**2. Pathophysiology**

When irradiation performed, the radiation will affect the young cells, makes them to divide rapidly. Therefore, when acting on the skin, radiation causes damage to the germ cells of the skin, hair follicles, sebaceous glands, sweat glands. In the other hand, radiation affects vascular endothelial cells, fibroblasts, etc., thereby causing post-radiotherapy skin lesions. Early-stage common lesions after radiotherapy may be edema, congestion, dry desquamation, moist desquamation, acute ulcers or mild pigmentation disorders. In the late stages, the most common lesions are skin atrophy, sclerosis, loss of skin appendages (hair, sebaceous glands, sweat glands), hyperpigmentation or hypopigmentation, dilated capillaries, vascular lesion, ulcers, necrosis or secondary cancer.

#### **2.1 Mechanism of RT-induced skin reactions**

RT-induced skin reactions occurred possibly related to tissue damage and inflammation.

Firstly, radiation could cause DNA breaks due to its ability to release electrons from atoms or molecules. Secondly, it could generate reactive oxygen species resulting in the oxidation of proteins and lipids. Consequently, these effects lead to cell death and the impairment of miotic ability [7]. When a great amount of cell death happened and could not recover, cell death, including basal keratinocytes in the basal layer, would distract the self-renewal ability of the epidermis [8]. As a result, the proliferation of new cells could not completely replace damaged cells resulting in a broken epidermis.

Skin reactions in the epidermis could be followed by inflammation. There is a variety of cytokines and chemokines. They include interleukin IL-1α, IL-1β, TNF-α, TGF-β, IL-6, IL-8, CCL-4, CCL2 [9–11]. The upregulation of these molecules consequently increases the expression of adhesion molecules such as intercellular adhesion molecule-1, vascular cell adhesion molecule, and E-selectin [9, 12, 13]. The transendothelial migration of immune cells from the circulation to damaged areas could be deemed as a hallmark of the inflammatory process.

### **2.2 Mechanism of RT on wound healing**

Normally, the wound healing process undergoes some stages: vasoconstriction and hemostasis (immediately after the lesion), inflammatory reaction (0–3 days), granulation regeneration/reproduction (3 days–3 weeks), repair and recovery (3 weeks–3 years). The wound healing is also influenced by local factors (wound moisture, wound ischemia, bacterial infection) and the systemic ones (congenital pathologies related to collagen deficiency or synthesis, pathologies increasing the risk of bacterial infection and nutrition…).

Influence of radiation on wound healing process [14]:


*Radiation-Induced Skin Reactions and Surgical Management Treating Radiation-Induced Ulcers DOI: http://dx.doi.org/10.5772/intechopen.109753*


According to the study by Hopewell, radiation makes the post-radiotherapy wound healing process more complicated and difficult than other common chronic lesions [15].
