Which α/β ratio and half-time of repair are useful for predicting outcomes in prostate cancer?

What do we know about the α/β for prostate cancer?

“…37 However, several reports were published ever since with new estimations for the prostate cancer a/b. 22,23,[25][26][27][28]44 Similarly, several studies comparing the biochemical outcome and late toxicity in patients treated with hypofractionation and conventional regimens are now available, showing the feasibility of hypofractionation used to treat prostate cancer by radiation. 22,24,25,28,[48][49][50][51][52] Although the first estimations from randomized trials have drawn the idea of a low a/b value for prostate cancer, 20,21 the associated large width of the 95% confidence intervals indicated a considerable uncertainty related with such evaluations.…”

“…8 Several recent studies have reported low a/b values for prostate cancer. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] If this a/b is proven to be lower than values estimated for late complications, then hypofractionated regimens are expected to improve the therapeutic ratio, 8,[29][30][31][32][33][34][35][36] beyond the advantages on cost saving and patient convenience.…”

“…Nevertheless, the question of how low the a/b ratio for prostate cancer is remains unanswered, [37][38][39] and many factors have been reported to contribute to the uncertainty about estimations of its value, such as heterogeneity of tumors 10,40 and interpatient variations, 41,42 influence of hypoxia, 42 onset of clonogenic cells repopulation, 15,17,26,41,43,44 repair during lowdose-rate brachytherapy (LDRBT), 11,15,17,26,41,44 value of the relative biological effectiveness (RBE) of permanent implants, 14,41,44,45 variations with clinical stage, [24][25][26][27]42 edema resulting from the insertion of radioactive seeds into the prostate, 17 dose heterogeneity of brachytherapy (BT) implants, 23,41 biological effectiveness of external-beam radiotherapy (EBRT) and LDRBT, 46 relevance of parameters determined in vitro and its relation to the in vivo environment, 18,42,47 use of combined data from multiple institutions with different modalities, 13 and imprecision of data assessed with only one modality. 20,23,27 Therefore, despite large evidence exists in favor of a low a/b ratio, caution must be taken when designing hypofractionated schedules, as small differences in its value may lead to marked changes in th...…”

“…9 However, Nickers et al 26 found an increase of more than 2 Gy when decreasing T 1/2 from 1.9 to 1.5 h. These authors attributed this variation as well as the large confidence interval to the diversity of the LDRBT patients' data and to the interpatient heterogeneity of tumors. In fact, the tumor heterogeneity may increase the actual a/b value, 42,131 and the use of homogeneous models overestimates its statistical significance.…”

“…Nahum et al 42 reported an increased a/b value for more radioresistent hypoxic tumors, comparing to welloxygenated tumor cells, although recent estimations did not find a correlation between the a/b ratio and different risk groups of prostate cancer. [24][25][26][27] Another factor that may influence the a/b estimations when using LDRBT clinical data is the onset of tumor cells repopulation after the beginning of treatment. Brenner and Hall 9 and Fowler et al 11 neglected repopulation during the radiation treatment and produced an a/b of $1.5 Gy.…”