Outcome following IMRT for T2 glottic cancer: the potential impact of image-guidance protocols on local control

Abstract

This study aims to report on the outcome of intensity-modulated radiation therapy (IMRT) for T2 glottic cancer and the impact of changes in image-guidance protocol on local control. The result is compared to a historical cohort treated to the same dose with parallel-opposed pairs radiotherapy (POP). Patients with T2N0M0 glottic cancers who received primary radiotherapy (60 Gy/25 fractions/5 weeks) between July 1, 2003 and March 30, 2010 were included. The gross tumor volume (GTV) was delineated according to endoscopy/radiology. The clinical target volume (CTV) for POP encompassed the whole larynx with 60 Gy. IMRT generally treated partial laryngeal volumes comprising two CTVs: CTV1 (GTV+ 0.3∼0.5 cm, receiving 60 Gy) and CTV2 (GTV+ ≥1.0 cm, receiving 50 Gy). Planning target volumes (PTVs) were CTVs+ 0.5 cm. Local control (LC) in the IMRT cohort were stratified by image-guidance protocols: matching to bone vertebrae (IMRT-bone, treated prior to 2008) or to laryngeal tissue (IMRT-laryngeal_tissue, treated after 2008), and compared to the POP cohort. Seventy IMRT (44 IMRT-bone and 26 IMRT-laryngeal_tissue) and 48 POP patients were identified. The 3-year LC was 81 % (95 % CI 65–90) for the POP and 77 % (95 % CI 64–85) for the IMRT cohorts (p = 0.52). The IMRT-bone cohort had decreased LC compared with IMRT-laryngeal_tissue (69 vs. 91 %, p = 0.03). A trend towards increasing local failure for IMRT-bone vs. IMRT-laryngeal_tissue remained after adjusting for various tumor factors. This modest cohort study demonstrates a comparable LC with IMRT for T2 glottic cancers compared to our historical POP cohort. It adds clinical evidence to previous technical observations that have hypothesized a potential impact of laryngeal_tissue movement independent of bone_vertebrae, when partial laryngeal irradiation is contemplated.