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DOI: 10.1148/radiol.2463061328
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(Radiology 2008;246:887-894.)
© RSNA, 2008

Nuclear Medicine

Initial Staging of Differentiated Thyroid Carcinoma: Continued Utility of Posttherapy 131I Whole-Body Scintigraphy1

Kevin P. Donahue, MD, Nirav P. Shah, MD, Stephanie L. Lee, MD, PhD, and M. Elizabeth Oates, MD

1 From the Nuclear Radiology Section, Department of Radiology (K.P.D., N.P.S., M.E.O.) and Section of Endocrinology, Diabetes, and Metabolism, Department of Medicine (S.L.L.), Boston Medical Center and Boston University School of Medicine, 88 E Newton St, Boston, MA 02118. From the 2004 RSNA Annual Meeting. Received August 22, 2006; revision requested October 27; revision received May 8, 2007; accepted June 11; final version accepted August 8. Address correspondence to M.E.O. (e-mail: meoate2{at}email.uky.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 
Purpose: To retrospectively compare pretherapy iodine 123 (123I) and posttherapy iodine 131 (131I) sodium iodide whole-body scintigraphy of patients with newly diagnosed differentiated thyroid cancer to determine if there is significant and clinically relevant discordance of nonphysiologic iodide-avid foci (IAFs) between the two examinations.

Materials and Methods: This study was approved by the Institutional Review Board, the requirement for informed consent was waived, and the study complied with HIPAA. The authors identified 108 patients (88 women, 20 men; age range, 16–86 years; mean, 47.5 years; 45 patients younger than 45 years, 63 patients 45 years and older) who previously had undergone total or near-total thyroidectomy for differentiated thyroid carcinoma. Each patient had undergone a pretherapy 123I whole-body scan followed by a posttherapy 131I whole-body scan. The number and location of IAFs were recorded on both scans. Data were compared by using a Wilcoxon signed rank test for paired data and assessed clinical relevance based on changes in tumor staging.

Results: Posttherapy 131I whole-body scans revealed additional IAFs outside the thyroid bed not detected on pretherapy 123I scans in 21 (19%, P < .001) of 108 patients. Nineteen (90%) of these 21 had IAFs in new locations (P < .001), with tumor upstaging of 11 (59%, 10% of total) of those 19 patients; six (55%, 6% of total) of those 11 had scintigraphic patterns consistent with unsuspected metastatic disease. Concordant scintigraphic patterns were observed in 87 (81%) of 108.

Conclusion: In patients with newly diagnosed differentiated thyroid cancer who had undergone thyroidectomy and 131I ablation, posttherapy 131I whole-body scintigraphy revealed new IAFs in 18% and clinical upstaging occurred in 10% of patients compared with pretherapy 123I whole-body scintigraphy. Therefore, posttherapy 131I whole-body scintigraphy provides incremental clinically relevant information as it helps to establish the true extent of IAFs and may contribute to altering of staging.

© RSNA, 2008


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 
Differentiated papillary and follicular thyroid cancers are unique neoplasms for which staging is determined by anatomic extent and age criteria (1). While less advanced stages of disease have extremely favorable survival rates, more advanced stages portend a less favorable prognosis (Table 1) (1). The iodide avidity of these neoplasms, including their metastases, allows noninvasive staging of the disease by using radioiodine (sodium iodide) whole-body scintigraphy. Furthermore, because of its iodide avidity, malignant tissue can be effectively treated with specific radiation therapy with iodine 131 (131I).


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  		Table 1. Staging Criteria and Observed 5-year Survival Rates for Differentiated Thyroid Carcinoma

 
Traditionally, pretherapy imaging of differentiated thyroid cancer was performed with a small (typically 1–2 mCi [37–74 MBq]) dose of 131I, then followed 48–72 hours later with whole-body scintigraphy. Thereafter, a therapeutic dose (typically 50–200 mCi [1850–7400 MBq]) was given and posttherapy whole-body scintigraphy was performed 7–10 days later (2–5). The radioisotope iodine 123 (123I) sodium iodide has become increasingly available, permitting its routine use in some institutions (6–8). The use of 123I has exposed some of the shortcomings of 131I as a pretherapy scintigraphic tracer that are related to its decay profile (364-keV gamma photon and beta emission). The beta decay that makes 131I an effective radiotherapeutic agent is believed to produce the thyroid tissue "stunning" effect reported in some studies (2–4,9–13). This effect may reduce the efficacy of the subsequent larger therapeutic dose and may contribute to incomplete eradication of tumor burden (2–4,9–11). However, the debate about the existence of stunning remains open, with more studies failing to demonstrate either tissue stunning after 131I diagnostic scanning or the clinical significance of the stunning phenomenon (5,14).

