Radiobiologic modeling of cytoprotection effects in radiotherapy.

Purpose: To investigate the potential for mathematical modeling of the normal tissue-sparing effects of cytoprotective agents used in conjunction with radiotherapy and chemotherapy.

Methods And Materials: The linear quadratic model was modified to include a "cytoprotection factor," in two alternative ways. The published results on the incidence of treatment-related oral mucositis in patients treated for head-and-neck carcinoma using radiotherapy alone or combined with chemotherapy were assessed against the model to determine the likely values of the cytoprotection factor required to confer a reasonable degree of cytoprotection.

Results: In both of the model alternatives considered, a cytoprotection factor value of < or = 0.85 was required for a clinically detectable degree of cytoprotection to be realized. A cytoprotection factor value of 0.85 would mean that the radiation sensitivity coefficients would be effectively reduced by 15% on account of the action of the cytoprotector.

Conclusion: The incorporation of a cytoprotection factor into an existing linear quadratic method would allow a quantitative assessment of cytoprotection and could be useful in the design of future clinical studies.