Performance of Radiation Dosimeters in Gradient Regions at Different Dose Rates of Linear Accelerators

Introduction: This work aimed to evaluate the accuracy of using parallel plane against thimble chambers in beam data commissioning of the high dose gradients region for versa HD linear accelerator performing clinical advanced modulated radiation treatment techniques.Material and Methods: All clinical commissioning data were collected from Elekta Versa HD for energies of ۶ MV, ۱۰ MV, ۶ MV FFF, and ۱۰ MV FFF for different field sizes using thimble ionization chamber CC۱۳, some from the pool of the measured data were rescanned using parallel plate chamber PPC۰۵ and Gafchromic films and compared to those collected using the thimble ionization chamber.Results: The skin doses differences measured by thimble chamber against reference films were (۰.۸%, ۰.۵%, ۱.۲% ۴.۷%) and for the parallel plane chamber against films were (۸.۴%, ۹.۷%, ۹%, ۱۲%) for ۶ MV, ۱۰ MV, ۶ MV FFF, ۱۰ MV FFF, respectively. The parried test-test showed a highly significant difference (p> ۰.۰۰۱) between the two chambers in measurements of penumbra regions taking over all the investigated field sizes and depths in both inline and crossline datasets. The parallel plate showed a wider and broader penumbra than the thimble chamber and films.Conclusion: Robust and consistent scans were obtained for the thimble chamber compared to the parallel plane chamber in the highest dose gradient of buildup and penumbra regions. Using a parallel plane chamber might bring dosimetric clinical uncertainties affecting the modeling of the gradient regions in the treatment planning system.

Keywords:

Flattening Filter Free (FFF) , Thimble ionization chamber , Parallel plate ionization chamber , Gafchromic films , Radiation dosimeter