Determining Pion, the correction factor for recombination losses in an ionization chamber

The 1983 AAPM protocol for the determination of absorbed dose from high-energy photon and electron beams recommends using Pion (the reciprocal of collection efficiency), as determined by the two-voltage technique, to correct for recombination losses in ionization chambers. Methods and data for the determination of ionization chamber collection efficiencies are scattered throughout the literature. The present work consolidates the available information, rectifies certain omissions, and provides several convenient and readily implemented methods for determining Pion. Computer programs, quadratic approximations, and data tables are presented to facilitate the determination of Pion for continuous, pulsed, and pulsed-swept beams.