Title: Assessment of the Incremental Value of Recombinant TSH Stimulation before
FDG PET/CT Imaging to Localize Residual Differentiated Thyroid Cancer
S Leboulleux1, PR Schroeder2, NL Busaidy3, A Auperin4, C Corone1, HA Jacene5, ME
Ewertz2, C Bournaud1, RL Wahl5, SI Sherman3, PW Ladenson2 and M Schlumberger1.
1Department of Nuclear Medicine and Endocrine Oncology, Institut Gustave Roussy, University Paris
Sud-XI, Villejuif, France, 94805
2Department of Medicine, Division of Endocrinology and Metabolism, Johns Hopkins University School
of Medicine, Baltimore, MD, United States, 21201
3Department of Endocrine Neoplasia and Hormonal Disorders, Unit 435, Department of Endocrine
Neoplasia and Hormonal Disorders, The M. D. Anderson Cancer Center, Houston, Texas, United
4Department of Statistics, Institut Gustave Roussy, Villejuif, France
5Russell H. Morgan Department of Radiology and Radiological Science, Division of Nuclear Medicine,
Johns Hopkins University School of Medicine, Baltimore, MD, United States, 21287
Short Title: Incremental value of rhTSH stimulation before FDG PET/CT
Precis: The use of rhTSH before FDG-PET/CT significantly increases the number of lesions detected
but lesions found only by rhTSH-PET contributed to treatment changes in 13% patients, among whom
only half were true-positive on pathology.
Key words: PET, PET/CT, FDG, fluorodesoxyglucose, thyroid cancer, recurrence, thyroglobulin
Word counts: abstract: 249 ; text: 3598
Number of tables: 3 ; Number of figures: 2, References: 38
This study was supported by an unrestricted grant from Genzyme. S.S., P.L. and M.S. S. received
lecture fees from Genzyme. HAJ., CC. received honoraria from Genzyme Corporation. S.L., P.R.S.,
N.L.B., A.A., M.E.E., C.B. R.L.W., have nothing to declare
ClinicalTrials.gov Identifier: NCT00181168
J Clin Endocrin Metab. First published ahead of print January 21, 2009 as doi:10.1210/jc.2008-1747
Copyright (C) 2009 by The Endocrine Society
PURPOSE: To assess prospectively the impact of recombinant human TSH (rhTSH)
administration on PET/CT imaging in differentiated thyroid cancer (DTC) patients who, after
primary treatment, had a suppressed or stimulated serum thyroglobulin >10 ng/mL and no
radioactive iodine uptake consistent with thyroid cancer on a whole body scan.
PATIENTS-METHODS: PET/CT was performed before (basal PET) and 24-48 hours after
rhTSH administration (rhTSH-PET) in 63 patients (52 papillary TC and 11 follicular TC).
Images were blindly analyzed by 2 readers. The proposed treatment plan was prospectively
assessed before basal PET, after basal PET and again after rhTSH-PET
RESULTS: One hundred and eight lesions were detected in 48 organs, in 30 patients. rhTSH
PET was significantly more sensitive than basal PET for the detection of lesions (95% vs.
81%, P=0.001) and tended to be more sensitive for the detection of involved organs (94% vs.
79%, P=0.054). However, basal PET and rhTSH PET did not have significant different
sensitivity for detecting patients with any lesions (49% vs. 54%, P=0.42).
Changes in treatment management plan occurred in 19% of the patients after basal PET.
Lesions found only by rhTSH-PET contributed to an altered therapeutic plan in 8 patients,
among whom only 4 were true-positive on pathology (6%).
CONCLUSION: The use of rhTSH for FDG-PET/CT significantly increased the number of
lesions detected, but the numbers of patients in whom any lesion was detected were no
different between basal and rhTSH-stimulated PET/CT scans. Treatment changes due to
true positive lesions occurred in 6% of cases.
A large majority of differentiated thyroid cancer patients (DTC) are cured following
initial treatment, but 15% have persistent disease, most often located in the neck (1).
However, there is no identifiable tumor focus in many patients and the only abnormality is
persistently detectable serum thyroglobulin (Tg) levels. In such patients, imaging is
performed to localize residual disease, including neck ultrasonography, neck and chest
computed tomography (CT) scan, bone scintigraphy, and whole body scan (WBS) after the
administration of a high activity of radioiodine (2).
