FDG Activity Research Articles

Feasibility of ultra-low activity 18F-FDG PET/CT imaging in children.

To investigate the feasibility of pediatric 18F-FDG total-body PET/CT imaging with an ultra-low activity and explore an optimized acquisition time range. A total of 38 pediatric patients were prospectively enrolled and underwent dynamic total-body PET/CT imaging using ultra-low 18F-FDG activity (0.37 MBq/kg). The 60-minute list-mode raw data were acquired and then reconstructed as static PET images by using 50-51, 50-52, 50-53, 50-54, 50-55, 50-58, 50-60, and 45-60 minutes data, which were noted as G1, G2, G3, G4, G5, G8, G10, and G15, respectively. Image qualities were subjectively evaluated using the Likert scale and were objectively evaluated by the quantitative metrics including standard uptake value (SUV), signal-to-noise ratio (SNR), target-to-background ratio (TBR), and contrast-to-noise ratio (CNR). The injected activity of FDG was 13.38 ± 5.68 MBq (4.40-28.16 MBq) and produced 0.58 ± 0.19 mSv (0.29-1.04 mSv) of effective dose. The inter-reader agreement of subjective image quality was excellent (kappa = 0.878; 95% CI, 0.845-0.910). The average scores of image quality for G1-G15 were 1.10 ± 0.20, 2.03 ± 0.26, 2.66 ± 0.35, 3.00 ± 0.27, 3.32 ± 0.34, 4.25 ± 0.30, 4.49 ± 0.36, and 4.70 ± 0.37, respectively. All image scores are above 3 and all lesions are detectable starting from G8. SNRs of backgrounds, TBRs, and CNRs were significant differences from the control group before G8 (all P < 0.05). The image quality of the 8 min acquisition for pediatric 18F-FDG total-body PET/CT with an ultra-low activity could meet the diagnostic requirements. This study confirms the feasibility of ultra-low dose PET imaging in children, and its methods and findings may guide clinical practice. pediatric patients will benefit from reduced radiation doses.

6850 A Case of Anaplastic Thyroid Carcinoma With a Complete Metabolic Response to Pembrolizumab

Abstract Disclosure: E. Tirthani: None. J.T. Kung: None. Background: Anaplastic thyroid carcinoma (ATC) is an aggressive disease with limited therapeutic options and generally poor prognosis. Post-surgery, most patients are treated with a combination of chemotherapy, radiation, and tyrosine kinase inhibitors +/- immune checkpoint inhibitors. We describe a unique case of ATC with a complete metabolic response to pembrolizumab, a selective PD-1 inhibitor, as evidenced by imaging. Clinical Case: A 69-year-old female presented to the clinic for evaluation of a rapidly enlarging neck mass. The initial ultrasound showed a large mixed cystic-solid right thyroid nodule with irregular margins with micro- and macrocalcifications, which was biopsied. Cytology showed discohesive high-grade malignant tumor cells with enlarged nuclei, nuclear hyperchromasia in the background of necrosis, and dense neutrophilic infiltration concerning for ATC. A CT scan of the neck and chest showed a complex cystic thyroid mass with central necrosis and calcification with paratracheal, supraclavicular, and mediastinal lymphadenopathy. MRI of the brain was negative for metastatic disease. The patient underwent a total thyroidectomy with right and left level 6 and 7 neck dissection. Intra-operatively, gross extrathyroidal extension of the tumor was noted to the right carotid, larynx, right recurrent laryngeal nerve, and esophagus, with residual tumor left behind near the larynx. Pathology confirmed stage IVC ATC, positive for PIK3CA, NF1, p53 mutations, and BRAF negative. 90% of tumor cells showed PD-L1 expression on immunohistochemical staining. The post-surgical PET scan showed two discrete, well-defined foci of very intense FDG uptake, corresponding to the right lower cervical and para-esophageal lymph nodes with no evidence of distant metastasis. Systemic chemotherapy with carboplatin and paclitaxel (5 cycles) was initiated with concurrent intensity modulated radiation therapy (total 60 Gy/40 fractions to thyroid bed and bilateral neck). Repeat imaging showed minimal change in the size of the PET-positive lymph nodes. Immunotherapy was initiated and with just 2 cycles of 400 mg IV pembrolizumab, a repeat PET scan was obtained, which showed a complete metabolic response to therapy. Minimal residual FDG activity in the right supraclavicular region was thought to be secondary to posttreatment changes. The patient was able to resume her activities of daily living and had an improvement in appetite. The plan is to continue 400 mg IV pembrolizumab every 6 weeks while cautiously assessing for adverse effects from immunotherapy. Conclusion: It is rare to see a complete metabolic response to therapy with pembrolizumab without concurrent use of tyrosine kinase inhibitors in patients with ATC. A high tumoral PD-L1 expression may be the key to having this kind of dramatic response. Presentation: 6/3/2024

FDG PET/CT Findings of Rapidly Progressive Interstitial Lung Disease in a Patient With Anti-MDA5 Dermatomyositis.

