Effect of body mass index on setup errors in intensity-modulated radiotherapy for cervical cancer / 中华放射肿瘤学杂志

ABSTRACT

Objective:To investigate the effect of body mass index (BMI) on setup errors in intensity-modulated radiotherapy for cervical cancer and explore the optimal position for patients with different BMI without taking into account the rotation error and the changes in target area and adjacent organs.Methods:A total of 90 patients were divided into three groups according to their BMI light weight group (BMI≤18.4 kg/m 2), normal weight group (18.5 kg/m 2≤BMI≤23.9 kg/m 2) and overweight group (BMI≥24 kg/m 2). Thirty patients were assigned into each group including15 patients in the supine position and 15 patients in the prone position. In total, 2 250 sets of CBCT scan data of 90 patients were obtained. The setup errors were recorded and analyzed in each group. The margins of the optimal position were calculated according to the formula of M PTV=2.5+ 0.7. Results:When BMI was not taken into account, there was no significant difference in the setup errors between the supine and prone positions in the x, y and z directions (all P>0.05). When BMI was considered, the setup error in the supine position were significantly smaller than those in the prone position in the x and y directions in the light weight group, whereas there was no significant difference in the setup errors between the supine and prone positions in the z direction ( P>0.05). The corresponding M PTV in the supine position was 4.76, 4.27 and 5.73 mm, respectively. In the normal weight group, there was no significant difference in the setup errors between the supine and prone positions in the x and y directions (both P>0.05), whereas the setup error in the prone position was smaller than that in the supine position in the z direction. The corresponding M PTV in the prone position were 6.42, 10.21 and 4.91 mm, respectively. In the overweight group, there was no significant difference in the setup errors between the supine and prone positions in the x and z directions (all P>0.05), whereas the setup error in the prone position was smaller than that in the supine position in the y direction. The corresponding M PTV in the prone position were 5.88, 5.26 and 5.32 mm, respectively. Conclusions:Without taking into account the rotation error and the changes in target area and adjacent organs, when the BMI≤18.4, the supine position is recommended. When the BMI≥18.5, it is better to choose the prone position.