In recent years, 2-[18F]-fluoro-2-deoxy-D-glucose (FDG) positron emission
tomography (PET) scanning became available in many centers. Thyroid cancer tissue is
often able to concentrate FDG, particularly when poorly differentiated and unable to
accumulate radioiodine (3-7). FDG PET was found to change treatment management plans
in 10 to 50% of patients undergoing scanning for the detection of thyroid cancer recurrence
In vitro studies showed increased FDG uptake in thyroid cells following thyrotropin
(TSH) stimulation (19-23). Several reports in patients with DTC have suggested that FDG
uptake in neoplastic foci increases following TSH stimulation obtained either during
withdrawal of thyroid hormone treatment or following recombinant humanized (rh) TSH
injections (10, 24-27). Both the intensity of FDG uptake measured with the maximum
standardized uptake value (SUVmax) and the number of lesions were reported to increase.
The benefits of TSH stimulation have not, however, been quantified in a large series of
patients. Furthermore, other studies comparing TSH-suppressed and rhTSH-stimulated
FDG-PET scans in different patients, rather than the same patients studied sequentially,
failed to find a difference in PET sensitivity (8, 28).
The aims of this prospective study were to evaluate the incremental value of rhTSH
administration before FDG PET scanning on the number of lesions detected and on the
changes in clinical management in a large number of patients with elevated serum Tg levels
with residual disease that was either not localized at all by other conventional imaging
techniques, or if some disease had been identified, was limited.
PATIENTS AND METHODS
The inclusion criteria for this study were: (i) papillary or follicular TC treated with total
thyroidectomy and radioiodine ablation, (ii) Tg level ? 10 μg/liter more than 1 year after initial
treatment, on thyroxine treatment or following TSH stimulation, obtained either during
thyroxine withdrawal or following rhTSH injections, (iii) no abnormal focus of uptake on a
radioiodine WBS performed within 12 months of the study after the administration of 150 to
3700 MBq (4 to 100 mCi) of 131I, (iv) no more than 3 known or suspected extra-cervical tumor
foci on conventional imaging, and (iv) age greater than 18 years. The exclusion criteria
included: (i) diabetes mellitus, (ii) thyroid withdrawal or rhTSH injections during the month
preceding the study, (iii) presence of Tg antibodies or a recovery test of less than 80%, (iv)
pregnancy or breast feeding, (v) TSH level above 0.5 mU/mL during thyroxine treatment, (vi)
known bone or cerebral metastases.
Patients first underwent a basal PET/CT during thyroxine treatment (whith a serum
TSH concentration <0.5 mU/L), and then a rhTSH (thyrotropin alfa, Thyrogen®, Genzyme
Corporation, Cambridge MA, USA) stimulated PET/CT. rhTSH-PET stimulation was
accomplished by intramuscular injections of 0.9 mg of rhTSH on 2 consecutive days.
In order to determine the optimal timing for rhTSH-PET, a pilot study was first
performed with rhTSH-PET performed 24 hours and 48 hours after the second rhTSH dose.
Subsequently, patients underwent only one PET/CT after rhTSH administration.
The treatment plan was prospectively assessed at three time points--before the
PET/CTs, after the basal PET/CT, and after the rhTSH-PET/CT--to determine whether the
use of rhTSH before PET/CT would lead to changes in management. The six categories of
potential subsequent treatment were: thyroid hormone suppression therapy alone, unilateral
± central neck surgery, bilateral ± central neck surgery, external beam radiation,
chemotherapy, or fine needle aspiration biopsy (FNAB). Any change in the management
strategy based on basal or rhTSH-stimulated PET/CT findings was noted.
The protocol was approved by each site’s institutional review board and/or
independent ethics committee. All patients provided written informed consent to participate in
Imaging was performed on a Discovery LS PET/CT scanner (GE Medical Systems,
Milwaukee, Wisconsin) at Johns Hopkins University (JHH), on a PET/CT Biograph LSO
system (Siemens Medical Solutions, Erlangen, Germany) at Institut Gustave Roussy (IGR)
and on a Discovery ST PET/CT scanner (GE Medical Systems, Milwaukee, Wisconsin) at
MD Anderson Cancer Center (MDACC).
PET/CT scanning was performed after an intravenous injection of 222 to 888 MBq
of FDG, followed by a mean 66 minute tracer uptake phase (range: 41-152). All patients
fasted for at least 6 h before FDG injection. Mean Capillary glucose was 5.5 mmol/liter
(range: 4.3– 7.7) in the 58 patients with available data.