Anti-MDA5 dermatomyositis is associated with an increased risk of developing rapidly progressive interstitial lung disease with a high mortality. We describe FDG PET/CT findings in a case of rapidly progressive noninfectious interstitial lung disease associated with anti-MDA5 dermatomyositis. The lung disease showed bilateral diffuse ground-glass opacities with diffuse heterogeneous FDG activity predominantly in middle and lower zones, mimicking infectious pneumonia. Familiarity with the imaging features of this rapidly progressive noninfectious interstitial lung disease can help to suggest the diagnosis and guide appropriate management.

Atypical Bone Involvement in Erdheim-Chester Disease Showing No or Subtle Structure Changes and Increased Activity on FDG PET/CT.

Bones are the most common sites involved in Erdheim-Chester disease. On imaging, the bone involvement in Erdheim-Chester disease typically presents as osteosclerotic lesions, and osteolytic lesions are unusual. Bone lesions showing no or subtle structure changes are rarely reported. We describe FDG PET/CT findings in a case of Erdheim-Chester disease with atypical bone involvement. The bone lesions showed no or subtle structure changes without obvious osteosclerosis or osteolysis on radiographs and CT, and increased FDG activity mimicking lymphoma. Familiarity with these atypical imaging findings of bone involvement in Erdheim-Chester disease is helpful for the diagnosis.

Correlation of FDG PET/CT, tumor markers and Ki-67 index with EGFR mutation or positive ALK expression in patients with non-small cell lung cancer.

Epidermal growth factor receptor (EGFR) and anaplastic lymphoma kinase (ALK) are the two most common druggable targets in non-small cell lung cancer (NSCLC). To investigate whether the EGFR mutation and ALK rearrangement could be predicted by the combination of FDG avidity, tumor markers and Ki-67 Index. A total of 168 newly diagnosed NSCLC patients who had undergone 18F-FDG PET/CT for staging were enrolled. PET/CT parameters of primary tumors including maximum standardized uptake value (pSUVmax), metabolic tumor volume (pMTV) and total lesion glycolysis (pTLG) were measured. Five serous tumor markers for lung cancer were recorded. Ki-67 labeling index was counted by immunohistochemical staining. EGFR mutation and ALK status were detected by ARMS-PCR and RT-PCR, respectively. Univariate and multivariate analyses were applied to identify the predictors of EGFR mutation and ALK positivity. EGFR mutation rate was 38.1% (64/168), which were found more frequently in female, ≤60 years old, non-smokers and adenocarcinoma patients, and were not related to lymph node involvements, distant metastases, stage and serum tumor markers. Low pSUVmax, pMTV, pTLG and Ki-67 were significantly associated with EGFR mutation. Logistic regression demonstrated that pSUVmax <6.75 and gender (female) were the independent factors affecting EGFR mutation, and the combination of them had a certain predictive value with the area under the curve of 0.784. ALK positive rate was 6.0% (10/168), all of them were adenocarcinoma patients, which were more common in non-smokers, low serum cytokeratin-19 fragment antigen (CYFRA21-1) and low Ki-67, and were not related to FDG activity. No independent factor for ALK positivity was found on Logistic regression. Low pSUVmax, rather than tumor markers or Ki-67, was correlated with EGFR mutation independently, which could be integrated with gender (female) to improve the identification for EGFR mutation in NSCLC patients.

Distribution and predictors of F-18-FDG uptake values of non-malignant cervical lymph nodes in pediatric patients

BackgroundF-18-flurodeoxyglucose (FDG) PET/CT is routinely used for staging, evaluation of response to treatment and follow-up of most pediatric malignancies. Cervical lymph nodes can be involved in some pediatric malignancies, but increased uptake in non-malignant cervical lymph nodes is not exceptional in this population. The aim of the present study is to identify predictors of the maximum uptake in non-malignant cervical lymph nodes in the pediatric population.Methods191 FDG PET/CT studies of pediatric patients without malignant involvement of cervical lymph nodes were retrospectively reviewed. The maximal Standard Uptake Value in the hottest cervical lymph node (SUVmaxCLN), as well as demographic, technical and imaging variables were recorded. The predictive effect of those variables on SUVmaxCLN was estimated using linear regression models.ResultsIncreased FDG activity in cervical nodes was observed in 136/191 studies (71%). The mean SUVmaxCLN was 2.2 ± 1.3. Ipsilateral palatine tonsil SUVmax, mean liver uptake, and treatment status were all statistically significant predictors of SUVmaxCLN. However, in multivariate regression analysis, only ipsilateral palatine tonsil SUVmax was found to be significant. In addition, SUVmaxCLN was greater than the mean liver uptake in 50% of all studies. This proportion was higher in younger children, reaching 77% of studies of children younger than six years.ConclusionSUVmax in ipsilateral palatine tonsil is a strong predictor of the maximal uptake value of non-malignant cervical lymph nodes in children. The intensity of uptake in non-malignant cervical lymph nodes is frequently higher than liver uptake in children, and this tendency increases for younger patients.Trial was registeredIn the internal hospital registry under TRN 0209-22-HMO on date 23.04.2022.

