50 does sound low, but much depends too on dose rate. 50/33=1.5 Gy/day, or so. You might ask your RO to explain the dose plan. They usually have very specific reasons for it, and perhaps can explain why your particular plan was selected.
Google is your friend....
As it turns out, the radiation tech gave me some incorrect dosage info. I saw my RO today for our weekly visit during treatments and he told me I was receiving 66 Gy over the 33 sessions. Today was #11.
Age 54 at diagnosis
Da Vinci prostatectomy Sept. 6, 2011
Gleason 3+4=7 Pre-op & Post-op
Undetectable PSA results until April 2016
April 2016 PSA .05
July 13, 2016 PSA .1
July 21, 2016-6 month dose of Eligard (Lupron) administered
No incontinence whatsoever and no ED issues
August 15, 2016 PSA .03