Posters

<span title="2013-02-21">2013</span> <i title="Springer Nature"> <a target="_blank" rel="noopener" href="https://fatcat.wiki/container/f735wttfsfclvof43wc6r5wgjq" style="color: black;">Clinical and translational imaging</a> </i> &nbsp;
Aim Primary brain tumors, in particular gliomas, are rare tumors that are difficult to diagnose and to treat. Current imaging modalities, such as FDG PET/CT, MRI and MR spectroscopy (MRS) have some limitations, particularly with regard to differentiate tumor from radiationinduced necrosis (RIN) and from normal cerebral metabolic uptake. 18 F-DOPA/ 18 F-choline PET/CT (FDOPA/FCH) seem to be useful diagnostic tools. Materials and methods 12 patients (6 females and 6 males; mean age 53 years,
more &raquo; ... 23-76) were prospectively studied with FDOPA/ FCH, performed between March 2011 and May 2012: 9 patients with gliomas (3 undergoing staging and 6 undergoing restaging) and 3 with brain metastasis (2 lung carcinomas and one breast cancer). In 6 patients undergoing restaging MRI failed to differentiate tumor relapse from RIN, therefore these patients were studied with FDOPA/FCH. Brain FDOPA/FCH was performed 10 minutes after iv injection of 3.5 MBq/kg of 18 F-FCH or 4 MBq/kg of 18 F-DOPA. FDOPA/FCH was compared with 99m Tc-sestaMIBI SPECT/CT (SPECT/CT), MRI, CT and subsequent pathological analysis. Results FDOPA/FCH was considered pathological in 12/12 (100%) patients. In one case, FDOPA disclosed three lesions (right frontal lobe, left parasagittal frontal and corpus callosum lesion), MRI showed only two (right frontal lobe and corpus callosum lesion) and SPECT/ CT only one (right frontal lobe lesion). This case was re-studied with a radiology specialist. In the other cases, FDOPA/FCH and MRI had the same sensitivity. FDOPA/FCH had an overall sensitivity of 100% while MRI sensitivity was 91%. The diagnostic accuracy of FDOPA/FCH was 100% vs 91% for MRI [95% confidence interval (CI) 74-99%]. Conclusions This study showed that FCH PET/CT may offer an advantage in imaging of brain tumors, similar to MIBI SPECT/CT, but with higher spatial resolution. FDOPA PET/CT in primary brain tumors, especially in patients with recurrent gliomas treated with radiation therapy, seems to be a good tool, especially when MRI fails to differentiate tumor from RIN. In our initial experience, FDOPA PET scan seems to have higher sensitivity than MRI. FDOPA/FCH PET/CT are optimal for imaging of high grade tumors, but also of low grade tumors. Our early experience with FCH tracer in PET imaging has been encouraging. 02 18 F-DOPA PET is able to prognosticate early progression of brain metastases Background Conventional magnetic resonance (MR) criteria often fail to distinguish between radionecrosis and progression of brain metastases. Additional MR parameters, such as regional perfusion, have several drawbacks as well. In this setting, few data exist on PET with amino acid tracers. We set out to explore the potential additive role of L-3,4-dihydroxy-6-[ 18 F]fluorophenylalanine (FDOPA) PET/CT in the differential diagnosis between radionecrosis and progression of brain metastases. Materials and methods Between July 2010 and August 2012, 21 patients with a total of 34 brain metastases from various primaries underwent FDOPA brain PET/CT at the Sant'Andrea Hospital in Rome, in addition to MR surveillance. Static images of the brain were acquired with a Philips Gemini camera over a 20-minute time, starting 15 minutes after the i.v. injection of 185 MBq of FDOPA. A low-dose CT scan was used for attenuation correction. PET was not taken into account in the patients' clinical management and subsequent, lesionspecific therapeutic decisions were based on the following criteria: (1) standard MR evaluation, based on contrast-enhanced T1-weighted and T2/FLAIR sequences, (2) increased regional perfusion, and (3) clinical symptoms. Patients (i.e. lesions) were referred for surgery or radiotherapy if all three criteria were positive for progression [+++, Group A]. If any of the three criteria