3164 - Apparent Diffusion Coefficient as an Early Prognostic Factor of Response to Treatment with Androgen Deprivation Therapy and Radiotherapy in Patients with Prostate Cancer

V. Duque-Santana¹, J. Fernandez Mata², A. A. Diaz-Gavela³, M. Recio², M. Peña Huertas³, S. Sanchez⁴, L. Guerrero⁴, D. Sanz-Rosa⁵, I. J. Thuissard⁶, C. Andreu-Vázquez⁵, F. Lopez⁷, V. Diez Nicolas⁸, E. del Cerro⁹, and F. Counago¹⁰; ¹Department of Radiation Oncology, Hospital Universitario Quiro´nsalud Madrid and Universidad Europea de Madrid, Madrid, Spain, ²Department of Radiology, Hospital Universitario Quironsalud Madrid, Madrid, Spain, ³Department of Radiation Oncology, Hospital Universitario Quironsalud Madrid, Madrid, Spain, ⁴La Luz Hospital. Radiation Therapy Department, Madrid, Spain, ⁵Medicine Department, School of Biomedical Sciences, Universidad Europea, Madrid, Spain, ⁶Department of Biomedical and Health Sciences, Universidad Europea de Madrid, Madrid, Spain, ⁷Department of Radiation Oncology, Hospital Universitario Ramon y Cajal, Madrid, Spain, ⁸Department of Urology, Hospital Universitario Quironsalud Madrid, Madrid, Spain, ⁹Quironsalud Madrid University Hospital. Radiation Therapy Department, Madrid, Spain, ¹⁰San Francisco de Asís and La Milagrosa Hospitals. National Chair of Research. GenesisCare Spain, Madrid, Spain

Purpose/Objective(s): To analysed the Apparent Diffusion Coefficient (ADC) as an early prognostic factor of response in patients with prostate cancer treated with radiotherapy (RT) and androgen deprivation therapy (ADT). Materials/

Methods: All prostate cancer patients classified as high or very high and unfavorable intermediate-risk according to NCCN criteria that received ADT and RT between 2008 and 2019 in whom an multiparametric magnetic resonance imaging (mpMRI) was performed were included. The ADC values were calculated by mpMRI performed 6 months after RT. We assessed the differences in the mean ADC values between patients with or without progression and/or local relapse after 10 years. Receiver-operating characteristics (ROC) analysis were used to obtain ADC cut-off values to predict 10y-progression-free survival and 10y-local progression survival in these patients. Additionally, differences in ADC values between diagnosis and post-RT were assessed.
Results: We retrospectively evaluated 98 consecutive patients, 25(25.5%) patients were intermediate-risk and 73 (74.5%) patients were high-risk. The median PSA at diagnosis was 10.15ng/ml [6.93-21]. After a mean follow-up of 95.36 months (SD:30.54), 19 (19.39%) patients progressed,10y biochemical relapse-free survival was 76.5%, 10y-PFS was 75.6%, 10y-LRFS was 93.8%, 10y metastatis-free survival was 85.5%, 10y overall survival was 89.5%. The mean ADC values at diagnosis and post-RT was 0.81±0.18 vs 1.30±0.18 x10^-3 mm²/sec, respectively (p<0.001); and the mean relative increase in ADC values was 70.11% (SD:46.80). A statistically significant difference in post-RT ADC values was noted between patients with and without recurrence (1.20 ±0.10 vs 1.30±0.20 x10^-3 mm²/sec, p=0.004). We also found significant differences in ADC values between patients with and without local relapse (1.10±0.10 vs 1.30±0.20 x10^-3 mm²/sec, p=0.020). The ROC analysis identified post-RT ADC cut-off point of 1.24x10^-3 mm²/sec for progression (area under curve (AUC) 0.705, sensitivity (S)72.2%, positive predictive value (PPV): 87.69%)) and a cut-off point of 1.11x10^-3 mm²/sec for local relapse (AUC: 0.843, S:89.4%, PPV: 98.82%). 10-y LRFS was 66.8% and 97.7% in patients with post-RT ADC values below and above 1.11x10^-3 mm²/sec, respectively (HR:724.8 [31.28-16.793]; p<0.001). 10-y PFS was 58.6% and 85.6% in patients with post-RT ADC values below and above 1.24 10-3 mm2/sec (HR: 2.916 [1.113-7.644] p=0.015). Patients whose ADC values increased >95% between diagnosis and post-RT had a lower risk of relapses (4.76% vs.26.56%, p < 0.001).
Conclusion: This is the first study with a long follow-up that shows that post-RT ADC value could be used as a prognostic factor of response in patients with prostate cancer treated with radiotherapy and ADT.