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Oncology-Basic Science: Therapy, Metrics & InterventionTherapy, Metrics & Intervention Posters |
1 Joint Department of Physics, Royal Marsden Hospital & Institute of Cancer Research, Sutton, London, United Kingdom; 2 Algeta ASA, Oslo, Norway
1381
Objectives: 223Ra is a bone-seeking radionuclide for the treatment of skeletal metastases. 223Ra decays in a chain of 6 isotopes to stable 207Pb. In total, an energy of 28 MeV is emitted per decay, of which 93.5% is emitted as alpha particles and the rest as betas and photons. This relationship means that a high absorbed dose per decay is locally delivered and that the number of photons useful for imaging is low. The purpose of this project was to investigate the possibility of quantitative imaging following intravenous administration of 223Ra-chloride.
Methods: Acquisition parameters (collimator, energy windows) for scintillation camera imaging of 223Ra were determined. The sensitivity, spatial resolution and effective attenuation coefficients were measured for planar images for the determined settings. A phantom study was conducted to perform quantitative imaging under clinically realistic acquisition conditions.
Results: The sensitivity for the three most suitable photon peaks was determined to be 67 cps/MBq (82 keV, 20%), 18 cps/MBq (154 keV, 15%) and 14 cps/MBq (270 keV, 10%) for a medium energy collimator. The sensitivity was constant for circular sources with areas over 10 cm2. The spatial resolution (FWHM) was 1.1 cm for the three energy windows. The quantified activity in the phantom study differed from the true by 8% - 57%.
Conclusions: It is possible to perform quantitative imaging for 223Ra. The imaging parameters for 223Ra are comparable to other radionuclides. The limiting parameter for imaging of 223Ra follwing radionuclide therapy is likely to be low injected activity.
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