Question regarding prostate cancer?

My dad was diagnosed with prostate cancer April of 2007. July 2007 he had the Da Vinci Robot remove his prostate. Now he goes in for regular checkups.....when he was diagnosed his PSA level was 4....now he just had the PSA again and it's .3. I know it's not nearly as high as what it was before .3 is a long ways from 4....but what does the .3 mean? The doctor didn't seem concerned....and my dad is going to go back for a bunch of opinions. Just wondering if anyone can help me undestand what the .3 means. Can those cells be killed off with working out and eating well (which he already does)...or will he prb need radiation or hormone therapy?