Re-irradiation: the “some like it hot – others not” dilemma

Although re-irradiation as a therapeutic procedure has already been explored over a few decades, it still remains a field of various uncertainties, and the majority of retrospective clinical studies contain quite a lot of "blank points". The critical point of this therapy is the severity of the radiation response of the normal organs at risk, which limits the planned and delivered dose. Re-irradiation is often considered a palliative treatment, although the results of the stereotactic hypofractionation (SHRT) strongly suggest that it can easily be used with radical intent. While tolerance doses (TD) were more or less arbitrarily established (not estimated) many years ago, they have not been verified during the passing time, but at least accounted for the 3/3 or 1/3 volume of the organ at risk. Regarding the so-called "remembered dose", it becomes crucial when the primary and re-irradiated volume of normal organs overlap. Knowledge of that parameter contains many loopholes. Such "doses" have mainly been approximately deduced from experimental and some clinical studies, and for a few organs at risk only. Present review the selected studies including 8,427 recurrences reported in a small number of the retrospective studies providing complete factors and parameters of the primary and re­-irradiation procedures. The review's results are presented and discussed. In 2022, the ESTRO/EORTC experts council defined re-irradiation procedures including three therapeutic scenarios, which are presently discussed. That consen­sus provides at least the detailed basics to optimize and improve quantitative knowledge on re-irradiation, which is the major aim of this paper.