Lic. Pedro Antonio Pérez. To develop a simple and versatile dosimetric method capable of...

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

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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

Outlines & main goals

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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.

Introduction

P. Pérez, V. Galván, M. Valente - Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke

dosimetry

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Boltzmann Radiation Transport Equation

Parallel beam

ma>>ms

Theoretical Background

drIrIrIntc

ssa

,4

ˆ1


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Contiuous light source

Then,

Wich solution is the Lambert-Beer eq.

zI

dsenzIzIdrIrI

a

sa

ssa

24

,4

z

zI

kz

zI

t

zI

crIn

tc

,0,0

ˆ1ˆ

1

zIdz

zdIa

zIaeIzI 0



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From L-B

Light absorption law

z≈Cd, then And the Optic al Density differences result:

zI

zI

0

ln

dCA

zA

d

a

I

IOD 10log



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Dosimeter preparation: Chemical composition

Protocol

Materials and methods

Comp. H2O G. H2O F. G.P.S. X.O. Sulf. Fe+2 H2SO 4

100ml 50ml 47ml 3,0389g 0,0125g 0,0196g 1,39ml


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Experimental Set Up: Dispositive description



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Developed software:

Get image Get red channel

Calculate XCM Calculate 2° moment

Calculate s(Rm)

Get ROI

Get definitive image

Calculate VM on new ROI and new s



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Radiation facilities:

Conventional X-Ray tube

W anode. Mo cathode. V=40kV. 40mA

CLINAC

Varian 6/100



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Results Experimental 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%


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Software validation by Gauss function

Some results

Some distributions

(ic,jc) y s escrito (ic,jc) calculado

(50,25) y 10 (50,25)

(25,50) y 10 (25,50)

(50,50) y 5 (50,50)

(75,75) y 5 (75,75)

Measurement and data processing Experimental Set Up characterization.

Preliminary tests.


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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:

Measurement and data processing Experimental Set Up characterization.

Preliminary tests.


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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”

Measurement and data processing On X-Ray tube.


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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”

Measurement and data processing On CLINAC


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Irradiated samples

Dose on depth and comparison with ionization

chamber

Preliminary measurementsOn CLINAC – in-depth dose


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Discussion, conclusions and outlook

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.


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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.

Discussion, conclusions and future lines


Lic. Pedro Antonio Pérez. To develop a simple and versatile dosimetric method capable of...

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