ok..you will prob have rectal spacer injected before radiation...so my advice is no riding for 3 weeks after spacer is injected so that you dont move the protective gel out of place...next, I would not ride over 10 miles at a time for now, particularly while you are being radiated and I would wear very padded biking shorts. Also, hydrate ALOT with ADT, especially on hot days...lastly, biking beofe PSA draws will make your PSA higher...all said, I think you can continue to bike, * ( except while spacer gel in settling)..if you notice any blood or extreme pain/discomfort, then stop.. I am a bike too and I hated my hiatus but glad I did it. Radiation can be tricky..side effects show up months down the road sometimes..months after you have finished..exercise is good for managing ADT side effects..just pay attention to what your body is telling you..!