**11.5 Pre-scouting**

In the latter application, RIS is performed as a scouting procedure prior to RIT to enable the confirmation of tumor targeting and the estimation of radiation dose delivered to both tumors and normal tissues. For this purpose, the radioimmunoconjugates used for RIS and RIT should demonstrate a similar biodistribution and therefore radionuclides with comparable chemical properties have to be chosen (Dearling & pedley, 2007). When using 131I for RIT, both 123I and 131I can be used for a RIS scouting procedure. When using 90Y for RIT, 111In can be used to represent this pure beta-emitter (Dearling & pedley, 2007). Finally, when aiming the therapeutic use of 186Re or 188Re, either these radionuclides themselves can be used for an imaging procedure or 99mTc (Pontus et al., 2004).
