RESUMO
Ionising radiation is increasingly used for the treatment of cancer, being the source of a considerable fraction of the medical irradiation to patients. With the increasing success rate of cancer treatments and longer life expectancy of the treated patients, the issue of secondary cancer incidence is of growing concern, especially for paediatric patients who may live long after the treatment and be more susceptible to carcinogenesis. Also, additional imaging procedures like computed tomography, kilovoltage and megavoltage imaging and positron emission tomography, alone or in conjunction with radiation therapy, may add to the radiation burden associated with the risk of occurrence of secondary cancers. This work has been based on literature studies and is focussed on the assessment of secondary doses to healthy tissues that are delivered by the use of modern radiation therapy and diagnostic imaging modalities in the clinical environment.
Assuntos
Neoplasias Induzidas por Radiação/etiologia , Neoplasias Induzidas por Radiação/prevenção & controle , Doses de Radiação , Proteção Radiológica/instrumentação , Proteção Radiológica/métodos , Radioterapia de Intensidade Modulada/instrumentação , Radioterapia de Intensidade Modulada/métodos , Antropometria , Íons Pesados/efeitos adversos , Humanos , Imagens de Fantasmas , Fótons , Tomografia por Emissão de Pósitrons/efeitos adversos , Prótons/efeitos adversos , Radiação Ionizante , Radioterapia de Intensidade Modulada/efeitos adversos , Tomografia Computadorizada por Raios X/efeitos adversosRESUMO
For both cancer therapy with protons and ions (hadron therapy) and space radiation environments, the spatial energy deposition patterns of the radiation fields are of importance for quantifying the resulting radiation damage in biological structures. Tissue-equivalent proportional counters (TEPC) are the principal instruments for measuring imparted energy on a microscopic scale and for characterizing energy deposition patterns of radiation. Moreover, the distribution of imparted energy can serve as a complementary quantity to particle fluences of the primary beam and secondary fragments for characterizing a radiation field on a physical basis for radiobiological models. In this work, the Monte Carlo particle transport code FLUKA is used for simulating energy depositions in TEPC by ion beams. The capability of FLUKA in predicting imparted energy and derived quantities, such as lineal energy, for microscopic volumes is evaluated by comparing it with a large set of TEPC measurements for different ion beams with atomic numbers ranging from 1 to 26 and energies from 80 up to 1000 MeV/n. The influence of different physics configurations in the simulation is also discussed. It is demonstrated that FLUKA can simulate energy deposition patterns of ions in TEPC cavities accurately and that it provides an adequate description of the main features of the spectra.
Assuntos
Modelos Teóricos , Método de Monte Carlo , Terapia com Prótons , Radioterapia/instrumentação , Íons/uso terapêutico , Dosagem RadioterapêuticaRESUMO
As carbon ions, at therapeutic energies, penetrate tissue, they undergo inelastic nuclear reactions and give rise to significant yields of secondary fragment fluences. Therefore, an accurate prediction of these fluences resulting from the primary carbon interactions is necessary in the patient's body in order to precisely simulate the spatial dose distribution and the resulting biological effect. In this paper, the performance of nuclear fragmentation models of the Monte Carlo transport codes, FLUKA and GEANT4, in tissue-like media and for an energy regime relevant for therapeutic carbon ions is investigated. The ability of these Monte Carlo codes to reproduce experimental data of charge-changing cross sections and integral and differential yields of secondary charged fragments is evaluated. For the fragment yields, the main focus is on the consideration of experimental approximations and uncertainties such as the energy measurement by time-of-flight. For GEANT4, the hadronic models G4BinaryLightIonReaction and G4QMD are benchmarked together with some recently enhanced de-excitation models. For non-differential quantities, discrepancies of some tens of percent are found for both codes. For differential quantities, even larger deviations are found. Implications of these findings for the therapeutic use of carbon ions are discussed.
Assuntos
Benchmarking/métodos , Carbono/química , Carbono/uso terapêutico , Modelos Teóricos , Método de Monte CarloRESUMO
An analytical algorithm based on the generalized Fermi-Eyges theory, amended for multiple Coulomb scattering and energy loss straggling, is used for calculation of the dose distribution of light ion beams in water. Pencil beam energy deposition distributions are derived for light ions by weighting a Monte Carlo (MC) calculated planar integral dose distribution with analytically calculated multiple scattering and range straggling distributions. The planar integral dose distributions are calculated using the MC code SHIELD-HIT07, in which multiple scattering and energy loss straggling processes are excluded. The contribution from nuclear reactions is included in the MC calculations. Multiple scattering processes are calculated separately for primary and secondary ions and parameters of the initial angular and radial spreads, and the covariance of these are derived by a least-square parameterization of the SHIELD-HIT07 data. The results from this analytical algorithm are compared to pencil beam dose distributions obtained from SHIELD-HIT07, where all processes are included, as well as to experimental data. The presented analytical approach allows for the accurate calculation of the spatial energy deposition distributions of ions of atomic numbers Z = 1 - 8.