For scanning, patients were positioned supine and head first on an in-line PET-CT
system with a single gantry and table and were allowed to breath quietly. Images from the
upper part of the thorax to mid-thigh level were obtained with arms raised above the head
followed by images from the top of the skull to the upper part of the thorax with arms along
CT parameters were set to 80 milliamperage-seconds (mAs) and 110 kilovolt peak
(kVp) at IGR, weight-adjusted for mAs and set to 140 kVp at JHH, and weight-adjusted for
both mA and kVp at MDACC. Slice thickness was 3.75 to 5 mm.
For PET scanning, four-minute emission acquisitions per FOV were obtained in three-
dimensional mode at IGR, five-minute emission acquisitions and three-minute emission
acquisitions in two-dimensional mode at JHH and MDACC, respectively. PET scans were
reconstructed in a 128 x 128 matrix with an ordered subset expectation maximum iterative
reconstructionalgorithm in the 3 centers.
All PET/CT images were reviewed by two board certified nuclear medicine physicians
(C.C. and H.J.) during separate reading sessions on a Xeleris (GE Medical Systems,
Milwaukee, Wisconsin, USA) or a Visio-Duo Keosys (Keosys, Saint Herblain, France) digital
workstation These physicians were unaware of patient-specific clinical and reviewed the
scans in a random order without knowledge of rhTSH administration. Lesions with FDG
uptake were graded on a scale of 0 to 4 (0: definitely benign; 1: probably benign; 2:
equivocal; 3: probably malignant; 4: definitely malignant). Only lesions with scores of 3 and 4
were considered as positive findings. Discrepancies were resolved by consensus review.
The single pixel maximum standardized uptake value (SUVmax) of each lesion with a
score of 3 or 4 was determined by drawing large region of interests (ROI) encompassing the
entire lesion. Mean SUV (SUVmean) of the liver was assessed by drawing a 3 cm diameter
ROI localized in the right liver lobe.
Sample size determination and statistical methods
For the outcome of the proportion of patients with detectable foci, assuming 60% of
the patients had foci detected on basal PET, 60 patients are required to detect, with a 95%
power, a difference of 20% (e.g., 80% compared to the 60%) on the rTSH-PET, with the
hypothesis that 23% of the exams are discordant between basal PET and rhTSH-PET and
using a two-sided test with alpha = 0.05.
For the outcome of alteration in management, the lower 95% confidence limit must be
at least 10%. For a sample size of 60 patients, if at least a 18% rate of alteration in treatment
is observed, the lower 95% confidence limit would be higher than 10%.
Rates and exact 95% confidence intervals (95% CI) of patients with at least one
lesion, of involved organs and of lesions detected on basal PET and/or rhTSH-PET are
presented. For the per-patient analysis, we used a composite reference standard for the
presence of tumor lesions, using all available cytological, histological, follow-up, and imaging
findings. Rates of patients with lesions detected on basal PET and rhTSH-PET were
compared using the McNemar test for matched proportions. Rates of involved organs or
lesions detected on basal PET and rhTSH-PET were compared using the McNemar test
extended to clustered data in order to account for within patient correlation (29). A mixed
model was used to test the SUV change between basal PET and rhTSH-PET and took into
account the patient effect. Comparisons of glycemia, of the interval of time between FDG
administration and images acquisition and of liver SUVmean between basal PET and rhTSH-
PET were performed using paired t-test.
Analyses were performed using SAS statistical software (SAS institute, Cary, NC,
Results of the pilot study
Fourteen patients (10 females, 4 males, mean age 55 yr, range 28–77 yrs.)
underwent basal PET/CT followed by rhTSH stimulated PET/CT scans performed 24 and 48
hours after the second injection of rhTSH. Eleven patients had PTC and 3 had FTC. Thirteen
lesions were detected in 5 patients with all lesions detected on the basal and 48-hour rhTSH
PET and 12 detected on the 24-hour rhTSH-PET. Lesions were localized to neck lymph
nodes in 4 cases, to mediastinal lymph node in 1, and to lung in 8 cases.
Mean SUVmax for basal PET was 2.1 (range, 1.0-5.8), 2.6 (range, 1.0-10.0) for 24-
hour rhTSH-PET and 2.8 (range, 1.1-11.0) for 48-hour rhTSH-PET. The mean increase of
SUVmax between baseline PET and 24-hour rhTSHPET was 12% (range, -29% to + 79%),
with an increase (>25%) in SUVmax in 3 cases and a decrease (> 25%) in SUVmax in 1 case.
