Hi,
Proton therapy is more targeted, resulting in less damage to surrounding healthy organs and tissue. This often causes fewer side effects, such as reduced fatigue or lower risk of gastrointestinal issues.
X-ray therapy is effective but can damage healthy tissues in the path of the beam. They are two very different types of external beams. Based on your comments on 2-3mm overlap, that why it is wise to use the spaceAOR gel as extra insurance in my humble non medical opinion. By using the gel and in the hands of an experienced technician the bladder damage should be minimal or non existent.