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28-30 April 2014
Fermi National Accelerator Laboratory
US/Central timezone

Measurement of stray neutron radiation within a proton therapy facility

Speaker

Vladimir Mares (Helmholtz Zentrum München, Institute of Radiation Protection, 85764 Neuherberg, Germany)

Description

Proton therapy is an advanced radiation treatment that destroys cancer cells with high accuracy. Proton treatment beams can be fine-tuned to deposit most of their energy at a specific depth within the patient, keeping irradiation of adjacent organs and healthy tissue to a minimum. However, proton interactions with materials in the beam line and with patient’s tissue create secondary neutrons with energies from thermal to several tens or hundreds of MeV. These secondary neutrons may increase the risk of a second cancer significantly, and should be taken seriously. Dosimetry measurements around medical proton accelerators are very complex due to heterogeneous radiation fields, for this reason the use of well proved and well known measurement systems is necessary. In 2013, organised by EURADOS Working Group 9 (Radiation Protection Dosimetry in Medicine) a large set of intercomparison measurement was carried out in the IBA (230 MeV) active-scanning proton beam therapy facility in Trento, Italy. Several types of active detectors and dosemeters were used: Bonner Sphere Spectrometers (BSS), HAWK TEPC, several REM-counters such as WENDI-II, Berthold, RadEye, NM2B, and new HMGU electronic dosemeters. The proton beam was directed into a water phantom (30 x 30 x 60 cm3) with a 1 liter (10 x 10 x 10 cm3) target volume, simulating the patient. The isocenter of the beam was in depth of 15 cm inside the water phantom. Neutron ambient dose equivalents, H*(10), were measured at several positions inside the treatment room at four angles: 0°, 45°, 90°, and 135° with respect to the beam line direction, and at different distances. A generally good agreement among H*(10) values within 30% was observed for the different types of used detectors. The highest neutron H*(10) value of about 60 µSv/Gy was measured along the beam axis at distance of 1.15 m from isocenter. However, the lowest neutron H*(10) value measured in the treatment room was about 1.1 µSv/Gy at distance of 4.25 m, and at 90° with respect to beam line. Measurements with BSS provided valuable information on the spectral energy distribution of secondary neutrons and H*(10) at 4 different angles around the water phantom. Secondary neutron spectra generated by a proton beam impinging a water phantom were also calculated using Monte Carlo simulation with the GEANT4 code. Dosimetry measurements in the phantom included different passive detectors (RPL, several types of TLDs and CR-39). Their future analysis will give insight in dose contributions from different radiation types depending on the position in the phantom and distance from the target volume. The results of this large set of intercomparison measurements and Monte Carlo simulations may be valuable for medical physicists and radiation protection officers.

Primary author

Vladimir Mares (Helmholtz Zentrum München, Institute of Radiation Protection, 85764 Neuherberg, Germany)

Co-authors

Carles Domingo (Departament de Física, Universitat Autònoma de Barcelona, Bellaterra, Spain) Carlo Algranati (Medical Physics Department, Trento Proton Therapy Center, Via Valentina Zambra, 16 - 38121 Trento, Italy) Erik Frojd (CERN, The European Organization for Nuclear Research, CH-1211 Geneva 23, Switzerland) Francesco Fellin (Medical Physics Department, Trento Proton Therapy Center, Via Valentina Zambra, 16 - 38121 Trento, Italy) François Trompier (Institute for Radiological Protection and Nuclear Safety, Human Health Division, BP17, 92260 Fontenay-aux-Roses; France) Jad Farah (Institute for Radiological Protection and Nuclear Safety, Human Health Division, BP17, 92260 Fontenay-aux-Roses; France) Jan Kubancak (Department of Radiation Dosimetry, Nuclear Physics Institute, CZ-250 68 Řež, Czech Republic) Konstantin Schinner (Helmholtz Zentrum München, Institute of Radiation Protection, 85764 Neuherberg, Germany) Liliana Stolarczyk (Institute of Nuclear Physics PAN, Radzikowskiego 152, 31-342 Krakow, Poland) Magdalena Klodowska (Institute of Nuclear Physics PAN, Radzikowskiego 152, 31-342 Krakow, Poland) Malgorzata Liszka (Institute of Nuclear Physics PAN, Radzikowskiego 152, 31-342 Krakow, Poland) Marco Schwarz (Medical Physics Department, Trento Proton Therapy Center, Via Valentina Zambra, 16 - 38121 Trento, Italy) Marek Wielunski (Helmholtz Zentrum München, Institute of Radiation Protection, 85764 Neuherberg, Germany) Marija Majer (Ruđer Bošković Institute, Bijenička c. 54, 10000 Zagreb, Croatia) María Teresa Romero Expósito (Departament de Física, Universitat Autònoma de Barcelona, Bellaterra, Spain) Ondrej Ploc (Department of Radiation Dosimetry, Nuclear Physics Institute, CZ-250 68 Řež, Czech Republic) Pawel Olko (Institute of Nuclear Physics PAN, Radzikowskiego 152, 31-342 Krakow, Poland) Roger Harrison (University of Newcastle upon Tyne, Newcastle, UK) Saveta Miljanić (Ruđer Bošković Institute, Bijenička c. 54, 10000 Zagreb, Croatia) Sebastian Trinkl (Helmholtz Zentrum München, Institute of Radiation Protection, 85764 Neuherberg, Germany) Stuart Patrick George (CERN, The European Organization for Nuclear Research, CH-1211 Geneva 23, Switzerland) Vladimir Dufek (National Radiation Protection Institute, Bartoškova 28, 140 00 Praha, Czech Republic) Werner Rühm (Helmholtz Zentrum München, Institute of Radiation Protection, 85764 Neuherberg, Germany) Željka Kneževič (Ruđer Bošković Institute, Bijenička c. 54, 10000 Zagreb, Croatia)

Presentation Materials