Physics Bucharest 2017

α/β ratio: Fractionation sensitivity in tumours and normal tissues

• DR curve more bendy for late responding tissues – LQ translates into lower α/β ratio • Late responding normal tissues (spinal cord, kidney): 1-4 Gy • Most tumours: 8-15 Gy • Other tumours such as melanomas, liposarcomas, prostate adenocarcinoma: 1-4 Gy • Early responding normal tissues (skin, mucosa): 8-15 Gy • Decrease dose per fraction (or dose rate) • Tissues with lower  /  ratios will be preferentially spared compared to those with higher  /  ratios. – i.e. reduction in cell kill