Relative doses to skin and superficial nodes from 10 MV photons as a function of field size and distance from shadow tray.

Although low entrance dosea are desirable for cosmetic and tolerance reasons, they may leave the superficial nodes underdosed. Surface dose dependence on area and distance from the shadow tray for 10 MV photons was studied and comparisons made with 60Co and 4 MV energies. The use of 10 MV photons would leave superficial nodes underdosed unless a bolus or supplementary treatment, such as electrons, is used. Treatment planning implications for a mantle field are discussed.