I hope you filed the claim. If not, do it ASAP. Prostate cancer is presumptive condition and it's pretty easy to file.
My husband was diagnosed in 2017 with prostate cancer ~ vietnam vet (in country with DD214 showing so). Erectile dysfunction claim also.
Claim filed 12/17 was granted in 2/18. $3336.15 per month ~ it is a lot of money to not file the claim.
My husband was like your father ~ really didn't want to file the claim. His doctor point blank told him to do it & did all the DBQ's immediately following diagnosis.
Filed online through ebenefits. You might have to go through VA.gov now. Submitted DD214, DBQs, surgery papers, pathology report.