Mauro Valente & Victor Galván CONICET & FaMAF-Universidad Nacional de Córdoba, Argentina.

1. Fricke Gel dosimetry by means of visible light transmission imaging: State of the Project at University of Cordoba Mauro Valente & Victor Galván CONICET & FaMAF-Universidad Nacional de Córdoba, Argentina.

2. Glossary and Outlines • Modern Radiotherapy: Demand of accurate 3D dosimetric systems • Current dosimetry techniques and Fricke gel dosimeters • Fricke gel dosimetry I: Preparation and characterization & ferric ion diffusion • Background • Optimizations and Developed preparation Protocol • Dose-response characterization and Tissue-Equivalence study • Diffusion coefficient determination & Correction with time-deconvolution algorithms • Fricke gel dosimetryII: Suitability of FGD layer imaging & preliminary tests • Characterization of the optical system & Limitations of the technique • Photon and electron beam characterization • Comparisons with simulation of unique beam irradiations & Complex techniques simulations (Dynamic and multiple field radiotherapy) • Fricke gel dosimetryIII: Dedicated software & 3D dose imaging • Image recognition Dedicated algorithms for dose distribution calculation • Target volume by means of Fricke gel layer dosimeters • Dose Imaging: 3D reconstruction & “AQUILES – Real 3D”: a novel tool for 3D dose Imaging • Fricke gel dosimetryIV: Non conventional (mixed fields) dosimetry & BNCT • Versatility for advance (non conventional) dosimetry • Boron Neutron Capture Therapy (BNCT) applications • Fricke gel dosimetryV: Project at the University of Cordoba (ARG) • Current state of the Project for Fricke Gel layer –optically analyzed- dosimetry.

3. Modern Radiotherapy: “Complex” irradiation techniques During the last years, significant developments in Radiotherapy techniques, mainly due to the increasing technology and computer capability • Conformal Radiotherapy • Dynamic Radiotherapy • Radiosurgery • Intraoperative Radiotherapy • High dose rate Brachitherapy • Micro Beam Radiotherapy (mBR) • Intensity Modulated RadioTherapy (IMRT)

4. Current traditional dosimeters

5. Fricke gel dosimetry • Continuous chemical dosimeter • Based on ferrous sulphate solution • Chemical yield: Fe2+→ Fe3+ • Fixed to gel matrix (Spatial resolution) • Originally imaged by MRI • Negligible alteration of in-phantom transport properties • Suitable for visible light tranmittance analysis • Not complicated correction algorithms (ref. Index variation) • Versatility regarding chemical composition • Important advantages for neutron field irradiations (dose contribution separation) Suitably shaped in form of thin layers

6. Fricke Gel solution Fricke gel main Preparation Procedure • Gel powder is combined with half of the total quantity of water • Solution is heated (constant stirring and monitoring of temperature) • Solution is maintained at 45 °C for 20 minutes (gel powder dissolution) • Separate flask: Fricke (fer. sulph., sulp. acid), and XO with rest of the water • Gel solution led to cool until Fricke solution is added (T=42-40ºC) • Mixed solution should become clear, transparent orange • Final solution is transferred into pre-elaborated suitable containers • Normal T, P conditions for 10 minutes. Put batches (at least 12 hours) into the fridge (T=6-10ºC) Developed dedicated PROTOCOL

7. Visible light (yellow-orange) Optical imaging method for Fricke gel layer dosimeters Spectroscopy Analysis • Fixing standard Fricke solution to gel matrix (information spatially firmed) • Adding X.O. (marker) → Abs. peak displacement (580nm) and Diffusion slow down Standard Fricke solution: Absorption peak around 302nm … therefore, optical analysis by means of visible light transmittance becomes suitable for Frickegel dosimetry

8. Detector (CCD) Monochr. filter Dosimeter Dark mask Illuminator (homog. plane paral. visible light beam) Fricke gel dosimeter Imaging: Optical system

9. Transmittance measurement Interaction Process: material (μa, μs) – Inc. beam (parallel filtered polychr.) Radiation Transport Equation Bouger-Lambert-Beer Law

10. Beer’s Law (Abs.): Fe3+ chemical yield: ABSORBED DOSE CORRELATED TO Fe3+ CONCENTRATION, MEASURABLE BY MEANS OF TRANSMITTANCE IMAGES

11. Fricke dosimeter (3% GPS) layer dose response curve and linear fit up to 30 Gy for a 18 MV photon beam. Fricke gel layer dosimeter dose-response The dosimeter dose response depends on several factors, but it has been shown that under proper conditions, dose response is linear to some extent. Characterization of some parameters affecting dosimeter dose-response

12. Ferric ion diffusion in Fricke gel layer dosimeters Diffusion effect in Fricke gel dosimeters. Gel matrix is used to locally fix the XO-infused ferrous sulphate solution, enabling spatial resolution due to the slowing down in the movement of the ferric ions produced. Dose distribution is deteriorated: Limitation of Time interval for sample imaging Accurate dose distribution measurements: Prompt Imaging or Correction Algorithms TASK Diffusion is a convolution process → correlation between concentration distributions at any time with the initial one. • Full description of the ferric ion diffusion effect: • 3D solution of the diffusion equation • Considering steepness of the concentration distribution.

