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

PURPOSE: We used a new web application for rapid review of radiation therapy (RT) target volumes to evaluate the relationship between target delineation compliance with the international guidelines and outcomes of definitive RT for nasopharyngeal carcinoma (NPC).

METHODS AND MATERIALS: The data set consisted of computed tomography simulation scans, RT structures, and clinical data of 354 patients with pathology-confirmed NPC treated with intensity modulated RT between 2005 and 2017. Target volumes were peer-reviewed in RT quality assurance rounds, and target contours were revised, if recommended, before treatment. We imported the contours of intermediate-risk clinical target volumes of the primary tumor (CTVp) of 332 patients into the application. Inclusion of anatomic sites within intermediate-risk CTVp was determined in accordance with 2018 international guidelines for CTV delineation for NPC and correlated with time to local failure (TTLF) using Cox regression.

RESULTS: In the peer-review quality assurance analysis, local and distant control and overall survival rates were similar between peer-reviewed and nonreviewed 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 overall survival 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 noncompliant cases was 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 nonconforming cases (93.6% vs 89.1%, P = .013). Multivariable analysis confirmed that cavernous sinus noncompliance was prognostic for TTLF.

CONCLUSIONS: Our application allowed rapid quantitative review of CTVp in a large NPC cohort. Although compliance with the international guidelines was high, undercoverage of the cavernous sinus was correlated with TTLF.