MRI target delineation may reduce long-term toxicity after prostate radiotherapy.

Aiming for minimal toxicity after radical prostate cancer (PC) radiotherapy (RT), magnetic resonance imaging (MRI) target delineation could be a possible benefit knowing that clinical target volumes (CTV) are up to 30% smaller, when CTV delineation on MRI is compared to standard computed tomography (CT). This study compares long-term toxicity using CT or MRI delineation before PC RT.Urinary and rectal toxicity assessments 36 months after image-guided RT (78 Gy) using CTC-AE scores in two groups of PC patients. Peak symptom score values were registered. One group of patients (n=72) had standard CT target delineation and gold markers as fiducials. Another group of patients (n=73) had MRI target delineation and a nickel-titanium stent as fiducial.At 36 months no difference in overall survival (92% in both groups, p=0.29) or in PSA-relapse free survival was found between the groups (MRI=89% and CT=94%, p=0.67). A significantly smaller CTV was found in the MRI group (p=0.02). Urinary retention and frequency were significantly reduced in the MRI group (p=0.03 in the matter of both). The overall urinary and rectal toxicity did not differ between the two groups.MRI delineation leads to a significantly reduced CTV. Significantly lower urinary frequency and urinary retention toxicity scores were observed following MRI delineation. The study did not find significant differences in overall urinary or rectal toxicity between the two groups. PSA-relapse survival did not differ between the two groups at 36 months.