was discordant or non-evaluable [+/-, Group B], MR was repeated three months later and the lesion was then reclassified as progressed [Group BA] or stable [Group BC]. If all three criteria were negative, patients were assigned to long-term follow-up [---, Group C]. PET studies were qualitatively classified as positive or negative, and additional semi-quantitative parameters, such as SUVmax, tumor-to-contralateral background ratio and tumor-tocontralateral basal ganglia uptake, were also considered. Two-tailed Student's t-test was applied to analyze differences in PET semi-quantitative parameters between the groups. Results Of the 21 patients enrolled, one patient with a single cerebellar lesion from breast carcinoma was lost to follow-up. Therefore, a final subset of 20 patients and 33 lesions was analyzed. Primary tumors included: non-small cell lung cancer (n=6), breast cancer (n=3), urothelial cancer (n=4), melanoma (n=2), colon cancer (n=2), small cell lung cancer (n=1), gastric cancer (n=1) and salivary gland cancer (n=1). All the patients had been previously treated with systemic chemotherapy associated with stereotactic radiosurgery on brain metastases. On the basis of the above criteria, 10 lesions were referred for subsequent treatment without additional imaging [Group A], 14 lesions had inconclusive MR [Group B], and 9 lesions without signs of progression were assigned to long term follow-up [Group C]. Within the Group B, 8/14 metastases progressed and were subsequently reclassified as Group BA, while 6/14 remained stable and were reclassified as Group BC. Both Group A and Group B metastases were PET-positive, while all Group C metastases had unremarkable PET. On average, SUVmax was 3.71 (± 0.8) and 2.29 (± 0.6) in Group A and Group B, respec- Posters S40 Clin Transl Imaging (2013) 1 (Suppl 1):S39-S140 04 Monitoring biological treatment of metastatic salivary gland cancer using FDG-PET/CT and a RECIST-adapted protocol for analysis of FDG findings Purpose In clinical practice, brain radionecrosis after stereotactic radiosurgery (SRS) is one of the most dreaded complications after brain radiotherapy and its clinical presentation can mimic tumor recurrence. Radionecrosis and relapse have distinct treatment approaches and prognoses. Usually radionecrosis is diagnosed using magnetic resonance imaging (MRI), magnetic resonance spectroscopy and finally histological examination. Single-photon emission computed tomography (SPECT) is a functional imaging technique that can provide additional and useful information during the diagnostic work-up and follow-up of brain lesions. A dual-modality integrated imaging system has been developed. This system allows the acquisition of SPECT and CT images in the same scanning session, and then image fusion. 99m Tc-MIBI (2-methoxyisobutylisonitrile) is a lipophilic radioligand that enters the mitochondria and accumulates significantly more in tumor tissue, where mitochondrial activity is higher than in normal tissues, and shows no uptake in fibrotic or necrotic lesions. Materials and methods Forty-seven patients with 59 metastases were evaluated using MRI and 99m Tc-MIBI-SPECT/CT before SRS, 3 months after SRS, and then at regular 6-month intervals. SPECT/CT images were obtained 15 minutes after the injection of 740 MBq of 99m Tc-MIBI with a dual-headed gamma camera equipped with low-energy highresolution collimators. Transverse, sagittal and coronal images were reconstructed and then fused with CT data. Semi-quantitative analysis was performed to obtain the MIBI uptake index as a ratio of counts in the lesion compared to counts in the contralateral normal areas. Results In 44 lesions, concordance was found between the MRI and SPECT/CT findings and in 16 lesions MRI showed a contrast enhancement judged non-specific. In 9 patients SPECT/CT was positive for relapse (MIBI uptake index > 2) and in 7 there was no uptake or an uptake index less than 2, judged as radionecrosis. Radionecrosis was confirmed by histological examination in 3 lesions and by close