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Purpose: A considerable amount of radioiodine is exhaled after radioiodine therapy leading to unwanted radiation exposure through inhalation. This study focused on the concentration of radioactivity exhaled and its chemical nature. Methods: Air exhaled by 47 patients receiving I-iodine for different thyroid diseases (toxic goitre n = 26, Graves' disease n = 13, thyroid cancer n = 8) was investigated with a portable constant air-flow sampler. Different chemical iodine species were collected separately (organic, elemental and aerosolic) up to 26 h after administration of the radioiodine capsule. The data approximated to a monoexponential time-activity curve when integrated over 100 h. The radioactivity in the filters was measured with a well counter at defined time points after administration. Results: The radioactivity of I in the exhaled air 1 h after administration ranged from 1 to 100 kBq/m. Two parameters (half-life of radioiodine exhalation and time-integrated activity over 100 h) were substantially higher in patients with cancer after near-total thyroidectomy (11.8 ± 2.1 h and 535 ± 140 kBq / m, respectively) than in patients with hyperfunctioning thyroid tissue due to toxic adenoma (7.6 ± 2.5 h and 115 ± 27 kBq / m, respectively) or Graves' disease (6.4 ± 3.6 h and 113 ± 38 kBq / m, respectively). The percentage of radioiodine in the exhaled air in relation to radioiodine administered to the patient was between 80 ppm and 150 ppm. The fraction of organically bound radioiodine (mean value) for all time points after administration was 94-99.9%. This percentage did not depend on the type of thyroid disease. Conclusion: The amount of exhaled radioiodine is small but by no means negligible on the first day after administration. This is the first study to provide experimental evidence on a systematic basis that radioiodine becomes exhalable in vivo, i.e. in the patient. The mechanism of organification of orally administered radioiodine remains to be investigated. [ABSTRACT FROM AUTHOR]

Radiation dosimetry is a basic requirement for targeted radionuclide therapies (TRT) which have become of increasing interest in nuclear medicine. Despite the significant role of the radiopharmaceutical 131I-metaiodobenzylguanidine (MIBG) for the treatment of metastatic neuroblastoma, phaeochromocytoma and paraganglioma details for a reliable dosimetry are still sparse. This work presents our procedures, the dosimetric data and experiences with TRT using 131I-MIBG. A total of 21 patients were treated with 131I-MIBG between 2004 and 2008 according to a clearly defined protocol. Whole-body absorbed doses were determined by a series of scintillation probe readings for all 21 cases. Tumour absorbed doses were calculated on the basis of quantitative imaging for an entity of 25 lesions investigated individually using the region of interest (ROI) technique based on five scans each. Typical whole-body absorbed doses are found in the region of 2 Gy (range: 1.0–2.9 Gy) whereas tumour absorbed doses in turn cover a span between 10 and 60 Gy. Nonetheless this variation of tumour absorbed doses is comparatively low. The trial protocol in use is a substantial advancement in terms of reliable dosimetry. A clearly defined modus operandi for MIBG therapies should involve precisely described dosimetric procedures, e.g. a minimum of 20 whole-body measurements using a calibrated counter and at least four gamma camera scans over the whole period of the inpatient stay should be carried out. Calculation of tumour volumes is accomplished best via evaluation of SPECT and CT images. [ABSTRACT FROM AUTHOR]