Abstract ID: 21 Simulation of synchrotron-based microbeam radiation therapy using Geant4

Abstracts / Physica Medica 42 (2017) 1–50 a Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Gothenburg, Sweden b Department of Radiation Physics, Sahlgrenska Academy at the University of Gothenburg, Sweden c Department of Radiation Physics, Skåne University Hospital, Lund, Sweden d Department of Oncology, Sahlgrenska Academy at the University of Gothenburg, Sweden ⇑ Presenting author.

The objective of the work is to develop and implement an automated MC system for patient specific VMAT QA generating treatment planning system (TPS) compliant DICOM objects and including a stand-alone module for 3D analysis of dose deviations based on the normalized dose difference (NDD) method. The MC system developed is based on the EGSnrc code package with modifications [1]. The workflow consists of a number of modules connected to the TPS by means of DICOM exports and imports which are executed sequentially without user interaction. DVH comparison is performed in the TPS. In addition, MC- and TPS dose distributions are imported to the stand-alone analysis module based on the NDD formalism [2]. NDD failure maps and a pass rate for a certain threshold are obtained. 70 clinical plans are selected for analysis; 21 thorax plans, 26 prostate plans, 13 H&N plans and 10 gynecological plans. Agreement within 1.5% has been found between clinical- and MC data for the mean dose to the target volumes. The agreement is within 3% for parameters more sensitive to the shape of the DVH, e.g. D95% PTV or minimum dose to CTV. Tolerance criteria of 2%/3 mm are recommended for NDD analysis of prostate plans and 3%/3 mm for rest of the cases. Evaluation procedure is suggested where NDD analysis is the first step. For pass rate lower than 95% the evaluation continues with comparison of DVH parameters. For deviations larger than 2%, a visual inspection of the clinical- and MC dose distributions is performed. A fully automated evaluation is hindered by artefacts in the CT images, presence of contrast in the bladder, dose to air included in the target volume, interpretation of HU in rectum etc.

References 1. Lobo J, Popescu IA. Two new DOSXYZnrc sources for 4D Monte Carlo simulations of continuously variable beam configurations, with applications to RapidArc, VMAT, TomoTherapy and CyberKnife. Phys Med Biol 2010;55:4431–43. 2. Jiang SB, Sharp GC, Neicu T, Berbeco RI, Flampouri S, Bortfeld T. On dose distribution comparison. Phys Med Biol 2006;51:759–76. http://dx.doi.org/10.1016/j.ejmp.2017.09.007

Abstract ID: 18 FLUKA validation of MONET code for dose calculation in Hadrontherapy Alessia Embriaco a,b,*, Valentina Elettra Bellinzona a, Andrea Fontana b, Alberto Rotondi a,b a

Dipartimento di Fisica, Università di Pavia, Pavia, Italy Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, Pavia, Italy ⇑ Presenting author. b

The accurate evaluation of the dose distribution is an open issue in Hadrontherapy. MONET (MOdel of ioN dosE for Therapy) is a code for the computation of the 3D dose distribution for protons in water. The model accounts for all the interactions and is benchmarked with the FLUKA code, that is already validated for protons and Helium

3

beams in water, as testified by its use in different facilities. In the FLUKA simulation, the physical process can be easily switched on or off: therefore the MC code is an important tools for the verification of our formulas, implemented in MONET. In particular, FLUKA has been used for the study of nuclear interactions in the lateral and longitudinal profiles. For the lateral profile, MONET is based on the Molière theory of multiple Coulomb scattering with an additional Cauchy-Lorentz function for the nuclear interactions, with two parameters obtained by a fit to FLUKA [1]. For the longitudinal profile, we have implemented a new calculation of the average energy loss, the straggling based on the convolution with a Gaussian function and a linear parametrization for the nuclear contributions, with two free parameters obtained by a fit to simulation [1]. After the implementation, MONET has been validated with FLUKA in two cases: a single Gaussian beam and a lateral scan as a sum of many beams. In both cases, we have obtained a good agreement for different energy of protons in water. Recently, we are investigating the possibility to extend MONET code to the case of He beam. For the implementation of Helium beam in the MONET code, we study the effect of nuclear interactions again with FLUKA. For the lateral profile, the nuclear interaction is parametrized with a Cauchy-Lorentz distribution, as in case of protons. With the lateral profile of FLUKA, we have estimated the decrease of primary particles as a function of depth, in good agreement with experimental data. For the last step, the implementation of MONET for Helium beams in water, we are studying the depth-dose distribution and the contributions of straggling and the nuclear interactions. References 1. Bellinzona et al., PMB 2016;61:N102. http://dx.doi.org/10.1016/j.ejmp.2017.09.008

