PSA doubling time for prediction of [11C]choline PET/CT findings in prostate cancer patients with biochemical failure after radical prostatectomy
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- Giovacchini, G., Picchio, M., Scattoni, V. et al. Eur J Nucl Med Mol Imaging (2010) 37: 1106. doi:10.1007/s00259-010-1403-7
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Previous studies have shown that the positive detection rate of [11C]choline positron emission tomography/computed tomography (PET/CT) depends on prostate-specific antigen (PSA) plasma levels. This study compared PSA levels and PSA doubling time (PSADT) to predict [11C]choline PET/CT findings.
PSADT was retrospectively calculated in 170 prostate cancer (PCa) patients with biochemical failure after radical prostatectomy who underwent [11C]choline PET/CT. PSADT was calculated as PSADT = ln2/m, where m is the slope of the linear regression line of the natural log of PSA values. At least three PSA measurements were used (median: 4; range: 3–16), separated by at least 3 months, each with a minimum increase of 0.20 ng/ml. PET/CT findings were validated using criteria based on histological analysis and clinical and imaging data. Statistical analysis was performed using the t test, chi-square test, analysis of variance and binary logistic regression. Regression-based coefficients were used to develop a nomogram predicting the probability of positive [11C]choline PET/CT and 200 bootstrap resamples were used for internal validation.
The median PSA was 1.25 ng/ml (range: 0.23–48.6 ng/ml), and the median PSADT was 7.0 months (range: 0.97–45.3 months). [11C]choline PET/CT was positive in 75 of 170 patients (44%). PET/CT findings were validated using histological criteria (11%) and clinical and imaging criteria (89%). The overall accuracy of [11C]choline PET/CT was 88%. Multivariate logistic regression showed that high PSA and short PSADT were significant (p < 0.05) predictors of positive [11C]choline PET/CT [PSA: odds ratio (OR) = 1.43; 95% confidence interval (CI): 1.15–1.78; PSADT: OR = 1.12; 95% CI: 1.04–1.21]. The percentage of patients with positive [11C]choline PET/CT was 27% for PSADT >6 months, 61% for PSADT between 3 and 6 months and 81% for PSADT <3 months. The percentage of patients who displayed pathological [11C]choline uptake in the skeleton significantly increased (p < 0.05) from 3% for PSADT >6 months to 52% for PSADT <3 months. Conversely, patients who displayed pathological [11C]choline uptake in the prostatectomy bed were 0% for PSADT <3 months and 17% for PSADT >6 months (p < 0.05). A nomogram based on age, PSA, PSADT, time to trigger PSA, Gleason score, pathological stage and androgen deprivation therapy demonstrated bootstrap-corrected predictive accuracy of 81%.
Like PSA, PSADT is an independent predictor of [11C]choline PET/CT. [11C]choline PET/CT is very sensitive to PCa tumour growth, as reflected by PSA kinetics. PSADT should be taken into account by physicians when referring PCa patients for [11C]choline PET/CT.