Abstract PO4-20-10: Value of 16α-18F-fluoro-17β-fluoroestradiol PET imaging in ER-positive breast cancer: a case report

Abstract Introduction: An appropriate use criteria workgroup recently recommended the use of PET imaging utilizing the 16α-18F-fluoro-17β-fluoroestradiol (FES) radiotracer as a measure of disease progression and endocrine treatment response for ER-positive breast cancers. Past studies report limitations of decreased FDG uptake, the most common PET radiotracer, when measuring low Ki-67 scoring tumors; FES-PET may noninvasively address this shortcoming in FDG activity detection. Its benefit of detecting low-grade, ER-positive tumor activity was demonstrated in a patient with breast cancer who exhibited tumor growth only on FES-PET while FDG-PET showed no measurable disease. Clinical Case: A 57-year-old postmenopausal woman presented in December 2017 with de novo metastatic invasive ductal carcinoma that was ER+ (100%), PR+ (100%), and HER2- involving the right breast, bone, lungs, and internal mammary, subcarinal, and right hilar lymph nodes. She received nab-paclitaxel and radiation to the right breast, regional lymph nodes, and T11 bone. In March 2019, she underwent a right mastectomy with pathology that noted residual disease in the breast measuring &amp;lt;5 mm and was placed on exemestane in April 2019. She transferred her care to City of Hope and follow-up FDG-PET restaging showed no evidence of new metabolically active metastatic disease. Her cancer antigen 27.29 levels were also within normal limits. In the absence of measurable disease growth, she continued to be treated with single agent exemestane. Due to persistent back discomfort that she attributed to breast asymmetry, she requested the left breast to be removed. One week prior to surgery, both FDG-PET/CT and bloodwork inclusive of tumor markers were normal. She underwent a left mastectomy in March 2023. Pathology identified an incidental 1.4 cm lymph node in the 2000 g specimen that was ER+ (&amp;gt;95%), PR-, and HER2- with a Ki-67 of 1-3%. Somatic gene testing of the tumor revealed an ESR1 D538G mutation. As her progressive disease was not evident on previous FDG-PET imaging, an FES-PET/CT was performed and demonstrated uptake in the ilium, T10, and T12 bones that was not identified on FDG-PET/CT. With objective evidence of evaluable disease, exemestane was discontinued and fulvestrant and ribociclib were initiated. Clinically, she has evidence of early response to therapy with improvement in back pain. Discussion: This case demonstrates the value of FES-PET/CT in identifying disease that was not appreciated on FDG-PET/CT or by cancer antigen 27.29 monitoring. Additionally, ESR1 status has not been consistently reported in studies of patients undergoing FES-PET imaging that investigate the radiotracer’s value in predicting response to subsequent endocrine therapy. Our patient has a documented ESR1 mutation, her disease was clearly identified only on FES-PET/CT, and FES uptake predicted for response to subsequent endocrine therapy. Incorporating FES-PET in routine staging should be considered in patients with metastatic breast cancer that is low-grade and ER-positive. Further evidence of response prediction in patients with ESR1 mutations will enhance the utility of FES-PET in the clinical management of these patients. Citation Format: Megan Wong, Veronica Jones, Dave Yamauchi, Joanne Mortimer. Value of 16α-18F-fluoro-17β-fluoroestradiol PET imaging in ER-positive breast cancer: a case report [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-20-10.

Dose Reduction in Pediatric Oncology Patients with Delayed Total-Body [18F]FDG PET/CT.

Our aim was to define a lower limit of reduced injected activity in delayed [18F]FDG total-body (TB) PET/CT in pediatric oncology patients. Methods: In this single-center prospective study, children were scanned for 20 min with TB PET/CT, 120 min after intravenous administration of a 4.07 ± 0.49 MBq/kg dose of [18F]FDG. Five randomly subsampled low-count reconstructions were generated using ¼, ⅛, [Formula: see text], and [Formula: see text] of the counts in the full-dose list-mode reference standard acquisition (20 min), to simulate dose reduction. For the 2 lowest-count reconstructions, smoothing was applied. Background uptake was measured with volumes of interest placed on the ascending aorta, right liver lobe, and third lumbar vertebra body (L3). Tumor lesions were segmented using a 40% isocontour volume-of-interest approach. Signal-to-noise ratio, tumor-to-background ratio, and contrast-to-noise ratio were calculated. Three physicians identified malignant lesions independently and assessed the image quality using a 5-point Likert scale. Results: In total, 113 malignant lesions were identified in 18 patients, who met the inclusion criteria. Of these lesions, 87.6% were quantifiable. Liver SUVmean did not change significantly, whereas a lower signal-to-noise ratio was observed in all low-count reconstructions compared with the reference standard (P < 0.0001) because of higher noise rates. Tumor uptake (SUVmax), tumor-to-background ratio, and total lesion count were significantly lower in the reconstructions with [Formula: see text] and [Formula: see text] of the counts of the reference standard (P < 0.001). Contrast-to-noise ratio and clinical image quality were significantly lower in all low-count reconstructions than with the reference standard. Conclusion: Dose reduction for delayed [18F]FDG TB PET/CT imaging in children is possible without loss of image quality or lesion conspicuity. However, our results indicate that to maintain comparable tumor uptake and lesion conspicuity, PET centers should not reduce the injected [18F]FDG activity below 0.5 MBq/kg when using TB PET/CT in pediatric imaging at 120 min after injection.

