Exhalation of 131I after radioiodine therapy: measurements in exhaled air

RADIATION PROTECTION IN THE RELEASE OF PATIENTS RECEIVING 131I TREATMENT

Radiation measurements were made to support radiation protection decisions and instructions concerning the release of patients receiving 131I treatment in Sudan. In hyperthyroidism, administered activity ranged from 370 to 1110 MBq (average: 817.8 MBq), and air-absorbed dose rate at 1 m in front of the patients varied from 20 to 66 μGy h-1 (average: 47.0 μGy h-1). For thyroid cancer patients, the administered activity ranged from 3700 to 7400 MBq (average: 4816.2 MBq), and the air-absorbed dose rate at 1 m in front of the patients ranged from 3 to 55 μSv h-1 (average: 19.2 μSv h-1). On average, the contamination activity was highest in the patients' clothes: 11.0 Bq cm-2, followed by the toilet: 6.6 Bq cm-2 and the front bed: 2.9 Bq cm-2. The estimated release times from the confinement were well with the radiation safety criteria, whereas instruction are given concerning precaution times to limit radiation exposure to family members and co-worker.

Occurrence of and radioanalytical methods used to determine medical radionuclides in environmental and biological samples. A review

Medical radionuclides are widely used in nuclear medicine practices today. Their production, handling and administration have different impacts on the environment and society due to the radioactive waste generated. Over recent years authors have taken an interest in the monitoring and safe disposal of this radiopharmaceutical waste, mainly in environmental and biological samples, and consequently a variety of radioanalytical methods for these matrices have been developed. The present review aims to outline the state of the art and the latest trends reported in the literature from 2007 to the present, focusing on the occurrence and determination of medical radionuclides in environmental and biological samples. Special attention is given to critically discussing the strengths and weaknesses of the different steps involved in determining medical radionuclides in these types of matrices. The methodologies presented are accompanied by examples.

Retention efficacy and release of radioiodine in fume hoods

Procedures to determine the release of hazardous gaseous substances including radioactive iodine are covered by different norms such as the European standard EN 14175 and the German national standard DIN 25466. The detection of sulphur hexafluoride (SF₆) is required to comply with the prescribed methodology. The detection limit of this test is 4.5·10^-7 mol/m³ in exhaust air. This detection limit would represent a very high activity in the region of 0.27 TBq/m³ leading to an unacceptable risk. We therefore developed a test using a filter system, consisting of a combination of filters capable of separating various chemical forms of airborne radioiodine. Air samples were collected directly in front of the fume hood and in the laboratory beside two different fume hoods of a similar construction with a final activated carbon filter for retention of radioiodine. Particular attention was therefore paid to air samples taken after passage over the filters. Significant differences in the degree of retention of iodine were found between the two fume hoods investigated. In one test a malfunction of the fume hood was demonstrated. In this case 0.148 × 10^-3% of the total released activity per m³ air was found 1 cm in front of the hood sash. A remarkably high fraction of the activity released in the fume hood (1.3 × 10^-3%/m³ air) was measured after the activated carbon filter. In the ambient air, values of up to 8.6 × 10^-6% pro m³ laboratory air sampled were measured, despite a 6-8-fold air exchange. The selected procedure is a factor of 10¹¹ (Schomäcker et al., 2001) more sensitive than the standard recommended methods (EN 14175). The standard test prescribed by the DIN/EN failed to reveal any inadequacy in the protective function of the radionuclide hood with respect to radioiodine retention.

The effectiveness of wastewater treatment in nuclear medicine: Performance data and radioecological considerations

For planned and ongoing storage of liquid radioactive waste in a designated plant for a nuclear medicine therapy ward (decontamination system/decay system), detailed knowledge of basic parameters such as the amount of radioactivity and the necessary decay time in the plant is required. The design of the plant at the Department of Nuclear Medicine of the University of Cologne, built in 2001, was based on assumptions about the individual discharge of activity from patients, which we can now retrospectively validate. The decontamination factor of the plant is at present in the order of 10^-9 for ¹³¹I. The annual discharges have been continuously reduced over the period of operation and are now in the region of a few kilobecquerels. This work emphasizes the high efficacy of the decontamination plant to reduce the amount of radioactivity released from the nuclear medicine ward into the environment to almost negligible levels.

Exhalation of 131I after radioiodine therapy: Dosimetric considerations based on measurements in exhaled air

It is well known that a considerable amount of radioiodine is exhaled after radioiodine therapy (RIT) leading to unwanted radiation exposure through inhalation for non-involved persons. This study focuses on the amount of exhalation in the breath-out air of RIT-patients and the dosimetric consequences. Furthermore, the correlation between radioiodine uptake and exhalation was investigated. The radioiodine species were collected in a filter system and quantified over time by measurements with a scintillation counter. The dosimetric implications were then studied for different exposure scenarios. Of the activity administered to the patient, approximately 10^-3% (50-110 ppm) is exhaled. The radioiodine inhalation taking place following exhalation in the vicinity yields doses of up to 500 μSv (children, staying with the patient immediately after application and for the next 8 h). Three days after administration the doses are significantly reduced. This study lays emphasis on previous assumptions that exhalation depends on thyroid storage. Regardless of the type of thyroid disease, the predominant form exhaled is organic radioiodine. The amount of exhaled radioiodine is small but from the point of view of radiation protection, by no means negligible immediately after administration. Radiation doses received by incorporation of exhaled radioiodine can easily exceed 100 μSv soon after administration of radioiodine. Three days after RIT the radioactivity can still be measured in the exhaled air but even at maximum, the annual doses lie far below 10 μSv and are thus comparatively low.

[Incorporation monitoring of employees of a radioiodine therapy ward. Is incorporation monitoring required for routine?]

Aim of the study was to determine the annual incorporation of staff on a radioiodine therapy ward and the resulting annual effective dose (aed). Following the German incorporation guideline (gig), incorporation monitoring is not necessary for potential aed below 0.5 mSv/a. For aed > 0.5 mSv/a adherence to the 1 mSv dose limit must be verified. For doses > 1 mSv/a incorporation has to be monitored by the authority. Furthermore, the (131)I incorporation factor from the gig should be verified.

METHODS

To determine the actual work related incorporation, the (131)I activity concentration in urine samples (collection over 24 h) of 14 employees of different professions were examined over a period of 27 months.

RESULTS

Measured activity concentrations were related to the individual time of exposure. A constant activity supply for at least three days was assumed. The mean annual effective doses were 2.4 · 10⁻¹ mSv/a (nursing staff; n = 3), 5.6 · 10⁻² mSv/a (cleaning staff; n = 2), 2.8 · 10⁻³ mSv/a (technical staff; n = 2) and 5.2 · 10⁻³ mSv/a (physicians; n = 7). All aed were below the dose limits of the gig. The calculated mean incorporation factors ranged from 3.0 · 10⁻⁸ for the nursing staff to 3.6 · 10⁻¹⁰ for the technical staff (cleaning staff: 7 · 10⁻⁹; physicians: 6.5 · 10⁻¹⁰) and were therefore well below the (131)I incorporation factor defined by the gig.

CONCLUSIONS

To estimate the aed caused by incorporation of (131)I it has to be subdivided for the different requirements in the diverse fields of activity of the employees. Regarding those who spend most of their time nearby the patient an incorporation monitoring by the authority might be required. The (131)I incorporation factor from the guideline (10⁻⁶) can be reduced by a factor of 10. For (99m)Tc and (18)F an incorporation factor of 10⁻⁷ is accepted.