The impact of the apparent diffusion coefficient for the early prediction of the treatment response after definitive radiotherapy in prostate cancer patients.

• Serum PSA value may be of limited value in determining the true treatment response after RT. • An early PSA response at 4 months in low/intermediate disease risk may not be indicative of treatment response. • The role of ADC value in treatment response evaluation after definitive RT is not well known. • A total of 229 low- and intermediate-risk PC patients treated with RT were analyzed. • Post-treatment mean ADC values were lower in patients with recurrence than in those without recurrence. We assessed early changes in apparent diffusion coefficient (ADC) and serum prostate specific antigen (PSA) values after definitive radiotherapy (RT) without androgen deprivation treatment in low- and intermediate-risk prostate cancer (PC) patients. The clinical data and ADC parameters of 229 PC patients were retrospectively evaluated. Pre-treatment and post-treatment serum PSA and primary tumor ADC values were calculated. Post-treatment DW-MRI was performed median 4.1 months after completion of definitive RT. The prognostic factors predicting freedom from biochemical failure (FFBF) and progression-free survival (PFS) were analyzed using univariable and multivariable analyses. With a median follow-up time of 80.8 months, the 5-year FFBF and PFS rates were 95.9% and 89.3%, respectively. Eleven patients (4.8%) had PSA relapse, with a median of 34.4 months after the completion of RT. A statistically significant difference in post-treatment ADC values was noted between patients with and without recurrence (0.94 ± 0.07 vs. 1.10 ± 0.20 × 10-3 mm2/sec; p< 0.001). Patients with a Gleason score (GS) of 6 and low-risk disease had significantly higher post-treatment tumor ADC and PSA levels than patients with a GS of 7 and intermediate-risk disease. The 5-year FFBF rate in patients with tumor ADC ≤ 0.96 × 10-3 mm2/sec was significantly lower than patients with tumor ADC > 0.96 × 10-3 mm2/sec (85.5% vs. 100; p< 0.001). In the multivariable analysis, a lower ADC value, GS 4 + 3 and intermediate-risk disease were independent predictors of worse FFBF. In the multivariate analysis, a lower post-treatment ADC value and a GS of 4 + 3 were significant prognostic factors for a lower PFS. These findings suggest that the post-treatment tumor ADC value could be used for early treatment response evaluation after definitive RT in PC patients. [ABSTRACT FROM AUTHOR]