Boehlen, T. T.

Chin, M. P. W.

Fasso, A.

Ferrari, A.

Ortega, P. G.

Sala, P. R.

English

Open Access Repository

Radiation Physics and Chemistry 95 (2014) 170–173Contents lists available at ScienceDirectRadiation Physics and Chemistry0969-80http://dn CorrE-mjournal homepage: www.elsevier.com/locate/radphyschemFLUKA and PENELOPE simulations of 10 keV to 10 MeV photons inLYSO and soft tissueM.P.W. Chin a,n, T.T. Böhlen a, A. Fassò c, A. Ferrari a, P.G. Ortega a, P.R. Sala ba CERN (European Organization for Nuclear Research), CH-1211 Geneva, Switzerlandb Istituto Nazionale di Fisica Nucleare, via Celoria 16, 20133 Milan, Italyc Jefferson Lab, 12000 Jefferson Avenue, Newport News, VA 23606, USAH I G H L I G H T S Monte Carlo simulations of electromagnetic particle interactions and transport by FLUKA and PENELOPE were compared. 10 keV to 10 MeV incident photon beams impinged a LYSO crystal and a soft-tissue phantom. The pulse height spectra, depth doses central-axis as well as off-axis were found to agree within statistical uncertainty; no systematic difference wasobserved.a r t i c l e i n f oArticle history:Received 30 September 2012Accepted 3 March 2013Available online 20 March 2013Keywords:Monte CarloFLUKAPENELOPEElectromagnetic showers6X/$ - see front matter & 2013 Elsevier Ltd. Ax.doi.org/10.1016/j.radphyschem.2013.03.024esponding author. Fax: þ41 227668159ail address: me@marychin.org (M.P.W. Chin).a b s t r a c tMonte Carlo simulations of electromagnetic particle interactions and transport by FLUKA and PENELOPEwere compared. 10 keV to 10 MeV incident photon beams impinged a LYSO crystal and a soft-tissuephantom. Central-axis as well as off-axis depth doses agreed within 1 s.d.; no systematic under- or over-estimate of the pulse height spectra was observed from 100 keV to 10 MeV for both materials, agreementwas within 5%. Simulation of photon and electron transport and interactions at this level of precision andreliability is of significant impact, for instance, on treatment monitoring of hadrontherapy where a codelike FLUKA is needed to simulate the full suite of particles and interactions (not just electromagnetic).At the interaction-by-interaction level, apart from known differences in condensed history techniques,two-quanta positron annihilation at rest was found to differ between the two codes. PENELOPE produceda 511 keV sharp line, whereas FLUKA produced visible acolinearity, a feature recently implemented toaccount for the momentum of shell electrons.& 2013 Elsevier Ltd. All rights reserved.1. IntroductionFLUKA (Ferrari et al., 2005; Battistoni et al., 2007) and PENE-LOPE (Salvat et al., 2001; Sempau et al., 1997, 2003) are MonteCarlo codes for simulating radiation transport and calculatingradiometric quantities. Independently developed, the former isreputed for seamless handling of a broad variety of particle typesand heavy ions from eV to TeV range, whereas the latter specia-lizes on electromagnetic showers (i.e. electron, positron andphoton only). Within the electromagnetic domain the codes differnotably in the treatment of charged particle scattering andenergy loss.This work focuses on the domain where FLUKA and PENELOPEoverlap, and draws on the opportunity to validate simulationoutput on measurable quantities (e.g. pulse height spectra fromll rights reserved.a scintillator crystal, 3D dose distributions) as well as quantitieswhich are inaccessible physically (e.g. double-differential energy–angle correlation at the point of interaction). Whereas the ultimatebenchmark would be to compare simulation against measure-ment, inter-code comparison allows clean and controlled access toquantities of interest untainted by inherent cross-calibrationfactors and confounding factors arising from the experimentalenvironment.2. SimulationsSimulations were ran in pairs using FLUKA version 2012 andPENELOPE version 2011. A 1 cm 1 cm square field impinged the3 cm 3 cm face of a 12 cm-deep LYSO crystal (Lu1:8Y0:2SiO5;density 7.40 g/cm3; mean excitation energy 411.0 eV), dividedinto 4 segments by a 0.2 mm-thick septa (C12H22O5; density1.13 g/cm3; mean excitation energy 69.3 eV) which form a crossin the beam's eye view. Pairs of simulations were ran0 5 10 15 2010−210−1100101102depth (cm)dose (keV/g)flukapenelope0 2 4 6 8 10 1210−210−1100depth (cm)dose (keV/g)flukapenelope0 0.5 1 1.5 2 2.510−610−410−2100depth (cm)dose (keV/g)flukapenelopeFig. 1. Depth dose in soft tissue by (a) 10 MeV; (b) 100 keV; (c) 10 keV photon beam. From top to bottom, where present: 0 cm, 0.5 cm, 0.7 cm, 0.9 cm, 1.1 cm and 1.3 cm offbeam central axis.0 1000 2000 3000 400010−410−310−210−1100E (keV)flukapenelope0 2000 4000 6000 8000 1000010−610−510−410−310−210−1E (keV)flukapenelope0 20 40 60 80 10010−610−510−410−310−210−1100E (keV)flukapenelopeFig. 2. Pulse height spectra in LYSO by a (a) 10 MeV; (b) 4 MeV; (c) 100 keV photon beam.M.P.W. Chin et al. / Radiation Physics and Chemistry 95 (2014) 170–173 1710 2000 4000 6000 8000 1000010−610−510−410−3E (keV)flukapenelope0 20 40 60 80 10010−610−510−410−310−210−1E (keV)flukapenelope0 2 4 6 8 1010−610−410−2100E (keV)flukapenelopeFig. 