Coarse Mesh Radiation Transport Code COMET Radiation Therapy Application*

Transcription

1 Coase Mesh Radiation Tanspot Code COMT Radiation Theapy Application* Fazad Rahnema Nuclea & Radiological ngineeing and Medical Physics Pogams Geogia Institute of Technology Computational Medical Physics Woking Goup Meeting Oak Ridge National Laboatoy Octobe * Funded by Geogia Cance Coalition This poject is in collaboation with moy Univesity Radiation Oncology Depatment

2 Objectives Develop an accuate 3-D paticle tanspot method which Is capable of coupled neuton photon and electon tanspot Does not equie homogenization Contains an accuate and self-consistent global dose econstuction pocedue Its accuacy is independent of the mesh size

3 . ψ Stat fom the tanspot equation with abitay bounday condition ( ) + ( ) ( σ ψ ) = Q( ) t with bounday condition + d' 0 4π d' σ s Method ( ' ' ) ψ ( ' ' ) ψ ( ) = Bψ ( ' ' ) b b n. < 0 and n. ' > 0 b V

4 Poblem Decomposition Decompose the global poblem exactly as a set of local fixed souce poblems ove nonovelapping coase meshes V i ( ) ( ) ( ) ( ) ( ) ( ) + = ' ' ' ' ' '. d d Q i s i i t i ψ σ ψ σ ψ π ( ) ( ) ij j ij i = + ψ ψ { } all fo j i ij V V V j bounding V i

5 Method - Appoximation An appoximation is pefomed on the angula flux at the bounday of the coase meshes m HR is ( wi ) = Q( wi ) m m Γ ( w with Ris ( wis ) = 0 is ) fo V othewise is Γ is the m th membe of a set of functions othogonal on the half-space expansion becomes; examples: Discete Legende polynomial Continuous Legende polynomial

6 Method Summay Libay Geneation: Pecomputed esponse functions as a function mateial density (CT index) xpansion coefficients with the maximum desied ode in phase space Define the mesh gid in the poblem Sweep though the mesh to convege on the dose distibution by coupling meshes though angula cuents (expansion coefficients) Use low ode solutions to acceleate the high ode solution

7 Medical Physics Benchmak Poblem A Homogeneous Poblem 30 cm cm 10X15 egions Mesh dimension: 2 cmx2 cm Homogeneous medium Incident photons impinges nomally Initial enegy: 4-5 Mev Seconday electons ae assumed to deposit enegy locally in both GS and Coase Mesh calculations

8 Compaison Relative eo between GS and Coase Mesh (3X2U2DP3) calculations Distibution of enegy deposition (Mev) Relative o GS Region 160 million paticles Uncetainty<0.3% CPU time: 3700 sec y (cm) x (cm) Coase Mesh (3X2U2DP3) Aveage R=1% Maximum R=2% CPU time: 122 sec

9 A Heteogeneous Poblem includes lung and bone 10X15 egions Mesh dimension: 2 cmx2 cm Heteogeneous medium Incident photons impinges nomally Initial enegy: 4-5 Mev Seconday electons ae assumed to deposit enegy locally in both GS and Coase Mesh calculations

10 Compaison Relative eo between GS and Coase Mesh (3X2U2DP3) calculations Distibution of enegy deposition (Mev) Relative o GS Region 2.0 billion paticles Uncetainty<1.4% CPU time: sec y (cm) x (cm) Coase Mesh (3X2U2DP3) Aveage R=1.2% Maximum R=2.4% CPU time: 122 sec

11 Planned xpeimental Benchmak Poblems Homogeneous Wate Phantom Coase-Mesh composed of only wate Compaisons made to 3D expeimental esults calculating dose deposition in wate phantom at moy Slab Benchmak Slabs composed of H2O Al and Lung Actual enegy deposition will be detemined by 3D expeimental esults obtained by using slab phantoms at moy CT Data A CT dataset of an anthopomophic phantom will povide the data fo the coase-mesh calculations The esults will be compaed to the dose deposition found expeimentally in the phantom

12 Conclusions Conclusion and Futue Wok COMT povides vey accuate esults fo photon tanspot in both homogeneous and heteogeneous media Results ae compaable to fine mesh Substantially faste than fine mesh deteministic tanspot and Monte Calo Futue wok Ceate new numeical and expeimental benchmak poblems (2D and 3D) Coupled photon electon and neuton tanspot xtension to 3D Impoved sweeping techniques

13 Questions?