1. Building clinical Monte Carlo code from Geant4, PENELOPE or EGSnrc Joao Seco 1, Christina Jarlskog 1, Hongyu Jiang 2 and Harald Paganetti 1 1 Francis H. Burr Proton Therapy Center Massachusetts General Hospital,Harvard Medical School, 30 Fruit Street, Boston, Massachusetts 02114 USA 2 University of Arkansas for Medical Sciences, 4301 W.Markham Street, Little Rock, Arkansas 72202 USA

2. GEANT4, PENELOPE and EGSnrc Monte Carlo Codes: Do you need to use Monte Carlo codes to solve your problem…? Can you use a faster PC or “clever” math's, physics or numerical tricks to solve your problem; How accurate is your Monte Carlo physics …? Possible issues are: 1.Multiple scattering 2.Bremsstrahlung 3.Photo-electric/Compton/Pair-Production/Rayleigh/Stopping Powers etc… How fast is you Monte Carlo code….? Can it run on 1 PC or does it need a large cluster … keeping in mind that clinical plans must not take more than 1 hour to generate; How versatile is your MC code… can it do photons, electrons, protons, carbon ions, etc… ?

3. Verhaegen and Seuntjens 2003, PMB, 48 R107-R164 Review of Physics within each code

4. Inter-comparison of electron Monte Carlo dose calculations for EGSnrc, GEANT and PENELOPE (2004) Joao Seco, Alex Howard and Frank Verhaegen AND Accuracy of the photon and electron physics in GEANT4 for radiotherapy applications (2005) Emily Poon and Frank Verhaegen

5. Our results with EGSnrc, STD_EM, LowE and PENELOPE ….. SLAB_THICKNESS = CSDA 100*  CSDA - continuos slowing down approximation in g/cm 2  – material density in g/cm 3 1 MeV incident electrons on homogeneous material

7. Consistency test of the electron transport algorithm in the GEANT4 Monte Carlo code Emily Poon, Jan Seuntjens and Frank Verhaegen Medical Physics Unit, McGill University, 1650 Cedar Avenue, Montreal, Quebec, H3G 1A4, Canada

8. Abstract In this work, the condensed history algorithm in GEANT4 (version 4.6.2.p01) is examined. Simulations of an ionization chamber composed of water for 1.25 MeV incident photon beams under Fano conditions, and evaluated the consistency of the cavity response for several combinations of electron transport parameters. GEANT4 permits electrons to reach geometric boundaries in large steps, and underestimates lateral displacement near interfaces. Step size artifacts due to distortions in electron fluence and angular distributions reduce the cavity dose by up to 39%. Accurate cavity response can be achieved using severe user-imposed step size restrictions. [They] suggest that improvements in the electron transport algorithm in GEANT4 should address the handling of boundary crossing.