Currently, a reliable diagnostic test for differentiating pseudoprogression from early tumor progression is lacking. We explored the potential of O-(2-[18F]fluoroethyl)-L-tyrosine (FET) positron emission tomography (PET) radiomics for this clinically important task. Thirty-four patients (isocitrate dehydrogenase (IDH)-wildtype glioblastoma, 94%) with progressive magnetic resonance imaging (MRI) changes according to the Response Assessment in Neuro-Oncology (RANO) criteria within the first 12 weeks after completing temozolomide chemoradiation underwent a dynamic FET PET scan. Static and dynamic FET PET parameters were calculated. For radiomics analysis, the number of datasets was increased to 102 using data augmentation. After randomly assigning patients to a training and test dataset, 944 features were calculated on unfiltered and filtered images. The number of features for model generation was limited to four to avoid data overfitting. Eighteen patients were diagnosed with early tumor progression, and 16 patients had pseudoprogression. The FET PET radiomics model correctly diagnosed pseudoprogression in all test cohort patients (sensitivity, 100%; negative predictive value, 100%). In contrast, the diagnostic performance of the best FET PET parameter (TBRmax) was lower (sensitivity, 81%; negative predictive value, 80%). The results suggest that FET PET radiomics helps diagnose patients with pseudoprogression with a high diagnostic performance. Given the clinical significance, further studies are warranted.

Purpose The aim of this study was to explore the positive predictive value and negative predictive value of FDG PET/CT. The prognostic impact of tumor burden of bone marrow infiltrates was diagnosed by FDG PET/CT at initial presentation. Methods This retrospective study enrolled 140 pediatric patients with pathologically proven lymphoma (113 Hodgkin disease and 27 Non-Hodgkin lymphoma). All patients had pretherapy FDG PET/CT. Bone marrow biopsy (BMB), clinical, radiological, and follow-up data were also collected. The skeleton was divided into 8 segments, and a 5-point scoring system was used for assessment of BM infiltration burden. Results Among the 140 lymphoma patients, FDG PET/CT revealed positive BM involvement in 41 patients; 2 of them were false-positive with negative BMB and regional MRI results. Positive predictive value was 95.1% for PET/CT compared with 100% with BMB. All patients diagnosed with positive BMI by BMB were detected by FDG PET/CT. On the contrary, BMB missed 25 patients (17.9%) with statistically significant difference. Negative predictive value was 100% for PET/CT compared with 80.2% for BMB (P < 0.05). FDG PET/CT upstaged 17.9% of the enrolled patients. Bone marrow involvement based on the 5-point scoring system was assessed. No significant difference was demonstrated in therapy outcome between patient with focal BMI (score 2) and extensive BMI (score 5; P = 0.06). Conclusions FDG PET/CT has optimum negative predictive value compared with BMB in detection of bone marrow infiltrations in pediatric lymphoma with upstaging cases missed with BMB. Prognostic impact of BMI based on the 5-point scoring system reveals that the main influence is presence or absence of BMI rather than its tumor burden.

FDG PET-CT appears to be a very efficient tool in post-surgical surveillance of patients with RCC with notable ability to probe even uncommon sites of distant recurrence.

Neuroblastoma (NBL) in infants has the potential to regress/mature spontaneously. The literature showed some cases, subjected to initial observation, with reasonable outcome. Deferring/avoiding active treatment was investigated in selected favorable NBL cases. Patients enrolled on the watch and see strategy (W&S) had small primary tumor, localized stages 1 to 2, uncomplicated stage 4s, or stage 3. Tissue biopsy was not mandatory for infants below 6 months with localized mass. On progression, active intervention was indicated according to disease stage and risk after biological characterization. In total, 32 patients were enrolled on W&S strategy; male/female:2.6/1. Twelve had stages 1 to 2, 16 had stage 4s, and 4 were stage 3. Primary adrenal site was reported in 85% patients, and 65% patients had small mass (≤5 cm). Five-year overall and event-free survival were 100% and 80.9±7%, respectively, with a 43-month median follow-up duration. Spontaneous total/near total resolution of mass occurred in 50% patients. Median time to regression was 1.7 months, and 20.7 months until resolution. Only 19% patients witnessed progression; median time to progression was 4.8 months. W&S is a reasonable approach for localized and uncomplicated stages 3 and 4S NBL. Extended tumor size is a newly investigated entity in the present study. All progressive cases were safely rescued with 100% survival outcome.