Development and validation of a contouring guideline for the taste bud bearing tongue mucosa

Purpose: To introduce a contouring guideline for the taste bud bearing tongue mucosa for head and neck cancer patients receiving radiotherapy. Methods and Materials: CT simulation images of oropharyngeal cancer patients were used to delineate both the whole tongue (extrinsic/intrinsic tongue muscles, floor of mouth) and the taste bud bearing tongue mucosa (method A: adaptation of the whole tongue structure; method B: axial adaptation of a mid-sagittal contour). Volumetric and dosimetric parameters of the whole tongue and the two methods of mucosal delineation, spatial overlap between methods A and B, and inter-observer variability for method B were calculated. Results: The study cohort was comprised of 70 patients with T1–4 N0–1 tonsillar (83%) and base of tongue (17%) cancers. Most of the comparative parameters between the whole tongue and mucosa (method A) significantly differed (mean, minimum, and maximum dose, V5–V70, D40–D90). The mean dose calculated for the whole tongue deviated on average 3.77 Gy compared to method A. No significant differences were found between methods A and B of the taste bud bearing tongue mucosa structure, and none of the dosimetric parameters differed more than 1.03 Gy on average. The mean Dice similarity coefficient for both mucosal structures was 0.79 ± 0.05, and 0.63 ± 0.12 for the inter-observer analysis of method B. Conclusions: We defined two methods for delineating the taste bud bearing mucosa and both are equally satisfactory procedures. Either method is preferable over delineation of the whole tongue as organ at risk for taste impairment.