Mean absorbed dose to the anal-sphincter region and fecal leakage among irradiated prostate cancer survivors.
OBJECTIVE
To supplement previous findings that the absorbed dose of ionizing radiation to the anal sphincter or lower rectum affects the occurrence of fecal leakage among irradiated prostate-cancer survivors. We also wanted to determine whether anatomically defining the anal-sphincter region as the organ at risk could increase the degree of evidence underlying clinical guidelines for restriction doses to eliminate this excess risk.


METHODS
We identified 985 men irradiated for prostate cancer between 1993 and 2006. In 2008, we assessed long-term gastrointestinal symptoms among these men using a study-specific questionnaire. We restrict the analysis to the 414 men who had been treated with external beam radiation therapy only (no brachytherapy) to a total dose of 70 Gy in 2-Gy daily fractions to the prostate or postoperative prostatic region. On reconstructed original radiation therapy dose plans, we delineated the anal-sphincter region as an organ at risk.


RESULTS
We found that the prevalence of long-term fecal leakage at least once per month was strongly correlated with the mean dose to the anal-sphincter region. Examining different dose intervals, we found a large increase at 40 Gy; ≥ 40 Gy compared with <40 Gy gave a prevalence ratio of 3.8 (95% confidence interval 1.6-8.6).


CONCLUSIONS
This long-term study shows that mean absorbed dose to the anal-sphincter region is associated with the occurrence of long-term fecal leakage among irradiated prostate-cancer survivors; delineating the anal-sphincter region separately from the rectum and applying a restriction of a mean dose <40 Gy will, according to our data, reduce the risk considerably.
Division of Clinical Cancer Epidemiology, Department of Oncology, Institute of Clinical Sciences, Sahlgrenska Academy at the University of Gothenburg, Sweden. david.alsadius@oncology.gu.se
David
D
Alsadius
Maria
M
Hedelin
Dan
D
Lundstedt
Niclas
N
Pettersson
Ulrica
U
Wilderäng
Gunnar
G
Steineck
D000368:Aged; D000369:Aged, 80 and over; D001003:Anal Canal / Q000000981:diagnostic imaging / Q000528:radiation effects*; D016022:Case-Control Studies; D005242:Fecal Incontinence / Q000453:epidemiology / Q000209:etiology* / Q000517:prevention & control; D006801:Humans; D008297:Male; D008875:Middle Aged; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects*; D015995:Prevalence; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000150:complications*; D011859:Radiography; D011879:Radiotherapy Dosage; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects*; D011795:Surveys and Questionnaires; D017741:Survivors