Can integrated 18F-FDG PET/MR replace sentinel lymph node resection in malignant melanoma?

PURPOSE: To compare the sensitivity and specificity of 18F-fluordesoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT), 18F-FDG PET/magnetic resonance (18F-FDG PET/MR) and 18F-FDG PET/MR including diffusion weighted imaging (DWI) in the detection of sentinel lymph node metastases in patients suffering from malignant melanoma. MATERIAL & METHODS: Fifty-two patients with malignant melanoma (female: n = 30, male: n = 22, mean age 50.5 ± 16.0 years, mean tumor thickness 2.28 ± 1.97 mm) who underwent 18F-FDG PET/CT and subsequent PET/MR & DWI for distant metastasis staging were included in this retrospective study. After hybrid imaging, lymphoscintigraphy including single photon emission computed tomography/CT (SPECT/CT) was performed to identify the sentinel lymph node prior to sentinel lymph node biopsy (SLNB). In a total of 87 sentinel lymph nodes in 64 lymph node basins visible on SPECT/CT, 17 lymph node metastases were detected by histopathology. In separate sessions PET/CT, PET/MR, and PET/MR & DWI were assessed for sentinel lymph node metastases by two independent readers. Discrepant results were resolved in a consensus reading. Sensitivities, specificities, positive predictive values and negative predictive values were calculated with histopathology following SPECT/CT guided SLNB as a reference standard. RESULTS: Compared with histopathology, lymph nodes were true positive in three cases, true negative in 65 cases, false positive in three cases and false negative in 14 cases in PET/CT. PET/MR was true positive in four cases, true negative in 63 cases, false positive in two cases and false negative in 13 cases. Hence, we observed a sensitivity, specificity, positive predictive value and negative predictive value of 17.7, 95.6, 50.0 and 82.3% for PET/CT and 23.5, 96.9, 66.7 and 82.3% for PET/MR. In DWI, 56 sentinel lymph node basins could be analyzed. Here, the additional analysis of DWI led to two additional false positive findings, while the number of true positive findings could not be increased. CONCLUSION: In conclusion, integrated 18F-FDG PET/MR does not reliably differentiate N-positive from N-negative melanoma patients. Additional DWI does not increase the sensitivity of 18F-FDG PET/MR. Hence, sentinel lymph node biopsy cannot be replaced by 18F-FDG-PE/MR or 18F-FDG-PET/CT.

Biodistribution and radiation dosimetry of 124I-mIBG in adult patients with neural crest tumours and extrapolation to paediatric models.

AIM: Positron emission tomography (PET) using 124I-mIBG has been established for imaging and pretherapeutic dosimetry. Here, we report the first systematic analysis of the biodistribution and radiation dosimetry of 124I-mIBG in patients with neural crest tumours and project the results to paediatric patient models. METHODS: Adult patients with neural crest tumours who underwent sequential 124I-mIBG PET were included in this retrospective single-center analysis. PET data were acquired 4, 24, 48, and/or 120 h after administration of a mean of 43 MBq 124I-mIBG. Whole-body counting and blood sampling were performed at 2, 4, 24, 48 and 120 h after administration. Absorbed organ dose and effective dose coefficients were estimated in OLINDA/EXM 2.2 according to the MIRD formalism. Extrapolation to paediatric models was performed based on mass-fraction scaling of the organ-specific residence times. Biodistribution data for adults were also projected to 123I-mIBG and 131I-mIBG. RESULTS: Twenty-one patients (11 females, 10 males) were evaluated. For adults, the organs exposed to the highest dose per unit administered activity were urinary bladder (1.54 ± 0.40 mGy/MBq), salivary glands (0.77 ± 0.28 mGy/MBq) and liver (0.65 ± 0.22 mGy/MBq). Mean effective dose coefficient for adults was 0.25 ± 0.04 mSv/MBq (male: 0.24 ± 0.03 mSv/MBq, female: 0.26 ± 0.06 mSv/MBq), and increased gradually to 0.29, 0.44, 0.69, 1.21, and 2.94 mSv/MBq for the 15-, 10-, 5-, 1-years-old, and newborn paediatric reference patients. Projected mean effective dose coefficients for 123I-mIBG and 131I-mIBG for adults were 0.014 ± 0.002 mSv/MBq and 0.18 ± 0.04 mSv/MBq, respectively. CONCLUSION: PET-based derived radiation dosimetry data for 124I-mIBG from this study agreed well with historical projected data from ICRP 53. The effective dose coefficients presented here may aid in guidance for establishing weight-based activity administration protocols.

Prognostic stratification of metastatic gastroenteropancreatic neuroendocrine neoplasms by 18F-FDG PET: feasibility of a metabolic grading system.

UNLABELLED: The tumor proliferation marker, Ki-67 index, is a well-established prognostic marker in gastroenteropancreatic neuroendocrine neoplasms (NENs). Noninvasive molecular imaging allows whole-body metabolic characterization of metastatic disease. We investigated the prognostic impact of (18)F-FDG PET in inoperable multifocal disease. METHODS: Retrospective, dual-center analysis was performed on 89 patients with histologically confirmed, inoperable metastatic gastroenteropancreatic NENs undergoing (18)F-FDG PET/CT within the staging routine. Metabolic (PET-based) grading was in accordance with the most prominent (18)F-FDG uptake (reference tumor lesion): mG1, tumor-to-liver ratio of maximum standardized uptake value ≤ 1.0; mG2, 1.0-2.3; mG3, >2.3. Other potential variables influencing overall survival, including age, tumor origin, performance status, tumor burden, plasma chromogranin A (≥600 µg/L), neuron-specific enolase (≥25 µg/L), and classic grading (Ki-67-based) underwent univariate (log-rank test) and multivariate analysis (Cox proportional hazards model), with a P value of less than 0.05 considered significant. RESULTS: The median follow-up period was 38 mo (95% confidence interval [CI], 27-49 mo); median overall survival of the 89 patients left for multivariate analysis was 29 mo (95% CI, 21-37 mo). According to metabolic grading, 9 patients (10.2%) had mG1 tumors, 22 (25.0%) mG2, and 57 (64.8%) mG3. On multivariate analysis, markedly elevated plasma neuron-specific enolase (P = 0.016; hazard ratio, 2.9; 95% CI, 1.2-7.0) and high metabolic grade (P = 0.015; hazard ratio, 4.7; 95% CI, 1.2-7.0) were independent predictors of survival. CONCLUSION: This study demonstrated the feasibility of prognostic 3-grade stratification of metastatic gastroenteropancreatic NENs by whole-body molecular imaging using (18)F-FDG PET.