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3D DOSIMETRY

3D DOSIMETRY. Prof. Mauro Valente, PhD. Medical Physics – FaMAF http://www.famaf.unc.edu.ar/~valente/. CONICET & Universidad Nacional de Cordoba ARGENTINA. The GOAL. Could be possible to develop a novel dosimetric

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3D DOSIMETRY

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  1. 3D DOSIMETRY Prof. Mauro Valente, PhD. Medical Physics – FaMAF http://www.famaf.unc.edu.ar/~valente/ CONICET & Universidad Nacional de Cordoba ARGENTINA

  2. The GOAL Could be possible to develop a novel dosimetric technique with tissue-equivalent properties and capable of 3D dosimetry as well as dose separation at mixed fields? HINT: water-based dosimeters with wide flexibility (chemical & isotopic composition, shape, density)

  3. Glossary and Outlines • Modern Radiotherapy: Demand of accurate 3D dosimetric systems • Standard dosimetry techniques and Fricke gel dosimetry • Preparation and characterization of Fricke gel dosimetry • Background – Optimizations and Developed preparation Protocol • Dose-response characterization and Tissue-Equivalence study • Ferric ion diffusion of Fricke gel layer dosimeters Diffusion coefficient determination – Correction by means of dedicated time-deconvolution algorithms • Suitable method for Fricke gel layer dosimeter imaging Characterization of the optical system – Limitations of the technique • Mixed field techniques requiring dose contribution separation Preliminary tests – BNCT applications – Soft tissue-equivalent and lung-equivalent compositions – Chemical & isotopic flexibility suitable for BNCT dosimtry • Suitable method for 3D dose distribution determination Modeling a target volume by means of Fricke gel layer dosimeters – Dose Imaging: 3D reconstruction – “AQUILES – Real 3D”: a novel tool for 3D dose Imaging • General conclusions Developed preparation Protocol – Applications to dose distribution measurements – Developed 3D dose imaging method: Highlights – Main Advantages-Disadvantages and future improvements

  4. Modern Radiotherapy: “Complex” irradiation techniques During the last years, sifnificant 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) • BNCT

  5. Modern RT: Demand for suitable detectors • High resolution • High accuracy and precision • Linearity of signal with dose over a wide range (prefered) • Three dimensionality • Independence of incident beam orientation • Dose integration capability • Independence of energy • Independence of dose rate • Tissue equivalence • Important to know the limitations (suitably characterizated)

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

  7. Current traditional dosimeters

  8. Demand and Motivation for accurate 3D dosimetry • Growth in multi-field techniques • Growth in 3-D planning • Growth in dynamic delivery • Verification of 3-D plans • Dosimetry in complex geometries • BNCT dose contributions separation • MC techniques and numerical algoritms for Dosimetry in 3-D FRICKE GEL DOSIMETERS ARE A PROMISING TOOL … some disadvantages?? • ACCESS TO MRI FACILITIES • FERRIC ION DIFFUSION

  9. Fricke gel chemical composition

  10. 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

  11. 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 (585nm) and Diffusion slow down Standard Fricke solution: Absorption peak around 302nm … therefore, optical analysis by means of visible light transmittance becomes suitable for Fricke gel dosimetry

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

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

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

  15. 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 • Xylenol Orange concentration • Cooling rate • Radiation quality and dose rate • Dosimeter layer width • Irradiation temperature • Time elapsed between preparation and irradiation 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

  16. 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: 1. 3D solution of the diffusion equation 2. considering steepness of the concentration distribution.

  17. 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

  18. T0 T=300min T=600min T=900min T=1200min T=3000min 1D solution (actual bond. and initial cond.) Diffusion: 1D Approach

  19. Some relative deviation of optimized model and experimental data. Top on the left: 30 minutes after irradiation, top on the right: 90 minutes after irradiation, bottom left: 600 minutes after irradiation and bottom right: 1200 minutes after irradiation. Sequence of some optical density differences (ΔOD) profiles and model fits (red solid lines) at several times after irradiation corresponding to the rectangular initial distribution. Top on the left: 30 minutes after, top on right: 90 minutes after, bottom on the left: 600 minutes after, bottom on the right: 1200 minutes after. Experimental data and proposed model Differences

  20. Square of 1D Gaussian spreads in function of time and linear fit for rectangular shape (left) and circular shape (right).

  21. Transmittance (585nm) image (45 minutes after irradiation) and region within D was calculated. Diffusion: 2D Approach n is the “isotropic dimensionality” n=1 for 1D and n=2 for 2D (isotropic media)

  22. Square of Gaussian spreads as a function of time and linear fit. Sequence of some relative deviations of experimental and the optimized proposed method for 2D approach. Top on the left: 45 minutes after, top middle: 94 minutes after, top on the right: 124 minutes after, bottom on the left: 163 minutes after, bottom middle: 203 minutes after and bottom right: 239 minutes after.

