131I Therapeutic Efficacy Is Not Influenced by Stunning after Diagnostic Whole-Body Scanning

Correction for hyperfunctioning radiation-induced stunning (CHRIS) in benign thyroid diseases

PURPOSE

Radioiodine-131 treatment has been a well-established therapy for benign thyroid diseases for more than 75 years. However, the physiological reasons of the so-called stunning phenomenon, defined as a reduced radioiodine uptake after previous diagnostic radioiodine administration, are still discussed controversially. In a recent study, a significant dependence of thyroid stunning on the pre-therapeutically administered radiation dose could be demonstrated in patients with goiter and multifocal autonomous nodules. A release of thyroid hormones to the blood due to radiation-induced destruction of thyroid follicles leading to a temporarily reduced cell metabolism was postulated as possible reason for this indication-specific stunning effect. Therefore, the aim of this study was to develop dose-dependent correction factors to account for stunning and thereby improve precision of radioiodine treatment in these indications.

METHODS

A retrospective analysis of 313 patients (135 with goiter and 178 with multifocal autonomous nodules), who underwent radioiodine uptake testing and radioiodine treatment, was performed. The previously determined indication-specific values for stunning of 8.2% per Gray in patients with multifocal autonomous nodules and 21% per Gray in patients with goiter were used to modify the Marinelli equation by the calculation of correction factors for hyperfunctioning radiation-induced stunning (CHRIS). Subsequently, the calculation of the required activity of radioiodine-131 to obtain an intra-therapeutic target dose of 150 Gy was re-evaluated in all patients. Furthermore, a calculation of the hypothetically received target dose by using the CHRIS-calculated values was performed and compared with the received target doses.

RESULTS

After integrating the previously obtained results for stunning, CHRIS-modified Marinelli equations could be developed for goiter and multifocal autonomous nodules. For patients with goiter, the mean value of administered doses calculated with CHRIS was 149 Gy and did not differ from the calculation with the conventional Marinelli equation of 152 Gy with statistical significance (p = 0.60). However, the statistical comparison revealed a highly significant improvement (p < 0.000001) of the fluctuation range of the results received with CHRIS. Similar results were obtained in the subgroup of patients with multifocal autonomous nodules. The mean value of the administered dose calculated with the conventional Marinelli equation was 131 Gy and therefore significantly below the CHRIS-calculated radiation dose of 150 Gy (p < 0.05). Again, the fluctuation range of the CHRIS-calculated radiation dose in the target volume was significantly improved compared with the conventional Marinelli equation (p < 0.000001).

CONCLUSIONS

With the presented CHRIS equation it is possible to calculate a required individual stunning-independent radioiodine activity for the first time by only using data from the radioiodine uptake testing. The results of this study deepen our understanding of thyroid stunning in benign thyroid diseases and improve precision of dosimetry in radioiodine-131 therapy of goiter and multifocal autonomous nodules.

Thyroid stunning in radioiodine-131 therapy of benign thyroid diseases

PURPOSE

Existence and cause of thyroid stunning was controversially discussed for decades but the underlying mechanism remains unclear. Numerous studies describe thyroid stunning in radioiodine-131 therapy (RIT) of differentiated thyroid carcinoma. However, there are no studies evaluating thyroid stunning in benign thyroid diseases caused by the radioiodine uptake test (RIUT). Therefore, the influence of pre-therapeutic tracer radiation dose on therapeutic iodine-131 uptake was evaluated retrospectively.

METHODS

A total of 914 RIT patients were included. Exclusion criteria were anti-thyroid drugs, pre- and/or intra-therapeutic effective half-lives (EHL) beyond 8.04 days and externally performed RIUT or 24 h RIUT. All patients received RIUT 1 week before RIT. Thyroid volume was estimated via ultrasound. Tracer radiation dose to the thyroid was calculated retrospectively. The dependence of changes in the pre-therapeutic to the therapeutic extrapolated-maximum-¹³¹I-uptake (EMU) from the dose in RIUT was evaluated statistically.

