Nasopharyngeal carcinoma volume measurements determined with computed tomography: study of intraobserver and interobserver variability.

Abstract

To investigate the intraobserver and interobserver variability of computed tomography-based volume measurements of nasopharyngeal carcinoma. Prospective study. Tertiary care centre. The primary tumour volume of 13 nasopharyngeal carcinomas was repeatedly measured by two trained observers independently in two different sessions, using the summation of area technique. Mean tumour volume and its standard deviation were calculated for each tumour. Statistical analysis was done with multivariate analysis, linear regression, and a two-way analysis of variance (ANOVA) random effects model. The coefficient of variation was less than 20% in 11 volume measurements, but a large discrepancy between observers was noted in two tumours with involvement of the paranasal sinuses. A good linear correlation was found between mean tumour volume and its standard deviation: standard deviation = 0.26 volume - 2.48 (r = .80). When the two tumours with a large coefficient of variation were excluded, the two-way ANOVA random effects model revealed that both the interobserver (p = .83) and the intraobserver (p = .90) effect are not statistically significant; interobserver variability was the major component of total variability (71.0%). Total variability in the computed tomography-based measurement of nasopharyngeal carcinoma volume is small by having the measurements done by a trained observer, except in tumours with involvement of the paranasal sinuses.