Radiation therapy (RT) has been used in the treatment of breast cancer for over 80 years. Technically, it should include a part or all of such areas as chest wall or breast, axilla, internal mammary nodes (IM) and supraclavicular nodes (SCL). Authors tried three-ield technique for the treatment of breast cancer using 6-V linear accelerator, exclusively the department of radiology, Kang-am St. Mary's Hospital, at Catholic Medical College. The field junction was checked by a phantom study and radiation doses measured by film densitometry and TLD. The 3 fields we used in this study were two isocentric opposing tangential fields encompassing the breast, chest wall and occasionally IM and one single anterior field encompassing the axilla and SCL. Using appropriate beam blocks and boluses. We were able to avoid unwanted intrinsic divergency of photon beam. Blocking also enabled us to set-p precise radiation field with ease.