OBJECTIVES: Major innovations in radiotherapy (RT) delivery (3D conformal RT, intensity modulated RT) now permit RT dose escalation to be tested as a means of improving control of localized prostate cancer. With delivery innovations, severe toxicity occurs rarely, but significant bladder and rectal toxicity is common. The investigators have studied a cohort of 98 patients who received dose-escalated 3D-CRT and have obtained evidence of dosimetric factors underlying rectal toxicity. They posit that the late radiation toxicity disease state has significant genetic determinants. These determinants are neither understood nor accounted for in selection of treatment, and the investigators propose to study the above well-characterized cohort, who are clinically well from a disease control perspective, given that comprehensive dosimetric and outcome information is available on all.