3. Pulse height spectra in soft tissue by a (a) 10 MeV; (b) 100 keV; (c) 10 keV photon beam.Fig. 4. Energy spectrum of photons emitted from positrons annihilating at rest asM.P.W. Chin et al. / Radiation Physics and Chemistry 95 (2014) 170–173172independently with 100 keV, 4 MeV and 10 MeV photons incidenton the LYSO crystal. Next, with a target of identical dimensions butinstead filled with ICRP Soft Tissue, simulation pairs were repeatedfor 10 keV, 100 keV and 10 MeV photons. In the case of 10 MeVbeams the depth of the target was doubled. For all runs transportand production thresholds were set to 1 keV.The following quantities were scored: 3D dose distribution at2 mm intervals, 1024-channel pulse height spectrum, as well asthe phase-space attributes at each interaction. This scoring com-bination is to minimize the chances of observing apparent agree-ments, where underlying differences could be masked by cancelingeffects or loss of details due to averaging. Whereas the dosedistribution is averaged over all histories, the pulse height spec-trum tests correlation at a history-by-history level. It follows thatattributes scored at each interaction test conservation laws at thecollision-by-collision level.produced by FLUKA; the spread is absent in PENELOPE. Data shown is for the4 MeV-LYSO setup.3. ResultsFrom the mean free path of the primary photon, as expectedphoton cross-sections were found to be the same for FLUKA andPENELOPE for all beam–target combination studied. Depth dosedistribution along the central beam axis, and that along differentoff-axis positions, agreed within statistical uncertainty (Fig. 1),addressing the absorption as well as lateral scatter of both codes.No systematic difference between FLUKA and PENELOPE wasobservable. Pulse height spectra in LYSO as well as soft tissueshowed tight agreement between FLUKA and PENELOPE over fiveorders of magnitude (Figs. 2 and 3), agreeing in photo-peaks,escape peaks and Compton edges.Photon pairs emitted from positron annihilation at rest werefound to be 511.0 keV, sharp, in PENELOPE. FLUKA, however,produced photon pairs with a visible acolinearity effect whichtranslates into a spread in both energy and angle (Fig. 4). Note thatthe FWHM of energy spread is no more than 2 keV, finer than the binsize of energy spectra shown in preceding plots. This is due to non-negligible momentum of shell electrons, recently implemented andbenchmarked in FLUKA (Böhlen et al., 2012). The spread differs fromthat by positron annihilation in-flight, where both codes producedcomparable double-differential characteristics (Fig. 5).4. DiscussionThe pulse height spectra produced by FLUKA and PENELOPEagreed very well despite the independent condensed historyFig. 5. Two-quanta positron annihilation in-flight: photon energy (Ei), positron energy (Eo) and angle between photon pair (θ). Data shown is for the 4 MeV-LYSO setup.M.P.W. Chin et al. / Radiation Physics and Chemistry 95 (2014) 170–173 173models. This homes in on the point of the condensed historytechnique—itself unphysical yet provides good representation ofphysical processes. While PENELOPE does go up to GeV energies,the incident energies chosen for this work were kept ≤10 MeV soas to avoid the onset of photonuclear reactions, which goesbeyond the overlap between the two codes.The beam–target combinations tested are of significant interestin various detector, dosimetry and medical applications. The4 MeV-LYSO setup simulated here is in fact an excerpt from alarger experiment (Agodi et al., 2012), for hadrontherapy, where a80 MeV/u carbon beam hit a PMMA target, emitting polyenergeticphotons (among them, 4 MeV) to be measured by a LYSO detector.The application was on the prospects of deducing the position ofthe Bragg peak from measured photon profiles.A notable difference between the two codes was observed atthe interaction level: PENELOPE does not model acolinearityeffects following positrons annihilating at rest, which is negligiblefor most applications, except, for instance, positron emissiontomography (PET), where minor effects become observable.5. ConclusionExcellent agreement between FLUKA and PENELOPE was foundin the pulse height spectra and dose distribution produced by10 keV to 10 MeV photon beams impinging LYSO and soft tissue.Seamless simulation of radiometric quantities under suchintermediate-energy and heterogeneous configurations addressesexactly the concerns where the radiation physics communityneeds confidence in, e.g. treatment monitoring of hadrontherapy.AcknowledgmentThis work is partially funded by the European Novel ImagingSystems for Ion Therapy Grant Agreement 241851-ENVISION-COOPERATION as a part of the Seventh Framework Programme.ReferencesAgodi, C., Bellini, F., Cirrone, G.A.P., Collamati, F., Cuttone, G., De Lucia, E., De Napoli,M., Di Domenico, A., Faccini, R., Ferroni, F., Fiore, S., Gauzzi, P., Iarocci, E.,Marafini, M., Mattei, I., Paoloni, A., Patera, V., Piersanti, L., Romano, F., Sarti, A.,Sciubba, A., Voena, C., 2012. Precise measurement of prompt photon emissionfrom 80 MeV/u carbon ion beam irradiation. J. Instrum. 7, P03001.Battistoni, G., Muraro, S., Sala, P.R., Cerutti, F., Ferrari, A., Rősler, S., Fassò, A., Ranft, J.,2007. In: Proceedings of the Hadronic Shower Simulation Workshop 2006,Fermilab, September 6–8, 2006, AIP Conference Proceedings, pp. 31–49.Böhlen, T.T., Ferrari, A., Patera, V., Sala, P.R., 2012. Describing compton scatteringand two-quanta positron annihilation based on compton profiles: two modelssuited for the Monte Carlo method. J. Instrum. 7, P07018.Ferrari, A., Sala, P.R., Fassò, A., Ranft, J., 2005. FLUKA: a multi-particle transport code.Technical Report CERN-2005–10, INFN/TC_05/11, SLAC-R-773. CERN, INFN,SLAC.Salvat, F., Fernandez-Varea, J., Acosta, E., Sempau, J., 2001. PENELOPE, A CodeSystem for Monte Carlo Simulation of Electron and Photon Transport.Sempau, J., Acosta, E., Baro, J., Fernandez-Varea, J., Salvat, F., 1997. An algorithm forMonte Carlo simulation of the coupled electron-photon transport. Nucl.Instrum. Methods B 132, 377–390.Sempau, J., Fernandez-Varea, J., Acosta, E., Salvat, F., 2003. Experimental bench-marks of the Monte Carlo code PENELOPE. Nucl. Instrum. Methods B 207,107–123.