P023 A case of ANCA-associated vasculitis with possible IgG4-related disease

Abstract Background/Aims IgG4-related disease (IgG4-RD) and granulomatous polyangiitis (GPA) have apparent different pathology. There are infrequent reports of the two conditions occurring simultaneously. We add to the literature by describing a patient who appears to have both conditions. Methods A 65-year-old male presented with low back pain radiating to the perineum. His past history included T2DM, CABG and ablation for AF. Initial investigations showed a CRP of 102mg/ml and an eGFR of &amp;gt; 90ml/hr. A CT urogram revealed possible aortitis. A dedicated aortogram showed a cuff of added tissue around the infrarenal aorta and iliac arteries. A whole aortogram showed an increase in the abnormal tissue and detected a left upper lobe cavitating lesion. A PET-CT scan showed activity in the infrarenal aortic tissue, with focal uptake in the aortic arch and right superficial femoral artery. Several pleural based and parenchymal lesions showing moderate increased FDG activity were seen. A CT scan of the sinuses showed multifocal sinonasal mucosal thickening without bony erosions. C-ANCA was positive at 1/40, with raised PR3 of 32U/ml and IgG4 of 2.2g/L. Other immunoglobulin levels were normal and IGRA was negative. A biopsy of the lung lesion showed necrotising granulomatous inflammation and surrounding palisading histocytes, withno vasculitic element. Treatment with prednisolone 40mg daily and methotrexate 15mg weekly was started. A quick symptomatic improvement followed. CRP fell to 14mg/ml within two months. It was discussed in the national IgG4-RD MDT, and the consensus was that he had features of both GPA and IgG4-RD. A follow-up CT scan showed reduction in the volume of para-aortic tissue, with regression of some lesions in the chest, while others increased. However, he remains well with a normal CRP, stable renal function and normal urinalysis. His latest IgG4 level dropped to 0.67 g/L. Results The ANCA positivity and lung biopsy findings satisfy classification criteria of GPA. While aortic involvement is not commonly seen in GPA; it is typical of IgG4-RD; however, its diagnostic criteria require a confirmatory biopsy. This is challenging due to the risk of sampling around the aorta and ureters. Our case fulfils criteria for ‘possible’ IgG4-RD. In retrospect, an earlier PET CT scan may have spared the patient several CT scans. Conclusion The co-existence of IgG4-RD and ANCA-associated vasculitis may be more common than might be expected. Our case highlights the usefulness of early PET-CT scanning in rheumatic conditions. It is important to check ANCA in suspected IgG4-RD cases. It is possible that future AI programmes may help clinicians better judge the timing of investigations that may be more expensive, invasive or have increased radiation exposure in such complex cases. Finally, the usefulness of a national MDT for IgG4-RD is highlighted. Fortunately, treatment modalities are similar for both conditions. Disclosure H. Eltahir: None. M. Lloyd: None.

Unexpected focal fluorodeoxyglucose uptake in main organs; pass through or pass by?

Since the inception of fluorine-18 fluorodeoxyglucose (F-18 FDG), positron emission tomography/computed tomography (PET/CT) utilizing F-18 FDG has become widely accepted as a valuable imaging modality in the field of oncology, with global prevalence in clinical practice. Given that a single Torso PET/CT scan encompasses the anatomical region from the skull base to the upper thigh, the detection of incidental abnormal focal hypermetabolism in areas of limited clinical interest is both feasible and not uncommon. Numerous investigations have been undertaken to delineate the distinctive features of these findings, yet the outcomes have proven inconclusive. The incongruent results of these studies present a challenge for physicians, leaving them uncertain about the appropriate course of action. This article provides a succinct overview of the characteristics of fluorodeoxyglucose, followed by a comprehensive discussion of the imaging findings and clinical significance associated with incidental focal abnormal F-18 FDG activity in several representative organs. In conclusion, while the prevalence of unrecognized malignancy varies across organs, malignancies account for a substantial proportion, ranging from approximately one-third to over half, of incidental focal uptake. In light of these rates, physicians are urged to exercise vigilance in not disregarding unexpected uptake, facilitating more assured clinical decisions, and advocating for further active evaluation.

