Coronavirus disease 2019 (COVID-19) was first reported in Wuhan, China in December 2019,1 which is caused by severe acute respiratory syndrome coronavirus (SARS-CoV-2). The virus can be transmitted from person to person through various routes such as droplets, aerosols and fomites.2,3 Radiation therapy is the main treatment for many malignant tumors, but the course of treatment for patients may take several weeks. Cancer patients are more susceptible to infection than healthy people because radiation therapy may cause systemic immunosuppression in patients.4 Therefore, these susceptible patients need to be protected from SARS-CoV-2 without interrupting treatment or extending the duration of radiation therapy. This is a serious problem that must be faced.

Prior to the start of the COVID-19 pandemic, it was not standard practice in our department for patients to wear surgical masks during radiotherapy. Considering that the main route of transmission of coronavirus is droplets and aerosols from patients with COVID-19, wearing a mask during medical treatment is a preventive method to reduce droplet and aerosol transmission.5 In our department meeting, we discussed that there might be a risk of exposure via asymptomatic COVID-19 infected patients in clinical practice in the future. Starting from April 2020, we first allowed the wearing of surgical masks during radiotherapy for head and neck cancer patients with a high risk of infection, mainly to minimize virus contamination and reduce the exposure risk to radiation therapists. The purpose of this study was to evaluate the position error of wearing a surgical mask during radiotherapy in head and neck cancer patients.

This study was approved by the institutional review board at our institution (No. 202101085B0). The need for informed consent from each patient was waived by the institutional review board because this study was non-invasive and utilized routine treatment data based on patient data confidentiality and compliance with the Declaration of Helsinki. We collected and analyzed 2351 imaging records of 81 patients with head and neck cancer (HNC) who underwent image-guided radiotherapy (IGRT) in our department between January 2020 and May 2021. All patients were subjected to an energy of 6 or 10 megavolts (MV) of volume modulated arc therapy (VMAT). The characteristics of all patients are shown in Table 1. All patients underwent planning CT simulation in the supine position with a GE Discovery RT 16 Slice CT Simulator (GE Healthcare, Waukesha, USA) using a 2.5 mm slice thickness. Images results were then sent to a RayStation 8B treatment planning system (TPS; Raysearch Laboratories AB, Stockholm, Sweden), which performed target delineation and designed the treatment plan. The patient immobilization currently methods used are mainly S-Type thermoplastic masks, which was used to divide patients into the head and neck (HN) group and the head-neck-shoulder (HNS) group according to the fixed area. The selection criteria for the immobilization mask depends on the doctor’s clinical considerations and preferences. Type B/C Timo headrests (CIVCO, Kalona, USA) are commonly used clinically and are shown in Figure 1.

Table 1 Patient Characteristics

Figure 1 Patient Immobilization: (A) Head and neck (HN) mask and type B headrests. (B) Head-neck-shoulder (HNS) mask and type C headrest.

First, during the preparation of the HN immobilization devices, the metal strips of the medical mask for nose clipping were removed by radiation therapists. Secondly, before immobilization mask molding, it must be confirmed that it should completely cover the patient’s nose and mouth and there is no gap. The patient’s breathing should be confirmed to avoid discomfort. Finally, the anatomical reference points of the patient’s face and the position of the mask were delineated on the thermoplastic mask.

Timo headrests are constructed of durable polyurethane foam with a washable coating. The main difference is that the height of the headrest is different, so the comprehensive range of neck angulations is also different. The selection criteria are based on the comfort and support of the patient when lying flat. In order to reduce the time spent in contact with the patient and in a confined space, we implemented the IGRT strategy and prioritized the use of faster kV imaging technology for patient position correction. Daily on-line image verification with two orthogonal high-resolution kV images and automatic couch corrections were performed using the On-Board Imager® (OBI) on the Edge™ radiosurgery system (Varian Medical Systems, Palo Alto, USA). Finally, the daily displacement error correction value of each patient was recorded. The coordinates of all axes are based on the supine position on the treatment couch. The X axis is the patient’s right-left (RL) direction, positive toward the right and negative toward the left, the Y axis is the patient’s superior-inferior (SI) direction, positive toward the head and negative toward the feet, and the Z axis is the patient’s anterior-posterior (AP) direction, positive toward the abdomen and negative toward the back. Pitch is based on the Y axis, such that head raising is positive and foot raising is negative, while yaw is based on the Z axis, in which rotating clockwise is positive and rotating counterclockwise is negative. We used independent t-tests to evaluate the difference between the four groups. The statistical analyses were performed with IBM SPSS Statistics 22.0 (IBM Corp., Armonk, USA). A p-value less than 0.05 (p < 0.05) was considered statistically significant.

Finally, we calculated the required Planning Target Volume (PTV) margin for clinical data to provide a clinical reference for non-imaging guided patients. The PTV margin (MPTV)proposed by van Herk et al6 was estimated as follows:

(1)

The box plots of the position error s for each axis of the entire patient with/without a surgical mask during radiotherapy are presented in Figure 2.

