Physiologically based pharmacokinetic [PBPK] model for biodistribution of radiolabeled peptides in patients with neuroendocrine tumours

Objective[s]: The objectives of this work was to assess the benefits of the application of Physiologically Based Pharmacokinetic [PBPK] models in patients with different neuroendocrine tumours[NET] who were treated with Lu-177 DOTATATE. The model utilises clinical data on biodistribution of radiolabeled peptides [RLPs] obtained by whole body scintigraphy [WBS] of the patients

Methods: The blood flow restricted [perfusion rate limited] type of the PBPK model for biodistribution of radiolabeled peptides [RLPs] in individual human organs is based on the multi-compartment approach, which takes into account the main physiological processes in the organism: absorption, distribution, metabolism and excretion [ADME]. The approach calibrates the PBPK model for each patient in order to increase the accuracy of the dose estimation. Datasets obtained using WBS in four patients have been used to obtain the unknown model parameters. The scintigraphic data were acquired using a double head gamma camera in patients with different neuroendocrine tumours who were treated with Lu-177 DOTATATE. The activity administered to each patient was 7400 MBq

Results: Satisfactory agreement of the model predictions with the data obtained from the WBS for each patient has been achieved

Conclusion: The study indicates that the PBPK model can be used for more accurate calculation of biodistribution and absorbed doses in patients. This approach is the first attempt of utilizing scintigraphic data in PBPK models, which was obtained during Lu-177 peptide therapy of patients with NET

Using digitally reconstructed radiographs from MRI (MRI-DRR) to localize pelvic lymph nodes on 2D X-ray simulator-based brachytherapy treatment planning

Purpose: In this work we present a handheld, solid-state detector based gamma camera system. We validated the camera physically and demonstrated the usefulness of the device for intra-operative detection of radiolabeled tissue. Methods: We measured the intrinsic uniformity, the intrinsic energy resolution, the system uniformity, the spatial resolution without scatter, the system planar uniformity, the detector shielding and the peak deviation according to the NEMA NU1-2001 standard. Results: The gamma camera can be used for isotopes with an energy range between 50-250 keV. A standard laptop is used to control of the camera and to visualize Preliminary clinical data show that the devices can be used successfully for a number of clinical applications. Conclusion: The performance evaluation of a novel handheld gamma camera shows good spatial resolution, sensitivity and energy resolution. Due to the small size and weight the portable device can be used for untraoperative acquisitions

new approach to scatter correction in SPECT images based on Klein_Nishina equation

Scattered photon is one of the main defects that degrade the quality and quantitative accuracy of nuclear medicine images. Accurate estimation of scatter in projection data of SPECT is computationally extremely demanding for activity distribution in uniform and non-uniform dense media. The objective of this paper is to develop and validate a scatter correction technique that use an accurate analytical model based on Klein_Nishina scatter equation and compare Klein_Nishina scatter estimation with triple energy window. In order to verify the proposed scattering model several cylindrical phantoms were simulated. The linear source in the cylindrical Phantoms was a hot rod filled with 99mTc. K factor defines as the ratio of scatter resulting from MC simulation to scatter estimated from Klein_Nishina formula. Also a SPECT/CT scan of the image quality phantom was acquired. Row data were transferred to a PC computer for scatter estimation and processing of the images using MLEM iterative algorithm in MATLAB software. The scatter and attenuation compensated images by the proposed model had better contrast than uncorrected and only attenuation corrected images. The K-factors that used in proposed model doesn't vary with different activities and diameters of linear source and they're just a function of depth and composition of pixels. Based on Mont Carlo simulation data, the K_N formula that used in this study demonstrates better estimation of scattered photons than TEW. Proposed scattered correction algorithm will improve 52.3% in the contrast of the attenuated corrected images of image quality phantom

Improved quantification of salivary gland scintigraphy by means of factor analysis

In this study the automatic separation of oral and salivary gland activity and spontaneous secretion by means of factor analysis for quantitative salivary gland scintigraphy is introduced. After intravenous administration of 99mTc sodium pertechnetate, dynamic scintigraphy was performed. 20 minutes after tracer application 2 ml of lemon juice was delivered to stimulate the glands. Applying elliptical regions of interest for oral cavity and four major salivary glands and using factor analysis of medical image sequences [FAMIS] results in factor images and curves, which are used for quantification of the oral, sublingual and glandular activity indexes. With FAMIS it is possible to automatically separate the three superimposed processes seen in salivary gland scintigraphy: glandular and oral activity and spontaneous secretion that results in significant different quantitative results. The application of factor analysis improves the results of salivary gland scintigraphy by separation of superimposed dynamic processes of oral and glandular activity and spontaneous secretion

Coronary artery calcium [CAC] score - a prognostic tool in coronary artery disease?

The aim of this study was to evaluate the impact of measurement of coronary artery calcification score [CAC] in patients with suspected coronary artery disease [CAD] and a normal myocardial perfusion scan. In a prospective study we measured the calcium score of 74 patients [29 m, 45 f, mean age 58.7 [m] and 64.4 [f]] with suspicion of CAD and a normal perfusion scan. In all patients a pharmacological stress scintigraphy and calcium scoring were performed on a T6 Symbia gamma camera [Siemens, Knoxville, USA]. Attnuation correction was performed using a low dose CT. the mean total CAC score was 182.6 +/- 435.7 and ranged from 0-2309. 21/29 of the male patients [72%] and 17/45 of the female patients [38%] had an Agatst on score of >10. There were 9 cases [5m, 4f] with a calcium score of >400 and 3 cases [2m, 1f] with a calcium score >1000. No cardiac event was noted in these cardiac death of a patient with total Agatston score of 278. Seven patients also underwent angiography because of their clinical symptoms, 4 of which [57%] had an elevated Agatston score. Our study showed that calcium score measurement accompanied with SPECT imaging is feasible in routine myocardial perfusion imaging with SPECT/CT machines. Calcium score measurement in patients with normal stress myocardial perfusion scintigraphy, may be useful in risk stratification of the patients. Further prospective studies with larger patient numbers and longer follow-up time are needed to find out the impact of this advantage by hybrid imaging