Delta-radiomics features during radiotherapy improve the prediction of late xerostomia

Lisanne V Van Dijk,Tian-Tian Zhai,Walter Noordzij,Nanna M Sijtsema,Johannes A Langendijk,Roel J H M Steenbakkers,Thea A Vedelaar

doi:10.1038/s41598-019-48184-3

Abstract

The response of the major salivary glands, the parotid glands, to radiation dose is patient-specific. This study was designed to investigate whether parotid gland changes seen in weekly CT during treatment, quantified by delta-radiomics features (Δfeatures), could improve the prediction of moderate-to-severe xerostomia at 12 months after radiotherapy (Xer12m). Parotid gland Δfeatures were extracted from in total 68 planning and 340 weekly CTs, representing geometric, intensity and texture characteristics. Bootstrapped forward variable selection was performed to identify the best predictors of Xer12m. The predictive contribution of the resulting Δfeatures to a pre-treatment reference model, based on contralateral parotid gland mean dose and baseline xerostomia scores (Xerbaseline) only, was evaluated. Xer12m was reported by 26 (38%) of the 68 patients included. The most predictive Δfeature was the contralateral parotid gland surface change, which was significantly associated with Xer12m for all weeks (p < 0.04), but performed best for week 3 (ΔPG-surfacew3; p < 0.001). Moreover, ∆PG-surfacew3 showed a significant predictive contribution in addition to the pre-treatment reference model (likelihood-ratio test; p = 0.003), resulting in a significantly better model performance (AUCtrain = 0.92; AUCtest = 0.93) compared to that of the pre-treatment model (AUCtrain = 0.82; AUCtest = 0.82). These results suggest that mid-treatment parotid gland changes substantially improve the prediction of late radiation-induced xerostomia.

Highlights

Xerostomia is one of the most frequently reported side effects following radiotherapy of head and neck cancer (HNC) patients and affects patient-reported quality of life[1]
Moderate-to-severe xerostomia was reported by 26 (38%) of all 68 patients included at 12 months after radiotherapy (22 in the training set and 4 in the test set)
The current study shows that surface change of the contralateral parotid gland (∆PG-surface) assessed during the course of radiotherapy was strongly associated with the development of late xerostomia (Xer12m and xerostomia at 6 months (Xer6m))

Summary

Introduction

Xerostomia is one of the most frequently reported side effects following radiotherapy of head and neck cancer (HNC) patients and affects patient-reported quality of life[1]. Since in-treatment parameters contain information on the patient-specific response to treatment, they may resolve some of the unexplained variability that remains for NTCP models that are based on pre-treatment variables only These in-treatment parameters could be used to improve the prediction of late xerostomia. That study showed that the parotid gland surface reduction (∆PG-surface6w-postRT) was strongly associated with the development of xerostomia at 6 and 12 months after radiotherapy[8] This post-treatment model does not allow for treatment adaptation, as the total prescribed radiation dose has already been administered. The aim of the current study was to identify quantitative parotid gland changes during treatment that predict the development of late xerostomia These parotid gland changes were extracted from pre-treatment and weekly. CT-images during radiotherapy, from which delta radiomics features (∆features) were quantified, representing differences in intensity, texture and geometric characteristics of the parotid glands

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