  23. Optical density differences at 200 minutes after irradiation. Gaussian’s “presumed” centres indicayed with the coloured cross. Spatial distribution corrections by means of calculated Dif. Coef. Dedicated experiment • 120x120mm2 Fricke gel dosimeter • 12MeV electron beam (Varian Clinac) F.S. 20x20 cm2 • suitable shielding cerrobend block (collimation): narrow beam • irradiated positioning the hole of the shielding at two different positions and delivering 8 and 16Gy, respectively.

  24. Experimental (left) and calculated (rigth) dose distributions at 45 minutes after irradiation and dose difference (bottom). Dose distributions at 200 (rigth) and 45 (left) minutes after irradiation and dose difference (bottom).

  25. 60Co Gamma Beam (F.S.:10x10cm2, SSD:80cm) Fricke gel layer dosimeters: Single Beam Application to Photon (Gamma and high energy R-X) beams

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

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

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

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

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

  31. AQUILES:Dedicated software for 3D dose imaging • Read out Images (GLBef,GLAft). Convert to matrices. • Correct power supply and optical path variations. • Choose the ROI. • Calculate DDO and Dose (suitable coef.). • For 3D imaging: definition of dose tensor. • Scale according pix:=mm. • Calculate corresponding errors. • Visualization: punctual, profiles, surfaces or volumetric dose distribtions.

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

  33. κ Calculation Algorithms - AQUILES: γ

  34. AQUILES: Application Examples TPS data process and analysis Fricke gel layer dosimeters (Scanner Imaged) Fricke gel layer dosimeters (CCD Imaged) Monte Carlo dose distributrion analysis

  35. Suitable method for 3D dose Imaging TASK … but,… hard procedure?? Large time-consuming??? • Novel method for 3D dose Imaging by means of Fricke gel layer dosimeters • Dedicated Graphic Interface for volume visualization • 3D body reconstruction (single slices, e.g. computerized tomography) • 3D sensitive volumes suitably conformed by piling up several gel layers • Defining Tensor from claculated single layers • 3D Reconstruction by means of 3rd order spline method • Sample-to-sample sensitivity normalization (pre-irradiation,…???) AQUILES - Real 3D

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

  37. 3D dose Imaging by means of 7 piled up Fricke gel layer dosimeters for Multiple-Field (Box) technique 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

  38. Surface Intersection (ARBITRARY) 3D Reconstruction

  39. Fricke gel layer dosimeters for “Complex” Tenchnique Irradiations Multiple-field irradiation techniques Dynamic radiotherapy IMRT technique Multileaf collimator technique Conformal block technique

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

  41. 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

  42. PhB BNCT: Examples of utilized phantoms • Cylindric phantoms (height 14 cm, diameter 16 cm). • Phantom 0 (Ph0) is of homogeneous Polyethylene. • Phantom A (PhA) is a Polyethylene shell containing gel with • 10 ppm of 10B. • Phantom B (PhB) is like • PhA, with a cylindrical • volume containing 35 • ppm of 10B. One half of phantom PhB

  43. and SEPARATION of the doses due to ( + nfast) and to the charged particles from 10B (35 ppm). Example of results: TOTAL DOSE (gamma, fast neutrons, charged particles emitted in the 10B(n,)7Li reaction with 35 ppm of 10B) in the central plane of a cylindrical gel phantom containing 10 ppm of 10B in all the volume (PhA).

  44. Flux profile in the central axis of the phantom, obtained from the 10B dose image and comparison with the results of TLDs and activation foils. Control of the correctness of the separation • The central profile has been extracted from the 10B dose image. • From the dose profile, by means of kerma factors, the flux profile has been evaluated. • The so obtained flux profile has been compared with the results obtained by means of TLDs or Au foils.

  45. Gamma and fast neutron doses are separated by means of a couple of gel dosimeters, one made with H2O and the other with D2O.

  46. CONCLUSIONS • General conclusions: 1. 3D Dosimetric system (Fricke gel layers, illuminator CCD, dedicated developed software for image acquisition, analysis and dose distribution evaluation) has proved to provide overall consistent and reliable results for dose Imaging • 2. This technique offers significant advantages over others, specially for achieving dose distributions for “complex” irradiations. • 3. relevant drawbacks: diffusion limits the time elapsed between irradiation and sample imaging • 4. versatility: chemical composition suitably changed to achieve good tissue-equivalence for different organs In view of its capability and reliability for 3D dose imaging, the Fricke gel layer dosimetry method represents a valuable promising tool for several complex dosimetric purposes including mixed field techniques and moddern radiotherapy TPS verification.

  47. 3D DOSIMETRY ... Do you remember our initial question-goal? Could be possible to develop a novel dosimetric technique with tissue-equivalent properties and capable of 3D dosimetry as well as dose separation at mixed fields? Optically analized Fricke gel dosimeter layer may be our solution for the desired “magic” dosimetric method!!! ... KEEP THIS IN MIND...

  48. 3D DOSIMETRY Prof. Mauro Valente, PhD. Medical Physics – FaMAF http://www.famaf.unc.edu.ar/~valente/ Thanks for your kind attention !!! CONICET & Universidad Nacional de Cordoba ARGENTINA

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