Activity standard and calibrations for 227Th with ingrowing progeny.

Thorium-227 was separated from its progeny and standardized for activity by the triple-to-double coincidence ratio (TDCR) method of liquid scintillation counting. Confirmatory liquid scintillation-based measurements were made using efficiency tracing with 3H and live-timed anticoincidence counting (LTAC). The separation time and the efficiency of the separation were confirmed by gamma-ray spectrometry. Calibrations for reentrant pressurized ionization chambers, including commercial radionuclide calibrators, and a well-type NaI(Tl) detector are discussed.

Realization and dissemination of activity standards for medically important alpha-emitting radionuclides.

Interest in targeted cancer therapy with alpha-emitting radionuclides is growing. To evaluate emerging radiotherapeutic agents requires precise activity measurements for consistent dose-response relationships and patient-specific dosimetry. National metrology institutes around the world have reported on the development and comparison of activity standards for medically important alpha emitters. This review describes the relevant methods and models underpinning these standards, the generation of new nuclear decay data, and the impacts on preclinical and clinical activity assays using radionuclide calibrators and γ-ray spectrometry.

Ra-224 activity, half-life, and 241 keV gamma ray absolute emission intensity: A NIST-NPL bilateral comparison.

The national metrology institutes for the United Kingdom (UK) and the United States of America (USA) have compared activity standards for 224Ra, an α-particle emitter of interest as the basis for therapeutic radiopharmaceuticals. Solutions of 224RaCl2 were assayed by absolute methods, including digital coincidence counting and triple-to-double coincidence ratio liquid scintillation counting. Ionization chamber and high-purity germanium (HPGe) γ-ray spectrometry calibrations were compared; further, a solution was shipped between laboratories for a direct comparison by HPGe spectrometry. New determinations of the absolute emission intensity for the 241 keV γ ray (Iγ = 4.011(16) per 100 disintegrations of 224Ra) and of the 224Ra half-life (T1/2 = 3.6313(14) d) are presented and discussed in the context of previous measurements and evaluations.

Radionuclide calibrator responses for 224Ra in solution and adsorbed on calcium carbonate microparticles.

A suspension of 224Ra adsorbed onto CaCO3 microparticles shows promise for α-therapy of intracavitary micro-metastatic diseases. To facilitate accurate activity administrations, geometry-specific calibration factors for commercially available reentrant ionization chambers (ICs) have been developed for 224RaCl2 solutions and 224Ra adsorbed onto CaCO3 microparticles in suspension in ampoules, vials, and syringes. Ampoules and vials give IC responses consistent with each other to <1%. Microparticles attenuation leads to a ≈1% to ≈2.5% reduction in response in the geometries studied.

Primary standardization of 224Ra activity by liquid scintillation counting.

A standard for activity of 224Ra in secular equilibrium with its progeny has been developed, based on triple-to-double coincidence ratio (TDCR) liquid scintillation (LS) counting. The standard was confirmed by efficiency tracing and 4παß(LS)-γ(NaI(Tl)) anticoincidence counting, as well as by 4πγ ionization chamber and NaI(Tl) measurements. Secondary standard ionization chambers were calibrated with an expanded uncertainty of 0.62% (k = 2). Calibration settings were also determined for a 5 mL flame-sealed ampoule on several commercial reentrant ionization chambers (dose calibrators).

Hemimegalencephaly in an adult with normal intellectual function and mild epilepsy.

Hemimegalencephaly is a rare congenital brain malformation, usually associated with mental retardation, * refractory epilepsy, and progressive neurological deficits. We report the case of a 19-year-old female with de novo diagnosis of right hemimegalencephaly, normal intellectual function, and history of non-refractory epilepsy. She presented with weakness and paraesthesia of the left leg. Extensive evaluation was negative for other causes for the weakness, which was attributed to progressive neurological damage secondary to long-standing subclinical epileptic activity in the hemimegalencephalic hemisphere. This patient underwent a cerebral fluorodeoxyglucose positron emission tomography that demonstrated near-normal cortical metabolism. Formal neuropsychological evaluation revealed mild deficits in the affected hemisphere, but preserved general intellectual function. This case illustrates the wide phenotypic variations in this condition and raises questions about prenatal counselling for hemimegalencephaly.