Dose fractionation schedules--biologic aspects and applications to high LET radiotherapy.

The main differences between biologic effects of high and low LET irradiation are reviewed with special reference to multiple dose fractionation schedules. Some new results relating to RBE values of normal tissues (skin) at low doses per fraction are presented. Recent results of experiments to investigate optimum x-ray or fast neutron fractionation schedules are summarized. It is concluded that, until much more is known about the processes occurring inside tumors during treatment, high LET radiation is likely to be more reliable for eradicating tumors.