Fifty-seventh annual meeting of the American association of physicists in medicine
SU-E-T-588: Optimization of Imaging Following 223Ra Administration in Targeted Alpha-Emitting Radionuclide Therapy of Bone Metastases
With a growing demand of alpha-emitting radiopharmaceuticals, especially Xofigo (223RaCl2) which is used in the treatment of metastatic bone disease, the optimization of dosimetry becomes necessary. Indeed, in Europe, as stated on the council directive 2013/59/euratom, exposures of target volumes for radiotherapeutic purposes shall be individually planned taking into account that doses to non-target volumes and tissues shall be as low as reasonably achievable. To that aim, the possibility of imaging 223Ra was first investigated.
The experiments were conducted at the Hopital Europeen Georges Pompidou with an Infinia Hawkeye 4 gamma camera, equipped with a medium-energy collimator. Imaging parameters, such as sensibility, spatial resolution and energy spectrum, were determined using several physical phantoms with a source of 6 MBq of 223Ra. Bone metastases were modeled with a NEMA Body Phantom to investigate image degradation based on the concentration of 223Ra.
The acquired energy spectrum allowed to visualize several photon peaks: at 85, 154 and 270 keV. Camera sensitivity measured from the phantom study was 102.3 cps/MBq for the 85 keV ± 20 %, 89.9 cps/MBq for the 154 ± 20 % window and 65.4 cps/MBq for the 270 ± 10 % window. The spatial resolution (full-width at half-maximum) was respectively 1.7, 1.9 and 1.8 cm for the three energy windows. SPECT/CT images of NEMA Body Phantom without and with attenuation have permitted to determine the best reconstruction parameters.
This study has demonstrated that it is possible to obtain clinically relevant information from images of 223Ra. All these results will be valuable to analyze biodistribution imaging of the radiopharmaceutical in the patient body and go further in the reconstruction of patient images in order to personalize the dosimetry.