Prostate brachytherapy in patients with prostate volumes >= 50 cm(3): Dosimetic analysis of implant quality

Objectives: Permanent implantation with I-125 in patients with localized pr ostate cancer who have prostate volumes greater than or equal to 50 cm(3) i s often technically difficult owing to pubic arch interference. The objecti ve of this study was to describe dosimetry outcomes in a group of patients who were implanted using the real-time ultrasound-guided technique who had prostate volumes greater than or equal to 50 cm(3) Materials and Methods: A total of 331 patients received an I-125 prostate s eed implant from January 1, 1995, to June 1, 1999, of whom 66 (20%) had pro state volumes greater than or equal to 50 cm(3) at the time of the procedur e. The real-time seed implant method war used in al patients and consisted of intraoperative planning and real-time seed placement using a combination of axial and sagittal ultrasound imaging. Pubic arch interference was mana ged using an extended lithotomy position or by angling the tip of the ultra sound probe in an anterior direction. No preimplant pubic arch CT scan stud y was performed and no patients were excluded from treatment because of pro state size. Implant quality was assessed using CT-based dosimetry performed 1 month postimplant. Dose-volume histograms for the prostate, bladder, rec tum, and urethra volumes were generated. The target dose for these implants was 160 Gy and an adequate implant was defined as the dose delivered to 90 % of the prostate (D90) greater than or equal to 140 Gy. The dose delivered to 95% of the prostate (D95) and doses to 30% of the rectal (DRECT30) and urethral (DURE30) volumes were also calculated. Results: Prostate volumes in the 66 patients ranged from 50 to 93 cm(3) (me dian 57, mean 61 cm(3)). Total activity implanted was 27.8-89.1 mCi (median 57 mCi),with a range in activity per seed of 0.36-0.56 mCi (median 0.4 mCi ). The prostate D90s and D95s ranged from 13,245 to 22,637 cGy (median 18,7 50) and 11,856 to 20,853 cGy (median 16,725), respectively. Only one patien t (1.5%) had a D90 < 140 Gy. The DURE30 values ranged from 15,014 to 27,800 cGy (median 20,410) and the DRECT30 values were 3137-9910 cGy (median 5515 ). Conclusion: Implantation of the large prostate can be accomplished using th e real-time method. A total of 98.5% of the patients receive a high-quality implant. In addition, these implants should not put patients at increased risk for significant urinary and bowel complications because urethral and r ectal doses can be kept at acceptable levels. (C) 2000 Elsevier Science Inc .