ESTRO 2020 Abstract Book

S363 ESTRO 2020

that different software packages are transparent about the precise features they calculate. Further, investigators should be aware of potential uncertainties introduced by differences in the way mathematically identical features are implemented. PH-0653 Sacrum D30% >38.8Gy3 predicts for insufficiency fracture following pelvic chemo- radiotherapy R. Mir 1 , A. Dragan 2 , Y. Tsang 1 , A. Padhani 2 , P. Hoskin 1 1 Mount Vernon Cancer Centre, Clinical Oncology, Middlesex, United Kingdom ; 2 Paul Strickland Scanner Centre, Radiology Department, Middlesex, United Kingdom Purpose or Objective Sacral insufficiency fracture (IF) following pelvic concurrent chemo-radiotherapy (cCRT) is a known late toxicity, with incidence between 10 – 89%. Age >50 years, female sex, and osteoporosis are established risk factors. Radiotherapy delivery techniques are advancing, the impact of contemporary techniques and variations in patient anatomy on the development of IF are poorly understood. This study evaluates the impact of fixed field intensity modulated radiotherapy (FF-IMRT), non-adaptive arc (Non-AA), and adaptive arc (AA) treatment delivery on the probability of sacral IF. Material and Methods Patients who received radical or adjuvant pelvic cCRT (45– 50.2Gy/25–27#) at a single center between 2014-2019 for gynaecological malignancy with or without simultaneous integrated boost (SIB) (60Gy) to positive lymph nodes and high-dose rate brachytherapy were identified. The sacrum was manually contoured on the radiotherapy planning CT along with the site of IF as identified by an experienced radiologist on the routine 3, 12, and 24-month follow-up T1-weighted MRI and STIR sequence. Sacral slope and sacral volume (cc) were recorded. IF were graded for severity on predefined MRI criteria.Dosimetric data (maximum, minimum, mean, D10 % –100 % , V15 Gy –V60 Gy ) for sacrum and IF were converted to an equivalent dose in 2- Gy fractions (EQD 2 ) using a α/β of 3for bone.Demographic, anatomical, and dosimetric data were analysed for correlation with IF. Results 115 patients were identified. The median imaging follow- up period was 12.0 months (range 3-47 months). The median age was 54 years (range 21-86 years); 50 patients (43.8%) were pre-menopausal. 57 (49.6%) had an SIB to 60Gy; in 14 instances the SIB planning target volume (PTV) abutted the sacrum, in 10 instances the SIB PTV overlapped the sacral contour. Overall 43 (37.4%) had sacral IF on imaging, with a median of 2 IF per patient (range 1-3); 19/36 (52.8%) with FF-IMRT, 6/26 (23.1%) with Non-AA, and 18/53 (34.0%) with AA. The absolute minimum and maximum radiotherapy dose to contoured IF sites were 28.9Gy (range 11.5-46.3Gy), and 44.1Gy (range 30.2- 67.0Gy). On Univariate analysis, age ≤50 years, post- menopause, sacrum V40 Gy >37.2%, and sacrum D30 % >38.8Gy 3 were predictors for sacral IF (table).

Multi-variate analysis demonstrated age ≤50 years HR 0.3 (95% CI 0.15-0.64 p=0.02) and sacrum D30 % >38.8Gy 3 HR 2.22 (95% CI 1.19-4.14 p=0.01) as independent factors in the development of sacral IF. Sacral volume (p=0.54), sacral slope (p=0.17), radiotherapy delivery technique (p=0.86), and SIB (p=0.84) were not associated with development of sacral IF. Conclusion Sacrum D30% >38.8Gy 3 along with age >50 years are independent predictors for sacral IF following radical or adjuvant pelvic cCRT for gynaecological cancer. Anatomical variations, radiotherapy delivery technique, and SIB did not impact on the development of IF. PD-0654 The Correlation Between Linoleic Acid Metabolic Pathway and Nutritional Risk of Radiation Enteritis C. Ma 1 , X. Xu 1 , M. Zhang 2 , X. He 1 , S. Qin 1 , J. Zhou 1 1 The First Affiliated Hospital of Soochow University, Dept. of Radiotherapy & Oncology, Suzhou, China ; 2 The First Affiliated Hospital of Soochow University, Dept. of Clinical Nutrition, Suzhou, China Purpose or Objective Radiation enteritis is the most common adverse effect after radiotherapy (RT) in cervical cancer, which may lead to nutritional risks in some degrees. Lionoleic acid is an essential fatty acid of the human body, and its metabolic pathway invovled in the lipid metabolism of the intestine and is closely related to diary nutrition. This study aimed to investigate the relationship between changes of intestinal metabolite expression in the fecal samples from cervical cancer patients and radiation-induced intestinal symptoms during radiotherapy. Material and Methods A total of 50 cervical cancer patients who received radiotherapy in our hospital from September 2017 to June 2018 and 15 healthy female controls were enrolled. The information of body weights, body fat contents, scheletal muscle masses, body mass indexes (BMI), body fat percentages and phase angles on the baseline and after radiotherapy were collected and analyzed with general linear model and paired t test. The NRS2002 scale was used to screen and evaluate the nutritional risks of patients at the same time. Fecal samples were collected from patients at four time points during radiotherapy, i.e. baseline, 2 weeks post-RT starting, 4 weeks post-RT starting and ending of RT, and the control group on the baseline, respectively. The samples were analyzed by non- targeted metabolomics using liquid chromatography-mass spectrometry (LC-MS). Data were analyzed with statistical methods including partial least squares-discriminant analysis (PLS-DA), agglomerate hierarchical clustering to investigate the trend of metabolites expression in feces, and finally with Spearman rank correlation to investigate the relationship between metabolite changes and nutritional risks. Results There were no significant differences between cervical cancer patients and the control group on the baseline. After radiotherapy, nutritional risks were noted in 86% cervical cancer patients (46/50), and the decreases in body weights, scheletal muscle masses, BMI and phase angles were statistically significant ( P <0.05). In the mean time, fecal supernatent samples were detected by the Poster discussion: CL: Gynaecology