F-18 FDG perfusion PET: intraprocedural assessment of the liver tumor ablation margin.

PURPOSE: To evaluate 18F-fluorodeoxyglucose (FDG) perfusion PET during FDG PET/CT-guided liver tumor microwave ablation procedures for assessing the ablation margin and correlating minimum margin measurements with local progression. METHODS: This IRB-approved, HIPAA-compliant study included 20 adult patients (11 M, 9 F; mean age 65) undergoing FDG PET/CT-guided liver microwave ablation to treat 31 FDG-avid tumors. Intraprocedural FDG perfusion PET was performed to assess the ablation margin. Intraprocedural decisions regarding overlapping ablations were recorded. Two readers retrospectively interpreted intraprocedural perfusion PET and postprocedural contrast-enhanced MRI. Assessability of the ablation margin and minimum margin measurements were recorded. Imaging follow-up for local progression ranged from 30 to 574 days (mean 310). Regression modeling of minimum margin measurements was performed. Hazard ratios were calculated to correlate an ablation margin threshold of 5 mm with outcomes. RESULTS: Intraprocedural perfusion PET prompted additional overlapping ablations of two tumors, neither of which progressed. Incomplete ablation or local progression occurred in 8/31 (26%) tumors. With repeat ablation, secondary efficacy was 26 (84%) of 31. Both study readers deemed ablation margins fully assessable more often using perfusion PET than MRI (OR 69.7; CI 6.0, 806.6; p = 0.001). Minimum ablation margins ≥ 5 mm on perfusion PET correlated with a low risk of incomplete ablation/local progression by both study readers (HR 0.08 and 0.02, p < 0.001). CONCLUSION: Intraprocedural FDG perfusion PET consistently enabled complete liver tumor microwave ablation margin assessments, and the perfusion PET minimum ablation margin measurements correlated well with local outcomes. Clinical trial registration clinicaltrials.gov (NCT02018107).

Intraprocedural Ablation Margin Assessment by Using Ammonia Perfusion PET during FDG PET/CT-guided Liver Tumor Ablation: A Pilot Study.

Purpose To prospectively determine whether nitrogen 13 (13N) ammonia perfusion positron emission tomography (PET) during fluorine 18 fluorodeoxyglucose (FDG) PET/computed tomography (CT)-guided liver tumor ablation can be used to intraprocedurally assess ablation margins. Materials and Methods Eight patients (five women and three men; age range, 36-74 years; mean age, 57 years) were enrolled in this pilot study and underwent FDG PET/CT-guided microwave ablation of 11 FDG-avid liver metastases (mean diameter, 22 mm; range, 11-34 mm). All procedures were performed between March 2014 and December 2016. Complete ablation margin visibility and minimum ablation margin thickness were assessed by using intraprocedural 13N-ammonia perfusion PET compared with 24-hour postprocedural MR imaging by two independent blinded radiologists. Local tumor progression for each ablated tumor was assessed at follow-up imaging for 3-38 months (median, 17.6 months). Descriptive analysis was performed. Results Eleven of 11 (100%) ablation margins were fully assessable by using intraprocedural perfusion PET by both readers; six of eleven (55%) margins were fully assessable by both readers at postprocedural 24-hour MR imaging. By using perfusion PET, one tumor that had been judged by both readers to have a minimum margin of 0 mm progressed locally. No tumors judged to have a minimum margin greater than 0 mm at perfusion PET progressed locally. Conclusion 13N-ammonia perfusion PET during FDG PET/CT-guided liver tumor ablations can potentially be used to intraprocedurally assess the entire ablation margin, including the minimum margin. © RSNA, 2018.

Occupational radiation dosimetry assessment using an automated infusion device for positron-emitting radiotracers.

UNLABELLED: Handling and administration of radiopharmaceuticals are a key contributor to staff radiation dose. Shielded automated infusion devices potentially standardize and reduce radiation exposure during procedures. However, loading the devices adds incremental radiation exposure, which may mitigate dose savings. We measured radiation doses from the loading and use of an automated infusion device and compared these with those from manual injection of (18)F radiotracers. METHODS: Adult patients were administered (18)F-FDG or (18)F-FLT before 3-dimensional PET whole-body or brain imaging, respectively. Radioactivity amounts from manual injections performed with protective syringe shields and vial holders were measured by a standard dose calibrator before and after injection. Automated infusions were performed using the shielded infusion device. Staff wore electronic dosimeters at the wrist and trunk. Electronic dosimeters were also worn while multidose (18)F-FDG vials were loaded and unloaded. For each task, background radiation was determined and subtracted from the electronic dosimeter values. RESULTS: Twenty-seven manually injected unit doses yielded a mean administered dose to patients of 480.7 ± 66.2 MBq (12.99 ± 1.79 mCi), compared with 431.9 ± 22.7 MBq (11.67 ± 0.61 mCi) in 34 automated injections. The mean difference was statistically significant. To control for this difference, results were expressed as a standardized dose per unit of activity. With the automated infusion device, the mean extremity dose per injection was 0.003 ± 0.002 µSv/MBq, compared with 0.026 ± 0.017 µSv/MBq with manual injections. Mean body dose per procedure with automated infusion was 0.001 µSv/MBq, versus 0.011 µSv/MBq with manual injection (P < 0.001). The changing of bulk (18)F-FDG vials in 37 procedures added a mean dose per vial change of 0.89 ± 1.3 µSv to the extremities and 0.47 ± 2.0 µSv to the body. CONCLUSION: The use of a shielded automatic infusion device in a clinical PET setting resulted in an approximately 10-fold decrease in staff extremity and body doses during the administration of (18)F-labeled radiopharmaceuticals. Loading and unloading bulk vials of radiotracer did not significantly offset these dose savings.

