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1.
PLoS One ; 17(7): e0271028, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-35905102

RESUMO

Neutron contamination as a source of out-of-field dose in radiotherapy is still of concern. High-energy treatment photons have the potential to overcome the binding energy of neutrons inside the nuclei. Fast neutrons emitting from the accelerator head can directly reach the patient's bed. Considering that modern radiotherapy techniques can increase patient survival, concerns about unwanted doses and the lifetime risk of fatal cancer remain strong or even more prominent, especially in young adult patients. The current study addressed these concerns by quantifying the dose and risk of fatal cancer due to photo-neutrons for glioma patients undergoing 18-MV radiotherapy. In this study, an NRD model rem-meter detector was used to measure neutron ambient dose equivalent, H*(10), at the patient table. Then, the neutron equivalent dose received by each organ was estimated concerning the depth of each organ and by applying depth dose corrections to the measured H*(10). Finally, the effective dose and risk of secondary cancer were determined using NCRP 116 coefficients. Evidence revealed that among all organs, the breast (0.62 mSv/Gy) and gonads (0.58 mSv/Gy) are at risk of photoneutrons more than the other organs in such treatments. The neutron effective dose in the 18-MV conventional radiotherapy of the brain was 13.36 mSv. Among all organs, gonads (6.96 mSv), thyroid (1.86 mSv), and breasts (1.86 mSv) had more contribution to the effective dose, respectively. The total secondary cancer risk was estimated as 281.4 cases (per 1 million persons). The highest risk was related to the breast and gonads with 74.4 and, 34.8 cases per 1 million persons, respectively. Therefore, it is recommended that to prevent late complications (secondary cancer and genetic effects), these organs should be shielded from photoneutrons. This procedure not only improves the quality of the patient's personal life but also the healthy childbearing in the community.


Assuntos
Glioma , Segunda Neoplasia Primária , Glioma/radioterapia , Humanos , Nêutrons , Aceleradores de Partículas , Imagens de Fantasmas , Fótons/efeitos adversos , Radiometria/métodos , Dosagem Radioterapêutica
2.
Cancer Res Treat ; 53(3): 621-634, 2021 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-34176253

RESUMO

Charged-particle therapy (CPT) such as proton beam therapy (PBT) and carbon-ion radiotherapy (CIRT) exhibit substantial physical and biological advantages compared to conventional photon radiotherapy. As it can reduce the amount of radiation irradiated in the normal organ, CPT has been mainly applied to pediatric cancer and radioresistent tumors in the eloquent area. Although there is a possibility of greater benefits, high set-up cost and dearth of high level of clinical evidence hinder wide applications of CPT. This review aims to present recent clinical results of PBT and CIRT in selected diseases focusing on possible indications of CPT. We also discussed how clinical studies are conducted to increase the number of patients who can benefit from CPT despite its high cost.


Assuntos
Radioterapia com Íons Pesados/efeitos adversos , Neoplasias/radioterapia , Seleção de Pacientes , Fótons/efeitos adversos , Lesões por Radiação/epidemiologia , Análise Custo-Benefício , Radioterapia com Íons Pesados/economia , Radioterapia com Íons Pesados/métodos , Humanos , Incidência , Órgãos em Risco/efeitos da radiação , Lesões por Radiação/etiologia , Resultado do Tratamento
3.
Phys Med Biol ; 65(15): 155016, 2020 08 11.
Artigo em Inglês | MEDLINE | ID: mdl-32442990

RESUMO

Monte Carlo simulations are used to investigate skin dose resulting from chest wall radiotherapy with bolus. A simple model of a female thorax is developed, which includes a 2 mm-thick skin layer. Two representative 6 MV source models are considered: a tangents source model consisting of a parallel opposed pair of medial and lateral fields and subfields, and an arc source model. Tissue equivalent (TE) boluses (thicknesses of 3, 5 and 10 mm) and brass mesh bolus are considered. Skin dose distributions depend on incident photon obliquity: for tangents, radiation is incident more obliquely, resulting in longer path lengths through the bolus and higher skin dose compared to the arc source model in most cases. However, for thicker TE boluses, attenuation of oblique photons becomes apparent. Brass bolus and 3 mm TE bolus result in similar mean skin dose. This relatively simple computational model allows for consideration of different bolus thicknesses, materials and usage schedules based on desired skin dose and choice of either tangents or an arc beam technique. For example, using a 5 mm TE bolus every second treatment would result in mean skin doses of 89% and 85% for tangents and the arc source model, respectively. The hot spot metric D[Formula: see text] would be 103% and 99%, respectively.


