Hotspot on 18F-FET PET/CT to Predict Aggressive Tumor Areas for Radiotherapy Dose Escalation Guiding in High-Grade Glioma

18F-FET PET/CT can aid in diagnosing patients with indeterminate MRI findings for brain tumors: a prospective study

OBJECTIVE

This prospective study aimed to evaluate the diagnostic value of fluorine-18-labeled fluoroethyltyrosine (18F-FET) positron emission tomography (PET)/computed tomography (CT) in diagnosing brain tumors within an Asian patient population.

METHODS

Patients suspected of having primary or recurrent brain tumors were prospectively recruited. Each patient underwent 18F-FET and fluorine-18 fluorodeoxyglucose (18F-FDG) PET/CT on separate days within 1 week. We calculated the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy to compare the diagnostic performance of the two PET scans. The standardized uptake value (SUV) and tumor-to-background ratio (TBR) of the lesions were determined using static images. Additionally, time-activity curves (TACs) and time-to-peak (TTP) were generated from the dynamic PET images.

RESULTS

From September 2019 to December 2023, 33 subjects were enrolled for reasons including suspected brain tumors (n = 20) or suspicious glioma recurrence (n = 8) on magnetic resonance imaging (MRI) and restaging for glioma (n = 5). Among the patients with suspected brain tumors or glioma recurrence on MRI, 25% had false-positive results. 18F-FET PET/CT accurately identified 86% of these false positives. The sensitivity, specificity, PPV, NPV, and accuracy of visual interpretation of 18F-FET PET/CT were 96.2%, 85.7%, 96.2%, 85.7%, and 93.9%, respectively. The corresponding 18F-FDG PET/CT values were 73.1%, 71.4%, 90.5%, 41.7%, and 72.7%. 18F-FET PET/CT demonstrated significantly higher sensitivity and accuracy than 18F-FDG PET (p = 0.031 and p = 0.030, respectively). Using TBRmean as an adjunct reference index enhanced the diagnostic accuracy of 18F-FET PET/CT, achieving a sensitivity and NPV of 100%. Wash-out TAC or TTP < 20 min was associated with a PPV of 100% for brain tumors.

CONCLUSIONS

18F-FET PET/CT appears to be a valuable tool for assessing brain tumors with indeterminate MRI findings in this Asian cohort. 18F-FET PET/CT offers benefits over 18F-FDG PET in differentiating brain tumors from nontumor brain lesions, particularly when using semiquantitative analysis with TBR. This study was registered on CinicalTrial.gov (NCT06563024).

The role of amino acid PET in radiotherapy target volume delineation for adult-type diffuse gliomas: A review of the literature

PURPOSE

To summarise existing literature examining amino acid positron emission tomography (AA-PET) for radiotherapy target volume delineation in patients with gliomas.

METHODS

Systematic search of MEDLINE and EMBASE databases.

RESULTS

Twenty studies met inclusion criteria. Studies comparing MRI- and AA-PET- derived target volumes consistently found these to be complementary. Across studies, AA-PET was a strong predictor of the site of subsequent relapse. In studies examining AA-PET-guided radiotherapy at standard doses, including one study using reduced margins, survival outcomes were similar to historical cohorts whose volumes were generated using MRI alone. Four prospective single-arm trials examining AA-PET-guided dose-escalated radiotherapy reported mixed results. The two trials that used both a higher biologically-effective dose and boost-volumes defined using both MRI and AA-PET reported promising outcomes.

CONCLUSION

AA-PET is a promising complementary tool to MRI for radiotherapy target volume delineation, with potential benefits requiring further validation including margin reduction and facilitation of dose-escalation.

Contribution of [18F]FET PET in the Management of Gliomas, from Diagnosis to Follow-Up: A Review

Gliomas, the most common type of primary malignant brain tumors in adults, pose significant challenges in diagnosis and management due to their heterogeneity and potential aggressiveness. This review evaluates the utility of O-(2-[18F]fluoroethyl)-L-tyrosine ([18F]FET) positron emission tomography (PET), a promising imaging modality, to enhance the clinical management of gliomas. We reviewed 82 studies involving 4657 patients, focusing on the application of [18F]FET in several key areas: diagnosis, grading, identification of IDH status and presence of oligodendroglial component, guided resection or biopsy, detection of residual tumor, guided radiotherapy, detection of malignant transformation in low-grade glioma, differentiation of recurrence versus treatment-related changes and prognostic factors, and treatment response evaluation. Our findings confirm that [18F]FET helps delineate tumor tissue, improves diagnostic accuracy, and aids in therapeutic decision-making by providing crucial insights into tumor metabolism. This review underscores the need for standardized parameters and further multicentric studies to solidify the role of [18F]FET PET in routine clinical practice. By offering a comprehensive overview of current research and practical implications, this paper highlights the added value of [18F]FET PET in improving management of glioma patients from diagnosis to follow-up.

Correlation between rCBV Delineation Similarity and Overall Survival in a Prospective Cohort of High-Grade Gliomas Patients: The Hidden Value of Multimodal MRI?

