Bladder won't fill for radiation

Mccarthy22

My wife had her 8th radiation treatment for stage 2 cervical cancer last night. Before going to radiation she was given 2.5 hours of fluids intravenously and was done with that approx 45 minutes before radiation. In that 45 min. she drank 48 oz. of water and her bladder still wasn't full? Out of the 8 treatments her bladder has been full 2 times! She has tried adjusting to get it right by starting drinking earlier and adding more water. One night she drank 72 oz of water in 1.5 hours and it still wasn't full. She is very frustrated by this due to the fact that she is holding her urine for up to 2 hours when we were told treatment should'nt be more than a half hour. In sugestions on what to try to help her would be welcomed.