Dual phase FDG-PET imaging of brain metastases provides superior assessment of recurrence versus post-treatment necrosis.

To study the ability of dual phase FDG-PET/CT imaging to accurately distinguish tumor versus necrosis in patients treated for brain metastases. 32 (22 female, 10 male) consecutive patients with treated brain metastases, lesion size greater than 0.5 cm(3) and suspected recurrence on MRI underwent dual-phase FDG-PET/CT. Clinical outcome was assessed by biopsy or by MRI. SUVmax and SUVmean values of the lesion (L) and gray matter (GM) at the level of the thalamus were measured on early (1) and delayed (2) imaging. L1/GM1 and L2/GM2 and the change of L/GM ratios as a function of time were calculated [(L2/GM2 - L1/GM1)/(L1/GM1)]. Cut-off values were obtained by ROC analysis. P < 0.05 defined statistical significance. Seven patients were excluded due to indeterminate outcomes. 25 patients (16 female, 9 male; 27 lesions; 28 scan sessions) had clear outcomes, proven by either biopsy (n = 16 patients) or serial follow-up MRI (n = 9 patients). Primary subtypes included breast (n = 9), lung (n = 7), melanoma (n = 3), squamous cell cancer of the head and neck (n = 2) and other (n = 4). Twenty-two patients underwent prior radiation (2-113 months) and three received only prior chemotherapy (5 months to 3 years). A change >0.19 of L/GM ratios as a function of time was 95% sensitive, 100% specific, and 96.4% accurate (P = 0.0001; AUC = 0.97) for distinguishing tumor versus radiation necrosis. The ratio of the change of the lesion to WM ratios over time was the second best indicator of outcome when compared to all indices used (ROC cut-off = 0.25, sensitivity 89.5% and specificity 90.9%, and accuracy 89.2%; P = 0.0001; AUC = 0.95), Early or late SUVs of the lesion alone did not differentiate between tumor and necrosis. Regardless of histological type, differentiation of necrosis from metastatic brain lesions was improved by using the change of lesion to gray matter SUVmax ratios as a function of time.

A Multimodality Imaging Review of Malignant Pleural Mesothelioma Response Assessment.

Assessment of response is important to interpret early phase clinical trial results and to guide individual patient management. In malignant pleural mesothelioma (MPM), the circumferential growth pattern of the disease, the presence of pleural effusion and atelectasis, and the common use of pleurodesis make this a challenging task for imaging specialists and clinicians. This article reviews the current evidence for radiological and positron emission tomography (PET) response assessment in MPM, and the pitfalls and challenges in its application. Current research and future directions in radiological and PET response are discussed, including the use of novel radiotracers.

Assessment of malignant pleural mesothelioma with (18)F-FDG dual-head gamma-camera coincidence imaging: comparison with histopathology.

UNLABELLED: Malignant pleural mesothelioma is an aggressive primary neoplasm for which early detection and accurate staging are known diagnostic challenges. The role of (18)F-FDG dual-head gamma-camera coincidence imaging ((18)F-FDG-CI) is yet to be defined. The purpose of this study was to evaluate the usefulness of (18)F-FDG-CI in the assessment of malignant pleural mesothelioma using histopathology as the gold standard. METHODS: Fifteen consecutive patients with CT scan evidence of pleural thickening, fluid, plaques, or calcification underwent (18)F-FDG imaging 1.5 h after the intravenous administration of 370 MBq (18)F-FDG. Imaging was performed with a dual-head gamma camera equipped with 2.54-cm-thick NaI crystals operating in coincidence mode. Using an iterative algorithm, whole-body images were reconstructed as transaxial, sagittal, and coronal images. No attenuation correction was applied. The results of (18)F-FDG-CI scans were compared with CT and with histopathologic diagnosis. RESULTS: Eleven of 15 patients had histologically proven malignant mesotheliomas (10 epithelial, 1 sarcomatoid). All 11 primary tumors were detected by (18)F-FDG, and absence of disease was confirmed in the 4 patients who were disease free. Thirty-four lesions were biopsied; among these, 29 were found to be positive for tumor. (18)F-FDG was true-positive in 28 lesions, true-negative in 4, false-negative in 1 (0.5 cm in diameter), and false-positive in 1 (inflammatory pleuritis). The smallest lesion detected was 0.8 cm. For biopsied lesions, overall sensitivity, specificity, and accuracy for (18)F-FDG-CI were 97%, 80%, and 94% respectively, compared with 83%, 80%, and 82% for CT. Twenty-one of 29 positive lesions involved the pleura, lung parenchyma, or chest wall and were all (18)F-FDG avid. In the mediastinum, (18)F-FDG-CI detected 7 of 8 biopsy-positive lesions (88%), whereas CT was positive in 6 of 8 lesions (75%). (18)F-FDG identified extrathoracic metastases in 5 patients, excluding them from surgical therapy. CONCLUSION: These preliminary results suggest that (18)F-FDG-CI appears to be an accurate method to diagnose and to define the extent of disease in patients with diffuse malignant pleural mesothelioma.