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Miguel A. Cortés-Giraldo *, José M. Quesada, M. Isabel Gallardo (Universidad de Sevilla)

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

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Miguel A. Cortés-Giraldo *, José M. Quesada, M. Isabel Gallardo (Universidad de Sevilla)

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  1. 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) (*) e-mail: miancortes@us.es 6th DITANET Topical Workshop on Particle Detection Techniques Seville (Spain) November 8th, 2011

  2. Contents • Introduction • Methods • Results • Conclusions

  3. Introduction • Methods • Results • Conclusions

  4. 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.

  5. The MC code (phase-space files) Francis H Burr Proton Therapy Center (Boston, MA, USA) • 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)

  6. Introducton • Methods • Results • Conclusions

  7. 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.)

  8. Time spent along the nozzle IC2 2nd scatterer RMW IC1

  9. Proton tracking filtering • The basic idea is to terminate the tracking of protons which, very likely, will not reach the aperture

  10. Proton tracking filtering An example… A tolerance margin is taken into account. Open field conditions. • There is a strong correlation of the protons reaching the nozzle exit and their dynamical conditions at the exit of the scatterer.

  11. 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.

  12. 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.

  13. Introduction • Methods • Results • Conclusions

  14. 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%.

  15. Simplifications of the monitor chambers The efficiency improvement varies between 5% and 15%. The improvement increases with the proton beam range

  16. 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. Using a global production cut value too high may change the energy distribution at the exit of the nozzle. (Geant4.9.0.p01)

  17. Output fluence verification 12 cm diameter snout Range = 12.00 cm Modulation width = 4.0 cm

  18. Output fluence verification 12 cm diameter snout Range = 17.19 cm Modulation width = 6.78 cm

  19. New time profiles 12 cm diameter snout 25 cm diameter snout

  20. Introduction • Methods • Results • Conclusions

  21. 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.

  22. Acknowledgements • Ministerio de Ciencia e Innovación (P07-FQM-02894 y FIS2008-04189). • Junta de Andalucía (FPA2008-04972-C03-02). • PO1 Grant. • Physics Research group at Dep. Radiation Oncology (Massachusetts General Hospital, Boston, MA, USA).

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