Prostate-specific antigen density is predictive of outcome in suboptimal prostate seed brachytherapy

In prostate seed brachytherapy, a D₉₀ of <130 Gy is an accepted predictive factor for biochemical failure (BF). We studied whether there is a subpopulation that does not need additional treatment after a suboptimal permanent seed brachytherapy implantation.

A total of 486 patients who had either BF or a minimum followup of 48 months without BF were identified. BF was defined according to the Phoenix definition (nadir prostate-specific antigen + 2). Univariate and multivariate analyses were performed, adjusting for known prognostic factors such as D₉₀ and prostate-specific antigen density (PSAD) of ≥0.15 ng/mL/cm³, to evaluate their ability to predict BF.

Median followup for patients without BF was 72 months (interquartile range 56-96). BF-free recurrence rate at 5 years was 95% and at 8 years 88%. In univariate analysis, PSAD and cancer of the prostate risk assessment score were predictive of BF. On multivariate analysis, none of the factors remained significant. The best prognosis had patients with a low PSAD (<0.15 ng/mL/cm³) and an optimal implant at 30 days after implantation (as defined by D₉₀ ≥ 130 Gy) compared to patients with both factors unfavorable (p = 0.006). A favorable PSAD was associate with a good prognosis, independently of the D₉₀ (<130 Gy vs. ≥130 Gy, p = 0.7).

Patients with a PSAD of <0.15 ng/mL/cm³ have little risk of BF, even in the case of a suboptimal implant. These results need to be validated in other patients' cohorts.