Medical and Environmental Dosimetry Group Projects

" Dosis sola facit venenum "
(The dose makes the poison)
            Paracelsus(1493-1541)

Mission: Quantification of radiation exposures for prevention and determination of radiation risks

Focus of our work is the quantification of individual radiation dose in medical applications. This will allow to avoid unnecessarily high doses to patients and occupationally exposed individuals. In that way, we contribute towards minimization of radiation-induced health risks. Furthermore, our data on exposure serve as input for biologically-based mechanistic models developed by IMO and for applied risk models developed by SR.

Our strengths include measurements of high-energetic secondary neutrons, as for example produced within patients undergoing tumor therapy with protons or heavy ions. Additionally, we have long-lasting expertise in the simulation of various radiation fields (X-rays, gamma rays, proton, neutrons) and in the development of electronic dosimeters.

Hadron Therapy

Proton Therapy Facility

Measurement of stray radiation within a proton therapy facility

Proton therapy is a type of particle therapy whose main advantage over other external beam radiotherapy techniques is that it can very precisely localize the radiation dose within the diseased tissue (mainly cancers), keeping irradiation of healthy tissue to a minimum. However, interactions of primary protons with materials in or around the beam line, in the irradiation room, and with the patient's tissue result in the production of secondary neutron and gamma radiation. Such out-of-field doses, deposited far from the target volume (cancer), may increase the probability of late effects including the generation of secondary cancers. To properly evaluate the benefits and risks related to the use of protons in cancer treatments, it is necessary to determine the secondary doses delivered to normal tissues. The neutrons are particularly of concern due to their high relative biological effectiveness, and have thus been extensively studied in this project. In the framework of EURADOS WG-9 "Radiation dosimetry in radiotherapy" a large inter-comparison exercise was carried out in order to investigate the secondary radiation generated by a scanning proton beam. In 2013-2014,  our working group participated in an experimental campaign within the IBA active-scanning proton beam therapy facility in Trento, Italy, and Kraków, Poland using an extended-range Bonner Sphere Spectrometer, NM2B REM-counters, and new HMGU electronic dosemeters. In 2014, secondary neutron energy spectra and ambient dose equivalent values H*(10) were also measured around a PMMA phantom within the treatment room of Rinecker Proton Therapy Center (RPTC) in Munich, Germany.


Trento Centro di Protonterapia -Faciility,  Trento, Italy. 


Centrum Cyklotronowe Bronowice  IFJ PAN- Facility, Krakow, Poland

Narodowe Centrum Hadronowe

zobacz więcej na: http://www.zwrotnikraka.pl/protonoterapia-raka-terapia-protonowa/ |

Instytucie Fizyki Jądrowej Polskiej Akademii Nauk

zobacz więcej na: http://www.zwrotnikraka.pl/protonoterapia-raka-terapia-protonowa/ |

Narodowe Centrum Hadronowe

zobacz więcej na: http://www.zwrotnikraka.pl/protonoterapia-raka-terapia-protonowa/ |

Narodowe Centrum Hadronowe

zobacz więcej na: http://www.zwrotnikraka.pl/protonoterapia-raka-terapia-protonowa/ |

Instytucie Fizyki Jądrowej Polskiej Akademii Nauk

zobacz więcej na: http://www.zwrotnikraka.pl/protonoterapia-raka-terapia-protonowa/ |

Reference:

V. Mares, M. Romero-Expósito, J. Farah, S. Trinkl, C. Domingo, M. Dommert, L. Stolarczyk, L. Van Ryckeghem, M. Wielunski, P. Olko and R. M. Harrison, A comprehensive spectrometry study of a stray neutron radiation field in scanning proton therapy, Phys. Med. Biol. 61 (2016) 4127–4140; doi:10.1088/0031-9155/61/11/4127

J. Farah, V. Mares, M. Romero-Expósito, S. Trinkl, C. Domingo, V. Dufek, M. Kłodowska, J. Kubancak, Ž. Knežević, M. Liszka, M. Majer, S. Miljanić, O. Ploc, K. Schinner, L. Stolarczyk, F. Trompier, M. Wieluński, P. Olko and R.M. Harrison, Measurement of stray radiation within a scanning proton therapy facility: EURADOS WG9 inter-comparison exercise of active dosimetry systems, Med. Phys. XX, (2015)

Konstantin Schinner, Bestimmung der Empfindlichkeit von REM-Counter und Bonner-Kugeln auf Gammastrahlung - Messungen im gemischten Feld an Protonentherapiezentren, Masterarbeit, TU Ilmenau, 20.05.2014

Christian Glas, Einsatz von aktiven Sensoren auf Basis von Si-PIN-Dioden zur Messung von thermischen und schnellen Neutronen im Phantom und erste Testmessungen an einer Protonentherapieanlage des Rinecker Proton Therapy Centers, Bachelorarbeit, Hochschule München, 04.12.2014

Carbon Therapy Facility

The carbon therapy facility

In carbon therapy, instead of protons, carbon ions are used to irradiate patients. Compared to protons, carbon ions show a higher relative biological effectiveness(RBE) and are therefore particularly suitable for the treatment of radiation-resistant tumors such as glioblastomas. C
arbon ions are heavy compared to protons,and in interaction with the tissue of the patient, they can fragment (break), producing lighter fragments (secondary particles), such as alpha particles and neutrons. In particular, the secondary neutrons contribute to an unintended exposure of the patient outside the tumor. Future measurements of the secondary neutron field are necessary for future risk assessments for the development of secondary tumors, since the biological effect of neutrons is strongly energy-dependent. To determine the energy-resolved secondary neutron field in carbon therapy, measurements were carried out at the Heidelberg Ion-Beam Therapy Center (HIT), the world's most advanced radiation source, in cooperation with the Chair of Medical Physics at the Ludwig-Maximilians-University in Munich. In addition to irradiation with carbon ions and protons, HIT also offers the possibility of irradiation with helium and oxygen ions. In a large series of comparative measurements important factors of influence on the secondary neutron field, in the case of irradiation with four different types of ions, were investigated.


