48 Objectives: This study aimed to evaluate the recovery time from hyperthyroidism after individualized radioiodine therapy in patients with uni or multifocal autonomy. Methods: One hundred and nine patients (age 67+/-10 years,78F,31M) with uni (44%) or multifocal (56%) autonomy were treated over the last 5 years. A subclinical hyperthyroidism was found in 52% of patients with suppressed TSH (normal range: 0.26-4.2 mU/L) and normal serum values of FT3 and FT4 (range: 3.8-8.0 pmol/l and 9.0-20.0 pmol/l respectively). Clinical hyperthyroidism was observed in the remaining 48% with suppressed TSH and high FT3 and/or FT4 serum values. After a 123I dosimetric study based on thyroid uptake measurements at five time points, each patient received an individualized 131I dose. Patients were free from antithyroid drugs over 1 month before dosimetry and therapy. Patient clinical status was monitored by repeated TSH, FT3 and FT4 serum value assays 1,3,6,12 months after therapy and then once a year. Mean administered activity was 364+/-129 MBq [range 111-625 MBq] and mean delivered dose was 145+/-45 Gy [range 59-311 Gy]. Mean follow up was 2.9+/-1.8 years with a maximum of 5 years and more than 71% of patients for each follow up time point was monitored. Results: Clinical conditions following therapy at different follow up time points are reported in the table. Eighty-two percent of patients was cured within 6 months. Among the remaining patients with persistent hyperfunction of thyroid gland 53% became euthyroid within a year after the treatment. The latest resolutions of hyperthyroidism were observed up to 3 yrs. Conclusions: Although the re-treatment of hyperthyroidism is mandatory after unsuccessful 131I therapy, a late normalization of thyroid function is not uncommon. Our data suggest that a second 131I dose should be administered at least one year after the first treatment.
1278 Objectives: This study aimed to evaluate the clinical outcome of patients affected by uni or multifocal autonomy of thyroid gland treated with an individualized radioiodine therapy in order to achieve euthyroidism. Methods: One hundred and nine patients (age 67+/-10 yrs; 78F and 31M) affected by uni (44%) or multifocal (56%) autonomy were studied. Before 131I therapy patient accurate medical history was collected about hormonal status and previous treatments (percutaneous ethanol injections and/or antythyroid drug cycles). Each patient underwent a pretreatment dosimetric study to calculate the 131I activity to administer for therapy, based on repeated measurements of uptake (5 time-points) with a gammacamera after 123I administration. The same study was performed after therapeutic administration of 131I to calculate the real delivered dose. Patients were antithyroid drug free for at least one month before dosimetry and therapy. Each patient was required to check the serum levels of TSH, FT3 and FT4 once a year after therapy. Results: The mean administered activity and the mean delivered target dose were 364+/-129 MBq [range 111-625 MBq] and 145+/-45 Gy [range 59-311 Gy] respectively. The mean follow-up was 2.9+/-1.8 years with a maximum of 5 years, and more than 71% of patients for each follow up time point were monitored. An almost stable euthyroidism incidence rate of 85% was reached after the first year, while 13 patients became hypothyroid and 6 remained in a hyperthyroid status. No significant differences were found in the 3 groups of patients about the pre 131I treatment clinical status and previous treatments, as well as about the administered activities and target doses. Conclusions: Our clinical data showed that 131I activities and target doses lower than those reported in the literature may be administered to obtain excellent clinical outcome in patients with uni or multifocal thyroid autonomy. Few unsuccessful treatments were observed and no significant differences in pretreatment conditions or administered doses were found in comparison with euthyroid patients.
