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Top Line: Is there a difference in intrafraction motion between open and closed immobilization masks?

The Study: This is a particular concern for patients receiving brain radiosurgery who require both immobilization with a face mask as well as long times in said masks. And the cruel irony is the more grueling the immobilization requirements, the more patients work against you. This practical analysis asked if there was any difference in intrafraction motion with either of two commonly-used commercially available immobilization masks: a closed mask (by the Dutch company Macromedics) versus an open-face mask (by the Pennsylvania-based company Qfix). We’ll pause here to note that, refreshingly, the authors aren’t paid by either of these companies. Changes in patient positions per pre- and post-treatment cone beam CTs were calculated for 76 patients receiving brain radiosurgery over 3-5 fractions using the closed (n=38) versus open-faced mask (n=38). Fortunately, intra-fraction motion was minimal with either mask. ​​Mean intrafraction motion with the open mask was  0.1, 0.2, and 0.0 mm in the anterior-posterior, superior-inferior, and left-right directions compared to 0.2, 0.2, and 0.0 mm for the closed mask. Mean rotational errors with the open mask were -0.1, 0.0, and 0.0 degrees for pitch, roll, and yaw compared to -0.1, -0.1, and 0.0 degrees for the closed mask. There were no differences in 3D translational or rotational intrafraction motion. Finally, the authors found that a 1 mm margin adequately compensated for observed intrafraction motion.

TBL: This comparison of open and closed immobilization masks for radiosurgery found no major difference in intrafraction motion. | Ohira, J Appl Clin Med Phys 2022