Analysis of Intraprostatic Therapeutic Effects in Prostate Cancer Patients Using [¹¹C]-Choline pet/ct after External-Beam Radiation Therapy

Purpose: The objective of the present study was to analyze, with relatively high sensitivity and specificity, uptake properties of [¹¹C]-choline in prostate cancer patients by means of positron-emission tomography (pet)/computed tomography (ct) imaging using objectively defined pet parameters to test for statistically significant changes before, during, and after external-beam radiation therapy (ebrt) and to identify the time points at which the changes occur. Methods: The study enrolled 11 patients with intermediate-risk prostate cancer treated with ebrt, who were followed for up to 12 months after ebrt. The [¹¹C]-choline pet scans were performed before treatment (baseline); at weeks 4 and 8 of ebrt; and at 1, 2, 3, 6, and 12 months after ebrt. Results: Analysis of [¹¹C]-choline uptake in prostate tissue before treatment resulted in a maximum standardized uptake value (suv_max) of 4.0 ± 0.4 (n = 11) at 40 minutes after injection. During week 8 of ebrt, the suv_max declined to 2.9 ± 0.1 (n = 10, p < 0.05). At 2 and 12 months after ebrt, suv_max values were 2.3 ± 0.3 (n = 10, p < 0.01) and 2.2 ± 0.2 (n = 11, p < 0.001) respectively, indicating that, after ebrt, maximum radiotracer uptake in the prostate was significantly reduced. Similar effects were observed when analyzing the tumour:muscle ratio (tmr). The tmr declined from 7.4 ± 0.6 (n = 11) before ebrtto 6.1 ± 0.4 (n = 11, nonsignificant) during week 8 of ebrt, to 5.6 ± 0.03 (n = 11, p < 0.05) at 2 months after ebrt, and to 4.4 ± 0.4 (n = 11, p < 0.001) at 12 months after ebrt. Conclusions: Our study demonstrated that intraprostatic [¹¹C]-choline uptake in the 11 analyzed prostate cancer patients significantly declined during and after ebrt. The pet parameters SUV_max and tmr also declined significantly. These effects can be detected during radiation therapy and up to 1 year after therapy. The prognostic value of these early and statistically significant changes in intraprostatic [¹¹C]-choline pet avidity during and after ebrt are not yet established. Future studies are indicated to correlate changes in [¹¹C]-choline uptake parameters with long-term biochemical recurrence to further evaluate [¹¹C]-choline pet changes as a possible, but currently unproven, biomarker of response.