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How low is the alpha/beta ratio for prostate cancer?
Henk B Kal1, Marion P R Van Gellekom
1Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands. H.kal@radcl.med.uu.nl
Purpose:
Recently, low alpha/beta values of 1.2 and 1.5 Gy for prostate tumors have been derived from clinical results of external beam radiotherapy and of permanent implants of (125)I and (103)Pd. In the analyses the contributions of tumor repopulation, and edema as a result of inserting radioactive seeds in the prostate, have been ignored. In this paper we reanalyzed the clinical data and introduced the contribution of repopulation and edema.
Methods And Materials:
The linear quadratic-biologically effective dose model was used for reanalysis. In this model, the influence of repopulation and edema has been taken into account. The biologically effective dose was calculated as a function of alpha/beta for 2 brachytherapy regimens with (125)I and (103)Pd and 2 fractionated treatments, and for different half-times for repair of sublethal damage for the brachytherapy regimens.
Results:
We have found a plausible alpha/beta value of 3.1 to 3.9 Gy, an alpha value of 0.1 to 0.15 Gy(-1), and a half-time of repair of about 0.5 h.
Conclusions:
It seems now that the alpha/beta value is low, 3.1-3.9 Gy, but not as low as the 1.2 and 1.5 Gy reported earlier.