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Fitting Bladder Doses to Acute Urinary Symptoms During Post-Prostatectomy Radiotherapy

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K Pearlstein

K Pearlstein*, J Dooley , S Saripalli , J Sun , S Das , R Chen , P Mavroidis , Univ North Carolina, Chapel Hill, NC


WE-G-FS1-4 (Wednesday, August 2, 2017) 4:30 PM - 6:00 PM Room: Four Seasons 1

Purpose: To determine the correlation of different dosimetric metrics with acute urinary symptoms during post-prostatectomy radiotherapy. To estimate the radiobiological parameters of three popular NTCP models that describe the dose-response relations of those symptoms.

Methods: 90 consecutive patients treated from 2010-2015 with post-prostatectomy image-guided IMRT were included in this study. Patient-reported urinary symptoms were collected pre-RT and weekly during treatment using the validated Prostate Cancer Symptom Indices (PCSI). The assessed symptoms were frequency, urinary urgency, flow, dysuria, nocturia, and leakage. For this analysis, an increase by ≥2 levels in a symptom at any time during treatment compared to baseline was considered clinically significant. The dose volume histograms of the whole bladder and those of the outer 5 mm shell of bladder were calculated. The Lyman-Kutcher-Burman (LKB), Relative Seriality (RS) and Logit NTCP models were used to fit the clinical data. The fitting of the different models was assessed through the area under the receiver operating characteristic curve (AUC) and the Odds Ratio methods.

Results: The AUC values between the V10-V50 bladder doses and the acute symptoms of urinary urgency, leakage, frequency and nocturia were highest (0.62-0.70). The derived LKB model parameters were: 1. D50=64.2Gy, m=0.50, n=1.0; 2. D50=95.0Gy, m=0.45, n=0.50; 3. D50=83.1Gy, m=0.56, n=1.00; and 4. D50=85.4Gy, m=0.60, n=1.00, respectively. The differences in the V10, V30 and V50 metrics between patients with and without toxicity were largest for the symptoms of frequency (38.4%, 25.7%, 10.9%) and nocturia (24.6%, 21.2%, 13.5%), respectively.

Conclusion: It was shown that low and medium dose-volume metrics to the bladder are correlated with acute worsening of urinary urgency, frequency, nocturia and leakage. Additionally, model parameter values were derived for four structures that correlated best with the symptoms examined.

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