3310 - Predictive Value of Pre- and Post-Treatment Tumor Apparent Diffusion Coefficient in High-Risk Prostate Cancer Patients Undergoing Definitive Radiotherapy: Long-Term Analysis from a Single-Institution Study

12:45pm - 02:00pm PT

Hall F

Screen: 20

POSTER

Presenter(s)

Huseyin Cem Onal, MD - Baskent University Faculty of Medicine, Adana, Yuregir

H. C. Onal^1,2, G. Erbay³, B. Demirhan⁴, A. Elmali¹, and O. C. C. Guler²; ¹Baskent University Faculty of Medicine, Department of Radiation Oncology, Ankara, Turkey, ²Baskent University Faculty of Medicine, Adana Dr Turgut Noyan Research and Treatment Center, Department of Radiation Oncology, Adana, Turkey, ³Baskent University Faculty of Medicine, Adana Dr Turgut Noyan Research and Treatment Center, Department of Radiology, Adana, Turkey, ⁴Iskenderun Gelisim Hospital, Hatay, Turkey

Purpose/Objective(s):

This study aimed to evaluate whether quantitative multiparametric MRI, performed before and after treatment, can predict biochemical outcomes and survival in high-risk prostate cancer patients receiving definitive radiotherapy (RT).

Materials/Methods:

The records of 186 high-risk prostate cancer patients who underwent definitive RT between September 2010 and January 2023 were retrospectively analyzed. Inclusion criteria included a minimum follow-up of 24 months, at least 12 months of ADT, and treatment with pelvic RT plus prostate RT of at least 78 Gy. A radiologist delineated the index lesion and normal prostate tissue, measuring apparent diffusion coefficient (ADC) values. The primary endpoints were biochemical disease-free survival (bDFS) and prostate cancer-specific survival (PCSS). Kaplan-Meier survival estimates and Cox proportional hazards models were used to identify independent predictors.

Results:

Post-treatment diffusion-weighted MRI (DW-MRI), performed at a median of 4.1 months after RT, showed a significant increase in tumor ADC values (0.712 ± 0.140 vs. 1.002 ± 0.189 × 10?³ mm²/s; p < 0.001) with no significant change in normal prostate tissue (p = 0.44). The median follow-up was 10.7 years (IQR: 9.8–11.5 years). The 8-year bDFS and PCSS rates were 86.1% and 87.1%, respectively. Patients with disease progression had significantly lower post-treatment ADC values (0.876 ± 0.174 vs. 1.029 ± 0.181 × 10?³ mm²/s; p < 0.001), whereas pre-treatment ADC values were not predictive. Receiver operating characteristic (ROC) analysis showed post-treatment ADC values had significant predictive value (AUC = 0.724, p < 0.001 for progression; AUC = 0.696, p = 0.001 for prostate cancer mortality). A post-treatment ADC cutoff of 0.939 × 10?³ mm²/s was identified for predicting disease progression and mortality. Univariate analysis identified ISUP grade, treatment with simultaneous integrated boost (SIB), ADT duration, and post-treatment ADC values as significant prognostic factors for bDFS and PCSS. Serum PSA levels were also predictive of bDFS. Patients with lower post-treatment ADC values (<0.939 × 10?³ mm²/s) had significantly worse 8-year bDFS (75.2% vs. 93.8%; p = 0.003) and PCSS (79.8% vs. 92.5%; p = 0.03). In multivariable analysis, higher PSA levels (=20 ng/mL), ISUP grade 4–5, and shorter ADT duration (=18 months) were independent predictors of worse bDFS and PCSS. Post-treatment ADC value was an additional independent predictor for worse bDFS.

Conclusion:

Post-treatment tumor ADC values were significantly associated with bDFS and PCSS in high-risk prostate cancer patients, whereas pre-treatment ADC values had no prognostic significance. Lower post-treatment ADC values correlated with worse outcomes, highlighting their potential role as an imaging biomarker for risk stratification and treatment optimization.