With the use of 123I, clinicians avoid this controversy, as it has not been associated with stunning (6). Furthermore, 123I (energy level, 159-keV gamma photon) produces conventional planar images and single photon emission computed tomographic (CT) images with higher resolution and improved contrast when compared with 131I (8). 123I has been shown in several studies to be equal or superior to 131I as an alternative pretherapy imaging tracer for differentiated thyroid carcinoma (13,15–18). However, there are drawbacks to the use of 123I. Its 13-hour physical half-life renders images obtained after 24 hours inferior because of count paucity. Routine images obtained at 24 hours may be limited by a lower lesion-to-background ratio, rendering subtle lesions difficult to detect.

With this 123I paradigm in place, the effectiveness of posttherapy 131I whole-body scintigraphy has been called into question (19,20). The earlier protocol compared the concordance of pretherapy 131I and posttherapy 131I whole-body scintigraphy. With that protocol, posttherapy 131I whole-body scintigraphy was useful, as it identified (a) additional iodide-avid foci (IAFs), because the much higher dose and timing of the scan enhanced the posttherapy foci contrast relative to the rest of the body, and (b) tissue seen as iodide avid (so-called stunned tissue) on the pretherapy scan, but not on the posttherapy scan (20–22). Recent studies that used the new paradigm of comparing pretherapy 123I whole-body scintigraphy with posttherapy 131I whole-body scintigraphy have suggested a high degree of concordance between the two scans (8,15–18,23). However, the significance of any discordance and its effect on clinical staging and patient treatment remain uncertain. Therefore, the purpose of our study was to retrospectively compare pretherapy 123I and posttherapy 131I whole-body scintigraphy in patients with newly diagnosed differentiated thyroid cancer to determine if there is significant and clinically relevant discordance of nonphysiologic IAFs between the two examinations.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 
Patients
Prescriptions for 131I from January 1, 2002, to July 31, 2005, were reviewed with the approval of our Institutional Review Board that approved our study. The requirement for informed consent was waived, and the study complied with the Health Insurance Portability and Accountability Act. Patients were included in the study if they had a primary differentiated thyroid carcinoma and had undergone total or near-total thyroidectomy for initial treatment followed by 131I ablation. Patients with recurrent disease were not eligible. All patients had a tissue diagnosis of differentiated papillary or follicular thyroid cancer made by our Pathology Department, or Endocrinology Section records indicating that the clinician's diagnosis was in accordance with the tissue diagnosis made at an outside institution. Further inclusion criteria required that pretherapy and posttherapy whole-body scintigraphy had been performed at our institution by using 131I and 123I, respectively, and that pretherapy whole-body scans were performed 24 hours after 123I oral administration, and posttherapy whole-body scans were performed 7–8 days following 131I oral administration.

Whole-Body Scintigraphic Imaging
All patients were instructed to avoid iodinated intravenous contrast material for at least 6 weeks and maintain a low-iodine diet for 7–10 days prior to scintigraphic imaging and were prepared for imaging and therapy with withdrawal from synthetic thyroid hormone replacement and 30 µU/mL (30 mIU/L) or more of thyroid-stimulating hormone serum. Women of child-bearing age had a negative blood pregnancy test within 2 days of 123I administration in anticipation of 131I therapy. At 24 hours prior to imaging, 123I was administered orally. The next day, whole-body scanning with the neck hyperextended was performed with images acquired in anterior and posterior projections at a rate of 4 cm/min by using a dual-detector gamma camera (ecam; Siemens Medical Solutions, Hoffman Estates, Ill) equipped with low-energy, high-resolution collimators and peaked at 159 keV with a 15% window. Protocols for the dosing of 123I varied over the course of this study from 5 mCi to 1.5–2 mCi (185 MBq to 55.5–74 MBq) as evidence became available that lower doses produced results comparable to those produced with higher doses (7,24).

