Synopsis

Simultaneous PET/MRI has the potential to improve the detection accuracy in recurrent prostate cancer, since it combines the excellent soft-tissue contrast of MRI with the high molecular sensitivity of PET in one imaging session. The aim of this observational study is to assess the detection rate of recurrent prostate cancer by simultaneous ¹⁸F-Fluciclovine PET/MRI. We demonstrate that18F-Fluciclovine PET/MRI can detect suspicious lymph node, prostatic and bone lesions in patients with a wide range of PSA levels and that the number of equivocal findings is reduced when MR images are evaluated in conjunction with PET uptake. .

Purpose

Materials and methods

Patients that fulfilled the European Association of Urology criteria for biochemical relapse following radical treatment (two consecutive measurements with PSA ≥ 0.2 ng/ml following radical prostatectomy or PSA ≥ 2.0 ng/ml above the nadir following definitive radiotherapy [5]) and who were potential candidates for salvage treatment, were recruited and examined with simultaneous ¹⁸F-Fluciclovine PET/MRI (3 T Biograph mMR, Siemens, Erlangen, Germany). An overview of the imaging protocol is given in Figure 1.

MR images were reviewed by two radiologists blinded to the PET data. Subsequently, PET images were reviewed by a nuclear medicine physician with access to the initial results from MRI. Findings were scored as 1-negative, 2-equivocal or 3-recurrence/metastasis. A combined PET/MRI score was given after consensus between the reviewers. Detection rates for MR, PET and combined PET/MR are reported, calculated as the number of patients with suspicious findings divided by the total number of patients. Detection rates were divided into groups based on PSA level at time of imaging. Detection rates were compared with the chi-squared test. Median PSA levels in patients with and without suspicious PET findings were compared with the Mann-Whitney U test.

Results

Patient characteristics (n=79) are listed in Table 1. In 53% of the patients there were no suspicious findings (negative score on MR, PET and PET/MR). In the remaining 37 patients there were 52 suspicious lesions (median 1, range 1-4 lesions per patient) in lymph nodes, prostate area and bone (Table 2)(Fig 2).

The detection rate for MR, PET and PET/MR were 43.0, 30.4 and 40.5% respectively when score 2 and 3 were considered positive. The PET/MR score was different from the MR score in 10 (12.7%) of the patients. Eight equivocal MR scores were changed to negative (score1, n=4) or positive (score 3, n=4) scores, while two negative MR scores were upgraded to equivocal (score 2, n=1) or positive(score 3, n=1) based on PET. When only considering score 3 as positive, PET/MR had higher detection rate than MR alone (29.1% vs 22.8% respectively, p<0.001)(Table 3).

Patients with PSA ≥ 1ng/ml had higher detection rates than patients with lower PSA levels at time of imaging (Table 3). Patients with elevated ¹⁸F-Fluciclovine uptake lesions (score 2 and 3) had higher median PSA level (2.2 ng/ml, range of 0.2-12.3 ng/ml), than PET negative patients (median PSA 0.5ng/ml, range 0-12.9 ng/ml)(p=0.001).

Discussion

We have demonstrated that simultaneous ¹⁸F-Fluciclovine PET/MRI can detect suspicious lymph node, prostatic and bone lesions in patients with a wide range of PSA levels. The overall detection rate is in the same range as previously reported for ¹⁸F-Flucoclovine PET/CT [6] and ¹¹C-Choline PET-CT [7].

We observe that the number of equivocal findings is reduced when MR images are evaluated in conjunction with PET uptake. There were also cases of lesions with elevated tracer uptake that had been missed by the MR evaluation. This could indicate that a combined ¹⁸F-Fluciclovine PET/MR examination may play a role in detection of recurrent prostate cancer, and that the two modalities offer complementary information.

Although there is a higher detection rate among patients with PSA levels ≥1ng/ml, ¹⁸F-Fluciclovine PET/MR also detected suspicious lesions in patients with PSA as low as 0.2 ng/ml.

A limitation in this initial report is that there is no reference standard that can be used to categorize the findings as true or false positive. In future work, we aim to establish a reference standard based on PSA-levels, follow-up imaging, and lesion biopsies to define presence and absence of disease.

Conclusion

Acknowledgements

References

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