ESTRO 2021 Abstract Book

S400

ESTRO 2021

Purpose or Objective In 2013 the Danish Head and Neck Cancer Group (DAHANCA) introduced consensuses guidelines that presented a geometric 5 mm margin from GTV to high dose clinical treatment volume(CTV1) and 10 mm to intermediate CTV2. This was a change from former guidelines where the margin varied from 0 to 10 mm and could include anatomical compartments for CTV1 generation. This approach has been shown to produce more consistent and smaller treatment volumes. The current study aimed to analyse the local control in patients treated three years before and three years after the implementation of the 5+5 mm CTV margin guidelines. Materials and Methods All patients with squamous cell carcinomas in the larynx (except T1 glottis), oropharynx, hypopharynx receiving the standard IMRT based 66-68Gy/33-34fx, 6 fx/w in three DAHANCA centres were included. A total of 788 and 870 patients received treatment in 2010-2012 and 2013-2015, respectively, and all data were prospectively recorded. Local failure included both tumour persistence and recurrence up to three years after IMRT. The local control between the two treatment periods was estimated using a univariate Kaplan-Meier plot and log-rank test. A Multivariate Cox regression model was used to determine possible factors influencing local control. Results Median follow-up for all 1658 patients was 48 months; 49 and 47.5 months for 2010-2012 and 2013-2015 periods, respectively. Patient groups were similar in both treatment periods, except for more HPV p16+ oropharyngeal cancers and more frequent use of radiosensitiser in 2013-2015. The three-year local failure rate was 15% and 11% in 2010-2012 and 2013-2015, respectively, with a univariate log-rank test being significant (p=0.03, Figure 1). The highest failure rate in both periods was for the hypopharynx. The significant factors related to local failure were sex, tumour site, tumour stage (TNM 7 th ), chemotherapy, radiosensitiser (figure 2). No significant hazard difference was observed between the three centres (p = 0.53), and for the two different guidelines periods (p = 0.14).