CALCULATION OF RADIATION-INDUCED COMPLICATION PROBABILITIES FOR BRAIN, LIVER AND KIDNEY, AND THE USE OF A RELIABILITY MODEL TO ESTIMATE CRITICAL VOLUME FRACTIONS

Radiation induced normal tissue complication probability is calculated for three different organs: brain, liver and kidney. The model applie d is a reliability model where the volume effect of the tissue is desc ribed by the structural parameter, k, which reflects the architecture of the functional subunits of the organ. The complication probability depends on k, the inactivation probability of the functional subunits (p) and the irradiated volume fraction (n). For partial, homogeneous i rradiation of the brain, a k-value close to unity was found, and the r espective values for liver and kidney were 0.92 and 0.77. An extension of the reliability model to account for individual inactivation proba bility of the subunits allows calculation of complication probability for inhomogeneous dose distributions. For the brain, intercomparison o f-a three-held and a two-field technique demonstrated a small reductio n in complication probability for the former at low total doses. At hi gh total doses a minimum complication probability was achieved applyin g a three-field technique, being three times less than that associated with the two-held technique.