Determination of Percentage Depth Dose (Pdd) of Pagat Gel Dosimeter By Electron Beams

Background: The purpose of this study was to determine the percentage depth dose (PDD) of PAGAT normoxic polymer gel dosimeter by electron beams using MRI technique for a standard clinically used Co-60 therapy unit and an electa linear accelerator. Materials and Methods: Using MRI, the formulation to give the maximum change in the transverse relaxation rate R2(1/T2) was determined to be 4.5% N,N'-methylen-bis-acrylamide(bis), 4.5% acrylamid(AA), 5% gelatine, 5 mM tetrakis (hydroxymethyl) phosphonium chloride (THPC), 0.01 mM hydroquinone (HQ) and 86% HPLC(Water). When the preparation of final polymer gel solution is completed, it is transferred into phantoms and allowed to set by storage in a refrigerator at about 4C. Results: The response of PAGAT gel with electron beams is very similar in the lower dose region and the R2-dose response was linear up to 30Gy. The R2-dose response of the PAGAT polymer gel dosimeter is linear between 10 to 30Gy. In this study, the percentage depth dose (PDD) of PAGAT polymer gel dosimeter is determined and the vials of PAGAT gels were irradiated to 25Gy of doses with electron beams. In electron beams the maximum percentage depth dose (PDD) is located at the depths of 1, 2 and 3cm. At depth of 21cm, the percentage depth dose for 8, 12 and 18MeV is determined, 40.08%, 49.79% and 53.11% respectively. Conclusion: Therefore, to determine PDD dependence of PAGAT gel in electron beams, we concluded that in the case of the higher energy electron beams, higher doses can be delivered to deep-seated tumors. Key word: PAGAT gel, electron and photon beams, PDD, post time, MRI.