Extrapolated surface dose measurements with radiochromic film

A radiochromic film extrapolation method is described for the measurement o f surface dose from high energy photon beams. Extrapolated central axis ent rance surface dose using Gafchromic film for a 10 x 10 cm(2) field size is 15% +/- 2% and 13% +/- 2% of D-max for 6 and 10 MV x rays, respectively. Ex trapolated surface dose for a 30 X 30 cm(2) field with a 10 mm perspex bloc k tray is 49% +/- 2% and 48% +/- 2% of D-max for 6 and 10 MV beams, respect ively. All results agree with uncorrected Attix parallel plate ionization c hamber surface ionization within 4% for the same beam energies and configur ations. (C) 1999 American Association of Physicists in Medicine. [S0094-240 5(99)01902-1].