False Liver Metastasis by Positron Emission Tomography/Computed Tomography Scan after Chemoradiotherapy for Esophageal Cancer-Potential Overstaged Pitfalls of Treatment.

In patients with esophageal cancer undergoing neoadjuvant chemoradiotherapy (nCRT), subsequent restaging with F-18-fluorodeoxyglucose (18F-FDG) positron emission tomography-computed tomography (PET-CT) can reveal the presence of interval metastases, such as liver metastases, in approximately 10% of cases. Nevertheless, it is not uncommon in clinical practice to observe focal FDG uptake in the liver that is not associated with liver metastases but rather with radiation-induced liver injury (RILI), which can result in the overstaging of the disease. Liver radiation damage is also a concern during distal esophageal cancer radiotherapy due to its proximity to the left liver lobe, typically included in the radiation field. Post-CRT, if FDG activity appears in the left or caudate liver lobes, a thorough investigation is needed to confirm or rule out distant metastases. The increased FDG uptake in liver lobes post-CRT often presents a diagnostic dilemma. Distinguishing between radiation-induced liver disease and metastasis is vital for appropriate patient management, necessitating a combination of imaging techniques and an understanding of the factors influencing the radiation response. Diagnosis involves identifying new foci of hepatic FDG avidity on PET/CT scans. Geographic regions of hypoattenuation on CT and well-demarcated regions with specific enhancement patterns on contrast-enhanced CT scans and MRI are characteristic of radiation-induced liver disease (RILD). Lack of mass effect on all three modalities (CT, MRI, PET) indicates RILD. Resolution of abnormalities on subsequent examinations also helps in diagnosing RILD. Moreover, it can also help to rule out occult metastases, thereby excluding those patients from further surgery who will not benefit from esophagectomy with curative intent.

Intense 18 F-Prostate-Specific Membrane Antigen Uptake and Mild 18 F-FDG Uptake in a Biopsy-Proven Pulmonary Hemangioma.

We present intense radiotracer activity in a soft tissue density abutting the aortic arch of the left lung on 18 F-prostate-specific membrane antigen PET/CT scan in a patient with prostate cancer, mimicking metastatic disease from prostate cancer versus primary lung malignancy. 18 F-FDG PET/CT scan, however, shows no elevated FDG activity. The results of pathology examination from resected specimen are consistent with pulmonary hemangioma.

Comparison of 18 F-FDG and 18 F-FAPI PET/CT Findings of Signet-Ring Cell Carcinoma of the Stomach.

A 66-year-old man with gastric signet-ring cell carcinoma underwent both 18 F-FDG and 18 FAl-NOTA-FAPI PET/CT imaging. There was no abnormal FDG activity in the stomach, but there was diffuse intense 18 FAl-NOTA-FAPI uptake in the known lesion and an adjacent metastasis.

FDG PET/CT Imaging 1 Week after a Single Dose of Pembrolizumab Predicts Treatment Response in Patients with Advanced Melanoma.

Immunologic response to anti-programmed cell death protein 1 (PD-1) therapy can occur rapidly with T-cell responses detectable in as little as one week. Given that activated immune cells are FDG avid, we hypothesized that an early FDG PET/CT obtained approximately 1 week after starting pembrolizumab could be used to visualize a metabolic flare (MF), with increased tumor FDG activity due to infiltration by activated immune cells, or a metabolic response (MR), due to tumor cell death, that would predict response. Nineteen patients with advanced melanoma scheduled to receive pembrolizumab were prospectively enrolled. FDG PET/CT imaging was performed at baseline and approximately 1 week after starting treatment. FDG PET/CT scans were evaluated for changes in maximum standardized uptake value (SUVmax) and thresholds were identified by ROC analysis; MF was defined as >70% increase in tumor SUVmax, and MR as >30% decrease in tumor SUVmax. An MF or MR was identified in 6 of 11 (55%) responders and 0 of 8 (0%) nonresponders, with an objective response rate (ORR) of 100% in the MF-MR group and an ORR of 38% in the stable metabolism (SM) group. An MF or MR was associated with T-cell reinvigoration in the peripheral blood and immune infiltration in the tumor. Overall survival at 3 years was 83% in the MF-MR group and 62% in the SM group. Median progression-free survival (PFS) was >38 months (median not reached) in the MF-MR group and 2.8 months (95% confidence interval, 0.3-5.2) in the SM group (P = 0.017). Early FDG PET/CT can identify metabolic changes in melanoma metastases that are potentially predictive of response to pembrolizumab and significantly correlated with PFS.

