Maria H. Listewnik

Patient-Specific Radiation Dosimetry of 99mTc-HYNIC-Tyr3-Octreotide in Neuroendocrine Tumors

99mTc-hydrazinonicotinamide-Tyr3-octreotide (99mTc-HYNIC-TOC) is increasingly gaining acceptance as a new radiopharmaceutical for the diagnosis of pathologic lesions overexpressing somatostatin receptors. However, little information has been published about the radiation dosimetry of this agent. The aim of this study was to assess the biodistribution and radiation dosimetry of commercially available 99mTc-HYNIC-TOC. A dose calculation procedure designed to be feasible to implement in a busy clinical environment was used. Methods: Twenty-eight patients were imaged for suspected neuroendocrine tumors using a series of whole-body planar, dynamic planar, and SPECT/CT studies, after injection with 99mTc-HYNIC-TOC. Patient-specific dosimetry was performed using the OLINDA/EXM software with time-integrated activity coefficients estimated from a hybrid planar/SPECT technique. A phantom experiment was performed to establish adaptive thresholds for determination of source region volumes and activities. Results: Pathologic uptake, diagnosed as due to neuroendocrine tumors, was observed in 12 patients. Normal organs with significant uptake included the kidneys, liver, and spleen. The mean effective dose after 99mTc-HYNIC-TOC injection was 4.6 ± 1.1 mSv. Average normal-organ doses were 0.030 ± 0.012, 0.021 ± 0.007, and 0.012 ± 0.005 mGy/MBq for the spleen, kidneys, and liver, respectively. The interpatient kidney dose ranged from 0.011 to 0.039 mGy/MBq, whereas the range of tumor doses varied from 0.003 to 0.053 mGy/MBq. The ratio of tumor to kidney dose ranged from 0.13 to 2.9. The optimal thresholds for recovery of true activity in the phantom study were significantly lower than those used for volume determination. Conclusion: The patient-specific 3-dimensional dosimetry protocol used in this study is a clinically feasible technique that has been applied to demonstrate large dose variations in tumors and normal organs between patients imaged with 99mTc-HYNIC-TOC.

Long-term monitoring of radiation exposure of employees in the department of nuclear medicine (Szczecin, Poland) in the years 1991-2007.

Occupational radiation exposure is a hazard that should be avoided or at least minimised. This study aimed to evaluate the radiation exposure of nuclear medicine department employees monitored during the 1991-2007 period, and to investigate the relationship between the annual effective doses of the personnel and the number of radioisotope procedures performed. Overall, 2014 quarterly effective whole-body doses, categorised into six occupational groups, monitored with personal dosemeters, were analysed statistically. There was a wide variation in the average annual doses among the different occupational groups. During the 17 years covered by this study, there was no incidence of a dose exceeding the annual dose limit of 20 mSv. There was a weak correlation between the average annual dose for monitored employees and the number of nuclear medicine procedures performed. Apart from exposure, personal skill in dealing with radioactive substances, compliance with radiation protection rules is an important factor to minimise the effective dose.

Optimization of Low-Dose CT Protocol in Pediatric Nuclear Medicine Imaging

This study was performed to find the optimal low-dose CT protocol for children being imaged on SPECT/CT scanners not equipped with automatic dose control. For SPECT/CT systems with manually adjustable x-ray tube voltage (kV) and anode current (mA), an optimized protocol makes it possible to minimize the dose to patients. Methods: Using the 4-slice low-dose CT component of a commercially available SPECT/CT scanner, we compared the signals reaching the CT detector after radiation passes through objects of different sizes. First, the exit dose rates were measured for combinations of available voltages and currents. Next, imaging parameters were selected on the basis of acceptable levels of exit dose rates, cylindric phantoms of different diameters approximating children of different sizes were scanned using these parameters, and the quality of the CT images was evaluated. Finally, weighted CT dose indexes for abdomen and head CT dose phantoms simulating, respectively, adult and pediatric patients were measured using exactly the same techniques to estimate and compare doses to these 2 groups of patients. Results: For children with torsos smaller than 150 mm, imaging can be performed using the lowest available voltage and current (120 kV and 1 mA, respectively). For children with torsos less than 250 mm, 140 kV and 1.5 mA can be used. For patients with torsos greater than 250 and less than 300 mm, 140 kV and 2 mA can be used. Regarding the signal-to-noise ratio, all these parameters give an excellent signal and fully acceptable noise levels. Conclusion: For the SPECT/CT system studied, even the lowest available voltage and current used for scanning pediatric patients did not cause signal-to-noise degradation, and the use of these settings substantially lowered the dose to the patients.

Multivariate generalized Gaussian function mixture for volume modeling of parathyroid glands

The main contribution of this paper is the proposal of volume modeling of parathyroid gland. Multivariate generalized Gaussian distribution (Multivariate GGD) mixture is assumed. Random walk optimization algorithm is applied for the estimation of parameters. There are 800 synthetic test cases applied for the evaluation of algorithm properties. Example result for real SPECT data are also shown. The essential is the computation time, so GPGPU implementation is proposed for reduction of processing time. Obtained parameters of mixture are required for further analysis of relation to patient data.