Heidelberger Ionenstrahl Therapiezentrum (HIT)-Facility, Heidelberg, Germany

Reference Field for Hadron Therapy

CERF- CERN-EU High Energy Reference Field (Switzerland)

Measurement of high-energy neutrons in a reference field

Our working group performed a measurement campaign at the CERN-EU High Energy Reference Field (CERF). The CERF-facility provides a high-energy neutron field. This field is similar to that of secondary
neutrons from cosmic rays at typical flight altitudes (10-15 km a.s.l.). This neutron spectrum is specified by a wide range of energies with three peaks (thermal- (about 25 meV), evaporation- (1-2 MeV) und cascade-peak (ca. 100 MeV)) and an epithermal region (between thermal-and evaporation-peak).
During the campaign, we perform measurements with our Extended-Range Bonner-Sphere-Spectrometer to survey the energy distribution of this neutron field. An electronic neutron dosimeter and two REM-counters came into operation to measure the neutron ambient dose equivalent (H*(10)) over the whole energy range.
The aim of this campaign was to test our various measurement systems and to compare the measurements with the reference values provided by CERF and with our Monte Carlo simulations.

Simulated GEANT4, ERBSS measured and FLUKA reference


Group of MED researchers

RCNP Osaka (Japan)

Quasi-mono-energetic neutron field at RCNP, Osaka University, Japan

In order to monitor neutrons in high-energy fields above 20 MeV, in particular concerning dosimetry in radiotherapy, onboard aircraft and spacecraft, and radiation protection monitoring of workplaces outside high-energy accelerators, proper calibration of neutron detectors is needed. It is necessary to calibrate instruments in reference fields at energies from 20 MeV up to several hundreds of MeV - preferably in mono-energetic neutron fields - with known spectral fluence rate distribution. One of the most unique facilities worldwide providing quasi-mono-energetic neutron fields with energies up to 400 MeV using 7Li(p,n)7Be reaction is the cyclotron facility at the Research Center for Nuclear Physics (RCNP), Osaka University, Japan. At the RCNP in Osaka the protons are pre-accelerated up to 65 MeV in an AVF cyclotron and then can be boosted up to energies of 400 MeV in the ring cyclotron. The quasi-mono-energetic neutron spectrum consists of peak neutrons and continuum component (tail), which comes from breakup reactions. The number of neutrons in peak per solid angle per electric charge is 0.9 - 1.1x1010 sr-1 µC-1 in the 80-389 MeV energy region of incident protons.

Since 2009, staff members of Medical and Environmental Dosimetry group (Vladimir Mares, Christian Pioch, and Sebastian Trinkl) have participated in three international measurement campaigns in RCNP related to spectrometry measurement of quasi-mono-energetic neutrons for 100-400 MeV 7Li(p,xn) reaction and its application to calibration of monitors, using extended range Bonner sphere spectrometer (ERBSS), different Rem counters, and electronic neutron dosimeter (ELDO).  

Neutron energy distribution per solid angle per electric charge produced by 7Li(p,xn) reaction at 0° measured by TOF method (courtesy of  Iwamoto et al. 2015)



100m long experimental tunnel within the RCNP cyclotron facility


 

References:

V. Mares, S. Trinkl, Y. Iwamoto, A. Masuda, T. Matsumoto, M. Hagiwara, D. Satoh, H. Yashima, T. Shima, and T. Nakamura, Neutron spectrometry and dosimetry in 100 and 300 MeV quasi-mono-energetic neutron field at RCNP Osaka University Japan, Proceedings of ICRS13&RPSD2016 conference, Paris, 2016, submitted

V. Mares, C. Pioch, W. Rühm, H. Iwase, Y. Iwamoto, M. Hagiwara, D. Satoh, H. Yashima, T. Itoga, T. Sato, Y. Nakane, H. Nakashima, Y. Sakamoto, T. Matsumoto, A. Masuda, H. Harano, J. Nishiyama, C. Theis, E. Feldbaumer, L. Jaegerhofer, A. Tamii, K. Hatanaka, and T. Nakamura, Neutron Dosimetry in Quasi-Monoenergetic Fields of 244 and 387 MeV,. IEEE Transactions on Nuclear Science Vol. 60, No. 1 (2013) page 299-304

A. Masuda, T. Matsumoto, H. Harano, J. Nishiyama, Y. Iwamoto, M. Hagiwara, D. Satoh, H. Iwase, H. Yashima, T. Nakamura, T. Sato, T. Itoga, Y. Nakane, H. Nakashima, Y. Sakamoto, C. Theis, E. Feldbaumer, L. Jaegerhofer, C. Pioch, V. Mares, A. Tamii, and K. Hatanaka, Response Measurement of a Bonner Sphere Spectrometer for High-Energy Neutrons, IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 59, NO. 1, FEBRUARY (2012) 161

C. Pioch, V. Mares, W. Rühm, H. Iwase, Y. Iwamoto, T. Sato, M. Hagiwara, D. Satoh, Y. Nakane, H. Nakshima, Y. Sakamoto, H. Yashima, T. Matsumoto, A. Masuda, J. Nisahiyama, T. Itoga, C. Theis, E. Feldbaumer, L. Jägerhofer, A. Tamii, K. Hatanaka, T. Nakamura, Calibration of a Bonner sphere spectrometer in quasi-monoenergetic neutron fields of 244 and 387 MeV. Journal of Instrumentation (2011), 6, P10015.