Abstract ID: 21 Simulation of synchrotron-based microbeam radiation therapy using Geant4 Susanna Guatelli a,*, Matthew Cameron a, Andrew Dipuglia a, Jeremy Davis a, Iwan Cornelius a,b, Anatoly Rozenfeld a, Michael Lerch a a

University of Wollongong, Centre for Medical Radiation Physics, Wollongong, NSW, Australia b Amentum Defence and Security, Sydney, NSW, Australia ⇑ Presenting author. Microbeam Radiation Therapy (MRT) is a preclinical radiotherapy modality characterised by the use of many micron-sized, spatially fractionated, high intensity radiation fields produced by a MultiSlit Collimator and synchrotron light [1]. A typical MRT radiation field consists of multiple high dose ‘peaks’ separated by low dose ‘valleys’ (width 25–50 lm; pitch 100–400 lm) delivered with dose rates of up to 10 kGy/s. The minute field size and high dose rate of MRT requires good Quality Assurance in order to transition into the clinical field. Dose Verification and Treatment Planning Systems (TPS) are crucial aspects of quality assurance, allowing for independent prediction and verification of dose distributions delivered to patients. The most accurate form of TPS is Monte Carlo computer simulations. The Centre for Medical Radiation Physics (CMRP), University of Wollongong, has developed a Geant4-based synchrotron beamline model for dose verification at the Australian Synchrotron Imaging and Medical Beamline (IMBL). This model, denoted G4IMBL, uses a multi-stage procedure to generate synchrotron light, transport through the beamline model, and calculate dose deposition in a phantom. G4IMBL models the production of X-ray photons entirely using Geant4 by transporting electrons through the sinu-

4

Abstracts / Physica Medica 42 (2017) 1–50

soidal magnetic field of a wiggler. This allows for optimisation of multiple operation modes via tuning of wiggler magnetic field strength and electron steering angle. The simulation has been validated against experimental measurements and is used to characterise novel Quality Assurance silicon based detectors with submm spatial resolution, developed at CMRP. The development, optimisation, and validation of this Geant4-based software tool for MRT Quality Assurance will be presented.

successive public releases of Geant4 to check that the accuracy of the physics models did not change over time.

References

http://dx.doi.org/10.1016/j.ejmp.2017.09.010

1. Brauer-Krisch E, Serduc R, Siegbahn E, et al. Effects of pulsed, spatially fractionated, microscopic synchrotron X-ray beams on normal and tumoral brain tissue. Mutation Res 2010;704:160–6. http://dx.doi.org/10.1016/j.ejmp.2017.09.009

Abstract ID: 22 Validation of Geant4 fragmentation for heavy ion therapy David Bolst a, Giuseppe Cirrone b, Giacomo Cuttone b, Gunter Folger c, Sebastien Incerti d, Vladimir Ivantchenko e, Tatsumi Koi f, Davide Mancusi g, Luciano Pandola b, Francesco Romano b,h, Anatoly Rosenfeld a, Susanna Guatelli a,* a

