Investigation of the Importance of Applying Various Methods of Calculation in Determining the Blood-Absorbed Dose for Patients with Differentiated Thyroid Carcinoma.

The objective was to compare estimated total blood-absorbed doses obtained by applying 4 methods to the same group of patients. In addition, these results were compared with those for the patients of other researchers, who used various other techniques over a period of more than 20 y. Methods: Twenty-seven patients (22 women and 5 men) with differentiated thyroid carcinoma were enrolled in the study. Whole-body measurements were performed as conjugate-view (anterior and posterior) counts by scintillation camera imaging. All patients received 3.7 GBq of 131I for thyroid ablation. Results: The mean total blood-absorbed doses by the first, second, third, and fourth methods in the 27 patients were estimated to be 0.46 ± 0.12, 0.45 ± 0.13, 0.46 ± 0.19, and 0.62 ± 0.23 Gy, respectively. The maximum values were 1.40, 0.81, 1.04. and 1.33 Gy, respectively. The difference between the mean values was 37.22%. In the comparison with the total blood-absorbed doses for the patients of other researchers, the difference was 50.77% (difference between the means of 0.65 and 0.32 Gy). Conclusion: None of the total absorbed doses to the blood by the 4 methods in my 27 patients was 2 Gy, the maximum permissible dose. The difference between the total absorbed doses to the blood obtained by different teams of researchers was 50.77%, whereas the difference between the values by the 4 different methods in the 27 patients was 37.22%.

An indirect high iodine (131 I) effective dose used for thyroid ablation in patients with thyroid cancer. Is the method of measurement important?

BACKGROUND: Radiation effective dose to the red bone-marrow, a critical organ in the therapy of differentiated thyroid carcinoma (DTC) with radioiodine-131 (131 I), cannot be measured directly. As radioiodine concentration is comparable in blood and most organs, and is believed to be similar in red marrow, the effective dose to the blood seems to be a good first-order approximation of the radiation effective dose to the hematopoietic system and a better means to quantifying exposure from therapy compared to the total amount of activity administered. PURPOSE: We applied four formulas (Lassmann et al (standard) [2008], Eur J Nucl Med Molecul Imaging, 35:1405-1412), (Thomas et al. [1993], Nucl Med Biol, 20:157-162), (Sisson et al. [2003], J Nucl Med, 44:898-903; Ha¨nscheid et al. [2009], Endocr Relat Cancer, 16:1283-1289) and (Ha¨nscheid et al. [2006], J Nucl Med, 47:648-654) and compared between the estimated values of the effective dose that were obtained by three formulas and those obtained by the standard one. MATERIALS AND METHODS: Twenty-seven patients, 22 women and 5 men, suffering from DTC were enrolled in this study. Whole-body probe measurements and blood collections (2 mL whole-blood samples) were conducted at 2, 6, 24, 48, 72-96 h after the administration of 131 I to obtain time-activity curves. Whole-body measurements were performed as conjugate view (anterior and posterior) counts by scintillation camera imaging. RESULTS: By comparing the values of blood effective dose that were obtained by applying Thomas et al. [1993], Nucl Med Biol, 20:157-162; Sisson et al. [2003], J Nucl Med, 44:898-903 and Ha¨nscheid et al. [2009], Endocr Relat Cancer, 16:1283-1289, and Ha¨nscheid et al. [2006], J Nucl Med, 47:648-654, techniques, with those obtained by (Lassmann et al (standard technique) [2008], Eur J Nucl Med Molecul Imaging, 35:1405-1412), we found that these values are, respectively, 15.0%, 40.0%, and 41.0% more than those obtained by using the standard method. To our knowledge no papers have been published previously that compare between these dosimetric approaches. CONCLUSION: Highly overestimated or highly underestimated results obtained by a certain method or technique, compared with those obtained by the standard method, are not desirable, they tend to exaggerate in applying radiation protection procedures, by increasing or decreasing, which, in both cases, become far from the realistic or recommended procedures. As an operating philosophy, the objective of radiation safety practices simply should not be to keep radiation doses within legal limits or maximum permissible doses (MPDs ), but to keep them "as low as reasonably achievable" (ALARA concept). MPDs should not be considered as thresholds below which exposure to radiation is of no concern, they are not assumed to be totally risk free, and any reasonable technique for reducing radiation dose may have potential benefits in the long run.

Radioprotection using iodine-131 for thyroid cancer and hyperthyroidism: a review.

Radioiodine (iodine-131, or I-131) therapy has been used successfully for thyroid therapy for more than 50 years. Protocols for treatment with I-131 differ from country to country and even from hospital to hospital in the same country. Daily area surveys of hallways, stairwells, and rooms adjacent to isolation rooms must be conducted and documented to ensure that doses to any individuals in unrestricted areas do not exceed 20 mcSv (2 mrem) in one hour. Nursing and housekeeping staffs must realize that once therapy has begun, no items are to be removed from the room unless first cleared by nuclear medicine or radiation safety personnel. With proper education and instructions for patients and their family members, radiation exposure to healthcare professionals and the general public can be minimized. The objectives of this article are to review (a) practical radiation safety concerns associated with hospitalized patients receiving I-131 therapy, (b) preventive measures to minimize potential exposure and contamination problems, and (c) radiation safety precautions and preventive measures to minimize radiation exposure to family members and helpers living with patients receiving outpatient I-131 therapy.