Y. Iwamoto, M. Hagiwara, D. Satoh, H. Iwase, H. Yashima, T. Itoga, T. Sato, Y. Nakane, H. Nakashima, Y. Sakamoto, T. Matsumoto, A. Masuda, J. Nishiyama, A. Tamii, K. Hatanaka, C. Theis, E. Feldbaumer, L. Jaegerhofer, C. Pioch, V. Mares, T. Nakamura, Quasi-monoenergetic neutron energy spectra for 246 and 389 MeV 7Li(p,n) reactions at angles from 0° to 30°, Nuclear Instruments and Methods in Physics Research A 629 (2011) 43-49.

UFS Zugspitze (Germany)

Measurement of secondary neutrons from cosmic radiation at mountain altitudes (Alps, Germany)

In 2005 a Bonner multi-sphere spectrometer has been installed at the Environmental Research Station “Schneefernerhaus”  (2,660 m above sea level ) on the Zugspitze mountain (4,1 GV -effective vertical cutoff rigidity), Germany, to measure the energy spectrum of cosmic ray neutrons at high altitudes continuously. The spectrometer consists of 16 3He proportional counters. Thirteen counters are covered by polyethylene shells with various thicknesses, while two are covered by polyethylene shells including lead, to increase the response to neutrons above 20 MeV (Fig. 1 and Fig. 2). Because the count rate at such high altitudes is about a factor of 5 larger than at sea level, the system can be used to investigate small temporal variations in the cosmic radiation intensity. For example, in July and September 2005 measurements were performed during periods of two Forbush decreases of the cosmic radiation intensity. Please visit the Enviromental research station "Schneefernerhaus" (UFS)



Bonner sphere spectrometer(Fig.1) installed in the measurement shed (Fig. 2) on Zugspitze mountain, Germany

See more info about HMGU Zugspitze neutrons spectrometer.

The NMDB Neutron Monitor Data Base
Recently, the data obtained on the Environmental Research Station “Schneefernerhaus” (UFS) with the Bonner multi-sphere spectrometer system have been included in  the real-time database for high resolution neutron monitor measurements. Please visit the Neutron Monitor Database (NMDB) 

References:
W. Rühm, U. Ackermann, C. Pioch, and V. Mares. Spectral neutron flux oscillations of cosmic radiation on the Earth's surface. Journal of Geophysical Research, VOL. 117, A08309, doi:10.1029/2012JA017524, 2012.

W. Rühm, V. Mares, C. Pioch, G. Simmer and E. Weitzenegger. Continuous measurement of secondary neutrons from cosmic radiation at mountain altitudes and close to the North Pole-A Discussion in terms of H*(10). Radiation Protection Dosimetry (2009), Vol. 136, No. 4, pp. 256-261.

W. Rühm, V. Mares, C. Pioch, E. Weitzenegger, H.G. Paretzke. Continuous Measurement of Secondary Neutrons from Cosmic Radiation at Low Atmospheric and Geomagnetic Shielding by Means of Bonner sphere spectrometers. Proceeding of 21stEuropean Cosmic Ray Symposium, 9 - 12 September 2008, Kosice, Slovakia.

G. Leuthold, V. Mares, W. Rühm, E. Weitzenegger, H.G. Paretzke. Long-term measurements of cosmic ray neutrons by means of a Bonner spectrometer at mountain altitudes – first results. Radiation Protection Dosimetry, Vol. 126, No. 1-4, pp. 506-511, 2007.

AWI Spitsbergen (Arktic)

Measurement of solar particle events on Spitsbergen, Arctic

Air crew members and airline passengers are continuously exposed to cosmic radiation during their flights. Particles ejected by the sun (“Solar Particle Events” – SPEs) during periods of high solar activity contribute to this exposure. In rare cases the dose from a single SPE might even exceed the annual dose limit of 1 mSv above which dose monitoring of air crews is legally required. Because SPEs can be best studied close to the magnetic pols where the shielding of cosmic radiation due to the geomagnetic field is low, we have installed a Bonner sphere spectrometer at the Koldewey station in Ny-Alesund, Spitsbergen. The station belongs to the Alfred-Wegener-Institute, Germany, and is located 79oN by effective vertical cutoff rigidity 0 GV, at a hight of 0 m above sea level. The project will provide first experimental data on the time-dependent energy spectrum of neutrons produced in the atmosphere after an SPE. Please visit the Alfred-Wegener-Institute


HMGU BBS spectrometer in Koldewey station on Ny-Alesund,Arctic (Fig. 1).  Some of the spheres of the HMGU BSS spectrometer in the window (Fig. 2); the statue represents Roald Amundsen. (Foto: R. Vockenroth, AWI).

