The potential radio-immunotherapeutic α-emitter 227Th - part I: Standardisation via primary liquid scintillation techniques and decay progeny ingrowth measurements

Thorium-227 is a potential therapeutic radionuclide for applications in targeted α-radioimmunotherapy for the treatment of various types of cancer. To provide nuclear medicine departments involved in Phase I clinical trials traceability to the SI unit of radioactivity (Bq), a standardisation of a radiochemically pure ²²⁷Th aqueous solution has been performed at the National Physical Laboratory. This was achieved via two primary liquid scintillation (LS) techniques -4π(LS)-γ digital coincidence counting (DCC) and 4π LS counting. These absolute techniques were supported by the indirect determination of the ²²⁷Th activity via the measurement of the ingrowth and decay rate of the decay progeny by both ionisations chambers and high purity germanium (HPGe) gamma-ray spectrometry. The results of the primary techniques were found to be consistent, both with each other (zeta score = 1.1) and to the decay progeny ingrowth measurements. An activity per unit mass of 20.726 (51) kBq g^-1 was determined for the solution. A procedure has been developed that provided an effective separation of the ²²⁷Th from its decay progeny, which was shown by the effective time zero of the ²²⁷Th-²²³Ra nuclear chronometer measured by HPGe gamma-ray spectrometry.

Development of the NPL gamma-ray spectrometer NANA for traceable nuclear decay and structure studies

We present a brief report on the progress towards the construction of the National Nuclear Array (NANA), a gamma-ray coincidence spectrometer for discrete-line nuclear structure and decay measurements. The proposed spectrometer will combine a gamma-ray energy resolution of approximately 3% at 1MeV with sub-nanosecond timing discrimination between successive gamma rays in mutually coincident decay cascades. We also review a number of recent measurements using coincidence fast-timing gamma-ray spectroscopy for nuclear structure studies, which have helped to inform the design criteria for the NANA spectrometer.

An approach based on the SIR measurement model for determining the ionization chamber efficiency curves, and a study of and photon emission intensities

The measurement model used to determine ionization chamber efficiency curves accounts from the outset for impurity corrections and beta spectrum shapes. The curves are represented by exponentials of polynomials whose coefficients are adjusted using non-linear least-squares minimization. The curves are validated by comparing with SIR key comparison reference values (KCRVs) and other published curves. The associated covariance matrix is also evaluated. Deviations from model predictions for 65Zn and 201Tl using recommended nuclear data are studied.

Secondary standardisation of 95mTc

The radionuclide 95mTc, which has a half-life of 61(2)days and emits a number of gamma-rays, may be used in radiochemical analysis as a yield tracer for the long-lived fission product 99Tc. In this work, we present (i) the production of 95mTc via an (alpha, 2n) reaction with stable 93Nb (a method which does not result in the production of any 97mTc, 98Tc or 99Tc), (ii) the chemical separation of 95mTc from niobium via coprecipitation, liquid-liquid extraction and liquid chromatography, and (iii) the secondary standardisation of 95mTc with high-resolution gamma-ray spectrometry and an ionisation chamber system.

Primary standardisation of 204Tl using the efficiency tracing method

The electron-capture and beta(-) -emitting radionuclide 204Tl has been known from previous experience to show discrepancies between different methods of standardisation. Source preparation is also difficult due to the complex chemistry of thallium. The Bureau International des Poids et Mesures (BIPM) intercomparison held in 1997, showed discrepancies of up to 10% between measurements of solid sources and liquid scintillation methods. These problems have been the subject of a BIPM CCRI(II) working group since 1999. This paper presents the results from a primary standardisation of a 204Tl solution using 4pibeta-gamma coincidence counting and liquid scintillation counting. The tracer technique was used for the 4pibeta-gamma coincidence counting, where 204Tl was traced with 134Cs and 60Co. The extrapolation to 100% beta-efficiency was performed by three different approaches: foiling, adding carrier and measuring sources of different initial masses. The results showed that tracing with 60Co and using external foiling gave the same result as obtained by liquid scintillation counting. A comparison of the results achieved by the different methods of measurement, tracers and methods for extrapolation is presented and discussed in this paper.

Standardisation of 11C

The increasing use of positron emission tomography for medical imaging and the availability of short-lived positron emitters has raised concerns about the accuracy of calibration of secondary standard measurement systems and the viability of using a single long-lived positron emitter as a reference calibration source for all positron emitters. Potential problems arise because the 511 keV quanta arising from positron annihilation are not generally produced at the same point as the original disintegration. In addition, the secondary standard may also be responsive to the associated bremsstrahlung radiation. The magnitude of both effects depends on the positron end-point energy. In order to resolve these problems, it is necessary to produce absolute standards of these positron-emitting radionuclides and the work presented here details the results of such work with 11C.

Integrating stress-response and cell-cycle checkpoint pathways

The DNA integrity checkpoint and stress kinase (SAPK/JNK and p38) pathways function to modulate cell-cycle, apoptotic and transcriptional responses to stress. Although initially considered to function independently, recent advances indicate a number of links between the stress-response and checkpoint pathways. Here, we consider the relationship between the stress-response and checkpoint pathways and how they interact to modulate cell-cycle control.