Physics Bucharest 2017

Why does fractionation reduce risk of late effects?

• Individual dose fractions create lethal (fixed) and sub- lethal (repairable) damage. • Sub-lethal damage (SLD) repairs between one fraction and the next. • Normal tissues generally have a greater capacity to repair SLD than tumours. • The process of fractionation therefore “spares” the normal tissues relatively more than the tumour. • If fewer, larger fractions are delivered, normal tissue damage may be excessive, i.e. tolerance may be exceeded.