Abstract: Background and purpose: Accurate target location is an important factor in stereotactic radiotherapy of the chest. The aim of this study was to analyze the effects of patient’s arm stability on placement and treatment in chest tumor radiotherapy. Methods: Forty patients with chest tumors were selected from Apr. 2018 to Oct. 2018 in Department of Radiation Oncology, Fudan University Shanghai Cancer Center in this study, were divided into two groups (20 in each group). In the two groups of patients, the same thermoplastic film was used to fix the chest, and the patients in group A were given arm support. In group B, the arm was not effectively supported, and the patient's elbow was placed on the forehead. Each patient underwent cone beam computed tomography (CBCT) scan before and after each treatment, and the data were registered with the planned CT image to obtain the patient's placement error on the X, Y, and Z axes and the parallel error in the treatment. Results: A total of 619 CBCT images were obtained from 40 patients. The pre-treatment placement errors of group A patients and group B patients were head and foot direction ［(2.10±1.67) mm, (2.90±2.05) mm］, left and right direction［(1.15±.0.96) mm, (1.59±1.51) mm］ and ventral direction ［(1.52±1.22) mm, (2.10±1.67) mm］; the position errors after treatment were head and foot direction ［(1.05±0.89) mm, (1.12±0.94) mm], left and right direction ［(0.65±0.75) mm, (0.69± 0.71) mm］ and ventral direction ［(0.63±0.68) mm, (0.71±0.78) mm］. The results showed that the placement error of group A patients before treatment was smaller than that of group B, and the three groups were placed in three axial directions. After the error comparison, the P value was less than 0.05, which was statistically significant. In the case of good chest fixation after treatment, the displacement error of group A was still smaller than that of group B. Conclusion: In chest radiotherapy, when the chest is also fixed, the patient with arm fixation is more relaxed and comfortable during the treatment, which makes the placement more repeatable and accurate.

Key words: Arm fixation, Multifunctional body plate, Placement error, Chest tumor, Chest radiotherapy