Some optimisation studies relevant to the production of high-purity 124I and 120gI at a small-sized cyclotron

Optimisation experiments on the production of the positron emitting radionuclides 124I (T1/2=4.18 d) and 120g I (T1/2=1.35 h) were carried out. The TeO2-target technology and dry distillation method of radioiodine separation were used. The removal of radioiodine was studied as a function of time and the loss of TeO2 from the target as a function of oven temperature and time of distillation. A distillation time of 15 min at 750°C was found to be ideal. Using a very pure source and comparing the intensities of the annihilation and X-ray radiation, a value of 22.0±0.5% for the β+ branching in 124I was obtained. Production of 124I was done using 200 mg/cm2 targets of 99.8% enriched 124TeO2 on Pt-backing, 16 MeV proton beam intensities of 10 μA, and irradiation times of about 8 h. The average yield of 124I at EOB was 470 MBq (12.7 mCi). At the time of application (about 70 h after EOB) the radionuclidic impurity 123I (T1/2=13.2 h) was <1%. The levels of other impurities were negligible (126I<0.0001%; 125I=0.01%). Special care was taken to determine the 125I impurity. For the production of 120gI only a thin 30 mg target (on 0.5 cm2 area) of 99.9% enriched 120TeO2 was available. Irradiations were done with 16 MeV protons for 80 min at beam currents of 7 μA. The 120gI yield achieved at EOB was 700 MBq (19 mCi), and the only impurity detected was the isomeric state 120mI (T1/2=53 min) at a level of 4.0%. The radiochemical purity of both 124I and 120gI was checked via HPLC and TLC. The radioiodine collected in 0.02 M NaOH solution existed >98% as iodide. The amount of inactive Te found in radioiodine was <1 μg. High purity 124I and 120gI can thus be advantageously produced on a medium scale using the low-energy (p,n) reaction at a small-sized cyclotron.