With radiotherapy however, the radiation dose is not in the hormetic zone, rather it is a high dose that is restricted mostly to the tumour.
Since Chernobyl the fractionation regimes in radiotherapy have changed dramatically. Now they hit the tumour harder and more frequently because healthy tissue recovers much more quickly from dose than assumed prior to Chernobyl. Trials are now being conducted in mice where the entire prescribed dose is delivered in 1-3 fractions. Admittedly that's not conventional radiotherapy.