(18)FDG, an analogue of glucose labelled with the radionuclide (18)F, is the most widely used radiopharmaceutical in positron emission tomography/computed tomography technique. In Brazil, there are currently eight (18)FDG plants in operation and other facilities are expected to start their production in the near future. The growth in the production and clinical use of (18)FDG represents an increasing risk of worker exposures. According to national regulations and international recommendations, internal exposures should be effectively controlled in order to keep doses as low as possible. The implementation of a routine monitoring programme towards the estimation of internal doses related to the incorporation of (18)F is difficult, mainly due to its short physical half-life, the cost of a bioassay laboratory and the need of a monitoring service promptly available near the production plant. This paper describes the implementation and evaluation of a methodology for in vivo brain monitoring of (18)F to be applied in cases of suspected incorporation of (18)FDG. The technique presented a minimum detectable effective dose in the order of nanoSieverts, which allows its application for occupational monitoring purposes.
The manipulation of a wide variety of unsealed sources in Nuclear Medicine results in a significant risk of internal exposure of the workers. 131I should be highlighted among the most frequently used radionuclides because of its large application for diagnosis and therapy of thyroid diseases. The increasing use of radionuclides for medical purposes creates a demand for feasible methodologies to perform occupational control of internal contamination. Currently in Brazil, there are approximately 300 nuclear medicine centres in operation but individual monitoring is still restricted to the control of external exposure. This work presents the development of in vivo and in vitro bioassay techniques aimed to quantify incorporation of radionuclides used in Nuclear Medicine. It is also presented the results of a preliminary survey of internal exposure of a group of workers involved in the preparation of therapeutic doses of 131I. Workers were monitored with a gamma camera available in the Nuclear Medicine Service of the University Hospital of Rio de Janeiro and at the Institute of Radiation Protection and Dosimetry Whole-Body Counter (IRD-WBC). The in vivo detection systems were calibrated with a neck-thyroid phantom developed in IRD. Urine samples from radiopharmacy workers were collected after preparation and administration of therapeutic doses (10-250 mCi) of 131I and measured with a HPGe detection system available in the Bioassay Laboratory of IRD. The results show that the bioassay methods developed in this work present enough sensitivity for routine monitoring of nuclear medicine workers. All workers monitored in this survey presented positive results for 131I in urine samples and two workers presented detectable activities in thyroid when measured at the IRD-WBC. The highest committed effective dose per preparation was estimated to be 17 microSv.
The concern about accidents involving radioactive materials has led to the search of alternative methods to quickly identify and quantify radionuclides in workers and in the population. One of the options to face up an eventual demand for mass monitoring of internal contamination is the use of a nuclear medicine diagnostic equipment known as gamma camera, a device used to scan patients who have been administered specific amounts of radioactive materials for medical purposes. Although the gamma camera is used for image diagnosis, it can be calibrated with anthropomorphic phantoms or point sources for the quantification of radionuclide activities in the human body. This work presents a protocol for the calibration of gamma cameras for such application. In order to evaluate the suitability of this type of equipment, a gamma camera available in a public hospital located in Rio de Janeiro was calibrated for the in vivo measurement of 131I. The calibration includes the determination of detection efficiencies and minimum detectable activities for each radionuclide. The results show that the gamma camera presents enough sensitivity to detect activity levels corresponding to effective doses below 1 mSv. The protocol is the basis to establish a network of Nuclear Medicine Centres, located in public hospitals in eight countries of Latin America (Argentina, Brazil, Colombia, Cuba, Chile, Mexico, Peru and Uruguay) and in Spain that could be requested to collaborate in remediation actions in the event of an accident involving incorporation of radioactive materials. This protocol is one of the most significant outputs of the IAEA-ARCAL Project (RLA/9/049-LXXVIII) aimed to the Harmonization of Internal Dosimetry Procedures.
The manipulation of 131I in Nuclear Medicine involves significant risks of internal contamination of the staff. In the event of an accidental contamination, or when the Radiological Protection Program includes routine individual monitoring of internal contamination, it is necessary to implement internal dose estimation through in vivo and in vitro bioassay techniques. Due to the huge extension of the Brazilian country, this type of monitoring becomes unfeasible if all measurements have to be performed at the institutes of the CNEN. Thus, if the Nuclear Medicine Centres (NMC) become able to conduct the monitoring of their employees, this skill would be of great significance. The methodology proposed in this work consists in a simple and inexpensive protocol for auto-monitoring the internal contamination by 131I, using the resources available at the NMC. In order to verify the influence of the phantom in the calibration factor for the measurement of 131I in thyroid, it was performed a comparison among a variety of phantoms commercially available, including the Neck-Thyroid Phantom developed in IRD. A protocol for performing in vivo and in vitro measurements by the NMC was established. The applicability of the individual monitoring techniques was also evaluated by comparing the detection limits with the derived limits associated with the annual dose limits for workers.
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