An investigation into the accuracy of Acuros(TM) BV in heterogeneous phantoms for a (192)Ir HDR source using LiF TLDs.

The aim of this study was to evaluate the accuracy of the new Acuros(TM) BV algorithm using well characterized LiF:Mg,Ti TLD 100 in heterogeneous phantoms. TLDs were calibrated using an (192)Ir source and the AAPM TG-43 calculated dose. The Tölli and Johansson Large Cavity principle and Modified Bragg Gray principle methods confirm the dose calculated by TG-43 at a distance of 5 cm from the source to within 4 %. These calibrated TLDs were used to measure the dose in heterogeneous phantoms containing air, stainless steel, bone and titanium. The TLD results were compared with the AAPM TG-43 calculated dose and the Acuros calculated dose. Previous studies by other authors have shown a change in TLD response with depth when irradiated with an (192)Ir source. This TLD depth dependence was assessed by performing measurements at different depths in a water phantom with an (192)Ir source. The variation in the TLD response with depth in a water phantom was not found to be statistically significant for the distances investigated. The TLDs agreed with Acuros(TM) BV within 1.4 % in the air phantom, 3.2 % in the stainless steel phantom, 3 % in the bone phantom and 5.1 % in the titanium phantom. The TLDs showed a larger discrepancy when compared to TG-43 with a maximum deviation of 9.3 % in the air phantom, -11.1 % in the stainless steel phantom, -14.6 % in the bone phantom and -24.6 % in the titanium phantom. The results have shown that Acuros accounts for the heterogeneities investigated with a maximum deviation of -5.1 %. The uncertainty associated with the TLDs calibrated in the PMMA phantom is ±8.2 % (2SD).