On the same or next day, therapeutic 131I was administered orally. When the patient returned 7–8 days later for posttherapy 131I scintigraphy, scanning with the neck hyperextended was performed, with images acquired in anterior and posterior projections at a rate of 4 cm/min by using the same dual-detector gamma camera equipped with high-energy collimators and peaked at 364 keV with a 15% window. Dosing of 131I was predicated on the extent of IAFs observed on the 123I whole-body scans and the original surgical staging.

Scintigraphic Analysis
Scintigraphic images had been interpreted and reported by one of three experienced nuclear radiologists (a nonauthor, N.P.S., and M.E.O., with 30, 3, and 20 years experience, respectively). The radiologists reported the number and location of abnormal IAFs on 123I and 131I scans. Radiologists were not blinded to the results of 123I scans when interpreting 131I scans and routinely compared them when interpreting the second scan, as is done in clinical practice.

Data Collection and Staging
Original scintigraphic reports were then reviewed. The number and location of IAFs outside the thyroid bed on pretherapy 123I and posttherapy 131I whole-body scans were recorded and cataloged for each patient (K.P.D. and M.E.O.) as being located in the regional lymph nodes, mediastinum, lungs, abdomen, and/or bone. These tabulated results from the pretherapy and posttherapy scans were then compared (K.P.D., N.P.S., M.E.O.) to assess discordance (ie, IAFs observed on only one scan) between the two scans. Doses of 123I and 131I were recorded (K.P.D.) to enable the authors to examine the relationship between the dose of radioiodine and the number of IAFs seen at whole-body scintigraphy. Patient age at the time of posttherapy 131I scintigraphy, an important criterion in differentiated thyroid cancer staging, was recorded (K.P.D.).

Surgical pathologic and operative reports were reviewed for patients found to have discordant 123I and 131I scan findings. The size of the primary thyroid tumor, capsular penetration, extension into surrounding tissues, and regional nodal involvement were recorded and combined with the results of the pretherapy 123I scan to provide an initial staging for this investigation by all authors of the manuscript through consensus. Tumors were then restaged and categorized in patient age cohorts by using the results of posttherapy scans and the age cohorts used in the staging criteria by all authors through consensus (1). Patients with discordant scans then had their 123I and 131I dosing data reviewed to ensure that aberrantly low doses of 123I were not associated with aberrantly high doses of 131I, as this phenomenon would play a confounding role in the discordance between the studies.

Statistical Analysis
The outcome variables (differences in IAFs outside the thyroid bed between the 123I and 131I whole-body scans) exhibited a distribution with a high frequency of zero values and consequently could not be reasonably approximated by using a Gaussian distribution; thus, nonparametric methods were used. To assess the significance of differences in the numbers of IAFs, the Wilcoxon signed rank test for paired data was used. This test was used first to test all discordant studies and then twice more to test individually for significance in (a) IAFs in new sites, and (b) additional IAFs in previously identified sites.

To assess for possible confounding factors, the dose of 123I, the dose of 131I, patient sex, and patient age (younger than 45 years or 45 years and older) for all 108 patients were examined by using the Spearman rank correlation coefficient and the {chi}2 test for correlation to the difference in IAFs outside the thyroid bed seen on 123I and 131I scans. A further confounding effect, that the possibility that low doses of 123I were associated with high doses of 131I, was also addressed by using the Spearman rank correlation coefficient. This possibility was evaluated for the entire study population and for the subpopulation of discordant studies. Possible association between 123I and 131I doses with total IAFs detected on the respective whole-body scans was assessed by using the Spearman rank correlation coefficient in an effort to examine a possible dose-focus relationship. All statistical computations were performed (K.P.D.) in consultation with a nonauthor biostatistician by using software (SPSS, version 12.0.1; SPSS, Chicago, Ill).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 
Demographics and Dosing
The medical record review yielded 108 patients who met our study criteria. The study comprised 88 women and 20 men (age range, 16–86 years; mean, 47.5 years), with 45 patients younger than 45 years and 63 patients 45 years and older. Patients were administered 123I with a radioactivity range of 0.7–5.0 mCi (mean, 2.4 mCi [range, 25.9–185 MBq; mean, 88.8 MBq]) and 131I with a radioactivity range of 30–205 mCi (mean, 122.6 mCi [range, 1110–7585 MBq; mean, 4536.2 MBq]). Administered doses were in the ranges specified by protocols in use when the patient was treated, with the exception of a single dose (0.7 mCi [25.9 MBq]), which was below the specified limit of 1.5 mCi [55.5 MBq] for 123I.