RESULTS

EMU in RIUT ranged from 0.10 to 0.82 (median: 0.35) and EMU in RIT ranged from 0.10 to 0.74 (median: 0.33). Averaged over the whole cohort the therapeutic EMU decreased significantly (2.3% per Gray intra-thyroidal tracer radiation dose). A disease-specific evaluation showed dose-dependent thyroid stunning from 1.2% per Gray in solitary toxic nodules (n = 327) to 21% per Gray in goiters (n = 135) which was significant for the subgroups of disseminated autonomies (n = 114), multifocal autonomies (n = 178) and goiters (p < 0.05) but not for Graves' diseases (n = 160) and solitary toxic nodules (p > 0.05).

CONCLUSIONS

The presented data indicate for the first time a significant dependence of pre-therapeutic radiation dose on thyroid stunning in goiter and disseminated and multifocal autonomy. To achieve the desired intra-thyroidal radiation dose, RIT activity should be adapted depending on the dose in RIUT.

Nuclear Molecular and Theranostic Imaging for Differentiated Thyroid Cancer

Traditional nuclear medicine is rapidly being transformed by the evolving concepts in molecular imaging and theranostics. The utility of new approaches in differentiated thyroid cancer (DTC) diagnostics and therapy has not been fully appreciated. The clinical information, relevant to disease management and patient care, obtained by scintigraphy is still being underestimated. There has been a trend towards moving away from the use of radioactive iodine (RAI) imaging in the management of the disease. This paradigm shift is supported by the 2015 American Thyroid Association Guidelines (1). A more systematic and comprehensive understanding of disease pathophysiology and imaging methodologies is needed for optimal utilization of different imaging modalities in the management of DTC. There have been significant developments in radiotracer and imaging technology, clinically proven to contribute to the understanding of tumor biology and the clinical assessment of patients with DTC. The research and development in the field continues to evolve, with expected emergence of many novel diagnostic and therapeutic techniques. The role for nuclear imaging applications will continue to evolve and be reconfigured in the changing paradigm. This article aims to review the clinical uses and controversies surrounding the use of scintigraphy, and the information it can provide in assisting in the management and treatment of DTC.

Statistical and radiobiological analysis of the so-called thyroid stunning

Background

The origin of the reduction in thyroid uptake after a low activity iodine scan, so-called stunning effect, is still controversial. Two explanations prevail: an individual cell stunning that reduces its capability to store iodine without altering its viability, and/or a significant cell-killing fraction that reduces the number of cells in the tissue still taking up iodine. Our aim is to analyze whether this last assumption could explain the observed reduction.

Methods

The survival fraction after administration of a small radioiodine activity was computed by two independent methods: the application of the statistical theory underlying tissue control probability on recent clinical studies of thyroid remnant ¹³¹I ablation and the use of the radiosensitivities reported in human thyroid cell assays for different radioiodine isotopes.

Results

Both methods provided survival fractions in line with the uptake reduction observed after a low ¹³¹I activity scan. The second method also predicts a similar behavior after a low ¹²³I or ¹²⁴I activity scan.

Conclusions

This study shows that the cell-killing fraction is sufficient to explain the uptake reduction effect for ¹³¹I and ¹²³I after a low activity scan and that even if some still living cells express a stunning effect just after irradiation (as shown in vitro), they will mostly die with time. As the β/α value is very low, this therapy fractionation should not impact the patient outcome in agreement with recent studies. However, in case of huge uptake heterogeneity, pre-therapy scan could specifically kills high-uptake cells and by the way could reduce the cross irradiation to the low-uptake cells during the therapy, resulting in a reduction of the ablation success rate.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-015-0144-9) contains supplementary material, which is available to authorized users.

Differentiated thyroid carcinoma: an analysis of 249 patients undergoing therapy and aftercare at a single institution

PURPOSE

Well-differentiated thyroid cancer (WDTC) is rising in incidence across the world over the past 3 decades. We aimed to evaluate the natural history and clinical outcome of differentiated thyroid carcinoma by a retrospective analysis of 249 patients treated at a single institution.

METHODS

A cohort of 249 patients who underwent thyroidectomy for WDTC in the last 10 years in Maadi Military Hospital was studied. Main outcome measures were clinical management at the diagnosis, survival, morbidity, and prognostic risk factors.

