ESTRO 2021 Abstract Book

S1068

ESTRO 2021

Conclusion The inclusion of both weight loss and metastasis status independently improved the predictive power of initial cancer stage. A simple cutoff value of the predicted hazard ratio allows identification of a group of patients most likely to fail treatment. Intensification of treatment for this patient population should be investigated. PO-1298 Parameters predicting intestinal toxicity in cervical cancer patients with adjuvant radiotherapy B. Xu 1 1 The Second Affiliated Hospital of Soochow University, Radiotherapy & Oncology, Suzhou, China Purpose or Objective Postoperative adjuvant radiotherapy for cervical cancer reduces local recurrence in patients with adverse risk factors; however, treatment-derived toxicity is concerning. The most common one is intestinal toxicity among them. We aimed to identify dose–volume variables to predict acute intestinal toxicity for postoperative adjuvant radiotherapy in cervical cancer. Materials and Methods We retrospectively evaluated 93 patients who underwent postoperative adjuvant IMRT radiotherapy for cervical cancer with relevant dose–volume parameters available for analysis from March 2014 to December 2017.All patients were treated on Elekta Synergy Linear Accelerator (Elekta Oncology Systems, Crawley UK) with median prescribed dose of 50Gy (range 45.0-50.4Gy). The delineated organs at risk were the small bowel loops, large bowel loops, bowel loops (small + large bowel loops), rectum, and bladder. The dose–volume parameters analyzed comprised the volume of the organs receiving >5, >10, >15, >20, >25, >30, >35, >40, and >45 Gy of radiotherapy. Grade 2 and above acute intestinal toxicities were designated as clinically significant according to the RTOG criterion. The association between the irradiated bowel volume and acute intestinal complications was analyzed. Logistic multivariate analysis to determine independent predictors on relevant dosimetry parameters. Receiver operating characteristic curve (ROC) was used to identity the most relevant threshold ; and acute intestinal complications probability was calculated using binary logistic regression analysis. Results Among the 93 patients, 26 (28%) experienced grade ≥2 acute intestinal complications with median follow-up time of 6 months. A strong relationship between grade ≥2 acute intestinal complications and the irradiated small bowel volume was observed at each dose level from 0-15 Gy. None of the parameters of the large bowel, whole bowel (small + large bowel), and rectum significantly correlated with acute intestinal toxicity. The volume receiving 10 Gy (V10) had the most strongest validity on grade ≥2 intestinal toxicity(HR,1.028; 95 ％ CI,0.993-1.062; p=0.029).The optimal threshold of small bowelV10 is 307.20 cc(specificity: 0.43, sensitivity: 0.88),the speculated incidence of acute intestinal toxicity is 22%. Conclusion We clarified an important dosimetric association between the small bowel V10 and grade ≥2 acute intestinal complications. When planning intensity-modulated radiation therapy for postoperative adjuvant radiotherapy in cervical cancer, restricting V10 for the small bowel loops to <307cc to minimize grade ≥2 acute intestinal toxicity to <22% can be useful. PO-1299 Outcomes of cervical cancer patients treated with hybrid CT-X Ray based intracavitary applications. P. Sawant 1 , L. Gurram 1 , J. Mathew 1 , M. J 1 , S. Chopra 1 , D. A 2 , Y. Ghadi 2 , J. Ghosh 3 , S. Gupta 3 , S. Gulia 3 , S. TS 4 , A. Maheshwari 4 , U. Mahantshetty 5 1 Tata Memorial Centre, Radiation Oncology, MUMBAI, India; 2 Tata Memorial Centre, Medical Physics, MUMBAI, India; 3 Tata Memorial Centre, Medical Oncology, MUMBAI, India; 4 Tata Memorial Centre, Gynecologic Oncology, MUMBAI, India; 5 Homi Bhabha Cancer Hospital and Research Centre, Radiation Oncology, Visakhapatnam, India Purpose or Objective (1) PURPOSE : To evaluate oncological outcomes in locally advanced cervical cancer (LACC) patients treated with external beam radiotherapy (EBRT) and intracavitary brachytherapy (ICBT) (CT- X ray or CT-CT approach). To dosimetrically correlate OAR doses in CT planning with X ray planning and assess late gastrointestinal and genitourinary toxicities. Materials and Methods (2) METHODS AND MATERIALS : This is a retrospective study of LACC treated between 2015-2019 at our