DOSIMETRY OF SOLID TUMORS

Dosimetry data arising from a decade of radioimmunotherapy are summari zed along with techniques utilized to arrive at the reported dose esti mates. Generality of the MIRD methodology allows it to serve as a vehi cle for the calculation of solid tumor dosimetry although several limi tations exist. Nonstandard geometries of solid tumors will ultimately necessitate determination of absorbed fractions for the individual tum ors. Several approaches currently under investigation are described. F or reasons of practicality, solid tumor dosimetry estimates continue t o use the assumption of homogeneous activity distribution in a source organ, accounting for either all radiation or only nonpenetrating radi ation. As computation tools become available for incorporating inhomog eneous cellular level data, the currently used ''average dose'' as an index of tumor sterilization will likely be replaced with a statistica l distribution based on the number of viable cells in the tumor volume . Estimates of a tumor control dose would be based upon a linear exten sion of dose coupled with a threshold dose for cell sterilization.