Quantitative evaluation on [9°Y] DOTATOC PET and SPECT imaging by phantom acquisitions and clinical applications in locoregional and systemic treatments.

AIM: The aim of this paper was to compare [9°Y]-PET and SPECT imaging quantification for dosimetric applications in targeted radionuclide therapy. METHODS: Imaging studies were carried out by SPECT-CT and PET equipment performing phantom tests first. [9°Y]-SPECT and PET scans were compared in terms of sensitivity, minimum detectable activity concentration, recovery coefficients (RCs) and system spatial resolution (FWHM). Quantitative evaluations by PET and SPECT acquisitions were then assessed in patients who received therapeutic activity of [9°Y]-DOTATOC directly injected into the surgical cavity by locoregional route in glioma treatment and by systemic route in neuroendocrine tumour patients who underwent intravenous infusion. Finally 3D-dose distributions by SPECT and PET images were obtained. RESULTS: Sensitivity was proven to be about fivefold higher for SPECT than for PET. To obtain a good-quality PET imaging, the minimum detectable activity concentration was determined to be equal to 1 MBq/mL compared with 0.05 MBq/mL that was sufficient to assess adequate SPECT imaging. RCs were 100% for volume ≥ 25.5 mL for PET and ≥ 110 mL for SPECT. FWHM was 7 mm for PET and 19 mm for SPECT scans. With regard to locoregional therapy, excellent imaging was obtained with both PET and SPECT. On the contrary, systemic administration did not permit us to obtain suitable PET imaging. PET and SPECT images were affected by considerable noise, whose influence is much more important in the quantitative evaluation of dose volume histograms rather than in the visual interpretation of images. CONCLUSION: [9°Y]-activity quantification is feasible by SPECT and PET imaging. For clinical applications, SPECT-CT is the best technique for visualizing the radiopharmaceuticals following systemic infusion, while both SPECT and PET scans are effective in analyzing locoregional distribution. Nevertheless PET study demonstrates the best spatial definition.