Estimation of a self-consistent set of radiobiological parameters from hypofractionated versus standard radiation therapy of prostate cancer

Piernicola Pedicini, Lidia Strigari, Marcello Benassi

Research output: Contribution to journalArticle


Purpose: To determine a self-consistent set of radiobiological parameters in prostate cancer. Methods and Materials: A method to estimate intrinsic radiosensitivity (α), fractionation sensitivity (α/β), repopulation doubling time, number of clonogens, and kick-off time for accelerated repopulation of prostate cancer has been developed. Based on the generalized linear-quadratic model and without assuming the isoeffective hypothesis, the potential applications of the method were investigated using the clinical outcome of biochemical relapse-free survival recently reviewed in the literature. The strengths and limitations of the method, regarding the fitted parameters and 95% confidence intervals (CIs), are also discussed. Results: Our best estimate of α/β is 2.96 Gy (95% CI 2.41-3.53 Gy). The corresponding α value is 0.16 Gy-1 (95% CI 0.14-0.18 Gy -1), which is compatible with a realistic number of clonogens: 6.5 × 106 (95% CI 1.5 × 106-2.1 × 10 7). The estimated cell doubling time is 5.1 days (95% CI 4.2-7.2 days), very low if compared with that reported in the literature. This corresponds to the dose required to offset the repopulation occurring in 1 day of 0.52 Gy/d (95% CI 0.32-0.68 Gy/d). However, a long kick-off time of 31 days (95% CI 22-41 days) from the start of radiation therapy was found. Conclusion: The proposed analytic/graphic method has allowed the fitting of clinical data, providing a self-consistent set of radiobiological parameters for prostate cancer. With our analysis we confirm a low value for α/β with a correspondingly high value of intrinsic radiosensitivity, a realistic average number of clonogens, a long kick-off time for accelerated repopulation, and a surprisingly fast repopulation that suggests the involvement of subpopulations of specifically tumorigenic stem cells during continuing radiation therapy.

Original languageEnglish
JournalInternational Journal of Radiation Oncology Biology Physics
Issue number5
Publication statusPublished - Apr 1 2013


ASJC Scopus subject areas

  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Radiation
  • Cancer Research

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