Objective To analyze the setup errors of two immobilization techniques(pillow + head-and-neck shoulder mask and vacuum bag + head-and-neck shoulder mask)with KV- cone beam computed tomography(CBCT) for head-and-neck cancer radiotherapy.

Methods Sixty head-and-neck cancer patients who diagnosed and treated in Panyu central hospital were randomly selected and divided into two groups(29 patients of pillow + head-and-neck shoulder mask group and 31 patients of vacuum bag + head-and-neck shoulder mask group). CBCT was weekly carried out before treatment delivery. Then, the CBCT images were matched with the planned CT images in order to get the setup errors in left-right, superior-inferior and anterior-posterior directions. Independent t-test was used to evaluate the differences.

Results In the pillow + head-and-neck shoulder mask group, the average setup errors values in the left-right, superior-inferior and anterior-posterior directions were(0.07±1.70), (0.45±1.53), (0.39±1.62) mm, respectively. Also in the vacuum bag + head-and-neck shoulder mask group, the average setup errors values were(-0.05±1.39), (0.13±1.37), (0.08±1.25) mm, respectively. And in the left -right direction, there was no statistically significant difference(t=0.729, P > 0.05). While, in the superior-inferior and anterior-posterior directions, both of which had statistically significant difference(t=2.093 and 2.039, both P < 0.05).

Conclusion The vacuum bag+head-and-neck shoulder mask fixed technique was more accurate when compared to the pillow+head-and-neck shoulder mask fixation method, which has the smaller setup errors and the better position repeatability.