Radiobiological predictors of tumor and acute normal tissue response in radiotherapy for head and neck cancers.

ABSTRACT

Importance of two assay of the measurements of potential doubling time (Tpot.) and survival fraction at 2.0 Gy (SF2) and a method modifying acute radiation response of normal oral mucosa are discussed. Tumor clonogen repopulation accelerates around day 28 of treatment and the rate of repopulation is not constant but continuously increases from about 0.3 Gy/day to 1.0-1.3 Gy/day between day 28 and 65 of treatment. It may suggest that Tpot. values decrease respectively. The relevance of the Tpot. measurements prior to the treatment to clinical situations is discussed. The SF2 value reflects the intrinsic radiosensitivity of human tumors. The SF2 values are expected to be valuable as a predictors for tumor response to radiation. Variations in the SF2 values depending on tumor characteristics and assay methods are discussed in relation to the dose-response and tumor cure probability. The effect of modification of an accelerate repopulation in the oral mucosa by stimulation with 2% silver nitrate solution is presented. Although the presented prognosticators are different in their nature, they might provide a rational basis for selecting patients into optimal radiation treatment and might allow to modify radiation response of dose-limiting normal tissues.