Influence of lower limb movements on setup errors in radiotherapy for rectal cancer using kilovoltage cone-beam CT (KV-CBCT) / 中华放射肿瘤学杂志

ABSTRACT

Objective To investigate the influence of fixation of both lower limbs with negative pressure vacuum cushion and fixation of both ankles with self-made foam mat on setup errors in radiotherapy for rectal cancer.Methods A total of 12 patients with rectal cancer were enrolled in 2014 and randomly divided into group A (using negative pressure vacuum cushion) and group B (using self-made foam mat).An offline registration analysis was performed for the images of 108 times (A,B group of 54 times) of kilovoltage cone-beam CT (CBCT) before and after treatment.Grey scale translation error registration was used,and the results of registration were analyzed.The setup errors in x-axis (left-right direction),y-axis (cranial-caudal direction),and z-axis (anterior-posterior direction) were compared between the two groups.Results There was no significant difference in the absolute setup error in the y-axis between the two groups (2.13±0.64 mm vs.2.61±1.17 mm,P=0.399),while group A showed significantly lower absolute setup errors in the x-axis and z-axis than group B (x-axis1.51±0.28 mm vs.2.70±1.05 mm,P=0.039;with an error rate of 7.41％ vs.42.59％;z-axis1.10±0.29 mm vs.2.37±0.71 mm,P=0.002;with an error rate of 1.85％ vs.35.19％).Conclusions In the radiotherapy positioning for rectal cancer,fixation of both lower limbs with negative pressure vacuum cushion effectively avoids the translation and rotation of both lower limbs,reduces absolute setup errors,and has higher accuracy than fixation of both ankles with self-made foam mat.