Clinical radiobiology of head and neck cancer: the hypothesis of stem cell activation

P. Pedicini, R. Caivano, A. Fiorentino, L. Strigari

Research output: Contribution to journalArticlepeer-review


Purpose: To estimate and reduce uncertainties of a self-consistent set of radiobiological parameters based on the outcome of head and neck cancer (HNC) patients treated with radiotherapy (RT). Methods: Published studies comparing at least two RT schedules for HNC patients were selected. The method used to estimate the radiobiological parameters consists of three sequential steps that allow a significant reduction of uncertainties: the first, in which the intrinsic (α) and the repair (β) radio-sensitivities were estimated together with the doubling time (Td) by an analytical/graphical method; the second, in which the kick-off time for accelerated proliferation (Tk) was estimated applying the hypothesis of activation for sub-populations of stem cells during the RT; the third, in which the number of clonogens (N) was obtained by the Tumor Control Probability (TCP) model. Independent clinical data were used to validate results. Results: The best estimate and the 95 % confidence intervals (95 % CIs) were: α = 0.24 Gy−1 (0.23–0.26), β = 0.023 Gy−2 (0.021–0.025), α/β = 10.6 Gy (8.4–12.6), Td = 3.5 days (3.1–3.9), Tk = 19.2 days (15.1–23.3), N = 7 × 107 (4 × 107–1 × 108). From these data, the dose required to offset repopulation occurring in 1 day (Dprolif) and starting after Tk was also estimated as 0.69 Gy/day (0.52–0.86). Conclusions: The estimation of all the radiobiological parameters of HNC was obtained based on the hypothesis of activation for specifically tumorigenic sub-populations of stem cells. The similarity of results to those from other studies strengthens such a hypothesis that could be very useful for the predictivity of the TCP model and to design new treatment strategies for HNC.

Original languageEnglish
Pages (from-to)469-476
Number of pages8
JournalClinical and Translational Oncology
Issue number6
Publication statusPublished - Dec 9 2015


  • Fractionation
  • Radio-sensitivity
  • Stem cells
  • Tumor control probability

ASJC Scopus subject areas

  • Oncology
  • Cancer Research


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