Early choline levels from 3-tesla MR spectroscopy after exclusive radiation therapy in patients with clinically localized prostate cancer are predictive of plasmatic levels of PSA at 1 year.

Abstract

To investigate the time course response of prostate metabolism to irradiation using magnetic resonance spectroscopy (MRS) at 3-month intervals and its impact on biochemical control. Between January 2008 and April 2010, 24 patients with localized prostate cancer were prospectively enrolled in the Evaluation of the Response to Irradiation with MR Spectroscopy (ERIS) trial. All the patients had been treated with intensity-modulated radiation therapy with or without long-term adjuvant hormonal therapy (LTHT) and underwent 3-T MRS and prostate-specific antigen (PSA) assays at baseline and every 3 months thereafter up to 12 months. After radiation, the mean normalized citrate level (citrate/water) decreased significantly over time, both in the peripheral zone (PZ) (p = 0.0034) and in the entire prostate (p = 0.0008), whereas no significant change was observed in mean normalized choline levels (choline/water) in the PZ (p = 0.84) and in the entire prostate (p = 0.95). At 6 months after radiation, the mean choline level was significantly lower in the PZ for patients with a PSA value of ≤0.5 ng/mL at 12 months (4.9 ± 1.7 vs. 7.1 ± 1.5, p = 0.0378). Similar results were observed at 12 months in the PZ (6.2 ± 2.3 vs. 11.4 ± 4.1, p = 0.0117 for choline level and 3.4 ± 0.7 vs. 16.1 ± 6.1, p = 0.0054 for citrate level) and also in the entire prostate (6.2 ± 1.9 vs. 10.4 ± 3.2, p = 0.014 for choline level and 3.0 ± 0.8 vs. 13.3 ± 4.7, p = 0.0054 for citrate level). For patients receiving LTHT, there was no correlation between choline or citrate levels and PSA value, either at baseline or at follow-up. Low normalized choline in the PZ, 6 months after radiation, predicts which patients attained a PSA ≤0.5 ng/mL at 1 year. Further analyses with longer follow-up times are warranted to determine whether or not these new biomarkers can conclusively predict the early radiation response and the clinical outcome for patients with or without LTHT.