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Effect of observation size and apparent diffusion coefficient (ADC) value in PI-RADS v2.1 assessment category 4 and 5
Jorge Abreu-Gomez1, Daniel Walker1, Tareq Alotaibi1
1Department of Medical Imaging, The Ottawa Hospital, University of Ottawa, 1053 Carling Avenue, C1 Radiology, Ottawa, Ontario, K1Y 4E9, Canada.
Objective:
To compare observation size and apparent diffusion coefficient (ADC) values in Prostate Imaging Reporting and Data System (PI-RADS) v2.1 category 4 and 5 observations to adverse pathological features.
Materials And Methods:
With institutional review board approval, 267 consecutive men with 3-T MRI before radical prostatectomy (RP) between 2012 and 2018 were evaluated by two blinded radiologists who assigned PI-RADS v2.1 scores. Discrepancies were resolved by consensus. A third blinded radiologist measured observation size and ADC (ADC.mean, ADC.min [lowest ADC within an observation], ADC.ratio [ADC.mean/ADC.peripheral zone {PZ}]). Size and ADC were compared to pathological stage and Gleason score (GS) using t tests, ANOVA, Pearson correlation, and receiver operating characteristic (ROC) analysis.
Results:
Consensus review identified 267 true positive category 4 and 5 observations representing 83.1% (222/267) PZ and 16.9% (45/267) transition zone (TZ) tumors. Inter-observer agreement for PI-RADS v2.1 scoring was moderate (K = 0.45). Size was associated with extra-prostatic extension (EPE) (19 ± 8 versus 14 ± 6 mm, p < 0.001) and seminal vesicle invasion (SVI) (24 ± 9 versus 16 ± 7 mm, p < 0.001). Size ≥ 15 mm optimized the accuracy for EPE with area under the ROC curve (AUC) and sensitivity/specificity of 0.68 (CI 0.62-0.75) and 63.2%/65.6%. Size ≥ 19 mm optimized the accuracy for SVI with AUC/sensitivity/specificity of 0.75 (CI 0.66-0.83)/69.4%/70.6%. ADC metrics were not associated with pathological stage. Larger observation size (p = 0.032), lower ADC.min (p = 0.010), and lower ADC.ratio (p = 0.010) were associated with higher GS. Size correlated better to higher Gleason scores (p = 0.002) compared to ADC metrics (p = 0.09-0.11).
Conclusion:
Among PI-RADS v2.1 category 4 and 5 observations, size was associated with higher pathological stage whereas ADC metrics were not. Size, ADC.minimum, and ADC.ratio differed in tumors stratified by Gleason score.
Key Points:
• Among PI-RADS category 4 and 5 observations, size but not ADC can differentiate between tumors by pathological stage. • An observation size threshold of 15 mm and 19 mm optimized the accuracy for diagnosis of extra-prostatic extension and seminal vesicle invasion. • Among PI-RADS category 4 and 5 observations, size, ADC.minimum, and ADC.ratio differed comparing tumors by Gleason score.
Insights
Prostate MRI observation size, but not ADC values, correlates with higher pathological stage in PI-RADS 4 and 5 lesions. Larger sizes also indicate higher Gleason scores, aiding in prostate cancer assessment.
Area of Science:
- Radiology
- Oncology
- Medical Imaging
Background:
- Prostate Imaging Reporting and Data System (PI-RADS) v2.1 categorizes MRI findings.
- Higher PI-RADS scores (4 and 5) indicate a higher likelihood of clinically significant prostate cancer.
- Understanding pathological features associated with these scores is crucial for treatment planning.
Purpose of the Study:
- To compare observation size and apparent diffusion coefficient (ADC) values in PI-RADS v2.1 category 4 and 5 prostate MRI observations.
- To correlate these imaging metrics with adverse pathological features such as extra-prostatic extension (EPE), seminal vesicle invasion (SVI), and Gleason score (GS).
Main Methods:
- Retrospective analysis of 267 men with 3-T MRI before radical prostatectomy.
- Two blinded radiologists assigned PI-RADS v2.1 scores; discrepancies resolved by consensus.
- A third radiologist measured observation size and ADC metrics (ADC.mean, ADC.min, ADC.ratio).
- Statistical analysis included t tests, ANOVA, Pearson correlation, and ROC analysis to compare imaging findings with pathological outcomes.
Main Results:
- Observation size, but not ADC metrics, was associated with pathological stage (EPE and SVI).
- Size thresholds of ≥15 mm and ≥19 mm optimized accuracy for detecting EPE and SVI, respectively.
- Larger observation size, lower ADC.min, and lower ADC.ratio were associated with higher Gleason scores.
- Size correlated better with higher Gleason scores than ADC metrics.
Conclusions:
- In PI-RADS v2.1 category 4 and 5 observations, tumor size is a significant predictor of higher pathological stage.
- ADC metrics did not correlate with pathological stage but showed differences when stratified by Gleason score.
- Observation size is a valuable imaging biomarker for assessing the aggressiveness of high-risk prostate cancer lesions.
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