See  more info about HMGU Spitsbergen Neutron spectrometer

The NMDB Neutron Monitor Data Base

Recently, the data obtained on the Koldewey Station with the Bonner multi-sphere spectrometer system have been included in  the real-time database for high resolution neutron monitor measurements). Please visit the Neutron Monitor Database (NMDB) for more details.

References:
W. Rühm, V. Mares, C. Pioch, E. Weitzenegger, R. Vockenroth, H.G. Paretzke. Measurements of secondary neutrons from cosmic radiation with a Bonner sphere spectrometer at 79oN. Radiat Environ Biophys (2009), 48:125-133

W. Rühm, V. Mares, C. Pioch, G. Simmer and E. Weitzenegger. Continuous measurement of secondary neutrons from cosmic radiation at mountain altitudes and close to the North Pole-A Discussion in terms of H*(10). Radiation Protection Dosimetry (2009), Vol. 136, No. 4, pp. 256-261.

W. Rühm, V. Mares, C. Pioch, E. Weitzenegger, H.G. Paretzke. Continuous Measurement of Secondary Neutrons from Cosmic Radiation at Low Atmospheric and Geomagnetic Shielding by Means of Bonner sphere spectrometers. Proceeding of 21stEuropean Cosmic Ray Symposium, 9 - 12 September 2008, Kosice, Slovakia.

Development of Detector Systems for Medical Applications

GaN- Sensors

Ionization chambers have been used since the beginning of the 20th century for measuring ionizing radiation and still represent the “gold standard” in dosimetry.  However, since the sensitivity of the devices is proportional to the detection volume, ionization chambers are not common in numerous medical applications, such as imaging. In these fields, spatially resolved dose information is, beside film-systems, usually measured with scintillators and photo-multipliers, which is a relatively complex and expensive technique. Hence much effort has been focused on the development of novel detection systems in the last decades and especially in the last few years. Examples include germanium or silicon photoconductive detectors, MOSFETs, and PIN-diodes. Although for these systems, miniaturization for spatially resolved detection is possible, they suffer from a range of disadvantages. Characteristics such as poor measurement stability, material degradation, and/or a limited measurement range prevent routine application of these techniques in medical diagnostic devices. Our work focuses on the development and evaluation of gallium nitride (GaN) thin films and heterostructures to validate their application in x-ray detection in the medical regime.

 

In cooperation with:

Si-PIN Diode Detectors

Preface

Recently, two independent electronic dosimeters for individual monitoring have been developed at the Helmholtz Center Munich, Germany, one for photons and one for neutrons. These dosimeters have been designed to work in an energy range from 144 keV  to 14.8 MeV for neutrons and from 12 keV  to 1.3 MeV for photons respectively.

Development of an electronic neutron personal dosimeter

The dosimeter has three built-in sensors for three different neutron energy ranges. Each sensor consists of a silicon charged particle detector (PIN-diode) covered with a converter. The neutrons interacting with the converter produce charged particles which are detected by the diode.

 


Front panel of neutron dosimeter prototype (Fig.1) and the irradiation facility (Fig.2)

Energy range:

  • Low energy sensor: 23 meV-70 keV
  • Intermediate energy sensor: 70 keV-1.5 MeV
  • High energy sensor: 1.5 MeV-20 MeV

Technical data:

  • Dimensions [mm]: 115 x 60 x 16
  • Mass 160 g
  • Battery: Li/Ion-accumulator, 3.6 V 900 mAh
  • Operation time: 400 h per battery charge
  • Displayed doses: 1 µSv – 10 Sv

References:
M. Silari, S. Agosteo, P. Beck, R. Bedogni, E. Cale, M. Caresana, C. Domingo, L. Donadille, N. Dubourg, A. Exposito, G. Fehrenbacher, F. Fernández, M. Ferrarini, A. Fiechtner, A. Fuchs, M.J. García, N. Golnik, F. Gutermuth, S. Khurana, Th. Klages, M. Latocha, V. Mares, S. Mayer, T. Radon, H. Reithmeier, s. Rollet, H. Roos, W. Rühm, S. Sandri, D. Schardt, G. Simmer, F. Spurný, F. Trompier, C. Villa-Grasa, E. Weitzenegger, B. Wiegel, M. Wielunski, F. Wissmann, A. Zechner, M. Zielczynski. Intercomparison of radiation protection devices in a high-energy stray neutron field. Part III:Instrument response. Radiation Measurements 44 (2009), 673-691.

M. Wielunski, W. Wahl, N. EL-Faramawy, W. Rühm, M. Luszik-Bhadra, H. Roos. Intercomparison exercise with MeV neutrons using various electronic personal dosimeter. Radiation Measurements, 43, 1063-1067, 2008.

Wielunski, M., Schütz, R., Fantuzzi, E., Pagnamenta, A., Wahl, W., Palfalvi, J., Zombori, P., Andrasi, A., Stadtmann, H., Schmitzer, Ch. Study of the sensitivity of neutron sensors consisting of a converter plus Si charged-particle detector. Nucl. Instr. Meth. Phys. Res A 517, 240-253, 2004.


Development of an electronic photon personal dosimeter

Currently, efforts are made to develop an electronic personal photon dosimeter based on Si-pin diodes including special filter combinations. The diodes are covered by different filters and, for this reason, are sensitive to photons with different energies. The signals from the Si-detectors are evaluated both in an analogue and digital way, and finally doses are internally calculated.
Figure  shows t
he first prototype of the analogue electronic circuit, the new smaller SMD version (bottom, left) and two small detectors (bottom, right).


