Volumetric modulated arc therapy (VMAT) and simultaneous integrated boost in head-and-neck cancer: Is there a place for critical swallowing structures dose sparing?

Objective: To explore the potential of volumetricmodulated arc therapy (VMAT) to reduce the risk of swallowing problems after curative chemoradiotherapy. Methods: 20 patients with head and neck cancer who previously underwent radiotherapy were selected. Radiotherapy was prescribed according to simultaneous integrated boost technique with all targets irradiated simultaneously over 30 daily fractions. Doses of 70.5 (67.5), 60.0 and 55.5Gy were prescribed to primary tumour, high-risk nodal regions and low-risk nodal regions, respectively. Pharyngeal constrictor muscles (PCM) and glottic and supraglottic larynx (SGL) were considered organs at risk related to swallowing dysfunction (SW-OARs). Upper pharyngeal constrictor muscles (uPCM), middle pharyngeal constrictor muscles (mPCM) and lower pharyngeal constrictor muscles (lPCM) part of PCM were also outlined separately. Clinical standard plans (standard-VMAT) and plans aiming to spare SW-OARs (swallowing dysfunction-VMAT) were also created. Normal tissue complication probabilities (NTCP) for physician-rated swallowing dysfunction were calculated using a recently predictive model developed by Christianen et al. Results: Planning with two strategies demonstrated comparable planning target volume coverage and no differences in sparing of parotid glands and other nonswallowing organs at risk. SW-VMAT plans provided mean dose reduction for uPCM and SGL by 3.9 and 4.5Gy, respectively. NTCP values for Radiation Therapy Oncology Group grade 2-4 swallowing dysfunction was decreased by 9.2%. Dose reductions with SW-VMAT depended on tumour location and overlap with SW-OARs. Conclusion: VMAT plans aiming at sparing swallowing structures are feasible, providing a significant reduction in NTCP swallowing dysfunction with respect to conventional VMAT.