Comparison of Set-up Errors between Two Different Thermoplastic Masks for Brain Tumors Using Image-Guided Radiation Therapy

Abstract

Background and Objective: Thermoplastic masks serve as immobilization devices that improve the precision of patient positioning in radiation therapy for brain tumor radiation. In the Radiation Oncology Department of Srinagarind Hospital, two types of short thermoplastic masks are utilized: the U-shape head mask and the S-type head mask. The S-type head mask is compatible with the existing base utilized by the S-type head & shoulder mask within the department. This research were evaluated the differences in radiation setup errors and staff satisfaction associated with two types of masks.

Methods: This retrospective descriptive study involved 41 patients with brain tumors who received brain tumor radiation. Patients were categorized into two groups according to the type of mask. Treatments were delivered by intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) from November 2022 to November 2023. Treatment verification was confirmed through image-guided radiation therapy (IGRT). Total vector errors (TVE) were evaluated using kV orthogonal (kV-kV) and cone beam computed tomography (kV-CBCT). The clinical target volume to planning target volume margin was determined utilizing Van Herk equation. Furthermore, average staff satisfaction scores concerning mask preparation and usage were assessed for both types.

Results: The average setup errors of the two mask types presented no statistically significant differences. The TVE for kV-kV imaging was measured at 0.25 cm for the S-type head mask and 0.24 cm for the U-shape head mask. The TVE for kV-CBCT imaging was measured at 0.07 cm and 0.08 cm, respectively. The CTV to PTV margin was determinded to be less than 0.5 cm, which is within the acceptable limits for treatment planning at Srinagarind Hospital. The average staff satisfaction scores were 3.68 for the U-shape head mask and 3.43 for the S-type head mask.

Conclusion: Both mask types are appropriate for patient positioning in radiation therapy, as their setup errors remain within the established limits of the department. IGRT protocols, such as daily kV-kV and weekly kV-CBCT imaging, must be adhered to rigorously. The U-shape head mask was preferred by the staff over the S-type head mask, which is likely due to their increased familiarity with its application.