Usefulness of MRI Findings of Prostate Cancer before and after Tomotherapy-based IMRT

The aim of this work was to evaluate magnetic resonance imaging (MRI) findings of 150 prostate cancer patients at pre- and post- intensity-modulated radiotherapy (IMRT). 150 patients (mean age: 69 years; range: 51-84 years) with histologically proven non-metastatic prostate cancer were included in this study. Hormonal therapy was used in 88 of the 150 patients. The TomoTherapy-based IMRT prescription was 70-78 Gy (2 Gy/fraction) to the prostate and the proximal seminal vesicles, and the patients underwent daily megavoltage CT image-guided verification prior to each treatment. All the patients received one pre IMRT MRI scan and one or more post IMRT follow-up MRI scans of the pelvis at 1.5 Tesla. The T1-weigthed (WI), T2-WI and diffusion-WI MR images were retrospectively assessed by two independent observers. The toxicity scores were recorded every 3 months post IMRT with using the RTOG scoring criteria. This study received institutional approval, and written informed consent was obtained from all the patients. The median follow-up was 28 months. Four hundred two post IMRT follow-up MRI scans (mean, 2.7 times/a patient) were done. On the post IMRT MRI, the intensity of the prostate on the T2WI images was decreased in 150/150 prostates (100%). Twenty five of 62 patients who did not receive hormonal therapy were confirmed to have prostate cancer on MRI pre IMRT, and all of this prostate cancer (25/25) disappeared on MRI within 3 months post IMRT. Seminal vesicle atrophy was presented in 140/150 patients (93%), and the first MRI examination (mean, 3months) after IMRT showed seminal vesicle atrophy, and this continued thereafter. Seminal vesicle hemorrhage was presented in 10/150 patients (7%) and 3 of these 10 patients complained of blood mixed with semen. Rectal wall thickening was present in 16/150 (11%), and it was first seen at 6-12 months post IMRT. In the patient for whom rectal wall thickening was confirmed for more than 6 months, the possibility of the rectal bleeding (RTOG grades 1 and 2) was high. Bladder wall thickening was present in 4/150 patients (3%) within 6 months post IMRT, yet it disappeared in a few months in many cases without any toxicity. MRI was useful for the evaluation of IMRT to the prostate cancer. We believed that the MRI findings are important information not only for their therapeutic value, but also to evaluate the toxicity of IMRT.