Three-dimensional computed tomography-guided monotherapeutic pararectal brachytherapy of prostate cancer with seminal vesicle invasion

Abstract

Purpose: To treat patients with prostate cancer and seminal vesicle invasion with monotherapeutic three dimensional computed tomography (3-DCT)-guided posterior pararectal brachytherapy. Methods and materials: Three hundred and sixty two patients with clinical stage T1 a,b or T2 a,b of prostate cancer were referred for 3-DCT-guided brachytherapy. Each underwent ftirther staging with 3-D CT-guided pararectal biopsy of the seminal vesicles under local anesthesia during the pre-treatment CT-planning. Forty-three patients (12%) were upstaged to T3 cNoMo disease. In the set of 43 patients, Eight had Gleason's score≤6, 24 Gleason's score=7, and 11 patients ≥8. Initial PSA was <10 ng/ml in 14 patients, 10–20 ng/ml in 11 patients, and >20 in 18 patients. Of the 43 patients, 37 patients were treated monotherapeutically with 3-D CT-guided brachytherapy. No patients received hormone therapy after the implant. The prescribed dosage to the seminal vesicles and prostate is 120 Gy with Pd-103 seeds and 144 Gy with 1–125 seeds. Results: The prescribed dosage was achieved in all 37 patient's throughout the seminal vesicles whose range of target radiation extended 5–10 mm outside the target in the adjacent fat as calculated with post-implant CT-dosimetry with Varian Brachy Vision or MMS software. Prostate Specific Antigen (PSA) outcome data were available in 34 patients treated with monotherapy and follow up ranged from 12–56 months (median, 24 months). Decreased PSA levels were stratified into six groups based on the presenting Gleason's score and initial PSA. In the first group (with Gleason's score≤6 and initial PSA <20 ng/ml), PSA levels decreased to less than 0.5 ng/ml in all seven patients (100%) after brachytherapy. In the second group (with Gleason's=7 and initial PSA<20 ng/ml), PSA levels decreased to less than 1 ng/ml in 11 of 13 patients (85%); additionally PSA levels decreased to less than 0.5 ng/ml in ten patients (77% in this group). In the third group (with Gleason's score=7 and initial PSA> 20 ng/ml), PSA decreased to less than 0.5 ng/ml in four out of eight patients (50%). All of the patients in the fourth group (with Gleason's score≥8 and initial PSA<20 ng/ml) decreased their PSA levels to less than 0.5 ng/ml in three of three patients. PSA decreased less than 0.5 ng/ml in two out of three patients (67% in the last group with Gleason's score≥8 and initial PSA> 20 ng/ml). There were no patients with Gleason's score of 1–6 and greater than 20 ng/ml initial PSA. Patients, irrespective of the Gleason's score and PSA, had an overall response of decreased PSA (less than 1 ng/ml) of 79%. Conclusion: 3-D CT-guided brachytherapy delivers adequate dosage to the seminal vesicles. Clinical and biochemical results are encouraging in patients with low initial PSA levels regardless of their Gleason's scores, but longer-term data in a greater number of patients is necessary.