Discordant Scans
Comparison of the pretherapy 123I whole-body scans with the posttherapy 131I whole-body scans with respect to IAFs outside the thyroid bed revealed that all 131I scans showed the foci initially identified on 123I scans (Table 2). However, this analysis yielded discordant scintigraphic patterns between pretherapy 123I and posttherapy 131I scans where additional IAFs were identified on the 131I scan in 21 (19%) of 108 patients (Figs 1–3). These results indicated a significant difference (P < .001). Of these 21 patients with discordant scans, new IAF sites were identified in 19 versus additional IAFs identified in established sites in two (Table 2).


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  		Table 2. Comparison of Pretherapy 123I and Posttherapy 131I Scintigraphic Patterns and Statistical Analysis of Discordant Foci

 

Figure 1A
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  		Figure 1a: Regional scintigraphy of lymph nodes. (a) Anterior pretherapy 123I scan shows IAF (arrow) in thyroid bed, consistent with remnant thyroid tissue. (b) Anterior posttherapy 131I scan shows remnant tissue (arrow) and reveals new IAF (arrowhead) that indicates regional nodal disease.

 

Figure 1B
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  		Figure 1b: Regional scintigraphy of lymph nodes. (a) Anterior pretherapy 123I scan shows IAF (arrow) in thyroid bed, consistent with remnant thyroid tissue. (b) Anterior posttherapy 131I scan shows remnant tissue (arrow) and reveals new IAF (arrowhead) that indicates regional nodal disease.

 

Figure 2A
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  		Figure 2a: Whole-body scintigraphy of lung metastases. (a) Anterior and posterior pretherapy 123I scans show IAF cluster in thyroid bed, consistent with thyroid remnant tissue. (b) Anterior and posterior posttherapy 131I scans show multiple new IAFs (arrows), indicating pulmonary metastases and asymmetric physiologic activity in oropharynx.

 

Figure 2B
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  		Figure 2b: Whole-body scintigraphy of lung metastases. (a) Anterior and posterior pretherapy 123I scans show IAF cluster in thyroid bed, consistent with thyroid remnant tissue. (b) Anterior and posterior posttherapy 131I scans show multiple new IAFs (arrows), indicating pulmonary metastases and asymmetric physiologic activity in oropharynx.

 

Figure 3A
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  		Figure 3a: Whole-body scintigraphy of bone metastasis. (a) Anterior pretherapy 123I scan shows definite single thyroid bed remnant. (b) Anterior posttherapy 131I scan shows discrete, intense IAF (arrow) in middle lower thorax. In retrospect, this lesion is subtle and present in a. CT scan corroborated small lytic lesion in lower sternum.

 

Figure 3B
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  		Figure 3b: Whole-body scintigraphy of bone metastasis. (a) Anterior pretherapy 123I scan shows definite single thyroid bed remnant. (b) Anterior posttherapy 131I scan shows discrete, intense IAF (arrow) in middle lower thorax. In retrospect, this lesion is subtle and present in a. CT scan corroborated small lytic lesion in lower sternum.

 
Independent assessment for significance between the two groups of patients with discordant scans was undertaken. The patients with IAFs in new locations showed a significant increase in the number of foci (P < .001); however, those with additional IAFs at sites previously shown to have such foci did not attain significance (P = .157) (Table 2).

To address the issue of confounding by other variables, patients with concordant and discordant scans were compared for the variables of age (P = .42), 123I dose (P = .47), and 131I dose (P = .13) by using an independent sample t test. The proportion of male patients in the concordant and discordant groups was also examined (17% vs 23%, x = 0.15, P = .70).

