A study by the Jacksonville group published in the Green Journal aimed to identify baseline predictive factors that impact long-term erectile function. 676 potent men at base line with localized prostate cancer treated with HD-IGRT (high dose image-guided) protons alone, to a median dose of 78 Gy(RBE) (range, 72–82 Gy[RBE]) in 36 to 39 fractions. The potency rates at 6 months, 2 years, and 5 years were 81%, 68%, and 61%.

This study found that baseline response to EPIC Q57 (ability to have an erection) and pre-existing heart disease are two factors enabling prediction of sexual function. At 5 years, the most favorable group reported "very good" on Q57 had an 80% potency rate; the intermediate group reported "good" on Q57 had no baseline cardiac disease with a 62% potency rate; and the remaining poor risk group had a 37% potency rate.