Developing and improving a scanning system for dosimetric applications

1. Developing and improving a scanning system for dosimetricapplications P. Pérez, V. Galván, G. Castellano & M. Valente Facultad de Matemática, Astronomía y Física Universidad Nacional de Córdoba

2. 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 2D-scanning 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, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

3. Introduction • Nowadays, radiotherapy is one of the most used techniques for the treatment of different pathologies. • The accuracy regarding the application of these treatments depends mainly on the dosimetric measurements of absorbed dose within irradiated tissues. • The development of novel dosimetric techniques has become great interests. • A dosimetric device capable of performing bidimensional dose mapping suggests a high pontenciality for clinical applications P. Pérez, V. Galván, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

4. Introduction • 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, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

5. Theoretical Background • Boltzmann Radiation Transport Equation • Coherent and parallel beam • ma>>ms P. Pérez, V. Galván, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

6. Theoretical Background • Contiuous (stable) light source • Then, • Wich solution is the Lambert-Beer eq. P. Pérez, V. Galván, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

7. Theoretical Background • From L-B • Light absorption law • z≈Cd, then • And the Optical Density Differences (ΔOD) become: P. Pérez, V. Galván, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

8. Materials and methods • Dosimeter preparation: • Chemical composition (150ml final volume) • Protocol P. Pérez, V. Galván, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

9. Materials and methods • Experimental Set Up: • Device description for 1D acquisition P. Pérez, V. Galván, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

10. Materials and methods • Experimental Set Up: • Device description for 2D acquisition P. Pérez, V. Galván, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

11. Materials and methods Get image Get red channel • Developed software for 1D acquisition: 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, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

12. Materials and methods • Set up for dose mapping: • Conventional X-Ray tube • W anode. Mo cathode. V=40kV. 40mA • In-home X-Y shifter + dedicated control software • LINAC • Varian 6/100 P. Pérez, V. Galván, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

13. Measurement, data processing and some results.Experimental Set Up characterization. Preliminary tests. • Reproducibility and stability of the source-dosimeter-camera system for 1D acquisition • Results: • Stability: I=25,6+0,6 Reproducibility : I=26,7+0,4 • Discrepancies between different modalities lees than 4% • Software validation by means of testing with Gaussian function • Performance for Gaussian function center recognition • Examples of test distributions P. Pérez, V. Galván, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

14. Measurement, data processing and some results.Software validation • Software validation • 2 Mean Value (VM) a priori well-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, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

15. Measurement, data processing and some results.On 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, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

16. Measurement, data processing and some results.Preliminary tests on 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, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

17. Preliminary measurements On CLINAC – in-depth dose Irradiated samples In-depth dose and comparison with ionization chamber P. Pérez, V. Galván, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

18. Preliminary validations for 2D acquisition system Adjusting camera focus System sensor calibration by means of well- known reference sample P. Pérez, V. Galván, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

19. Preliminary measurements On 2D acquisition system P. Pérez, V. Galván, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

20. Preliminary measurements On 2D acquisition system P. Pérez, V. Galván, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

21. Discussion, conclusions andoutlook • Software validation for 1D acquisition • 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, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

22. Discussion, conclusions andoutlook • Some considerations for 2D aquisitions • The development of the 2D dose acquisition system should be based on the same theoretical background. • Disadvantages: need of a quite parallel incident beam (hard to assess). The lack of it may produce a unstable system. • To decide • Approach 1: To image the sample (mounted on the X-Y positioning system) at each mechanical step and to reconstruct (integrate) whole sample image at the end of the process. • Approach 2: To image the sample at each mechanical step acquiring signal analogue to the 1D case, i.e. to insert a collimation system along with automatized image processing algorithms. • In addittion • Device dimensions (40x30x20 cm3) allow its portability, therefore improving its comfortability for clinic measurements. • Preliminary measurements can determine de irradiated zone but have some problems with the border. • In view of obtained results, the overall performance of the system suggests its feasibility P. Pérez, V. Galván, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

23. 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, G. Castellano & M. Valente - Developing and improving a scanning system for dosimetric applications

24. Thanks