Theoretical dosimetry estimations for radioisotopes produced by proton-induced reactions on natural and enriched molybdenum targets

This study presents a summary of the dosimetry calculations performed for three technetium agents most commonly used in nuclear medicine diagnostic studies, namely sestamibi™, phosphonates and pertechnetate, labeled with cyclotron-produced technetium. Calculated patient doses were compared to those that would be delivered by the same radiotracers labeled with technetium obtained from a generator produced in a reactor. The main difference is that technetium from a generator is pure, i.e. contains only (99m)Tc and its decay product (99g)Tc, while in a cyclotron a large number of other stable and radioactive isotopes are created. In our calculations only technetium radioisotopes (ground and isomeric states) were considered as they will be included in the radiotracer labeling process and will contribute to the patient dose. Other elements should be removed by chemical purification. These dose estimates are based on our theoretical calculations of the proton-induced reaction cross sections and radioisotope production yields. Thick targets of enriched (three different compositions) and natural molybdenum, and three initial beam energies (16, 19 and 24 MeV) were considered for irradiation times of 3, 6 and 12 h with a beam current of 200 µA. The doses were calculated for injection times corresponding to 0, 2, 8, 12 and 24 h after the end of beam.