The alpha/beta ratio for prostate cancer: what is it, really?
Two recent studies of fractionated external beam radiotherapy in early prostate cancer provide outcome data that allow a statistical estimation of the alpha/beta-ratio of the linear-quadratic model when combined with clinical data on the steepness of the dose-response curve. Results of the large randomized PR5 trial by the Ontario Clinical Oncology Group/National Cancer Institute of Canada yield an estimate of alpha/beta at 1.12 Gy with 95% confidence interval (-3.3, 5.6) Gy. A non-randomized study by Valdagni and colleagues of hyper-fractionation delivered BID versus conventional fractionation yields an alpha/beta-estimate of 8.3 Gy with 95% confidence interval (0.7, 16) Gy. Thus, the confidence interval of this latter study cannot exclude even very low values of alpha/beta. Furthermore, this point estimate may be an over-estimate if incomplete repair plays a role in the BID group of the Italian study. Taken together, the outcomes of these two studies still favor a high fractionation sensitivity of prostate cancer.
Bentzen
Søren M
SM
Department of Human Oncology, University of Wisconsin Medical School, WI 53792, USA. bentzen@humonc.wisc.edu
Ritter
Mark A
MA
D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal