PET/CT with diagnostic CT in the evaluation of childhood sarcoma

Prospective Evaluation of Different Methods for Volumetric Analysis on [18F]FDG PET/CT in Pediatric Hodgkin Lymphoma

Rationale: Therapy response evaluation by 18F-fluorodeoxyglucose PET/CT (FDG PET) has become a powerful tool for the discrimination of responders from non-responders in pediatric Hodgkin lymphoma (HL). Recently, volumetric analyses have been regarded as a valuable tool for disease prognostication and biological characterization in cancer. Given the multitude of methods available for volumetric analysis in HL, the AIEOP Hodgkin Lymphoma Study Group has designed a prospective analysis of the Italian cohort enrolled in the EuroNet-PHL-C2 trial. Methods: Primarily, the study aimed to compare the different segmentation techniques used for volumetric assessment in HL patients at baseline (PET1) and during therapy: early (PET2) and late assessment (PET3). Overall, 50 patients and 150 scans were investigated for the current analysis. A dedicated software was used to semi-automatically delineate contours of the lesions by using different threshold methods. More specifically, four methods were applied: (1) fixed 41% threshold of the maximum standardized uptake value (SUVmax) within the respective lymphoma site (V41%), (2) fixed absolute SUV threshold of 2.5 (V2.5); (3) SUVmax(lesion)/SUVmean liver >1.5 (Vliver); (4) adaptive method (AM). All parameters obtained from the different methods were analyzed with respect to response. Results: Among the different methods investigated, the strongest correlation was observed between AM and Vliver (rho > 0.9; p < 0.001 for SUVmean, MTV and TLG at all scan timing), along with V2.5 and AM or Vliver (rho 0.98, p < 0.001 for TLG at baseline; rho > 0.9; p < 0.001 for SUVmean, MTV and TLG at PET2 and PET3, respectively). To determine the best segmentation method, we applied logistic regression and correlated different results with Deauville scores at late evaluation. Logistic regression demonstrated that MTV (metabolic tumor volume) and TLG (total lesion glycolysis) computation according to V2.5 and Vliver significantly correlated to response to treatment (p = 0.01 and 0.04 for MTV and 0.03 and 0.04 for TLG, respectively). SUVmean also resulted in significant correlation as absolute value or variation. Conclusions: The best correlation for volumetric analysis was documented for AM and Vliver, followed by V2.5. The volumetric analyses obtained from V2.5 and Vliver significantly correlated to response to therapy, proving to be preferred thresholds in our pediatric HL cohort.

Is True Whole-Body 18F-FDG PET/CT Required in Pediatric Lymphoma? An IAEA Multicenter Prospective Study

Guidelines recommend true whole-body ¹⁸F-FDG PET/CT scans from vertex to toes in pediatric lymphoma patients, although this suggestion has not been validated in large clinical trials. The objective of the study was to evaluate the incidence and clinical impact of lesions outside the "eyes to thighs" regular field of view (R-FOV) in ¹⁸F-FDG PET/CT staging (sPET) and interim (iPET) scans in pediatric lymphoma patients. Methods: True whole-body sPET and iPET scans were prospectively obtained in pediatric lymphoma patients (11 worldwide centers). Expert panel central review of sPET and iPET scans were evaluated for lymphoma lesions outside the R-FOV and clinical relevance of these findings. Results: A total of 610 scans were obtained in 305 patients. The sPET scans did not show lesions outside the R-FOV in 91.8% of the patients, whereas in 8.2% patients the sPET scans demonstrated lesions also outside the R-FOV (soft tissue, bone, bone marrow, and skin); however, the presence of these lesions did not change the clinical stage of any patient and did not affect treatment decision. Among the 305 iPET scans, there were no new positive ¹⁸F-FDG-avid lesions outside the R-FOV, when compared with their paired sPET scans. A single lesion outside the R-FOV on iPET occurred in 1 patient (0.3%), with the primary lesion diagnosed in the femur on sPET that persisted on iPET. Conclusion: The identification of additional lesions outside the R-FOV (eyes to thighs) using ¹⁸F-FDG PET/CT has no impact in the definition of the clinical stage of disease and minimal impact in the treatment definition of patients with pediatric lymphoma. As so, R-FOV for both sPET and iPET scans could be performed.

