Prostate specific antigen-monitored combination radiotherapy for patients with prostate cancer. I-125 implant followed by external-beam radiation.

Background: Because results of retropubic I-125 implantation for prostate cancer have been poor, external beam radiation was added postimplant. Serum prostate specific antigen (PSA) was used to assess this approach of combined irradiation.

Methods: Two hundred and thirty-nine patients with clinical Stage T1 or T2 but surgically node-negative prostate cancer were treated. Results were monitored by serial serum PSA evaluation. Positive clinical findings or a rising PSA level defined recurrent disease.

Results: With a median follow-up of 45 months (range, 24-120 months), the Kaplan-Meier projected disease free survival rate was 74% at 5 years and 66% at 10 years. Overall at a 60-month minimum follow-up, 77% of patients had a PSA of 0.5 ng/ml or less. This nadir level is highly predictive of a long term disease free survival, significantly better than pretreatment PSA, grade, or clinical Stage T1 or T2.

Conclusions: The PSA-monitored disease free survival rate after combination irradiation appears comparable with that after radical prostatectomy and perhaps superior to that after external-beam radiation. This effect was achieved even though lower-than-usual doses of radiation from both sources were administered. The combination of an I-125 implant followed by external-beam radiation produces high doses within the prostate and, to a lesser extent, in the periprostatic tissue. Additive and synergistic effects from simultaneous irradiation may be responsible for these results.