Assessment of four dose calculation algorithms using IAEA-TECDOC-1583 with medium dependency correction factor (K_med) application

Purpose: This study discusses the measurement of dose in clinical commissioning tests described in IAEA-TECDOC-1583. It explores the application of Monte Carlo (MC) modelled medium dependency correction factors (K_med) for accurate dose measurement in bone and lung materials using the CIRS phantom.

Methods: BEAMnrc codes simulate radiation sources and model radiation transport for 6 MV and 15 MV photon beams. CT images of the CIRS phantom are converted to an MC compatible phantom. The PTW 30013 farmer chamber measures doses within modeled CIRS phantom. K_med are determined by averaging values from four central voxels within the sensitive volume of the farmer chamber. K_med is calculated for D_m.m and D_w.w algorithm types in bone and lung media for both photon beams.

Results: Average modelled correction factors for D_m.m calculations using the farmer chamber are 0.976 (±0.1 %) for 6 MV and 0.979 (±0.1 %) for 15 MV in bone media. Correspondingly, correction factors for D_w.w calculations are 0.99 (±0.3 %) and 0.992 (±0.4 %), respectively. For lung media, average correction factors for D_m.m calculations are 1.02 (±0.3 %) for 6 MV and 1.022 (±0.4 %) for 15 MV. Correspondingly, correction factors for D_w.w calculations are 1.01 (±0.3 %) and 1.012 (±0.2 %), respectively.

Conclusions: This study highlights the significant impact of applying Kmed on dose differences between measurement and calculation during the dose audit process.