Would you offer prostate SBRT to a patient who cannot have an MRI?

Agree with Dr. @Dr. First Last, that yes, in a global sense, it's feasible. 

My only caveat - we routinely use the MRI to help delineate the urethra, as our institutional prostate SBRT dose is 40 Gy in 5 fractions to PTV, with hard constraint of limiting DMax of urethra to < 42  Gy. I routinely plan to do a urethral PRV to allow for some potential motion of the urethra, even if fiducials/prostate are lining up properly.

Some may be comfortable treating 40/5 without drawing the urethra or drawing the urethra on CT alone but I am not.

In the absence of being able to get an MRI, one could temporarily insert a Foley or red rubber catheter in the urethra at the time of CT sim and plan to do a urethra PRV in the absence of MRI, or turn the dose down to 36.25 in 5 and not worry about the urethra, prioritizing a relatively homogenous treatment plan.

Without MRI, FLAME-style boosting will not be feasible either as is our goal for prostate SBRT.

Yes