Evaluation of a Correction Method for 111In-Pentetreotide SPECT Imaging of Gastroenteropancreatic Neuroendocrine Tumors.

The number of patients with the extremely rare disease gastroenteropancreatic (GEP) neuroendocrine tumor (NET) has increased rapidly in recent years. 111In-pentetreotide SPECT in somatostatin receptor scintigraphy has been used for the assessment of GEP NET patients. To diagnose GEP NET, appropriate selection of image correction parameters is critical. Correction methods may improve the 111In-pentetreotide SPECT image quality, but there is currently no standard technique. The purpose of this study was to determine the optimal correction parameter settings for 111In-pentetreotide SPECT. Methods: A phantom study produced images with a tumor-to-background ratio of as high as 16:1. A triple energy window was used for scatter correction (SC), and attenuation correction (AC) was CT-based. Correlation analysis was performed in 4 groups: no correction (NC), SC, AC, and combined SC with AC (CC). The 111In-pentetreotide SPECT results for 20 randomly selected patients (13 men and 7 women; age range, 37-81 y) with confirmed GEP NET were analyzed using data collected 4 h after injection of 111 MBq of 111In-pentetreotide. Emission data were reconstructed using ordered-subset expectation maximization (OSEM) with different settings. Different combinations of the correction parameters were used to analyze the contrast-to-noise ratios (CNRs) obtained with the phantom. In the clinical study, 20 GEP NET patients were used to evaluate the GEP NET lesion CNR by 4 different image correction methods obtained from 111In-pentetreotide SPECT images: NC, SC, AC, and CC. NC was used as a reference method. Results: The phantom study revealed that the optimal energy window in the photopeak for somatostatin receptor scintigraphy was 171 keV ± 10% and 245 keV ± 7.5%, and the optimal OSEM reconstruction conditions were 8 subsets and 6 iterations. Among the OSEM collection conditions, CC produced a significantly higher CNR than NC or SC (P < 0.05). In the clinical study, CC was found to increase the CNR (P < 0.05). Conclusion: CC improves the correction in 111In-pentetreotide SPECT studies, compared with NC, providing better contrast and sharper outlines of lesions and organs.

The Impact of Gadolinium-based Contrast Agent for Carbon Ion Radiotherapy.

PURPOSE: The contrast agent used in the diagnostic department has high atomic numbers and might influence dose deposition in the particle therapy. In particular, the influence of gadolinium-based (Gd) contrast agent on range in carbon ion radiotherapy has not yet been evaluated. For this reason, we avoid carbon treatment and planning computed tomography (CT) acquisition on days when the contrast-enhanced magnetic resonance image (MRI) is performed. In this study, we evaluated the time required for this beam range effect to vanish by evaluating the temporal changes in the CT values after an enhanced MRI as well as the stopping power of Gd solution. MATERIALS AND METHODS: Two types of diluted solutions with Gd contrast agent were used for comparing their transferred stopping power (TSP) and measured stopping power (MSP). The TSP was calculated with a CT value to stopping power ratio table that was created previously. Additionally, to evaluate in vivo attenuation, we measured the CT values in the renal pelvis from the CT images with and without contrast agent for 73 patients. RESULTS: The maximum difference between the TSP and MSP was 85%. The difference between the TSP after 4 hours and the TSP with non-enhanced cases was less than 1%. Moreover, the difference between the MSP after 1 hour and the MSP with non-enhanced cases was less than 0.1%. CONCLUSION: It was found that the impact of Gd contrast agent can be neglected 1 hour after administration for carbon beam irradiation and 4 hours after for planning the CT image acquisition.