13. Diffusion model and diffusion coefficient calculation D-E derived from: 1. Langevin equation (considerating Brownian motion) 2. Fokker-Planck equation (evolution of stochastic systems) • Suitable initial dose distribution: Step-Function (Heaviside) • Experimental Arrengement: dedicated cerrobend blocks conforming circular (Ǿ=3cm) and rectangular (4x2cm2) • 12MeV electron beam F.S.=5x5cm2 1D approach for the diffusion coefficient calculation 2D approach for the diffusion coefficient calculation • Suitable initial dose distribution: Almost-punctual (Dirac Delta) • Experimental Arrengement: dedicated cerrobend block with hole circular (Ǿ=1mm) • 12MeV electron beam F.S.=10x10cm2

14. T0 T=300min T=600min T=900min T=1200min T=3000min Square of 1D Gaussian spreads in function of time and linear fit for rectangular shape (left) and circular shape (right). 1D solution Diffusion: 1D Approach

15. Square of Gaussian spreads as a function of time and linear fit.

16. 60Co Gamma Beam (F.S.:10x10cm2, SSD:80cm) Fricke gel layer dosimeters: Unique Beam Application to Photon (Gamma and high energy R-X) beams

17. Application to Photon (Gamma and high energy R-X) beams 6MV Beam Varian 600C (F.S.: 10x10cm2, SSD:100cm)

18. Application to Photon (Gamma and high energy R-X) beams 10MV Beam Varian 18 (F.S.: 10x10cm2, SSD:100cm)

19. Application to Photon (Gamma and high energy R-X) beams 18MV Beam Varian 2100 (F.S.: 5x5cm2, SSD:100cm)

20. Application to high energy electron beams 16MeV Beam Varian 2100 (F.S.: 10x10cm2, SSD:100cm)

21. Application to high energy electron beams 6MeV Beam Varian 18 (F.S.: 20x20cm2, SSD:100cm)

22. AQUILES: Dose Imaging software • MatLab environment • Dedicated algorithms for Image recognition, process and analysis. • User Graphic Interface • Algorithm and Numeric Methods Optimization (speeding up)

23. κ Calculation Algorithms - AQUILES: γ

24. AQUILES: Application Examples IMRT: FGD layer dosimetrey & TPS data process and analysis

25. AQUILES – Real 3D: Versatile AQUILES subroutine for accurate 3D dose Imaging AQUILES – Real 3D

26. 3D dose Imaging by means of 7 piled up Fricke gel layer dosimeters for Multiple-Field (Box) technique Cortesy: Image from M. Valente PhD Thesis AQUILES – Real 3D:Application Great capability for 3D dose Imaging Multiple Volumes of Isodose Visualization Dynamic radiotherapy (90º Arc tenchnique) by means of dedicated MC simulations

27. HDRB: Scanner Image (right) and Dose distribution (left)

28. Fricke gel layer dosimeter (up) and TPS (bottom) for a typical IMRT (non-perpend. beam) Irradiation In terms of standard IMRT criteria for accuracy (Gamma-Function) this measurement represents the best one ever done (EPID, Film, scanning Sys) at an important Radiotherapy Institute

29. State of the Project at University of Cordoba (ARG) • Proper Laboratory facility: OK (already accomplished!) • Fricke gel dosimeter preparation: OK (already accomplished!) • FGD optical properties characterization: OK (already accomplished!) • Adaptation of test radiation facility: OK (already accomplished!) • Dedicated facility design & construction for FGD optical analysis by means of visible light transmission: OK (already accomplished!) • Characterization of optical analysis facility: Work in progress (curtrently perfomed) • Available for multitask purposes: Coming soon ….

30. This Study was partially supported by the Italian government (results up to 2007) whereas argentine entities like CONICET, ANPCyTandSeCyT-UNC have supported and granted it since 2008. THANKS FOR YOUR ATTENTION! GRACIAS POR SU ATENCIÓN!