Routine and fast verification of proton therapy...

©2014 MFMER | slide-1

Routine and fast verification of proton therapy treatment plans with a GPU-based Monte Carlo simulationH. Wan Chan Tseung1

NCCAAPM 201529 October, Middleton [email protected]


Motivation• Mayo Clinic Rochester recently opened a spot

scanning proton therapy center• A second one to open in Arizona mid 2016• ~2500 patients to be treated per year• Treatment planning with Eclipse (Varian Medical

Systems, Inc)• The dosimetric accuracy of the plans needs to

be verified


Goals

• Gold standard for dose calculations in proton therapy is Monte Carlo (MC) simulation (e.g. FLUKA, MCNP, Geant4)

• Geant4 MC calculations of a typical proton treatment plan take several hours on a large CPU cluster

• Aims:

(1) to perform MC calculations of proton plans with <2% statistical error on the prescribed dose in around 1 minute, with comparable accuracy to Geant4

(2) to use this fast MC as an accurate, inexpensive and high throughput dose verification system


Development hardware

$500 x2

Gaming PC with two NVIDIA GTX680 cardsDevelopment language: CUDA C


Particle phase space

GPU kernel

Energy loss, multiple scattering, nuclear elastic scattering

GPU kernel

Bertini cascadeGPU kernel

Nuclear evaporationGPU kernelHost

CPU

CT image

Simulation ComponentsGeant4

(TOPAS) PBS nozzle

simulation

NB: kernel = piece of code that runs on the GPU but can be called from the CPU


GPU kernels for simulating non-elastic proton-nucleus interactions

intranuclearcascade

particle evaporation

• First-ever detailed simulation of nuclear interactions on a GPU

• Two kernels to handle Bertini cascade and subsequent evaporation stage

• Ability to handle proton collisions with any therapeutically relevant nucleus

• Predictions of secondary proton and neutron properties following nuclear collisions in good agreement with Geant4

More details:H. Wan Chan Tseung & C. Beltran, Computer Physics Communications, 185 (2014) 2029


GPU kernels for simulating non-elastic proton-nucleus interactions : results

70 MeV protons on

Carbon

70 MeV protons on

Calcium

200 MeV protons on

Carbon

200 MeV protons on

CalciumOur GPU MC 0.97 s 1.5 s 1.14 s 1.89 s

Geant4 Binary 173.69 s 317.53 s 202.28 s 461.54 s

Time taken to compute 260k nuclear interactions:

×200 speedup


Benchmarking our Monte CarloWe performed extensive comparisons with Geant4. Example:

230 MeV pencil beam of protons in water 200 MeV pencil beam of protons in titanium

3-D gamma pass rate (2%-2mm) : 100%

More details:H. Wan Chan Tseung, J. Ma & C. Beltran, Medical Physics, 42 (2015) 2967


Our GPU MC Geant4/TOPAS

Geant4/TOPASOur GPU MC

Our GPU MC Our GPU MC Geant4/TOPAS Geant4/TOPAS

60 million proton histories, 1.5% statistical error on doseGeant4/TOPAS on a CPU cluster: 650 CPU-hoursOur GPU MC: 3.5 minutes on one NVIDIA GTX680 card

Complex Head and Neck plan 3-D gamma (2%-2mm) pass rate: 98.2%

Comparisons of DVHs for various structures


Very fast dose-averaged LET calculation on GPU

• Our MC does simultaneous LET and physical dose calculation• Our LET calculation takes into account secondary proton contributions• Exciting prospects for MC-based RBE-weighted treatment planning

TOPAS Our GPU MCLETd LETd

TOPAS Our GPU MCdose dose

6x107 proton histories 6x107 proton

histories3 mins using 2 GTX680 cards


Web interface for GPU-based dose 2nd check


Current status• All patient plans are ran through the dose

second check • So far, ~90 patients in total• Plans modified in certain cases based on Monte

Carlo results• LET calculations allow biological dose

distribution estimates. Plans were sometimes modified based on biological dose distributions.


Example: Biological dose hot spot in brain stem


Summary

• We developed a very fast and accurate GPU-based MC for proton therapy, with detailed modeling of nuclear interactions

• This allows us to calculate dose with more confidence, especially in cases where significant hardware is present

• Compared to a 100-node CPU cluster, proton treatment plans are simulated ~100 times faster using one single graphics gaming card

• A dosimetric verification system was deployed at Mayo Clinic, using a dual GPU server

• We obtain routine, near real-time Monte Carlo feedback on pencil-beam plan accuracy

• We are exploring other exciting applications: MC-based IMPT planning, biological planning, fast neutron dose calculation, extension to heavy ions…


Beyond plan verification:other applications of our GPU-based MC


• Steps:• Determine list of spots contained in target• Pre-calculate dose influence map for these spots with GPU MC• Find spot weights with gradient-based optimization, also on GPU

• 30 minutes net calc. time on 24 GPU system: clinically applicable

• Robust IMPT optimization currently under investigation

MC-based IMPT treatment planning

GPU MC-based 3-field H&N plan

J. Ma, C. Beltran, H. Wan Chan Tseung and M. Herman, Med. Phys. 41 (2014) 121707


MC-based biological planning for proton therapy

• Phase 1 clinical trial on proton biological dose escalation starting end 2015


AcknowledgementsThis work was funded in part by Varian Medical Systems, Inc.

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Routine and fast verification of proton therapy...

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