RESULTS

Mean age at diagnosis was 44.7 (SD, 14.6) years, where 52.2% were 45 years or older. Females represent 70.7% (P = 0.01), with female-to-male ratio of 4.1:1. Near-total thyroidectomy was done in 70.7% of the cases where papillary cancer was found in 80.8% and node metastasis in 10.5%. Radioactive I (RA I) was given an all cases (dose range, 80-150 mCi) with ablation success rate of 79.2%. Locoregional recurrence and metastasis (lungs and bones) were found in 2% and 6.8%, respectively. Multivariate Cox regression analysis showed that the mean ablation dose of RA I (odds ratio, 1.045; 95% confidence interval, 0.936-1.1189; P = 0.01) and presence of remote deposits (odds ratio, 1.049; 95% confidence interval, 0.836-1.1189; P = 0.01) are the significant influential factor in ablation success rate and survival, respectively.

CONCLUSIONS

Our data suggest that proper ablation dose of RA I and absence of remote metastasis are the powerful predictors for excellent outcome in WDTC patients.

No adverse affect in clinical outcome using low preablation diagnostic (131)i activity in differentiated thyroid cancer: refuting thyroid-stunning effect

CONTEXT

Published studies of thyroid stunning due to preablation (131)I scanning in the treatment of differentiated thyroid cancer after thyroidectomy had shown inconsistent clinical impact.

OBJECTIVE

The objective of the study was to evaluate the clinical outcome in patients who were given a low diagnostic (131)I activity (1.1 mCi or 40 MBq) 6 days prior to radioiodine ablation (RAI).

DESIGN/SETTING

Two cohorts of patients were treated in a cancer referral center in 2004-2011. The eligibility criteria were as follows: 1) diagnosis of differentiated thyroid cancer; 2) total or near total thyroidectomy; 3) no distant metastasis; and 4) receiving 82.4 mCi or greater (3050 MBq) therapeutic (131)I activity.

PATIENTS/INTERVENTIONS

Three hundred five consecutive patients treated in 2004-2008 (group A) had a diagnostic activity 1.1 mCi of (131)I prior to RAI. The second cohort treated in 2009-2011 (group B) consisted of 237 patients who did not undergo diagnostic (131)I scanning prior to RAI.

MAIN OUTCOME MEASURES

The tumor recurrence rate at 3 years and quantitative assessment using diagnostic whole-body radioiodine scans and TSH-stimulated thyroglobulin levels at 3-12 months after RAI were measured.

RESULTS

The 3-year recurrence-free survival rates were 96.4% in both groups, with 4.3% in group A and 3.4% in group B having tumor recurrence (P = .91). The ablation success rates measured by diagnostic whole-body radioiodine scans were 97.6% and 100% and by stimulated thyroglobulin were 85.3% and 85.8% in group A and B, respectively (P = .62).

CONCLUSIONS

The use of low diagnostic (131)I activity (1.1 mCi) given 6 days prior to RAI was safe and convenient without adversely affecting the long-term clinical outcome.

Usefulness of (99m)Tc-pertechnetate whole body scan with neck and chest SPECT/CT for detection of post-surgical thyroid remnant and metastasis in differentiated thyroid cancer patients

OBJECTIVE

The aim of the study was to evaluate the usefulness of (99m)Tc-pertechnetate whole body scan (WBS) with neck and chest SPECT/CT for detection of post-surgical thyroid remnant and metastasis in differentiated thyroid cancer (DTC) patients.

METHODS

Fifty-six post total thyroidectomy patients were included. All patients were prospectively imaged with (99m)Tc-pertechnetate WBS with neck and chest SPECT/CT before (131)I ablation. The post-ablative (131)I WBS with SPECT/CT was performed at 5-7 days after receiving (131)I. Both scans were directly compared to determine the concordance of sites and number of remnant and metastasis.

RESULTS

Overall per-patient analysis, the percentage of concordance between two scans was 96.4%. In thyroid bed, lymph node, lung and bone subgroups, the percentage of concordance between two scans was 96.4, 92.9, 98.2 and 100%, respectively. All of them show good correlation with unweighted kappa between 0.7 and 1. Overall per-lesion analysis, the percentage of concordance between two scans was 84%. In thyroid bed, lymph node, lung and bone subgroups, the percentage of concordance between two scans was 89.5, 55, 82.6 and 50%, respectively.

