Comparative study of setup errors between new and reused thermoplastic masks in irradiated head and neck cancer patients

Background: The accuracy and precision of patient setup are important in radiotherapy. The thermoplastic mask is used to immobilize head and neck cancer patient. However, the mask is reused for low-income patients. Therefore, the setup error should be evaluated to approve that these patients remain in the exact position during treatment. Objective: To investigate setup errors with the use of thermoplastic masks in head and neck cancer patients and to compare setup errors of new and reused thermoplastic masks. Materials and Methods: Eighty patients who underwent volumetric modulated arc radiotherapy (VMAT) for head and neck cancer lesions were retrospectively evaluated. The setup error, population systematic error, and population random error were calculated. Subsequently, setup errors in patients using the new and reused thermoplastic masks were compared. Results: The population systematic error in the vertical, longitudinal, and lateral directions for new masks was 2.02, 2.27, and 2.13 mm, respectively, and that for reused masks was 2.37, 1.96, and 2.33 mm, respectively. The population random error in the vertical, longitudinal, and lateral direction for new masks was 1.46, 1.54, and 1.57 mm, respectively, and that for reused masks was 1.65, 1.63, and 1.87 mm, respectively. The results showed no statistically significant difference supported by p value > 0.05 in the setup error between using the new and reused thermoplastic masks in all directions. Conclusion: For head and neck radiotherapy, the population setup errors were < 3 mm in all directions. Moreover, thermoplastic masks can be reused in patients with head and neck cancer.