral alpha radiation based tumor ablation treatment which was developed in our laboratories. Alpha DaRT seeds loaded with Radium-224 (3.77 days half-life) are inserted into solid tumors and release by recoil short-lived alpha-emitting atoms with cumulative half-life of about 12 hrs (Rn-220, Po-216. Pb- 212, Bi-212, Po-212, Tl-208). These atoms disperse in the tumor, and spray it with highly destructive alpha radiation. DaRT provides, for the first time, an efficient method for treatment of the entire volume of solid tumors by alpha radiation. Preclinical studies confirmed the destruction of tumors of various histotypes by DaRT. We performed a first in human clinical trial to examine the feasibility, safety and efficacy of Alpha DaRT in patients with skin and head and neck squamous cell carcinoma, which failed prior radiation and were not eligible for surgery. Material and Methods Methods: A feasibility and safety clinical study was performed with 7 patients, in an age range of 74-94 years, ineligible for any other treatment, with histopathological confirmation of recurrent skin or head and neck SCC. Tumor size < 5 centimeters in the longest diameter (lesions without nodal spread). Treatment was delivered based on a CT-simulation pre-treatment plan. The Ra-224 Alpha DaRT Seeds were inserted under local anesthesia using a specially designed Alpha DaRT Applicator. The seeds each carrying a dose of 2 µCi were placed 6 millimeters from each other. The total 224Ra activity administered was about 5 µCi per gram of tumor. The procedures lasted for 30-90 minutes, depending on the size of the tumor. CT was used to check the position of the radioactive seeds. Two to four weeks after implantation the seeds were removed, and six weeks after treatment CT was performed to assess the effect of treatment. Blood tests and urinalysis were performed during the treatment. Results Results: Three patients with recurrent oral cavity and four aggressive Skin SCC were treated by Alpha DaRT seeds within radiation failure fields, and the cumulative radiation exposure to a subject was below 5mSv. All tumors succumbed to the treatment; four patients had a complete response, and three patients had a partial response. No major toxicity was noted within a median follow up of 4.5 months. Conclusion Conclusions: In this initial human study we have demonstrated that alpha particles based DaRT exhibit enhanced radiobiological potential. The treatment was effective against radioresistant SCC tumors without major toxicity.

Conclusion This novel strategy for assessing bladder filling can significantly change bladder and bowel doses. Wide variation in individual anatomy can affect the positioning of OARs. We therefore recommend assessing both bladder empty and full scenarios to ascertain the optimal approach for the specific patient. Individualised bladder