Abstract

• The maximum ionization point of supervoltage X-ray radiation modality is moved to subcutaneous tissue by the build up effect, as the result, the surface dose of the skin is decreased. It is necessary to measure the accurate dose distribution of supervoltage X-ray radiation modality and determine its biological effect on the skin in order to increase the effect of radiation therapy. By using 6MV Linear accelerator, the absorbed dose of the skin and subcutaneous tissue was determined by physical aspect in relationship of 6 MV X-ray and tissue and a uniform formula was developed. For the experiment, guinea pigs were divided into 3 groups. A single irradiation group was irradiated with 10-60Gy, and a single irradiation group with 0.5cm, 1.0cm and 1.5cm bolus was irradiated with 10-40Gy, and fractionation group was irradiated with 20Gy by 3 fractionation for 1 week and with 30Gy, 2, 3, 5 fractionation for 1week and 2weeks respectively. The results were as follows: 1) The absorbed dose of 6MV X-ray was increased depending on the depth of skin and its maximum point was 1.5cm from skin surface. 2) The skin score by a single dose irradiation was proportionally increased by the dose and D_1-5, dose at the point of skin score 1.5 was 25Gy. 3) The maximum skin reaction by a single dose irradiation was developed about 24th day after irradiation and generally the skin reaction was developed earlier in higher dose. 4) By using the bolus, the skin score was increased by the ratio of 53%, 78%, and 100% of dose increment depending on the thickness of the bolus 0.5cm, 1.0cm and 1.5cm respectively. 5) The light microscopic finding of a single dose irradiation without bolus showed more prominent changes in the dermis than epidermis, whereas a single dose irradiation with bolus showed prominent epidermal change. 6) Electron microscopic findings of a single dose irradiation with bolus were severe edema and degeneative change of collagen and dermal appendages in dermis. 7) The skin score of fractionation group was decreased by incresing number of fractionation and duration of overall time in the same total dose. 8) The skin reaction in epidermis was correspond to depth dose of 0.4cm from the surface in biological effect. 9) The biological isodose effect by fractionation irradiation of 6MV X-ray was correspond to number of fractionation of Ellis formula, but the change by overall time is slightly decreased in longer time(T^0.08).