Interfractional and intrafractional errors assessed by daily cone-beam computed tomography in nasopharyn-geal carcinoma treated with intensity-modulated radiation therapy
Abstract：Objective To assess interfractional and intrafractional errors and to estimate appropriate margins for planning target volume(PTV) by using daily cone-beam computed tomography(CBCT) guidance in nasopharyngeal carcinoma(NPC) treaded with intensity-modulated readiation therapy(IMRT).Methods Daily pretreatment and post-treatment CBCT scans were acquired separately after initial patient setup and after the completion of each treatment frac-tion in 10 patients treated with IMRT.Online corrections were made before treatment if any translational setup error was found.Interfractional and intrafractional errors were recorded in the right-left(RL), superior-inferior(SI), and anteri-or-posterior( AP) directions.Results For the translational shifts, the interfractional errors >2 mm occurred in 21.7%of measurements in the RL direction, 12.7%in the SI direction, and 34.1%in the AP direction, respectively.Online correction resulted in 100%of residual errors≤2 mm in the RL and SI directions, and 95.5%of residual errors≤2 mm in the AP direction.No residual errors >3 mm occurred in the three directions.For the rotational shifts, significant re-duction was found in the magnitudes of residual errors compared with those of interfractional errors.A margin of 4.9 mm, 4.0 mm, and 6.3 mm was required in the RL, SI, and AP directions, respectively, when daily CBCT scans were not performed.With daily CBCT, the margins were reduced to 1.2 mm in all directions.Conclusion Daily CBCT guid-ance is an effective modality to improve the accuracy of IMRT for NPC.The online correction could result in a 70%~81%reduction in margin size.
Keywords：Nasopharyngeal carcinomaIntensity-modulated radiation therapyCone-beam computed tomographyImaged guided radiation therapySetup error
Publication Date：2014-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：5( 905-909 )