follow-up, which showed no disease progression, in the other 4. Relapse was confirmed by histological examination in all 9 patients. Conclusions 99m Tc-MIBI-SPECT fused with CT images is helpful in providing a precise localization of brain metastases and makes it possible to study their metabolic activity. In semi-quantitative analysis, MIBI uptake index can be related to treatment outcome. MIBI index was < 2 or remarkably reduced in the lesions which responded to treatment. Our experience has shown that MIBI-SPECT/CT is useful, in combination with MRI, in the follow-up of patients with brain tumors who have undergone SRS and can be used in clinical practice to differentiate between radionecrosis and relapse. Introduction Thyroid incidental uptake is defined as a thyroid uptake incidentally and newly detected by imaging techniques performed for an unrelated purpose and especially for non-thyroid diseases. Thyroid incidental uptake may be diffuse or focal, corresponding to Basedow disease or thyroiditis and nodular lesion respectively. Aim The aim of our study was to establish the prevalence, clinical significance and pathological nature of focal thyroid incidentalomas detected on 18 F-FDG-PET/CT in patients studied for oncological purposes and not for thyroid disease. The secondary end point was to establish a possible maximum standardized uptake value (SUV max ) cutoff over which a malignant lesion should be suspected. Materials and methods We retrospectively evaluated 49519 patients who underwent 18 F-FDG-PET/CT for oncological purposes in three nuclear medicine centers (center n.1 = 11278, center n.2 = 31076, center n.3 = 7165). Results Focal incidental thyroid uptake was diagnosed in 729 (1.5%) patients (287 -39.4% males and 442 -60.6% females; average age 65.26 years). Of these 729 thyroid incidentalomas, 211 (28.9%) were submitted to further investigation to determine the nature of the nodule; 124/211 (58.8%) incidentalomas were benign, 72/211 (34.1%) were malignant, 4/211 (1.9%) were non-diagnostic on cytological examination in the absence of surgery and histological evaluation, and 11/211 (5.2%) were indeterminate on cytological examination. A center-based receiver operating curve (ROC) analysis of the patients with a definitive diagnosis was performed to identify a SUV max cut-off useful in differentiating benign from malignant incidentalomas. In center n.1 it was 4.8 (sensitivity = 95.7%, specificity = 46.4%, area under the curve = 0.758); in center n.2 it was 5.3 (sensitivity = 76.3%, specificity = 72.5%, area under the curve = 0.815); in center n.3 it was 7 (sensitivity = 57.1%, specificity = 79.3%, area under the curve = 0.627). Conclusions 18 F-FDG-PET/CT thyroid incidentalomas are not infrequent and are therefore an important diagnostic entity that requires further investigations and clinical management, especially considering that approximately one third of focal thyroid uptakes are malignant. Aim Conventional planar 131 I whole-body scintigraphy associated with serum thyroglobulin (TG) measurement is still considered the routine diagnostic procedure of choice in thyroidectomized patients with welldifferentiated thyroid carcinoma (DTC). More recently, SPECT/CT was found to be a more effective diagnostic tool, capable of improving planar scintigraphy, increasing sensitivity and accuracy, and allowing precise anatomical localization and characterization of iodine-fixing foci. We further investigated whether SPECT/CT may contribute to the reassessment of the current diagnosis and therapeutic post-operative management protocol of DTC patients. Methods We studied 552 thyroidectomized DTC patients, 113 males and 439 females, aged 20 to 81 years, 134 classified as being at high risk (H) and 418 at low risk (L), including 204 at very low risk (VL). Fourteen cases were observed after thyroidectomy and before radioiodine therapy in hypothyroidism condition and 538 in long term followup; 501/552 patients underwent diagnostic and 51/552 post-therapeutic ¹³¹I scintigraphy, for a total of 