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Background: Radiation treatment with simultaneous integrated boost against suspected lymph node metastases may be a curative therapeutic option in patients with high-risk prostate cancer (>15% estimated risk of pelvic lymph node metastases according to the Cagiannos nomogram). 11C-acetate positron emission tomography/computed tomography (PET/CT) can be used for primary staging as well as for detection of suspected relapse of prostate cancer. The aims of this study were to evaluate the association between positive 11C-acetate PET/CT findings and the estimated risk of pelvic lymph node metastases and to assess the impact of 11C-acetate PET/CT on patient management in high-risk prostate cancer patients.

Methods: Fifty consecutive prostate cancer patients referred for primary staging with 11C-acetate PET/CT prior to radiotherapy with curative intention were enrolled in this retrospective study.

Results: All patients showed increased 11C-acetate uptake in the prostate. Pelvic lymph node uptake was seen in 42% (21/50) of the patients, with positive external iliac lymph nodes in 71% (15/21) of these. The overall observed proportion of PET/CT-positive pelvic lymph nodes at patient level was higher than the average estimated risk, especially in low-risk groups (<15%). There was a significant association between observed proportion and estimated risk of pelvic lymph node metastases in groups with ≤45 and >45% estimated risk. Treatment strategy was altered due to 11C-acetate PET/CT findings in 43% (20/47) of the patients.

Conclusions: The observed proportion of 11C-acetate PET/CT findings suggestive of locoregional metastases was higher than the estimated risk, suggesting that the Cagiannos nomogram underestimates the risk for metastases. The imaging results with 11C-acetate PET/CT have a considerable impact on patient management.

Aim: The aim of this study was to evaluate the detection rate of bone metastases and the added value of C-11-acetate (ACE) positron-emission tomography/computed tomography (PET/CT) compared to bone scintigraphy (BS) in high-risk prostate cancer (PC).

Materials and Methods: A total of 66 untreated patients with high-risk PC with ACE-PET/CT and planar BS findings within 3 months of each other were retrospectively enrolled. Findings were compared and verified with follow-up data after an average of 26 months.

Results: The rate of detection of bone metastases was superior with ACE-PET/CT compared to BS (p<0.01). Agreement between the methods and between BS and follow-up was moderate (Cohen's kappa coefficient of 0.64 and 0.66, respectively). Agreement between ACE-PET/CT and follow-up was excellent (kappa coefficient of 0.95). Therapy was changed in 11% of patients due to ACE-PET/CT results.

Conclusion: ACE-PET/CT performed better than planar BS in detection of bone metastases in high-risk PC. ACE-PET/CT findings influenced clinical management.

Introduction ¹¹C-acetate (ACE)-PET/CT is used for staging of high-risk prostate cancer. PET data is reconstructed with iterative algorithms, such as VUEPointHD ViP (VPHD) and VUEPoint HD Sharp IR (SharpIR), the latter with additional resolution recovery. It is expected that the resolution recovery algorithm should render more accurate maximum and mean standardized uptake values (SUV_max and SUV_mean) and functional tumor volumes (FTV) than the ordinary OSEM. Performing quantitative analysis, choice of volume-of-interest delineation algorithm (SUV threshold) may influence FTV. Optimizing PET acquisition time is justified if image quality and quantitation do not deteriorate. The aim of this study is to identify the optimal reconstruction algorithm, SUV threshold and acquisition time for ACE-PET/CT. Methods ACE-PET/CT data acquired with a General Electric Discovery 690 PET/CT from 16 consecutive high-risk prostate cancer patients was reconstructed with VPHD and SharpIR. Forty pelvic lymph nodes (LNs) and 14 prostate glands were delineated with 42% and estimated threshold. SUV_max, SUV_mean, FTV and total lesion uptake were measured. Default acquisition time was four minutes per bed position. In a subset of lesions, acquisition times of one, two and four minutes were evaluated. Structural tumor volumes (STV) of the LNs were measured with CT for correlation with functional volumetric parameters. To validate SUV quantification under different conditions with SharpIR 42%, recovery coefficients (RCs) of SUV_mean and FTV were calculated from a phantom with ¹⁸F-fluoro-deoxy-glucose (FDG)-filled volumes 0.1–9.2cm³ and signal-to-background (S/B) ratios 4.3–15.9. Results With SharpIR, SUV_max and SUV_mean were higher and FTV lower compared with VPHD, regardless of threshold method, in both prostates and LNs. Total lesion uptake determined with both threshold methods was lower with SharpIR compared with VPHD with both threshold methods, except in subgroup analysis of prostate targets where estimated threshold returned higher values. Longer acquisition times returned higher FTV for both threshold methods, regardless of reconstruction algorithm. The FTV difference was most pronounced with one minute’s acquisition per bed position, which also produced visually the highest noise. SUV parameters were unaffected by varying acquisition times. FTV with SharpIR 42% showed the best correspondence with STV. SharpIR 42% gave higher RCs of SUV_mean and FTV with increasing phantom size and S/B-ratio, as expected. Conclusions Delineation with SharpIR 42% seems to provide the most accurate combined information from SUV_max, SUV_mean, FTV and total lesion uptake. Acquisition time may be shortened to two minutes per bed position with preserved image quality.