Radiation risk estimates after radiotherapy: application of the organ equivalent dose concept to plateau dose-response relationships.

Estimates of secondary cancer risk after radiotherapy are becoming more important for comparative treatment planning. Modern treatment planning systems provide accurate three-dimensional (3D) dose distributions for each individual patient. The dose distributions can be converted into organ equivalent doses to describe radiation-induced cancer after radiotherapy (OED(rad-ther)) in the irradiated organs. The OED(rad-ther) concept assumes that any two dose distributions in an organ are equivalent if they cause the same radiation-induced cancer risk. In this work, this concept is applied to dose-response relationships, which are leveling off at high dose. The organ-dependent operational parameter of this dose-response relationship was estimated by analyzing secondary cancer incidence data of patients with Hodgkin's disease. The dose distributions of a typical radiotherapy treatment plan for treating Hodgkin's disease was reconstructed. Dose distributions were calculated in individual organs from which cancer incidence data were available. The model parameter was obtained by comparing dose and cancer incidence rates for the individual organs.