Nobes JP, Khaksar SJ, Hawkins MA, Cunningham MJ, Langley SE, Laing RW. Radiother Oncol. 2008 May 20.

St. Luke’s Cancer Centre, The Royal Surrey County Hospital, Guildford, UK.

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. 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 145Gy. No patients received external beam radiotherapy or hormone treatment. There was no significant difference in age or pre-implant potency score  between the two groups. RESULTS: The new technique delivers lower penile bulb doses (D(25) as %mPD - Group 1: 61.2, Group 2: 29.7; D(50) as %mPD - Group 1: 45.8+ Group 2: 21.4) whilst improving prostate dosimetry (D(90) - Group 1: 147Gy+/-21.1, Group 2: 155Gy+/-16.7, p=0.03). At 2 years, the potency rate was also improved: Group 1: 61.7%; Group 2: 83.3%. 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.

The importance of radiation doses to the penile bulb vs. crura in the development of postbrachytherapy erectile dysfunction.

Merrick GS, Butler WM, Wallner KE, Lief JH, Anderson RL, Smeiles BJ, Galbreath RW, Benson ML. Int J Radiat Oncol Biol Phys. 2002 Nov 15;54(4):1055-62.

Schiffler Cancer Center, Wheeling Hospital, 1 Medical Park, Wheeling, WV 26003-6300, USA. schifonc@wheelinghosp.com

Recent studies have implicated the proximal penis as a potential site-specific structure for radiation-related erectile dysfunction (ED). In this study, we evaluated by means of a validated patient-administered questionnaire whether radiation doses to the bulb of the penis and/or the proximal corporeal bodies were predictive for the development of brachytherapy-induced ED. METHODS AND MATERIALS: Thirty patients who underwent permanent prostate brachytherapy between April 1995 and October 1999 and developed brachytherapy-induced ED were paired with 30 similar men who maintained potency after implantation. None of the 60 patients received supplemental external beam radiation therapy, either before or after implantation. Potency was assessed by patient self-administration of the specific erectile questions of the International Index of Erectile Function. The questionnaire consisted of 5 questions with a maximum score of 25. Postimplant potency was defined as an International Index of Erectile Function score > or =11. Mean and median follow-up was 48.3 +/- 14.4 months and 48.0 months, respectively (range: 26.6-79.3 months). The bulb of the penis and the proximal crura were outlined at 0.5-cm intervals on the Day 0 postimplant CT scan. The radiation dose distribution to the bulb of the penis and adjacent crura was defined in terms of the minimum dose delivered to 25%, 50%, 70%, 75%, 90%, and 95% of the bulb (D(25), D(50), D(70), D(75), D(90), and D(95)). RESULTS: The radiation dose delivered to the bulb of the penis and the proximal crura in men with brachytherapy-induced ED was statistically greater for all evaluated dosimetric parameters (D(25), D(50), D(70), D(75), D(90), and D(95)). Stepwise linear regression analysis indicated that penile bulb dose parameter D(50), the postimplant prostate CT volume, and patient age at implant were predictive of postimplant ED, whereas the crura dose D(25) approached statistical significance. Seventy-five percent of the impotent men had a bulb D(25) >60% of prescribed minimum peripheral dose (mPD), whereas 80% of potent men had a bulb D(25) < or =60% mPD. Using the D(50) bulb parameter, 70% of ED men had a dose >40% mPD, whereas 90% of potent men had a dose < or =40% mPD. Similar cut points for D(25) and D(50) crura doses were 40% and 28% mPD. The crura D(25) cut point was exceeded by 50% of the ED patients and only 7% of the potent patients. CONCLUSION: This is the first study to evaluate potency preservation and radiation doses to the proximal penis by means of a validated patient-administered quality-of-life instrument. Our data confirm prior reports that radiation doses to the proximal penis are predictive of brachytherapy-induced ED. In a stepwise linear regression analysis, the strongest predictors of potency preservation were bulb D(50), postimplant prostate CT volume, and patient age. With Day 0 dosimetric evaluation, the penile bulb D(50) and D(25) should be maintained below 40% and 60% mPD, respectively, whereas the crura D(50) and D(25) should be maintained below 40% and 28% mPD, respectively, to maximize posttreatment potency.

Radiation dose to the neurovascular bundles or penile bulb does not predict erectile dysfunction after prostate brachytherapy.

Kiteley RA, Lee WR, deGuzman AF, Mirzaei M, McCullough DL.Brachytherapy. 2002;1(2):90-4.

Department of Radiation Oncology, Wake Forest University School of Medicine, Winston-Salem, NC 27157-1030, USA.

PURPOSE: To examine the relationship between calculated doses to the neurovascular bundles (NVBs) and the penile bulb (PB) and the development of erectile dysfunction (ED) after low-dose-rate prostate brachytherapy (LDRPB) alone. METHODS AND MATERIALS: Between September 1997 and June 1999, 84 men were treated with LDRPB alone. Inclusion criteria for this study were (1) no ED according to a self-administered questionnaire before PB, (2) treatment with PB alone (125I; 144 Gy), (3) postimplant CT scan of the prostate 1 month after PB, and (4) minimum of 24 months of continuous follow-up. Fifty men met all inclusion criteria. ED was assessed by a self-administered questionnaire completed before and at each follow-up visit after LDRPB. Radiation doses to the NVB and PB were calculated on the basis of axial postimplant CT images. Multiple variables (patient-related and dosimetric quantifiers) that may predict for the development of ED were examined by univariate analysis. RESULTS: Thirty of the 50 men (60%) were potent at last follow-up. The only patient-related variable that predicted for the development of ED was patient age (<65 vs. >65 years; p=0.03). The calculated mean maximum doses to the NVB and PB were 684 Gy (range, 195-1277 Gy) and 498 Gy (range, 44-971 Gy), respectively. The mean calculated doses to 50% of the NVB and PB were 158 Gy (range, 76-240 Gy) and 43 Gy (range, 19-101 Gy), respectively. The calculated mean maximum, mean minimum, and mean doses to 50% of the NVB or PB did not differ between those men who developed ED and those men who did not develop ED. None of the dosimetric variables examined predicted the development of ED after LDRPB. CONCLUSIONS: In our experience, higher calculated doses to the NVB or PB are not associated with ED after LDRPB.