**4. Risk factors of radiation-induced ulcers**

There are some risk factors associated with the development of radiation dermatitis.

#### **4.1 Radiotherapy-related factors**

Higher total dose and higher irradiated volume are possibly related to a higher risk of skin injury [22–24]. Several articles revealed that hypofractionated RT contributed to a lower risk of radiation-induced skin injuries [25, 26]. However, a conflict result was shown as a hyperfractionated regime resulting in preferable outcomes [27]. Besides, intensity-modulated radiotherapy (IMRT) could lead to a reduction of skin reactions compared to 2D radiotherapy [28, 29].

Concurrent chemotherapy (i.g. cetuximab) or concurrent targeted therapy might result in a higher risk of skin injuries induced by RT as well [30–32].

#### **4.2 Patient-related factors**

Some regions of the body that are more sensitive to radiation such as the scalp, face, neck, extremities, chest, and abdomen, may be prone to develop skin reactions in patients receiving RT [33]. Patients who are obese (BMI > 30), contract connective tissue diseases, or have skin disorders also have a higher risk of developing radiation burns [34–36]. In addition, there are some genetic polymorphisms that were supposed to increase incidences of radiation dermatitis. They included polymorphisms in ABCA1 and IL12RB2, stefinA3, and S100A8 genes [37, 38].