Similarly, the mean increase of SUVmax between the baseline and 48-hour rhTSH-PET was
35% (range, -35% to + 260%), with an increase (>25%) in SUVmax in 6 cases and a decrease
(> 25%) in SUVmax in 1 case. Finally, the mean increase of SUVmax between 24-hour PET and
48-hour rhTSHPET was 23% (range, -36% to + 260%) with an increase (>25%) in SUVmax in
2 cases and a decrease (> 25%) in SUVmax in 2 cases. This relative change between 24 and
48-hour rhTSH-PET was not statistically significant, whether the intra-patient correlation was
taken into account or not (P=0.35 and P=0.28, respectively). Therefore, the subsequent
rhTSH stimulated FDG-PET scans were performed at either 24h or 48h after the second
Sixty-eight patients were included in the study, including the 14 patients from the pilot
study for whom the PET scan results at 24h were used in the final data analysis. Two
patients underwent the first PET/CT, but declined further investigations. In 3 cases, rhTSH-
PET/CT was not performed because of bone metastases diagnosed on the basal PET/CT.
The remaining 63 patients (38 females, 25 males, mean age 52 years, range 25–77 years)
form the basis of this report.
Fifty two patients (83%) had PTC and 11 (18%) had FTC. Among PTC, pathological
subtypes included classical PTC in 40 cases, follicular variant in 7, insular variant in 1, tall
cell variant in 2 and diffuse sclerosing variant in 2 cases. Among FTC, pathological subtypes
included FTC in 4 cases, Hürthle cell in 4, and poorly differentiated carcinoma in 3 cases.
The initial pTNM characteristics of the tumors according to the 2002 pTNM scoring
system (30) were as follows: pT1N0 n=2, pT1N1 n=10, pT1Nx n=4, pT2N0 n=2, pT2N1 n=6
cases, pT2Nx n=2, pT3N0 in=1, pT3N1 n=14 cases, pT3Nx in n=4 cases, pT4N0 n=3 cases,
pT4N1 n=9 cases, pT4Nx in 3 cases and pTxNx in 3 cases. Patients were therefore
classified as stage I, II, III, IV in 16 (25%), 1 (2%), 3 (5%), 26 (41%) cases, respectively.
Stage was undetermined in the 17 (27%), remaining cases.
Initial treatment included total thyroidectomy in all patients, central neck dissection in
39 (62%), ipsilateral neck dissection in 18 (29%) and bilateral neck dissection in 24 (38%)
patients. All patients were treated postoperatively with a high activity of radioactive iodine
with a mean number of radioiodine administrations of 2.2 (median 2; range, 1 to 4). The
mean interval of time between initial treatment and the present study was 71 months (median
52 months, range, 4 months to 23 years).
When entering the study, the mean serum Tg level during thyroxine treatment, which
was available in 62 patients, was 31 μg/liter (range, <1 – 538 μg/liter). Mean stimulated Tg
level, which was available in 59 patients, was 126 μg/liter (range, 10 - >1000 μg/liter).
Previous imaging work up revealed a neck recurrence in 9 patients (14%) and lung
metastases in 7 patients (11%), but no tumor was identified in the remaining 47 patients.
rhTSH-PET/CT scans were performed 24 hours or 48 hours after the last
administration of rhTSH in 40 and 23 cases, respectively. The mean interval of time between
basal PET and rhTSH-PET was 5 days (range: 3-13 days).
Median follow-up after the PET-study was 18 months (range, 6 days to 40 months).
Histopathological Correlation of Image Findings
One or more lesions were identified on FDG PET/CT imaging in 40 of the 63 patients
(63%). In 30 patients, foci were confirmed to be true positives based on pathology in 20
cases and on imaging tests and follow-up data that showed disease progression in the
remaining 10 cases. Five patients with 8 FDG foci in 5 organs (cervical lymph node in 4
cases and thyroid bed in 1 case) were considered to have false positive FDG foci based on
benign cytology in 4 cases or based on pathology showing a muco-epidermoid carcinoma of
the parotid in 1 case. The identities of the FDG foci remained uncertain in 5 (8%) patients in
whom FDG-PET did not alter management. False positives were not included in the data
Among the 35 patients (63%) without false-positive findings, lesion(s) were seen on
both PET/CT scans in 30 patients (86%), on basal PET only in one patient (3%) and on the
rhTSH-PET only in 4 patients (11%). Basal PET localized disease in 31 (49%, 95% CI 36–62
%) patients and rhTSH-PET in 34 (54%, 95% CI 41–67 %) (P=0.42).
