Feasibility of linear diode array based small field data acquisition for 6 MV & 15 MV photon beams - An intercomparison with micro ion chamber

This study aims at evaluating the response of different radiation detectors for measurement of small field radiotherapy beam profiles for high energy photon beams. Micro ion chamber (IC, CC01, IBA) and linear diode array (LDA-99SC, IBA) were used to measure beam data on Siemens ONCOR Impression linear accelerator for 6 MV and 15 MV photon beams. For both detectors the beam profiles were acquired in water phantom for nominal small field sizes ranging from 1 x 1 cm(2) to 5 x 5 cm(2) at depths of maximum dose (d(max)), 5 cm and 10 cm. Measured profiles were inter compared using gamma analysis at pass criteria of 1.5%/1.5 mm and 1%/1 mm and characterized with full width half maximum (FWHM) and penumbrae width. The gamma pass rate for all profiles of both energies has been found to be 100% (using 1.5%/1.5 mm) and 90% (using 1%/1 mm) except for 15 MV - 1 x 1 cm(2) field size. Though, the effect of measurement depth has been found to be insignificant on beam matching with two detectors. For both energies, no considerable difference has been observed in FWHM of profiles as measured with the two detectors, with a slight increase in penumbrae size for LDA. It has been found that 6 MV beam profiles of IC and LDA show a reasonable match whereas a noticeable difference has been observed for 15 MV beam in penumbrae region. In addition, a substantial dose overestimation can be seen for LDA in the out of field region for both energies.