CONCLUSIONS

Pre-ablative pertechnetate WBS with neck and chest SPECT/CT has good correlation for the detection of post-surgical thyroid remnant, cervical node and discrete lung nodule metastasis as compared to (131)I WBS with SPECT/CT per-patient basis. Because (131)I therapeutic activity is desired base on metastatic site and less concerning about the number of lesions, pre-ablative (99m)Tc-pertechnetate WBS with SPECT/CT was a good alternative tool to avoid radioiodine stunning in post-surgical DTC patients.

Is thyroid stunning clinically relevant? A retrospective analysis of 208 patients

OBJECTIVE

Current guidelines have advised against the performance of (131)I-iodide diagnostic whole body scintigraphy (dxWBS) to minimize the occurrence of stunning, and to guarantee the efficiency of radioiodine therapy (RIT). The aim of the study was to evaluate the impact of stunning on the efficacy of RIT and disease outcome.

SUBJECTS AND METHODS

This retrospective analysis included 208 patients with differentiated thyroid cancer managed according to a same protocol and followed up for 12-159 months (mean 30 ± 69 months). Patients received RIT in doses ranging from 3,700 to 11,100 MBq (100 mCi to 300 mCi). Post-RIT-whole body scintigraphy images were performed 10 days after RIT in all patients. In addition, images were also performed 24-48 hours after therapy in 22 patients. Outcome was classified as no evidence of disease (NED), stable disease (SD) and progressive disease (PD).

RESULTS

Thyroid stunning occurred in 40 patients (19.2%), including 26 patients with NED and 14 patients with SD. A multivariate analysis showed no association between disease outcome and the occurrence of stunning (p = 0.3476).

CONCLUSION

The efficacy of RIT and disease outcome do not seem to be related to thyroid stunning.

Stunning phenomenon after a radioactive iodine- ¹³¹I diagnostic whole-body scan: Is it really a point of clinical consideration?

PURPOSE

Stunning of thyroid remnants after diagnostic scanning (Dx-WBS) using radioactive iodine- (¹³¹I) may limit the efficacy of I therapy. We aimed to evaluate this assumption in a prospectively designed study.

METHODS

Forty patients who underwent thyroidectomy for differentiated thyroid carcinoma were studied and divided into two identical groups: G1 and G2. In the G1 group, no Dx-WBS was performed and the ablation dose was given directly on the basis of the risk stratification; in the G2 group, Dx-WBS was performed with 185 MBq (5 mCi) of ¹³¹I, and ablation was given for a mean number of 11 ± 1.1 days; stunning was found on a semiquantitative basis in all patients. At a mean of 6.5 ± 0.3 months, the ablation success rate (ASR) was evaluated on the basis of Dx-WBS, thyroglobulin levels, and neck sonography. Complete ASR was considered when no ¹³¹I uptake could be seen in the neck or elsewhere, thyroglobulin was less than 2 ng/ml, and neck sonography was negative for any disease-related abnormalities.

RESULTS

G1 and G2 groups were completely identical as no significant differences were found between their different characteristics, including the mean ablative dose. ASR was 81.7 and 78.3% in G1 and G2 groups, respectively (P=0.6). Multivariate Cox regression analysis showed the mean ablation dose to be the most influential factor in ASR (odds ratio 1.045; 95% confidence interval 0.936-1.1189; P=0.01).

CONCLUSION

Our data suggest that stunning had no influence on ASR and is not a point of clinical consideration with respect to this aspect.

Imaging surveillance of differentiated thyroid cancer

Intensive imaging surveillance has resulted in the ability to detect small-volume, often clinically occult, residual or recurrent disease. For most patients with differentiated thyroid cancer (DTC), such findings are unlikely to have an impact on disease-specific survival but our ability to predict which patients are at greatest risk and should receive the most aggressive therapies is surpassed by our ability to detect recurrence. Thus, the optimal treatment and surveillance regimens will surely continue to evolve as our ability to predict tumor behavior and aggressiveness improves. This article explains the rationale underlying current surveillance strategies and the utility and implications of imaging findings that are critical for the appropriate care of patients with DTC.

