RESUMEN
For radiotherapy of total skin including sub-cutaneous tissue up to a depth of 3 cm on the entire left leg of an adult [Angiosarcoma skin], a complex treatment with multiple stationary electron fields was planned at our clinic. The details of dosimetry, clinical dose measurements are presented. The treatment planned with 6 overlapping 9 MeV electron fields in Clinac 2300CD linac. With 25x25 cm cone, a cut-out insert provided 56 × 30 cm field at FSD 213 cm, while patient lying on the floor. Dose distributions were checked using Kodak V densitometric film in cylindrical plastic can phantom. The calibration was carried out using solid water phantom, water equivalent IMRT phantom and water can leg phantom. A dose of 45 Gy in 23 fractions at 5 fractions/week was prescribed. 6 field overlapping field factor was measured by the method described for total body electron irradiation [AAPM]. Skin doses were estimated at random selected points using TLD chips and semiconductor diodes. Measured absorbed doses by three methods were 0.174 cGy/MU, 0.166 cGy/MU and 0.162 cGy/MU agreed well with the calculated value 0.163 cGy/MU. 6 field overlap factor was 2.315. Clinical dose estimates of mean skin dose was 246.0 + 14 cGy [n=18], delivering higher dose by 23%. The gonad dose estimate under shield was <5%. The excess dose to skin delivered in first 14 fractions was adjusted in following 9 fractions. It appears that the excess dose in real situation may be due to either floor backscatter or non uniform overlap of dose from adjacent fields