Analysis of setup errors using two immobilization techniques in the radiotherapy of head-and-neck cancer

Abstract

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. Key words: Head and neck neoplasms; Setup error; Position immobilization techniques; Cone beam computed tomography