1.   In vivo changes in the rectal values of eicosanoid inflammatory mediators induced by pelvic ratiotherapy were measured to study the pathophysiology of the early radiation bowel reaction.

2.   Steady state rectal CSA values had a non-linear relation to increasing distension pressure.

3.   We determined the steady state rectal CSA values for further analysis of the biomechanical parameters.

4.   Furthermore, we used a Wilcoxon signed ranks test to test the in vivo reproducibility of steady state rectal CSA values.

5.   Steady state rectal CSA values had a non-linear relation to the increasing distension pressure.

6.   Rectal CSA values in women showed a tendency to be slightly higher than in men.

7.   Rectal CSA values related to height, weight, and surface area showed no significant relation.

8.   This shows that the rectal luman is bigger and that the rectum is more compliant at low induced pressures in women.