Does timing of androgen deprivation influence radiation-induced toxicity? A secondary analysis of radiation therapy oncology group protocol 9413.
OBJECTIVE
We conducted a secondary analysis of the Radiation Therapy Oncology Group protocol 9413 to compare whether the timing of antiandrogen therapy (concomitant versus adjuvant) and testosterone levels influences the incidence of rectal and urinary toxicity in whole pelvic radiotherapy.


METHODS
We analyzed two of four study arms, in which all patients received radiotherapy to the whole pelvis followed by a boost to the prostate. The two arms differed solely in the timing of the total of 4 months of total androgen deprivation: arm I (320 patients, given concomitantly) and arm III (319 patients, given as adjuvant therapy). The influence of testosterone levels (measured at baseline and yearly thereafter) and its recovery on late rectal and urinary toxicity were modeled by multivariate logistic regression analysis and Fine and Gray's regression models.


RESULTS
The occurrence of late rectal toxicity (grade 0-1 versus 2-5, P = 0.16) and late urinary toxicity (grade 0-1 versus 2-5, P = 0.52) was not significantly different statistically between the two arms. The time to testosterone recovery was significantly lower in the adjuvant arm (mean difference of 3.2 months, P = 0.0103). Age and radiation field size are statistically significant risk factors for late urinary toxicity (P = 0.01 and P = 0.02). Baseline testosterone levels, before beginning total androgen deprivation, were a statistically significant predictive factor for late urinary toxicity (P = 0.03).


CONCLUSIONS
Older patients and patients with low testosterone levels at baseline are risk factors for late urinary and rectal toxicities, possibly through impaired tissue repair.
Taussky
Daniel
D
Department of Radiation Oncology, Montreal University, Montreal, Quebec, Canada. daniel.taussky.chum@ssss.gouv.qc.ca
Bae
Kyounghwa
K
Bahary
Jean-Paul
JP
Roach
Mack
M
Lawton
Colleen A
CA
Shipley
William U
WU
Sandler
Howard M
HM
D000368:Aged; D000369:Aged, 80 and over; D000726:Androgen Antagonists / Q000008:administration & dosage*; D017024:Chemotherapy, Adjuvant; D002985:Clinical Protocols; D015331:Cohort Studies; D004334:Drug Administration Schedule; D006801:Humans; D008297:Male; D008875:Middle Aged; D020360:Neoadjuvant Therapy; D011471:Prostatic Neoplasms / Q000097:blood / Q000188:drug therapy* / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000209:etiology*; D011878:Radiotherapy / Q000009:adverse effects; D012189:Retrospective Studies; D012307:Risk Factors; D013739:Testosterone / Q000097:blood
D000726:Androgen Antagonists; D013739:Testosterone