How prostate volume is measured
PI-RADS v2.1 states that prostate volume should always be reported in prostate MRI reports. It may be determined by segmentation or with the ellipsoid formula: maximum anteroposterior dimension × maximum longitudinal dimension (both on the mid-sagittal T2-weighted image) × maximum transverse dimension (on the axial T2-weighted image) × 0.52.
This calculator uses π/6 (≈0.5236), the same ellipsoid constant as the main volume calculator, giving volumes 0.69% higher than calculations that use 0.52.
PSA density
PSA density (PSAD) is serum PSA divided by prostate volume, reported in ng/mL². In 61 men with clinically organ-confined disease (41 with prostate cancer undergoing radical prostatectomy, 20 with BPH), mean PSAD was 0.581 for cancer and 0.044 for BPH (Benson 1992).
In a population-based study of 5,291 men with PSA of 3 ng/mL or higher (STHLM3), the median PSAD was 0.10 ng/mL². PSAD cutoffs of 0.10 and 0.15 ng/mL² detected 77% and 49% of Gleason score 7 or higher cancers, respectively. The authors noted that PSA density is not commonly recommended in guidelines.
In men with nonpalpable (stage T1c) prostate cancer undergoing radical prostatectomy (Epstein et al., JAMA 1994), the best model predicting insignificant prostate cancer was a PSA density of less than 0.1 ng/mL per gram with no adverse pathologic findings on needle biopsy, or a PSA density of 0.1 to 0.15 ng/mL per gram with a low- to intermediate-grade cancer smaller than 3 mm found in only one needle biopsy core.
Worked example
A prostate measuring 4.5 × 4.0 × 3.8 cm has a volume of 4.5 × 4.0 × 3.8 × π/6 ≈ 35.81 mL. With a PSA of 4.5 ng/mL, the PSAD is 4.5 ÷ 35.81 ≈ 0.126 ng/mL².
Frequently asked questions
How is prostate volume calculated?
With the ellipsoid formula: anteroposterior × longitudinal × transverse dimension × a constant. PI-RADS v2.1 uses 0.52; this calculator uses π/6 (≈0.5236).
How do you calculate PSA density?
Divide the serum PSA (ng/mL) by the prostate volume (mL). For example, a PSA of 4.5 ng/mL and a volume of 35.81 mL give a PSAD of about 0.126 ng/mL².
What PSA density cutoff is used?
Cutoffs of 0.10 and 0.15 ng/mL² have been studied. In the STHLM3 study they detected 77% and 49% of Gleason score 7 or higher cancers, respectively. This calculator flags values at or above 0.15 ng/mL² (Bazinet 1994, PMID 7506853), a cut-off derived in 142 men with PSA 4.1–10 ng/mL and no suspicion on DRE or TRUS.
References
- American College of Radiology. PI-RADS: Prostate Imaging – Reporting and Data System, version 2.1 (2019). https://www.acr.org/Clinical-Resources/Clinical-Tools-and-Reference/Reporting-and-Data-Systems/PI-RADS ; and Turkbey B, Rosenkrantz AB, Haider MA, et al. Prostate Imaging Reporting and Data System Version 2.1: 2019 update of Prostate Imaging Reporting and Data System Version 2. Eur Urol. 2019;76(3):340-351. doi:10.1016/j.eururo.2019.02.033. PMID 30898406.
- Benson MC, Whang IS, Pantuck A, et al. Prostate specific antigen density: a means of distinguishing benign prostatic hypertrophy and prostate cancer. J Urol. 1992;147(3 Pt 2):815-816. doi:10.1016/s0022-5347(17)37393-7. PMID 1371554.
- Nordström T, Akre O, Aly M, Grönberg H, Eklund M. Prostate-specific antigen (PSA) density in the diagnostic algorithm of prostate cancer. Prostate Cancer Prostatic Dis. 2018;21(1):57-63. doi:10.1038/s41391-017-0024-7. PMID 29259293.
- Epstein JI, Walsh PC, Carmichael M, Brendler CB. Pathologic and clinical findings to predict tumor extent of nonpalpable (stage T1c) prostate cancer. JAMA. 1994;271(5):368-374. PMID 7506797.
- Bazinet M, Meshref AW, Trudel C, et al. Prospective evaluation of prostate-specific antigen density and systematic biopsies for early detection of prostatic carcinoma. Urology. 1994;43(1):44-51. PMID 7506853.