Optimized protocol for (18)F-choline PET/CT in patients with biochemically relapsed prostate cancer: experiences on 250 consecutive cases

Impact of pelvic dynamic acquisition on final reading of 18 F-Fluorocholine positron emission tomography in patients with prostate adenocarcinoma: True need or unnecessary burden?

INTRODUCTION

Despite the increasing use of ¹⁸ F-fluorocholine (¹⁸ F-FCH) positron emission tomography (PET) in patients with prostate cancer, the acquisition protocol remains debated. We have evaluated the influence of the pelvic dynamic phase on the final reading of whole-body ¹⁸ F-FCH PET, to assess the need for a two-stage protocol. Reading the physician's experience and patient's previous treatment profile was also considered as potential influencing factors on final PET interpretation.

METHODS

All ¹⁸ F-FCH PET/CT performed from January 2018 to September 2019 in patients with prostate cancer and including a pelvic dynamic phase followed by a delayed whole-body acquisition were retrospectively retrieved. PET/CT were analysed by one expert nuclear medicine physician and one resident. The whole-body scan was analysed blinded (first reading) and nonblinded from the results of the dynamic phase.

RESULTS

221 consecutive PET/CT were selected from 201 patients previously treated by radical prostatectomy (n = 31), pelvic radiation therapy (n = 60), or both (n = 94). 24 patients had no previous treatments, and 12 benefited from other focal treatments. In the whole population, dynamic acquisition modified final interpretation of 32/221 scans (14.5%) for residents, 26 (11.8%) for experts and 19 (8.6%) for consensual reading. No influence of previous treatments was found. The availability of a dynamic phase would have been responsible for treatment modification in 5/221 scans (2.3%). Considering only the prostate bed, dynamic acquisition modified the final interpretation in 7/125 (5.6%) studies (consensual reading) from patients with previous prostatic surgery and 4/84 (4.8%) scans from patients without a history of prostatic surgical intervention. No significant influence of dynamic acquisition was found on the final PET interpretation on prostate lodge accordingly to previous prostatic surgery.

CONCLUSION

The dynamic phase changes the interpretation of ¹⁸ F-FCH PET in about 9% of cases and the therapeutic strategy in <3% of patients. The influence of the early phase reduces with physician experience. Patient's treatment profile does not appear to have a significant influence on the variability of interpretation, also including the prostate bed.

Optimization of temporal sampling for 18F-choline uptake quantification in prostate cancer assessment

Background

Suboptimal temporal sampling of time-activity curves (TAC) from dynamic ¹⁸F-fluoromethylcholine (FCH) PET images may introduce bias in quantification of FCH uptake in prostate cancer assessment. We sought to define an optimal temporal sampling protocol for dynamic FCH PET imaging.

Seven different time samplings were tested: 5 × 60″, 10 × 30″, 15 × 15″–1 × 75″, 6 × 10″–8 × 30″, 12 × 5″–8 × 30″; 10 × 5″–4 × 10″–3 × 20″–5 × 30″, and 8 × 3″–8 × 12″–6 × 30″. First, the irreversible and reversible one-tissue compartment model with blood volume parameter (VB) (respectively, 1T1K+VB and 1T2k+VB, with K1 = transfer coefficient from the arterial blood to the tissue compartment and k2 = transfer coefficient from the tissue compartment to the arterial blood) were compared for 37 lesions from 32 patients who underwent FCH PET imaging for initial or recurrence assessment of prostate cancer, and the model was selected using the Akaike information criterion. To determine the optimal time sampling, K1 values extracted from 1000 noisy-simulated TAC using Monte Carlo method from the seven different time samplings were compared to a target K1 value which is the average of the K1 values extracted from the 37 lesions using an imaging-derived input function for each patient. K1 values extracted with the optimal time sampling for each tumoral lesion were compared to K1 values extracted from each of the other time samplings for the 37 lesions.

