Abstract：Objective To compare the set-up errors of thermoplastic film with Styrofoam and thermoplastic film with Vacuum
negative pressure pad in gamma knife radiotherapy on brain metastases. Methods Twenty patients with brain metastases
radiotherapy from November 2019 to June 2020 were randomly divided into A group (thermoplastic film with Styrofoam, n=10)
and B group (thermoplastic film with Vacuum negative pressure pad, n=10). After the patients had completed MRI positioning and
the first treatment, the Philips big bore CT was used to acquire images, respectively. Then two scanned images were transmitted
to DATU medical system for image registration. And finally the set-up errors in the six directions of x (left and right)、y (front
and back), z (head and foot), Rx（front and back rotation), Ry（head and foot rotation), Rz（left and right rotation) were obtained.
Results The set-up errors of group A in the x, y, z, Rx, Ry, Rz directions were (0.07±0.04) cm, (0.08±0.05) cm and (0.08±0.04) cm,
（0.46±0.39)°,（0.36±0.39)°,（0.42±0.50)°, respectively. The set-up errors of group B in the x, y, z, Rx, Ry, Rz directions were
(0.13±0.07) cm, (0.09±0.07) cm and (0.27±0.16) cm,（1.40±1.11)°,（0.91±0.34)°,（0.83±1.14)°, respectively. There were
no significant difference in the set-up errors of group A and group B in the y and Rz directions (P＞0.05). The set-up error of group
A in the x, z, Rx, Ry directions was smaller than that of group B (P＜0.05). Conclusion The set-up error of thermoplastic film with
Styrofoam in gamma knife radiotherapy on brain metastases is less than that of thermoplastic film with vacuum negative pressure
pad, which is worth popularizing.