Lesions were located in 48 organs (neck in 23 cases, lung in 11 cases, mediastinum
in 8 cases, bone in 3 cases and other in 3 cases). Metastatic organs were identified by both
scans in 35 (73%) cases, by basal PET only in 3 (6%) cases and by rhTSH-PET only in 10
(21%) cases. Basal PET imaging detected 38 (79%, 95% CI 65–90%) of the involved organs
and rhTSH-PET/CT 45 (94%, 95% CI 83–99 %) (P=0.054).
One hundred and eight lesions were identified. Lesions were located in the neck in 35
cases, lung in 51 cases, mediastinum in 14 cases, bone in 3 cases and other organs in 5
cases (Table 2). Among these 108 lesions, 72 (67%) were seen on both scans, 30 (28%)
were seen on the rhTSH-PET only and 6 (6%) were recognized only on the basal PET (Table
1) (Figure 1A). Basal PET imaging detected 78 (72%, 95% CI 63–80 %) of these lesions and
rhTSH-PET 102 (94%, 95% CI 89–98%). (P=0.005).
Changes in FDG uptake
Parameters potentially interfering with FDG uptake were comparable for basal PET
and rhTSH-PET scans. Mean glycemia was 5.5 mmol/L (range, 4.6-7.7) for basal PET and
5.4 mmol/L (range, 4.3-7.7) for rhTSH-PET (P=0.65). The mean interval of time between
FDG administration and image acquisition was 66 min (range, 41-134 min) for basal PET
and 67 min (range, 50-152) for rhTSH-PET (P=0.48). Finally, mean liver SUVmean did not
differ between basal PET (mean SUVmean: 2.22, range 1-3.7) and rhTSH-PET (mean
SUVmean: 2.15, range 1.2-3.1) (P=0.21).
The mean SUVmax of the 78 lesions detected on the basal PET was 5.6 (range, 0.8-
35.7) and the mean SUVmax of the 102 lesions detected on the rhTSH was 5.3 (range, 0.4-
42.2). For the 75 lesions detected on basal and rhTSH-PET scans, mean SUVmax was 5.7
(range, 0.8-35.7) on the basal PET and increased to 6.6 (range, 0.97-42.2) on rhTSH-PET (P
<0.001). In these 75 lesions, the SUVmax increased by more than 25% in 19 (25%) lesions,
decreased by more than 25% in 5 (7%) lesions and remained stable in the 51 (68%)
remaining lesions (Figure 2).
Resulting changes in clinical management
Changes in clinical management were prospectively assessed and were, therefore,
based on routine PET/CT reports. Results of the baseline PET/CT scan induced changes in
the management plan in 12 (19%, 90% CI 11%-29%) patients (Table 3). Lesions found only
by rhTSH-PET contributed to an altered management plan in 8 patients (13%, 90% CI 6%-
22%) among whom 4 proved to be true-positive findings on pathology (6%, 90% CI 2-14%),
which was not statistically significant (Figure 1B). Thyroid hormone suppression therapy
planned after baseline PET/CT was changed after rhTSH PET/CT to neck surgery in 2
cases, to mediastinal surgery in 1 case, to spine surgery in 1 case and to fine needle
aspiration biopsy (FNAB) of neck lymph nodes in 3 cases. Finally, unilateral neck surgery
planned after baseline PET/CT was changed after rhTSH PET/CT to a more extended neck
surgery. No thyroid cancer was found in the patients who underwent mediastinal surgery and
cytology was normal in the 3 patients who underwent FNAB.
Disease localization in thyroid cancer patients with isolated elevated Tg level and no
revealing radioiodine concentration is a common and challenging clinical problem. This
search for residual sites of cancer is motivated by the possibility of curative surgical
treatment in cases with localized disease (17, 31) and prevention of disease complications.
Patients are otherwise typically managed with thyroxine suppressive treatment alone and
FDG PET in our study has a sensitivity of 63%, in accordance with previous reports
(18). Several reports have suggested that FDG PET is more sensitive when performed after
TSH stimulation (10, 24-27). Initial studies were performed after thyroxine withdrawal, but
later studies demonstrated that rhTSH stimulation, which avoids the deleterious impact of
hypothyroidism on quality of life, was also effective (26, 27, 32). An identical rhTSH regimen
to that used for 131I scanning and rhTSH-stimulated Tg measurement was used (26, 27).
There was no available data on the optimal time to perform rhTSH-PET after rhTSH
administration (19-21). Consequently, a pilot study was carried out to determine whether
rhTSH-PET should be performed 24 or 48 hours after the second administration of rhTSH. In
this limited set of observations, we did not observe any significant difference in the results,
suggesting that rhTSH-PET can be performed at either 24 or 48 hours post rhTSH.
