Henrietta Nittby Redebrandt (Sweden)
Department of Clinical Sciences, Lund University The Rausing Laboratory, Division of NeurosurgeryAuthor Of 1 Presentation
HYPOFRACTIONATED FLASH RADIOTHERAPY VERSUS CONVENTIONAL RADIOTHERAPY IN AN IMMUNOCOMPETENT RAT GLIOMA MODEL
Abstract
Background and Aims
For a clinical translation of FLASH radiotherapy, evidence of an enhanced therapeutic index within the same biological system is needed. In this study we aim to simultaneously investigate the tumor response (TCP) and skin toxicity (NTCP) of hypofractionated FLASH compared to conventional radiotherapy (CONV) in a fully immunocompetent rat glioma model.
Methods
Fisher 344 rats with subcutaneously inoculated NS1 glioma cells were treated with FLASH (450-550 Gy/s) or CONV in three fractions of either 8 Gy, 12.5 Gy or 15 Gy (n=9-10) using a 10 MeV electron beam. Animals were followed for 100 days. The tumor control probability was determined as the ratio of animals with no tumor progression at the end of the study period. Local dermal side effects were evaluated weekly.
Results
There was a statistically significant difference in overall survival between controls and all treatment groups, but no significant difference between FLASH and CONV for any of the dose levels (log-rank test). The tumor control probability for 3x8 Gy, 3x12.5 Gy and 3x15 Gy, respectively, were 3/9, 5/10 and 9/10 for CONV and 3/10, 5/9 and 9/10 for FLASH. Local dermal side effects were generally mild, consisting of hair loss, erythema, and dry desquamation. The ratio of animals with erythema or more severe effects during the study period was 78%/60%/90% for CONV and 50%/78%/70% for FLASH.
Conclusions
In this study we demonstrate that hypofractionated FLASH is equally effective as CONV in terms of controlling glioma in rats. No difference in acute effects could be resolved. Late effects will be histologically evaluated.