FLUKA and PENELOPE simulations of 10 keV to 10 MeV photons in LYSO and soft tissue

M.P.W. Chin

T.T. Böhlen

A. Fassò

A. Ferrari

P.G. Ortega

P.R. Sala

Crossref

Radiation Physics and Chemistry

FLUKA and PENELOPE simulations of 10keV to 10MeV photons in LYSO and soft tissue

Monte Carlo simulations of electromagnetic particle interactions and transport by FLUKA and PENELOPE were compared. 10 key to 10 MeV incident photon beams impinged a LYSO crystal and a soft-tissue phantom. Central-axis as well as off-axis depth doses agreed within 1 s.d.; no systematic under- or overestimate of the pulse height spectra was observed from 100 keV to 10 MeV for both materials, agreement was within 5\%. Simulation of photon and electron transport and interactions at this level of precision and reliability is of significant impact, for instance, on treatment monitoring of hadrontherapy where a code like FLUKA is needed to simulate the full suite of particles and interactions (not just electromagnetic). At the interaction-by-interaction level, apart from known differences in condensed history techniques, two-quanta positron annihilation at rest was found to differ between the two codes. PENELOPE produced a 511 key sharp line, whereas FLUKA produced visible  acolinearity, a feature recently implemented to account for the momentum of shell electrons

FLUKA and PENELOPE simulations of 10 keV to 10 MeV photons in LYSO and soft tissue

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