Partial Laryngeal IMRT for T2N0 Glottic Cancer: Impact of Image Guidance and Radiotherapy Intensification
Menée à partir de données portant sur 139 patients atteints d'un cancer glottique de stade T2N0 traité entre 2006 et 2013 (durée médiane de suivi : 5 ans), cette étude analyse, du point de vue du contrôle local de la maladie, l'intérêt d'une radiothérapie partielle du larynx avec modulation d'intensité et guidage thérapeutique par l'imagerie
Objectives : To assess the impact of radiotherapy (RT) regimen and image-guidance (IGRT) protocol on local control (LC) for T2N0 glottic cancer treated with partial laryngeal IMRT. Methods : All T2N0 glottic cancer treated with IMRT from 2006-2013 at a single institution were retrospectively reviewed. GTV, delineated from endoscopic / radiological findings, was expanded 0.5 cm for high-dose CTV (CTV1) and additional 0.5 cm for lower-dose CTV (CTV2) (total of 1.0 cm from GTV). PTV margin was 0.5 cm radially and 1 cm superiorly and inferiorly. RT regimens evolved from hypofractionated IMRT (RT-hypo, 60 Gy in 25 fractions over 5 weeks [60 Gy/25f/5w]) to moderately accelerated IMRT (RT-acc, 66-70 Gy/33-35f/5.5-6w) since 2010. IGRT matching surrogate changed from cervical vertebral bone (IGRT-bone) to laryngeal soft tissue (IGRT-larynx) in 2008. LC was compared between 3 sequential cohorts: RT-hypo/IGRT-bone, RT-hypo/IGRT-larynx and RT-acc/IGRT-larynx. Multivariable analysis (MVA) assessed the relative impact of RT regimen and IGRT technique on local failure (LF), separately. Results : Of 139 eligible patients [median follow-up: 5.03 years (range: 0.8-10.5)], 28 local, 6 regional and 2 distant failures were identified. Higher 3-year LC was observed for RT-acc/IGRT-larynx [89% (78-95)] vs. RT-hypo/IGRT-larynx [80% (54-91)] vs. RT-hypo/IGRT-bone [70% (53-80)] (p=0.02)]. MVA adjusted for GTV volume (cm3) and smoking status confirmed that IGRT-larynx vs IGRT-bone (HR=0.40, p=0.019) and RT-acc vs RT-hypo (HR 0.34, p=0.012) both reduced risk of LF. Conclusions : This single-institutional cohort study shows a high LC (89%) for T2N0 glottic cancer following moderately accelerated partial laryngeal IMRT with daily laryngeal soft tissue matching IGRT. These results appear to represent an improvement attributable to changes in both IGRT matching and dose delivered but their independent significance is unknown and warrant further confirmation in a larger cohort.