بررسي درصد دز عمقي باريكه هاي فوتوني و وابستگي آن به آهنگ دز در دزيمتر - پلي مري نورمكسيك PAGAT با استفاده از تكنيك ام.آر.آي

Investigation of Percentage Depth Dose (PDD) and Dose Rate Dependence of PAGAT Polymer Gel Dosimeter for Photon Beams Using MRI Technique

In this work, the investigation of the normoxic PAGAT polymer-gel dosimeter percentage depth dose (PDD) and itʹs dose rate dependence has been made. Using MRI, the formulation to give the maximum change in the transverse relaxation rate R2 was determined to be 4.5% N,Nʹ-methylen-bis-acrylamide©(bis), 4.5% acrylamid (AA), 5% gelatine, 5mM tetrakis (hydroxymethyl) phosphonium chloride (THPC), 0.01 mM hydroquinone (HQ) and 86% HPLC(Water). Irradiation of vials was performed using photon beams of Co-60 therapy unit and an Electa linear accelerator. Gel dosimeters were imaged in a Siemens Symphony 1.5 Tesla clinical MRI scanner using a head coil. Post-manufacture irradiation and post imaging times were both selected to be 1 day. For determing the percentage depth dose of the PAGAT gel it was found that at the depth of 21cm, the percentage depth dose for 1.25 MeV y-ray photons of 60Co and for 4,6 and 18 MV x-ray photons of Electa linear accelerator, are 48%, 52%, 57.3% and 59.73%, respectively. Thus, in the case of the higher energy photon beams, a higher dose can be delivered to deep-seated tumors. The dose rate dependence of PDD was studied for 6 MV x-ray photons with the use of dose rates of 80, 160, 240, 320, 400 and 480cGy/min. No trend in polymer-gel dosimeter 1/T2 dependence was found on the mean dose rate and energy for the photon beams.