miguel a. cortés-giraldo *, josé m. quesada, m. isabel gallardo (universidad de sevilla)
DESCRIPTION
Improvement of the Monte Carlo Simulation Efficiency of a Proton Therapy Treatment Head Based on Proton Tracking Analysis and Geometry Simplifications. Miguel A. Cortés-Giraldo *, José M. Quesada, M. Isabel Gallardo (Universidad de Sevilla) Harald Paganetti - PowerPoint PPT PresentationTRANSCRIPT
Improvement of the Monte Carlo Simulation Efficiency of a Proton
Therapy Treatment Head Based on Proton Tracking Analysis and
Geometry Simplifications
Miguel A. Cortés-Giraldo*, José M. Quesada, M. Isabel Gallardo
(Universidad de Sevilla)
Harald Paganetti(Massachusetts General Hospital - Boston, MA, USA)
6th DITANET Topical Workshop on Particle Detection TechniquesSeville (Spain)
November 8th, 2011
(*) e-mail: [email protected]
Motivation Monte Carlo (MC) simulations are:
A precise technique to calculate dose in patients… but expensive in terms of CPU time.
The aim of this work is: To decrease the CPU time needed to create a
phase-space file in the MC simulation of a passive scattering proton therapy treatment head.
To develope techniques capable of increasing the computational efficiency in the simulation of nozzles with similar geometry.
The MC code (phase-space files)
Geant4.9.0.p01
Only proton tracking is taken into account in detail in order to create a phase-space file as fast as possible.
Secondary radiation is evaluated separately
Monte Carlo treatment head model:Paganetti et al. Med. Phys. 31:2107-18
(2004)
Physics settings (Geant4 physics list):Zacharatou and Paganetti IEEE-TNS 55:1018-25
(2008)
Francis H Burr Proton Therapy Center (Boston, MA, USA)
Methodology
The efficiency improvement is evaluated for various nozzle set-ups:
Covering the energy range of the proton beam.
Output efficiency: 25-cm (maximum) and 12-cm diameter snout (most typical case in proton therapy).
Validation with published results.
Identical computational conditions.
(Paganetti et al. Med. Phys. 31:2107-18, 2004.)
Time spent along the nozzle
IC2
2nd scattererRMW
IC1
Modulator Wheels PatientAperture
Compensator
Double scattering system
Modulator Wheels PatientAperture
Compensator
Double scattering system
Proton tracking filtering
The basic idea is to terminate the tracking of protons which, very likely, will not reach the aperture
Modulator Wheels PatientAperture
Compensator
Double scattering system
Modulator Wheels PatientAperture
Compensator
Double scattering system
Proton tracking filtering
There is a strong correlation of the protons reaching the nozzle exit and their dynamical conditions at the exit of the scatterer.
An example… A tolerance margin is taken into account.
Open field conditions.
Simplifications of the monitor chambers
A detailed geometry model of the monitor chambers slows down the MC simulation.
Considering all the layers grouped together simplifies the tracking of particles, improving the efficiency.
Production cuts per region
Production cut: key parameter in Geant4 simulations.
The secondary production cut value is higher in regions filled by air (magnets, jaws…)
The scattering and modulation devices require a lower value of the production cuts.
Modulator Wheels PatientAperture
Compensator
Double scattering system
Modulator Wheels PatientAperture
Compensator
Double scattering system
Proton tracking filtering
The efficiency increases by about 30% with a 12 cm snout. In the worst case scenario (25
cm), it improves by about 5%.
Simplifications of the monitor chambers
The efficiency improvement varies between 5% and 15%. The improvement increases with the
proton beam range
Production cuts per region
0.2 mm for devices filled by air (jaws, aperture…); the CPU time decreases by about 5%.
For scatterers and modulators the production cut value is 0.05mm.
Modulator Wheels PatientAperture
Compensator
Double scattering system
Modulator Wheels PatientAperture
Compensator
Double scattering system
Using a global production cut value too high may change the energy distribution at the exit of the nozzle.
(Geant4.9.0.p01)
Conclusions We have developed techniques to increase the
computational efficiency of Geant4 simulations to obtain phase-space files of a passive scattering proton therapy nozzle.
For the most typical case in the facility, the efficiency increases by about 35%; in the worst case scenario, it improves by about 15%.
These techniques can be applied to other treatment heads, simulated either with Geant4 or another MC transport code.