Abstract
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Introduction: It has been postulated that the molecular response evaluated by PET-CT with 18F-Fluxesoxyglucose (FDG) may be a useful tool in the evaluation of bone metastases response; however, compared with the radiotracer sodium fluoride (18F-NaF), it has been shown to be superior for the detection of blastic metastatic disease; because the mechanism of incorporation into the blastic lesions is very similar to Radium-223 (223Ra); The recent introduction of 68Ga-PSMA (prostate-specific membrane antigen) has been particularly useful in patients with suspected visceral disease. AIM:The purpose of this study is to determine if PET-CT with 18F-NaF and 68Ga-PSMA can predict response to 223Ra treatment.
Methods: From November 2014 to July 2019, thirty-seven patients with metastatic castration-resistant prostate cancer (mCRPC), and seven patients with high-grade prostate cancer (hgPC), were evaluated with 18F-NaF and 68Ga-PSMA PET-CT prior to receipt 223Ra therapy a standard dose (55kBq/kg), and 4-6 weeks after the last dose, with simultaneous measurements Prostate specific antigen (PSA) and alkaline phosphatase (AP). A semiquantitative analysis of each patient allowed to establish 3 study groups based on the molecularly active volume: low-overall burden (<1000 cm³), medium-overall burden (1001-3000 cm³); and high-overall burden (> 3001 cm³). Thus, 25 patients were classified as high burden, 9 patients as medium burden and 10 patients as low burden.
Results: Twenty-nine patients completed 6 cycles (7-hgPC, 22-mCRPC), of which 19 were of low burden and 10 of medium burden, which showed a decrease in PSA and AP levels (p <0.05); Of the other patients we obtained variable results according to the number of doses; the value of 18F-NaF and 68Ga-PSMA as a predictive tool in response therapy according to the degree of overall tumor burden. Patients with low burden treated with 223Ra showed to be a predictor of good prognosis in response to treatment (p <0.05); while patients with high burden have a high probability of do not complete the 6 cycles.
Conclusions: The PET-CT in the evaluation of response to 223Ra is an extremely useful tool in the selection of those patients who are likely to improve according to their degree of overall tumor burden, in addition to timely evaluation of therapeutic efficacy.
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