The systemic impact of different COVID-19 vaccines in 2-[18F] FDG-PET/CT

Austria started its COVID-19-vaccination program in December 2020 with three different vaccines. As the vaccination program continues, we encountered increased 2-[18F] FDG-activity not only in axillary lymph nodes ipsilateral to the injection site but also in other organs. The aim of this retrospective study is to present results of the metabolic activity of ipsilateral axillary lymph nodes, liver, blood pool, spleen, and bone marrow after three different vaccines. To our knowledge, this is the first study to examine systemic response changes in relation to time after COVID-19 vaccination using three different vaccines. The collected data of 220 eligible vaccinated patients (127 with BioNTech/Pfizer BNT162b2, 61 with Moderna, and 32 with AstraZeneca) examined with 2-[18F] FDG-PET/CT were enrolled. The PET/CT examinations were evaluated from day 1 to day 135 (SD: 23.2, median: 26) after different vaccinations. Seventy-one out of these 220 patients underwent a pre-vaccination 2-[18F] FDG -PET/CT. SUVmax of axillary node(s), and blood pool, liver, spleen, and bone marrow as reference organs were calculated. The ratio of SUVmax activity of axillary lymph node to reference organs was also compared in all patients. The tracer activity dynamics were investigated in three different vaccines. After BioNTech/Pfizer vaccination 2-[18F] FDG activity in axillary lymph nodes shows a steady decrease in all patients. Ten days after vaccination the 2-[18F] FDG uptake was at its highest activity. Seventy days after vaccination, tracer activity is not different from the background activity of 2-[18F] FDG in the axillary region. This result also applies to other two vaccines; however, in the 4th week after Moderna vaccination SUVmax in lymph nodes showed the highest peak of tracer activity. With AstraZeneca the highest activity was at the earlier days. There was no significant statistical difference of SUVmax of lymph nodes or its ratios to other reference organs between three groups of vaccines. SUVmax in lymph nodes was statistically significant lower than SUVmax in the liver, spleen, and bone marrow with p-values of < 0.001, 0.044, and 0.001, respectively. In the group of 71 patients with a pre-vaccination PET/CT examination, the median SUVmax of lymph nodes increased significantly after vaccination from 0.82 (IQR 0.59–1.38) to 1.80 (IQR 1.07–3.89)(p < 0.001). In contrast median tracer activity in the liver decreased from 3.37 (IQR 2.83–3.91) to 3.11 (2.56–3.70) (p = 0.032). There was no significant change of tracer activity after vaccination in other reference regions (mediastinum, spleen, and bone marrow). In this group of 71 patients, there was also no significant difference in tracer activity in different types of vaccines. Local site and ipsilateral axillary lymph node activity in 2-[18F] FDG PET/CT after COVID19-vaccination is suggested in many studies. The main challenge is recognizing the changes in lymph nodes during time after vaccination to minimize false interpretation, foremost in patients with oncological diagnoses. Moreover, different vaccines cause different system metabolic changes. The knowledge of vaccine type, the time interval between vaccination and PET/CT scan is essential, especially in therapy evaluation.

Image Quality and Quantitative PET Parameters of Low-Dose [18F]FDG PET in a Long Axial Field-of-View PET/CT Scanner.

PET/CT scanners with a long axial field-of-view (LAFOV) provide increased sensitivity, enabling the adjustment of imaging parameters by reducing the injected activity or shortening the acquisition time. This study aimed to evaluate the limitations of reduced [18F]FDG activity doses on image quality, lesion detectability, and the quantification of lesion uptake in the Biograph Vision Quadra, as well as to assess the benefits of the recently introduced ultra-high sensitivity mode in a clinical setting. A number of 26 patients who underwent [18F]FDG-PET/CT (3.0 MBq/kg, 5 min scan time) were included in this analysis. The PET raw data was rebinned for shorter frame durations to simulate 5 min scans with lower activities in the high sensitivity (HS) and ultra-high sensitivity (UHS) modes. Image quality, noise, and lesion detectability (n = 82) were assessed using a 5-point Likert scale. The coefficient of variation (CoV), signal-to-noise ratio (SNR), tumor-to-background ratio (TBR), and standardized uptake values (SUV) including SUVmean, SUVmax, and SUVpeak were evaluated. Subjective image ratings were generally superior in UHS compared to the HS mode. At 0.5 MBq/kg, lesion detectability decreased to 95% (HS) and to 98% (UHS). SNR was comparable at 1.0 MBq/kg in HS (5.7 ± 0.6) and 0.5 MBq/kg in UHS (5.5 ± 0.5). With lower doses, there were negligible reductions in SUVmean and SUVpeak, whereas SUVmax increased steadily. Reducing the [18F]FDG activity to 1.0 MBq/kg (HS/UHS) in a LAFOV PET/CT provides diagnostic image quality without statistically significant changes in the uptake parameters. The UHS mode improves image quality, noise, and lesion detectability compared to the HS mode.

