My understanding is that the amount of radiation at the end of the Rx is the same whether you get IMRT or SBRT. Thus, your statement that one gets less radiation (half?) doesn't make sense to me. It should be the reverse. I'd like to hear your reply please.
IMRT is usually 40 treatments of 2 Gy each = 80 Gy. SBRT is usually 5 treatments of 7-8 Gy each =35-40 Gy. However, the biologically equivalent dose of SBRT is actually higher
for SBRT vs IMRT. This is because the low alpha-beta ratio (about
1.5) of prostate cancer has a multiplier effect on the cancer cell kill rate when the radiation is given in fewer more intense doses.
One problem I have with SBRT is the lack of enough (if any) long term follow up, well controlled studies published regarding side effects.
Six years is the longest I've seen for SBRT. Ten years is the longest I've seen for dose-escalated IMRT (from MSK).
I agree that it would be great to have randomized controlled studies for any
treatment. To my knowledge, they do not exist for IMRT vs SBRT, IMRT vs RP, IMRT vs BT, IMRT vs PT, IMRT vs AS, or any pair of those five common alternatives for initial PC therapy.