View on internals of photon dosimeter prototype

Technical data

  • Power supply: 3.3V 200µA.
  • Noise level: about 5keV.

Reference: 
M Wielunski, S Trinkl, D de Souza-Santos, W Wahl, W Rühm. The HMGU Combined Neutron and Photon Dosemeter. Radiat Prot Dosim, 2017, accepted

Ge-Detectors for Partial Body Counters

In vivo measurements with a partial body counter

Motivation

  • Measurement of incorporated radionuclides
  • Dose estimates after incorporation of radioactive substances
  • Emphasis on bone-seeking radionuclides
  • Examples: 226Ra, 210Pb, 241Am

Experimental Setup

  • shielding chamber about 8 m below the surface of the earth
  • materials used: sand, steel, lead, copper
  • detection: 4-6 Germanium detectors (crystal thickness: 1.2 – 3 cm; diameter: 5 – 7 cm)
  • emphasis on detection of low energies
  • calibration: 241Am and 210Pb skull phantoms (from BfS, Neuherberg, Germany) 
  • calibration: 241Am knee phantoms (from CIEMAT, Spain, and DOE, USA) 

Future - Towards Personalised Dosimetry
Future work aims at developing methods to calibrate the partial body counter based on individual body parameters. This work will include development of suitable voxel phantoms for computational calibration of the counter, and development of tools to quantify the influcence of critical body parameters on the detection efficiency of the counter. In the end, this work will allow a more precise "personalised" quantification of internal doses after incorporation of various radionuclides.  

 

References:
Kramer, G. H.; Loprez M.A.;Broggio, D.;Tolmachev, S.; Rühm, W.: Natural vs. artificial anthroporometic phantoms for measuring b one-seeking radionuclides. Health Phys. 102, 354-355 (2012).

Gary H. Kramer, Barry Hauck, Kevin Capello, Werner Rühm, Nabil El-Faramawy, David Broggio, Didier Franck, Maria Antonia Lopez, Teresa Navarro, Juan Francisco Navarro, Begona Perez, and Sergei Tomachev. Comparison of two leg phantoms containing 241AM in Bone. Health Phys. 101(3):248-258, 2011.

M. A. Lopez, D. Broggio, K. Capello, E. Cardenas-Mendez, N. El-Faramawy, D. Franck, A. C. James, G. H. Kramer, G. Lacerenza, T. P. Lynch, J. F. Navarro, B. Perez, W. Rühm, S. Y. Tolmachev, E. Weitzenegger. Eurados Intercomparison on measurement and Monte Carlo Modelling for the assessment of Americium in  A ustur leg phantom. Radiation Protection Dosimetry (2011), Vol. 144, No. 1-4, pp. 295-299.

Shielding chamber and four Germanium detectors of HMGU partial body counter

Shielding chamber and four Germanium detectors of HMGU partial body counter

Monte Carlo Particle Transport Simulation

Secondary Particle Fields in Hadrontherapy

Secondary particle fields in hadron therapy

In hadron therapy the primary radiation undergoes nuclear interactions with beam line elements and the patient's body. Due to these nuclear reactions secondary radiations like photons and neutrons are produced. This secondary radiation leads to additional unwanted doses to the patient outside the target tumor in hadron therapy. Doses from secondary radiation may increase the risk for secondary cancer. The radiation effects on the patients tissue  (organs) strongly depends on the relative biological effectiveness (RBE) of the radiation. Different radiation qualities have different relative biological effectiveness. For neutrons the situation is more complex, because the RBE of neutrons strongly depends on the energy of the neutron. Measurements of the spectral energy distribution over about 13 orders of magnitude in energy inside the patient's body is currently impossible. As a consequence, to estimate (and to understand the origin of) the doses to the patient from secondary radiation it is necessary to simulate the particle energy distributions inside patient and phantoms using Monte-Carlo particle transport simulations. The Geometry and Tracking Monte-Carlo particle transport simulation framework in version 4 (Geant4) is used to simulate these secondary particle energy distributions. Geant4 is in extensive use to simulate doses and energy distributions of secondary neutrons to the phantoms in our measurement campaigns in Trento (Italy), Krakow (Poland) and Heidelberg (Germany).

Simulated secondary neutron energy distributions inside the phantom used for the measurements in Trento.

Secondary Particle Fields in the Atmosphere

 Transport Calculation of High Energy Particles in the Atmosphere

The cosmic radiation field in the Earth’s atmosphere is a complex environment consisting of neutrons, protons, photons, electrons, positrons, pions, muons and heavy ions with energy ranges extending up to hundrets of GeV, which is generated via interactions of the primary cosmic ray (CR) particles with the nuclei in the atmosphere.
To complement the continuous detection of secondary neutrons from CR ( see also "Measurement on the Zugspitze" and "Measurement on Spitsbergen" projects) and determine the particle dose components obtained for example by persons onboard of aircrafts (EPCARD - Air Crew Dosimetry ), we focus on transport calculations of secondary particles from CR in the atmosphere.
In the past the FLUKA Monte Carlo code was used to simulate the transport of secondary cosmic particles in the atmosphere.
Recently, the GEANT4 Monte Carlo code is used to calculate the spectral particle fluences of secondary CR for different altitudes between sea level and top of atmosphere at altitude of about 80 km, and for a set of solar modulation and vertical cutoff rigidity parameters to cover all possible values of each variable.
The figure below shows, as an example, a neutron spectrum in the atmosphere calculated with GEANT4 at a typical flight altitude.

