Prostate-specific antigen (PSA) control following focal low-dose-rate brachytherapy for hemi-gland prostate cancer with Cesium-131

Purpose: Prostate cancer is the most common non-cutaneous malignancy diagnosed in men in the United States. The current standard of care for prostate brachytherapy is to treat the whole gland. The purpose of this study is to evaluate biochemical (PSA) control outcomes in men treated with focal, hemi-gland brachytherapy utilizing Cesium-131 (Cs-131).

Methodology: Focal, hemi-gland brachytherapy was administered to 15 patients to a total dose of 115 Gy prescribed to the periphery of the hemi-gland of the prostate with Cs-131. Brachytherapy was given as monotherapy for all but 1 patient, who received androgen-deprivation therapy (ADT). Implants were delivered via a pre-planned, template-based, pre-loaded needle technique to ensure adequate treatment. The Phoenix definition, nadir PSA +2 ng/mL, was used to determine biochemical failure (BF).

Results: Sixty percent (N=9) of the men in this group had low-risk disease while 33.3% (N=5) had intermediate-risk disease and 6.7% (N=1) had high-risk disease. Average age at time of implant was 74.1 years (range 66.1-84.6 years). Most patients had T1c (93.8%) and Gleason 3+3=6 (66.7%) disease treated without ADT (93.8%). Three men (20%) had Gleason 3+4=7 disease and 1 (6.7%) had Gleason 4+4=8 disease. Median PSA at diagnosis was 5.5 ng/mL (range 4.0-13.4 ng/mL). Median follow-up was 31.3 months (range 21-48 months). PSA was drawn at 3-6 month intervals and an average of 8.7 PSA levels were drawn per patient for disease monitoring. In total, 7 patients (46.7%) experienced BF by Phoenix criteria definition after focal brachytherapy; however, PSA on follow up then decreased for the majority of these patients (N=5/7, 71.4%). One patient (14.2%) had PSA continue to rise after BF by Phoenix definition and one had failure defined at last follow up.

Conclusions: Focal brachytherapy with Cs-131 appears to allow for durable PSA control in appropriately selected patients. While there is currently no standardized definition for PSA failure after focal, hemi-gland brachytherapy for the treatment of localized prostate cancer, the results of this study indicate that the Phoenix criteria are an inadequate measure of response to this treatment type. Additional study and long-term follow up are needed to determine the optimal means of following patients treated with focal brachytherapy, as the majority of patients treated with this modality experienced subsequent decrease in PSA after failure by the Phoenix definition in this study.

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