Effect of Radiation Therapy Quality Assurance on Nasopharyngeal Carcinoma: Usage of a Novel, Web-Based Quality Assurance Application

Abstract

We used a new web application for rapid review of radiotherapy (RT) target volumes to evaluate the relationship between target delineation compliance with the international guidelines and outcomes of definitive RT for nasopharyngeal carcinoma (NPC). The dataset consists of CT simulation scans, RT structures, and clinical data of 354 pathology-confirmed NPC patients treated with intensity-modulated RT between 2005 and 2017. Target volumes were peer-reviewed in RT QA rounds, and target contours were revised, if recommended, before treatment. We imported the contours of intermediate-risk clinical target volumes of the primary tumor (IR-CTVp) of 332 patients into the application. Inclusion of anatomic sites within IR-CTVp was determined in accordance with 2018 International guideline for CTV delineation for NPC and correlated with time to local failure (TTLF) using Cox-regression. In the peer-review QA analysis, local and distant control and overall survival (OS) rates were similar between peer-reviewed and non-reviewed cases and between cases with and without target contour changes. In the CTV compliance analysis, with a median follow-up of 5.6 years, 5-year TTLF and OS rates were 93.1% and 85.9% respectively. The most frequently non-guideline compliant anatomic sites were sphenoid sinus (n=69, 20.8%), followed by cavernous sinus (n=38, 19.3%), left and right petrous apices (n=37 and 32, 11.1% and 9.6%), and clivus (n=14, 4.2%). Among 23 patients with a local failure (6.9%), the number of non-compliant cases were 8 for sphenoid sinus, 7 cavernous sinus, 4 left and 3 right petrous apices, and 2 clivus. Cavernous sinus-conforming cases showed higher TTLF in comparison with non-conforming cases (93.6% vs 89.1%, p=0.013). Multivariable analysis confirmed that cavernous sinus non-compliance was prognostic for TTLF. Our application allowed rapid quantitative review of CTVp in a large NPC cohort. While compliance with the international guidelines was high, under-coverage of the cavernous sinus was correlated with TTLF.