###### Abstract  
Brachytherapy is a practical, effective procedure for the local treatment of cancer; it delivers a high radiation dose to a limited tissue volume while sparing the surrounding normal tissues. Although the clinical benefit of brachytherapy is clear, there have been very few studies on the radiation dose received by physicians during the procedure. Furthermore, no study has investigated the eye radiation dose received by physicians performing \({}^{198}\)Au grain (seed) brachytherapy, using an eye dosimeter. Recently, the International Commission on Radiological Protection (ICRP) recommended significantly reducing the occupational lens dose limit, from 150 to 20 mSv/yr (100 mSv/5 years). Therefore, it has become essential to evaluate the eye radiation doses of medical workers. We evaluated the eye radiation dose of a brachytherapy physician performing \({}^{198}\)Au permanent grain implantation for tongue cancer; this is the first study on this topic. The maximum eye dose was -0.1 mSv/procedure, suggesting that it is unlikely to exceed the ICRP limit (20 mSv/yr) for the lens, unless many procedures are performed with inappropriate radiation protection. To reduce the dose of radiation received by \({}^{198}\)Au grain brachytherapy physicians, it is necessary to use additional lead shielding equipment when preparing the treatment needles, i.e., when loading the grains. This study provides useful information on radiation exposure of physicians conducting \({}^{198}\)Au permanent grain brachytherapy. radiation protection and safety; \({}^{198}\)Au grain (Au-198 permanent grain); brachytherapy; radiation therapy; oral cancer; eye lens dose; topue cancer; occupational radiation exposure; resilience; 3 mm dose equivalent [Hp(3)] +
Footnote †: journal: Medicaland full-dose external radiation therapy is typically associated with mandibular osteo-radionecrosis, xerostomia, and an impaired sense of taste after treatment [16; 17; 18]. These complications often lower patients' post-treatment quality of life [19]. The incidence rate of tongue cancer with advanced age is increasing in Japan. Brachytherapy is typically chosen to treat oral cancer, particularly tongue cancer, because it preserves the shape and functions of the tongue [20; 21; 22]. Until recently, \({}^{192}\)Ir hairpins and \({}^{137}\)Cs needles were widely used for the treatment of tongue cancer via brachytherapy [23]. However, these methods have negative impacts on patients of advanced age and/or with underlying conditions such as dementia, diabetes, and apoplexy [24; 25; 26]. Hence, \({}^{198}\)Au grains have gradually become more common as an alternative source of radiation [27]. As shown in Figure 1, these grains are small and can easily be inserted, permanently, under local anesthesia, without causing severe pain or discomfort during either the insertion or the subsequent treatment and therefore can be prescribed for patients who cannot tolerate the previously used procedures [28]. Furthermore, patients can eat immediately after implantation, unlike those who receive treatment using \({}^{192}\)Ir or \({}^{137}\)Cs. In addition, \({}^{198}\)Au has a short half-life of 2.7 days, which shortens the hospital stay [29; 30]. Therefore, \({}^{198}\)Au permanent grain brachytherapy has become a very useful treatment for tongue cancer [31; 32]. Although the clinical benefit of brachytherapy is clear, there have been very few studies on the radiation dose received by the physician during the procedure [33]. Furthermore, no study has investigated the eye dose received by physicians performing \({}^{198}\)Au grain brachytherapy. In 2011, the International Commission on Radiological Protection (ICRP) recommended significantly reducing the occupational eye lens dose limit, from 150 to 20 mSv/yr (100 mSv/5 years) [34; 35]. Therefore, it has become essential to evaluate the eye radiation doses received by medical workers.