THE CURRENT STATUS OF TARGETED RADIOTHERAPY IN CLINICAL-PRACTICE

Biologically targeted radiotherapy in clinical practice requires a mol ecule which has a relative specificity for tumour tissue-the missile-c oupled to a radionuclide with appropriate physical characteristics-the warhead. When administered to a patient this combination should resul t in selective irradiation of the target tumour cells with relative sp aring of normal tissues. Simple ions and small molecules which follow physiological pathways as either the natural substrates or analogues f orm the best examples of biological targeting. Clinically valuable res ults are seen with, for instance, iodine uptake by normal and malignan t thyroid cells, incorporation of the calci-mimetic element strontium in areas of increased bone metabolism and accumulation of the catechol amine analogue meta-iodobenzylguanidine in neuroblastoma. The use of m onoclonal antibodies as targeting vehicles has not proved to be a pana cea, yet some patients with lymphoma, hepatoma and ovarian carcinoma h ave obtained benefit. Current clinical studies in targeted radiotherap y focus on the integration of radionuclide treatment with conventional treatments, and the optimization of such combined approaches. The dev elopment of modifications to offset the limitations inherent in the us e of crude antibodies also offers an opportunity for improved clinical outcomes.