ESTRO 2022 - Abstract Book

S213

Abstract book

ESTRO 2022

Materials and Methods IBDM was applied to data from 104 oropharyngeal cancer patients treated with definitive (Chemo)RT and assessed for swallow function pre-treatment and at 1 year by a Swallow Assessment Specialist. We spatially normalised all patient’s planning dose matrices (in equivalent dose at 2Gy/fraction, α / β =3Gy) to three arbitrary reference anatomies using a combination of thin-plate splines deformation (for neck alignment) and NiftyReg. To reduce target laterality bias, all patients were mirrored in the left-right axis and mapped twice to the reference patient. Regions where the dose was associated with outcome at 1 year were found by performing voxel-wise statistics (t-test for WT, Spearman correlation for MDADI/HN-PSS) and permutation testing (n=1000). Mean and maximum doses of the overlap of the significant regions for all outcomes were averaged across the three reference patients. Clinical factors, treatment variables and pre-treatment measures for WT, HN-PSS and MDADI (table 1) were used in multivariable analysis to predict WT (logistic regression), HN-PSS and MDADI (linear regression) at 1 year. A clinical model was found using backward stepwise selection for each outcome. Improvement of model discrimination after adding the mean/max doses was quantified using Akaike information criterion (AIC).

Results IBDM revealed significant association between dose to distinct regions and the three outcomes tested (p<0.005), overlapping around the inferior section of the brainstem (figure 1). Models for WT and HN-PSS at 1 year were significantly improved by including mean dose to the overlap region (p=0.02); this was not the case for the MDADI model. Inclusion of max dose did not significantly improve discrimination of any model.