Role of radiation dosimetry in radioimmunotherapy planning and treatment dosing

Cancer-seeking antibodies (Abs) carrying radionuclides can be powerful drug s for delivering radiotherapy to cancer. As with all radiotherapy, undesire d radiation dose to critical organs is the limiting factor. It has been pro posed that optimization of radioimmunotherapy (RIT), that is, maximization of therapeutic efficacy and minimization of normal tissue toxicity, depends on a foreknowledge of the radiation dose distributions to be expected. The necessary data can be acquired by established tracer techniques, in indivi dual patients, using quantitative radionuclide imaging. Object-oriented sof tware systems for estimating internal emitter radiation doses to the tissue s of individual patients patient-specific radiation dosimetry), using compu ter modules, are available for RIT, as well as for other radionuclide thera pies. There is general agreement that radiation dosimetry (radiation absorb ed dose distribution, cGy) should be utilized to establish the safety of RI T with a specific radiolabded Ab in the early stages (i.e, phase I or II) o f drug evaluation. However, it is less well established that radiation dose should be used to determine the radionuclide dose (amount of radioactivity , GBq) to be administered to a specific patient (i.e. radiation dose-based therapy). Although treatment planning for individual patients based upon tr acer radiation dosimetry is an attractive concept and opportunity, particul arly for multimodality RIT with intent to cure, practical considerations ma y dictate simpler solutions under some circumstances. (C) 2001 Elsevier Sci ence Ireland Ltd. All rights reserved.