Figure 2 The box plots of the position error for each axis. (A) Translational errors in the X, Y, and Z directions (B) Rotational errors in the Yaw, Pitch, and 3D vector.

Note: *p<0.05.

Although the medians of the X, Y and Z axes did not change much, the Z axis error range was significantly increased in the group without masks, which also means that the Z-axis error had a larger range of varied changes. The median error on the pitch axis increased and moved to a positive value, which was statistically significant (p<0.01). Further analysis showed that patients wearing surgical masks in the HN mask group had no significant differences in the average displacement error of the different types of headrests (p>0.05). In the HNS mask group, only the type C headrest group showed a significant difference (P < 0.05). The X axis values were −0.05±0.07 and −0.11± 0.01 cm (P = 0.04), and the pitch axis values were 0.34±0.29° and 0.83±0.08° (P = 0.01). The position errors and t-test results of the four groups are shown in Tables 2 and 3, with the systematic errors, random errors and estimated PTV margins proposed by van Herk et al Table 4 lists the recommended MPTV for the two groups of patients. In the surgical mask group (including HN and HNS), the estimated margins in the X, Y and Z axes were 0.36, 0.44 and 0.42 cm, respectively. In the groups without surgical masks, the estimated margins were 0.33, 0.47 and 0.46 cm, respectively.

Table 2 Position Errors and Independent t-Test Results of 59 Cases of the HN Mask

Table 3 Position Errors and Independent t-Test Results of 22 Cases of the HNS Mask

Table 4 Systematic Errors, Random Errors and Estimated Margins Between the Two Groups

In our results, in the HNS mask group, only in type C headrest group showed a statistically significant difference. The possible causes are as follows:

1. Patients wearing masks were mainly treated during the epidemic. It was the consensus of the department to take on a reduced number of fractions with a higher dose to reduce the risk of infection. Therefore, patients treated during the pandemic may have less variation in increased displacement errors due to tumor shrinkage and weight loss.

2. The use of HNS masks also mainly consider neck and shoulder displacements, when patients show differences in clearance within the thermoplastic mask, which may also cause displacements due to changes in the neck angle, especially the pitch axis.

From the overall results, it can be seen that although there were significant differences between patients with and without surgical masks in some axial directions, the overall mean position error range was within 2 mm, and the calculated MPTV was also within a reasonable range.7–12 In the literature, Yu et al11 suggested the if it is not possible to perform image guidance every day, it is recommended that the MPTV should be at least 5 mm.

Chen et al7 suggested for patients with head and neck cancer, if IGRT can be performed daily, 3-mm PTV expansion margins seem to be sufficient and do not increase the risk of local treatment failure. In our experience, beyond being easy to implement and comfortable for patients, a good immobilization device should be highly reproducible during the course of treatment and maximally limit patient motion. The mask contains different types of immobilization devices, ie, the thermoplastic mask material, head support and mask wearing position will affect imaging reproducibility. The surgical mask is divided into three layers: a water blocking layer (hydrophobic non-woven layer), a filtering layer (melt-blown layer) and a water-absorbing layer (soft absorbent non-woven), with particulate filterability, waterproof and anti-spray properties. The physical thickness of the mask is about 0.5 mm. Assessing the reproducibility of the mask wearing position was one goal of our research.

During treatment, the position of the thermoplastic mask should also be aligned or adjusted with reference to the markings on the thermoplastic mask. At present, in the other studies have also started to study the feasibility of patients wearing masks to receive different radiotherapy techniques.13–15

In the literature, Ding et al.13 The CBCT was mainly used to measure the difference of patient’s position when patient was treated using HN and HNS thermoplastic mask with/without Surgical Mask. Miura et al14 mainly used ExacTrac positioning combined with IGRT evaluate the fixation of patients undergoing intracranial stereotactic radiosurgery and stereotactic radiotherapy (SRS/SRT) with/without surgical masks. Ohhira et al15 compared the intrafractional setup error with and without a bite block during fractionated intracranial stereotactic irradiation of patients wearing medical masks.

Unlike the above studies, we used 2D kV image for image guiding because only 15 to 20 seconds were needed for image acquisition in 2D kV image and 2 to 3 minutes were needed for image acquisition in CBCT. Using orthogonal 2D kV to reduce treatment time might have the chance to reduce the virus contamination time or exposure risk in the confined spaces during the epidemic period. Therefore, the imaging data collected in this study are mainly analyzed based on the interfractional error of the patients.

However, since the immobilization devices and setup techniques of each hospital are different, more clinical data needs to be collected for verification in the future.

In clinical practice, interfractional error is usually defined as anatomic structures deviation between pre-treatment position and treatment planning patient’s position; intrafractional error is usually defined as the errors caused by organ motion or patient position change during treatment.

Our research has some limitations. First, this was a retrospective study, and there might be some selection bias in the enrolled patients. Secondly, the immobilization mask and treatment may not always be performed by the same group of therapists; IGRT image‐matching skills are not necessarily the same for each therapist, although standard operating procedures are used to reduce differences between observers. Third, wearing surgical masks during radiotherapy is only an intervention during epidemics is not routine, so the study did not specifically explore the possibility that patients undergo tumor shrinkage and weight loss during radiotherapy, which may lead to increased displacement errors.

