Variability of individual normal tissue radiation sensitivity. An international empirical evaluation of endogenous and exogenous response modifiers.

BACKGROUND: The variability of normal-tissue response is of major concern for radiation therapy. Multiple endogenous and exogenous factors are qualitatively known to alter the acute and late tissue response. Which of them are regarded most important by the European radiation oncologists and what is, empirically, their quantitative influence on the acute or late tissue tolerance?
METHODS: In August 1997, we sent a questionnaire to 255 European radiation oncology departments. Among others, the questionnaire asked for endogenous and exogenous factors modifying the tissue response to radiation therapy and their quantitative influence on the acute and late radiation morbidity (TD 5/5). Fifty-five questionnaires (21.5%) were answered.
RESULTS: Empirically, the most important endogenous factors to modify the acute tissue tolerance are a) metabolic/other diseases with macro- or microangiopathia (17 answers [a]/32% mean decrease of tissue tolerance), b) collagen diseases (9 a/37%) and c) immune diseases (5 a/53%). As endogenous response modifiers for the TD 5/5 are recognized a) metabolic or other diseases leading to macro- or microangiopathia (15 a/31%), b) collagen diseases (11 a/38%) and c) immune diseases (2 a/50%). Inflammations from any reason are assumed to alter the acute tissue tolerance by (6 a/26%) and the TD 5/5 by (10 a/24%). Exogenous modifiers of the acute tissue response mentioned are a) smoking (34 a/44%), b) alcohol (23 a/45%), c) nutrition/diets (16 a/45%), d) hygiene (9 a/26%) and e) medical therapies (10 a/37%). Exogenous factors assumed to influence the TD 5/5 are a) smoking (22 a/40%), b) alcohol (15 a/38%), c) nutrition/diets (9 a/48%), d) hygiene (5 a/34%) and e) medical therapies (10 a/30%).
CONCLUSIONS: Exogenous factors are regarded more important by number and extent on the acute and late tissue response than endogenous modifiers. Both may have an important influence on the individual expression of normal tissue response.