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 (
suvmax) of 4.0 ± 0.4 (
n = 11) at 40 minutes after injection. During week 8 of
ebrt, the
suvmax declined to 2.9 ± 0.1 (
n = 10,
p < 0.05). At 2 and 12 months after
ebrt,
suvmax 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.
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