Abstract Body

FLASH radiotherapy (FLASH-RT) has come at the center of the attention in the radiobiology and radiation oncology fields. Taking into consideration the current literature, a possible definition for FLASH-RT could be: “A radiotherapy technique delivered at ultra-high dose rate with specific beam parameters able to treat tumors without inducing drastic toxicities on the surrounding normal tissues.” Nevertheless, there has been no consensus on a definition for FLASH-RT yet, and intensive work is currently ongoing to understand and decipher the mechanisms underlying the so-called “FLASH effect.”

The antitumor effect associated to an absence of normal tissue injury has caught the field by surprise, questioning the most basic concepts or radiobiology. But even if more and more studies describe a normal tissue protection following exposures to ultra-high dose rate irradiation, few biological mechanisms differentiating conventional dose rate RT to FLASH-RT responses have been described so far. This lecture aims at reviewing the most recent FLASH-RT literature to analyze the normal tissue and tumor response after FLASH RT at the molecular, cellular and tissular levels. A comprehensive approach of the different models and endpoints used in these studies will be provided to build up hypotheses on biological mechanisms explaining the FLASH effect.