247. From CTDI-in-air to equilibrium dose

CTDI metric is currently used for standardized measures of dose-output. Recently, however, strengths/weaknesses of CTDI have been debated: (1) 100 mm-long ionization chambers may not be sufficiently long to measure the tails of scattered dose distribution, (2) phantoms used are shorter than an adult torso. Two approaches have been proposed: use longer ionization chambers and phantoms, or using small probes to determine the equilibrium dose ðDeqÞ [1]. The present study proposes a method based on CTDI-in-air metric to calculate Deq following the approach suggested by Li et al. [2]. The method was also validated using radiochromic films.