The researches find that the Incorrect prediction of skin dose in external beam radiotherapy (EBR) can have normal tissue complication such as acute skin desquamation and skin necrosis. Therefore The absorb dose of skin should be measure within a 50–100 m skin layer; place between the epidermis and dermis layers. However; current treatment planning systems (TPS) cannot correctly define the skin layer because of the limitation of voxel resolution in compute tomography (CT).
External beam radiotherapy
Recently, a new tetrahedral-mesh (TM) phantom is develop to evaluate radiation dose realistically. This study aims to develop a technique to evaluate realistic skin dose using the TM phantom in EBR. The TM phantom is model with thin skin layers; including the epidermis, basal layer, and dermis from CT images. Using the Geant toolkit; the simulation is perform to evaluate the skin dose according to the radiation treatment conditions.
The skin dose is evaluate at a surface depth of 50 μm and 2,000 μm. The difference in average skin dose between depths is up to 37%, depending on the thickness and region of the skin to be measure Presently; more than half the cancer patients are prescribe treatment using an external radiation beam with a linear accelerator (LINAC) (Jemal A et al 2011, Delaney et al 2005). With a growing number of cancer patients undergoing external beam radiotherapy (EBR); various studies on treatment techniques have been performed for improving tumor control while minimizing the normal tissue complication.
The normal tissue
Although the reduction in severe radiation induce skin toxicity due to particular attention to skin dose and technological advances of EBR, various normal tissue complication is reported to occur until recently in areas where the skin folds. The most common side effects are erythema, edema, and fibrosi. The skin consists of different three layers: epidermis, dermis, and subcutis.
These layers are compose of different types of cellular level elements. Among these, the epidermis is the outermost layer of skin and 0.2-mm thickness. Furthermore; the epidermis is divide into five sub layers. The deepest layer of the five sub layers is the basal layer (Igarashi T et al 2007). The Radiation Therapy Oncology Group (RTOG) and the European Organization for Research and Treatment of Cancer (EORTC) describe the acute skin toxicity as 4-grade according to the severity; one of the frequent normal tissue complication is the moist desquamation that defined as grade as acute skin toxicity.