It is risky to wait for a biopsy, even if the PSA test is low. (See other questions and articles on this site relating to the importance of the digital rectal exam.) There are some prostate cancers that can be very aggressive but do not produce much PSA. The only hope of diagnosing these cancers are through a digital rectal examination and appropriate follow-up. Accordingly, I would not advise waiting 6 months to see whether the nodule is still present.