Effects of full-neck volumetric-modulated arc therapy vs split-field intensity-modulated head and neck radiation therapy on low neck targets and structures.

OBJECTIVE: While split-field intensity-modulated radiation therapy (SF-IMRT) decreases dose to low neck (LAN) structures such as the glottic larynx compared with full-neck intensity-modulated radiation therapy (IMRT), it is unknown whether SF-IMRT affords superior dose avoidance to organs than whole neck-field volumetric-modulated arc therapy (WF-VMAT).

METHODS: 10 patients treated definitively with radiation for oropharyngeal, oral cavity or nasopharyngeal carcinoma were compared. Only patients ideally suited for SF-IMRT plans were included. The glottic larynx, supraglottic larynx, arytenoids, pharyngeal constrictors, oesophagus, brachial plexus and target volume coverage in the LAN were compared between WF-VMAT and SF-IMRT.

RESULTS: Volumetric-modulated arc therapy (VMAT) yielded statistically significant decreases in maximum dose to the arytenoids and mean dose to the oesophagus. There was no difference in dose to the glottic larynx, supraglottic larynx, pharyngeal constrictors and brachial plexus. WF-VMAT led to improved coverage to 50/2 Gy fraction equivalent in LAN compared with SF-IMRT using an anteroposterior (AP) LAN field but no difference to the 60/2 Gy fraction equivalent between SF-IMRT and WF-VMAT using AP/posterior-anterior LAN boost.

CONCLUSION: WF-VMAT affords equivalent glottic and supraglottic larynx dose and lower dose to the arytenoids and oesophagus. WF-VMAT better covers most LAN target structures. Given these findings as well as concerns with matchline cold spots or hotspots with SF-IMRT, patients requiring comprehensive elective nodal irradiation should typically be treated with WF-VMAT.

ADVANCES IN KNOWLEDGE: SF-IMRT for larynx sparing has better dosimetric results to normal structures than whole-neck IMRT, but with increased matchline recurrence risk. We show dosimetric equivalence or superiority of WF-VMAT compared with SF-IMRT.