The Predictive Role of Multiparametric MR imaging after Salvage Radiation Therapy for Local Failure after Radical Prostatectomy


      To assess the predictive role of multiparametric MR imaging (mpMRI) in the setting of salvage RT (sRT) for a presumed local failure after radical prostatectomy (RP).


      This is a cross-sectional study including all patients treated with sRT at a single Institution from Feb 2014 to Sept 2016. All patients had failed biochemically after RP and underwent pre-sRT mpMRI (including a dynamic contrast-enhanced-DCE MRI) on a 3-T system with the evidence of a presumed local recurrence. All patients were treated with a homogeneous approach delivering 73.5 Gy and 69 Gy to the nodule and to the prostatic bed, respectively, in 30 fractions (IGRT-VMAT, SIB technique). Patients underwent a re-evaluation mpMRI at the time of the study. Patients without a complete response (CR), underwent repeated mpRM at 3-6 month-intervals until CR and/or a maximum of 3 repeated mpMRI. CR was defined as complete disappearance of the nodular area of early contrast enhancement in DCE-MRI or persistence of an area of contrast enhancement with a slower wash-in rate and/or a hypointense (more than muscles) appearance on T2-weighted sequence. On baseline DCE-MRI, the wash-in and wash-out were derived from the whole-volume time-intensity curve using home-made software as per Casciani et al, AJR, 2008. The two-sided Mann–Whitney rank test was used to compare the variables. Receiver operating characteristic (ROC) curves were performed for the most significant DCE-MRI parameters.


      Thirty-seven patients were identified. The mean (SD) time interval between RP and sRT was 71.1 (58.1) mths. At sRT, mean (SD) serum PSA was 1.47 (1.58) ng/ml and the mean (SD) volume of the recurrence delineated on mpMR plus a 8 mm margin (rPTV) was 12.5 cc (6.3 cc). Eleven (29.7%) patients received also androgen deprivation (AD). All patients ended up showing a complete response, 28 (75.7%), 7 (18.9%) and 2 (5.4%) at the 1st, 2nd or 3rd re-eval mpMRI. The mean (SD) time from the end of sRT to CR was 16.5 (10.0) and 24.1 (5.8) mths for patients who responded at the 1st mpMRI (N=28) vs the slower ones (N=9), p= 0.0436. Compared to slower responders, patients achieving a CR at the 1st re-eval mpRM had significantly smaller rPTVs (9.4cc vs 13.1cc, p=0.0214) and a trend towards lower pre-sRT PSA values (1.21 vs 2.28, p=0.06). However, the stronger correlation was found for the wash-out parameter with a lower value highly predicting a delayed response (0.06 s-1 vs -0.99 s-1,continuum, p=0.0087). The sensitivity and specificity of the wash out parameter were 78.6% and 75%, respectively (area under ROC curve 0.808 p=0.0001, cut-off value ≥0.46 s-1). No correlation was found between time to response and AD (p= 0.3030).


      sRT is highly effective in achieving a complete response at mpMRI. There is a strong correlation between the time to response and baseline wash-out features.


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