Results

The 1T2k + VB model was selected. The target K1 value as the objective was 0.506 mL/ccm/min (range 0.216–1.246). Results showed a significant difference between K1 values from the simulated TAC with the seven different time samplings analyzed. The closest K1 value from the simulated TAC to the target K1 value was obtained by the 12 × 5″–8 × 30″ time sampling. Concerning the clinical validation, K1 values extracted from the optimal time sampling (12 × 5″–8 × 30″) were significantly different with K1 values extracted from the other time samplings, except for the comparison with K1 values extracted from the 10 × 5″–4 × 10″–3 × 20″–5 × 30″ time sampling.

Conclusions

A two-phase framing of dynamic PET reconstruction with frame durations of 5 s (blood phase) and 30 s (tissue phase) could be used to sample the TAC for uptake quantification in prostate cancer assessment.

Comparison of choline influx from dynamic 18F-Choline PET/CT and clinicopathological parameters in prostate cancer initial assessment

AIM

The aim of the study was to compare the kinetic analysis of ¹⁸F-labeled choline (FCH) uptake with static analysis and clinicopathological parameters in patients with newly diagnosed prostate cancer (PC).

MATERIALS AND METHODS

Sixty-one patients were included. PSA was performed few days before FCH PET/CT. Gleason scoring (GS) was collected from systematic sextant biopsies. FCH PET/CT consisted in a dual phase: early pelvic list-mode acquisition (from 0 to10 min post-injection) and late whole-body acquisition (60 min post-injection). PC volume of interest was drawn using an adaptative thresholding (40% of the maximal uptake) on the late acquisition and projected onto an early static frame of 10 min and each of the 20 reconstructed frames of 30 s. Kinetic analysis was performed using an imaging-derived plasma input function. Early kinetic parameter (K1 as influx) and static parameters (early SUVmean, late SUVmean, and retention index) were extracted and compared to clinicopathological parameters.

RESULTS

K1 was significantly, but moderately correlated with early SUVmean (r = 0.57, p < 0.001) and late SUVmean (r = 0.43, p < 0.001). K1, early SUVmean, and late SUVmean were moderately correlated with PSA level (respectively, r = 0.36, p = 0.004; r = 0.67, p < 0.001; r = 0.51, p < 0.001). Concerning GS, K1 was higher for patients with GS ≥ 4 + 3 than for patients with GS < 4 + 3 (median value 0.409 vs 0.272 min^- 1, p < 0.001). No significant difference was observed for static parameters.

CONCLUSIONS

FCH influx index K1 seems to be related to GS and could be a non-invasive tool to gain further information concerning tumor aggressiveness.

A Feasibility Study Showing [68Ga]Citrate PET Detects Prostate Cancer

PURPOSE

The management of advanced or recurrent prostate cancer is limited in part by the lack of effective imaging agents. Metabolic changes in prostate cancer have previously been exploited for imaging, culminating in the recent US FDA approval of [¹¹C]choline for the detection of subclinical recurrent disease after definitive local therapy. Despite this milestone, production of [¹¹C]choline requires an on-site cyclotron, limiting the scope of medical centers at which this scan can be offered. In this pilot study, we tested whether prostate cancer could be imaged with positron emission tomography (PET) using [⁶⁸Ga]citrate, a radiotracer that targets iron metabolism but is produced without a cyclotron.

PROCEDURES

Eight patients with castrate-resistant prostate cancer were enrolled in this single-center feasibility study. All patients had evidence of metastatic disease by standard of care imaging [X-ray computed tomography (CT), bone scan, or magnetic resonance imaging (MRI)] prior to PET with [⁶⁸Ga]citrate. Patients were intravenously injected with increasing doses of [⁶⁸Ga]citrate (136.9 to a maximum of 259 MBq). Uptake time was steadily increased from 1 h to approximately 3.5 h for the final 4 patients, and all patients were imaged with a PET/MRI. Qualitative and semi-quantitative (maximum standardized uptake value (SUV_max)) assessment of the metastatic lesions was performed and compared to the standard of care imaging.