Radiation-induced thyroid stunning: differential effects of (123)I, (131)I, (99m)Tc, and (211)At on iodide transport and NIS mRNA expression in cultured thyroid cells

Recent clinical and experimental data demonstrate that thyroid stunning is caused by previous irradiation and may influence the efficacy of (131)I radiation therapy of thyroid cancer and possibly hyperthyroidism. To avoid stunning, many clinics have exchanged (131)I for (123)I for pretherapeutic diagnostic imaging and dose planning. Furthermore, recent in vitro studies indicate that (131)I irradiation reduces iodide uptake by downregulating the expression of the sodium iodide symporter (NIS). The rationale for this study was therefore to study effects on iodide transport and NIS messenger RNA (mRNA) expression in thyrocytes exposed to both (123)I and (131)I in addition to some other potentially interesting radionuclides.

METHODS

Thyrotropin-stimulated thyroid cell monolayers were exposed to 0.5 Gy of (123)I, (131)I, (99m)Tc, or (211)At, all being radionuclides transported via NIS, in the culture medium for 6 h, or to various absorbed doses of (123)I or (131)I for 48 h. NIS mRNA expression was analyzed using quantitative reverse-transcriptase polymerase chain reaction.

RESULTS

Iodide transport and NIS mRNA expression were reduced by all radionuclides. At the same absorbed dose, iodide transport was reduced the most by (211)At, followed by (123)I and (99m)Tc (equally potent), whereas (131)I was least effective. The onset of NIS downregulation was rapid (<1 d after irradiation) in cells exposed to (123)I or (211)At and was delayed in cells irradiated with (131)I or (99m)Tc. Iodide transport and NIS expression were recovered only for (211)At. (123)I reduced the iodine transport and the NIS mRNA expression more efficiently than did (131)I at an equivalent absorbed dose, with a relative biological effectiveness of about 5.

CONCLUSION

The stunning effect per unit absorbed dose is more severe for (123)I than for (131)I. Despite the lower absorbed dose per unit activity for (123)I than for (131)I, stunning by (123)I cannot be excluded in patients. The degree to which iodide transport capacity and NIS mRNA expression are reduced seems to be related to the biological effectiveness of the type of radiation delivering the absorbed dose to the target, with (211)At (which has the highest relative biological effectiveness) causing the highest degree of stunning per unit absorbed dose in the present study.

Recombinant human thyroid stimulating hormone in 2008: focus on thyroid cancer management

Radioiodine (RAI) ablation following thyroidectomy is standard of care treatment for patients with intermediate or high risk differentiated thyroid cancer. Traditionally, this has been achieved by forgoing thyroid hormone replacement postoperatively, allowing endogenous thyroid stimulating hormone (TSH) levels to rise. This rise in TSH provides the stimulus for RAI uptake by the thyroid remnant, but is associated with clinical hypothyroidism and its associated morbidities. Recombinant human TSH (rhTSH, thyrotropin alfa [Thyrogen^®], Genzyme Corporation, Cambridge, MA, USA) was developed to provide TSH stimulation without withdrawal of thyroid hormone and clinical hypothyroidism. Phase III studies reported equivalent detection of recurrent or residual disease when rhTSH was used compared with thyroid hormone withdrawal (THW). These trials led to its approval as an adjunctive diagnostic tool for serum thyroglobulin (Tg) testing with or without RAI imaging in the surveillance of patients with differentiated thyroid cancer. Recently, rhTSH was given an indication for adjunctive preparation for thyroid remnant ablation after phase III studies demonstrated comparable outcomes for rhTSH preparation when compared with THW. Importantly, rhTSH stimulation has been found to be safe, well tolerated, and to result in improved quality of life. Here, we review the efficacy and tolerability studies leading to the approval for the use of rhTSH in well-differentiated thyroid cancer management.

Efficacy of nodal dissection for treatment of persistent/recurrent papillary thyroid cancer

CONTEXT

Although commonly performed, data are lacking regarding efficacy and safety of lymph node dissection (LND) for recurrent/persistent papillary thyroid cancer (PTC).

OBJECTIVE

Evaluate the efficacy and morbidity of LND in recurrent/persistent PTC.

DESIGN

Retrospective review of central or lateral LND performed for persistent/recurrent PTC between January 2004 and March 2006.

SETTING

Multidisciplinary thyroid cancer clinic with a single surgeon at an academic medical center.

PARTICIPANTS

Seventy-five patients who underwent 79 LND for persistent/residual PTC. Safety analysis included all 79 resections. Exclusion criteria for the efficacy analysis were factors prohibiting evaluation of thyroglobulin (Tg) response. Forty-one resections were included in the efficacy analysis.

