The use of molecular sieves to simulate hot lesions in (18)F-fluorodeoxyglucose--positron emission tomography imaging.

We investigated the use of a kind of zeolite, the Bowie chabazite, to produce radioactive sources of different shapes, dimensions and activity concentrations that can be used for lesion simulation in positron emission tomography (PET) imaging. The (18)F-fluorodeoxyglucose ((18)F-FDG) uptake of a group of 12 zeolites was studied as a function of their weight (120-1,520 mg) and of the activity concentration of the (18)F-FDG solution (1-37 MBq ml(-1)), using a multiple linear regression model. The reproducibility, homogeneity and stability over time of the (18)F-FDG uptake were assessed. The fit of the regression model is good (r(2) = 0.83). This relation allows the production of zeolites of a desired (18)F-FDG activity using knowledge of the concentration of the soaking solution and the weight of the zeolite. The reproducibility of the (18)F-FDG uptake after heating the zeolites is elevated (CV% = 3.68). The almost complete regeneration of the zeolites allows us to reuse them in successive experiments. The stability of the (18)F-FDG uptake on zeolites is far from ideal. When placed in a saline solution the 'activated' zeolites release the (18)F-FDG with an effective half-time of 53 min. The sealing of the zeolites in plastic film bags has been demonstrated to be effective in preventing any release of (18)F-FDG. These features, together with their variable dimensions and shapes, make them ideal (18)F-FDG sources with a fixed target-to-background ratio that can be placed anywhere in a phantom to study lesion detectability in PET imaging.

Permeability of gloves used in nuclear medicine departments to [(99m)Tc]-pertechnetate and [(18)F]-fluorodeoxyglucose: radiation protection considerations.

In order to evaluate the safety of the individual protection devices, the permeability of four different types of disposable gloves, commonly used in hospitals, was tested in relation to [(99m)Tc]-pertechnetate and to [(18)F]-fluorodeoxyglucose ([(18)F]-FDG). From these radiopharmaceutical solutions, a drop was deposited on the external surface of the glove which was opened and stretched with the external surface placed upward. The smear test technique permitted to evaluate the activity onto the inner surface of the glove at different times. The smear tests were measured in a well sodium iodide detector calibrated in efficiency for (99m)Tc and (18)F. The permeability was tested on ten samples of each type of gloves and was expressed as the ratio of the activity onto the inner surface at each time interval to the activity deposited on the external surface of the glove. For each type of gloves and for each sampling time, mean value, standard deviation and percentage coefficient of variation of permeability were evaluated. One type of gloves showed a low resistance to permeation of both radiopharmaceuticals, while another one only to pertechnetate. The other gloves were good performers. The results of this study suggest to test permeability for gloves used for handling radiopharmaceuticals, before their adoption in the clinical routine. This practice will provide a more careful service of radiation protection for nuclear medicine department staff.

Characterization of the [(153)Sm]Sm-EDTMP pharmacokinetics and estimation of radiation absorbed dose on an individual basis.

[(153)Sm]Sm-EDTMP is a radiopharmaceutical used in palliation cares of bone metastases. The purpose of this study is to provide an explicit description of [(153)Sm]Sm-EDTMP pharmacokinetics, adopting a simple three-compartmental model with the analytical expressions calculating the rate constants and determining biodistribution parameters, like radiopharmaceutical uptake and clearance. This biokinetic model allowed us to calculate on an individual basis the dose to bone surface and to red bone marrow and to assess the degree of variability in dosimetric parameters using a fixed administered activity based only on patient weight. In this study twenty patients were enrolled and were treated with [(153)Sm]Sm-EDTMP, administering a fixed activity per kilogram (37 MBq/kg); blood and urine samples were collected during 24 h post treatment. The median value of the administered activity was 2.7 GBq. Blood clearance confirmed that an aliquot of [(153)Sm]Sm-EDTMP rapidly localizes and is retained in bone, while the remainder is rapidly cleared from the blood pool by the urinary system. Our data show a bi-exponential clearance from blood: the rapid component has a half life median value of 6 min (range: 2-24 min), while the slow one has a half life median value of 1.4 h (range: 0.6-5.8 h). Median value of the urinary excretion is 40 (range: 3-75) % of the administered activity. Our model shows the behaviour of a tracer which is distributed in the extracellular space of the body, localized in the skeleton and excreted via glomerular filtration. Half life median values of [(153)Sm]Sm-EDTMP transferring between compartments, T(1/2) (blood→ECF), T(1/2) (ECF→blood) are 7.4 (range: 1.9-37) and 48 (range: 8-408) min, respectively. Median values of half lives of [(153)Sm]Sm-EDTMP clearance through the urine and of uptake into bone are 1.0 (range: 0.1-6.0) and 1.6 (range: 0.6-9.0) h, respectively. Median value of red marrow absorbed dose is 2.1 (range: 0.7-3.5) Gy and 0.8 (range: 0.3-2.1) Gy/GBq, while median value of bone surface absorbed dose is 11.5 Gy (range: 5.0-18.4) and 4.4 (range: 2.3-14.3) Gy/GBq. It is remarkable that there is a really great biological variability within patients, especially considering the excreted activity. The cumulated activity in bone and red marrow doses were significantly higher in prostate cancer, where metastatic bone lesions are osteoblastic, than in breast cancer where metastatic bone lesions are osteolytic or mixed (lytic/blastic). The relevant biological variability in biodistribution and metabolism of [(153)Sm]Sm-EDTMP suggests that the fixed administered activity based on patient weight is not sufficient to optimize the treatment and a better optimization would be reached by using a predictive dosimetry tailored to individual patient characteristics.