Prediction and monitoring of adaptive radiation therapy timing using two-dimensional X-ray image-based water equivalent thickness

Abstract

Background This study aimed to predict and monitor the optimal timing for implementing adaptive radiation therapy (ART) using two-dimensional X-ray image-based water equivalent thickness (2DWET). Methods The study included 40 patients with oropharyngeal and hypopharyngeal cancer who underwent CT rescanning during the treatment period. An adaptive score (AS) was proposed as a quantitative indicator to facilitate the decision regarding when to implement ART. The AS was derived from changes in four key dose indices: target coverage, spinal cord dose, parotid gland dose, and over-dose volume. Delivered dose distributions were reviewed by two oncologists specializing in head and neck radiation therapy, and the need for ART was evaluated using a four-point score. Logistic regression analysis was used to determine the AS cutoff value, and receiver operating characteristic analysis was used to assess 2DWET as a predictor of ART timing. Results The AS strongly correlated with the decisions made by the radiation oncologists, with Pearson correlation coefficients of 0.74 and 0.64. An AS cutoff value of 7.5 was identified as an indicator of the optimal time to implement ART, predicting two oncologists' decisions with sensitivities of 79.2% and 89.5% and specificities of 87.5% and 81.0%, respectively. The 2DWET method detected AS = 7.5 with a sensitivity of 63.2% and a specificity of 81.0%. Conclusions An adaptive score of 7.5 strongly correlated with the radiation oncologists' decision to implement ART and could therefore be used as a surrogate marker. Two-dimensional WET detected AS = 7.5 with high sensitivity and specificity and could potentially be used as a highly efficient and low-exposure tool for predicting and monitoring the optimal timing of ART implementation.