PT - JOURNAL ARTICLE AU - Nadia Benabdallah AU - William Scheve AU - Nicholas Dunn AU - Delynn Silvestros AU - Paul Schelker AU - Diane Abou AU - Richard Laforest AU - Farrokh Dehdashti AU - Daniel Thorek TI - Practical Considerations for Quantitative Clinical SPECT/CT Imaging of Alpha Particle Emitting Radioisotopes DP - 2020 May 01 TA - Journal of Nuclear Medicine PG - 532--532 VI - 61 IP - supplement 1 4099 - http://jnm.snmjournals.org/content/61/supplement_1/532.short 4100 - http://jnm.snmjournals.org/content/61/supplement_1/532.full SO - J Nucl Med2020 May 01; 61 AB - 532Objectives: There is great scientific and clinical interest in alpha particle emitting radiotherapies because of their potent antineoplastic effects and normal-tissue sparing properties. Currently, Radium-223 (223Ra) dichloride citrate (Xofigo) is the only alpha particle-emitting radiopharmaceutical approved for clinical use, for the treatment of patients with bone metastatic castration-resistant prostate cancer. Many other alpha particle-emitting therapies are undergoing clinical translation, primarily utilizing conjugates of Actinium-225 (225Ac) and Thorium-227 (227Th). These therapies have substantial potential to improve patient outcomes, however off-target accumulation of these cytotoxic agents is a concern. To evaluate their effectiveness, quantitative imaging is crucial for detecting and quantifying the radiopharmaceutical distribution and uptake. Major challenges towards this goal are the low photon abundance of these isotopes, and their low administered activities. The goal of this study was to establish a quantitative SPECT imaging protocol with clinically achievable conditions and to investigate its limitations for 223Ra, 225Ac, and 227Th. Materials & Methods: Radiochemical purification of 223Ra, 225Ac, and 227Th was performed to yield the needed activity for imaging (20-50 µCi). To compare hardware dependent characteristics, acquisition protocols were performed on three different gamma-cameras: a Discovery 670 Pro (GE Healthcare), an Optima 640 (GE Healthcare) and a Symbia T (Siemens Medical Solutions). Each gamma-camera was equipped with a MEGP (medium energy general purpose) or HEGP (high energy GP) collimator. For each isotope (223Ra, 225Ac, and 227Th), a set of phantoms (a vial, Triple Line and NEMA IEC phantom and a laboratory-made phantom) were used to obtain the necessary acquisition and calibration parameters and to compare the performance of each gamma-camera. We performed SPECT/CT acquisitions of each phantom with clinically achievable conditions such as keeping the acquisition times to a patient-tolerable time of 45min maximum. Results & Discussion: The acquisition parameters such as the collimator and windows setting were assessed for each isotope on the Discovery 670 Pro gamma-camera and implemented on the other gamma-cameras. The reconstruction parameters (iterations number and filter for the reconstruction algorithm, attenuation and scatter correction) were determined by measuring the sensitivity and the spatial resolution using vials and a Triple Line phantom separately filled with each isotope on the GE the Siemens reconstruction software. More complex phantoms were used to calibrate the gamma cameras and investigate the quantitative accuracy and the limits of detection of the implemented SPECT/CT imaging protocols. The calibration parameters and spatial limitations on each gamma-camera were assessed with a NEMA IEC phantom whose different diameter spheres contained the same concentration of each isotope. The limits of detection on each system were determined with a laboratory-made phantom, which contained six identical tubes with different concentration of each isotope. Conclusions: The increasing clinical interest and utilization of systemically administered alpha particle therapies for disseminated disease brings with it new challenges to better measure activity distribution. This is critical to both visualize and quantify uptake at metastatic foci, and be able to safely use these novel agents by understanding their distribution to radiosensitive normal tissues. This work provides an empirical framework imaging radionuclides of interest at patient-relevant activities across multiple, commonly implemented, SPECT/CT systems.