3D prostate gland uptake of 18F-choline - association with overall survival in patients with hormone-naïve prostate cancer

Artikel i vetenskaplig tidskrift, 2017

Objectives: To develop a completely automated method to quantify prostate gland uptake of 18F-choline in PET/CT images and to study the relationship between this measure, clinical data and overall survival in patients with prostate cancer.
Methods: An automated method for segmentation of the prostate gland in CT images was developed using a training group of 100 patients who had undergone PET/CT scanning. The algorithms were trained based on the manual segmentations of the prostate gland in the 100 CT scans performed by a single radiologist. A multi-atlas-based method was used applied for automated segmentation of the prostate gland. Each of a subset of the training images was registered separately to the test image. By applying the resulting transformations to the manual delineations a rough segmentation of the test image was obtained. This segmentation was refined using a random-forest classifier and the final segmentation was obtained with graph cuts. Voxels in the 18F-choline PET scans having a standard uptake value (SUV) >2.65 and localized in the prostate gland in the corresponding CT scan were defined as abnormal. Automated calculation of the following five PET measurements was performed: The maximal SUV within the prostate gland - SUVmax The average SUV within the abnormal part of the prostate gland - SUVmean The volume of abnormal uptake within the prostate gland - VOL The product SUVmean x VOL defined as Total Lesion Uptake - TLU The fraction of the prostate with abnormal uptake related to the whole volume of the prostate gland - FRAC The automated quantification method was retrospectively applied to a separate test group of 46 prostate cancer patients, aged 53-94 years, who had undergone 18F-choline PET/CT. These patients have previously been selected for a study aiming to compare whole-body bone scans, 18F-choline-PET/CT and 18F-NaF PET/CT with magnetic resonance imaging. The study entry criteria were biopsy-proven prostate cancer, a positive whole-body bone scan consistent with bone metastases, and no history of androgen deprivation. The association between the automated PET measurements, age, PSA, Gleason score and overall survival was evaluated using a univariate Cox proportional hazards regression model. Kaplan-Meier estimates were used to estimate the survival difference between patients with values above and below the median value for all variables analyzed.
Results: The fraction of the prostate with abnormal uptake related to the whole volume of the prostate gland - FRAC and age were significantly associated with overall survival (Table) while PSA, Gleason score and other PET measurements were not. The patients with a FRAC above the median value (58.2%) had a significantly shorter median survival time than patients with a value below the median value (2.8 years vs. 5.5 years; p=0.04), see Figure.
Conclusion: A completely automated method of quantifying 18F-choline PET uptake in the prostate gland yielded a measure of disease extent that was significantly associated with overall survival in patients with hormone-naïve prostate cancer. The method can also be applied to PET/CT scans with other tracers such as FDG or PSMA-targeted agents. It is our hope that these preliminary data will inspire further evaluation of this type of objective quantification of PET/CT scans.