Application of combined body position fixation in radiation therapy of lung cancer

Abstract

Objective To explore the CTV to PTV external expansion boundary and the effect of the dose of normal lung tissue under different fixed modes by a comparative analysis of combined body position and thermoplastic film fixed set-up error of radiation therapy for lung cancer. Methods From October 2016 to March 2018, the patients who received chest radiology at the Tangshan people′s hospital were enrolled as subjects retrospectively divided into two groups, including 50 patients with lung cancer radiotherapy with combined body position fixation, and 40 patients with lung cancer with thermoplastic film fixation. The two groups of patients drew the target areas in accordance with the unified standard, and the set-up error of left and right, up and down, front and rear (x, y, z axis) were recorded respectively after 1 time/week cone CT(CBCT) matched with the planned CT image and analyzed by t test. According to the MPTV=2.5Σ+ 0.7δ, CTV to PTV external expansion boundary in the combined body position group were calculated. And the V5、V20 and V30 of two groups of patients were calculated and analyzed by TPS system. Results The set-up error of the combined body position group and thermoplastic film group were respectively (1.00±0.58) mm and (3.28±0.43) mm on the x axis, (1.42±0.28) mm on the y axis and (4.03±0.41) mm, (1.06±0.44) mm and (3.18±0.34) mm on the z axis. The set-up errors of the two groups were statistically significant on x, y and z axis(t=-20.740, -35.596, -25.015, P 0.05). Through the MPTV=2.5Σ+ 0.7δ, CTV to PTV external expansion boundary in the combined body position fixation group was 2.906 , 3.746 and 2.958 mm on x, y and z axis respectively. The comparison between group A and B showed that the mean values of V5, V20 and V30 in group B were reduced by 1.5%, 3.1% and 4.8% respectively compared with group A. Conclusions The combined body position technique can improve the accuracy of lung cancer patients after radiation therapy, and further reduce the boundary of CTV to PTV, which is of certain value to reduce the occurrence of radiation pneumonitis. Key words: Lung cancer; Polystyrene foam; Thermoplastic film; Set-up error; Target volume