Dose distribution of high energy electron by shielding material

We studied for the shielding materials of normal tissue in high energy electron irradiation. The lead plate being choosed as the most appropriate shielding material and the dose distribution is transformed into following; 1) The thickness of lead for complete shielding of high energy electron is 3.2mmPb for 8 MeV 4.3mmPb for 10 MeV5.0 mmPb for 12 MeV 2) Sruface dose is increased about 3 to 10 percent of maximum dosage, if the lead plate isused for electron beam shielding. 3) The bremsstrahlung is occured from shielding lead plate from above 4 to 6percent of maximum dosage, yet this dosage is not above the practical error of radiotherapy.