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Combination of Dental Putty Based Bite Block and Immobilization Mask Improves the Setup Accuracy of Stereotactic Radiosurgery of Brain Metastasis


Z Liu

Z Liu*, A Tazi, J Barrett, S Sha, Watson Clinic, Lakeland, FL

SU-E-T-363 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate if the addition of dental putty based bite block improves the setup accuracy over the immobilization mask alone in the treatment of brain metastasis using linear accelerator based stereotactic radiosurery.

Methods: Localization shift data from on-board kV CBCT images relative to reference CT images of 16 patients receiving brain stereotactic radiosurgery were retrieved and analyzed for this study. Out of the 16 patients, 8 were treated with immobilization mask alone and the remaining were treated with a combination of dental putty based bite block and immobilization mask. Due to the unavailability of 6D couch in our clinic, we used only the translational registration between CBCT images and reference CT images for couch shifts in patient treatment. The clinical localization shifts were used for data analysis. To compare the two immobilization methods comprehensively, the CBCT images were retrospectively co-registered with the reference images with six degree of freedom (3 translations and 3 rotations). A paired t-test was used to evaluate the statistical significance of the two immobilization methods.

Results: For the clinical patient treatment, localization shifts from immobilization mask only were 1.5±1.8 mm, 0.1±2.6 mm, and -1.0±2.2 mm, in the vertical, longitudinal, and lateral directions respectively. The addition of dental putty based bite block improves the localization shifts to 0.2±0.2 mm, 0.7±0.6 mm, and 0.9±1.2 mm in the vertical, longitudinal, and lateral directions respectively. Furthermore, the addition of dental putty based bite block reduces significantly the rotational variations of patient head in the immobilization mask.

Conclusion: The combination of dental putty based bite block and immobilization mask improves the setup accuracy of linear accelerator based intracranial stereotactic radiosurgery. The formation of a reliable dental putty impression to the upper jaw of each patient is essential for a successful implementation of the procedure.

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