638 examinations. Whole-body scanning was performed in both anterior and posterior projections using two variable-angle dual-head gamma cameras, Millennium VG Hawkeye in 55 cases and Infinia Hawkeye (GE Medical System) in 497 cases, 05 Abnormal radioiodine uptake in an abdominal dermoid cyst in a patient affected by differentiated thyroid cancer Aim Post-therapy 131 I whole-body scan (WBS) is a sensitive procedure for diagnosing metastases in patients with differentiated thyroid carcinomas (DTC). Nevertheless, a wide spectrum of potentially misleading readings has been reported following its use. We describe, for the first time, a case of 131 I accumulation in an abdominal dermoid cyst. Patient and methods A 63-year-old woman underwent near-total thyroidectomy for a large multi-nodular goiter. Histopathological reports revealed a follicular thyroid carcinoma. Some months later, after conventional L-T4 withdrawal, the patient underwent: (a) measurement of radioiodine thyroid uptake (RTU) 24 hours after oral administration of 131 I tracer activity (1.8 MBq); (b) radioiodine therapy (RIT) with ablative activity (3700 MBq); (c) post-dose WBS, performed five days after RIT using a dual-headed gamma-camera equipped with a high-energy parallel-hole collimator. RTU corresponded to 11% of the administered tracer activity of 131 I. Post-dose WBS showed thyroid remnant, abnormal radioiodine uptake in the upper mediastinum, and a slight radioiodine uptake in an abdominal focal area. At the time WBS was performed, serum TSH and Tg were 39.5 UI/ml and 546 ng/ml, respectively. In the absence of TgAb, Tg levels were consistent with the presence of metastases. Magnetic resonance imaging revealed a non-homogeneous mass at the level of the inferior abdomen. Our patient was unaware of this lesion and was asymptomatic. The patient underwent a surgical exploration with complete excision of the mass. Pathological examination was conclusive for dermoid cyst. Some months later, the patient underwent a second RIT (5550 MBq) after recombinant human TSH (rhTSH) stimulation (0.9 mg daily for two consecutive days administered by intramuscular injections). Postdose WBS, performed five days later, confirmed abnormal radioiodine uptake in the upper mediastinum, but did not confirm either thyroid remnant or abdominal radioiodine uptake. At the time of the second RIT, the serum peaks of TSH and Tg were 112 UI/ml and 242 ng/ml, respectively. TgAb levels were negative. Conclusions This is the first report of 131 I uptake in a dermoid cyst. Dermoids (often clinically silent) are not unique to a single anatomical location. They are often located in the skin and subcutaneous tissues, but may also occur intracranially or intra-abdominally. It is likely that radioiodine uptake in the dermoid cyst was NIS-dependent. Due to its non-negligible frequency, this malformation should be taken into account in DTC patients as a potential pitfall of 131 I-WBS. 18 F-FDG-PET/CT thyroid incidentalomas: clinical and histopathological significance from a multicenter study Clin Transl Imaging (2013) 1 (Suppl 1):S39-S140 basis of ETA risk stratification, into group A (very-low-risk and lowrisk DTC: 494/1082) and group B (high-risk DTC: 588/1082). All patients were treated with thyroidectomy + RAI. Follow-up was based on neck sonography and measurement of A-Tg, S-Tg and, 1 year after RAI, R-Tg. Subjects with anti-Tg autoantibodies were excluded. Results Using the rh-TSH test as gold standard, the NPV for A-Tg <10 µg/l was 98.5% in group A and 95.5% in group B, rising to 99.2% and 99.3%, respectively, when it was associated with S-Tg <0.6 µg/l. Moreover, the NPV for A-Tg <15 µg/l was 98.6% in group A and 95.1% in group B, rising to 99% and 99.5%, respectively, when we considered the association with S-Tg <0.6 µg/l. Considering the whole population, the NPV was 97% for A-Tg <10 µg/l alone and 99.3% when it was associated with S-Tg <0.6 µg/l. When we considered a cut-off of 15 µg/l for A-Tg the NPV was 96.8%, rising to 99.3% when it was associated with