Four-dimensional CT analysis of vocal cords mobility for highly focused single vocal cord irradiation

Background and PurposeTo quantify respiratory motion of the vocal cords during normal respiration using 4D-CT. The final goal is to develop a technique for single vocal cord irradiation (SVCI) in early glottic carcinoma. Sparing the non-involved cord and surrounding structures has the potential to preserve voice quality and allow re-irradiation of recurrent and second primary tumors.Material and methodsFour-dimensional CTs of 1 mm slice thickness from 10 early glottic carcinoma patients were acquired. The lateral dimensions of the air gap separating the vocal cords were measured anteriorly, at mid-level and posteriorly at each phase of the 4D-CTs. The corresponding anterior–posterior gaps were similarly measured. Cranio-caudal vocal cords movements during breathing were derived from the shifts of the arythenoids.ResultsThe population-averaged mean gap size ± the corresponding standard deviation due to breathing (SDB) for the lateral gaps was 5.8 ± 0.7 mm anteriorly, 8.7 ± 0.9 mm at mid-level, and 11.0 ± 1.3 mm posteriorly. Anterior–posterior gap values were 21.7 ± 0.7 mm, while cranio-caudal shift SDB was 0.8 mm.ConclusionVocal cords breathing motions were found to be small relative to their separation. Hence, breathing motion does not seem to be a limiting factor for SVCI.