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Accuracy of tumor segmentation from multi-parametric prostate MRI and 18F-choline PET/CT for focal prostate cancer
Morand Piert1,2, Prasad R Shankar3, Jeffrey Montgomery4
1Radiology Department, University of Michigan, Ann Arbor, MI, USA. mpiert@med.umich.edu.
Background:
The study aims to assess the accuracy of multi-parametric prostate MRI (mpMRI) and 18F-choline PET/CT in tumor segmentation for clinically significant prostate cancer. 18F-choline PET/CT and 3 T mpMRI were performed in 10 prospective subjects prior to prostatectomy. All subjects had a single biopsy-confirmed focus of Gleason ≥ 3+4 cancer. Two radiologists (readers 1 and 2) determined tumor boundaries based on in vivo mpMRI sequences, with clinical and pathologic data available. 18F-choline PET data were co-registered to T2-weighted 3D sequences and a semi-automatic segmentation routine was used to define tumor volumes. Registration of whole-mount surgical pathology to in vivo imaging was conducted utilizing two ex vivo prostate specimen MRIs, followed by gross sectioning of the specimens within a custom-made 3D-printed plastic mold. Overlap and similarity coefficients of manual segmentations (seg1, seg2) and 18F-choline-based segmented lesions (seg3) were compared to the pathologic reference standard.
Results:
All segmentation methods greatly underestimated the true tumor volumes. Human readers (seg1, seg2) and the PET-based segmentation (seg3) underestimated an average of 79, 80, and 58% of the tumor volumes, respectively. Combining segmentation volumes (union of seg1, seg2, seg3 = seg4) decreased the mean underestimated tumor volume to 42% of the true tumor volume. When using the combined segmentation with 5 mm contour expansion, the mean underestimated tumor volume was significantly reduced to 0.03 ± 0.05 mL (2.04 ± 2.84%). Substantial safety margins up to 11-15 mm were needed to include all tumors when the initial segmentation boundaries were drawn by human readers or the semi-automated 18F-choline segmentation tool. Combining MR-based human segmentations with the metabolic information based on 18F-choline PET reduced the necessary safety margin to a maximum of 9 mm to cover all tumors entirely.
Conclusions:
To improve the outcome of focal therapies for significant prostate cancer, it is imperative to recognize the full extent of the underestimation of tumor volumes by mpMRI. Combining metabolic information from 18F-choline with MRI-based segmentation can improve tumor coverage. However, this approach requires confirmation in further clinical studies.
Insights
Accurate tumor segmentation for prostate cancer is challenging, with MRI and PET/CT methods underestimating volumes. Combining multi-parametric MRI (mpMRI) and 18F-choline PET/CT improves tumor coverage for focal therapies.
Area of Science:
- Radiology
- Oncology
- Medical Imaging
Background:
- Clinically significant prostate cancer requires accurate tumor delineation for effective treatment.
- Multi-parametric MRI (mpMRI) and 18F-choline PET/CT are advanced imaging modalities for prostate cancer assessment.
- Accurate segmentation of tumor volumes is crucial for planning focal therapies.
Purpose of the Study:
- To evaluate the accuracy of mpMRI and 18F-choline PET/CT in segmenting tumor volumes in prostate cancer.
- To compare manual mpMRI segmentation with semi-automatic 18F-choline PET/CT segmentation against histopathology.
- To determine the effectiveness of combining imaging modalities for improved tumor coverage.
Main Methods:
- Prospective study involving 10 patients with biopsy-confirmed Gleason ≥3+4 prostate cancer.
- 3T mpMRI and 18F-choline PET/CT performed prior to radical prostatectomy.
- Tumor boundaries delineated manually on mpMRI and semi-automatically on PET/CT, compared to whole-mount pathology.
- Analysis of segmentation accuracy using overlap and similarity coefficients and underestimation percentages.
Main Results:
- All segmentation methods significantly underestimated true tumor volumes (mpMRI: 79-80%, PET/CT: 58%).
- Combining mpMRI and PET/CT segmentations reduced underestimation to 42%, further improved with contour expansion.
- A 5mm contour expansion on combined segmentations reduced mean underestimation to 2.04%.
- Combining modalities reduced the required safety margin to 9mm, compared to 11-15mm for individual methods.
Conclusions:
- mpMRI alone significantly underestimates prostate cancer tumor volumes.
- Integrating 18F-choline PET/CT metabolic data with mpMRI-based segmentation enhances tumor volume coverage.
- This combined approach shows promise for improving focal therapy outcomes but requires further clinical validation.
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