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68Ga-PSMA-11 PET, 18F-PSMA-1007 PET, and MRI for Gross Tumor Volume Delineation in Primary Prostate Cancer:
Cédric Draulans1, Floris Pos2, Robert J Smeenk3
1Department of Radiation Oncology, University Hospitals Leuven, Leuven, Belgium; Department of Oncology, KU Leuven, Leuven, Belgium.
Practical Radiation Oncology
|May 4, 2021
Summary
The choice of prostate-specific membrane antigen (PSMA) tracer impacts gross tumor volume (GTV) delineation for focal boosting in prostate cancer. Gallium-68 (68Ga)-PSMA showed better contrast than fluorine-18 (18F)-PSMA.
Area of Science:
- Oncology
- Radiology
- Nuclear Medicine
Background:
- Accurate gross tumor volume (GTV) delineation is crucial for focal boosting in primary prostate cancer.
- Prostate-specific membrane antigen (PSMA) positron emission tomography (PET) and biparametric magnetic resonance imaging (bpMRI) are advanced imaging modalities for GTV assessment.
- Understanding intermodality and intertracer variability is essential for optimizing treatment planning.
Purpose of the Study:
- To compare the intermodality and intertracer variability of PSMA PET and bpMRI for GTV delineation in primary prostate cancer.
- To assess the influence of different PSMA tracers (68Ga vs. 18F) on GTV contouring and image characteristics.
- To evaluate the consistency of GTV delineation for focal boosting applications.
Main Methods:
- Nineteen prostate cancer patients underwent PSMA PET/MRI scans using either 68Ga-PSMA-11 or 18F-PSMA-1007.
- Four independent teams performed manual GTV contouring based on bpMRI and PSMA PET images.
- Interobserver variability and lesion coverage (overlap%) were analyzed.
- Voxelwise standardized uptake value (SUV%) distribution and SUV% contrast ratio (SUV%-CR) were determined to assess intertracer differences.
Main Results:
- 18F-PSMA PET showed significantly better overlap% compared to bpMRI (63.0% vs 53.1%, P = .004) in its subgroup.
- Interobserver variability was higher for 18F-PSMA (lower Sørensen-Dice, higher distance to agreement) compared to 68Ga-PSMA.
- Median patientwise SUV%-CR was higher for 68Ga-PSMA (3.3) than for 18F-PSMA (1.8), indicating better lesion contrast with 68Ga-PSMA.
Conclusions:
- Both MRI and PSMA PET consistently detect intraprostatic GTV lesions.
- The choice of PSMA tracer significantly influences GTV contour characteristics and SUV% distribution.
- 68Ga-PSMA demonstrates a higher contrast ratio, potentially offering advantages for GTV delineation in focal boosting strategies.
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