Relationships between dose to the gastro-intestinal tract and patient-reported symptom domains after radiotherapy for localized prostate cancer

Number of questions: 43; median time to follow-up: 3.6–6.4 years) and dose-response outcome variables were defined from these domains. Dose/volume parameters of the anal sphincter (AS) or the rectum were tested as predictors for each outcome variable using logistic regression with 10-fold cross-validation. Performance was assessed using area under the receiver operating characteristic curve (A z ) and model frequency.

Results. Outcome variables from Defecation urgency (number of symptoms: 2–3), Fecal leakage (4–6), Mucous (4), and Pain (3–6) were defined. In both cohorts, intermediate rectal doses predicted Defecation urgency (mean A z : 0.53–0.54; Frequency: 70–75%), and near minimum and low AS doses predicted Fecal leakage (mean A z : 0.63–0.67; Frequency: 83–99%).

In one cohort, high AS doses predicted Mucous (mean A z : 0.54; Frequency: 96%), whereas in the other, low AS doses and intermediate rectal doses predicted Pain (mean A z : 0.69; Frequency: 28–82%). Conclusion. We have demonstrated that Defecation urgency, Fecal leakage, Mucous , and Pain following primary EBRT for localized prostate cancer primarily are predicted by intermediate rectal doses, low AS doses, high AS doses, or a combination of low AS and intermediate rectal doses, respectively.

This suggests that there is a domain-specific dose-response for the GI tract. To reduce risk of GI morbidity, dose distributions of both the AS region and the rectum should, therefore, be considered when prescribing prostate cancer RT.