LAUSR

78 Background: HT may improve cancer control and quality of life by sensitizing tumors to RT and CT. Inoperable recurrent rectal cancer has marginal outcomes with current retreatment regimens. We report the results from a first-in-human phase I study of MR-HIFU hyperthermia combined with RT and CT for recurrent rectal cancer. Methods: This ethics-approved study enrolled 6 patients fit for re-irradiation and chemotherapy; and with a MRI-visible and HIFU-accessible lesion. Patients received 30.6 Gy (17 fractions) and daily oral capecitabine, plus MR-HIFU HT immediately before RT on days 1, 8, and 15. Primary objectives were safety (acute toxicity) and treatment feasibility. Secondary objectives included late toxicity, pain palliation, quality of life, and radiologic response. HT was delivered with the Sonalleve MR-HIFU system on a 3T MRI. MR-based feedback control parameters were prescribed to achieve a mean temperature of 42.5°C in an 18 mm diameter target region for 30 minutes without exceeding 45°C. Results: One patient withdrew after completing 1/3 HT sessions due to scheduling and sedation difficulties. Five patients completed HT, RT and CT. There were no intraoperative complications, no adverse events or unintended tissue damage attributable to HT, RT, or CT. Table shows the best single continuous HT and mean temperatures (T90, T10), cumulative time in range (TIR), cumulative number of equivalent minutes at 43oC(CEM43) and day 90 imaging response. Sonication and MRI suite times were 36±13 and 226±78min. Conclusions: MR-HIFU HT was safely delivered in patients with recurrent rectal cancer. Treatment planning and patient set-up times decreased while beam-on time increased with experience. MR-HIFU HT combined with RT and CT appears feasible for primary tumours. Clinical trial information: NCT02528175. [Table: see text]