Search

The article in the EJNMMI Research journal discusses the first-in-human experience with a GRPR antagonist, [68Ga]Ga-NOTA-PEG2-RM26, in prostate and breast cancer patients using PET/CT imaging. The study involved twelve participants with advanced-stage cancer, and the radiotracer was found to be safe and well-tolerated. The biodistribution of the tracer showed high uptake in the pancreas and kidneys, with excretion primarily through urine. The study concludes that [68Ga]Ga-NOTA-PEG2-RM26 is safe for use in molecular oncologic imaging, paving the way for further clinical investigations. [Extracted from the article]

Background: System calibration is essential for accurate SPECT/CT dosimetry. However, count losses due to dead time and pulse pileup may cause calibration errors, in particular for 131I, where high count rates may be encountered. Calibration at low count rates should also be avoided to minimise detrimental effects from e.g. background counts and statistical fluctuations. This paper aims to present experimental data illustrating count-rate dependencies and to propose practical routines to mitigate errors in the 131I calibration procedure without needing advanced analysis tools. Results: The sensitivities of two General Electric (GE) Discovery 670 Pro systems were assessed using two Jaszczak phantom geometries. SPECT/CT data were collected over two months, starting with an initial 131I content of > 2 GBq, decaying to approximately 20 MBq. This allowed for a detailed analysis of count losses due to dead time and pulse pileup. From the sensitivity analysis, it was shown that robust calibration was obtained for 131I phantom activities ranging between 250 and 1500 MBq. Conclusions: The results show that adequate corrections for dead-time and pulse-pileup counting losses are essential for accurate calibration. It is argued that loss corrections should be based on total spectrum count rates in projections and not only on the 364.5 keV energy window data. The measurement campaigns presented in this paper, using basic tools and equipment, may serve as a model for establishing routines for count-loss corrections as well as for system calibration and regular control of system sensitivity. The data suggest that analysis of source and count concentration in a homogeneous Jaszczak phantom offers robust calibration, whereas analysis of source strength and counts in a delineated phantom insert offers a practical and robust method for regular quality control. [ABSTRACT FROM AUTHOR]

Background: The aim was to investigate to what extent the quantification of myocardial blood flow (MBF) from dynamic 13N‐NH3 positron emission tomography (PET) images is affected by time frame schemes, time‐of‐flight (ToF), reconstruction algorithms, blood pool volume of interest (VOI) locations and compartment models in patients with suspected chronic coronary syndrome. Methods: A standard MBF value was determined from 25 patients' rest/stress 13N‐NH3 PET/CT images reconstructed with ordered subset expectation maximization (OSEM), 5 s time frame for the first frames without ToF, subsequently analyzed using a basal VOI and the deGrado compartment model. MBFs calculated using 2 or 10 s for the first frames, ToF, block‐sequential regularized expectation maximization (BSREM), apical or large VOI, Hutchins or Krivokapich compartment models were compared to MBFstandard in Bland–Altman plots (bias ± SD). Results: Good agreement in global rest/stress MBF (mL/min/g) was found when changing the time frame scheme or reconstruction algorithm (MBFstandard vs. MBF2s: −0.02 ± 0.06; MBF10s: 0.01 ± 0.07; MBFBSREM: 0.01 ± 0.07), while a lower level of agreement was found when altering the other factors (MBFstandard vs. MBFToF: −0.07 ± 0.10; MBFapical VOI: −0.27 ± 0.25; MBFlarge VOI: −0.11 ± 0.10; MBFHutchins: −0.08 ± 0.10; MBFKrivokapich: −0.47 ± 0.50). Conclusions: Quantification of MBF from 13N‐NH3 PET images is more affected by choice of compartment models, ToF and blood pool VOIs than by different time frame schemes and reconstruction algorithms. [ABSTRACT FROM AUTHOR]

Diagnosis and treatment of patients with suspected chronic coronary syndrome (CCS) currently relies on the degree of coronary artery stenosis and its significance for myocardial perfusion. However, myocardial perfusion can be affected by factors other than coronary stenosis. The aim of this study was to investigate to what extent sex, age, diabetes, hypertension and smoking affect quantitative myocardial perfusion, beyond the degree of coronary artery stenosis, in patients with suspected or established CCS. Eighty‐six patients [median age 69 (range 46−86) years, 24 females] planned for elective coronary angiography due to suspected or established CCS were included. All patients underwent cardiac 13N‐NH3 positron emission tomography to quantify myocardial perfusion at rest and stress. Lowest myocardial perfusion (perfusionmin) at stress and rest and lowest myocardial perfusion reserve (MPRmin) for all vessel territories was used as dependent variables in a linear mixed model. Independent variables were vessel territory, degree of coronary artery stenosis (as a continuous variable of 0%−100% stenosis), sex, age, diabetes, hypertension and smoking habits. Degree of coronary artery stenosis (p < 0.001), male sex (1.8 ± 0.6 vs. 2.3 ± 0.6 mL/min/g, p < 0.001), increasing age (p = 0.025), diabetes (1.6 ± 0.5 vs. 2.0 ± 0.6 mL/min/g, p = 0.023) and smoking (1.9 ± 0.6 vs. 2.1 ± 0.6 mL/min/g, p = 0.052) were independently associated with myocardial perfusionmin at stress. Degree of coronary artery stenosis (p < 0.001), age (p = 0.040), diabetes (1.8 ± 0.6 vs. 2.3 ± 0.7, p = 0.046) and hypertension (2.2 ± 0.7 vs. 2.5 ± 0.6, p = 0.033) were independently associated with MPRmin. Sex, increasing age, diabetes, hypertension and smoking affect myocardial perfusion independent of coronary artery stenosis in patients with suspected or established CCS. Thus, these factors need to be considered when assessing the significance of reduced quantitative myocardial perfusion of patients with suspected or established CCS. [ABSTRACT FROM AUTHOR]