Semi-quantitative method for the assessment of focal lesions in parathyroid scintigraphy with relation to histopathology: a prospective study

BBACKGROUND The aim of this paper was to analyse our own semi-quantitative method of assessing focal lesions localised in pre-operative diagnostic scintigraphy of primary hyperparathyroidism (PHPT) using 99mTc-MIBI with washout and comparing these data with the result of the histopathological examination (HP). MATERIAL AND METHODS A total of 40 (37 female, 3 male, average age 58.7 years) patients with a suspicion of PHPT were enrolled for prospective analysis. Dual phase planar and SPECT/CT examination with 99mTc-MIBI were performed. The tumour to background ratios in the 10th and 120th minute were calculated (TBR10 and TBR120) on the basis of the planar acquisition. PTH, ionised calcium and phosphate levels were measured. Parathyroid surgery alone or combined with subtotal/total thyreoidectomy was conducted in 23 (57.5%) and 17 (42.5%) patients, respectively. A HP was performed in all patients. RESULTS Average concentration of PTH in the whole group was 243.95 pg/ml. There was a statistically significant correlation between medians of PTH concentration and parathyroid histopathological results (p = 0.01). A total of 45 lesions of increased uptake were found in 32 (80.0%) and 34 (85%) patients in the early phase and the delayed phase, respectively. The post-operative material contained 20 (44.5%) parathyroid adenomas, 11 (24.5%) cases of hyperplasia, 2 (4.4%) cancers, 4 (8.9%) cases of normal parathyroid tissue, 2 (4.4%) lymph nodes and 6 (13.3%) cases of thyroid gland tissue. The medians of TBR10 and TBR120 for lesions examined in the HP were respectively: 3.64 and 2.59 for adenoma; 3.08 and 2.18 for hyperplasia; 7.7 and 5.5 for parathyroid cancer, 4.89 and 3.16 for normal tissue and 5.26 and 2.95 for lymph nodes or thyroid gland tissue. A high correlation coefficient of TBR10 to TBR120 in the parathyroid adenoma and parathyroid hyperplasia groups was observed with r = 0.867 and r = 0.964, respectively. The ρr correlation coefficient of TBR10 to TBR120 for normal parathyroid was 0.4. There was a statistically significant association between the HP and TBR10 medians (p = 0.047), but not between histopathology and TBR120 medians (p = 0.840). CONCLUSIONS The washout technique in pre-operative 99mTc-MIBI scintigraphy is effective in detecting lesions of the parathyroid (cancer, adenoma, hyperplasia, normal tissue of the parathyroid). Parathyroid cancers in semi-quantitative analysis were characterised by a slightly higher TBR. However, it is impossible to differentiate lesions based on this data. Histopathology results are significantly associated with TBR and PTH.

Prognostic value of myocardial perfusion scintigraphy for patients suspected of and diagnosed with coronary artery disease.

BACKGROUND The prognostic value of myocardial perfusion scintigraphy (MPS) continues to attract interest and provoke discussions.This study was an attempt to investigate the methods. OBJECTIVE Determination of the prognostic value of MPS for patients suspected of and diagnosed with coronary artery disease (CAD). MATERIAL AND METHODS The study group included 215 patients, 134 males and 81 females, aged 21-66, mean age 48. Tc-99m-MIBI myocardial perfusion scintigraphy was performed and information concerning the diagnosis, aim of the examination, past coronary episodes, clinical condition, duration and type of complaints, concomitant diseases, test results, revascularisation procedures and pharmacological treatment was gathered. Further history of the patients was monitored throughout the observation period of 52 months on average. The patients were divided into the following two groups: Group I - suspected coronary artery disease: 124 patients aged 21-65,59 males and 65 females; Group II - diagnosed coronary artery disease: 91 patients aged 31-66, 75 males and 16 females diagnosed with CAD, including 39 s/p myocardial infarct, 31s/p infarct and revascularisation, 21 s/p revascularisation. The probability of CAD was calculated using the Diamond method for the patients suspected of CAD. The obtained results were examined in a statistical analysis. RESULTS Normal MPS results were obtained for 94/124 patients suspected of CAD, 15/91 patients diagnosed with CAD,64/81 females and 45/134 males. In Group I, apart from pathological MPS results, reversible ischemia was determined in as many as 27/30 patients, and only 17/91 patients in Group II. No patients with normal MPS results suffered major cardiac events,only one of them underwent revascularisation. Major cardiac events occurred in the case of patients with pathological MPS results: Group I - 2 myocardial infarcts and 2 cardiac deaths,Group II - 3 infarcts and 10 cardiac deaths. Minor cardiac events, apart from one case, were also only observed in the case of patients with pathological MPS results: Group I - 10 revascularisations and one case of unstable CAD, Group II- 12 revascularisations and 7 cases of unstable CAD. Patients with normal MPS results and stenosis in coronary angioraphy suffered no cardiac events. Cardiac events occur mostly in the group with a medium and high risk of CAD and in the case of patients diagnosed with CAD. CONCLUSIONS 1. Normal MPS results for patients suspected of or diagnosed with CAD: s/p infarct and/or CABG prognosticate a mild course of the disease, without or with a minimal number of cardiac events, also in a longer observation period.2. Pathological MPS results clearly imply a greater risk of cardiac events, and the number of events increases with the greater probability of CAD and with the patients age. 3. Normal MPS results, even with significant stenosis in coronary angiography,prognosticate a low risk of cardiac events.