A limitation of this study is the absence of systematic histological verification of every
detected lesion. This was neither feasible nor ethical because of the high number of lesions
detected in some patients, and is a well-known limitation precluding true sensitivity and
specificity analyses (33, 34). Our gold standard was, however, histopathological findings in
31 patients, cytological findings in 4 patients, and evolution of imaged lesions on follow-up in
20 patients. Our rate of false positive FDG foci is 8%, based on cytology and is concordant
with previous studies (17, 35-38). FDG accumulation is not specific for cancer. Furthermore,
FDG uptake in differentiated thyroid neoplastic foci is often low, except for the more
aggressive histologies. Finally, lesions are often small and located in the neck, an anatomic
region submitted to benign inflammatory lymph nodes. Importantly, even lesions with an
incremental rise in uptake after rhTSH may not all represent thyroid tissue.
In a population selected with elevated Tg level and no Tg antibodies or a recovery
test of less than 80%, we confirmed that a greater number of lesions were detected on
rhTSH-PET (77 vs. 102) compared to basal PET. We also found an increase of mean
SUVmax (5.7 vs. 6.6) after rhTSH administration (10, 25-27). The changes in SUVmax after
rhTSH administration were, however, quite variable, with an increase in FDG uptake in some
of the lesions and a decrease in FDG uptake in others. We even observed a few lesions that
were only detected on the basal, but not rhTSH-stimulated PET. All these lesions were less
than one centimeter in diameter, and located in the neck or lung. Partial volume effects due
to small size and breathing movements or false positive baseline study may explain the
absence of visible FDG uptake on some rhTSH-PET scans.
Based on the number of patients in whom any disease was detected by PET/CT,
there was no statistically significant incremental value of rhTSH use before FDG PET.
Furthermore, rhTSH PET/CT findings changed clinical management in only 6% of patients,
which was less than the hypothesized 10%, which had been prospectively defined as being a
clinically significant proportion of such thyroid cancer patients. Overall, the number of
patients in whom rhTSH PET/CT led to appropriate management changes (4) equaled the
number of patients with apparently false-positive findings based on benign FNAB (4).
The frequency of clinical management plan changes are, of course dependent on the
patients studied. In fact, 16 patients were included who had previous imaging showing neck
recurrence in 9 patients and lung metastases in 7 patients. While it was expected that
patients with lung metastases would not benefit from rhTSH-PET imaging, this was not the
case for patients with neck recurrence or without known localization of the disease, in whom
the detection of disease foci may change the extent of surgery.
In conclusion, we confirmed in a large cohort of patients undergoing both basal
PET/CT and rhTSH PET/CT, a significant increase in both the number of lesions detected on
rhTSH PET/CT and in relative FDG uptake compared to basal PET/CT. While the frequency
with which rhTSH PET/CT findings altered the clinical management plan was not statistically
significant, it did alter therapy in 6% of patients. This subset of patients benefitting from
incremental rhTSH PET/CT findings might prove to be significant in a larger study focusing
on patients with an elevated serum Tg level and no known distant metastases.
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Figure 1 A-B
PET images of lesions only detected on rhTSH-PET related to a parapharyngal (plain
arrow) and subclavicular (open arrow) relapse (1A) and to a false positive neck FDG
foci (white arrow) (1B)
Changes in FDG uptake in each lesion on rhTSH PET compared to basal PET
Table 1: Number of metastatic organs and lesions detected with basal PET/CT and/or rhTSH-
Detected with rhTSH-PET/CT
Number of metastatic organs
Detected with basal PET/CT
Not detected with basal PET/CT
Number of lesions
Detected with basal PET/CT
Not detected with basal PET/CT
na, not applicable
Not detected with rhTSH-PET/CT
Table 2: Location of lesions detected on basal PET and/or rhTSH-PET
Location (number of
Mediastinal lymph nodes
Number of lesion detected on
rhTSH-PET only basal PET only Basal and rhTSH-PET
Table 3: Changes in treatment management plan due to lesions detected on basal PET (3A) and to lesions only detected on rhTSHPET (3B)
After basal PET
Bilateral +/- central
neck surgery Before basal PET
THST Unilateral +/-
1 1 1
Unilateral +/- central
Bilateral +/- central
Bilateral +/- central
After basal PET
THST Unilateral +/-
Unilateral +/- central
Bilateral +/- central
THST: thyroid hormone suppression therapy