The impact of hormone therapy on post-implant dosimetry and outcome following Iodine-125 implant monotherapy for localised prostate cancer.

ABSTRACT

BACKGROUND AND PURPOSE: Many patients with localised prostate cancer present with symptoms of benign prostatic hypertrophy (BPH) and require neoadjuvant hormone therapy to shrink the gland before brachytherapy. The impact of this hormone therapy has been evaluated in 667 patients treated with Iodine seed monotherapy. PATIENTS AND METHODS: Prospective data from 667 patients treated between 1995 and 2001 by I-125 seeds prostate implant as monotherapy were analysed. The mean age was 63 years (42--77 years). Three hundred and forty-six (51.9%) patients had a short course of neo adjuvant hormone therapy and 321 (49.1%) did not. The prescribed minimum peripheral dose was 145 Gy (TG 43). Patients were followed up to a maximum of 8.2 years and a minimum of 18 months. Statistical analysis was performed to identify factors that would predict PSA relapse-free survival (PSA-RFS) defined by the American Society for Therapeutic Radiology and Oncology (ASTRO). RESULTS: Overall the PSA relapse-free survival is 76.1 and 72.6% for patient cohorts being on pre-treatment hormones and not, respectively (P=0.107). Subdivided into risk groups the low risk group showed 92.5% PSA-RFS with hormones and 75.1% without (P=0.327). The intermediate group 75.7% with hormones and 72.9% without (P=0.148) and for the high-risk group 51.1% with and 51.1% without hormones (P=0.942). Evaluation of post-implant dosimetry in patients with and without hormone therapy showed that the D90 for those who received hormone therapy was 130.8 Gy compared with 145.1 Gy for those who did not (P<0.001). This may be related to the degree of oedema at the time of post-implant dosimetry. The CT to ultrasound prostate volume ratio was 1.17 for patients who received hormone therapy and 0.98 for those who did not (P<0.001). It is suggested that in the interval between stopping hormone therapy and doing post-implant dosimetry there was an increase in prostate volume, which results in a lower D90. Significant correlation was found between D90 and prostate volume on post-implant CT dosimetry with higher D90s for small volume prostates (P<0.001). CONCLUSIONS: Overall hormone therapy had no significant effect on outcome. The apparent lower D90 in hormone treated patients may be related to a change in volume between pre-implant and post-implant dosimetry.