Uncertainty in the positioning of patients receiving treatment for brain metastases and wearing surgical mask underneath thermoplastic mask during COVID‐19 crisis

Abstract Thermoplastic masks, used along with surgical masks, enable immobilization methods to reduce the risk of infection in patients undergoing intracranial stereotactic radiosurgery and stereotactic radiotherapy (SRS/SRT) during the COVID‐19 crisis. The purpose of this study was to investigate the feasibility of thermoplastic mask immobilization with a surgical mask using an ExacTrac system. Twelve patients each with brain metastases were immobilized using a thermoplastic mask and a surgical mask and only a thermoplastic mask. Two x‐ray images were acquired to correct (XC) and verify (XV) the patient’s position at a couch angle of 0°. Subsequently, the XC and XV images were acquired at each planned couch angle for non‐coplanar beams. When the position errors were detected after couch rotation for non‐coplanar beams, the errors were corrected at each planned couch angle until a clinically acceptable tolerance was attained. The position errors in the translational and rotational directions (vertical, lateral, longitudinal, pitch, roll, and yaw) were retrospectively investigated using data from the ExacTrac system database. A standard deviation of XC translational and rotational position errors with and without a surgical mask in the lateral (1.52 vs 2.07 mm), longitudinal (1.59 vs 1.87 mm), vertical (1.00 vs 1.73 mm), pitch (0.99 vs 0.79°), roll (1.24 vs 0.68°), and yaw (1.58 vs 0.90°) directions were observed at a couch angle of 0°. Most of patient positioning errors were less than 1.0 mm or 1.0° after the couch was rotated to the planned angle for non‐coplanar beams. The overall absolute values of the translational and rotational XV position errors with and without the surgical mask were less than 0.5 mm and 0.5°, respectively. This study showed that a thermoplastic mask with a surgical mask is a feasible immobilization technique for brain SRS/SRT patients using the ExacTrac system.


| INTRODUCTION
Stereotactic radiosurgery and stereotactic radiotherapy (SRS/SRT) are well-established techniques for high-precision treatment of intracranial benign and malignant lesions in 1-5 fractions. The accuracy of treatment planning and delivery is highly dependent on accurate patient positioning and immobilization to achieve local tumor control and spare normal tissue. Several stereotactic systems have been used to immobilize these patients accurately during treatment. [1][2][3][4][5][6][7][8] Conventionally, invasive immobilization, such as metal frames or rings fixed to the patient's skull, has been used for patient immobilization and target localization in the SRS/SRT treatment of intracranial lesions. 4 Noninvasive (frameless) SRS/SRT, such as thermoplastic mask systems, has become a standard immobilization method owing to the advent of image-guided radiotherapy (IGRT) systems. One of the advanced IGRT systems, the ExacTrac system (BrainLAB A.G., Heimstetten, Germany), is an integration of an infrared (IR)-based optical positioning system and a radiographic kilovolt (kV) x-ray imaging system that accurately determines patient positions and makes online corrections.
Pneumonia resulting from an unknown cause was reported to the World Health Organization (WHO) country office in Wuhan on December 31, 2019. The WHO named this unknown disease "coronavirus disease 2019" (COVID-19). COVID-19 has rapidly spread worldwide and is a global health concern. Several publications have provided recommendations and measures for radiation oncology clinics to prevent infection during the COVID-19 pandemic. [9][10][11][12][13][14] Effective protective methods are required to prevent the spread of COVID-19 during radiation implementation. Immobilization devices for head and neck patients should be cleaned using a sanitizer, as they are in contact with the patient's mouth/nose. Wearing a surgical mask is a lowcost and remarkably effective intervention to reduce the spread of the virus in people infected with COVID-19. Patients should wear the mask during the treatment or an additional face shield must be placed properly in cases where the patient has to take off the mask during treatment, such as a personalized head and neck immobilization mask. In our institution, patients undergoing treatments involving the head and neck area wear the surgical mask underneath the thermoplastic mask during treatment. We inquired whether wearing the surgical mask underneath the thermoplastic mask by patients receiving SRS/SRT leads to an inaccurate patient position.
In this study, we investigated the patient position errors for brain SRS/SRT-treated patients with and without a surgical mask underneath the thermoplastic mask using daily pretreatment imaging. This study analyzes patient positioning corrections that are performed during treatments using the ExacTrac system, which consists mainly of two procedures: kV x-ray images for initial patient setup and position verification.

2.A | Patients and simulation section
Between February 2020 and November 2020, 24 patients with intracranial lesions treated with SRS/SRT at our institution were included in this study. Twelve selected patients were treated with the surgical mask and thermoplastic mask combinatory design from June 2020. To compare the immobilization accuracy, 12 selected patients wearing only thermoplastic masks were selected prior to these preventive measures.    | 279 spectrum. ExacTrac system is a tool for quickly positioning and acquiring images for IGRT of the patient and could slightly shorten the hospital stay time. 14 Previous studies have reported that immobilization accuracy affects intra-fractional patient motion during treatment, and a single image acquired prior to treatment is not sufficient to monitor patient motion. 6 The duration of time spent by patients at the clinic or treatment room should be kept at a minimum to reduce the risk of COVID-19 infection. 14 After image guidance, the beam-on-time for each delivery beam is approximately 1-2 min. In addition, the Exac-Trac system is a useful image-guided option for patients with brain SRT, even at different couch rotations. Therefore, we believe that intra-fractional patient motion using a thermoplastic mask system with a surgical mask is small. We are aware that a thermoplastic mask with a surgical mask forces patients to keep their mouth closed during treatment, which is uncomfortable. Full-head masks can be cut open around the mouth to improve patient comfort. Previously published data showed that open-face masks, in which the superior and inferior edges were pressed against the forehead and chin, can provide immobilization within 2.0 mm. 7,8 We believe that immobilizing these two points is stable and effective, even if there is a space between the thermoplastic mask and the mouth. Some patients may claim that a thermoplastic mask with a surgical mask is uncomfortable. We will cut the thermoplastic mask around the mouth as a solution.

| RESULTS
Our study was limited to a small cohort of patients at the beginning of the COVID-19 crisis. We will not further investigate the impact of a surgical mask on patient positioning error in a large population because we hope the infection will cease to spread further.
We attempted to offer a solution to protect patients from COVID-19 infection without compromising oncologic outcomes. In the future, we plan to report our study of clinical outcomes and toxicity in patients with brain metastases using a thermoplastic mask with a surgical mask. We hope this manuscript will be useful for developing measures for attenuating the impact of the COVID-19 crisis while administering cranial SRS/SRT treatment in radiotherapy departments.

| CONCLUSIONS
Based on retrospective investigations using the ExacTrac system database, the position error for patient motion using a thermoplastic mask system and a surgical mask together was found to be small.
During the ongoing pandemic, a thermoplastic mask with a surgical mask is a feasible immobilization technique for brain SRS/SRT patients using the ExacTrac system.

ACKNOWLEDGMENT
All authors contributed to this study, and read and approved the final manuscript.

CONFLI CT OF INTEREST
The authors declare that they have no conflict of interest to disclose.

D A T A A V A I L A B I L I T Y S T A T E M E N T
The data that support the findings of this study are available from the corresponding author upon reasonable request.