High Energy Particle Transport Calculation - EURADOS comparison

The measurements with a Bonner sphere spectrometer (BSS) (see also "Measurement on Zugspitze" and "Measurement on Spitsbergen" projects) require determination of the response as function of neutron energy, for each sphere of the spectrometer. Response functions are often calculated by Monte Carlo (MC) codes. For neutron energies below 20 MeV, where evaluated cross sections are available, the response functions are rather similar whatever code is used. However, for energies above 20 MeV, where every neutron transport code is based on theoretical intranuclear cascade models (INC), rather large differences are observed.

EURADOS WG11
(on “High Energy Radiation Fields”) has initiated an intercomparison of different transport codes with emphasis on calculation of high-energy response functions. The goal of this intercomparison is to decide which MC codes and INC models are most suitable to calculate low Z material (such as PE) and high-Z material (such as lead). The participants of this intercomparison exercise calculate the response of two Bonner spheres (one made of PE, one made of PE plus lead) by different MC transport codes using different INC models. The codes to be included are MCNP/LAHET, FLUKA, MCNPX, GEANT4, PHITS, MARS.

The geometry of Bonner sphere with 3He counter, green lines: neutron tracks simulated with GEANT4

 

References
C. Pioch, V. Mares, W. Rühm. Influence of Bonner sphere response functions above 20 MeV on unfolded neutron spectra and doses. Radiation Measurements 45 (2010) 1263-1267.

C. Pioch, V. Mares, E.V. Vashenyuk, Yu.V. Balabin, W. Rühm. Measurement of cosmic ray neutrons with Bonner sphere spectrometer and neutron monitor at 79°N. Nuclear Instruments an Methods in Physics Research A 626-627 (2011) 51-57.

Detector Simulation

Simulation of photon response for photon dosimeter

Simulations of the photon dosimeter response were performed using the Geant4 framework version 10.01.p02.
In the simulation, the photon dosimeter was placed on the surface of a 30 x 30 x 15 cm³ PMMA phantom and irradiated with a parallel mono-energetic photon beam (cross section: 30 x 30 cm²). The photon sensor was implemented including filters and the electronic board. The energy deposition in the PIN-diodes was scored, and all events with an energy deposition above 12 keV were considered for the calculation of the dosimeter response. 
Simulations were performed using mean energies of ISO 4037 N-quality photon spectra (N15, N20, N25, N30, N40, N60, N80, N100, N120, N150, N200, N250, N300).
In addition, energies of 661.6 keV and 1.25 MeV were also used to simulate irradiation with photons from 137Cs and 60Co sources. The resulting comparison of simulated response functions with results of the experiments is shown figure below.

Results of the calibration measurements performed with the stand-alone photon dosimeter, for X-rays and 137Cs and 60Co gamma rays. Black line – measurement at 0°, blue line – measurement at 60°. Red line – results of MC simulation for 0°. Green solid lines represent requirements of type certification

  Simulation for neutron response for neutron dosimeter

The figure below shows the results of the calibration measurements performed with the stand-alone neutron dosimeter (Albedo, Fast, and Delta sensor), together with the results of Monte Carlo simulations. The neutron dosimeter was calibrated at the Physikalisch Technische Bundesanstalt (PTB) in Braunschweig, Germany, with mono-energetic neutrons at energies of 0.14, 0.23, 0.56, 1.2, 2.5, 5, 8, and 14.8 MeV. The response of the Fast, Albedo and Delta sensors were determined.
By simulations the sensor response was calculated as the ratio of the number of detected to incident neutrons. The simulations were performed with the Geant4 version 4.9.3, the nuclear data libraries from version 4.9.4, and the BinaryINC model for high neutron energies.
The figure below demonstrates reasonable agreement between measurements and simulations for the energy range between 140 keV and 14.8 MeV, for all three sensors. It is obvious that the Albedo sensor provides the highest signal at low neutron energies (up to about 2 MeV). The Fast sensor shows the highest signal for neutrons above 3 MeV. The Delta sensor contributes mostly in the energy range between 50 keV and 3 MeV. The neutron dose will be calculated with a proper combination of the responses of all three sensors. 

Response of the stand-alone neutron dosimeter measured and simulated at various neutron energies; solid lines serve as eye guide between data points simulated with GEANT4 including their statistical uncertainties; the solid symbols correspond to the response measured at PTB

 

 

Flight Dosimetry

Air Crew Dosimetry with EPCARD

EPCARD

As an immediate consequence of the ICRP recommendations in 1990, the GSF (currently Helmholtz Zentrum Munich) Institute of Radiation Protection (ISS) had issued research programmes which aimed at the theoretical and experimental assessment of the natural exposure to ionizing radiation in aircrafts. With support from the European Commission and scientists from the University of Siegen, the ISS has developed the EPCARD-European Program Package for the Calculation of Aviation Route Doses. This code allows calculation of doses from all components of penetrating cosmic radiation on any aviation route and for any flight profile. The officially approved (by the Federal Office for Aviation, LBA, and the National Metrology Institute, PTB) version of the EPCARD program is already in use by several European air companies. For more detail please visit the EPCARD portal

The next generation code EPCARD.Net was approved for official use for aircrew dosimetry by the German Aviation Authority (LBA) and the National Metrology Institute, Physikalisch-Technische Bundesanstalt (PTB) on April 23rd, 2010.

