Evaluation of the clinical validity of fixation accuracy using an open-face black mask in head stereotactic radiotherapy.

In stereotactic radiotherapy (SRT), precise alignment is crucial for treatment effectiveness and safety and has traditionally been achieved using cone beam computed tomography (CBCT). Recently, radiation-free optimal surface imaging (OSI) systems have gained popularity. Notably, the effectiveness of black face masks for identifying facial surfaces during OSI use has been increasingly reported. This study aimed to determine whether the fixation accuracy of an open-face black mask designed to facilitate detection using the OSI system is clinically acceptable. This study was approved by the institutional review board (protocol code E23-0162) on May 27th, 2023. We analyzed the accuracy and correlation of CBCT- and OSI-based measurements before and after treatment in 20 patients who underwent SRT using open-face black mask fixation. Additionally, intra-fractional motion was monitored in real time using the OSI system. Mean translational deviations measured by CBCT and OSI were 0.1 mm and 0.1 mm (lateral), -0.2 mm and 0.1 mm (longitudinal), and − 0.1 mm and 0.2 mm (vertical), respectively. Mean rotational deviations were 0.1° and − 0.1° (rotation), -0.4° and − 0.1° (roll), and 0.1° and − 0.1° (pitch). All measurements met clinical accuracy criteria. Weak correlations between CBCT and OSI data were observed only in the lateral and roll directions. Several transient outliers were noted in real-time OSI monitoring. The fixation accuracy achieved with the open-face black mask was within clinically acceptable limits based on both CBCT and OSI measurements. Further research is warranted to clarify the source of noise and improve the reliability of real-time OSI-based monitoring.