Evaluating the radiation chemistry of Flash radiotherapy via Monte Carlo simulations

Flash radiotherapy is an emerging cancer treatment that employs ultra-high dose rates to enhance tumor control while significantly reducing damage to healthy tissue, compared to conventional radiotherapy. This differential tissue response is known as the Flash effect, and its underlying mechanism remains unknown. It has been hypothesized that increased radical-radical reactions might potentially correlate with the Flash effect, as these could substantially affect the indirect DNA damage.

During my PhD I developed an innovative multiple pulse extension for gMicroMC, a Monte Carlo track-structure algorithm, to explore the impact of dose rate on radical-radical reactions. I validated the model against external algorithms and pulse radiolysis experimental data. I conducted simulations of multiple pulse irradiations, which indicated a dose rate threshold.

Below this threshold, a steady-state in the concentration of species was consistently maintained within every pulse, resulting in a constant postirradiation chemical yield. In contrast, above the threshold, the high pulse frequency prevented the achievement of the steady-state, leading to an accumulation of reactive species throughout the irradaition. This reactive species build-up significantly promoted radical-radical reactions, increasing the post-irradiation yield of hydrogen peroxide. This phenomenon is more likely to boost radical-radical reactions compared to the inter-track mechanism.