| 1. |
- Hultqvist, Martha, et al.
(författare)
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Evaluation of nuclear reaction cross-sections and fragment yields in carbon beams using the SHIELD-HIT Monte Carlo code. Comparison with experiments
- 2012
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 57:13, s. 4369-4385
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Tidskriftsartikel (refereegranskat)abstract
- In light ion therapy, the knowledge of the spectra of both primary and secondary particles in the target volume is needed in order to accurately describe the treatment. The transport of ions in matter is complex and comprises both atomic and nuclear processes involving primary and secondary ions produced in the cascade of events. One of the critical issues in the simulation of ion transport is the modeling of inelastic nuclear reaction processes, in which projectile nuclei interact with target nuclei and give rise to nuclear fragments. In the Monte Carlo code SHIELD-HIT, inelastic nuclear reactions are described by the Many Stage Dynamical Model (MSDM), which includes models for the different stages of the interaction process. In this work, the capability of SHIELD-HIT to simulate the nuclear fragmentation of carbon ions in tissue-like materials was studied. The value of the parameter., which determines the so-called freeze-out volume in the Fermi break-up stage of the nuclear interaction process, was adjusted in order to achieve better agreement with experimental data. In this paper, results are shown both with the default value k = 1 and the modified value k = 10 which resulted in the best overall agreement. Comparisons with published experimental data were made in terms of total and partial charge-changing cross-sections generated by the MSDM, as well as integral and differential fragment yields simulated by SHIELD-HIT in intermediate and thick water targets irradiated with a beam of 400 MeV u(-1) C-12 ions. Better agreement with the experimental data was in general obtained with the modified parameter value (k = 10), both on the level of partial charge-changing cross-sections and fragment yields.
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| 2. |
- Hultqvist, Martha, et al.
(författare)
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Monte Carlo simulation of correction factors for IAEA TLD holders
- 2010
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Ingår i: Physics in Medicine and Biology. - 0031-9155 .- 1361-6560. ; 55:6, s. N161-N166
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Tidskriftsartikel (refereegranskat)abstract
- The IAEA standard thermoluminescent dosimeter (TLD) holder has been developed for the IAEA/WHO TLD postal dose program for audits of high-energy photon beams, and it is also employed by the ESTRO-QUALity assurance network (EQUAL) and several national TLD audit networks. Factors correcting for the influence of the holder on the TL signal under reference conditions have been calculated in the present work from Monte Carlo simulations with the PENELOPE code for Co-60 gamma-rays and 4, 6, 10, 15, 18 and 25 MV photon beams. The simulation results are around 0.2% smaller than measured factors reported in the literature, but well within the combined standard uncertainties. The present study supports the use of the experimentally obtained holder correction factors in the determination of the absorbed dose to water from the TL readings; the factors calculated by means of Monte Carlo simulations may be adopted for the cases where there are no measured data.
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| 3. |
- Hultqvist, Martha, et al.
(författare)
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Nanodosimetry in a (12)C ion beam using Monte Carlo simulations
- 2010
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Ingår i: Radiation Measurements. - : Elsevier BV. - 1350-4487 .- 1879-0925. ; 45:10, s. 1238-1241
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Tidskriftsartikel (refereegranskat)abstract
- The dose-mean lineal energy, (y) over bar (D), has been calculated in water for irradiation with (12)C ions with initial energies 290 MeV/u. The y, was evaluated from the energy distributions of carbon and secondary boron ions, and from their energy-dependent pp-values. The energy distributions were obtained from simulations with the Monte Carlo code SHIELD-HIT07 and the energy-dependent (y) over bar (D)-values were obtained from ion-track simulations with PITS99 coupled with the electron transport code KURBUC. The ratio of the (y) over bar (D)-value determined in the vicinity of the Bragg peak to that calculated in a reference (60)Co gamma beam was compared with the corresponding ratio of alpha-values from the linear-quadratic model used in fractionated radiotherapy, showing a good correlation for an object size of around 10 nm.