PURPOSE

The accuracy of target delineation in radiation treatment planning of high-grade gliomas (HGGs) is crucial to achieve high tumor control, while minimizing treatment-related toxicity. Magnetic resonance imaging (MRI) represents the standard imaging modality for delineation of gliomas with inherent limitations in accurately determining the microscopic extent of tumors. The purpose of this study was to assess the survival impact of multi-observer delineation variability of multiparametric MRI (mpMRI) and [18F]-FET PET/CT.

MATERIALS AND METHODS

Thirty prospectively included patients with histologically confirmed HGGs underwent a PET/CT and mpMRI including diffusion-weighted imaging (DWI: b0, b1000, ADC), contrast-enhanced T1-weighted imaging (T1-Gado), T2-weighted fluid-attenuated inversion recovery (T2Flair), and perfusion-weighted imaging with computation of relative cerebral blood volume (rCBV) and K2 maps. Nine radiation oncologists delineated the PET/CT and MRI sequences. Spatial similarity (Dice similarity coefficient: DSC) was calculated between the readers for each sequence. Impact of the DSC on progression-free survival (PFS) and overall survival (OS) was assessed using Kaplan-Meier curves and the log-rank test.

RESULTS

The highest DSC mean values were reached for morphological sequences, ranging from 0.71 +/- 0.18 to 0.84 +/- 0.09 for T2Flair and T1Gado, respectively, while metabolic volumes defined by PET/CT achieved a mean DSC of 0.75 +/- 0.11. rCBV variability (mean DSC0.32 +/- 0.20) significantly impacted PFS (p = 0.02) and OS (p = 0.002).

CONCLUSIONS

Our data suggest that the T1-Gado and T2Flair sequences were the most reproducible sequences, followed by PET/CT. Reproducibility for functional sequences was low, but rCBV inter-reader similarity significantly impacted PFS and OS.

[18]F-fluoroethyl-l-tyrosine positron emission tomography for radiotherapy target delineation: Results from a Radiation Oncology credentialing program

Background and purpose

The [18]F-fluoroethyl-l-tyrosine (FET) PET in Glioblastoma (FIG) study is an Australian prospective, multi-centre trial evaluating FET PET for newly diagnosed glioblastoma management. The Radiation Oncology credentialing program aimed to assess the feasibility in Radiation Oncologist (RO) derivation of standard-of-care target volumes (TVMR) and hybrid target volumes (TVMR+FET) incorporating pre-defined FET PET biological tumour volumes (BTVs).

Materials and methods

Central review and analysis of TVMR and TVMR+FET was undertaken across three benchmarking cases. BTVs were pre-defined by a sole nuclear medicine expert. Intraclass correlation coefficient (ICC) confidence intervals (CIs) evaluated volume agreement. RO contour spatial and boundary agreement were evaluated (Dice similarity coefficient [DSC], Jaccard index [JAC], overlap volume [OV], Hausdorff distance [HD] and mean absolute surface distance [MASD]). Dose plan generation (one case per site) was assessed.

Results

Data from 19 ROs across 10 trial sites (54 initial submissions, 8 resubmissions requested, 4 conditional passes) was assessed with an initial pass rate of 77.8 %; all resubmissions passed. TVMR+FET were significantly larger than TVMR (p < 0.001) for all cases. RO gross tumour volume (GTV) agreement was moderate-to-excellent for GTVMR (ICC = 0.910; 95 % CI, 0.708-0.997) and good-to-excellent for GTVMR+FET (ICC = 0.965; 95 % CI, 0.871-0.999). GTVMR+FET showed greater spatial overlap and boundary agreement compared to GTVMR. For the clinical target volume (CTV), CTVMR+FET showed lower average boundary agreement versus CTVMR (MASD: 1.73 mm vs. 1.61 mm, p = 0.042). All sites passed the planning exercise.

Conclusions

The credentialing program demonstrated feasibility in successful credentialing of 19 ROs across 10 sites, increasing national expertise in TVMR+FET delineation.

Integrating multi-modal imaging in radiation treatments for glioblastoma

Advances in diagnostic and treatment technology along with rapid developments in translational research may now allow the realization of precision radiotherapy. Integration of biologically informed multimodality imaging to address the spatial and temporal heterogeneity underlying treatment resistance in glioblastoma is now possible for patient care, with evidence of safety and potential benefit. Beyond their diagnostic utility, several candidate imaging biomarkers have emerged in recent early-phase clinical trials of biologically based radiotherapy, and their definitive assessment in multicenter prospective trials is already in development. In this review, the rationale for clinical implementation of candidate advanced magnetic resonance imaging and positron emission tomography imaging biomarkers to guide personalized radiotherapy, the current landscape, and future directions for integrating imaging biomarkers into radiotherapy for glioblastoma are summarized. Moving forward, response-adaptive radiotherapy using biologically informed imaging biomarkers to address emerging treatment resistance in rational combination with novel systemic therapies may ultimately permit improvements in glioblastoma outcomes and true individualization of patient care.