Background: Somatostatin receptor 68Ga PET imaging is standard for evaluation of a patient's suitability for 177Lu peptide receptor radionuclide therapy of neuroendocrine tumours (NETs). The 68Ga PET serves to ensure sufficient somatostatin receptor expression, commonly evaluated qualitatively. The aim of this study is to investigate the quantitative relationships between uptake in 68Ga PET and absorbed doses in 177Lu therapy. Method: Eighteen patients underwent [68Ga]Ga-DOTA-TATE PET imaging within 20 weeks prior to their first cycle of [177Lu]Lu-DOTA-TATE. Absorbed doses for therapy were estimated for tumours, kidney, spleen, and normal liver parenchyma using a hybrid SPECT/CT–planar method. Gallium-68 activity concentrations were retrieved from PET images and also used to calculate SUVs and normalized SUVs, using blood and tissue for normalization. The 68Ga activity concentrations per injected activity, SUVs, and normalized SUVs were compared with 177Lu activity concentrations 1 d post-injection and 177Lu absorbed doses. For tumours, for which there was a variable number per patient, both inter- and intra-patient correlations were analysed. Furthermore, the prediction of 177Lu tumour absorbed doses based on a combination of tumour-specific 68Ga activity concentrations and group-based estimates of the effective half-lives for grade 1 and 2 NETs was explored. Results: For normal organs, only spleen showed a significant correlation between the 68Ga activity concentration and 177Lu absorbed dose (r = 0.6). For tumours, significant, but moderate, correlations were obtained, with respect to both inter-patient (r = 0.7) and intra-patient (r = 0.45) analyses. The correlations to absorbed doses did not improve when using 68Ga SUVs or normalized SUVs. The relationship between activity uptakes for 68Ga PET and 177Lu SPECT was stronger, with correlation coefficients r = 0.8 for both inter- and intra-patient analyses. The 177Lu absorbed dose to tumour could be predicted from the 68Ga activity concentrations with a 95% coverage interval of − 65% to 248%. Conclusions: On a group level, a high uptake of [68Ga]Ga-DOTA-TATE is associated with high absorbed doses at 177Lu-DOTA-TATE therapy, but the relationship has a limited potential with respect to individual absorbed dose planning. Using SUV or SUV normalized to reference tissues do not improve correlations compared with using activity concentration per injected activity. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate if satisfactory post-therapeutic image-based dosimetry can be achieved for Lu-177-DOTATATE treatments using a reduced number of image acquisitions to improve patient comfort and reduce economical costs. Methods: 39 patients who underwent 147 treatment cycles of Lu-177-DOTATATE for neuroendocrine tumors were included in the study. A total of 291 and 284 absorbed doses were calculated to kidneys and tumors, respectively. Single-point dosimetry was performed using one SPECT/CT image acquired at 1 d or 7 d post-treatment using a fixed effective half-life (Teff) or using a patient-specific Teff determined for the initial cycle. Also, dose-per-activity values, (D/A)1, were determined from the first cycle and used to calculate doses for subsequent cycles. All absorbed doses were evaluated against "true" doses calculated using both the 1 d and 7 d images. The relation between tumor grade and absorbed doses was also investigated. All dosimetry was performed on SPECT images. Results: Absorbed doses to kidneys were most accurate when single-point dosimetry was performed using 1 d images with median ratios in relation to "true" doses in total dose of 1.00 (IQR: 0.97–1.03) when using fixed Teff and 1.01 (IQR: 0.98–1.04) when using Teff from the initial cycle. Calculations based on the 7 d image were most accurate for tumors with corresponding ratios in total absorbed dose of 0.98 (IQR: 0.96–1.00) and 1.00 (IQR: 0.99–1.01) when using a fixed Teff or Teff from the first cycle, respectively. The (D/A)1 approach performed worse, as 2 of 77 total absorbed doses to the kidneys deviated with > 30%, and tumor-absorbed doses were increasingly overestimated with every cycle. Absorbed doses, Teff and 1 d uptake were higher for G1 tumors than G2 tumors. Conclusion: Dosimetry can be performed with satisfactory accuracy when using single SPECT/CT images acquired at 1 d for kidneys or at 7 d for tumors. [ABSTRACT FROM AUTHOR]