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| 4. |
- Hultqvist, Martha, 1983-
(författare)
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Secondary absorbed dose distributions and radiation quality in light ion therapy
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Radiotherapy with light ions offers the possibility of achieving a dose distribution which is highly conformed to the target volume while sparing normal tissues. For ions heavier than protons, an additional advantage is the increased Relative Biological Effectiveness (RBE) as compared to conventional photon and electron beams. During light ion therapy, nuclear fragments are produced in nuclear inelastic collisions of the projectile and the atomic nuclei in the material. In a cascade of events, the nuclear fragments in turn produce secondaries during their transport. The organs of the patient are thus exposed to a complex secondary radiation field and secondary doses can be delivered to normal tissues both close to and relatively far from the treated volume. In this thesis, secondary doses were evaluated in anthropomorphic phantoms which were developed for simulations with the Monte Carlo code SHIELD-HIT. Simulations of lung tumor, prostate and brain tumor irradiation with 1H, 4He, 7Li, 12C and 16O ion beams in the energy range 80-400 MeV/u were performed with SHIELD-HIT. The simulated organ absorbed doses were in the range 10-6-10-1 mGy per treatment Gy. In general, the organ absorbed doses decreased with increasing distance from the target volume and increased with increasing atomic number of the primary ions.The produced nuclear fragments also influences the radiation quality in the target volume and thus the biological effectiveness of the beam. The dose-mean lineal energy, D>, was studied in a 290 MeV/u 12C beam by simulating the energy distributions of both primary and secondary ions and weighting their relative dose fractions with the corresponding energy-dependent D> which were obtained by ion-track simulations with PITS99 coupled with the electron transport code KURBUC. D> were evaluated in the target volume for object diameters 10-100 nm and were used in estimations of clinically useful weighting factors.
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| 5. |
- Hultqvist, Martha, et al.
(författare)
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Secondary absorbed doses from light ion irradiation in anthropomorphic phantoms representing an adult male and a 10 year old child
- 2010
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 55:22, s. 6633-6653
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Tidskriftsartikel (refereegranskat)abstract
- Secondary organ absorbed doses were calculated by Monte Carlo simulations with the SHIELD-HIT07 code coupled with the mathematical anthropomorphic phantoms CHILD-HIT and ADAM-HIT. The simulated irradiations were performed with primary 1H, 4He, 7Li, 12C and 16O ion beams in the energy range 100–400 MeV/u which were directly impinging on the phantoms, i.e. approximating scanned beams, and with a simplified beamline for 12C irradiation. The evaluated absorbed doses to the out-of-field organs were in the range 10−6 to 10−1 mGy per target Gy and with standard deviations 0.5–20%. While the contribution to the organ absorbed doses from secondary neutrons dominated in the ion beams of low atomic number Z, the produced charged fragments and their subsequent charged secondaries of higher generations became increasingly important for the secondary dose delivery as Z of the primary ions increased. As compared to the simulated scanned 12C ion beam, the implementation of a simplified beamline for prostate irradiation with 12C ions resulted in an increase of 2–50 times in the organ absorbed doses depending on the distance from the target volume. Comparison of secondary organ absorbed doses delivered by 1H and 12C beams showed smaller differences when the RBE for local tumor control of the ions was considered and normalization to the RBE-weighted dose to the target was performed. General scientific summary. During light ion therapy, the production of nuclear fragments results in a complex secondary radiation field which the organs and normal tissues of the patient are exposed to. In the present work, the absorbed doses to out-of-field organs and the energy distribution of secondary particle fluences in anthropomorphic phantoms have been simulated by the Monte Carlo code SHIELD-HIT07 for brain tumor and prostate irradiation with approximated scanned beams of 1H, 4He, 7Li, 12C and 16O ions in the energy range 100–400 MeV/u, as well as with a simplified beam line for 12C irradiation. The evaluated organ absorbed doses were in the range 10−6 to 10−1 mGy per target Gy. The absorbed dose contribution from secondary neutrons dominated in the ion beams of low atomic number Z, while the produced charged fragments and their subsequent charged secondaries became increasingly important for the secondary dose delivery as Z of the primary ion increased.
