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Fast neutron dosimetry: a study of basic dosimetric properties of fast-neutrons for external beam radiotherapy and problems associated with corrections of measured charged particle cross-sections
Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences.
2001 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Basic dosimetric properties of fast-neutron beams with energies ≤80 MeV were explored using Monte Carlo techniques. Elementary pencil-beam dose distributions taking into account transport of all relevant types of released charged particles (protons, deuterons, tritons, 3He and a particles) were calculated and used to derive several absorbed dose distributions. Broad-beam depth doses in phantoms of different materials were compared and scaling factors calculated to convert absorbed dose in one material to absorbed dose in another. The scaling factors were in good agreement with available published data and show that water is a good substitute for soft tissue even at neutron energies as high as 80 Me V. The inherent penumbra and fraction of absorbed dose due to photons were also studied, and found to be consistent with published values.

Treatment planning in fast-neutron therapy is commonly performed using dose calculation algorithms designed for photon beam therapy. These algorithms have limitations in the physical models when applied to neutron beams. Monte Carlo derived neutron pencil-beam kernels were parameterized and implemented into the photon dose calculation algorithms of the TMS (MDS Nordion) treatment planning system. It was shown that these algorithms yield good results in homogeneous water media. However, the heterogeneity correction method of the photon dose calculation algorithm failed to calculate correct results in heterogeneous media for neutron beams.

Fundamental cross-section data are needed when calculating absorbed doses. To achieve results with adequate accuracy, neutron cross-sections are still not sufficiently well known. At the The Svedberg Laboratory in Uppsala, Sweden, an experimental facility has been designed to measure neutron-induced charged-particle production cross-sections for (n,xp), (n,xd), (n,xt), (n,x3He) and (n,xα) reactions at neutron energies up to 100 MeV. In order to derive the energy distributions of charged particles generated inside the production target, the measured data have to be corrected for the energy lost by the particles in the target. In this work a code (CRAWL) was developed for the reconstruction of the true spectrum. It uses a stripping method. With the limitation of reduced energy resolution, results using CRAWL compare well with those of other methods.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet , 2001. , 44 p.
Series
Linköping Studies in Health Sciences. Thesis, ISSN 1100-6013 ; 48
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-27572Local ID: 12235ISBN: 91-7219-975-X (print)OAI: oai:DiVA.org:liu-27572DiVA: diva2:248124
Presentation
2013-06-05, Ögonklinikens föreläsningssal, Universitetssjukhuset, Linköping, 09:15 (Swedish)
Opponent
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2013-07-10
List of papers
1. Fast neutron absorbed dose distributions in the energy range 0.5-80 MeV: a Monte Carlo study
Open this publication in new window or tab >>Fast neutron absorbed dose distributions in the energy range 0.5-80 MeV: a Monte Carlo study
2000 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 45, no 10, 2987-3007 p.Article in journal (Refereed) Published
Abstract [en]

Neutron pencil-beam absorbed dose distributions in phantoms of bone, ICRU soft tissue, muscle, adipose and the tissue substitutes water, A-150 (plastic) and PMMA (acrylic) have been calculated using the Monte Carlo code FLUKA in the energy range 0.5 to 80 MeV. For neutrons of energies ≤20 MeV, the results were compared to those obtained using the Monte Carlo code MCNP4B. Broad-beam depth doses and lateral dose distributions were derived. Broad-beam dose distributions in various materials were compared using two kinds of scaling factor: a depth-scaling factor and a dose-scaling factor. Build-up factors due to scattered neutrons and photons were derived and the appropriate choice of phantom material for determining dose distributions in soft tissue examined. Water was found to be a good substitute for soft tissue even at neutron energies as high as 80 MeV. The relative absorbed doses due to photons ranged from 2% to 15% for neutron energies 10-80 MeV depending on phantom material and depth. For neutron energies below 10 MeV the depth dose distributions derived with MCNP4B and FLUKA differed significantly, the difference being probably due to the use of multigroup transport of low energy (<19.6 MeV) neutrons in FLUKA. Agreement improved with increasing neutron energies up to 20 MeV. At energies >20 MeV, MCNP4B fails to describe dose build-up at the phantom interface and penumbra at the edge of the beam because it does not transport secondary charged particles. The penumbra width, defined as the distance between the 80% and 20% iso-dose levels at 5 cm depth and for a 10×10 cm2 field, was between 0.9 mm and 7.2 mm for neutron energies 10-80 MeV.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-14360 (URN)10.1088/0031-9155/45/10/317 (DOI)000089865300017 ()
Available from: 2007-03-22 Created: 2007-03-22 Last updated: 2017-12-13
2. Evaluation of a photon dose calculation algorithm applied to fast-neutron therapy treatment planning using a neutron pencil-beam kernel
Open this publication in new window or tab >>Evaluation of a photon dose calculation algorithm applied to fast-neutron therapy treatment planning using a neutron pencil-beam kernel
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Treatment planning in fast-neutron therapy is commonly performed using conventional treatment planning systems designed for photon beam therapy. In this work Monte Carlo derived neutron pencil-beam kernels in water were parameterised using an algorithm developed for photon beams and implemented in the TMS photon dose treatment planning system. A rectangular fast-neutron fluence spectrum with energies 0-40 Me V was used. Central axis depth doses and lateral dose distributions were calculated by the dose planning system and compared with corresponding dose distributions using direct Monte Carlo calculations in homogeneous water phantom and heterogeneous phantoms. Good agreement was found in both lateral and depth dose distributions in a homogeneous water phantom. However, considerable deviations were obtained between absorbed doses calculated by the dose planning system and the Monte Carlo calculated absorbed doses in heterogeneous media. The multipurpose Monte Carlo code FLUKA was used both for the calculation of the pencil-beam kernel and in the direct calculations of absorbed dose in the phantom.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-95604 (URN)
Available from: 2013-07-10 Created: 2013-07-10 Last updated: 2013-07-10
3. Correction of measured charged-particle spectra for energy losses in the target: A comparison of three methods
Open this publication in new window or tab >>Correction of measured charged-particle spectra for energy losses in the target: A comparison of three methods
2002 (English)In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 195, no 3-4, 426-434 p.Article in journal (Refereed) Published
Abstract [en]

The experimental facility, MEDLEY, at the The Svedberg Laboratory in Uppsala, has been constructed to measure neutron-induced charged-particle production cross-sections for (n, xp), (n, xd), (n, xt), (n, x3He) and (n, xα) reactions at neutron energies up to 100 MeV. Corrections for the energy loss of the charged particles in the target are needed in these measurements, as well as for loss of particles. Different approaches have been used in the literature to solve this problem. In this work, a stripping method is developed, which is compared with other methods developed by Rezentes et al. and Slypen et al. The results obtained using the three codes are similar and they could all be used for correction of experimental charged-particle spectra. Statistical fluctuations in the measured spectra cause problems independent of the applied technique, but the way to handle it differs in the three codes.

Keyword
Neutron, Cross-section, Charged particle, Energy-loss corrections
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-14359 (URN)10.1016/S0168-583X(02)01090-X (DOI)000178915500023 ()
Available from: 2007-03-22 Created: 2007-03-22 Last updated: 2017-12-13

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