Lic. Pedro Antonio Pérez

Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry Lic. Pedro Antonio Pérez Facultad de Matemática, Astronomía y Física Universidad Nacional de Córdoba

Outlines & main goals • To develop a simple and versatile dosimetric method capable of determining changes in matter (Xylenol Orange added Fricke gel) due to ionizing radiation. • To design and construct a preliminar device (hardware and software) in order to quantify absorbed dose by means of visible light absorption. • To establish applicability limits of extremely simple devices. P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Introduction • Nowadays, the development of novel dosimetric techniques has become great interests. • Optical analysis: Standard Fricke solution presents maximum absorption at 294nm (ultraviolet). • X. O. Fricke gel has maximum absorption at 585nm (visible). • Spatial resolution can be obtained fixing the X.O. Fricke solution to a gel matrix. • X. O. Fricke gel dosimeters, which constitute tissue-equivalent media for radiotherapy purposes, are capable of providing real 3D dose mapping. P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Theoretical Background • Boltzmann Radiation Transport Equation • Parallel beam • ma>>ms P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Theoretical Background • Contiuous light source • Then, • Wich solution is the Lambert-Beer eq. P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Theoretical Background • From L-B • Light absorption law • z≈Cd, then • And the Optic al Density differences result: P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Materials and methods • Dosimeter preparation: • Chemical composition • Protocol P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Materials and methods • Experimental Set Up: • Dispositive description P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Materials and methods Get image Get red channel • Developed software: Calculate XCM Calculate 2° moment Calculate s (Rm) Get ROI Get definitive image Calculate VM on new ROI and new s P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Materials and methods • Radiation facilities: • Conventional X-Ray tube • W anode. Mo cathode. V=40kV. 40mA • CLINAC • Varian 6/100 P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

ResultsExperimental Set Up characterization. Preliminary tests. • Repetitivty and stability of the sistem source-dosimeter-camera • Results: • Stability: I=25,6+0,6 Repetitity: I=26,7+0,4 • Diference on both modes: 4% P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Measurement and data processingExperimental Set Up characterization. Preliminary tests. • Software validation by Gauss function • Some results • Some distributions P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Measurement and data processingExperimental Set Up characterization. Preliminary tests. • Software validation • 2 VM known functions • Constant I píxel to píxel (VM) • Variable I pixel to pixel (ROI) • Results: • Fixed I: VM=1, s=0 • Variable I: P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Measurement and data processingOn X-Ray tube. • Characterization of the developed device for optical analysis • Results: • Serie 1:DOD=0,16+0,01. Error: 6,7%. • Serie 2: characteristic curve “exposition time-response” P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Measurement and data processingOn CLINAC • Two elaboration series to be irradiated by means of CLINAC: characteristic curve of “dose-response” and “depth dose” (to compare with standard dosimetric system -ionization chamber). • One elaboration serie to be irradiated by means of X-Ray tube and repeat the experience to obtain characteristic curve “exposition-response” P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Preliminary measurements On CLINAC – in-depth dose Irradiated samples Dose on depth and comparison with ionization chamber P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Discussion, conclusions andoutlook • Software validation • It has been verified the correct determination of relevant qquantities (VM, Rm, CM and ROI). • It has been established the consistency for the realization of the diferent steps relative to communication with hardware, signal acquisition and data interpretation and subsequent processing. • Response of the integral system (source-dosimeter-software) • It was possible to stablish the REPRODUCIBILITY (non-distinguishable), stability (less than 1.6%) and repetitivity (less than 2.4%). • The reults show clearly linearity region, as it was expected, even with supra and sub linear zones. • Response curves, which have been found to be indistinguishable, demonstrated the reproducibility of the whole dosimeter elaboration procedure. • In addittion • Device dimensions (20cm side box) allow its portability, therefore improving its comfortability for CLINAC measurements. • Preliminary PDD determination, as compared with ionization chamber, show hopeful results. P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Discussion, conclusions and future lines • Main conclussions • It was demonstrated that, even considering extremely simplcity of the the device component, it is possible to develop suitable systems capable of determining absorbed dose by means of visible light transmittance measurements, particularly with radiochromic dosimeters. • Perspectives • A lot of future improvements are been considered for the developed device regarding its applicability limits and accuracy. Specially, a better detector quality may improve significantly the overall performance. • Several techniques devoted to 1D and 2D dose mapping are under investigation. P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

Lic. Pedro Antonio Pérez