Dose Characteristics of Total-Skin Electron-Beam Irradiation with Six-Dual Electron Fields

Choi, Tae Jin; Kim, Jin Hee; Kim, Ok Bae

Abstract

PURPOSE: To obtain the uniform dose at limited depth to entire surface of the body, the dose characteristics of degraded electron beam of the large target-skin distance and the dose distribution of the six-dual electron fields were investigated. MATERIALS AND METHOD: The experimental dose distributions included the depth dose curve, spatial dose and attenuated electron beam were determined with 300 cm of target-skin distance (TSD) and full collimator size (35x35 cm2 on TSD 100 cm) in 4 MeV electron beam energy. Actual collimated field size of 105 cmx105 cm at the distance of 300 cm could include entire hemibody. A patient was standing on step board with hands up and holding the pole to stabilize his/her positions for the six-dual fields technique. As a scatter-degrader, 0.5 cm of acrylic plate was inserted at 20 cm from the body surface on the electron beam path to induce ray scattering and to increase the skin dose .
RESULTS
The full width at half maximum (FWHM) of dose profile was 130 cm in large field of 105x105 cm2. The width of 100+/-10% of the resultant dose from two adjacent fields which were separated at 25 cm from field edge for obtaining the dose unifomity was extended to 186 cm. The depth of maximum dose lies at 5 mm and the 80% depth dose lies between 7 and 8 mm for the degraded electron beam by using the 0.5 cm thickness of acrylic absorber. Total skin electron beam irradiation (TSEBI) was carried out using the six dual fields has been developed at Stanford University. The dose distribution in TSEBI showed relatively uniform around the flat region of skin except the protruding and deeply curvatured portion of the body, which showed excess of dose at the former and less dose at the latter.
CONCLUSION
The percent depth dose, profile curves and superimposed dosedistribution were investigated using the degraded electron beam through the beam absorber. The dose distribution obtained by experiments of TSEBI showed within+/-10% difference except the protruding area of skin which needs a shield and deeply curvatured region of skin which needs boosting dose.