Nuclear medicine staff exposure to ionising radiation in 18F-FDG PET/CT practice: a preliminary retrospective study.

This retrospective study provides an insight into the levels of radiation exposure of six nuclear medicine (NM) staff (four technologists and two nurses) performing routine diagnostic 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography-computed tomography (PET/CT) at the University Clinical Centre of the Republic of Srpska, Department of Nuclear Medicine and Thyroid Disorders, Banja Luka, Bosnia and Herzegovina. Data analysis included monthly staff exposure measured with personal thermoluminescent dosimeters (TLD) between June and December 2018, quantified in terms of normalised dose for the whole body [Hp(10)] and dominant hand [Hp(0.07)] and their comparison between each staff member and between the two groups (technologists and nurses). The study goal was to establish how our Department compared with reports from other PET/CT centres worldwide in terms of annual number of procedures and exposure limits and whether there could be room for further improvements in radiation protection. The number of procedures rose considerably from 208 in 2016 to 876 in 2019 and was 423 in the observed seven-month period. Mean individual whole-body exposure dose per GBq of injected 18F-FDG activity, [Hp(10)/A] was 18.55 µSv/GBq for the four technologists and 15.61 µSv/GBq for the two nurses. Mean dominant-hand exposure dose per GBq of injected 18F-FDG activity [Hp(0.07)/A] was 16.99 µSv/GBq and 25.44 µSv/GBq for the two groups, respectively. The average annual cumulative dose for all staff was (1.06±0.29) mSv for Hp(10) and (1.15±0.32) mSv for Hp(0.07). These results are comparable with those of similar studies. Staff doses were well below the annual limits. Nurses received slightly higher extremity doses than technologists. In view of the increasing trends in the number of PET/CT procedures, dose monitoring should be continued to identify exposure hotspots and maintain doses as low as possible.

Investigation of factors influencing radioiodine (131I) biokinetics in patients with benign thyroid disease using nonlinear mixed effects approach.

PURPOSE: Radioiodine (131I) therapy is the common treatment option for benign thyroid diseases. The objective of this study was to characterize 131I biokinetics in patients with benign thyroid disease and to investigate and quantify the influence of patients' demographic and clinical characteristics on intra-thyroidal 131I kinetics by developing a population model. METHODS: Population pharmacokinetic analysis was performed using a nonlinear mixed effects approach. Data sets of 345 adult patients with benign thyroid disease, retrospectively collected from patients' medical records, were evaluated in the analysis. The two-compartment model of 131I biokinetics representing the blood compartment and thyroid gland was used as the structural model. RESULTS: Results of the study indicate that the rate constant of the uptake of 131I into the thyroid (ktu) is significantly influenced by clinical diagnosis, age, functional thyroid volume, free thyroxine in plasma (fT4), use of anti-thyroid drugs, and time of discontinuation of therapy before administration of the radioiodine (THDT), while the effective half-life of 131I is affected by the age of the patients. Inclusion of the covariates in the base model resulted in a decrease of the between subject variability for ktu from 91 (3.9) to 53.9 (4.5)%. CONCLUSIONS: This is the first population model that accounts for the influence of fT4 and THDT on radioiodine kinetics. The model could be used for further investigations into the correlation between thyroidal exposure to 131I and the outcome of radioiodine therapy of benign thyroid disease as well as the development of dosing recommendations.

99m Tc-sestamibi scintimammography in detection of recurrent breast cancer.

The aim of this study was to asses the accuracy of 99mTc-sestamibi scintimammography in patients with suspected recurrent breast cancer in the breast or loco regional tissues. After routine analyses in twenty-eight women (clinical examination, ultrasound, X-ray mammography, and fine needle aspiration biopsy) they were examined by scintimammography. All patients with suspected recurrent cancer in the breast or loco regional tissues (19) undergone surgery and the final diagnosis was determined by histopathological examination. Another 9 patients were followed 6-24 months. The scintigraphic studies were correlated with radiological findings and/or with histopathology. There were 19 patients with recurrent tumours (15 with loco-regional recurrent and 4 in another breast). X-ray mammography identified 13 of these cancers. 99mTc-sestamibi scintimammography identified seventeen of recurrent breast cancers. In the seven out of nine patients without cancer, scintimammography were reported as having no changes consistent with cancer. X-ray mammography showed suspected cancer lesions in four out of nine patients without cancer. There were two false-positive scintimammograms and one false negative. Axillary lymph node recurrence occurred in four patients. All of them were positive on scintimammography. 99mTc-sestamibi scintimammography showed higher sensitivity, specificity and accuracy per patient than did X-ray mammography (90,9% vs. 63,6%, 71,4% vs. 57,1% and 83,3% vs. 61,1%, respectively). To identifying recurrent breast cancer disease is better to use scintimammography than X-ray mammography.