Brain Linac-Based Radiation Therapy: Test Drive of New Immobilization Solution and Surface Guided Radiation Therapy

Aim: To test inter-fraction reproducibility, intrafraction stability, technician aspects, and patient/physician's comfort of a dedicated immobilization solution for Brain Linac-based radiation therapy (RT). Methods: A pitch-enabled head positioner with an open-face mask were used and, to evaluate inter- and intrafraction variations, 1-3 Cone-Beam Computed Tomography (CBCT) were performed. Surface Guided Radiation Therapy (SGRT) was used to evaluate intrafraction variations at 3 time points: initial (i), final (f), and monitoring (m) (before, end, and during RT). Data regarding technician mask aspect were collected. Results: Between October 2019 and April 2020, 69 patients with brain disease were treated: 45 received stereotactic RT and 24 conventional RT; 556 treatment sessions and 863 CBCT's were performed. Inter-fraction CBCT mean values were longitudinally 0.9 mm, laterally 0.8 mm, vertically 1.1 mm, roll 0.58 degrees, pitch 0.59 degrees, yaw 0.67 degrees. Intrafraction CBCT mean values were longitudinally 0.3 mm, laterally 0.3 mm, vertically 0.4 mm, roll 0.22 degrees, pitch 0.33 degrees, yaw 0.24 degrees. SGRT intrafraction mean values were: i_, m_, f_ longitudinally 0.09 mm, 0.45 mm, 0.31 mm; i_, m_, f_ laterally 0.07 mm, 0.36 mm, 0.20 mm; i_, m_, f_ vertically 0.06 mm, 0.31 mm, 0.22 mm; i_, m_, f_ roll 0.025 degrees, 0.208 degrees, 0.118 degrees; i_, m_, f_ pitch 0.036 degrees, 0.307 degrees, 0.194 degrees; i_, m_, f_ yaw 0.039 degrees, 0.274 degrees, 0.189 degrees. Conclusions: This immobilization solution is reproducible and stable. Combining CBCT and SGRT data confirm that 1 mm CTV-PTV margin for Linac-based SRT was adequate. Using open-face mask and SGRT, for conventional RT, radiological imaging could be omitted.

Automated summary

The study tested the inter-fraction reproducibility and intrafraction stability of a dedicated immobilization solution for Brain Linac-based radiation therapy, showing that the solution is accurate and stable. Combining CBCT and SGRT data confirmed the adequacy of a 1 mm CTV-PTV margin for Linac-based SRT. The use of an open-face mask and SGRT may allow for the omission of radiological imaging for conventional RT.