Feasibility of using a transmission reference detector for beam commissioning measurements

This study investigates the feasibility of using a transmission detector (Stealth Chamber, IBA) as a reference detector for beam commissioning measurements by comparing the beam data measured with an air-filled ionization chamber (CC13, IBA). The percentage depth doses (PDDs) and dose profiles of 6 MV, 6 MV flattening-filter-free (FFF), and 15 MV photon beams were acquired with CC13 chamber as the field detector and the Stealth Chamber and CC13 chamber as reference detectors. The PDDs and dose profiles were measured under various field sizes. The profiles were acquired at 5, 10, 20, and 30 cm depths, as well as at the depth of maximum dose (dmax) for each beam quality. For PDD comparisons, the differences in selected dosimetric parameters were evaluated. The agreement between the profiles was determined by calculating the root mean square error (RMSE). The study found that the differences in dmax, depth of 80% of the maximum dose deposition (d80%), and d50% between the Stealth Chamber and CC13 chamber were within 0.2 cm for field sizes up to 25 x 25 cm2. The differences between PDD at 10 and 20 cm were less than 1% for all field sizes and beam qualities. Strong profile agreements were confirmed, with RMSE values consistently below 1% across beam qualities, depths, and sizes. Using the Stealth Chamber as the reference chamber for measuring commissioning beam data is a viable option for field sizes of up to 25 x 25 cm2, though caution is necessary for larger field sizes.