On absorbed dose in narrow 60Co gamma-ray beams and dosimetry of the Gamma Knife

Using separate analytical functions describing primary dose, P-0(d(m),r), collimator scatter, S-c(r), and phantom scatter, TAR(d,r), an expression for absorbed dose in narrow Co-60 gamma-ray beams is developed and each function is quantified: D(d, r)= P-0(d(m),r) S-c(r) TAR(d, r). The absorbed dose is calculated in beams as narrow as 0.2 cm in radius. Analytical and experimental results are compared using measured dose data for the Gamma Knife. Close agreement with experimental data is observed. (C) 1998 American Association of Physicists in Medicine. [S0094-2405(98)02612-1].