Intention-to-Treat Analysis of 68Ga-PSMA and 11C-Choline PET/CT Versus CT for Prostate Cancer Recurrence After Surgery

Abstract

Biochemical recurrence (BCR) after prostate cancer surgery is common, even after additional salvage radiotherapy. BCR might be explained by target miss. Improved diagnostic accuracy provided by PET could potentially circumvent this therapeutic gap. Therefore, we evaluated consecutive ⁶⁸Ga-prostate-specific membrane antigen (PSMA) PET/CT, ¹¹C-choline PET/CT, and standard CT imaging in the same patient with regard to TNM-stage migration and accordingly adapted curative radiotherapy options including ablative treatment of oligometastases (n ≤ 5). The cost efficacy of PET- versus CT-based treatment was also calculated. Methods: The prospective register database (064/2013BO1) was retrospectively searched for patients fulfilling the following 3 inclusion criteria: BCR after radical prostatectomy (pT2-pT4 pN0-pN1 cM0, postoperative radiotherapy allowed); ¹¹C-choline PET/CT, ⁶⁸Ga-PSMA PET/CT, and diagnostic CT performed within 24 h; and available clinical data. Ten treatment routines were defined according to current practice. Furthermore, intention-to-treat and treatment-related costs depending on the shift of TNM stage after imaging were analyzed. Eighty-three patients were eligible (median prostate-specific antigen level, 1.9 ng/mL). Results: Both PET examinations led to concordant results in 72% of patients, whereas the concordance of TNM staging between ⁶⁸Ga-PSMA PET and diagnostic CT was only 36%. Incorrect staging would lead to "wrong" treatment and therefore to additional costs. A ⁶⁸Ga-PSMA PET study would be cost-effective if additional costs do not exceed €3,844 ($4,312) (vs. CT). The number needed to image was 2 (for CT) and 4 (for ¹¹C-choline PET) to avoid 1 incorrect treatment. In addition, ⁶⁸Ga-PSMA PET staging enabled new curative options in half the patients with previous radiotherapy who otherwise receive palliative androgen deprivation therapy. Conclusion:⁶⁸Ga-PSMA PET/CT is cost-effective in all patients with regard to avoidance of incorrect treatment. It enabled new curative options for patients with previous radiotherapy who are usually treated palliatively. Therefore, ⁶⁸Ga-PSMA PET/CT staging should become standard for BCR after surgery with or without radiotherapy.

Keywords: 68Ga-PSMA PET/CT; SBRT; oligometastasis; prostate cancer.