Unilateral radiotherapy for tonsil cancer: Potential dose distribution optimization with a simple two-field intensity-modulated radiation therapy beam arrangement

Background and purpose

To evaluate the feasibility and dosimetric optimization potential of a unilateral two-field intensity-modulated radiotherapy (IMRT) technique in the curative treatment of lateralized tonsil cancer.

Materials and methods

Six patients with lateralized tonsillar carcinoma were treated unilaterally with a two-field IMRT technique (oblique-anterior and oblique-posterior fields, with or without collimator and couch rotation). Alternative IMRT plans using seven non-opposed coplanar fields were compared with the two-field plans for each patient.

Results

Planning target volume (PTV) coverage was excellent with the two-field technique, using a relatively low number of monitor units (MU) (median, 441; range, 309-550). Dose constraints were respected for all organs at risk (OAR). Mean doses to contralateral parotid and submandibular glands were 3.9 and 17.7 Gy, respectively. Seven-field IMRT provided similar PTV coverage, with statistically significant better dose homogeneity and conformality. However, the mean delivered dose to the contralateral parotid (3.9 vs. 9.0 Gy, p = 0.001) as well as the mean number of MU (437 vs. 814, p = 0.002) and consequently machine time were lower with two-field IMRT.

Conclusions

Unilateral two-field IMRT is a simple and feasible technique providing excellent tumor coverage and optimal OAR sparing while reducing the number of MU and treatment time.