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| 6. |
- Hultqvist, Martha, et al.
(författare)
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Secondary doses delivered to an anthropomorphic male phantom under prostate irradiation with proton and carbon ion beams
- 2010
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Ingår i: Radiation Measurements. - : Elsevier BV. - 1350-4487 .- 1879-0925. ; 45:10, s. 1410-1413
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Tidskriftsartikel (refereegranskat)abstract
- Secondary radiation exposure of patients undergoing radiation therapy with light ions is of great concern due to possible tissue damage and risk of induction of secondary cancers. Secondary particles such as neutrons, protons and heavier ions are produced when the primary ions interact through nuclear inelastic reactions with the beam-line components, and with the tissues of the patient. Evaluations of secondary doses delivered to an anthropomorphic male phantom under prostate irradiation with (1)H and (12)C ion beams with energies 172 MeV and 330 MeV/u, respectively, have been performed with the Monte Carlo code SHIELD-HIT. Fluences of secondary particles with atomic mass A = 1-7 and energies up to 200-600 MeV/u are observed in organs even at larger distances (40-50 cm) from the irradiated volume. The secondary absorbed doses in selected organs are discussed taking into account the dose contribution from secondary neutrons, and the contribution from charged fragments that are not the products of neutron interactions. For (12)C ion irradiation, a substantial contribution to the absorbed organ dose is due to charged fragments. This contribution decreases from 81% in the organs close to the irradiated volume to 35-40% in the organs at larger distances.
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| 7. |
- Hultqvist, Martha, 1983-, et al.
(författare)
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Secondary doses in anthropomorphic phantoms irradiated with light ion beams
- 2009
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Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 168:1, s. 123-127
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Tidskriftsartikel (refereegranskat)abstract
- The mathematical anthropomorphic phantoms EVA-HIT and ADAM-HIT have been used in the Monte Carlo code SHIELD-HIT07 for simulations of lung tumor and prostate irradiation with light ions. Calculations were performed for 1H, 7Li, and 12C beams of energies in the range of 80 to 330 MeV/u. The secondary doses to organs, due to scattered primary ions and secondary particles produced in the phantoms, were studied taking into account the contribution from secondary neutrons, secondary protons, pions, and heavier fragments from helium to calcium. The doses to organs per dose to target (tumor) are of the order of 10-6 to 10-1 mGy Gy-1 and decrease with increasing distance from the target. In general the organ dose per target dose increases with increasing Z of the primary particle; however, for lighter primary ions (Z 3) and for organs close to the target, scattered primary particles show a nonnegligible dose contribution.
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| 8. |
- Liamsuwan, Thiansin, et al.