RESULTS

At 1- and 2-h imaging times post injection, there were no detectable lesions with [⁶⁸Ga]citrate PET. At 3- to 4-h uptake time, there were a total of 71 [⁶⁸Ga]citrate-positive lesions (67 osseous, 1 liver, and 3 lymph node). Of these, 65 lesions were visible on the standard of care imaging (CT and/or bone scan). One PET-avid osseous vertebral body metastasis was not apparent on either CT or bone scan. Twenty-five lesions were not PET-avid but seen on CT and bone scan (17 bone, 6 lymph node, 1 pleural, and 1 liver). The average of the maximum SUVs for bone or soft tissue metastases for patients treated at higher doses and uptake time was statistically higher than the corresponding parameter in normal liver, muscle, and bone. Visually obvious blood pool activity was observed even 3-4 h post injection, suggesting that further optimization of the [⁶⁸Ga]citrate imaging protocol is required to maximize signal-to-background ratios.

CONCLUSIONS

Our preliminary results support that PET with [⁶⁸Ga]citrate may be a novel tool for imaging prostate cancer. Future studies are needed to determine the optimal imaging protocol, the clinical significance of [⁶⁸Ga]citrate uptake, and its role in therapeutic decisions.

PET and PET/CT with radiolabeled choline in prostate cancer: a critical reappraisal of 20 years of clinical studies

We here aim to provide a comprehensive and critical review of the literature concerning the clinical applications of positron emission tomography/computed tomography (PET/CT) with radiolabeled choline in patients with prostate cancer (PCa). We will initially briefly summarize the historical context that brought to the synthesis of [¹¹C]choline, which occurred exactly 20 years ago. We have arbitrarily grouped the clinical studies in three different periods, according to the year in which they were published and according to their relation with their applications in urology, radiotherapy and oncology. Studies at initial staging and, more extensively, studies in patients with biochemical failure, as well as factors predicting positive PET/CT will be reviewed. The capability of PET/CT with radiolabeled choline to provide prognostic information on PCa-specific survival will also be examined. The last sections will be devoted to the use of radiolabeled choline for monitoring the response to androgen deprivation therapy, radiotherapy, and chemotherapy. The accuracy and the limits of the technique will be discussed according to the information available from standard validation processes, including biopsy or histology. The clinical impact of the technique will be discussed on the basis of changes induced in the management of patients and in the evaluation of the response to therapy. Current indications to PET/CT, as officially endorsed by guidelines, or as routinely performed in the clinical practice will be illustrated. Emphasis will be made on methodological factors that might have influenced the results of the studies or their interpretation. Finally, we will briefly highlight the potential role of positron emission tomography/magnetic resonance and of new radiotracers for PCa imaging.

Acquisition with (11)C-choline and (18)F-fluorocholine PET/CT for patients with biochemical recurrence of prostate cancer: a systematic review and meta-analysis

The objective of the systematic review and meta-analysis was to evaluate whether the choice between two radiotracers, (11)C-choline ((11)C-cho) and (18)F-fluorocholine ((18)F-FCH) for PET/CT, and different acquisition protocols contributed to detect metastases for patients with biochemical recurrence of prostate cancer after radical prostatectomy or radiotherapy. We searched in January 2016 in Pubmed and Embase for articles that had used radiolabeled choline PET/CT in restaging. The meta-analysis evaluated technical and clinical aspects. Across 18 articles 1 219 of 2 213 patients (54.9 %) had a positive radiolabeled PET/CT image. Mean of the mean/median restaging PSA levels was 3.6 ± 2.7 ng/mL (range 0.5-10.7 ng/mL). Six articles with (11)C-cho PET/CT had a radiation activity of 561 ± 122 MBq and it was 293 ± 47 MBq in 12 articles with (18)F-FCH PET/CT. The difference was significant (P = 0.007, t test). Uptake time was 5 min in articles with (11)C-cho PET/CT and it was 29 ± 24 min in articles with (18)F-FCH PET/CT. The difference was significant (P = 0.02, t test). Thereby the detection rates of metastatic sites in articles with (11)C-cho (30 ± 5 %) and (18)F-FCH (39 ± 5 %) did not differ significantly (P = 0.26, t test). In linear regression analyses of the articles, the radiation activity of (11)C-cho and (18)F-FCH was not significantly associated with the detection rate of metastatic sites (P = 0.75 and P = 0.60). Restaging with radiolabeled choline PET/CT detected metastatic sites for patients with biochemical recurrence and PSA levels of 1-10 ng/mL at clinically relevant level. The choice between the two choline radiotracers and different acquisition protocols had no significant impact on detection.