[Positron emission tomography-computed tomography in tumors of the locomotor apparatus]

Positron emission tomography/computed tomography (PET/CT) is a hybrid imaging technique that combines the anatomic information from CT with the metabolic information acquired from PET after the administration of specific radiotracers, the most commonly used of which is F18-fluorodeoxyglucose (FDG). In oncology, this technique is based on the increased uptake of FDG by malignant lesions. In the locomotor apparatus, some uptake by bones and soft tissues is physiological or benign and this uptake must be differentiated from uptake by malignancies, whether primary or secondary. The most important limitations are active inflammatory or infectious processes, which are positive on PET images, and malignant lesions that are smaller than 1cm, cystic, necrotic, or low-grade, which are negative on PET images. PET/CT in the locomotor apparatus is especially useful for the detection of metastases from the most common tumors. It is also used for staging and monitoring the response to treatment of some hematological tumors like lymphoma, where it is fundamental to determine whether the bone marrow has been infiltrated, or myeloma. Lastly, although it is not yet an established indication, PET/CT is being increasingly used to study sarcomas, because it can provide additional information that can be useful for the characterization and grading of tumors, for guiding biopsies, for staging and re-staging, and for evaluating the response to neoadjuvant therapy as well as for evaluating new drugs in clinical trials.

Role of limited whole-body PET/CT in pediatric lymphoma

OBJECTIVE

Performing true whole-body FDG PET/CT is standard practice in pediatric lymphoma staging and follow-up. In adults, imaging is typically limited whole-body PET/CT, which has advantages over true whole-body PET/CT, primarily decreased scanning time and decreased radiation. We hypothesize that in pediatric lymphoma, limited whole-body PET/CT is sufficient for routine follow-up when disease on the true whole-body staging study is confined to the limited whole-body field of view (FOV).

MATERIALS AND METHODS

True whole-body PET/CT studies performed for staging and follow-up of pediatric lymphoma patients between November 2004 and July 2009 at two tertiary pediatric referral hospitals were retrospectively reviewed. Abnormalities on the limited whole-body and additional true whole-body FOV were documented.

RESULTS

One hundred seventy patients met the inclusion criteria (752 examinations). At staging, disease involved the limited whole-body FOV without involving the additional true whole-body FOV in 150. Of the 150, 145 had routine follow-up (508 examinations). In these patients, no new (18)F-FDG-avid disease was identified outside of the limited whole-body FOV on routine follow-up (positive predictive value, 0%, 95% CI, 0-0.02).

CONCLUSION

The limited whole-body PET/CT for routine follow-up when disease is confined to the limited whole-body FOV at staging is appropriate. Given its definite advantages over true whole-body PET/CT, it is preferred.

FDG PET imaging of childhood sarcomas

BACKGROUND

Positron-emission tomography (PET) imaging using [(18)F]fluorodeoxyglucose (FDG) is useful for detection, staging, and monitoring a variety of malignancies, including lymphoma, in adults, but its utility in sarcomas, especially soft tissue sarcomas (STS), in children and young adults is not clear.

PROCEDURE

To evaluate the potential utility of FDG PET in the care of STS in children and young adults, we analyzed 46 PET scans in 25 patients acquired over 12 years. Scans were interpreted by two imaging physicians blinded to findings from other imaging studies and clinical information. Results were compared with computed tomography and magnetic resonance imaging, biopsy results, where available, and clinical follow-up of at least 12 months.

RESULTS

For a total of 46 scans in 25 patients, there were 25 true-positive scans, 3 false-positive scans, 12 true-negative scans, and 6 false-negative scans. The sensitivity of the PET scan was 86%, specificity was 80%, positive predictive value was 89%, and negative predictive value was 67%.

CONCLUSION

FDG PET may be a useful imaging modality in the management of children and young adults with STS, although prospective studies are needed to establish its true utility.

Guidelines for 18F-FDG PET and PET-CT imaging in paediatric oncology

OBJECTIVE

The purpose of these guidelines is to offer to the nuclear medicine team a framework that could prove helpful in daily practice. These guidelines contain information related to the indications, acquisition, processing and interpretation of (18)F-fluorodeoxyglucose positron emission tomography ((18)F-FDG PET) in paediatric oncology. The Oncology Committee of the European Association of Nuclear Medicine (EANM) has published excellent procedure guidelines on tumour imaging with (18)F-FDG PET (Bombardieri et al., Eur J Nucl Med Mol Imaging 30:BP115-24, 2003). These guidelines, published by the EANM Paediatric Committee, do not intend to compete with the existing guidelines, but rather aim at providing additional information on issues particularly relevant to PET imaging of children with cancer.

CONCLUSION

The guidelines summarize the views of the Paediatric Committee of the European Association of Nuclear Medicine. They should be taken in the context of "good practice" of nuclear medicine and of any national rules, which may apply to nuclear medicine examinations. The recommendations of these guidelines cannot be applied to all patients in all practice settings. The guidelines should not be deemed inclusive of all proper procedures or exclusive of other procedures reasonably directed to obtaining the same results.