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Measurements aimed at investigating the quenching of sensitivity of Gafchromic EBT3 films irradiated with charged particles at radiotherapy energy levels have been carried out. Films have been irradiated with beams of protons and carbon ions of interest for Hadron Therapy. The broadening of pencil beams in water phantom as a function of initial energy has been studied and the quenching of EBT3 film sensitivity has been quantified. A procedure for correcting the dose images obtained by means of EBT3 films has been improved and its application to an irradiation test has show the validity of the proposed methodology.

The quenching of sensitivity of non-gaseous dosimeters exposed to charged particles was studied, in particular with reference to gel dosimeters and gafchromic EBT3 films. The studies were focused to dosimetry for Hadron Therapy and boron neutron capture therapy (BNCT). A correction coefficient can be more easily determined for BNCT dosimetry, while it is complex to correct the dosimeter response in the case of charged particle beams for Hadron Therapy. A proposed method for correcting the measured images is in continuous development.

Introduction Fricke gel dosimeters allow measurements of 3D dose distributions and can be an effective tool for dosimetry verifications in radiotherapy. Various authors have reported drawbacks of the gels affecting the accuracy in case of low dose measurements. Purpose This study aims at investigating such drawbacks and at establishing the conditions for an optimal use of the gels. Materials and methods Our dosimeters consist of gels infused with a Fricke ferrous sulphate solution combined with xylenol orange (XO). Two kinds of xylenol orange (XO) and two different gelling agents (gelatin from porcine skin and Agarose) were utilized. Gels are red out by light absorption techniques: images of absorbance in two wavelength regions (around 430 nm and 585 nm) are acquired with a CCD camera. Absorbance spectrum measurements were done with a compact spectrometry based on optical fibres. Magnetic resonance (MR) measurements of Longitudinal Relaxation Time (T1) were also performed. Results Different trends characterized the absorbance spectra of dosimeters obtained with different gelling agents or different XOs. Moreover, the trends were different for different absorbed doses and varied over a few hours after irradiation. Conclusion The variation of the absorbance spectra is consistent with various previously unexplained effects reported in literature and may explain them. The results are a valid aid for a better use of these dosimeters and warrant further studies of the changes in the Fricke gel matrices after irradiation. Disclosure Authors declare no relationship that may bias the presentation.