Geant4 in Brachytherapy

Transcription

1 Geant4 in Brachytherapy Brachytherapy: Brief Overview Clinical applications Basic research Ultrafast & biology applications Issues for the work group 1

2 Brachytherapy: Overview Brachy: Greek word for short Fast (targeted) radiation treatment Catheter-driven insertion system breast, head, neck, colon, prostate, esophagus, eyes etc. Typical sources Gamma & beta emitters Small: few mm3 Geometry: cylindrical (Iridium-192, Palladium-103) 2

3 Modeling of encapsulated 192Ir source (Courtesy of McGill University) 3.5 mm 1.1 mm 0.6 mm 5 mm 2m MicroSelectron Classic HDR source (part no ) 3

4 Radial dose and anisotropy functions of encapsulated source F (r, theta) radial dose function g(r) (Courtesy of McGill University) GEANT Williamson and Li 0.60 r = 0.25 cm r = 0.5 cm r = 1 cm r = 2 cm r = 3 cm r = 5 cm Radial dose function GEANT4: ~0.4% higher than Williamson and Li angle (degree) radial distance (cm) Anisotropy function GEANT4: ±1% agreement with Williamson and Li (Med. Phys. 22, , 1995) 4

5 Modeling of rectal applicator (Courtesy of McGill University) made of silicone rubber allows for insertion of shielding materials We collect phase space files of photons reaching the applicator surface and use the data for dose calculations in patient geometry. 5

6 Isodose distributions (Courtesy of McGill University) Presence of lead shielding reduces the dose distribution in a lucite phantom by up to 20%, and it is confirmed by ion chamber measurements. 6

7 Octree geometry compression DICOM images Voxel-based geometry Objectives: Reduce the number of voxels Keep the critical information Indexing of the density distributions using a density gradient threshold: High resolution kept only in heterogeneous area Can easily reduce the number of voxels by 75% Does not affect dose distribution V. Hubert-Tremblay, MSc project 7

8 Octree geometry compression DICOM images Examples: CT phantom + thorax patient Voxel number v/s DGT 8

9 Prostate brachytherapy - LDR LDR I source, Amersham Validation of the model: radial dose fonction J.-F. Carrier, Ph.D. project 9

10 Prostate brachytherapy - LDR MC simulations on clinical treatment plans 1) Interseed attenuation RED PLAN 77 seeds 0.6 mci activity 1.7% 3.3% 1.7% of the D90 value is lost due to interseed attenuation BLUE PLAN 137 seeds 0.3 mci activity This interseed attenuation is not considered in TG43 (clinical) dose calculations 3.3% of the D90 value is lost due to interseed attenuation 10

11 Prostate brachytherapy - LDR MC simulations on clinical treatment plans 2) Medium composition: CT-based MC G4 DICOM reader[1] Organ contours Seed positions CT image G4 geometry D90: 5-7% differences between water MC and CT-based MC [1] 11

12 (Collaboration: NIST, EVMS) z 32 1 Scintillating Fiber based Beta Detector Absolute calibration of sources z Lawrence Tynes, Ph.D.: Detector Nnenna Onumah, Ph.D.: Geant4 y 12

13 (Collaboration: Proxima Therapeutics, depaul) Active Mammosite Absolute real-time position measurement (within ±1 mm) Absolute real-time dose measurement Modelization of the dose distribution using CT scan data & 4D phantom Jacquelyn Winston, M.Sc.: Detector Rachel Black, Ph.D. : Detector, Geant4 & VTK 13

14 (Collaboration: Jefferson Lab, EVMS, ODU) Dipole Breast cancer cells Collimator and Sr-90 source Monoenergetic Brachytherapy Sources Energy dependence of irradiated breast cancer cells Ariano Munden, M.Sc. 14

15 ALLS Facility Ultrafast Laser & Biomedical Research Advanced Laser Light Source 10 Hz, 300 mj, 25 fs Varennes, Canada Dynamics of biological processes 100 Hz, 100 mj, 25 fs 15

16 Issues for the Working Group Physics Electromagnetic shower Multiple scattering Experimental cross sections (JLab data, others) Theory (?) Treatment verification Bench marks Examples Micro-dosimmetry Simulation at molecular level Mono-energetic dose distribution Other topics Group organization Therapy Physics (I. Chetty, MC in Treatment Planning) Where to go from here? To be discussed!!! 16

17 Prostate brachytherapy - HDR HDR Ir source, MicroSelectron 192 Preliminary results Ejection spectrum kev A. Allard, Summer Project 17