Quantitative Radiation Dose-Response Relationships for Normal Tissues in Man: I. Gustatory Tissue Response during Photon and Neutron Radiotherapy

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Abstract
Quantitative radiation dose-response curves for normal gustatory tissues in man were studied. Taste function, expressed as taste loss, was evaluated in 84 patients who were given either photon or neutron radiotherapy for tumors in the head and neck region. Patients were treated to average tumor doses of 6600 cGy [centigray] (photon) or 2200 cGy (neutron) using standard treatment techniques. Taste loss was determined in patients using a standrd forced-choice, 3-stimulus drop technique prior to radiotherapy and at 1000-cGy intervals for photon patients and 320-cGy intervals for neutron patients during radiotherapy. The dose-response curves for photons and neutrons were analyzed by fitting a 4-parameter logistic equation to the data. Photon and neutron curves differed principally in their relative position along the dose axis. Comparison of the dose-response curves was made by determination of RBE [relative biological effectiveness]. At 320 cGy, the lowest neutron dose at which taste measurements were made, RBE = 5.7. If this RBE is correct, then the therapeutic gain faactor may be < 1, indicating no biological advantage in using neutrons over photons for this normal tissue. These studies suggest measurements of taste function, and evaluation of dose-response relationships may also be useful in quantitatively evaluating the efficacy of chemical modifiers of radiation response such as hypoxic cell radiosensitizers and radioprotectors.

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