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

Abstract 

Background and Purpose

To 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 methods

Four-dimensional CTs of 1mm 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.

Results

The population-averaged mean gap size±the corresponding standard deviation due to breathing (SD_B) for the lateral gaps was 5.8±0.7mm anteriorly, 8.7±0.9mm at mid-level, and 11.0±1.3mm posteriorly. Anterior–posterior gap values were 21.7±0.7mm, while cranio-caudal shift SD_B was 0.8mm.

Conclusion

Vocal 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.

Keywords: Early glottic carcinoma, 4D-CT, Voice quality, IGRT, Vocal cords