Staging
Staging was undertaken by using the guidelines for differentiated thyroid cancer promulgated by the American Joint Commission on Cancer (Table 1) (1). Of 19 patients with discordant 123I and 131I scans indicating new IAF sites, changes in clinical staging were seen in 11 (58%), representing 10% of the total population (Table 3). Eight of those 19 patients had unsuspected distant IAFs in the lung or bones.


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  		Table 3. Age-related Incidence of Discordance and Altered Stage with Posttherapy 131I Scintigraphy

 
Staging of differentiated thyroid carcinoma is heavily influenced by patient age (Table 1). As such, the patients were divided into age cohorts, those younger than 45 years and those 45 years and older, and reexamined. The age cohorts were chosen for their relevance to staging criteria. The cohorts were similar in size, with 45 (42%) of 108 patients younger than 45 years and 63 (58%) 45 years or older. The incidence of scintigraphic discordance within these two groups was similar (eight of 45, 18%; 11 of 63, 17%, respectively), as were the locations where the scintigraphic discordance was noted, with the exception of bone metastases (Table 4). However, upstaging was more common in patients 45 years and older (eight of 63, 13%) when compared with patients younger than 45 years (three of 45, 7%) (Table 3).


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  		Table 4. Age-related Biodistribution of New 131I Foci

 
Dose-Dose and Dose-Foci Relationship
There was no significant association between doses of 123I and 131I in the entire population (r = –0.13, P = .16) or in the subpopulation of discordant studies (r = –0.12, P = .60). Further, doses of 123I and 131I were not significantly associated with the total number of IAFs (r = 0.07, P = .5; r = 0.17, P = .08, respectively). However, it is noted that the association of 131I does trend toward significance.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 
In our study, we evaluated differences in the scintigraphic patterns between pretherapy 123I and posttherapy 131I whole-body scans and found a significant difference (P < .001) between the IAFs detected on pretherapy 123I and posttherapy 131I whole-body scans. There were two groups of patients with discordance: one group with IAFs in one or more new sites (n = 19) and one group with additional IAFs (n = 2) in previously identified sites of disease. The first group was not only significant (P < .001), but was also clinically relevant because IAFs in new locations often alter staging. The second group lacked significance (P = .157) and there is no clinical relevance because additional IAFs in an area of established foci do not affect staging.

Tumor staging of a patient with differentiated thyroid carcinoma is undertaken with a combination of surgical and radiographic staging. While surgical pathology greatly influences the process of staging, radiologic imaging is relied on quite heavily (1). Thus, the clinical relevance of the interpretation of a given study by a radiologist is quite important and affects clinical management. A second round of surgical staging to confirm or disprove the radiographic interpretation of metastatic nodal or distant disease is not common. Therefore, radiographic findings do lead to changes in clinical staging, as seen in 11 patients in this study.

Of 21 patients with discordant 123I and 131I scans, 11 were found to be clinically upstaged on the basis of a posttherapy 131I whole-body scan that showed additional IAFs in new locations when compared with the pretherapy 123I whole-body scan. The specific changes in patient treatment brought about by the changes in clinical stage are beyond the scope of this study, but the changes in prognosis can be dramatic (Table 1).

It is with this concept in mind that the comparison between the discordance and clinical changes in age cohorts was undertaken. While the incidence of discordant scans was equivalent between the two age cohorts, the incidence of upstaging was not, rather it was more common in patients 45 years and older (Table 3). This result was not surprising, as there are more staging options available for individuals 45 years and older; there is a less onerous burden to meet criteria for a higher stage as compared with those younger than 45 years, where the single criterion is the presence of distant metastatic disease (Table 1). However, while these results are not surprising, they are important. The patients 45 years and older are frequently upstaged higher than those younger than 45 years, thereby placing them in stages with lower 5-year survival rates (Tables 1, 3).

A key feature of our study was its retrospective nature. It was thought that use of radiographic reports and data originally generated for the exclusive purpose of patient care would introduce less bias. Further, these were the studies used for tumor staging in patients after initial surgery. As such, it allowed the authors to state that the staging changes and associated effect on expected survival were actual and not theoretical. The authors did not follow patients to ensure they conformed to the reported 5-year survival data as this was outside the scope of the study.

