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PSA outcome after metastasis directed therapy (MDT) of oligometastatic prostate cancer patients diagnosed by 68Ga-PSMA-PET/CT


International Journal of Radiology & Radiation Therapy
Christoph Dumke, Farshin Mortasawi, Markus Thiemer, Stefan Lautenschläger, Alexandra Jensen, Rita Engenhart-Cabillic

Abstract

Background: Metastasis Directed Therapy (MDT) of oligometastatic prostate cancer (OPCa) is an emerging treatment option which may delay systemic therapy and its side effects. Identifying OPCa patients suitable for local treatment by imaging modalities with a high sensitivity and specificity is crucial. Therefore, we analyzed PSA outcome after MDT of OPCa patients diagnosed by 68Ga-PSMA PET/CT retrospectively.
 
Methods: Overall 20 OPCa patients with ≤3 metastases in 68 Ga-PSMA PET/CT treated with radiotherapy (RT) doses >50 Gy (EQD2, α/β=2) were identified. Biochemical progression free survival (bPFS) was calculated with Kaplan Meier method. After stratifying patients by clinical and pathological parameters, differences in bPFS were compared using log rank tests. Cox regression analysis was performed to identify predictors of bPFS. Toxicity was assessed using CTCAE (V.4).
 
Results: A total of 31 metastases were treated. Localizations were pelvic lymph nodes (n=21), and bones (n=9) of which were pelvic bones (n=4), ribs and sternal (n=3), vertebral body (n=2). On patient had a metastasis of the penis (n=1). The median follow-up was 13.5 months (3–48) with an overall survival of 100%. A treatment response was detected in 18/20 (90%) patients. The median PSA of 1.47ng/ml (0.38–8.82) prior to MDT decreased significantly to 0.20 ng/ml (0.0–1.93) after treatment (p<0.001). For the entire cohort (n=20) median bPFS was 14 months (9.3–18.7). Patients with solitary metastases had a significant longer bPFS with mean 20.2 months (10.6–29.9) compared to 9.7 months (4.9–14.6) for those with 2-3 metastases (p=0.037). Furthermore, patients without additional ADT and 2-3 metastases in 68Ga-PSMA PET/CT had a significant higher risk for PSA progression after MDT (HR 10.928, CI 1.053–113.421, p=0.045). Of 20 patients 9 (45%) had acute toxicity I° and 1 patient (5%) also experienced acute toxicity II°. Late toxicities I° occurred in 1 patient (5%). No acute or late toxicities >II° were observed.
 
Conclusion: Using PSMA-PET/CT guided RT for MDT of OPCa led to a significant decrease in PSA-levels with minimal therapy associated toxicity. Especially patients with solitary metastases may benefit from this treatment approach. However, randomized trials with larger patient collectives are necessary.

Keywords

prostate cancer, oligometastasis, metastasis directed therapy, radiotherapy, 68 GA-PSMA-PET/CT, biochemical recurrence, radiotherapy toxici

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