REPORTING AND ANALYZING DOSE DISTRIBUTIONS - A CONCEPT OF EQUIVALENT UNIFORM DOSE

Modern treatment planning systems for three-dimensional treatment plan ning provide three-dimensionally accurate dose distributions for each individual patient. These data open up new possibilities for more prec ise reporting and analysis of doses actually delivered to irradiated o rgans and volumes of interest. A new method of summarizing and reporti ng inhomogeneous dose distributions is reported here. The concept of e quivalent uniform dose (EUD) assumes that any two dose distributions a re equivalent if they cause the same radiobiological effect. In this p aper the EUD concept for tumors is presented, for which the probabilit y of local control is assumed to be determined by the expected number of surviving clonogens, according to Poisson statistics. The EUD can b e calculated directly from the dose calculation points or, from the co rresponding dose-volume distributions (histograms). The fraction of cl onogens surviving a dose of 2 Gy (SF2) is chosen to be the primary ope rational parameter characterizing radiosensitivity of clonogens. The a pplication of the EUD concept is demonstrated on a clinical dataset. T he causes of flattening of the observed dose-response curves become ap parent since the EUD concept reveals the finer structure of the analyz ed group of patients in respect to the irradiated volumes and doses ac tually received. Extensions of the basic EUD concept to include nonuni form density of clonogens; dose per fraction effects, repopulation of clonogens, and inhomogeneity of patient population are discussed and c ompared with the basic formula. (C) 1997 American Association of Physi cists in Medicine.