In 2009, a workshop was held at the Physikalisch Technische Bundesanstalt (PTB) in Braunschweig , Germany, on cosmic radiation and aircrew exposure. Contributions were published in a special issue of Radiation Protection Dosimetry.

References:
J. Chen and V. Mares. Significant impact on effective doses received during commercial flights calculated using the new ICRP radiation weighting factors. Health Phys. 98(1):74-76;2010.

V. Mares, H. Yasuda. Aviation route doses calculated with EPCARD.Net and JISCARD EX. Radiation Measurements 45 (2010), 1553 - 1556.

V. Mares, T. Maczka, G. Leuthold and W. Rühm. Air Crew Dosimetry with an new version of EPCARD. Radiation Protection Dosimetry (2009), Vol. 136, No. 4, pp. 262-266.

V. Mares, G. Leuthold. Altitude-dependent dose conversion coefficients in EPCARD. Radiation Protection Dosimetry, Vol. 126, No. 1-4, pp. 581-584, 2007.

EPCARD.Net ver 5.4.3 software CD and box(virtual)

EPCARD.Net ver 5.4.3 software CD and box(virtual)

Flight Dosimetry with EPCARD Online

Using this Web site, the users can calculate online and for free the dose which they would receive along a specified flight due to cosmic radiation. Additionally, they can determine the dose which is accumulated during a stay of one hour at any flight position in the atmosphere.

 

 

 

Human Phantoms

Numerical dose calculations

Organ and tissue doses are quantities that are related to risk from ionizing radiation. Since doses in organs and tissues of the human body cannot be measured, they have to be calculated. This is done by simulating the radiation transport inside virtual human models using Monte Carlo code packages. Virtual human models are computer representations of the body and range from simple geometric forms to complex representations of the body like the mathematical MIRD-type phantoms or voxel phantoms.

The radiation sources considered are external (broad parallel beams for occupational radiation protection, collimated point sources for radiographic examinations, and environmental geometries) or internal (monoenergetic volume sources, radionuclides incorporated at the workplace or in the environment, and radiopharmaceuticals).

The dose quantities considered are organ and effective doses, specific absorbed fractions, spatial absorbed dose distributions, particle fluences, energy spectra, and various dose conversion coefficients that link a measurable quantity to an organ dose. This allows an easy application of such calculations.

 

Key publications:

Petoussi-Henss, N. ; Bolch, W.E. ; Eckerman, K.F. ; Endo, A. ; Hertel, N. ; Hunt, J. ; Menzel, H.G. ; Pelliccioni, M. ; Schlattl, H. ; Zankl, M. The first ICRP/ICRU application of the male and female adult reference computational phantoms. Phys. Med. Biol. 59, 5209-5224 (2014)

Saito, K. ; Petoussi-Henß, N. Ambient dose equivalent conversion coefficients for radionuclides exponentially distributed in the ground. J. Nucl. Sci. Technol. 51, 1274-1287 (2014)

Petoussi-Henss, N. ; Schlattl, H. ; Zankl, M. ; Endo, A.* ; Saito, K.* Organ doses from environmental exposures calculated using voxel phantoms of adults and children. Phys. Med. Biol. 57, 5679-5713 (2012)

Saito, K. ; Ishigure, N. ; Petoussi-Henss, N. ; Schlattl, H. Effective dose conversion coefficients for radionuclides exponentially distributed in the ground. Radiat. Environ. Biophys. 51, 411-423 (2012)

Schlattl, H. ; Zankl, M. ; Becker, J. ; Hoeschen, C. Dose conversion coefficients for paediatric CT examinations with automatic tube current modulation. Phys. Med. Biol. 57, 6309-6326 (2012)

Zankl, M. ; Schlattl, H. ; Petoussi-Henss, N. ; Hoeschen, C. Electron specific absorbed fractions for the adult male and female ICRP/ICRU reference computational phantoms. Phys. Med. Biol. 57, 4501-4526 (2012)

Petoussi-Henss, N. ; Bolch, W.E. ; Eckerman, K.F. ; Endo, A. ; Hertel, N. ; Hunt, J. ; Pelliccioni, M. ; Schlattl, H. ; Zankl, M. ; International Commission on Radiological Protection ; International Commission on Radiation Units and Measurements Conversion coefficients for radiological protection quantities for external radiation exposures. Ann. ICRP 40, 257 S. (2010)

Schlattl, H. ; Zankl, M. ; Beckers, J. ; Hoeschen, C. Dose conversion coefficients for CT examinations of adults with automatic tube current modulation. Phys. Med. Biol. 55, 6243-6261 (2010)

Schlattl, H. ; Zankl, M. ; Petoussi-Henss, N. Organ dose conversion coefficients for voxel models of the reference male and female from idealized photon exposures. Phys. Med. Biol. 52, 2123-2145 (2007)

Petoussi-Henss, N. ; Zankl, M. ; Nosske, D. Estimation of patient dose from radiopharmaceuticals using voxel models. Cancer Biother. Radiopharm. 20, 103-109 (2005)

Zankl, M. ; Petoussi-Henss, N. ; Fill, U. ; Regulla, D.F. The application of voxel phantoms to the internal dosimetry of radionuclides. Radiat. Prot. Dosim. 105, 539-548 (2003)

Human phantoms

Since the early eighties, our research group plays a leading role in the development of voxel phantoms (voxel = volume element). These are constructed from medical image data (Computed Tomography, Magnetic Resonance Imaging) of real persons using image processing tools. Due to their realistic body anatomy, these phantoms exceed the MIRD-type phantoms for many applications in radiation protection.

