Verification of the PAGAT polymer gel dosimeter by photon beams using magnetic resonance imaging

Background: In this work investigation of the normoxic PAGAT polymer gel dosimeter such as sensitivity, the R2-dose response with post time and the percentage depth dose (PDD) of PAGAT polymer gel dosimeter have been undertaken. Materials and Methods: Using MRI, the formulation to give the maximum change in the transverse relaxation rate R2 was determined to be 4.5% N,N'-methylenbis- acrylamide ©(bis), 4.5% acrylamid(AA), 5% gelatin, 5 mM tetrakis (hydroxymethyl)phosphonium chloride (THPC), 0.01 mM hydroquinone (HQ) and 86% HPLC (Water). Irradiation of vials was performed using photon beams by 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. Gel dosimeters were irradiated 1 day post-manufacture, and imaged 1 day post irradiation. Results: The R2- dose response was linear up to 30 Gy. The response of the PAGAT gel is very similar in the lower dose region and the R2-dose response for doses less than 2 Gy is not exact. The R2-dose response of the PAGAT polymer gel dosimeters varies between 10 to 30 Gy with R2-dose sensitivities of 0.0905, 0.1037, 0.1023, 0.0907 and 0.123 S-1Gy-1 when imaged at 1, 8, 15, 29 and 38 days post-irradiation respectively. The percentage depth dose (PDD) of PAGAT gel dosimeter was determined and at depth of 21cm, the percentage depth dose for 1.25, 4, 6 and 18 MV photons were determined to be, 48%, 52%, 57.3% and 59.73% respectively. Conclusion: Calibration curve of the PAGAT polymer gel dosimeter, were found to be linear between 2-10 Gy and 10-30 Gy with different slopes of the R2-dose sensitivity also showed stability with post time imaging after 38 days. In this study, the percentage depth dose (PDD) of the PAGAT gel dosimeter was measured. It can be concluded that in case of higher energy of photon beams, higher doses can be delivered to deep-seated tumors.