Assuntos
Algoritmos , Íons/química , Método de Monte Carlo , Radioterapia de Alta Energia/métodos , Espalhamento de Radiação , Simulação por Computador , Luz , Modelos Biológicos , Radioisótopos/química , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador , Água/químicaRESUMO
Nanodosimetric single-event distributions or their mean values may contribute to a better understanding of how radiation induced biological damages are produced. They may also provide means for radiation quality characterization in therapy beams. Experimental nanodosimetry is however technically challenging and Monte Carlo simulations are valuable as a complementary tool for such investigations. The dose-mean lineal energy was determined in a therapeutic p(65)+Be neutron beam and in a (60)Co gamma beam using low-pressure gas detectors and the variance-covariance method. The neutron beam was simulated using the condensed history Monte Carlo codes MCNPX and SHIELD-HIT. The dose-mean lineal energy was calculated using the simulated dose and fluence spectra together with published data from track-structure simulations. A comparison between simulated and measured results revealed some systematic differences and different dependencies on the simulated object size. The results show that both experimental and theoretical approaches are needed for an accurate dosimetry in the nanometer region. In line with previously reported results, the dose-mean lineal energy determined at 10 nm was shown to be related to clinical RBE values in the neutron beam and in a simulated 175 MeV proton beam as well.
Assuntos
Modelos Biológicos , Método de Monte Carlo , Nanotecnologia/métodos , Terapia por Captura de Nêutron/métodos , Radiometria/métodos , Simulação por Computador , Modelos Estatísticos , Dosagem Radioterapêutica , Análise de Regressão , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
A comparison of calculated and measured values of the dose mean lineal energy (y(D)) for the former neutron therapy beam at Louvain-la-Neuve is reported. The measurements were made with wall-less tissue-equivalent proportional counters using the variance-covariance method and simulating spheres with diameters between 10 nm and 15 microm. The calculated y(D)-values were obtained from simulated energy distributions of neutrons and charged particles inside an A-150 phantom and from published y(D)-values for mono-energetic ions. The energy distributions of charged particles up to oxygen were determined with the SHIELD-HIT code using an MCNPX simulated neutron spectrum as an input. The mono-energetic ion y(D)-values in the range 3-100 nm were taken from track-structure simulations in water vapour done with PITS/KURBUC. The large influence on the dose mean lineal energy from the light ion (A > 4) absorbed dose fraction, may explain an observed difference between experiment and calculation. The latter being larger than earlier reported result. Below 50 nm, the experimental values increase while the calculated decrease.
Assuntos
Modelos Biológicos , Nanotecnologia/métodos , Nêutrons/uso terapêutico , Radiometria/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Eficiência Biológica Relativa , Animais , Simulação por Computador , Humanos , Dosagem RadioterapêuticaRESUMO
Secondary neutrons produced in high-energy therapeutic ion beams require special attention since they contribute to the dose delivered to patient, both to tumour and to the healthy tissues. Moreover, monitoring of neutron production in the beam line elements and the patient is of importance for radiation protection aspects around ion therapy facility. Monte Carlo simulations of light ion transport in the tissue-like media (water, A-150, PMMA) and materials of interest for shielding devices (graphite, steel and Pb) were performed using the SHIELD-HIT and MCNPX codes. The capability of the codes to reproduce the experimental data on neutron spectra differential both in energy and angle is demonstrated for neutron yield from the thick targets. Both codes show satisfactory agreement with the experimental data. The absorbed dose due to neutrons produced in the water and A-150 phantoms is calculated for proton (200 MeV) and carbon (390 MeV/u) beams. Secondary neutron dose contribution is approximately 0.6% of the total dose delivered to the phantoms by proton beam and at the similar level for both materials. For carbon beam the neutron dose contribution is approximately 1.0 and 1.2% for the water and A-150 phantoms, respectively. The neutron ambient dose equivalent, H(10), was determined for neutrons leaving different shielding materials after irradiation with ions of various energies.
Assuntos
Radioterapia com Íons Pesados , Modelos Biológicos , Nêutrons , Monitoramento de Radiação/instrumentação , Proteção Radiológica/instrumentação , Eficiência Biológica Relativa , Simulação por Computador , Desenho de Equipamento , Análise de Falha de Equipamento , Humanos , Teste de Materiais , Doses de Radiação , Proteção Radiológica/métodos , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
Clinical application of light ion beams requires correct understanding of the complex processes of ion interaction with matter and the development of accurate transport methods. Knowledge of the fluence differential in energy of primary and secondary particles is important since it allows evaluation of different linear energy transfer (LET) dose components in the patient. The low LET and high LET particle distributions and the corresponding absorbed doses due to primary and secondary particles were evaluated for different depths in a water phantom using the Monte Carlo code SHIELD-HIT. SHIELD-HIT calculations are compared with the experimental LET distributions for a carbon beam of energy 278 MeV u(-1) from the HIMAC facility in Japan. The capability of the code for the evaluation of particle transport in thin layers of a few micrometres is demonstrated.