1811 Objectives: The aim of this study was to verify the capability of a dosimetric method based on the MIRD formula, 123I i.v. administration and 5 uptake values determined with a gamma camera, in prediction of radioiodine kinetics (fraction of administered iodine transferred to the thyroid, U0, and effective clearance rate, λeff) and absorbed dose after oral therapeutic 131I administration. A gamma camera was used to study separate structures within the thyroid. A dosimetric method based on the 24-h uptake and a fixed λeff value was also considered. Methods: Ninety hyperthyroid patients (11 with Graves’ disease and 79 with autonomously functioning nodules), for a total of 133 thyroidal structures, were studied. The mean time interval between dosimetry and therapy was 20+/-10 d. Uptake values were measured at 2, 4, 24, 48, and 120h during dosimetry and at 2, 4, 24, 48, 96, and 168h during therapy. The value 0.125d-1 was chosen in the fixed-λeff method. The planned doses were from 120 to 250 Gy depending on the thyroid disease and the severity of hyperthyroidism. Results: The following significant correlations were found: U0ther=0.87U0dos (r=0.97 p Conclusions: In hyperthyroid patients, the 5 uptake value dosimetric method predicts with a good consistency the radioiodine kinetics and the dose after the therapeutic administration in about 72% of the thyroid structures analyzed. The fixed-λeff method is less reliable.
Purpose: In recent years, segmentation algorithms and activity quantification methods have been proposed for oncological 18 F‐fluorodeoxyglucose (FDG) PET. A full assessment of these algorithms, necessary for a clinical transfer, requires a validation on data sets provided with a reliable ground truth as to the imaged activity distribution, which must be as realistic as possible. The aim of this work is to propose a strategy to simulate lesions of uniform uptake and irregular shape in an anthropomorphic phantom, with the possibility to easily obtain a ground truth as to lesion activity and borders. Methods: Lesions were simulated with samples of clinoptilolite, a family of natural zeolites of irregular shape, able to absorb aqueous solutions of 18 F‐FDG, available in a wide size range, and nontoxic. Zeolites were soaked in solutions of 18 F‐FDG for increasing times up to 120 min and their absorptive properties were characterized as function of soaking duration, solution concentration, and zeolite dry weight. Saturated zeolites were wrapped in Parafilm, positioned inside an Alderson thorax–abdomen phantom and imaged with a PET–CT scanner. The ground truth for the activity distribution of each zeolite was obtained by segmenting high‐resolution finely aligned CT images, on the basis of independently obtained volume measurements. The fine alignment between CT and PET was validated by comparing the CT‐derived ground truth to a set of zeolites’ PET threshold segmentations in terms of Dice index and volume error. Results: The soaking time necessary to achieve saturation increases with zeolite dry weight, with a maximum of about 90 min for the largest sample. At saturation, a linear dependence of the uptake normalized to the solution concentration on zeolite dry weight ( R 2 = 0.988), as well as a uniform distribution of the activity over the entire zeolite volume from PET imaging were demonstrated. These findings indicate that the 18 F‐FDG solution is able to saturate the zeolite pores and that the concentration does not influence the distribution uniformity of both solution and solute, at least at the trace concentrations used for zeolite activation. An additional proof of uniformity of zeolite saturation was obtained observing a correspondence between uptake and adsorbed volume of solution, corresponding to about 27.8% of zeolite volume. As to the ground truth for zeolites positioned inside the phantom, the segmentation of finely aligned CT images provided reliable borders, as demonstrated by a mean absolute volume error of 2.8% with respect to the PET threshold segmentation corresponding to the maximum Dice. Conclusions: The proposed methodology allowed obtaining an experimental phantom data set that can be used as a feasible tool to test and validate quantification and segmentation algorithms for PET in oncology. The phantom is currently under consideration for being included in a benchmark designed by AAPM TG211, which will be available to the community to evaluate PET automatic segmentation methods.
A dosimetry study was performed on 26 patients with an autonomous thyroid nodule and suppressed serum thyroid-stimulating hormone, to determine the dose to extranodular tissue when the nodule receives 300 Gy for 131I therapy.Parameters of radioiodine turnover to be used in the dosimetry formula were separately obtained for the nodule and the contralateral lobe, as a measurable example of the extranodular tissue, using 55 MBq 123I and a computer-assisted gamma camera. The biologic half-life of 123I was then converted into the effective half-life of 131I, and the volumes of the nodule and the lobe were obtained by scintigraphy or sonography.The mean dose to the contralateral lobe from uptake and irradiation by the nodule was calculated to be 32 Gy, and that to the ipsilateral lobe was estimated to be 34 Gy.During radioiodine therapy for autonomous thyroid nodules, the extranodular tissue receives a higher dose than is generally assumed, which explains the relatively high rate of post-treatment hypothyroidism reported in the literature.