S-Tg <0.6 µg/l. Conclusions Our data confirm the usefulness of associating A-Tg and S-Tg in the early risk stratification of DTC patients, as this may allow the rh-TSH test to be avoided in a large number of patients, and a much less expensive follow-up program. We suggest that the association between A-Tg <15 µg/l and S-Tg <0.6 µg/l, together with negative neck ultrasonography, can be considered good parameters to identify disease-free DTC patients. Negative thyroglobulin (Tg) and positive radioiodine whole-body scan ( 131 I-WBS) in patients with differentiated thyroid carcinoma (DTC) Design The initial treatment for differentiated thyroid cancer (DTC) consists of total thyroidectomy followed by 131 I remnant ablation (RAI). Serum thyroglobulin (Tg) measurement is a key element in the followup and it is commonly used as a specific marker in order to differentiate disease-free status from persistence or recurrence of disease. In this field, measurements of the Tg concentration on L-T4 suppressive treatment (S-Tg) and after stimulation with exogenous TSH (R-Tg) are of particular importance. However, this test is quite expensive and, due to the large number of cured patients, recent studies suggested that it could be avoided in selected populations of low-risk DTC patients. The aim of our study was to verify whether the association of different ablation thyroglobulin (A-Tg) cut-off levels with undetectable S-Tg concentrations has sufficient negative predictive value (NPV) for recurrent/persistent disease, making it possible to avoid rh-TSH test in all DTC patients. Methods We enrolled 1082 DTC patients, who were divided, on the Clin Transl Imaging (2013) 1 (Suppl 1):S39-S140 S43 pT1a-pT1b lesions was relatively low (about 10%) but their prevalence was significantly higher in the patients with isthmus lesion respect to patients with right or left lobe lesions (33.3, 7.6 and 5.6 per cent, respectively). Hence, our preliminary data suggest that the isthmic location of DTC can be considered an additional risk factor in the patients with pT1a or pT1b lesions regardless of age and sex of the patients and of the histological variant. Therefore, in these patients we suggest TRA and pWBS that in our series has permitted to identify patients with metastases and their localizations. 11 18 F-FDG TOF-PET/CT in restaging patients with suspected recurrence of differentiated thyroid cancer (DTC) Aim An increase in thyroglobulin (Tg) without detectable Tg antibodies is generally the first indicator of relapse of DTC after surgery and radioiodine ablation. Neck ultrasonography and 131 I-scintigraphy are first used in order to localize disease recurrence; however, these imaging tools have been found to have limited sensitivity, especially indetecting distant metastasis due to the frequent dedifferentiation of tumor tissue. The usefulness of 18 F-FDG PET/CT in this setting has been already evaluated, the technique showing a satisfactory level of sensitivity and specificity. However, two main questions are still open: first, false negative PET results are frequently reported in miliary lung spread and in small lymph node metastases; second a Tg cut-off level for a better accuracy of PET/CT examination has not yet been established. We report our experience in restaging patients treated for DTC, in order to evaluate the diagnostic performance of 18 F-FDG PET/CT with TOF reconstruction and to correlate its results with Tg levels. Materials and methods Eighty-three 18 F-FDG PET/CT scans were performed in 65 patients (42 women, 23 men, mean age 61 years) with a history of treated DTC. They showed increased Tg levels (mean 213.86 ng/ml; range 0.26-4362) or detectable Tg antibodies -in 3 cases-; in 9 subjects Tg was undetectable, but there was clinical or instrumental suspicion. PET/CT examinations were acquired with standard protocol using a Philips Gemini TOF scanner. Abnormal findings were confirmed by histopathology, by other imaging modalities and/or by follow-up (median 30 months; range 4-51). Negative PET results