FRI228 Primary Adrenal T-cell Lymphoma: A Case Report

Abstract Disclosure: H. Tabassum: None. S. Xu: None. A. Manavalan: None. Introduction: Primary T-cell adrenal lymphoma (PAL) is exceedingly rare. Adrenal insufficiency (AI) is common in these cases. Here we describe a patient with bilateral, large, T-cell PAL with rapid progression, without adrenal insufficiency. Clinical Case: A 62-year-old male, with coronary artery disease and recent coronary intervention, hyperlipidemia and hypertension presented to the hospital with abdominal pain, fever, night sweats and weight loss for a month. Work up revealed a 5.8 cm left adrenal mass with 14% absolute washout, measuring 34 Hounsfield Units (HU) pre-contrast, 68 HU postcontrast, and 63 HU on delayed images, and a 5.2 cm right adrenal mass with 42% absolute washout, measuring 35 HU pre-contrast, 81 HU postcontrast, and 62 HU on the delayed images with no other suspicious lesions or lymphadenopathy. The patient demonstrated no clinical symptoms or signs of adrenal hormone excess or deficiency. Levels of renin, aldosterone, serum cortisol, ACTH, 24-hour urine free cortisol, serum metanephrines, and thyroid function were normal. Additional tests to rule out adrenal cortical carcinoma (ACC) revealed normal levels of androstenedione, 17-hydroxyprogesterone, dehydroepiandrosterone sulfate, and estradiol. Persistent non-significant elevation of 11-deoxycortisol was observed at 51 ng/dL and 63ng/dL (Ref &amp;lt; 42 ng/dL). Adrenal biopsy was suggested but deferred due to the increased risk of hemorrhage given recent coronary revascularization and use of dual antiplatelet therapy. Follow up imaging in a few weeks revealed diffuse, retroperitoneal lymphadenopathy with unchanged adrenal masses. A lymph node biopsy confirmed a diagnosis of peripheral T-cell lymphoma. The left adrenal gland demonstrated an uptake SUV of 22.7 and the right, 19.17 on FDG PET. The patient was initiated on chemotherapy with etoposide, prednisone, vincristine sulfate, cyclophosphamide, and doxorubicin. Imaging three months later revealed a marked decrease in FDG activity SUV 6.98 g/mL on the left and SUV up to 3.32 g/mL on the right. Adrenal function remained intact on follow up. Conclusion: Peripheral T-cell lymphoma with adrenal involvement is an extremely rare and aggressive disease with rapid progression. Mostly seen in males over the age of 50, it may present with abdominal pain, B symptoms or both. While ACC is usually unilateral, lymphoma and metastatic disease may present bilaterally, however, other imaging features can be similar. AI is expected when 90% of the adrenal glands are destroyed by tumor infiltration, however, this does not always correlate with tumor size. In our patient, AI was not observed on presentation or follow up. As adrenal insufficiency can occur at any time in the disease course and may mimic symptoms of cancer or chemotherapy, the clinician should always be vigilant for its development in these cases. Presentation: Friday, June 16, 2023

SAT329 Case Series Of Patients With FGFR-1 Related Pheochromocytoma With A Focus On Biochemical And Imaging Signatures

Abstract Disclosure: S. Jhawar: None. J. Del Rivero: None. K. Pacak: None. Introduction: Pheochromocytomas (PCCs) and paragangliomas (PGLs) are rare neuroendocrine tumors arising from chromaffin cells of adrenal gland and neural crest, respectively. 40% of cases are associated with germline mutations and 30-40% somatic driver mutations. Here, we present two patients with PCC who were found to have somatic FGFR1 mutation. FGFR signaling is involved in regulation of tissue repair, angiogenesis, and inflammation. Patient 1: A 70-year-old female with a history of resistant hypertension, episodic palpitations and sweating presented with diffuse abdominal pain and chest tightness. She was noted to have a blood pressure of 220/160 mm Hg. CT scan showed a 4.2 x 3.9 cm left adrenal mass, suspicious for malignancy and a &amp;lt;1 cm retroperitoneal mass. Blood work revealed elevated plasma normetanephrine (NM) 3543 pg/mL (normal 0- 145) and metanephrine (MN) 871 pg/mL (normal 0-62). 18F-FDG PET/CT showed a left adrenal mass without abnormal FDG activity. 68Ga-DOTATATE PET/CT was compatible with left PCC (SUVmax 28). 18F-DOPA PET/CT showed left PCC and a small retroperitoneal PGL. Two weeks after initiating phenoxybenzamine, she underwent total left adrenalectomy. Pathology was consistent with PCC. Molecular testing revealed FGFR1 pathogenic somatic mutation (c.1638C&amp;gt;G p.Asn546Lys). Patient 2: A 73-year-old male with known left renal cell carcinoma presented to our institution for management of recurrent right PCC. He was found to have a 3.8 cm right adrenal incidentaloma eight years ago and elevated plasma NM 6.3 nmol/L (normal &amp;lt;0.9), MN 1.5 nmol/L (normal &amp;lt;0.5). He underwent total right adrenalectomy, and the diagnosis of PCC was confirmed on histopathology. Two years later, he developed a 5.1 x 4.7 cm nodular mass in the right adrenal fossa and a &amp;lt;1 cm liver lesion on CT scan. The adrenal lesion showed intense avidity on 68Ga-DOTATATE PET/CT and 18F-DOPA PET/CT and mild avidity on 18FDG-PET/CT. 18F-DOPA PET/CT also showed avidity towards the liver lesion. He was started on doxazosin and underwent laparoscopic right adrenalectomy. Pathology demonstrated PCC. Whole exome sequencing of the tumor showed pathogenic FGFR1 mutation (c.1638C&amp;gt;G, p.Asn546Lys). Discussion: Activating FGFR1 mutations are associated with sporadic PCC. The biochemical phenotype of our patients showed higher levels of NM than MN. The imaging profile revealed that 18F-DOPA PET/CT was more sensitive than 68Ga-DOTATATE PET/CT and 18F-FDG PET/CT as it showed avidity towards other extra-adrenal lesions. Further studies in larger cohorts are needed to enhance understanding of pathogenesis, biochemical and imaging phenotype, which will help tailor the treatment and potential development of novel targeted therapies. Presentation: Saturday, June 17, 2023

