Quel rapport alpha/bêta pour le cancer prostatique en 2019 ?

Abstract

In 1999, Brenner and Hall reported for prostate cancer a very low alpha/beta ratio (1.5Gy). In the following years, this value has been confirmed by a large series of papers, so that this very low alpha/beta ratio became a dogma , on which a large number of hypofractionated schemes were being built. This was logical, since this very low value strongly suggested a beneficial advantage of hypofractionation for prostate cancer. However, more recently, several questions arose; first, a number of authors reported, from the analysis of their own data, values of alpha/beta ratio which were higher than the dogma . Secondly, the three modern superiority trials , aiming at demonstrating the advantages of hypofractionated schemes, actually failed to show such a superiority, in spite of high equivalent doses (calculated with an alpha/beta of 1.5Gy), reaching up to 84 - 90Gy. In 2018, three review papers/metanalyses shed a new light on what could be the value of the alpha/beta ratio for prostate cancer. In particular, those studies took into account a time factor (for repopulation), a parameter which had been either forgotten or underestimated before. In those three studies, the alpha/beta ratio was ranging from 2.7Gy to 4.9Gy. Those data do confirm the sensitivity to the fraction dose variation of prostate cancer, but this sensitivity could be lower than suggested by an alpha/beta ratio of 1.5Gy.