Toward a definition of a threshold for harmless doses to the anal-sphincter region and the rectum

Purpose

To investigate dysfunction caused by unwanted radiation to the anal-sphincter region and the rectum.

Methods and materials

A questionnaire assessing bowel symptoms, sexual function, and urinary symptoms was sent to 72 patients with clinically localized prostatic adenocarcinoma treated by external beam radiation therapy at the Radiumhemmet, Karolinska Hospital, in Stockholm, Sweden, 2–4 years after treatment. The mean percentage dose–volume histograms for patients with and without the specific symptom were calculated.

Results

Of the 65 patients providing information, 9 reported fecal leakage, 10 blood and mucus in stools, 10 defecation urgency, and 7 diarrhea or loose stools. None of the 19 and 13 patients who received, respectively, a dose of ≥35 Gy to ≤60% or ≥40 Gy to ≤40% of the anal-sphincter region volume reported fecal leakage (p < 0.05). In dose–volume histograms, a statistically significant correlation was found between radiation to the anal-sphincter region and the risk of fecal leakage in the interval 45–55 Gy. There was also a statistically significant correlation between radiation to the rectum and the risk of defecation urgency and diarrhea or loose stools in the interval 25–42 Gy. No relationship was found between anatomic rectal wall volume and the investigated late effects.

Conclusions

Although the limited data in this study prevent the definition of a conclusive threshold regarding volume and dose to the anal-sphincter region and untoward morbidity, it seems that careful monitoring of unnecessary irradiation to this area should be done because it can potentially help reduce the risk of adverse effects, such as fecal leakage. Future studies should pay more attention to the anal-sphincter region and help to more rigorously define its radiotherapeutic tolerance.

Keywords:  Dose , volume , prostate , bowel , fecal leakage , defecation urgency , diarrhea , conformal therapy