ESTRO 2021 Abstract Book

S1494

ESTRO 2021

Conclusion Layer rescanning with fixed and MML can improve the delivered dose distributions, thus enabling the treatment of some mediastinal lesions in free breathing. A new implementation of MMS is now being tested.

PO-1767 Surface guided FLASH radiotherapy A. Mannerberg 1 , E. Konradsson 1 , M. Kügele 1 , A. Edvardsson 2 , C. Ceberg 1 , H. Thomasson 2 , M.L. Arendt 3 , K. Bastholm Jensen 4 , S. Ceberg 1 1 Lund University, Department of Medical Radiation Physics, Lund, Sweden; 2 Skåne University Hospital, Department of Hematology, Oncology and Radiation Physics, Lund, Sweden; 3 University of Copenhagen, Department of Veterinary Clinical Sciences, Fredriksberg, Denmark; 4 Veterinärhuset Öresund, Limhamn, Malmö, Sweden Purpose or Objective Ultra-high dose rate radiotherapy (FLASH-RT) involves few fractions of high doses delivered in a fraction of a second and aims to widening the therapeutic window by reducing normal tissue toxicity. Although the fast delivery entails largely reduced intrafractional motion, it is crucial to have proper motion management to ensure precise delivery of the high dose. For motion management, surface guided radiotherapy (SGRT) provides real-time monitoring, sub-millimeter accuracy and a large field of view (FoV). Rendering of surface images (SI) requires that the projected light is reflected and detectable by the surface scanning (SS) system’s camera. In a novel approach, we aim to utilize SGRT for motion management during FLASH-RT. Materials and Methods Four canine cancer patients were treated with surface guided FLASH-RT at a modified linear accelerator (Precise, ELEKTA, Sweden). Prescribed doses of 28-35 Gy were delivered in 3.5 µs electron pulses (200 Hz) during a total treatment time of 60-125 ms. The patients were anesthetized prior to treatment. For SGRT, a single camera (Catalyst TM , C-RAD, Sweden) unit was used. To account for the wide range of fur colors, the appropriate integration time and gain was individually set for each patient to optimize the rendered SI. Also,