Deriving Prostate Alpha-Beta Ratio Using Carefully Matched Groups, Long Follow-Up and the Phoenix Definition of Biochemical Failure

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

“…Shaffer et al 44 estimated the a/b value for low and lowintermediate risk prostate cancer patients treated with EBRT or LDRBT. Patients were matched for the same outcomeassociated risk factors and follow-up time.…”

“…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.…”

“…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...…”

“…RBE of permanent implants may also influence the a/b estimations from LDRBT data. 14,41,44,45 The correction for this factor yielded lower values for the a/b ratio.…”

Stereotactic body radiotherapy for prostate cancer: ready for prime time?

“…This provides SBRT's hypofractionated delivery an opportunity to increase the biological equivalent dose delivered to the prostate while relatively decreasing the dose to the normal bladder and rectal tissues. While the fundamental concept of SBRT is relatively straightforward, debate focused on prostate cancer's α/β ratio initially hindered application of SBRT for localized prostate cancer [5,6]. Nevertheless, usage of SBRT for localized prostate cancer has steadily increased in recent years as clinical outcomes supporting the safety and increasingly longer-term efficacy of SBRT are published [7][8][9][10][11][12][13].…”