Penile bulb dose and impotence after three-dimensional conformal radiotherapy for prostate cancer on RTOG 9406: findings from a prospective, multi-institutional, phase I/II dose-escalation study.
OBJECTIVE
To assess the relationship between the dose to the bulb of the penis and the risk of impotence in men treated on Radiation Therapy Oncology Group (RTOG) 9406.


METHODS
Men enrolled on a Phase I/II dose-escalation study, RTOG 9406, who were reported to be potent at entry and evaluable (n = 158) were selected for inclusion. Follow-up evaluations were scheduled every 3, 4, and 6 months for the first, second, and the third through fifth years, then annually. At each follow-up visit an assessment of potency status was made. Penile structures were defined by a single observer blinded to the potency status, using Web-based, on-line software. The dosimetry for penile structures was calculated at the Quality Assurance Center at Washington University and provided to RTOG Statistical Headquarters to determine whether there was a relationship between dose and impotence.


RESULTS
Patients whose median penile dose was > or = 52.5 Gy had a greater risk of impotence compared with those receiving <52.5 Gy (p = 0.039). In a multivariate analysis neither age, the dose to the prostate, nor the use of hormonal therapy correlated with the risk of impotence.


CONCLUSIONS
Dose to the bulb of the penis seems to be associated with the risk of radiation-induced impotence.
Roach
Mack
M
University of California San Francisco, San Francisco, CA 94143, USA. roach@radonc17.ucsf.edu
Winter
Kathryn
K
Michalski
Jeffrey M
JM
Cox
James D
JD
Purdy
James A
JA
Bosch
Walter
W
Lin
Xiao
X
Shipley
William S
WS
D000328:Adult; D000368:Aged; D004307:Dose-Response Relationship, Radiation; D007172:Erectile Dysfunction / Q000209:etiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010413:Penis / Q000528:radiation effects*; D011446:Prospective Studies; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000379:methods*; D012044:Regression Analysis