Objective: To assess the role of magnetic resonance imaging (MRI) for evaluating changes in the prostate after transrectal high-intensity focused ultrasound (HIFU) for treating prostate cancer, correlating the findings with histology to assess its possible role in predicting the outcome, evaluating residual cancer or local recurrence of disease.
Patients and methods: Ten patients with prostate cancer were assessed with MR and MR spectroscopy (MRS) before and at 1, 4 and 12 months after HIFU, assessing the glandular volume and MRI and MRS data after HIFU. These data were correlated with the prostate-specific antigen (PSA) levels at each examination (suspicious for residual cancer if >0.5 ng/mL) and with histological findings of prostate biopsy sampling at 6-8 months (random or targeted at suspicious MR areas).
Results: Variations in volume during the follow-up were not associated with treatment outcome. MRI was suspicious for residual cancer in one patient at 1 month and in another two at 4 months; in all three patients (one with a PSA level of <0.5 ng/mL) targeted biopsies were positive for cancer. MRI was negative in seven patients; in six of these (one with a PSA level of >0.5 ng/mL) random biopsies were negative, and in one the random biopsies were positive for residual cancer. At 4 months there was a statistically significant difference (P = 0.015) between patients responsive to treatment and those with persistent disease, by combining negative MRI with a PSA level of <0.5 ng/mL; MRS data were suitable for analysis only in three patients with partial necrosis.
Conclusion: Our preliminary data support the role of MRI in association with PSA levels as a useful and accurate tool in the follow-up of patients treated with HIFU for prostate cancer. However, considering the economic issue, it should not be used routinely and should be limited to detecting residual cancer (in patients with a PSA level of >0.5 ng/mL) with the main purpose of improving the detection rate of transrectal ultrasonography (TRUS)-guided prostate biopsy. MRS data had no additional value over MRI. Further evaluation is needed to compare the use of contrast media and other techniques (e.g. colour Doppler TRUS) in detecting residual or local recurrent cancer.