The spacer is mostly used for SBRT - Cyberknife type 5 dose treatment. Used to protect the rectum since they are high dose treatments. I guess your type of PCa or other conditions preclude your consideration for this?
It would be quicker but possibly worse symptomatically. They do, however, sometimes space these 5 visits farther apart; instead of every other day, perhaps each one a week or 10 days apart? Ask your RO about this, OK? As I said, radiation is cumulative so it adds up over time. 40 smaller doses and 5 larger ones may deliver the same total amount of radiation - the PCa cells can’t tell the difference.
You might have a reaction each time, but also time to recover from each visit. Lomotil is more effective for diarrhea than regular preparations; it contains a low dose, non addicting opioid that controls the gut spasms more effectively. Best,
Phil