Novel prostate brachytherapy technique: improved dosimetric and clinical outcome.

ABSTRACT

PURPOSE: Erectile dysfunction following prostate brachytherapy is reported to be related to dose received by the penile bulb. To minimise this, whilst preserving prostate dosimetry, we have developed a technique for I-125 seed brachytherapy using both stranded seeds and loose seeds delivered with a Mick applicator, and implanted via the sagittal plane on trans-rectal ultrasound. MATERIALS AND METHODS: Post-implant dosimetry and potency rates were compared in 120 potent patients. In Group 1, 60 patients were treated using a conventional technique of seeds implanted in a modified-uniform distribution. From January 2005, a novel technique was developed using stranded seeds peripherally and centrally distributed loose seeds implanted via a Mick applicator (Group 2). The latter technique allows greater flexibility when implanting the seeds at the apex. Each patient was prescribed a minimum peripheral dose of 145 Gy. No patients received external beam radiotherapy or hormone treatment. There was no significant difference in age or pre-implant potency score (mean IIEF-5 score 22.4 vs. 22.6, p=0.074) between the two groups. RESULTS: The new technique delivers lower penile bulb doses (D(25) as %mPD - Group 1 61.2+/-35.7, Group 2 29.7+/-16.0, p<0.0001; D(50) as %mPD - Group 1 45.8+/-26.9, Group 2 21.4+/-11.7, p<0.0001) whilst improving prostate dosimetry (D(90) - Group 1 147 Gy+/-21.1, Group 2 155 Gy+/-16.7, p=0.03). At 2 years, the potency rate was also improved Group 1 61.7%; Group 2 83.3% (p=0.008). CONCLUSIONS: In this study, the novel brachytherapy technique using both peripheral stranded seeds and central loose seeds delivered via a Mick applicator results in a lower penile bulb dose whilst improving prostate dosimetry, and may achieve higher potency rates.