{Reference Type}: Journal Article
{Title}: FLASH Effect Is Not Always Induced by Ultra-high Dose-rate Proton Irradiation Under Hypoxic Conditions.
{Author}: Nomura S;Hasegawa M;Kamiguchi N;Gotou H;Inoue J;Inoue K;Yoshimura H;Isohashi F;Mori E;
{Journal}: Anticancer Res
{Volume}: 44
{Issue}: 7
{Year}: 2024 Jul
{Factor}: 2.435
{DOI}: 10.21873/anticanres.17109
{Abstract}: <B>OBJECTIVE: </B>Pre-clinical studies have shown that irradiation with electrons at an ultra-high dose-rate (FLASH) spares normal tissue while maintaining tumor control. However, most in vitro experiments with protons have been conducted using a non-clinical irradiation system in normoxia alone. This study evaluated the biological response of non-tumor and tumor cells at different oxygen concentrations irradiated with ultra-high dose-rate protons using a clinical system and compared it with the conventional dose rate (CONV).<BR><B>METHODS: </B>Non-tumor cells (V79) and tumor cells (U-251 and A549) were irradiated with 230 MeV protons at a dose rate of >50 Gy/s or 0.1 Gy/s under normoxic or hypoxic (<2%) conditions. The surviving fraction was analyzed using a clonogenic cell survival assay.<BR><B>RESULTS: </B>No significant difference in the survival of non-tumor or tumor cells irradiated with FLASH was observed under normoxia or hypoxia compared to the CONV.<BR><B>CONCLUSIONS: </B>Proton irradiation at a dose rate above 40 Gy/s, the FLASH dose rate, did not induce a sparing effect on either non-tumor or tumor cells under the conditions examined. Further studies are required on the influence of various factors on cell survival after FLASH irradiation.