This study indicates that the treatment of thyroid cancer by applying radioiodine activities up to 7.4 GBq, on an outpatient basis, is a safe procedure, especially when supervised by qualified professionals. This alternative therapy should be a topic for careful discussion considering the high potential for reducing costs in healthcare and improving patient acceptance.

The objective of this study were to obtain dosimetric data from a patient with thyroid cancer simultaneously undergoing peritoneal dialysis therapy, so as to determine the appropriate amount of 131I activity to be applied therapeutically. Percentages of radioiodine in the blood and the whole-body were evaluated, and radiation absorbed doses were calculated according to OLINDA/EXM software. Whole-body 131I effective half-time was 45.5 hours, being four times longer than for patients without any renal dysfunction. Bone-marrow absorbed dose was 0.074 mGy/MBq, with ablative procedure maintenance at 3.7 GBq, as the reported absorbed dose was insufficiently restrictive to change the usual amount of radioiodine activity administered for ablation. It was concluded that radioiodine therapeutic-dose adjustment, based on individual patient dosimetry, is an important way of controlling therapy. It also permits the safe and potential delivery of higher doses of radiation to tumors and undesirable tissues, with a minimum of malignant effects on healthy tissues.

The efficacy and toxicity of radionuclide therapy are believed to be directly related to the radiation doses received by target tissues; however, nuclear medicine therapy continues to be based primarily on the administration of empirical activities to patients and less frequently on the use of internal dosimetry for individual therapeutic planning. This review aimed to critically describe the techniques and clinical evidence of dosimetry as a tool for therapeutic planning and the main limitations to its implementation in clinical practice. The present article is a nonsystematic review of voxel-based dosimetry. Clinical evidence pointing to a correlation between the radiation dose and therapeutic response in various diseases, such as thyroid carcinoma, neuroendocrine tumors and prostate cancer, is reviewed. Its limitations include technical aspects related to image acquisition and processing and the lack of randomized clinical trials demonstrating the impact of dosimetry on patient therapy. A more widespread use of dosimetry in therapeutic planning involves the development of user-friendly dosimetric protocols and confirmation that dose estimation implies good efficacy and low treatment-related toxicity.

Variability in the available diagnostic procedures as well as in the amount of activities administered within the same procedure was appreciable not only in Brazil, but worldwide. Global efforts are needed to establish a concise DRL that can be applied in adult and pediatric nuclear medicine procedures as the application of DRL in clinical routine has been proven to be an important tool for controlling and reducing radiation doses received by patients in medical exposure.

Radioactive patients may expose others after radiopharmaceutical administrations, and evaluation of the absorbed dose or exposure rates close to patients is important in keeping radiation doses as low as reasonably achievable. Two theoretical exposure models, point source and line source models, are frequently used to calculate exposure or dose rates without the support of actual measurements. If measurements of exposure rates were performed near patients, an experimental exposure model could be implemented. When measurements of exposure rates are performed, these measurements are made inside therapy rooms or other confined places, in which case scattered radiation may significantly influence the measurements. In this study we measured exposure rates from radioactive patients without the influence of scattered radiation and determined correction factors for the theoretical exposure models. The exposure rates from a total of 110 radioactive patients were measured at 1.0 h after oral administration of Na131I for thyroid therapy; the results +/-1 SD at distances of 0.5, 1.0, 1.5, 2.0, 3.0, and 4.0 m in front of the patients were (29 +/- 6), (9.9 +/- 1.7), (4.6 +/- 0.9), (2.7 +/- 0.5), (1.31 +/- 0.25) and (0.74 +/- 0.12) x 10(-10) C kg(-1) MBq(-1) h(-1) [1.0 x 10(-10) C kg(-1) MBq(-1) h(-1) = 14.34 x 10(-6) R mCi(-1) h(-1)], respectively. To obtain more accurate estimates of the actual exposure rates from patients using the theoretical exposure models, we found that correction factors should be applied; the functions CFEM = 1.19 + 32.80e(5.92D) and CFLS = 0.022LnD + 0.639 describe these correction factors for distances less than or equal to 1.0 m from the patients for experimental and line source exposure models, respectively. The function that describes the correction factors to the point source model is CFPS = 0.224LnD + 0.638 at the same distances; applying these correction factors leads to a reduction from 56% to 1% in the difference between measured exposure rates and theoretical exposure rates calculated by the point source exposure model at a distance of 1.0 m from patients. The results given here provide more accuracy in evaluation of exposure rates and consequently absorbed doses near radioactive patients and allow for more effective radiological protection procedures during patient management.

GFR decreases in patients with normal kidney function during THW for RIT, and rhTSH preserves GFR in these patients. This GFR impairment following thyroidectomy is related to hypothyroidism due to a significant reduction in thyroid hormone levels and is not due to a rise in the TSH level.

Several dosimetric methods have been proposed for estimating red marrow absorbed dose (RMAD) when radionuclide therapy is planned for differentiated thyroid cancer, although to date, there is no consensus as to whether dose calculation should be based on blood-activity concentration or not. Our purpose was to compare RMADs derived from methods that require collecting patients' blood samples versus those involving OLINDA/EXM software, thereby precluding this invasive procedure. This is a retrospective study that included 34 patients under treatment for metastatic thyroid disease. A deviation of <10 % between RMADs was found, when comparing the doses from the most usual invasive dosimetric methods and those from OLINDA/EXM. No statistical difference between the methods was discovered, whereby the need for invasive procedures when calculating the dose is questioned. The use of OLINDA/EXM in clinical routine could possibly diminish data collection, thus giving rise to a simultaneous reduction in time and clinical costs, besides avoiding any kind of discomfort on the part of the patients involved.

The evaluation of the absorbed dose from radioactive patients during the treatment of thyroid disease is an important factor in establishing precautions in these procedures, and the I retention/excretion by patients' bodies provides additional information to medical and radioprotection service. In 94 patients, the measurement of exposure rates was performed over 7 d following NaI administration, and the rates permitted the study of the dynamics of excretion and the potential dose evaluation. The administered activities ranged from 3.7 GBq (100 mCi) to 16.65 GBq (450 mCi), and the results proved that the majority of the activity is excreted by patients in the first 3 d after NaI administration. The average (131)I activity excreted at 24, 48, 72, 96, and 120 h after oral administration was (72 +/- 10), (91 +/- 6), (97 +/- 3), (98.9 +/- 1.5), and (99.6 +/- 0.7)%, respectively. According to the administered activity, the evaluation of the accumulated absorbed dose from patients ranged from 3.0 +/- 0.7 to 8.4 +/- 1.1 mSv at 1 m and 1.2 +/- 0.4 to 3.2 +/- 0.4 mSv at 2 m. The data reported here are important to radioprotection policy and to add to and improve on the guidelines reported in U.S. NRC Regulatory Guide 8.39.