ESTRO 2024 - Abstract Book

S5240 ESTRO 2024 Both normal-ODRT (60Gy/30F/qd) and normal-TDRT (45Gy/30F/bid) to the spinal cord were safe for mice , as mice could complete the whole experiment course successfully. TEM could show the BSCB structures clearly (Fig 2A-B). TEM showed BSCB structural changes over time after completing the irradiation, particularly on d21 and d28 (Fig 1A-D). The basement membrane was thickened and more layers were detected. The BSCB structural change was more obvious in the normal-ODRT arm and less in the normal-TDRT arm. The penetration of EB on d8 (0.360 ng/ml in normal-ODRT vs. 0.321 ng/ml in normal-TDRT, P = 0.71) and d15 (0.357 ng/ml in normal-ODRT vs. 0.255 ng/ml in normal-TDRT, P = 0.64) after irradiation was not significantly different between arms. Shortening the irradiation period (hypofractionated radiotherapy), modified it to hypo-ODRT(60Gy/3F/qd) vs. hypo-TDRT(45Gy/3F/bid) was fatal, as most mice died within 1 week after being irradiated. TEM also showed severe damage of the BSCB 24 hours after irradiation (Fig 2 C-D), but the BSCB was less damaged with hypo-ODRT (60Gy/3F/qd) versus hypo-TDRT (45Gy/3F/bid). The penetration of EB on d2 after irradiation was increased in the ODRT arm (0.306 ng/ml in hypo-ODRT vs. 0.009 ng/ml in hypo-TDRT, P = 0.04). The overall survival (OS) was significantly shorter in the hypo-ODRT arm compared with hypo-TDRT arm ( median, 4d vs. 6d, P=0.001). Radiobiology - Normal tissue radiobiology