Quality Assurance in SPECT/CT for Radionuclide Therapy with Lutetium-177

This study was done to quality assure the Hawkeye SPECT/CT at the St. Olav’s hospital and create a clinical method for doing individual dosimetry with 177Lu-octreotate in targeted radionuclide therapy for neuroendocrine tumors. Various quality control parameters were performed on Infinia Hawkeye SPECT/CT. A calibration dose of 160% ± 2% MBq was ordered and first calibrated for all the dose calibrators. The uniformity test was obtained using a 40 MBq Tc-99m point source positioned 2.5 m away from the two detectors. A 200 MBq Tc-99m was diluted in 70 ml of water, dispersed in six syringes for the registration test. A Lu-177 point source was placed in front of the detectors, one at a time, to check the energy peaks. The Jaczczak phantom with a hollow sphere set (volumes: 0.5, 1, 2, 4, 8, and 16) ml with an additional 60 ml sphere was used for the 3D sensitivity and recovery with Lu-177. Total activity of 945.3 MBq was added to 160 ml of water yielding an activity concentration of 5.908 MBq/ml in the spheres. The phantom was then scanned at various time intervals. A cylindrical phantom with a volume of 6283 ml was also used to obtain the cross-calibration measurement (cps/MBq). Total activity of 995.6 MBq was added and the phantom was scanned at days 0, 6, 13 and 23. The dose calibration factor was changed from 762 to 760 to achieve correct doses. The 2D mean sensitivity factor was 5.56 cps/MBq. Uniformities for both detectors were approved after iteration calibration of the PM tubes. The X-ray to SPECT registration was found to be accurate and within specifications. The energy peak test revealed off-centered 208 keV energy peaks for the two detectors. Quality assurance of imaging devices using radiation is essential for radiation protection and ensures a high-quality image.

Image Quality Assessment Using NEMA Standards for Lu-177 Radionuclide

A lutetium 177 (177Lu) radiopharmaceutical has been used as a theragnostic agent in molecular radiotherapies. This study aimed to produce images simulating those obtained in a total body imaging study with hot lesions to assess and investigate the image quality of the Hawkeye SPECT/CT images from Lu-177. The NEMA image quality phantom (PTW) with spheres (inner diameters of 10, 13, 17, 22, 28 and 37 mm) and lung insert was used. The measured volume in the background of the current phantom setting was 9482 mL. The five smaller spheres were filled with an activity concentration of 0.461 MBq/mL and the biggest sphere was filled with water. The phantom was placed on the couch and scanned at four hot sphere-to-background concentrations, which are no background, 16:1, 8:1 and 4:1. The images obtained from the scans were imported onto the OXIRIS image analysis tool. Regions of interest (ROIs) were drawn on each sphere of the reconstructed SPECT image. Image contrast and background variability ratios for hot spheres were used as measures of image quality. In addition, the accuracy of corrections were determined from the uniform background and cold lung insert regions. The 37 mm cold sphere had the highest percent contrast, whiles the 10 mm hot sphere had the least for the various hot sphere to background ratios. The background variability for each hot sphere was also determined. The average lung residual error was calculated to be 23.13% for the 16:1 and 22.57% for both the 8:1 and 4:1 hot sphere to background ratio. The results show that the scanner has very good overall performance.