INTERVENTION

Selective LND per standard of care.

MAIN OUTCOME MEASURE

Primary outcome was the Tg response to LND. Secondary outcomes were surgical complications.

RESULTS

Thirty-nine of the 41 evaluable resections also had Tg data allowing classification of Tg response. Of 39 classifiable resections, 16 (41%) resulted in undetectable postoperative stimulated Tg levels. An additional 12 resections resulted in significant (> or =50%) reductions in suppressed or stimulated Tg levels for an overall improvement rate of 72%. Of all 79 resections, 25 (32%) resulted in minor and 7 (9%) resulted in major complications.

CONCLUSIONS

LND for persistent/recurrent PTC is a relatively safe procedure in experienced hands. It can lead to an undetectable Tg in 41% of cases and produce a major Tg reduction in an additional 31%. Its efficacy in short-term follow-up is comparable with that reported for I-131, and it should be considered in the management of persistent/recurrent PTC.

Postoperative management of thyroid carcinoma

Survival from differentiated thyroid carcinoma is generally good, but postoperative management plays an important role in minimizing the likelihood of disease recurrence. Postoperative management is generally performed by endocrinologists and nuclear medicine physicians, who exploit thyroid cells' inherent iodineavidity and sensitivity to hormonal manipulation in a unique cancer management paradigm. Endocrinologists manage thyroid hormone replacement/thyroid stimulating hormone suppression and coordinate surveillance. Nuclear physicians administer targeted therapy with radioactive iodine and perform imaging studies to assess disease status. This article provides an overview of the postoperative assessment, treatment, and follow-up of patients who have thyroid carcinoma.

A new functional parameter measured at the time of ablation that can be used to predict differentiated thyroid cancer recurrence during follow-up

BACKGROUND

This study addresses the questions whether patients with a high risk for recurrent thyroid cancer can be identified at initial stage, i.e. at the time of ablation.

METHODS

We evaluated tumor recurrence in consecutive patients treated for differentiated thyroid cancer (DTC). Prognostic factors were statistically analyzed. We defined prognostic parameters based on thyroglobulin (Tg) levels, 24-h I-131 uptake rates and TSH values: (a) Tg/TSH, (b) Tg/24-h I-131 uptake value, and (c) Tg/(TSHx24-h I-131 uptake).

RESULTS

We included 190 patients (50 male, 140 female; mean age 47 years) with DTC for analysis, 146 without distant metastases and 44 with M1 tumor stage at initial presentation. The mean period of follow-up was 10.4 years (s.d. +/- 3.7 years). In 18 out of the 146 DTC patients with M0 disease (12.4%), tumor recurrence was found during follow-up. Although tumor stage, age, and standard biochemical values significantly differ between patients with and without recurrent disease or between patients with M0 and M1 tumor stage, the newly defined parameter Tg/(TSHx24-h I-131 uptake) was the best independent significant prognostic parameter in the assessment whether patients will develop a tumor recurrence during follow-up or not.

CONCLUSION

High Tg/(TSHx24-h I-131 uptake) ratios justify an adjustment of the I-131 activity for ablation therapy. To assess the optimal cut-off value for a dose adjustment, however, further studies are required in more patients, but the initial results are encouraging with respect to improving outcome in DTC patients.

Evaluation of the Cell Death Pathway and Apoptosis-Stunning Effect Relationship After Low- and High-Dose I-131 Administrations in Rat Thyroid Tissue

OBJECTIVES

This study had two aims; (1) to describe the cell death pathway (apoptosis or necrosis) induced by a low and high dose of radioiodine (I-131) in rat thyroid tissue in in vivo conditions and (2) to determine the role of apoptosis in the development of "stunning effect" in the thyroid tissue with low and high doses of I-131 application.

DESIGN

The experimental group consisted of 18 rats; low and high I- 131 doses with a 1-week interval were administered to this group. At first, low doses were injected intraperitoneally (i.p.) (net injected dose was 51.54 +/- 8.6 microCi). After 1 week of the low-dose injection, high doses were also injected (net injected dose was 934.9 +/- 211.8 microCi). Thyroidal I-131 uptakes for both low- and high-dose applications were calculated by using a gamma camera after 24 hours of injections. Immediately after the uptake calculation, thyroid tissues were resected. A control group of 10 rats was also included in the study; in this group, I-131 was not administered. Thyroid tissues of this group rats were also resected. DNA was extracted from thyroid tissues, and damage was examined with the "DNA ladder by agaroz gel electrophoresis."