Assuntos
Radioisótopos de Carbono/uso terapêutico , Radioterapia com Íons Pesados , Transferência Linear de Energia , Modelos Biológicos , Radiometria/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Animais , Carga Corporal (Radioterapia) , Simulação por Computador , Humanos , Dosagem Radioterapêutica , Eficiência Biológica Relativa , Espalhamento de RadiaçãoRESUMO
The lateral and longitudinal distributions of absorbed dose of broad and narrow light ion beams in water are investigated. An analytical algorithm based on the generalized Fermi-Eyges theory is developed and used to calculate the effects of multiple scattering and range straggling on the dose distribution of light ion beams in water. A first-order Gaussian multiple scattering and energy loss straggling approach is generally sufficiently accurate for describing the lateral and longitudinal spread of the Bragg peak and the associated energy deposition distribution of therapeutic light ion beams at ranges of clinical interest. Nuclear reactions are not taken into account in this study. The analytical algorithm given in the present study allows an accurate description of the radial spread and the range straggling of light ions traversing matter. A verification of this approach by comparing with experimental data, Monte Carlo methods and other analytical techniques will be presented in a forthcoming paper.
Assuntos
Íons , Planejamento da Radioterapia Assistida por Computador/métodos , Espalhamento de Radiação , Água , Algoritmos , Elétrons , Luz , Modelos Estatísticos , Método de Monte Carlo , Distribuição Normal , Aceleradores de Partículas , Planejamento da Radioterapia Assistida por Computador/instrumentaçãoRESUMO
Based on irradiation with 45 MeV/u N and B ions and with Co-60 gamma rays, cellular parameters of Katz's track structure model have been fitted for the survival of V79-379A Chinese hamster lung fibroblasts. Cellular parameters representing neoplastic transformations in C3H10T/1/2 cells after their irradiation with heavy ion beams, taken from earlier work, were also used to model the radiation hazard in deep space, following the system for evaluating, summing and reporting occupational exposures proposed in 1967 by a subcommittee of NCRP. We have performed model calculations of the number of transformations in surviving cells, after a given fluence of heavy charged particles of initial energy 500 MeV/u, penetrating thick layers of cells. We take the product of cell transformation and survival probabilities, calculated along the path lengths of charged particles using cellular survival and transformation parameters, to represent a quantity proportional to the "radiation risk factor" discussed in the NCRP document. The "synergistic" effect of simultaneous charged particle transfers is accounted for by the "track overlap" mode inherent in the model of Katz.
Assuntos
Sobrevivência Celular/efeitos da radiação , Transformação Celular Neoplásica/efeitos da radiação , Radiação Cósmica , Íons Pesados , Modelos Biológicos , Animais , Carbono , Linhagem Celular , Cricetinae , Cricetulus , Relação Dose-Resposta à Radiação , Meio Ambiente Extraterreno , Fibroblastos , Hidrogênio , Ferro , Transferência Linear de Energia , Pulmão/citologia , Pulmão/efeitos da radiação , Física Nuclear , UrânioRESUMO
The absorbed dose due to photonuclear reactions in soft tissue, lung, breast, adipose tissue and cortical bone has been evaluated for a scanned bremsstrahlung beam of end point 50 MeV from a racetrack accelerator. The Monte Carlo code MCNP4B was used to determine the photon source spectrum from the bremsstrahlung target and to simulate the transport of photons through the treatment head and the patient. Photonuclear particle production in tissue was calculated numerically using the energy distributions of photons derived from the Monte Carlo simulations. The transport of photoneutrons in the patient and the photoneutron absorbed dose to tissue were determined using MCNP4B; the absorbed dose due to charged photonuclear particles was calculated numerically assuming total energy absorption in tissue voxels of 1 cm3. The photonuclear absorbed dose to soft tissue, lung, breast and adipose tissue is about (0.11-0.12)+/-0.05% of the maximum photon dose at a depth of 5.5 cm. The absorbed dose to cortical bone is about 45% larger than that to soft tissue. If the contributions from all photoparticles (n, p, 3He and 4He particles and recoils of the residual nuclei) produced in the soft tissue and the accelerator, and from positron radiation and gammas due to induced radioactivity and excited states of the nuclei, are taken into account the total photonuclear absorbed dose delivered to soft tissue is about 0.15+/-0.08% of the maximum photon dose. It has been estimated that the RBE of the photon beam of 50 MV acceleration potential is approximately 2% higher than that of conventional 60Co radiation.