in patients with negative clinical and or instrumental follow-up were taken as true negative. Sensitivity, specificity, PPV, NPV and accuracy of 18 F-FDG PET/CT were determined; a receiver operating characteristic curve (ROC) was used to identify the diagnostic value of Tg in predicting PET/CT results. Results Twenty-five PET/CT scans were negative: 15 were true negative (no detected recurrence in a median follow-up of 32.5 months), while 10 were false negative since disease was detected by other imaging modalities: 6 patients with lymph node and 4 with lung metastases. Fifty-eight PET/CT scans were positive: abnormal findings were all confirmed except for two: one lymph node uptake (reactive at biopsy) and one bone uptake (arthrosis). Distant metastases were found in 32 patients, lymphnodal in 28 cases and local recurrence in 12; numerous patients had multiple localizations. In 2 patients PET/CT showed additional findings unrelated to DTC: one Hodgkin lymphoma and one breast cancer. Overall sensitivity, specificity, PPV, NPV and accuracy were 86%, 88%, 97%, 63% and 87%, respectively. Tg level was significantly higher (p<0.007) in patients with positive PET/CT than in patients with negative scans (256.51 ng/mL versus 8.9 ng/ml). PET/ -positive AbTPO indicates the presence of thyroid autoimmunity. -systematic preoperative Tg, AbTg and AbTPO measurement should be performed to identify patients in whom negative Tg cannot be related to the absence of normal or pathological thyroid cells. -the follow-up of DTC patients should be based on stimulated Tg and 131 I-WBS. 124 I-WBS will provide better sensitivity. 10 Can the position of malignant thyroid nodule be considered as additional risk factor for recurrent and/or metastatic disease in patients affected by low-risk differentiated thyroid cancer? Introduction Differentiated thyroid cancer (DTC) is the most common endocrine malignancy. In recent decades, the incidence of DTC, particularly of the low-risk forms, has been increasing. The utility of radioiodine thyroid remnant ablation in patients with low-risk DTC is still debated, even though it is not rare for low-risk patients to develop recurrent disease or metastases (often locoregional) during follow-up. Risk re-stratification based on 131 I-post-dose whole-body scan (pWBS), or performed at the first clinical check-up (after initial therapy), was recently proposed. The aim of our study was to evaluate whether the position of the malignant thyroid nodule can be considered as additional risk factor for recurrent or metastatic disease in patients with pT1a-pT1b lesions (TNM 7 th edition). Material and methods We retrospectively reviewed the records of 133 patients (F=114, M=19; F/M ratio 6:1 age 47.4 ± 11.8 years, range 22-75) with DTC [122/133 (92%) were papillary histotypes (PTC), 11/133 (8%) were follicular histotypes (FTC)] admitted to our nuclear medicine unit for radioiodine treatment (RIT) after total thyroidectomy. The patients, all without known metastasis at the time of recruitment, underwent: -Neck ultrasonography; -Serum measurement of: TSH, thyroglobulin (Tg) and anti-thyroglobulin antibodies (Tg-Ab); -Radioiodine thyroid uptake (RTU) obtained 24 hours after Na 131 I (1.8 MBq) administration; -RIT in hypothyroidism (TSH ≥ 30 µUI/ml) or after recombinant human TSH (rhTSH) stimulation (conventional protocol) for thyroid remnant ablation (TRA). The administered radioiodine activity ranged from 555 to 4588 MBq (mean 2344 ± 1131); -pWBS performed 5-7 days after RIT. Results Metastases were discovered with pWBS in 13/133 (9.7%) patients (F=10, M=3, age 45.2 ± 14.6 years, range 22-70). In all metastatic patients the histotype was papillary; 9/13 metastatic patients had pT1a lesions. In the metastatic patients, the malignant lesions were localized in: right lobe 5/65 (7.6%; F=4, M=1, mean age 45 years, range 23-65; histological variant: classic variant (CV)=3, follicular variant (FV)=2); left lobe 3/52 (5,6%; F=3; mean age 48 years, range 42-55; histological variant: CV=1, FV=2 ); isthmus 5/15 (33.3%; F=3, M=2; mean age 43 years, range 22-70; histological variant: CV=4, FV=1); pyramidal lobe 0/1 (0%). All metastatic patients but one (with lung metastases) had lymph-nodes metastasis located in: upper medi-astinum= 4, left lateral neck=2, right lateral neck=3; anterior central compartment= 3). Only one woman among the metastatic patients had associated Hashimoto Thyroiditis (HT). The incidence of metastases was significantly higher in patients with DTC located in the isthmus, compared with other sites (χ 2 4.8, p<0.05). Conclusions In our series the frequency of metastases in patients with 13 Comparison of [ 18 F]FDG PET/CT and CT in the evaluation of residual cervical lymph nodes in patients with head and neck squamous cell carcinoma treated with radiotherapy or radiochemotherapy: our experience Aim The aim of the present study was to study the role of [ 18 F]FDG PET/CT in the status evaluation of residual cervical lymph nodes in patients undergoing radiotherapy as a single modality (RT) or in combination with chemotherapy (RCT) for advanced head and neck squamous cell carcinoma (HNSCC), stage N2-N3. Methods Thirty-two consecutive patients (22 males and 10 females), aged between 49 and 74 years and affected by HNCC (primary sites: 9 rhinopharynx, 3 oral cavity, 7 oropharynx/epiglottis and 13 larynx), were submitted to [ 18 F]FDG PET/CT and CT with contrast agent 9-12 weeks after the end of RT or RCT to minimize the number of false negatives (FNs) and false positives (FPs). 18 patients with suspected persistent lymphadenopathy underwent neck dissection (6 patients with both [ 18 F]FDG PET/CT and CT positive, 3 patients with [ 18 F]FDG PET/CT positive and CT negative, 9 patients with [ 18 F]FDG PET/CT negative and CT positive) and imaging results were correlated with the pathological findings of the residual lymphadenopathy. Results [ 18 F]FDG PET/CT detected residual disease in cervical lymph nodes in 9 patients (28%) while no significant areas of uptake of [ 18 F] FDG were found in the remaining 23 patients (72%). Differently, CT detected lymph node residual disease in 15 patients (46.8%) and no lymph node morphological anomalies in 17 patients (53.2%). Both methods showed lymph node residual disease in six patients (18.7%) and no lymph node residual disease in 14 patients (43.7). Concordance was found only in 20 patients (62.5%). The six patients with positive [ 18 F]FDG PET/CT and positive CT underwent cervical lymph node dissection with subsequent pathological examination: 5 true positive (TP) and 1 FN (diagnosed as lymph node inflammation). The remaining 12 patients with discordance (37.5%) also underwent cervical lymph node dissection: 3 patients were [ 18 F]FDG PET/CT positive (2 TP, 1FP) and CT negative [2 FN, 1 true negative (TN)], 9 patients were [ 18 F]FDG PET/CT negative [8 TN, 1 FN (lymph node with concomitant necrosis and low FDG uptake)] and CT positive (8 FN, 1TP). All patients found to be negative for both examinations were followed up for 4-14 months. They are still considered to be disease-free on the basis of clinical and diagnostic examinations. The sensitivity and specificity of each evaluation method were, respectively, 87.5% and CT scan was positive in the 3 patients with raised Tg antibodies and in 7/9 patients without Tg increase but clinical/instrumental suspicion. On ROC analysis we found a Tg cut-off of 9.4 ng/ml to provide better sensitivity and specificity with an AUC of 72% (p=0.006). Conclusions We confirm the reported usefulness of 18 F-FDG PET/CT in detecting recurrent DTC in patients with elevated Tg levels, with good sensitivity, specificity and very high PPV, especially for distant metastases. In our experience using TOF reconstruction, we obtained a slightly higher sensitivity than the majority of studies in the literature. To further increase accuracy, PET/CT could be preferred when Tg levels exceed 9.4 ng/ml. 12 Papillary thyroid cancer and relapse time: the right tools, the right times
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