The IMPACT of 68GA-PSMA-PET in definitive radiotherapy planning for prostate cancer patients.

Abstract

79 Background: The implementation of 68Ga-PSMA-PET-imaging for staging and the impact on stage adaption during treatment radiotherapy (RT) planning is not well studied yet. The present work is to evaluate the integration of 68Ga-PSMA-PET into standard RT planning and to determine the influence on staging and on changes in the initially planned treatment concept for definitive RT in prostate cancer patients. Methods: A total of 66 prostate cancer patients with PSMA-PET delivered before treatment were retrospectively analyzed. All patients had bone scintigraphy and magnetic resonance imaging (MRI) of abdomen (52 patients; 79%) or thoraco-abdominal computed tomography (CT) (14 patients; 21%). After PSMA-imaging, all information was reviewed and re-classification was performed with the additional information taken into account. Thereafter, patients were evaluated with the information obtained by PSMA-PET imaging led to a change in staging and subsequently resulted in a change of the RT concept and treatment fields. Results: Median age of patients was 66 years (range 46 – 84 years). Median pretreatment PSA level was 25.2 ng/mL (range 4.4 – 130.8 ng/mL). The initial stage was changed in 27 patients (41%); 8 patients (12%) under-staged, 11 patients (17%) over-staged and 8 patents (12%) had distant metastasis. RT fields changed in 9 patients (14%) and RT cancelled because of distant metastasis detected with PSMA-PET in 6 patients (9%). The mean pretreatment PSA values were significantly higher in over-staged patients or patient with distant metastasis compared to under-staged patients (55.0±38.8 ng/mL vs. 28.1±19.1 ng/mL; p = 0.02). Also upstaging was observed more frequently in patients with ≥ T3a disease compared to patients with < T3 disease (15 patients [56%] vs. 4 patients [15%]; p = 0.04). However, Gleason score and primary tumor SUV had no significant impact on stage change and particularly on RT decision and treatment plan changes. Conclusions: The performance of a PSMA-PET frequently leads to changes in the stage, altering the RT treatment regimen especially in patients with extensive stage disease and higher pretreatment PSA values.