Functional, Radiological Imaging and Biochemical (PET PSMA, MRI, ADC, PSA) Response and its Correlation in Low and Intermediate Risk Prostate Cancer Treated with SBRT by Robotic Radiosurgery Alone

Abstract

Robotic radiosurgery SBRT for Prostate cancer is popularizing due to good local control & low toxicity in low and intermediate risk patients. While PSA & MRI ADC values are established markers for diagnosis and response assessment, PSMA PET CT functional imaging is emerging as a promising diagnostic tool. PSA are susceptible to infections and poses challenges for response assessment and ADC values are usually change slowly and might not detect response in time. This study is an attempt to evaluate the non-inferiority of PSMA PET SUV values as a surrogate marker along with PSA and ADC values for response to robotic radiosurgery SBRT. Thirty-six patients of biopsy-confirmed early prostate cancer were retrospectively analysed. Patients underwent baseline and followup PSMA PET CT scan, MRI, ADC value, PSA. Patients underwent PSMA PET CT, MRI based SBRT by robotic radiosurgery planning to the GTV prostate to dose of 37.50 Gy in 5 fractions alternate day treatment. All 36 patients were analysed for PSA value, PSMA PET CT SUV of tumor, MRI prostate volume, ADC values. Wilcoxon signed rank tests were used. Among 36 patients, mean age was 64.2 years range 51-75 years. Eleven patients were low risk, and 25 were intermediate risk. Mean PSA at baseline, 3 months, 6 months, 12 months, and 24 months was 13.5 ± 7.5 ng/ml, 4.56 ± 5.71 ng/ml, 2.73 ± 1.77 ng/ml, 1.42 ± 1.25 ng/ml, and 0.66±.39 ng/ml, respectively. Mean PSMA PET CT SUV at baseline, 6 months, 12 months, and 24 months were 10.45±12.54, 3.76±1.74, 3.92±0.91, and 2.63±1, respectively. Mean ADC values at baseline, 6 months, 12 months, and 24 months were 0.7913±0.2108, 1.19±0.18, 1.32±0.23, and 4.28±1.06, respectively. Mean MRI volume at baseline, 6 months, 12 months, and 24 months were 4.4±1.2cc, 4.56±0.75cc, 4.42±4.77cc, and 4.28±1cc, respectively. Base line values were compared with their respective post treatment values using the Wilcoxon Signed Rank Test with appropriate Bonferroni corrections. Abstract SU_34_2333; Table 1PSAPSA3MTH- PSApresPSA6mth- PSApresPSA12mth- PSApresPSA24mth- PSApresZ-2.201bBased on positive ranks.-3.724bBased on positive ranks.-3.408bBased on positive ranks.-2.803bBased on positive ranks.Asymp. Sig. (2-tailed).028.000.001.005PSMA PETCT SUVSUV at 6months - SUV at PresentSUV at 12Months - SUV at PresentSUV at 24Months - SUV at Presentz-2.936bBased on positive ranks.-2.310bBased on positive ranks.-1.069bBased on positive ranks.Asymp. Sig. (2-tailed).003.021.285ADC6MMriAdc - DiagMriAdc12MMriAdc - DiagMriAdc12MMriAdc - 6MMriAdcZ-2.670bBased on positive ranks.-1.826bBased on positive ranks.-1.342bBased on positive ranks.Asymp. Sig. (2-tailed).008.068.180MRI6mmmri - Mrisize12mri - Mrisize24mri - Mrisizez-2.532bBased on positive ranks.-2.070bBased on positive ranks.-1.841bBased on positive ranks.Asymp. Sig. (2-tailed).011.038.066aWilcoxon Signed Ranks Test.b Based on positive ranks. Open table in a new tab aWilcoxon Signed Ranks Test. In our study there was a significant reduction in PSA, PSMA PETCT SUV, MRI Tumor Size and ADC values in 6 months of robotic radiosurgery SBRT. Hence, PSMA PET CT SUV values could be used as functional surrogate marker along with PSA biochemical marker earlier than MRI and ADC values. A prospective trial with PSMA done at 3 months is underway and a study with larger numbers may be required to generate stronger towards this conclusion.