A comparison of simplified protocols of personalized dosimetry in NEN patients treated by radioligand therapy (RLT) with [177Lu]Lu-DOTATATE to favor its use in clinical practice.

The role of internal dosimetry is usually proposed for investigational purposes in patients treated by RLT, even if its application is not yet the standard method in clinical practice. This limited use is partially justified by several concomitant factors that make calculations a complex process. Therefore, simplified dosimetry protocols are required. METHODS: In our study, dosimetric evaluations were performed in thirty patients with NENs who underwent RLT with [177Lu]Lu-DOTATATE. The reference method (M0) calculated the cumulative absorbed dose performing dosimetry after each of the four cycles. Obtained data were employed to assess the feasibility of simplified protocols: defining the dosimetry only after the first cycle (M1) and after the first and last one (M2). RESULTS: The mean differences of the cumulative absorbed doses between M1 and M0 were - 10% for kidney, - 5% for spleen, + 34% for liver, + 13% for red marrow, and + 37% for tumor lesions. Conversely, differences lower than ± 10% were measured between M2 and M0. CONCLUSION: Cumulative absorbed doses obtained with the M2 protocol resembled the doses calculated by M0, while the M1 protocol overestimated the absorbed doses in all organs at risk, except for the spleen.

(90)Y-PET/CT Imaging Quantification for Dosimetry in Peptide Receptor Radionuclide Therapy: Analysis and Corrections of the Impairing Factors.

PURPOSE: We evaluated the possibility to assess (90)Y-PET/CT imaging quantification for dosimetry in (90)Y-peptide receptor radionuclide therapy. METHODS: Tests were performed by Discovery 710 Elite (GE) PET/CT equipment. A body-phantom containing radioactive-coplanar-spheres was filled with (90)Y water solution to reproduce different signal-to-background-activity-ratios (S/N). We studied minimum detectable activity (MDA) concentration, contrast-to-noise ratio (CNR), and full-width-at-half-maximum (FWHM). Subsequently, three recovery coefficients (RC)-based correction approaches were evaluated: maximum-RC, resolution-RC, and isovolume-RC. The analysis of the volume segmentation thresholding method was also assessed to derive a relationship between the true volume of the targets and the threshold to be applied to the PET images. (90)Y-PET/CT imaging quantification was then achieved on some patients and related with preclinical tests. Moreover, the dosimetric evaluation was obtained on the target regions. RESULTS: CNR value was greater than 5 if the MDA was greater than 0.2 MBq/mL with no background activity and 0.5-0.7 MBq/mL with S/N ranging from 3 to 6. FWHM was equal to 7 mm. An exponential fitting of isovolume RCs-based correction technique was adopted for activity quantification. Adaptive segmentation thresholding exponential curves were obtained and applied for target volume identification in three signal-to-background-activity-ratios. The imaging quantification study and dosimetric evaluations in clinical cases was feasible and the results were coherent with those obtained in preclinical tests. CONCLUSIONS: (90)Y-PET/CT imaging quantification is possible both in phantoms and in patients. Absorbed dose evaluations in clinical applications are strongly related to targets activity concentration.

Prognostic value of myocardial ischemia in patients with uncomplicated acute myocardial infarction: direct comparison of stress echocardiography and myocardial perfusion imaging.

UNLABELLED: This study directly compared the prognostic value of predischarge dobutamine stress echocardiography (DSE) and dobutamine myocardial SPECT perfusion imaging in patients with prior myocardial infarction. METHODS: The study population consisted of 146 consecutive patients who underwent predischarge DSE and SPECT with (99m)Tc-sestamibi after a first acute uncomplicated myocardial infarction treated with thrombolysis. Fifty patients who underwent revascularization within 90 d from the imaging studies were excluded. Cardiac death and nonfatal myocardial infarction were considered events. Follow-up was 98% complete in a mean period of 44 +/- 19 mo. RESULTS: Myocardial ischemia was detectable in 55 (58%) patients at SPECT and in 63 (67%) patients at DSE. Concordance between SPECT and DSE in detecting ischemia was observed in 68 (72%) of the 94 patients (kappa value, 0.41). During the follow-up, there were 20 cardiac events (9 deaths and 11 nonfatal myocardial infarctions). Ischemia at SPECT was a significant predictor of events (hazards ratio = 4.8; 95% confidence interval, 1.4-16.3; P < 0.01). However, ischemia at DSE (biphasic or worsening patterns) was not associated with events, whereas biphasic pattern alone was associated with a poor outcome compared with direct worsening (P < 0.05). Finally, at Cox multivariate analysis, ischemia at SPECT but not biphasic pattern at DSE was a significant independent predictor of events (P < 0.01). CONCLUSION: These results indicate that, after uncomplicated myocardial infarction, ischemia at SPECT is associated with an increased risk of cardiac events at long-term follow-up. However, ischemia at DSE was unable to stratify patients after myocardial infarction.