University of Wollongong, Centre for Medical Radiation Physics, Wollongong, NSW, Australia b INFN, Laboratori Nazionali del Sud, Catania, Italy c The European Organisation for Nuclear Research, Geneva, Switzerland d CNRS/IN2P3, Centre d’Etudes Nucléaires de Bordeaux-Gradignan, Bordeaux, France e Lebedev Physical Institute, Moscow, Russia f SLAC National Accelerator Laboratory, Menlo Park, CA, USA g French Alternative Energies and Atomic Energy Commission (CEA), Saclay, France h National Physical Laboratory, Teddington, UK ⇑ Presenting author. C-12 ion therapy has had growing interest in recent years for its excellent dose conformity. However at therapeutic energies, which can be as high as 400 MeV/u, carbon ions produce secondary fragments. For an incident 400 MeV/u C-12 ion beam, 70% of the beam will undergo fragmentation before the Bragg Peak. The dosimetric and radiobiological impact of these fragments must be accurately characterised, as it can result in increasing the risk of secondary cancer for the patient as well as altering the relative biological effectiveness. This work investigates the accuracy of three different nuclear fragmentation models available in the Monte Carlo Toolkit Geant4, the Binary Intranuclear Cascade (BIC), the Quantum Molecular Dynamics (QMD) and the Liege Intranuclear Cascade (INCL++). The models were benchmarked against experimental data for a pristine 400 MeV/u C-12 beam incident upon a water phantom [1], including fragment yield, angular and energy distribution. Geant4 version 10.2p2 was used. For fragment yields the three alternative models (QMD, BIC and INCL++) agreed between 5 and 35% with experimental measurements, the QMD using the ‘‘Frag” option gave the best agreement for lighter ions but had reduced agreement for heavier ions. For angular distributions INCL++ was seen to provide the best agreement among the models for all elements with the exception of Hydrogen. BIC and QMD showed to produce broader distributions compared to experiment. BIC and QMD performed similar to one another for kinetic energy distributions while INCL++ suffered from producing softer energy distributions compared to the other models and experiment. This set of tests were repeated with

References 1. Haettner E, Iwase H, Kramer M, Kraft G, Schardt D. Experimental study of nuclear fragmentation of 200 and 400 Mev/ u C-12 ions in water for applications in particle therapy. Phys Med Biol 2013;58:8265.

Abstract ID: 28 Evaluation of silicon and diamond based microdosimetry for boron neutron capture therapy quality assurance Susanna Guatelli *, James Vohradsky, Jeremy Davis, Linh T. Tran, Anatoly Rosenfeld University of Wollongong, Centre for Medical Radiation Physics, Wollongong, NSW, Australia ⇑ Presenting author. The shift from reactor to accelerator based neutron production has created a renewed interested in Boron Neutron Capture Therapy (BNCT). BNCT is reliant upon the favourable uptake of boron 10 by tumour cells along with the interaction with neutrons to produce high LET fragments (He and Li nuclei) that deposit energy locally within the tumour site. As with any radiation based treatment, Quality Assurance (QA) is crucial. This study extends previous work regarding the application of solid state microdosimetry in the field of BNCT by means of a dedicated Monte Carlo simulation [1]. Geant4 was used to model and optimise the design of silicon on insulator and diamond based microdosimeters [2,3]. Detector optimisation in this context pertains to the geometry and materials (i.e., sensitive volume size and probability of neutron activation) to be used in the fabrication of detectors. The study has shown conclusively that whilst the materials currently used in the fabrication of silicon and diamond based microdosimeters are appropriate, there are changes with respect to the sensitive volume thickness that must be addressed. Lastly, the applicability of previously determined correction factors [4] to match the energy deposition response of charged particles within silicon/diamond to water was evaluated within the context of BNCT. Full results and analysis will be presented.

References 1. Bradley PD, Rosenfeld AB, Allen B, Coderre J, Capala J. Performance of silicon microdosimetry detectors in boron neutron capture therapy. J Radiat Res 1999;151:235–43. 2. Tran LT, Guatelli S, Prokopovich DA, Petasecca M, Lerch MLF, Reinhard MI, Ziegler JF, Zaider M, Rosenfeld AB. A novel silicon microdosimeter using 3D sensitive volumes: modeling the response in neutron fields typical of aviation. IEEE Trans Nucl Sci 2014;61(4):1552–7. 3. Davis JA, Ganesan K, Alves ADC, Prokopovich DA, Guatelli S, Petasecca M, Lerch MLF, Jamieson DN, Rosenfeld AB. Characterization of an alternative diamond based microdosimeter prototype. IEEE Trans Nucl Sci 2014;61(6):3479–84. 4. Guatelli S, Reinhard MI, Mascialino B, Prokopovich DA, Dzurak AS, Zaider M, Rosenfeld AB. S, , , and Tissue equivalence correction in silicon microdosimetry for protons characteristic of the LEO space environment. IEEE Trans Nucl Sci 2008;55:3407–13. http://dx.doi.org/10.1016/j.ejmp.2017.09.011