Thermoplasticfilm routinely placed in the treatment room always led to uncomfortable feeling in patients receiving thorax radiation therapy because of significant temperature difference between thermoplastic film and body surface. Therefore, it may result in setup error and further affect accuracy of radiation therapy. Here, we designed a randomized controlled study to investigate the efficacy of preheat thermoplastic film to reduce setup error in patients receiving thorax radiotherapy. Patients with thoracic cancer receiving radiotherapy once daily with five fraction per week were enrolled in this study from October 2022 to January 2023. All participants were randomly assigned into room-temperature group and preheating group in a 1:1 ratio. For the preheating group, the thermoplastic film was preheated for 10 minutes in a 37°C thermostat before it was used for patients' setup. For controlled group, the thermoplastic film with room-temperature was used for patients' setup. The cone beam computed tomography (CBCT) was used to evaluate setup errors once a week. The setup errors in translational directions X, Y and Z were recorded based on CBCT image. to measure the left-right as well as anterior-posterior diameter of the thorax in cross-section to observe whether there was any difference in thorax size from that at positioning. A modified Likert questionnaire was conducted to investigate the setup comfort level between two groups before radiotherapy and Day 5 of radiotherapy. A total of 34 patients were enrolled in this study. Patient characteristics were well balanced in both arms. The setup errors in the X, Y, and Z axes in group A were 1(-1,1) mm, 0(-1,2.75) mm and 0(-1,1) mm, respectively, while those in group B were 0(-2,2) mm, 1(-1.25,3) mm, and -1(-2,1) mm in the X, Y, and Z axes, respectively. Setup error in preheating group was smaller than room-temperature group in the X-axis direction (Z = 2.04, P = 0.042), but no significant differences were detected in Y and Z axes. Comparison of changes in anteroposterior thoracic diameter between the two groups. The preheated group was smaller than the normothermic group (-0.19 ± 0.48 vs -0.38 ± 0.36, P < 0.01). The total comfort scale scores of the two groups were 30.88 ± 3.39 vs 30.59 ± 3.34 (p = 0.42) before treatment and 32.125 ± 4.31 vs 31.06 ± 3.15 (p = 0.80) after treatment. Among the eight sub-items, only the fourth dimension of temperature was statistically different (pre 3.12 ± 0.48 vs 2.88 ± 0.60, P = 0.218; post 4.12 ± 0.78 vs 2.94 ± 0.43, P < 0.01). Ourcenter proposed the first method of heating the mold for postural fixation during patient radiotherapy. Compared with room-temperature thermoplastic film, our study found preheating thermoplastic film with 37°C could significantly reduce setup error in the X direction with less effect on the anterior-posterior diameter change of the thorax and higher patient temperature comfort satisfaction.
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