1074 - Implications on Radiation Treatment Planning of 18F-Fluciclovine PET/CT in Patients with Biochemical Recurrence of Prostate Cancer and a Negative PSMA PET/CT

04:15pm - 04:20pm PT

Room 20/21

Presenter(s)

Adam Eakin, MD - Oregon Health and Science University, Portland, OR

A. J. Eakin¹, N. Mallak¹, J. Y. Lim¹, L. Szidonya¹, S. Obrzut¹, G. Choudhary¹, and A. Y. Hung²; ¹Oregon Health and Science University, Portland, OR, ²Department of Radiation Medicine, Oregon Health & Science University, Portland, OR

Purpose/Objective(s): PSMA PET/CT is the current standard of care imaging modality to localize tumor sites in the setting of biochemical recurrence (BCR) of prostate cancer. Prior to PSMA, ¹⁸F-Fluciclovine was an early agent used in this setting. It may have advantages in the prostate bed because it is not obscured by urinary excretion as are most PSMA agents. Our prospective study evaluated whether ¹⁸F-Fluciclovine PET can identify sites of disease recurrence in patients with a negative or equivocal PSMA PET, and analyzes the implications of Fluciclovine PET findings for treating prostate cancer with radiation.

Materials/Methods: 49 patients with BCR, PSA of at least 0.2 ng/mL, and no definitive recurrence on PSMA PET scan were recruited on an ongoing prospective single-arm cohort study (NCT 05722925). Patients are imaged with ¹⁸F-Fluciclovine PET/CT within 30 days of the PSMA PET/CT scan and the PSMA and ¹⁸F-Fluciclovine PET/CTs are interpreted according to established criteria.

Results: 49 men with BCR following prostatectomy (n=21 (42.9%)), definitive radiation (n=7 (14.3%)), surgery + radiation (n=18 (36.7%)), and ADT alone (n=1 (2%)) have been enrolled to date. ¹⁸F-Fluciclovine PET/CT was positive in 28 patients (57.1%), with local recurrence in 14 patients, regional nodal metastases in 5 patients , and distant metastatic disease in 9 patients. There was no statistically significant difference in the PSA levels between patients with positive Fluciclovine scan (0.20 to 14.75 ng/mL, mean of 2.9 ng/mL and median of 0.53 ng/mL) and patients with negative Fluciclovine scan (0.21 to 4.28 ng/mL, mean of 0.75 ng/mL and median of 0.41 ng/mL) (p = 0.19 Wilcoxon rank sum test).

20 patients were specifically being considered for salvage radiation post-prostatectomy. Of these, 11 (55%) of them had a positive fluciclovine PET. 7 had avidity identified in the prostate fossa, 2 had avidity in pelvic nodes, 1 had avidity in retroperitoneal nodes and 1 in an ischial bone. The median PSA for intended-salvage patients with positive findings was 0.3 ng/mL and the median PSA for these patients with negative findings was 0.275 ng/mL. 4 of 20 patients (25%) had disease outside of a salvage radiation field that intended to treat the prostate fossa alone.

Conclusion: In this prospective study evaluating the utility of ¹⁸F-Fluciclovine PET after a negative PSMA PET, ¹⁸F-Fluciclovine PET detected disease in over 50% of the patients. That ratio held true for patients being considered for salvage radiation but additional nodal or distant disease was identified in 25% of patients with a negative PSMA PET. In evaluating patients for oligometastatic disease and salvage radiation treatment, Fluciclovine PET may add additional information when a PSMA PET is negative.

Table 1: Positive ¹⁸F-Fluciclovine PET findings with a negative ⁶⁸Ga-PSMA-11 and ¹⁸F- Piflufolastat PSMA PET

Site of Disease	n (%)
Local Recurrence	14 (50%)
Regional Nodes	5 (18%)
Distant Mets	9 (32%)
Distant Nodes	3 (11%)
Bone	4 (14%)
Adrenal Gland	1 (3.5%)
Distant Nodes + Bone	1 (3.5%)