Volumetric histograms-based analysis of apparent diffusion coefficients and standard uptake values for the assessment of pediatric sarcoma at staging: preliminary results of a PET/MRI study.

PURPOSE: To assess the relationship between apparent diffusion coefficients (ADC) and standard uptake values (SUV) of pediatric sarcomas at staging by using volumetric histograms analyses. METHODS: Children with histologically proven sarcoma, referring to our tertiary center for a whole-body 18F-FDG PET/MRI for staging and including diffusion weighted imaging in the MRI protocol were investigated. Firstly, turbo inversion recovery magnitude (TIRM) and PET images were resliced and resampled according to the ADC maps. Regions of interests were drawn along tumor margins on TIRM images and then copied on PET and ADC datasets. Pixel-based SUVs and ADCs were collected from the entire volume of each lesion. Mean, median, skewness, and kurtosis of SUVs and ADCs values were computed, and the Pearson correlation coefficient was then applied (for the entire population and for histological subgroups with more than five patients). RESULTS: Thirteen patients met the inclusion criteria (six females; mean age 8.31 ± 6.03 years). Histology revealed nine rhabdomyosarcomas, three Ewing sarcomas, and one chondroblastic osteosarcoma. A significant negative correlation between ADCs' and SUVs' mean (rmean = - 0.501, P < 0.001), median (rmedian = - 0.519, P < 0,001), and skewness (rskewness = - 0.550, P < 0.001) emerged for the entire population and for rhabdomyosarcomas (rmean = - 0.541, P = 0.001, rmedian = - 0.597, P < 0.001, rskewness = - 0.568, P < 0.001), whereas a significant positive correlation was found for kurtosis (rkurtosis = 0.346, P < 0.001, and rkurtosis = 0.348, P < 0.001 for the entire population and for rhabdomyosarcomas, respectively). CONCLUSION: Our preliminary results demonstrate that, using volumetric histograms, simultaneously collected SUVs and ADCs are dependent biomarkers in pediatric FDG-avid sarcomas. Further studies, on a larger population, are necessary to confirm this evidence and assess its clinical implications.

Radiologic Response Assessment in Pediatric Soft Tissue Sarcoma: Computed-Assisted Volume Evaluation.

OBJECTIVES: To compare 3 methods of dimensional assessment, with particular attention to a new software assisted method of volume calculation, in soft tissue sarcoma, and to investigate the interobserver agreement and the intermethod agreement in chemotherapy response classification and resultant clinical repercussions. STUDY DESIGN: We studied 34 pediatric patients with nonmetastatic soft tissue sarcoma who had undergone only diagnostic biopsy. Tumor size was measured both at diagnosis and after induction chemotherapy by 3 observers and using 3 measurement methods: maximum axis (1 diameter), estimated volume (3 diameters), and computed volume (software-assisted volume calculation). We used overall concordance correlation coefficient and Bland-Altman statistical methods to assess interobserver agreement and overall concordance correlation coefficient and the κ Cohen coefficient to assess intermethod agreement. RESULTS: According to overall concordance correlation coefficient, the interobserver agreement was very high for each method, with a slight superiority of the software assisted method; this agreement was not confirmed in Bland-Altman plots for maximum axis and estimated volume methods. According to kappa coefficients, the intermethod agreement in chemotherapy response evaluation was poor. CONCLUSIONS: Computed volume was the most accurate method in soft tissue sarcoma tumor size assessment. One- and 3-dimensional methods are not concordant in chemotherapy response classification. In particular, the maximum axis method underestimates chemotherapy response and can lead to switching the chemotherapy regimen erroneously.

Pediatric Rhabdomyosarcomas: Three-Dimensional Radiological Assessments after Induction Chemotherapy Predict Survival Better than One-Dimensional and Two-Dimensional Measurements.

Radiological response to neoadjuvant chemotherapy is currently used to assess the efficacy of treatment in pediatric patients with rhabdomyosarcoma (RMS), but the association between early tumor response on imaging and survival is still controversial. The aim of this study was to investigate the prognostic value of assessing radiological response after induction therapy in pediatric RMS, comparing four different methods. This retrospective, two-center study was conducted on 66 non-metastatic RMS patients. Two radiologists measured tumor size on pre- and post-treatment magnetic resonance (MR) or computed tomography (CT) images using four methods: considering maximal diameter with the 1D-RECIST (Response Evaluation Criteria in Solid Tumors); multiplying the two maximal diameters with the 2D-WHO (World Health Organization); multiplying the three maximal diameters with the 3D-EpSSG (European pediatric Soft tissue sarcoma Study Group); obtaining a software-assisted volume assessment with the 3D-Osirix. Each patient was classified as a responder or non-responder based on the proposed thresholds for each method. Tumor response was compared with survival using Kaplan-Meier plots, the log-rank test, and Cox's regression. Agreement between methods and observers (weighted-κ) was also calculated. The 5-year event-free survival (5yr-EFS) calculated with the Kaplan-Meier plots was significantly longer for responders than for non-responders with all the methods, but the 3D assessments differentiated between the two groups better than the 1D-RECIST or 2D-WHO (p1D-RECIST = 0.018, p2D-WHO = 0.007, p3D-EpSSG and p3D-Osirix < 0.0001). Comparing the 5yr-EFS of responders and non-responders also produced adjusted hazard ratios of 3.57 (p = 0.0158) for the 1D-RECIST, 5.05 for the 2D-WHO (p = 0.0042), 14.40 for the 3D-EpSSG (p < 0.0001) and 11.60 for the 3D-Osirix (p < 0.0001), indicating that the volumetric measurements were significantly more strongly associated with EFS. Inter-method agreement was excellent between the 3D-EpSSG and the 3D-Osirix (κ = 0.98), and moderate for the other comparisons (0.5 < κ < 0.8). The 1D-RECIST and the 2D-WHO tended to underestimate response to treatment. Inter-observer agreement was excellent with all methods (κ > 0.8) except for the 2D-WHO (κ = 0.7). In conclusion, early tumor response was confirmed as a significant prognostic factor in RMS, and the 3D-EpSSG and 3D-Osirix methods predicted response to treatment better than the 1D-RECIST or 2D-WHO measurements.

Radiological Assessment of Paediatric Fungal Infections: A Pictorial Review With Focus on PET/MRI.

Paediatric invasive fungal infections have significantly increased over the past few decades, in particular among the immunocompromised population. Candida and Aspergillus spp. are still the most commonly isolated organisms. Image-based assessment of fungal infections can indeed be challenging especially in oncological patients where the differential diagnosis relative to other infections and neoplastic lesions cannot be often obvious. Therefore, the knowledge of the main radiological features associated with fungal infections is crucial to achieve an early correct diagnosis and address the most appropriate therapeutic approach. Thus, our aim was to review the main radiological features of paediatric fungal infections with particular focus on positron emission tomography/magnetic resonance imaging (PET/MRI), referring to the experience of our tertiary level hospital.

Non Lipomatous Benign Lesions Mimicking Soft-tissue Sarcomas: A Pictorial Essay.

The incidental finding of soft tissue masses is a challenge for the radiologist. Benign and malignant lesions can be differentiated relying on patient history, symptoms and mostly with the help of imaging. Ultrasound (US), computed tomography (CT) and magnetic resonance imaging (MRI) become fundamental in order to distinguish these lesions but the radiologist needs to know the main characteristics of benign soft tissue masses and sarcomas. Herein, we present a pictorial review of lesions mimicking soft tissue sarcomas features.