Quantifying the impact of seminal vesicle invasion identified using endorectal magnetic resonance imaging on PSA outcome after radiation therapy for patients with clinically localized prostate cancer.

Purpose: This study examined the impact that seminal vesicle invasion (SVI), observed on endorectal magnetic resonance imaging (erMRI), had on prostate-specific antigen (PSA) outcome after external beam radiation therapy (EBRT) for patients with clinically localized prostate cancer.

Methods And Materials: The study cohort was comprised of 250 patients who received 3D conformal radiation therapy without hormones for clinically localized prostate cancer between 1992 and 2001. The primary end point was PSA failure, defined using the American Society for Therapeutic Radiology and Oncology consensus definition. Cox regression multivariable analysis was used to determine the ability of the pretreatment risk group and erMRI SVI to predict for time to PSA failure after EBRT.

Results: Both risk group (p(Cox) = 0.001) and erMRI SVI (p(Cox) = 0.003) were independent and significant predictors of time to PSA failure. For patients beyond low risk, 4-year estimates of PSA failure-free survival for erMRI SVI-negative vs. erMRI SVI-positive patients were 68% vs. 33% (p(log-rank) = 0.0014), respectively.

Conclusion: Patients with clinically localized disease and PSA >10 or biopsy Gleason score >or=7 or clinical T category T2b or T2c who also have erMRI evidence of SVI have PSA outcomes similar to patients with locally advanced prostate cancer after EBRT monotherapy. Consideration should be given to combining EBRT with hormonal therapy in these patients.