It has been suggested that the number of IAFs observed on pretherapy 123I scans may be related to the dose of 123I given, and by extension, posttherapy discordance may be a product of this dose dependence (16). The data compiled in our study fail to demonstrate a correlation between the dose of 123I in our study range (0.7–5 mCi [25.9–185 MBq]) and the number of IAFs visualized (r = 0.07, P = .5). Consequently, it is unlikely that the significant difference we observed in IAFs is a product of decreasing diagnostic dose of 123I over time. That is, despite our initial use of 5 mCi (25.9 MBq) of 123I and a downward trend to our current dose of 2 mCi (74 MBq), it is unlikely this trend resulted in the observed discordance between 123I and 131I scans. A trend toward significance (r = 0.17, P = .08) is noted when the correlation between the therapeutic dose of 131I (30–205 mCi [1110–7585 MBq]) and the number of IAFs is examined. This result is not surprising, given that the therapeutic dosage of 131I is generally chosen on the basis of the extent of IAFs seen at pretherapy scintigraphy and with the original surgical staging.

Further possible confounding factors were explored and eliminated to ensure that the significant difference between pretherapy 123I and posttherapy 131I whole-body scans was as robust as possible. Patient age (P = .42), dose of 123I (P = .47), dose of 131I (P = .13), and patient sex (P = .7) all lacked significant correlation to the difference seen in IAFs. Additionally, the doses of 123I and 131I lacked any significant inverse correlation among the study population as a whole and in the subgroup of those patients with discordant scans (r = –0.13, P = .16; r = –0.12, P = .6, respectively). This finding is significant as it indicates that the discordant scans were not the product of low doses of 123I followed by high doses of 131I, thereby producing discordance by means of aberrant dosing patterns.

Some studies have shown greater concordance between pretherapy 123I and posttherapy 131I whole-body scans (12,23). It is important to note that the purpose, scope, and methods of those studies differ from ours. Some focused on the diagnostic role of 123I versus 131I exclusively, or in part, on the imaging of recurrent differentiated thyroid carcinoma, a group that was explicitly excluded from our study (12,23). Further, posttherapy 131I whole-body scans were performed sooner after dosing (23) than in our study, possibly confounding results.

Our study was limited in that it reports patients from a single institution, and thus, the possibility of population bias exists. Another limitation was that the data rely on original report quality and consistency and the inherent difficulty in resolving the exact number and location of sites of pathologic radioiodine activity. While we recognize these limitations, it was considered important that the images not be reinterpreted for the purpose of this study, as that could introduce bias and reduce the clinical applicability of the study. Further, the staging of differentiated thyroid cancer does not require exact localization of distant metastatic disease (Table 1). Posttherapy 131I scan interpretation was not blinded to the results of pretherapy 123I scans. However, this interpretive process is consistent with clinical practice. Finally, this study does not address the relationship of thyroglobulin levels through the course of diagnosis, pretherapy imaging, and posttherapy imaging, as the data were not available for all patients.

In conclusion, there is a significant difference in scintigraphic patterns between pretherapy 123I and posttherapy 131I whole-body scans when evaluating pathologic IAF outside the thyroid bed. Discordant scintigraphic patterns may lead to altered staging; in our study, this change occurred in 11 (10%) of 108 patients, often with unsuspected distant metastatic IAF. When using 123I as the pretherapy imaging tracer, we believe that posttherapy 131I whole-body scintigraphy should be performed routinely because it provides clinically relevant information, especially in patients 45 years and older. Further, it is not the intent of the authors to imply that pretherapy scans are rendered obsolete, as they can guide selection of therapeutic radioiodine dose, given the extent of metastatic disease and degree of uptake by the thyroid remnant. The number of IAFs identified is not significantly related to the dose of 123I, but does influence the therapeutic dose of 131I administered, as expected.


   ADVANCES IN KNOWLEDGE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE
 References
 


   IMPLICATION FOR PATIENT CARE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
References
 


   ACKNOWLEDGMENTS
 
The authors thank Al Ozonoff, PhD, for his biostatistical help and support.


   FOOTNOTES
 

Abbreviations: IAF = iodide-avid focus

Author contributions: Guarantors of integrity of entire study, all authors; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, K.P.D., N.P.S., M.E.O.; clinical studies, all authors; statistical analysis, K.P.D., N.P.S.; and manuscript editing, all authors

Authors stated no financial relationship to disclose.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 

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