Abstract
1877
Objectives: 210Po is unique among alpha emitters that may be applied to tumor radiotherapy. This radionuclide has a 138 day half life, a single alpha emission (with no beta-particle and negligible gamma-ray emissions), it decays to a stable daughter, and is not considered a bone seeking isotope. In addition, it has been suggested that 210Po can be produced in a highly-pure radionuclidic form by neutron irradiation via the reaction 209Bi(n,γ)210Bi, followed by ingrowth of 210Bi daughter 210Po. With a highly stable chelate, these properties may allow effective therapy of tumor angiogenesis and micrometastatic disease. In this study, we investigated the gamma-emitting radionuclidic impurities of a production run of 210Po.
Methods: 210Po was produced at the Avant Guard production facilities in Sarov, Russia. After sufficient time for ingrowth, 210Po was separated from the target matrix by sublimation and dissolved in nitric acid. Assay of gamma-emitting impurities was conducted at the National Institute of Standards and Technology (NIST). For this purpose, point sources were prepared by evaporation of a precisely-weighed single-drop aliquot of the 210Po solution. The single drop was deposited at the center of a circular-source backing prepared by affixing a single layer of 0.6 mm thickness polyester tape to an anodized aluminum annulus (3.8 cm inner diameter, 5.4 cm outer diameter). After sufficient time for drying, a second layer of tape was affixed to encapsulate the radioactivity. Gamma-ray spectra were collected for 24-48 hours using a high-purity germanium (HPGe) detector. Analysis was performed using commercially-available software and careful visual inspection of spectra.
Results: No significant gamma-ray impurities were observed from gamma-ray energies of 30 keV to 3600 keV in these experiments, with a detection limit of less than 20 gammas per second. Levels of known background peaks for the detector employed were found to be within normal limits. No unexplainable peaks were observed upon careful visual inspection gamma-ray spectra.
Conclusions: Our results indicate that 210Po solution produced by neutron irradiation of 209Bi results in a solution free of unwanted long-lived gamma-emitting radionuclides, with little or no post-sublimation purification required.
- Society of Nuclear Medicine, Inc.