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

Abstract

Since last decade, the debate on the parameter which reflects prostate cancer sensitivity to fractionation in a radiotherapy treatment, the α/β, has become extensive. Unlike most tumors, the low labeling indices (LI) and large potential doubling time that characterize the prostate tumor led some authors to consider that it may behave as a late responding tissue. So far, the existing studies with regard to this subject point to a low value of α/β, around 2.7 Gy, which may be considered as a therapeutic gain in relation to surrounding normal tissues by using fewer and larger fractions. The aim of this paper is to review several estimates that have been made in the last few years regarding the prostate cancer α/β both from clinical and experimental data, as well as the set of factors that have potentially influenced these evaluations.

A TCP model for external beam treatment of intermediate‐risk prostate cancer

“…18 All of the optimized radiosensitivity values listed in Table III produced by the NM simplex algorithm are biologically plausible with tight confidence intervals. These values are in good agreement with both experimental and clinical observations reported in the literature through meta-analysis, 7,8 falling well within the bounds of the previously reported ranges. 7,9,46,47…”

“…Another review of the clinical and experimental data regarding the radiobiological differential that might exist between prostate tumors and the late normal tissues surrounding the prostate suggested that the α/β ratio of the prostate is low, 2.7 Gy. 8 This value for α/β is similar to theᾱ/β value of 2.48 Gy in Table III. While values obtained from in vitro work are useful, there are reservations with them as tumors in vivo exist and proliferate in an environment different from those in vitro.…”

“…These initial guesses span the known plausible range of radiosensitivity. 7,8 The algorithm was employed to minimize the sum of the square of errors produced by the TCP model, weighted to the number of patients per data point.…”

“…The choice of cancer type is due to the debate associated with the α/β ratio of prostate cancer. [3][4][5][6][7][8][9] The intermediaterisk patient cohort was selected because of the availability of clinical outcome data for these patients across the full spectrum of RT regimes, hyper, standard, and hypofractionated treatment. [9][10][11][12][13][14][15][16][17] Previous TCP modeling studies have been fitted to hyper and standard-fractionated RT regimes, with conflicting and contradictory results.…”

Evolution of advanced technologies in prostate cancer radiotherapy

“…Trials comparing conventionally fractionated and hypofractionated EBRT were inconsistent in their results: the methods of early studies are not comparable to modern techniques, and the modern studies have rejected their hypotheses of superiority of hypofractionated EBRT. 69 Thus, although there is preclinical evidence to support a low α:β ratio for prostate cancer, multiple values have been reported (with most <3 Gy), 70 and the clinical data supporting the hypothetical evidence is lacking. 71 As of 2013, hypofractionated regimens are typically reserved for patients enrolled in clinical trials, 69 the theory of prostate cancer Limited data *2D and 3D IGRT.…”