(450d) Automated Systems for Processing of Cyclotron Irradiated Solid Targets

Development of agents for Positron Emission Tomography (PET) is a rapidly growing field.  The isotopes ¹⁸F and ¹¹C are the most commonly used for labeling compounds of interest, but the short half-lives of these isotopes (120 minutes and 20 minutes respectively) often limits the studies which can be conducted to ones which occur on a rapid timescale.  The production of longer-lived positron-emitting radionuclides (t_1/2= hours-days) often requires the use of solid materials as targets.         The processing of these solid targets presents different challenges than the liquid targets (used for production of ¹⁸F and ¹³N) or gas targets (used for the production of ¹¹C).  We have developed automated systems for the production of ⁶⁴Cu via the ⁶⁴Ni(p,n) reaction, ^76,77Br via the ^76,77Se(p,n) reaction and for ⁸⁶Y via the ⁸⁶Sr(p,n) reaction.  These systems are at different stages of development, with the ⁶⁴Cu processing system being the most advanced.

⁶⁴Cu (t_1/2= 12.7 hours) is an important radioisotope as it decays via both positron emission and negatron emission. Thus it has sparked interest as a potential isotope for both imaging and therapy.  We have been producing this isotope for over 15 years and are currently shipping out substantial quantities (200-400 mCi) to some 12-15 institutions on a weekly basis for both preclinical studies and clinical trials.  This isotope is produced via irradiation of an enriched ⁶⁴Ni target plated on a gold disk support.  After irradiation, the target material is dissolved and the ⁶⁴Cu/⁶⁴Ni separation is conducted remotely via ion exchange.  The system is designed in such a manner as to recover the ⁶⁴Ni target material for recycling.

^76,77Br are two isotopes which are of interest as an imaging therapy pair.   Our group has been producing these radiobromine isotopes for imaging and therapy using brominated estrogen and androgen analogues.  The target material is doubly enriched ⁶³Cu₂^76,77Se.  The purpose of the enriched ⁶³Cu is to prevent the long-lived contaminant ⁶⁵Zn (t_1/2 = 244 d) from building up in the system.  The radiobromine is extracted via a remote distillation apparatus where the target is heated in a quartz tube furnace to distill the radiobromine which subsequently condenses on a cooler section of the tube.  The radioactivity is eluted from the tube and the target can be re-irradiated.

⁸⁶Y is of interest as an imaging analogue for ⁹⁰Y therapeutics.  This is desirable as ⁹⁰Y is a pure β emitter and thus understanding the biodistribution and pharmacokinetics of new agents labeled with this isotope is difficult.  These compounds can be labeled with ⁸⁶Y and imaging studies can be carried out before the therapeutic experiments with ⁹⁰Y.  ⁸⁶Y is produced via proton bombardment of ⁸⁶Sr in the form of ⁸⁶SrO.  The target material is dissolved and separated using the differences in solubility of strontium and yttrium in acidic and basic solutions.  This technique is currently in the process of being automated.