Variability of segmented prostate volume on MRI: impact on PSA density for prostate cancer diagnosis

Abstract

Purpose

PSA density (PSAd), based on prostate volume (PV), is a decision-making parameter for prostate cancer (PCa) diagnosis and risk stratification. We assessed variability in prostate manual segmentation on MRI and its impact on PV and PSAd.

Materials and Methods

We retrospectively analyzed 68 treatment-naïve patients, aged 66.2±6.9 years, with increased PSA and/or positive digital endorectal examination who underwent MRI, with available biopsy/follow-up. Three radiologists (R1, R2, R3) manually segmented the gland on T2-weighted images slice-by-slice. Dice similarity coefficient (DSC), Welch’s t-test, and 95% confidence intervals (CIs) were used.

Results

Of 68 patients with a PSA of 7.59±4.80 ng/mL, 38 had biopsy-confirmed PCa, and the remaining 30 were negative on biopsy/follow-up. The segmentation time per patient ranged from 4 to 7 min. Pairs R1-R2, R1-R3, and R2-R3 showed a different number of segmented slices (p<0.001) and PV (p<0.001). DSC for prostate gland segmentation ranged from 0.871 to 0.890. An outlier (prostatitis with PSA 35 ng/mL) was excluded from PSA/PSAd analysis. Based on segmentation by R1, the PSA was 7.37±3.70 ng/mL and PSAd was 0.124±0.070 ng/mL/mL in the 38 patients with PCa, while these values were 6.91±2.79 ng/mL and 0.111±0.062 ng/mL/mL, respectively, in the 29 patients without PCa. Using the threshold of ≥0.15 ng/mL/mL, variations in segmented PV impacted PSAd-based classification, resulting in 1 false negative for R1 and another false negative for R2 (false-negative rate for both 1/38, 2.63%, 95% CI 0.10–13.8%).

Conclusion

Segmentation of PV is a time-intensive task. Inter-reader variability can impact PSAd-based diagnosis of PCa. Automated prostate segmentation methods are welcome.

Key Points

• Manual prostate segmentation is a time-consuming task performed in clinical practice

• Inter-reader variability of PV segmentation was low, with high DSC values

• Minor PV differences led to false-negative PSAd classification in 2.63% cases.

Citation Format

• Colarieti A, Venturi A, Cressoni M et al. Variability of segmented prostate volume on MRI: impact on PSA density for prostate cancer diagnosis. Rofo 2025; DOI 10.1055/a-2624-7634

Zusammenfassung

Zweck

Die PSA-Dichte (PSAd), basierend auf dem Prostatavolumen (PV), ist ein entscheidungsrelevanter Parameter für die Diagnose von Prostatakrebs (PCa) und die Risikostratifikation. Wir untersuchten die Variabilität der manuellen Segmentierung der Prostata in der MRT und deren Einfluss auf PV und PSAd.

Material und Methoden

Retrospektiv wurden 68 behandlungsnaive Patienten im Alter von 66,2 ± 6,9 Jahren mit erhöhtem PSA und/oder positivem digital-rektalem Befund, die sich einer MRT unterzogen hatten und bei denen Biopsie/Nachbeobachtung verfügbar war, analysiert. Drei Radiologen (R1, R2, R3) segmentierten die Drüse manuell scheibenweise auf T2-gewichteten Bildern. Dabei wurden der Dice-Ähnlichkeitskoeffizient (DSC), Welch’s t-Test und 95%-Konfidenzintervalle (CIs) verwendet.

Ergebnisse

Von den 68 Patienten mit einem PSA von 7,59 ± 4,80 ng/mL hatten 38 einen bioptisch bestätigten PCa, während bei den übrigen 30 Patienten Biopsie/Nachbeobachtung negativ war. Die Segmentierungszeit pro Patient lag zwischen 4 und 7 Minuten. Die Paare R1–R2, R1–R3 und R2–R3 zeigten signifikante Unterschiede in der Anzahl segmentierter Schnitte (p < 0,001) sowie im PV (p < 0,001). Der DSC für die Segmentierung der Prostatadrüse lag zwischen 0,871 und 0,890. Ein Ausreißer (Prostatitis mit PSA 35 ng/mL) wurde aus der PSA/PSAd-Analyse ausgeschlossen. Basierend auf der Segmentierung durch R1 betrug bei den 38 PCa-Patienten das PSA 7,37 ± 3,70 ng/mL und die PSAd 0,124 ± 0,070 ng/mL/mL; bei den 29 Patienten ohne PCa lagen die Werte bei 6,91 ± 2,79 ng/mL bzw. 0,111 ± 0,062 ng/mL/mL. Bei Anwendung der Schwelle von ≥0,15 ng/mL/mL beeinflussten Variationen im segmentierten PV die PSAd-basierte Klassifikation, was zu einem falsch-negativen Befund bei R1 und zu einem weiteren falsch-negativen Befund bei R2 führte (falsch-negatives Rate für beide 1/38, 2,63%, 95%-CI 0,10–13,8%).

Schlussfolgerung

Die manuelle Segmentierung des PV ist sehr zeitintensiv. Die Inter-Reader-Variabilität kann die PSAd-basierte Diagnose des PCa beeinflussen. Methoden für eine automatisierte Segmentierung der Prostata sind daher willkommen.

Schlüsselpunkte

• Die manuelle Prostata-Segmentierung ist zeitaufwendig im klinischen Alltag.

• Geringe Variabilität zwischen Befundern bezüglich der PV-Segmentierung, mit hohen DSC-Werten.

• Kleine Volumenabweichungen führten zu 2,63% falsch-negativen PSAd-Ergebnissen.

Keywords

Digital Rectal Examination - Multiparametric Magnetic Resonance Imaging - prostate - Prostate-Specific Antigen - Prostatic Neoplasms

Publication History

Received: 16 March 2025

Accepted after revision: 27 May 2025

Article published online:
23 June 2025

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