## 3. Monte Carlo simulation of radiation-matter interaction

#### Books

M. H. Kalos and P. A. Whitlock, Monte Carlo methods, Wiley-VCH, Weinheim, 2008.
*In this book a readable survey of Monte Carlo techniques can be found. Therein different applications in radiation transport, statistical physics and many-body quantum theory are developed and analyzed.*

F. Salvat, PENELOPE, a code system for Monte Carlo simulation of electron and photon transport, OECD Nuclear Energy Agency, Barcelona, 2019.
*This is the manual of PENELOPE, a Monte Carlo code that permits the coupled simulation of electrons, photons and positrons in matter. Apart from a description of this code, where the details about the Monte Carlo simulation of the radiation transport in materials is described, the first chapter provides with a nice basic text of Monte Carlo techniques.*

A. F. Bielajew and D. W. O. Rogers, Variance-reduction techniques, in T. M. Jenkins, W. R. Nelson, and A. Rindi (editors), “Monte Carlo Transport of Electrons and Photons", Plenum, New York, 1988.
*The chapter 18 of this book includes the contribution of Bielajew and Rogers where a practically oriented review about the so-called variance-reduction methods in radiation transport can be found. These methods are fundamental in simulation of dosimeters based on MOSFET or similar devices.*

#### Scientific articles

M. Vilches, S. García-Pareja, R. Guerrero, M. Anguiano and A. M. Lallena. Monte Carlo simulation of the electron transport through thin slabs: A comparative study of PENELOPE, GEANT3, GEANT4, EGSnrc and MCNPX. Nuclear Instruments and Methods in Physics Research B 254 (2007) 219-223.
*Abstract: The Monte Carlo simulation of the electron transport through thin slabs is studied with five general purpose codes: PENELOPE, Geant3, Geant4, EGSnrc and MCNPX. The different material foils analyzed in the old experiments of Kulchitsky and Latyshev [L.A. Kulchitsky, G.D. Latyshev, Phys. Rev. 61 (1942) 254] and Hanson et al. [A.O. Hanson, L.H. Lanzl, E.M. Lyman, M.B. Scott, Phys. Rev. 84 (1951) 634] are used to perform the comparison between the Monte Carlo codes. Non-negligible differences are observed in the angular distributions of the transmitted electrons obtained with the some of the codes. The experimental data are reasonably well described by EGSnrc, PENELOPE (v.2005) and Geant4. A general good agreement is found for EGSnrc and penelopePENELOPE (v.2005) in all the cases analyzed.*

M A Carvajal, S García-Pareja, D Guirado, M Vilches, M Anguiano, A J Palma and A M Lallena, Monte Carlo simulation using the PENELOPE code with an ant colony algorithm to study MOSFET detectors. Physics in Medicine & Biology 54 (20), 6263, 2009.
*Abstract: In this work we have developed a simulation tool, based on the PENELOPE code, to study the response of MOSFET devices to irradiation with high-energy photons. The energy deposited in the extremely thin silicon dioxide layer has been calculated. To reduce the statistical uncertainties, an ant colony algorithm has been implemented to drive the application of splitting and Russian roulette as variance reduction techniques. In this way, the uncertainty has been reduced by a factor of ~5, while the efficiency is increased by a factor of above 20. As an application, we have studied the dependence of the response of the pMOS transistor 3N163, used as a dosimeter, with the incidence angle of the radiation for three common photons sources used in radiotherapy: a 60Co Theratron-780 and the 6 and 18 MV beams produced by a Mevatron KDS LINAC. Experimental and simulated results have been obtained for gantry angles of 0o, 15o, 30o, 45o, 60o and 75o. The agreement obtained has permitted validation of the simulation tool. We have studied how to reduce the angular dependence of the MOSFET response by using an additional encapsulation made of brass in the case of the two LINAC qualities considered.*

P. A. Mayorga, L. Brualla, A. Flühs, W. Sauerwein and A.M. Lallena. Testing Monte Carlo absolute dosimetry formalisms for a small field `D'-shaped collimator used in retinoblastoma external beam radiotherapy. Biomedical Physics & Engineering Express 2, 065008, 2016.
*Abstract: Purpose. To investigate the validity of two Monte Carlo simulation absolute dosimetry approaches in the case of a small field dedicated 'D'-shaped collimator used for the retinoblastoma treatment with external photon beam radiotherapy. Methods. The Monte Carlo code PENELOPE is used to simulate the linac, the dedicated collimator and a water phantom. The absolute doses (in Gy per monitor unit) for the field sizes considered are obtained within the approach of Popescu et al. in which the tallied backscattered dose in the monitor chamber is accounted for. The results are compared to experimental data, to those found with a simpler Monte Carlo approximation for the calculation of absolute doses and to those provided by the analytical anisotropic algorithm (AAA). Our analysis allows for the study of the simulation tracking parameters. Two sets of parameters have been considered for the simulation of the particle transport in the linac target. Results. The change in the tracking parameters produced non-negligible differences, of about 10% or larger, in the doses estimated in reference conditions. The Monte Carlo results for the absolute doses differ from the experimental ones by 2.6% and 1.7% for the two parameter sets for the collimator geometries analyzed. For the studied fields, the simpler approach produces absolute doses that are statistically compatible with those obtained with the approach of Popescu et al. The AAA underestimates the experimental absolute doses with discrepancies larger than those found for Monte Carlo results. Conclusions. The approach studied can be considered for absolute dosimetry in the case of small, 'D'-shaped and off-axis radiation fields. However, a detailed description of the radiation transport in the linac target is mandatory for an accurate absolute dosimetry.*

#### Presentations

A.M. Lallena. Monte Carlo Dosimetry. International Conference on Medical Accelerators and Particle Therapy. Sevilla, 2019.
*A comprehensive training approach to the application of the Monte Carlo method to the dosimetry issue.*