Any side effects you are having should be bought to the attention of your team so that they are aware of them & can then support you. If your next session is tomorrow then you can do that then or alternatively give them a ring in the morning.
I've seen and experienced this when I had my radiotherapy. First line of treatment is Tamulosin if you're not already taking it.
A friend of mine had quite serious retention and he was trained to self-catheterise during treatment.
I found that the first session of the week following the weekend break tended to make things worse for me but things then settled down for the rest of the week.
This is fairly normal as the radiotherapy can cause inflammation around the urethra in some patients.
Your prostate is wrapped around your urethra and it gets really bad tempered when it gets bombarded with radiation. As a consequence the urethra suffers.
I had 20 days of RT and after 3 or 4 sessions I was struggling to fully empty my bladder. Mention it to your radiography team at the next visit and they should be able to give you something to help. Tamsulosin is very good as it helps relax the muscles around the bladder and prostate, which makes going for a pee easier
