Endoradiotherapie (ERT) and PET

Besides the modern diagnosis of normal and disturbed neurological and oncological problems with PET, it is important to develop adequate radiotherapeutics. These utilize the high affinity of tumor-specific compounds but another way of radioactive transformation of the labelling isotope: the emission of particles (?-, ?, Auger-electrons). In an ideal case, the whole energy of the radioactive decay causes the selective destruction of the tumor cell DNA. The total deposition of the transformation energy in the area of the tumor however prevents the non-invasive measurement of the uptake kinetics of the radiopharmaceutical, the control of the therapeutical process and the quantification of the success in therapy.

To solve these problems homologous positron-emitters (is available) can be inserted into the targeting vector as surrogate label. Suitable isotopes are:

•	the system 77As/72As: 77As (T1/2=38,8 h, 100% β-) for the ERT with 77As-Radiotherapeutika
	versus 72As (T1/2=26,0 h, 88% β+) for the PET-diagnostics with analogus 72As-radiodiagnostics
•	the system 90Y/86Y: 90Y (T1/2 = 64 h, 100% β-) for the ERT with 90Y-Radiotherapeutika
	versus 86Y (T1/2 = 14.7 h, 33% β+) for the PET-diagnostics with analogus 86Y-Radiodiagnostika
•	the sytem 140Nd/140Pr: 140Nd (T1/2 = 3.37 d, 100% Auger-Elektronen-Emitter) for ERT;
	versus 140Pr (T1/2 = 3.4 min, 51% β+) for inherent diagnosis with PET

The main radiochemical challenge is to produce those isotopes, another aspect is the improvement of the binding of trivalent metal cations to the bifunctional chelate ligands and their coupling to selected tumor-affine peptide structures.