RESULTS

Thyroidal I-131 uptakes were calculated as 11.3% +/- 3.6% and 9.8% +/- 5.3% at the 24th hour after low- and high-dose I-131 applications, respectively. When the low- and high-dose uptake values were compared for each rat; a significant relationship was not found between thyroidal uptakes and injected low and high doses of I-131. When the chromosome images were examined, there was healthy DNA appearance in 1 rat; in 4 rats, only necrotic hyperfragmentations were observed; in 9 rats, both apoptotic specific fragmentations and necrotic hyperfragmentations were observed; and in 4 rats, apoptosis, necrosis, and healthy DNA appearances were seen together. In none of the rats, specific fragmentations concordant only with apoptosis was found. When the thyroidal uptake alterations were taken into consideration, significant difference was not found between first and second uptake calculations (p = 0.28). No significant relationship was also observed between thyroidal uptake alterations and apoptosis-necrosis-healthy DNA findings. Additionally, when we take into consideration the DNA results of only 13 of the rats that had reduced thyroidal uptake, a significant relationship could also not be observed between reduced uptake and apoptotic, necrotic, or healthy tissue findings. Interestingly, apoptotic and necrotic tissue or only necrotic, tissue findings were observed in the other 5 rats which had increased thyroidal uptake.

CONCLUSIONS

Following I-131 administration, two types of cell death--both apoptosis and necrosis findings--have been observed in most of the rats. We think that the decreased uptake values are because of the probable stunning effect in thyroid tissue. We also investigated whether the stunning effect is related to apoptosis. According to our results, it can be concluded that the stunning effect is not related to tissue damage, cell decrease, or cell death. Alternatively, we think that this can be related to a radiation-induced reduction of iodine uptake/metabolism or a modified iodine transport mechanism. For further in vivo studies, this experimental model using normal rat thyroid tissue may be useful in investigating the cell death pathways induced by I-131 and its probable roles in the development of the stunning phenomenon.

Radioiodine therapy in hyperthyroid disease: poorer outcome in patients with high 24 hours radioiodine uptake

PURPOSE

To evaluate the importance of 24 h radioiodine uptake (24 h RIU) for the outcome of radioiodine treatment of hyperthyroidism.

METHODS

Retrospective analysis of 72 patients who underwent radioiodine treatment for toxic goiter at our outpatient clinic [29 diffuse goiters (DG), 30 toxic multinodular goiters (TMG) and 13 toxic adenomas (TA)]. Thyroid status was determined by TSH, fT3 and fT4 levels, and outcome was rendered successful when hyperthyroidism was absent. Relation between low 24 h RIU (below median) or high 24 h RIU (above or equal to median) and outcome was evaluated.

RESULTS

Of patients with DG and low 24 h RIU, 15% remained hyperthyroid, as opposed to 56% of patients with DG and high 24 h RIU (P<0.05). Of patients with TMG and low 24 h RIU, none remained hyperthyroid, as opposed to 44% of patients with TMG and high 24 h RIU (P<0.01). Of patients with TA and low 24 h RIU, none remained hyperthyroid, as opposed to 43% of patients with TA and high 24 h RIU (NS, P = 0.19).

CONCLUSION

In patients with hyperthyroid disease treated with radioiodine the outcome is poorer for patients with high 24 h RIU compared with low 24 h RIU measured prior to treatment when the radioiodine dose is calculated on the basis of 24 h RIU.

Changing Concepts in the Management of Differentiated Thyroid Cancer

The management of patients with differentiated thyroid cancer has changed significantly over the last few decades. Mortality has decreased as the result of earlier detection, refined surgical approaches, subsequent radioiodine ablation, and the development of more sensitive methods for detecting and monitoring disease recurrence. The latter has been facilitated by serum thyroglobulin measurements, the use of recombinant human thyrotropin, and the use of 18F-deoxyglucose/positron emission tomography in selected instances where radioiodine imaging fails to locate known or suspected recurrent or metastatic disease.