[en] Generally upon completing calibration of a linear accelerator, the factors for all the x-ray and electron energies are obtained in water. For certain types of tumors it is required that they be treated with electron beams but it is commonly found that the surface to be treated on the patient's body may not be plane that is not in the same way as the said radiation beam was calibrated. Besides, the factors found during calibration of the equipment are for plane surfaces as well as for square areas which rarely coincide with anatomical areas to be treated. In this paper preliminary results are presented on how to block the primary radiation beam utilizing Lipowitz alloys (cerrobend) to conform to the therapeutic area. The factor found was directly affected by calibration as was also the fact that an air space may exist between the applicator and the tumor patient. (Author)