Pentetreotide

Early cancer detection is crucial for patients' survival. The image quality in ¹¹¹In-octreotide SPECT imaging could be improved by using Monte Carlo (MC)-based reconstruction. The aim of this observational study was to determine the detection rate of simulated liver lesions for MC-based ordered subset expectation maximization (OSEM) reconstruction compared to conventional attenuation-corrected OSEM reconstruction.

Thirty-seven SPECT/CT examinations with ¹¹¹In-octreotide were randomly selected. The inclusion criterion was no liver lesions at the time of examination and for the following 3 years. SPECT images of spheres representing lesions were simulated using MC. The raw data of the spheres were added to the raw data of the established healthy patients in 26 of the examinations, and the remaining 11 examinations were not modified. The images were reconstructed using conventional OSEM reconstruction with attenuation correction and post filtering (fAC OSEM) and MC-based OSEM reconstruction without and with post filtering (MC OSEM and fMC OSEM, respectively). The images were visually and blindly evaluated by a nuclear medicine specialist. The criteria evaluated were liver lesion yes or no, including coordinates if yes, with confidence level 1-3. The percentage of detected lesions and accuracy (percentage of correctly classified cases), as well as tumor-to-normal tissue concentration (TNC) ratios and signal-to-noise ratios (SNRs), were evaluated.

The detection rates were 30.8% for fAC OSEM, 42.3% for fMC OSEM, and 50.0% for MC OSEM. The accuracies were 45.9% for fAC OSEM, 45.9% for fMC OSEM, and 54.1% for MC OSEM. The number of false positives was higher for fMC and MC OSEM. The observer's confidence level was higher in filtered images than in unfiltered images. TNC ratios were significantly higher, statistically, with MC OSEM and fMC OSEM than with AC OSEM, but SNRs were similar due to higher noise with MC OSEM.

One in two lesions were found using MC OSEM versus one in three using conventional reconstruction. TNC ratios were significantly improved, statistically, using MC-based reconstruction, but the noise levels increased and consequently the confidence level of the observer decreased. For further improvements, image noise needs to be suppressed.

The interactions between the administration of cold somatostatin analogs (cSAs) and their radiolabeled counterpart remain unclear, and discontinuation before imaging is still advised as a precaution. The aim of this systematic review is to evaluate the consequences of cSA administration on tumoral and surrounding healthy organs' uptake at somatostatin receptor (SSTR) imaging with SPECT or PET.

After registration of the study on Prospero (CRD42022360260), an electronic search of PubMed and Scopus databases was performed. Inclusion criteria were as follows: human patients referred for SSTR imaging for oncological purposes; at least 1 examination performed either before cSA administration or after a long-enough withdrawal of cSA treatment; at least 1 examination was performed under cSA treatment. Included articles were independently appraised by 2 authors using the standardized protocol provided by the Quality Assessment of Diagnostic Accuracy Studies. Discrepancies were solved by consensus.

A total of 12 articles were included, 4 using 111In-pentetreotide and 8 using 68Ga-DOTA peptides. Administration of cSAs consistently resulted in decreased spleen and liver uptake (from 6.9% to 80% for spleen, 10% to 60% for liver) and increased tumor-to-background or tumor-to-healthy organ ratios. After cSA treatment, tumor uptake alone was unchanged or moderately decreased. Similar results were noted whether patient was octreotide-naive.

Impairment in SSTR imaging quality after cSA administration has not been demonstrated. On the contrary, the administration of cSAs seems to improve the contrast between tumoral lesions and the surroundings.