PV QA 4 - Poster Viewing Q&A 4
Purpose/Objective(s): To evaluate whether our institutional approach of less than whole uterus (LTWU) irradiation affects locoregional control (LRC) in patients with advanced cervical cancer undergoing definitive concurrent chemoradiation.
Materials/Methods: We retrospectively reviewed 48 patients with locally advanced cervical cancer treated at our institution between 2011 and 2017. All patients had a PET-CT planning scan and were treated with image-guided IMRT followed by brachytherapy. The entire uterus was not included in the CTV, per our institutional standard, however, depending on the size of the GTV, variable amounts of uterus ultimately received the prescription dose. Dosimetric parameters were obtained, including: GTV PET tumor volume, uterus volume excluding GTV, proportion of uterus receiving the prescription dose (%), volume of overlap between uterus and prescription dose (cc), minimum and mean dose to the uterus, and bowel V40 and D200cc. Local, regional (pelvic and para-aortic), and distant failure and death were recorded. The relationship between all failures and individual continuous predictors was analyzed in a logistic regression model. A Student’s t-test was performed to assess for differences in bowel dose based on proportion of uterus included in the PTV. Overall survival time was analyzed using a Kaplan-Meier method. Time to any failure was analyzed using competing risk analysis with death as the competing risk.
Results: A total of 48 patients were included in the analysis. Median age was 52 years and 56% (n=27) had lymph nodes involved on imaging at the time of diagnosis. Most (n=36, 75%) had FIGO stage IIB disease or higher. Median follow-up time was 22 months (range 2-74 months). A total of 15 patients recurred. There was 1 local failure, 5 regional failures, 1 para-aortic failure, and 11 distant failures. Median time to any failure was 20.5 months. A total of 6 patients died. Median time to death was 66 months. The 2-year incidence of locoregional failure (LRF) was 10.2% (95% CI, 3.1% - 22.2%), which compares favorably to the 9.5% LRF rate seen in the INTERTECC-2 trial. Median proportion of uterus included in the PTV was 63% (range 18-100%). Logistic regression analysis did not reveal any significant correlations between dosimetric parameters and failure, except for a trend towards increased incidence of any failure with increasing GTV PET tumor volume (p=0.086; 95% CI, 0.986-1.017). Compared to patients who had ≥90% of the uterus included in the PTV (n=10), those who had <90% (n=38) of the uterus irradiated had borderline significant lower bowel V40 (p=0.051) and D200cc (p=0.061).
Conclusion: LTWU irradiation for advanced cervical cancer does not compromise LRC and reduces bowel V40 and D200cc. Further investigation is required to evaluate whether this reduction in bowel dose translates to a clinically significant reduction in bowel toxicity and whether modifications should be made to recommended definitive cervix IMRT volumes.
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