DIFFUSION AND SENSITIVITY CHARACTERISTICS OF A CHEMICALLYCROSS-LINKED PVA-FRICKE GEL DOSIMETER

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Abstract

Introduction: Current radiotherapy techniques implement treatment plansbased on volumetric distributions of dose with complex shapes and sharpgradients. The agreement between these plans and the dose that is trulydelivered is very challenging to verify. Thus, there is the need for a dosimetricsystem that is truly three dimensional, sensitive to radiation in eachpoint and tissue equivalent. In this framework, great interest is encounteredby radio-chromic gel dosimeters. In order to address the limitations of gels based on natural matrices, someinvestigators have proposed dosimeters based on poly vinyl alcohol (PVA)made by freezing-thawing cycles. Even though these gels have a low diffusionrate, they are also difficult to prepare and they have low sensitivity.Furthermore, depending on the gelation temperature they can only be readout by MRI. We hereby present a PVA gel that is chemically crosslinked,and that offers high sensitivity and low diffusion. These gels can be readout with optical techniques.Materials and Methods: The proposed gel contains 10% w/v of PVA andis crosslinked by adding glutaraldehyde (GTA). A common formulation gelatingel was also prepared and studied for comparison. Both gels contain XylenolOrange and the “Fricke” chemical dosimeter: 25 mM sulphuric acid and0.5 mM iron ammonium sulphate.Absorbance measurements were done to assess sensitivity and diffusioncoefficient of the gel.Results: The dose response of our dosimeter is linear between 0 and 30 Gyand its sensitivity is equal to 0.073 Gy−1. The diffusion coefficient of the PVAbasedgel is 0.23 mm2/h. These characteristics were compared to gelatinand to data available for so called PVA hydrogels and cryogels.Conclusions: Our dosimeter made with PVA and crosslinked with GTAshowed a sensitivity that is comparable to gelatin, and greater than PVAhydrogels. The diffusion coefficient is 0.23mm2/h, against 0.56 and 0.14 ofgelatine and cryogels.
Lingua originaleEnglish
Numero di pagine1
RivistaPHYSICA MEDICA
Stato di pubblicazionePublished - 2016

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