n.202 – TECHNICAL CONSIDERATIONS PRECEDING THE SETUP OF AN ACQUISITION PROTOCOL FOR IN VIVO IMAGING OF 223RA-DICHLORIDE

BACKGROUND-AIM
The aim of this study is to obtain scintigraphic images from Ra-223’s distribution through a common Anger camera despite its decay is characterized by a multiple gamma emissions with different peaks amounted to only 1.1%.
METHODS
Two gamma cameras available in our department were evaluated for imaging: Infinia II Hawkeye (GE Healthcare, Milwaukee, WI, US) and Discovery 670 NM/CT (GE Healthcare, Waukesha, WI, US), differing in crystal thickness and available collimators. Theoretical and practical assessments of the response of the two gamma cameras were performed. We compared the energy spectrum detected by each gamma-camera using a Radium-223-dichloride vial as source and all available collimators. We also acquired an anterior and posterior static scintigraphy of the same Radium-223 source. Then we performed a scintigraphy of the same source placed inside a scattering phantom to investigate for scatter contribution. Results were evaluated by our Health Physicist to choose useful energy peaks and best crystal thickness/collimator combination. Finally, imaging protocol was applied for in vivo imaging of Radium-223-dichloride distribution.
RESULTS
Given the results of previous evaluations we decided to set up an acquisition protocol using Discovery 670 NM/CT, equipped with 3/8’ NaI(Tl) crystals and MEGP collimator. Better results were obtained by using an energy session with three peaks with lower energy (84, 154, 270 keV) with an energy window of 10%, matrix 128×128 and zoom 1. In order to simplify further evaluations we chose to keep the same distance between the two Anger cameras (radial distance 20cm). Imaging of in-vivo Radium-223-dichloride distribution shows activity in the areas affected by skeletal metastases, in agreement with previously performed bone scintigraphy. However physiological Ra-223-dichloride uptake within the bowel could compromise image quality.
CONCLUSION
Despite the expected technical difficulties it is possible to obtain quantitative images of the distribution of Radium-223 using a standard gamma camera. Since the early results are encouraging further evaluations are necessary to optimize the timing and duration of the acquisitions.

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