Unspecific¹⁸F-PSMA-1007 Bone Uptake Evaluated Through PSMA-11 PET, Bone Scanning, and MRI Triple Validation in Patients with Biochemical Recurrence of Prostate Cancer

Abstract

F-PSMA-1007 PET is used in the management of patients with prostate cancer. However, recent reports indicate a high rate of unspecific bone uptake (UBU) with 18 F-PSMA-1007, which may lead to a falsepositive diagnosis. UBU has not been evaluated thoroughly. Here, we evaluate the frequency of UBU and bone metastases separately for 18 F-PSMA-1007 and 68 Ga-PSMA-11 in biochemical recurrence (interindividual comparison). Additionally, we investigate UBU seen in 18 F-PSMA-1007 through follow-up examinations (intraindividual comparison) using 68 Ga-PSMA-11 PET, bone scintigraphy, and MRI. Methods: First, all patients (n 5 383) who underwent 68 Ga-PSMA-11 PET between January 2020 and December 2020 and all patients (n 5 409) who underwent 18 F-PSMA-1007 PET between January 2020 and November 2021 due to biochemical recurrence were included for an interindividual comparison of bone metastases and UBU rate. In a second approach, we regarded all patients with UBU in 18 F-PSMA-1007, characterized by focal bone uptake with an SUV max . 4 and prostate-specific antigen (PSA) # 5 ng/mL, who underwent additional 68 Ga-PSMA-11 PET (n 5 17) (interindividual comparison). Of these, 12 patients also had bone scintigraphy and whole-body MRI within a 1-to 5-wk interval. Bone uptake seen on 18 F-PSMA-1007 but not on any of the other 4 modalities (CT, MRI [n 5 1], bone scanning, and 68 Ga-PSMA-11 PET) was recorded as false-positive. Results: Patients scanned with 18 F-PSMA-1007 PET had a significantly higher rate of UBU than those scanned with 68 Ga-PSMA-11 (140 vs. 64; P , 0.001); however, the rate of bone metastases was not significantly different (72 vs. 64; P 5 0.7). In the intraindividual comparison group, workup by CT, MRI, bone scanning, and 68 Ga-PSMA-11 PET resulted in a positive predictive value for 18 F-PSMA-1007 focal bone uptake (mean SUV max , 6.1 6 2.9) per patient and per lesion of 8.3% and 3.6%, respectively. Conclusion: In patients with PSA # 5 ng/mL and SUV . 4 at biochemical recurrence, most 18 F-PSMA-1007 focal bone uptake is likely to be false-positive and therefore due to UBU. In the case of low clinical likelihood of metastatic disease, 18 F-PSMA-1007 bone uptake without morphologic surrogate should be assessed carefully with regard to localization and clinical context. However, the rate of bone metastases was not higher with 18 F-PSMA-1007 in the clinical routine, indicating that experienced reporting physicians adjust for UBU findings.

The Role of GA⁶⁸-PSMA PET/CT in Restaging of Biochemical Recurrent Prostate Cancer After Radical Prostatectomy and/or Radiotherapy

“…In another study with F18-PSMA and Ga68-PSMA (24), similar metastasis detection rates were found with both radiopharmaceuticals (n=72 vs 64). Unspeci c bone uptake was more common with F18-PSMA PET/CT than with Ga68-PSMA PET/CT (34.2% vs. 16.7%).…”

The Role of Ga⁶⁸-PSMA PET/CT in restagingof biochemical recurrent prostate cancer after radical prostatectomy and/or radiotheraphy

“…In a recent retrospective analysis of 348 patients, unspeci c bone involvement was observed in 51.4% and the most common localisation was the costa and pelvis (23). In another study with F18-PSMA and Ga68-PSMA (24), similar metastasis detection rates were found with both radiopharmaceuticals (n = 72 vs 64). Unspeci c bone uptake was more common with F18-PSMA PET/CT than with Ga68-PSMA PET/CT (34.2% vs. 16.7%).…”

The Role of Radiation Therapy in the Management of Prostate Cancer and Posttreatment Imaging Appearances

“…Early detection of oligometastatic disease with PSMA-PET also raises the possibility of targeted RT to avoid or prolong progression to systemic therapies such as ADT. 36 To optimize the utility of PSMA PET after definitive treatment, false negatives can be mitigated by repeat, interval imaging (especially at lower, initial PSA levels), but the potential for false positives, especially for bone lesions 37 as well as benign diseases, 38 should be recognized.…”