Positron emission tomography and radioimmunotargeting - General aspects

To optimize radioimmunotherapy, in vivo information on individual patients, such as radionuclide uptake, kinetics, metabolic patterns and optimal admi nistration methods, is important. An overriding problem is to determine acc urately the absorbed dose in the target organ as well as critical organs. P ositron Emission Tomography (PET) is a superior technique to quantify regio nal kinetics in vivo with a spatial resolution better than I cm(3) and a te mporal resolution better than 10 s. However, target molecules often have di stribution times of several hours to days. Conventional PET nuclides are no t applicable and alternative positron-emitting nuclides with matching half- lives and with suitable labelling properties are thus necessary. Over many years we have systematically developed convenient production methods and la belling techniques of suitable positron nuclides, such as In-110(T1/2 = 1.1 5 h), Y-86(T1/2 = 14 h); Br-76(T1/2 = 16 h) and I-124(T1/2 = 4 days). 'Dose planning' can be done, for example, with Y-86- Or I-124-labelled ligands b efore therapy, and Y-90-and I-131-labelled analogues and double-labelling, e.g. with a Y-86/(90)-labelled ligand, can be used to determine the true ra dioactivity integral from a pure beta-emitting nuclide. The usefulness of t hese techniques was demonstrated in animal and patient studies by halogen-l abelled MAbs and EGF-dextran conjugates and peptides chelated with metal io ns.