Proton MR Spectroscopic Imaging of Prostate Cancer. Metabolite Patterns and Response to External Beam Irradiation

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The purpose of this study was to evaluate change in prostate metabolites after external radiation therapy in patients with prostate carcinomas. Patients with prostatic cancer underwent pelvic irradiation 66.6 Gy. MR spectroscopic imaging and the measurement of serum prostate-specific antigen (PSA) levels underwent before irradiation therapy, at 33.2 Gy irradiation, 2 weeks-post irradiation and 10 weeks-post irradiation. A two dimensional 7 x 7 phase encoded MR spectroscopic imaging data set was acquired by a 1.5-T system with the body coil for radio-frequency transmission and an expandable endorectal coil. According to comparisons between citrate and choline peak levels, the metabolite patterns of the prostate were classified into citrate dominant, choline dominant and equilibrium pattern in which choline peak level is lower than citrate level but more than 90 % of citrate level.The mean area with choline dominant pattern before irradiation was 1.86 〓 1.18 cm3. Choline dominant areas were remained after irradiation although those at 2 and 10 weeks-postirradiation were significantly decreased to 0.85 〓 0.72 cm3 (p = 0.03) and 0.73 〓 0.40 cm3 (p = 0.01), respectively.