(författare)
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Microdosimetry of proton and carbon ions
- 2014
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405 .- 2473-4209. ; 41:8, s. 239-250
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To investigate microdosimetry properties of 160 MeV/u protons and 290 MeV/u C-12 ion beams in small volumes of diameters 10-100 nm. Methods: Energy distributions of primary particles and nuclear fragments in the beams were calculated from simulations with the general purpose code SHIELD-HIT, while energy depositions by monoenergetic ions in nanometer volumes were obtained from the event-by-event Monte Carlo track structure ion code PITS99 coupled with the electron track structure code KURBUC. Results: The results are presented for frequencies of energy depositions in cylindrical targets of diameters 10-100 nm, dose distributions (y) over bar (D) in lineal energy y, and dose-mean lineal energies YD For monoenergetic ions, the hp was found to increase with an increasing target size for high-linear energy transfer (LET) ions, but decrease with an increasing target size for low-LET ions. Compared to the depth dose profile of the ion beams, the maximum of the hp depth profile for the 160 MeV proton beam was located at similar to 0.5 cm behind the Bragg peak maximum, while the PD peak of the 290 MeV/u C-12 beam coincided well with the peak of the absorbed dose profile. Differences between the (y) over bar (D) and dose-averaged linear energy transfer (LETD) were large in the proton beam for both target volumes studied, and in the C-12 beam for the 10 nm diameter cylindrical volumes. The (y) over bar (D) determined for 100 run diameter cylindrical volumes in the C-12 beam was approximately equal to the LETD. The contributions from secondary particles to the (y) over bar (D) of the beams are presented, including the contributions from secondary protons in the proton beam and from fragments with atomic number Z = 1-6 in the C-12 beam. Conclusions: The present investigation provides an insight into differences in energy depositions in subcellular-size volumes when irradiated by proton and carbon ion beams. The results are useful for characterizing ion beams of practical importance for biophysical modeling of radiation-induced DNA damage response and repair in the depth profiles of protons and carbon ions used in radiotherapy.
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| 9. |
- Lindborg, L, et al.
(författare)
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Lineal energy and radiation quality in radiation therapy: model calculations and comparison with experiment
- 2013
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Ingår i: Physics in Medicine and Biology. - : Institute of Physics: Hybrid Open Access. - 0031-9155 .- 1361-6560. ; 58:10, s. 3089-3105
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Tidskriftsartikel (refereegranskat)abstract
- Microdosimetry is a recommended method for characterizing radiation quality in situations when the biological effectiveness under test is not well known. In such situations, the radiation beams are described by their lineal energy probability distributions. Results from radiobiological investigations in the beams are then used to establish response functions that relate the lineal energy to the relative biological effectiveness (RBE). In this paper we present the influence of the size of the simulated volume on the relation to the clinical RBE values (or weighting factors). A single event probability distribution of the lineal energy is approximated by its dose average lineal energy ((y) over bar (D)) which can be measured or calculated for volumes from a few micrometres down to a few nanometres. The clinical RBE values were approximated as the ratio of the alpha-values derived from the LQ-relation. Model calculations are presented and discussed for the SOBP of a C-12 ion (290 MeV u(-1)) and the reference Co-60 gamma therapy beam. Results were compared with those for a conventional x-ray therapy beam, a 290 MeV proton beam and a neutron therapy beam. It is concluded that for a simulated volume of about 10 nm, the alpha-ratio increases approximately linearly with the (y) over bar (D)-ratio for all the investigated beams. The correlation between y and alpha provides the evidence to characterize a radiation therapy beam by the lineal energy when, for instance, weighting factors are to be estimated.
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| 10. |
- Lindborg, Lennart, et al.
(författare)
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Nanodosimetry and RBE values in radiotherapy
- 2015
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Ingår i: Radiation Protection Dosimetry. - : OXFORD UNIV PRESS. - 0144-8420 .- 1742-3406. ; 166:1-4, s. 339-342
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Tidskriftsartikel (refereegranskat)abstract
- In a recent paper, the authors reported that the dose mean lineal energy, (y) over bar (D) in a volume of about 10-15 nm is approximately proportional to the alpha-parameter in the linear-quadratic relation used in fractionated radiotherapy in both low- and high-LET beams. This was concluded after analyses of reported radiation weighting factors, W-isoE (clinical RBE values), and (y) over bar (D) values in a large range of volumes. Usually, microdosimetry measurements in the nanometer range are difficult; therefore, model calculations become necessary. In this paper, the authors discuss the calculation method. A combination of condensed history Monte Carlo and track structure techniques for calculation of mean lineal energy values turned out to be quite useful. Briefly, the method consists in weighting the relative dose fractions of the primary and secondary charged particles with their respective energy-dependent dose mean lineal energies. The latter were obtained using a large database of Monte Carlo track structure calculations.
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