The mean position error of most patients treated with masks was not greater than that of patients without masks. The way in which patients wear masks to receive treatment is a low-cost and easy-to-implement prevention method, which can reduce the risk of virus transmission and therapist contact. At this stage, it is a preventive approach that has more advantages than disadvantages.

COVID-19, coronavirus disease 2019; IGRT, image-guided radiotherapy; HN, head-neck; HNS, head-neck-shoulder; 3D, three dimensional; VMAT, volume modulated arc therapy; PTV, Planning Target Volume.

This study was approved by the Chang Gung Medical Foundation Institutional Review Board (No. 202101085B0).

The authors report no conflicts of interest in this work.

1. Chen H, Guo J, Wang C., et al. Clinical characteristics and intrauterine vertical transmission potential of COVID-19 infection in nine pregnant women: a retrospective review of medical records. Lancet. 2020;395(10226):809–815. doi:10.1016/S0140-6736(20)30360-3

2. Wei W, Zheng D, Lei Y, et al. Radiotherapy workflow and protection procedures during the Coronavirus Disease 2019 (COVID-19) outbreak: experience of the Hubei Cancer Hospital in Wuhan, China. Radiotherapy Oncol. 2020;148:203–210. doi:10.1016/j.radonc.2020.03.029

3. Wang J, Du G. COVID-19 may transmit through aerosol. Ir J Med Sci. 2020;189(4):1143–1144. doi:10.1007/s11845-020-02218-2

4. Liang W, Guan W, Chen R, et al. Cancer patients in SARS-CoV-2 infection: a nationwide analysis in China. Lancet Oncol. 2020;21(3):335–337. doi:10.1016/S1470-2045(20)30096-6

5. Moschovis PP, Yonker LM, Shah J, Singh D, Demokritou P, Kinane TB. Aerosol transmission of SARS‐CoV‐2 by children and adults during the COVID‐19 pandemic. Pediatr Pulmonol. 2021;56(6):1389–1394. doi:10.1002/ppul.25330

6. van Herk M. Errors and margins in radiotherapy. Semin Radiat Oncol. 2004;14(1):52–64. doi:10.1053/j.semradonc.2003.10.003

7. Chen AM, Farwell DG, Luu Q, Donald PJ, Perks J, Purdy JA. Evaluation of the planning target volume in the treatment of head and neck cancer with intensity-modulated radiotherapy: what is the appropriate expansion margin in the setting of daily image guidance? Int J Radiat Oncol Biol Phys. 2011;81(4):943–949. doi:10.1016/j.ijrobp.2010.07.017

8. Duma MN, Kampfer S, Wilkens JJ, Schuster T, Molls M, Geinitz H. Comparative Analysis of an Image-Guided Versus a Non–Image-Guided Setup Approach in Terms of Delivered Dose to the Parotid Glands in Head-and-Neck Cancer IMRT. Int J Radiat Oncol Biol Phys. 2010;77(4):1266–1273. doi:10.1016/j.ijrobp.2009.09.047

9. Graff P, Hu W, Yom SS, Pouliot J. Does IGRT ensure target dose coverage of head and neck IMRT patients? Radiotherapy Oncol. 2012;104(1):83–90. doi:10.1016/j.radonc.2011.09.024

10. Schwarz M, Giske K, Stoll A, et al. IGRT versus non-IGRT for postoperative head-and-neck IMRT patients: dosimetric consequences arising from a PTV margin reduction. Radiation Oncol. 2012;7(1):1–7. doi:10.1186/1748-717X-7-133

11. Yu Y, Michaud AL, Sreeraman R, Liu T, Purdy JA, Chen AM. Comparison of daily versus nondaily image‐guided radiotherapy protocols for patients treated with intensity‐modulated radiotherapy for head and neck cancer. Head Neck. 2014;36(7):992–997. doi:10.1002/hed.23401

12. Zeidan OA, Langen KM, Meeks SL, et al. Evaluation of image-guidance protocols in the treatment of head and neck cancers. Int J Radiat Oncol Biol Phys. 2007;67(3):670–677. doi:10.1016/j.ijrobp.2006.09.040

13. Ding Y, Ma P, Li W, et al. Effect of Surgical Mask on Setup Error in Head and Neck Radiotherapy. Technol Cancer Res Treat. 2020;19:1533033820974021. doi:10.1177/1533033820974021

14. Miura H, Hioki K, Ozawa S, et al. Uncertainty in the positioning of patients receiving treatment for brain metastases and wearing surgical mask underneath thermoplastic mask during COVID‐19 crisis. J App Clin Med Phys. 2021;22(6):274–280. doi:10.1002/acm2.13279

15. Ohira S, Kanayama N, Komiyama R, et al. Intra-fractional patient setup error during fractionated intracranial stereotactic irradiation treatment of patients wearing medical masks: comparison with and without bite block during COVID-19 pandemic. J Radiat Res. 2021;62(1):163–171. doi:10.1093/jrr/rraa101