Randomized Trial of Five or Two MRI-Guided Adaptive Radiotherapy Treatments for Prostate Cancer

"Eligible subjects will be randomly assigned to 5 or 2 fraction treatment groups in a 1:1 ratio using a computer-generated randomization scheme.~After consent and eligibility verification, patients will undergo CT/MRI simulation and radiotherapy planning. Patients will receive treatment to the prostate +/- seminal vesicles per treating physician's discretion in either 37.5 Gy in 5 fractions or 25 Gy in 2 fractions. SIB use is at treating physician's discretion and should be concordant with imaging and biopsy findings with no PTV expansion.~Subjects on 5 fraction arm should be treated on non-consecutive days. Subjects on the 2 fraction arm must have \>72 hours between beginning of each fraction."