A family of voxel phantoms was developed in our research group at the Helmholtz Zentrum München including phantoms of both genders, from newborn to adult. Furthermore, we have created a voxel phantom of a pregnant woman in the 24th week of gestation. Some of these phantoms are available for research purposes under certain conditions .

A software tool called ‘VolumeChange’ has been developed to modify the masses and location of organs of virtual human voxel models. With this tool, two human voxel models were adjusted to fit the reference organ masses of a male and a female adult, as defined by the International Commission on Radiological Protection (ICRP). 

Organ modelling and their segmentation from medical images is an interesting part of our work. Here a new approach of an organ model description transfers the mathematical description of electric fields to image analysis and connects potential and field lines to edge gradients. Automatic generated organ boundaries are suggested which can be edited by the user.

Ongoing research includes also the development of so-called »hybrid« or »dual-lattice« voxel phantoms that contain high-resolution details of selected body regions like breast or lungs in addition to the normal voxel resolution. This feature permits direct studies of the relation of image quality and dose.

 Key publications:

Petoussi-Henß, N. ; Becker, J. ; Greiter, M.B. ; Schlattl, H. ; Zankl, M. ; Hoeschen, C. Construction of anthropomorphic hybrid, dual-lattice voxel models for optimizing image quality and dose in radiography. Proc. SPIE 9033:90331W (2014)

Becker, J. ; Zankl, M. ; Fill, U. ; Hoeschen, C. Katja - the 24 week of virtual pregnancy for dosimetric calculations. Pol. J. Med. Phys. Eng. 14, 13-20 (2008)

Becker, J. ; Zankl, M. ; Petoussi-Henss, N. A software tool for modification of human voxel models used for application in radiation protection. Phys. Med. Biol. 52, 195-205 (2007)

Hoeschen, C. ; Fill, U. ; Zankl, M. ; Panzer, W. ; Regulla, D.F. ; Döhring, W. A high-resolution voxel phantom of the breast for dose calculations in mammography. Radiat. Prot. Dosim. 114, 406-409 (2005)

Fill, U.A. ; Zankl, M. ; Petoussi-Henss, N. ; Siebert, M. ; Regulla, D.F. Adult female voxel models of different stature and photon conversion coefficients for radiation protection. Health Phys. 86, 253-272 (2004)

Petoussi-Henss, N. ; Zankl, M. ; Fill, U. ; Regulla, D.F. The GSF family of voxel phantoms. Phys. Med. Biol. 47, 89-106 (2002)

Saito, K. ; Wittmann, A. ; Koga, S. ; Ida, Y. ; Kamei, T. ; Funabiki, J. ; Zankl, M. Construction of a computed tomographic phantom for a Japanese male adult and dose calculation system.  Radiat. Environ. Biophys. 40 , 69-75 (2001)

Reference Computational Human Phantoms

For national and international regulations (guidelines, dose limitation for radiation workers and the population), »average« persons have to be represented in the calculations. For this purpose, adult male and female voxel phantoms have been developed in our research group that have body characteristics and organ masses in compliance with the reference anatomical data published by the International Commission on Radiological Protection (ICRP).

For this, two segmented phantoms have been selected whose external dimensions were similar to the reference data. These were then modified in several steps:

  • Voxel scaling
  • Adjustment of individual organ masses
  • Adjustment of whole body mass by adding adipose tissue

These computational phantoms of the adult Reference Male and Reference Female have been adopted by the ICRP and the ICRU (International Commission of Radiation Units and Measurements) for calculating reference dose quantities and are available from the ICRP.

Key publications:

Zankl, M. ; Schlattl, H. ; Petoussi-Henss, N. ; Hoeschen, C. Electron specific absorbed fractions for the adult male and female ICRP/ICRU reference computational phantoms. Phys. Med. Biol. 57, 4501-4526 (2012)

Petoussi-Henss, N. ; Bolch, W.E.* ; Eckerman, K.F.* ; Endo, A. ; Hertel, N.* ; Hunt, J.* ; Pelliccioni, M.* ; Schlattl, H. ; Zankl, M. ; International Commission on Radiological Protection ; International Commission on Radiation Units and Measurements Conversion coefficients for radiological protection quantities for external radiation exposures. Ann. ICRP 40, 257 S. (2010)

Zankl, M. ; Eckermann, K.F.* ; Petoussi-Henss, N. ; Bolch, W.E. ; Menzel, H.G.* Adult reference computational phantoms. Ann. ICRP 110, 165 S. (2009)

Schlattl, H. ; Zankl, M. ; Petoussi-Henss, N. Organ dose conversion coefficients for voxel models of the reference male and female from idealized photon exposures. Phys. Med. Biol. 52, 2123-2145 (2007)

Zankl, M. ; Eckerman, K.F.* ; Bolch, W.E.* Voxel-based models representing the male and female ICRP reference adult--the skeleton. Radiat. Prot. Dosim. 127, 174-186 (2007)