Abstract
Cyclotron production of technetium-99m (99mTc) is a promising route to supply 99mTc-radiopharmaceuticals. Higher 99mTc yields can be obtained with medium-energy cyclotrons in comparison to those dedicated to PET isotopes production. To take advantage of this capability, evaluation of radioisotopic purity of 99mTc produced at medium energy (20-24 MeV) and its impact on image quality and dosimetry was required. Methods: Thick 100Mo (99.03% and 99.815%) targets were irradiated with incident energy of 20, 22, and 24 MeV for 2 or 6 h. The targets were processed to recover an effective thickness corresponding to ~5 MeV energy loss and the resulting sodium pertechnetate 99mTc was assayed for chemical, radiochemical, and radionuclidic purity. Radioisotopic content in final formulation was quantified using gamma-ray spectrometry. Internal radiation dose for 99mTc-pertechnetate was calculated based on experimentally measured values and biokinetic data in humans. Planar and SPECT imaging was performed using thin capillary and water filled Jaszczak phantoms. Results: Extracted sodium pertechnetate 99mTc met all provisional quality standards. The formulated solution for injection had pH 5.0-5.5, contained >98% of radioactivity in the form of pertechnetate ion, and was stable for at least 24 h after formulation. Radioisotopic purity of 99mTc produced with 99.03% enriched 100Mo was >99.0% decay corrected (d.c.) to the end of bombardment (EOB). Radioisotopic purity of 99mTc produced with 99.815% enriched 100Mo was ≥99.98% (d.c. EOB). Estimated dose increase relative to 99mTc without any radionuclidic impurities was below 10% for sodium pertechnetate 99mTc produced from 99.03% 100Mo if injected up to 6 h post-EOB. For 99.815% 100Mo, the increase in effective dose would be <2% at 6 h post-EOB and <4% at 15 h post-EOB when the target is irradiated at Ein = 24 MeV. Image spatial resolution and contrast with cyclotron-produced 99mTc were equivalent to that obtained with 99mTc eluted from a conventional generator. Conclusion: Clinical grade sodium pertechnetate 99mTc was produced with a cyclotron at medium energies. Quality control procedures and release specifications were drafted as part of a clinical trial application that received approval from Health Canada. The results of this work are intended to contribute to establishing a regulatory framework for using cyclotron-produced 99mTc in routine clinical practice.
- Quality Assurance
- Radiobiology/Dosimetry
- Radiopharmaceuticals
- 99mTc-pertechnetate
- cyclotron
- dosimetry
- imaging
- radionuclidic and radioisotopic purity
- Copyright © 2015 by the Society of Nuclear Medicine and Molecular Imaging, Inc.