PV QA 1 - Poster Viewing Q&A 1
Purpose/Objective(s): In prostate intensity-modulated radiotherapy (IMRT), genitourinary (GU) toxicity is an important problem not only at acute phase but at late phase. There are few reports about the international prostate symptom score (IPSS) after urethra-sparing (US) IMRT. The aim was to present the results of interim analysis on acute and late urinary toxicity using the IPSS after high-dose US-IMRT.
Materials/Methods: Forty patients with intermediate- or high-risk localized prostate cancer received US-IMRT, which included the prospectively designed investigation to evaluate GU toxicity with IPSS. Two gold fiducial markers were inserted into the prostate of each patient. The PTV were treated 80 Gy in 40 fractions with 5% dose reduction for urethral PRV. At planning CT, urethra was identified by 6-Fr catheter and urethral PRV was applied surrounding margin of 2 mm. GU toxicity were evaluated using the CTCAE v4.0, and IPSS were assessed at baseline, just after treatment and every 3–6 months thereafter. Statistical analyses were performed using univariate analysis.
Results: The median follow-up period was 31.5 (2–51) months. The IPSS sum at baseline, and 0, 12, 24, and 36 months after treatment course were 10.2 ± 1.1 (n = 40), 12.5 ± 1.3 (n = 40), 7.5 ± 0.8 (n = 31), 6.8 ± 0.6 (n = 29), 6.0 ± 1.4 (n = 11), with a tendency to gradually improve over time. The IPSS sum at baseline was found as a treatment parameter with better correlation to the change in IPSS after 24 months from univariate analyses. In contrast to the lower baseline IPSS sum group (baseline IPSS sum <10, n = 21) which has no significant change in IPSS during the follow-up period, the higher baseline group (baseline IPSS sum ≥10, n = 19) showed a continuous decrease in IPSS sum until 24 months. While it is reported that high-dose prostate IMRT gave rise to IPSS sum increase with ≥10 in >10% of all received patients after 24 months, our interim analysis revealed that there was only one out of 29 patients (3%) who presented IPSS sum increase with ≥10. Grade 2 acute GU toxicity was observed in 9 patients (22.5%). There was no G3 or higher toxicity in both of acute phase and late phase. These results are better than previous reports of toxicity in high-dose prostate IMRT.
Conclusion: US-IMRT is considered to be a better method to deliver a high irradiation dose to the prostate while preventing GU adverse events effectively.
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