BACKGROUND: To assess the feasibility, early toxicity of selective, IMRT-based dose escalation (simultaneous integrated boost) to biopsy proven dominant intra-prostatic lesions visible on MRI METHODS: Patients with localized prostate cancer, an abnormality within the prostate on endorectal coil MRI were eligible All patients underwent a MRI-guided transrectal biopsy at the location of the MRI abnormality Gold fiducial markers were also placed Several days later patients underwent another MRI scan for fusion with the treatment planning CT scan This fused MRI scan was used to delineate the region of the biopsy proven intra-prostatic lesion A 3 mm expansion was performed on the intra-prostatic lesions, defined as a separate volume within the prostate The lesion + 3 mm, the remainder of the prostate + 7 mm received 94 5/75 6 Gray (Gy) respectively in 42 fractions Daily seed position was verified to be within 3 mm RESULTS: Three patients were treated Follow-up was 18, 6, and 3 months respectively Two patients had a single intra-prostatic lesion One patient had 2 intra-prostatic lesions All four intra-prostatic lesions, with margin, were successfully targeted, treated to 94 5 Gy Two patients experienced acute RTOG grade 2 genitourinary (GU) toxicity One had grade 1 gastrointestinal (GI) toxicity All symptoms completely resolved by 3 months One patient had no acute toxicity CONCLUSION: These early results demonstrate the feasibility of using IMRT for simultaneous integrated boost to biopsy proven dominant intra-prostatic lesions visible on MRI The treatment was well tolerated