SDPS-08 OSSEOUS METASTASES IN H3G34-MUTANT DIFFUSE HEMISPHERIC GLIOMAS

Abstract Subset of patients with H3G34 gliomas may present with extra-CNS metastasis further complicating both diagnosis and treatment. We describe a case of a 19-year-old female presenting initially with focal motor seizure in right leg along with leg pain. MRI of the leg showed an ill-defined right distal femur expansile osteolytic lesion with central fluid signal, thick rim enhancement, endosteal scalloping, cortical invasion, and smooth enhancing periosteal reaction/soft tissue extension associated with surrounding enhancing marrow signal abnormality worrisome for lesion extension. Contrast brain MRI exhibited multiple frontal and partial lobe T2 FLAIR hyperintense lesions. The largest lesion demonstrated contrast enhancement, internal foci of restricted diffusion, and a focus of intratumoral hemorrhage. A whole-body PET/CT showed intensely FDG-avid lytic lesion in the right distal femur, with FDG activity along the biopsy tract. Hypermetabolic lytic metastases to the right femoral head and mid-sacral body were also observed. A craniotomy with brain lesion biopsy two months later indicated preliminary histopathology of malignant small round blue cell neoplasm. A biopsy from the distal right femur was non-diagnostic of malignancy but a sacral bone biopsy reported malignant small blue cell neoplasm, consistent with involvement by the patient's known cranial neoplasm. Final pathological diagnosis including molecular diagnostics was consistent with WHO grade 4 IDH-wildtype H3G34 mutant diffuse hemispheric glioma with osseous metastases. Patient was treated with chemoradiotherapy with temozolomide (TMZ). Following the sixth cycle of TMZ, MRI brain imaging was stable. Apart from holocephalic headaches, the patient had no significant medication side effects and was seizure-free. A second whole-body PET scan showed improvement and interval decrease in FDG uptake of the sacrum and right femoral head. Given the stress that patients with H3G34 can experience and the poor prognosis, it is imperative to expand our knowledge and ascertain accurate screening and diagnostic methodologies.

Type 2 Endoleak Detection After Endovascular Aneurysm Repair: Can Low-Flow Endoleaks Also Be Visualized in Silicon-Photomultiplier-Based Positron Emission Tomography/Computed Tomography Scans?

To present a novel clinical application of silicon-photomultiplier-based positron emission tomography (SiPM-based PET)/computed tomography (CT), detecting a type II endoleak 5 years after endovascular aneurysm repair (EVAR). SiPM-based PET/CT scans with a standard whole-body protocol were performed for a 73-year-old man with a past medical history of abdominal aortic aneurysms treated with EVAR and currently under investigation of his duodenal papillary carcinoma. The PET/CT demonstrated 18F-fluorodeoxyglucose (FDG) accumulation outside the stent graft in the native sac of the aneurysm. The site of accumulation corresponded to that of the contrast enhancement depicted in the CT angiography taken 1 month earlier. Another CT scan performed 3 months later revealed enlargement of the aneurysm. SiPM-based PET/CT, with its superior sensitivity and spatial resolution over conventional PET/CT, can detect type II low-flow endoleaks. Abnormal intra-aneurysmal FDG activity incidentally detected on SiPM-based PET/CT is worthy of attention because it may be indicative of endoleaks. Additional imaging using different modalities should be considered so that the patient would not miss the additional treatment opportunity upon observing sac enlargement. For patients with contraindications for iodine CT contrast media, SiPM-based PET/CT would serve as a suitable alternative.