ESTRO 2023 - Abstract Book

S1895

Digital Posters

ESTRO 2023

the results, without changing the model, i.e. the p values and the AUC are unaffected. In the current analysis, the difference between raw- and normalised odds ratios is studied in a set of published multivariable models, and in a model of post-operative pulmonary complications (POPC) for patients with oesophageal cancer treated with neoadjuvant chemoradiotherapy in our institution. Materials and Methods A retrospective analysis of 94 patients with oesophageal cancer treated with chemoradiotherapy followed by surgery was performed. Clinical and dosimetric variables were collected from a local quality registry and the radiotherapy treatment planning system. Multivariable logistic regression was performed, considering the damaged volume (DV) parameter (in cm3) from the critical volume model, in combination with ASA score and type of surgery. Normalisation of the regression coefficient was performed by multiplication with the standard deviation of the DV parameter in the cohort. The study was approved by the national ethics review authority. For comparison, examples of multivariable models including dose/volume predictors were collected from the literature and the published regression coefficient of continuous variables normalised by multiplication with the standard deviation. Results Fourty patients (43%) suffered from POPC. Absolute lung DV was a significant predictor in univariable analysis (p=0.03), but not in multivariable analysis (Table 1). However, while the raw odds ratio implies an extremely low dependence of POPC on the DV parameter, the normalised odds ratio reveals a more similar relative importance of the three explanatory variables. Given the large standard deviation of the DV parameter measured by the default volume unit this effect was particularly strong. A similar pattern was seen in the examples from the literature (Table 2). The mean raw odds ratio for dose/volume variables was 1.044 (per Gy, cm3 or %), while the mean normalised (unitless) odds ratio was 1.45.

Conclusion The apparent relative importance of continuous variables in multivariable models, in terms of odds ratios, depends on the selected unit of the variable. Thus, the assessment of the role of dose/volume parameters in predictive models is facilitated by the reporting of normalised odds ratios alongside raw odds ratios.

PO-2111 The role of combined radiomics features as predictor of response to CRT or BRT in patients with OPC

H. Inokuchi 1 , N. Mukumoto 1,1 , M. Sakagami 1 , M. Yamagishi 1 , N. Hamaura 1 , H. Itoyama 1 , S. Matsuda 1 , K. Shibuya 1

1 Osaka metropolitan university, Radiation oncology, Osaka, Japan

Purpose or Objective Minimally invasive therapies have been developed for HPV-associated oropharyngeal carcinoma (OPC), but prognostic factors and optimal patient selection are not clear. We evaluate the prognostic value of radiomics combined features based