The Association of Patient, Tumor, and Treatment Characteristics With Biochemical Response to Neoadjuvant Androgen Deprivation Therapy in Prostate Cancer Patients

Abstract

Materials/Methods: Nine hundred fifty-two patients with prostate cancer were treated with permanent interstitial implantation as monotherapy using a transrectal ultrasound-guided approach. Real-time intraoperative treatment planning software which incorporates inverse planning optimization was used for all patients. Nine hundred twenty-one patients were treated with I-125 and 31 patients were treated with Pd-103. Two hundred fiftynine patients (27.2%) received neoadjuvant androgen deprivation in most cases to achieve pre-implantation volume reduction for prostate volumes >50 cc. The median prostate volume was 35.9 cc (range, 7.6-99.7 cc). The breakdown between favorable and intermediate risk disease was 79% and 20%, respectively. Dose-volume constraints for this inverse-planning system included: prostate V100 95%, maximal urethral dose 140, the 7 year PSA-RFS was 98% compared to 93% for patients with lower D90 values (p Z 0.01). Multivariate analysis demonstrated that the D90 dose level was the only significant predictor of PSA relapse-free survival (p Z 0.04 value HR 0.32). The median maximum urethral dose was 134%, and the median urethra D20% was 127%. Maximum urethral doses exceeding 150% of the prescription dose were noted in 28% of patients. The median maximum rectal dose was 64% of the prescription dose (range, 29% -193%) and the median volume of the rectum receiving the prescription dose rectum V100 cc was 0.3 cc (range, 0-7.4 cc). No dosimetric parameter was identified linked to late urinary or rectal toxicities. Conclusions: Dosimetric analysis performed on the day of the brachytherapy procedure of a large cohort of patients confirms excellent coverage of the prostate with the prescription dose. Our data demonstrate that the D90 was the single most important variable associated with improved biochemical tumor control in these patients. These data further highlight the critical need for intraoperative real time dose modifications and corrections to achieve optimal dose delivery to the prostate to insure maximal tumor control probability. Author Disclosure: M. Ashamalla: None. M. Kollmeier: None. G.N. Cohen: None. X. Pei: None. M.J. Zelefsky: None.