Angular dependence of the TL and OSL dosimeters in the clinical 6 MV photon Beam.

The angular response of luminescent dosimeters (LD), in particular TLD and OSLD, has been compared by applying 6 MV X-ray photons from Versa HD clinical linear accelerator. The study admitted for the irradiation of TLD (n = 475) and OSLD (n = 475) under phantom set up in various gantry angles from 0 to ±90 and various field sizes from 10 x 10 cm to 30 x 30 cm. The variance in the output was observed between 4.4% for TLD and 3.9% for OSLD. A significant deviation from the desired output was detected, towards the angle of incidents, at ±80 to ±90. Additionally, there is no evidence of variation in the dose measurement due to the difference in field size. These results demonstrate a good approximation to the vendor-specified tolerance limits, justifying the use of these LDs within angular incidents of radiation up to ±70. The TLD and OSLD better dose-response is achieved to a gantry angle up to ±70 from the perpendicular incidents. The result shows that both TLD and OSLD could be used as dosimeters for a treatment field that does not extend beyond ±70 beam angle.