ESTRO 2020 Abstract book

S396 ESTRO 2020

correlation coefficient (ICC). The ICC and confidence intervals (CI) were stratified to indicate poor (ICC CI < 0.5), moderate (0.5 < ICC CI < 0.75), good (0.75 < ICC CI < 0.9) and excellent (ICC CI > 0.9) agreement. The agreement between features using default package parameters versus setting the same parameters (64 grey levels, Chebyshev distance 1) for the IBSI-compliant packages was also assessed. The impact of different packages on the prognostic value of the 17 radiomic features was investigated by comparing univariable cox models predicting survival for patients with H&N cancer. The Benjamini-Hochberg method was applied. Results The agreement of features between all four packages was only excellent for volume, and the maximum and mean intensity in both datasets (Table 1). Stratification of agreement was consistent across H&N and lung cancer for 10/17 features. Where disagreement occurred the agreement tended to be worse in the H&N dataset. When comparing IBSI-compliant packages only, the agreement was improved only when the same parameters were used per package. A calculation error for sphericity was identified in one package which is in the process of being corrected by the vendor following these results.

feature GLCM joint entropy calculated in each package, split on the median. The risk stratification is significant for GLCM joint entropy calculated in LIFEx, PyRadiomics and CERR (p=0.01, 0.013, 0.0095 respectively), but not in IBEX (p=0.64).

Conclusion IBSI-compliance improves feature repeatability between software packages, given the same parameters are used, and this improves prognostic model quality. It is important 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-

6 texture features were significant (p<0.05) for survival when calculated in LIFEx, PyRadiomics and CERR, but not IBEX. Figure 1 presents Kaplan-Meier analysis for the