Assuntos
Método de Monte Carlo , Imagens de Fantasmas , Doses de Radiação , Planejamento da Radioterapia Assistida por Computador/instrumentação , Pele/efeitos da radiação , Parede Torácica/efeitos da radiação , Feminino , Humanos , Órgãos em Risco/efeitos da radiação , Fótons/efeitos adversos , Fótons/uso terapêutico , Radiometria , Dosagem Radioterapêutica
4.
Phys Med ; 62: 13-19, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31153393

RESUMO

PURPOSE: The present work aimed to evaluate organ doses and related risk for cancer from external beam radiation treatment (EBRT) and high-dose-rate (HDR) brachytherapy (BT) involving Co-60 source for patients with cervical carcinoma in Tanzania based on Monte Carlo methods and to evaluate the secondary cancer risks in their lifetime. METHODS: EBRT and HDR-BR were modelled by using the MCNPX Monte Carlo (MC) code. The MC simulations were performed by using validated models and isocentric irradiation of an adult female computational phantom. The organ doses and cancer risks estimates were obtained. RESULTS: The highest absorbed doses of 6.98 × 10-2 and 5.74 × 10-2 Sv/Gy were recorded in the bladder for BT and EBRT. The higher risk was found for colon at 1.06 × 10-3 in the HDR-BT and 9.75 × 10-5 in the EBRT per 100,000 population at exposure age of 35 years than in the other organs. The risk magnitude decreased with increasing age at exposure. In general, the secondary cancer risks in all sites considered from EBRT and HDR-BR for cervical cancer patient were lower than the baseline risks. CONCLUSIONS: The chances of developing secondary cancer take years following radiation therapy are extremely low, but the results of present study can support to establish a future database on secondary cancer risks involving radiation therapy in patients with cervical cancer by using HDR-BR and EBRT with Co-60 source in Tanzania and other developing countries.


Assuntos
Radioisótopos de Cobalto/efeitos adversos , Método de Monte Carlo , Neoplasias Induzidas por Radiação/etiologia , Fótons/efeitos adversos , Doses de Radiação , Espalhamento de Radiação , Neoplasias do Colo do Útero/radioterapia , Braquiterapia/efeitos adversos , Radioisótopos de Cobalto/uso terapêutico , Feminino , Humanos , Pessoa de Meia-Idade , Segunda Neoplasia Primária/etiologia , Órgãos em Risco/efeitos da radiação , Fótons/uso terapêutico , Dosagem Radioterapêutica , Risco , Tanzânia
5.
Prostate Cancer Prostatic Dis ; 22(4): 509-521, 2019 12.
Artigo em Inglês | MEDLINE | ID: mdl-30967625

RESUMO

BACKGROUND: Advances in radiation technology have transformed treatment options for patients with localized prostate cancer. The evolution of three-dimensional conformal radiation therapy and intensity-modulated radiation therapy (IMRT) have allowed physicians to spare surrounding normal organs and reduce adverse effects. The introduction of proton beam technology and its physical advantage of depositing its energy in tissue at the end-of-range maximum may potentially spare critical organs such as the bladder and rectum in prostate cancer patients. Data thus far are limited to large, observational studies that have not yet demonstrated a definite benefit of protons over conventional treatment with IMRT. The cost of proton beam treatment adds to the controversy within the field. METHODS: We performed an extensive literature review for all proton treatment-related prostate cancer studies. We discuss the history of proton beam technology, as well as its role in the treatment of prostate cancer, associated controversies, novel technology trends, a discussion of cost-effectiveness, and an overview of the ongoing modern large prospective studies that aim to resolve the debate between protons and photons for prostate cancer. RESULTS: Present data have demonstrated that proton beam therapy is safe and effective compared with the standard treatment options for prostate cancer. While dosimetric studies suggest lower whole-body radiation dose and a theoretically higher relative biological effectiveness in prostate cancer compared with photons, no studies have demonstrated a clear benefit with protons. CONCLUSIONS: Evolving trends in proton treatment delivery and proton center business models are helping to reduce costs. Introduction of existing technology into proton delivery allows further control of organ motion and addressing organs-at-risk. Finally, the much-awaited contemporary studies comparing photon with proton-based treatments, with primary endpoints of patient-reported quality-of-life, will help us understand the differences between proton and photon-based treatments for prostate cancer in the modern era.


Assuntos
Análise Custo-Benefício , Fótons/uso terapêutico , Neoplasias da Próstata/radioterapia , Terapia com Prótons/economia , Radioterapia de Intensidade Modulada/economia , Tomada de Decisão Clínica , Redução de Custos , Intervalo Livre de Doença , Medicina Baseada em Evidências/economia , Medicina Baseada em Evidências/métodos , Medicina Baseada em Evidências/tendências , Humanos , Masculino , Medidas de Resultados Relatados pelo Paciente , Fótons/efeitos adversos , Neoplasias da Próstata/economia , Neoplasias da Próstata/mortalidade , Terapia com Prótons/efeitos adversos , Terapia com Prótons/tendências , Qualidade de Vida , Radioterapia (Especialidade)/economia , Radioterapia (Especialidade)/métodos , Radioterapia (Especialidade)/tendências , Dosagem Radioterapêutica , Radioterapia de Intensidade Modulada/efeitos adversos , Radioterapia de Intensidade Modulada/tendências , Taxa de Sobrevida , Resultado do Tratamento
6.
Med Phys ; 45(10): 4775-4782, 2018 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-30105825

RESUMO

PURPOSE: The objective of this study was to estimate the probability for cancer development due to radiotherapy for Graves' orbitopathy with 6 MV x rays. METHODS: Orbital irradiation was simulated with the MCNP code. The radiation dose received by 10 out-of-field organs having a strong disposition for carcinogenesis was calculated with Monte Carlo methods. These dose calculations were used to estimate the organ-dependent lifetime attributable risk (LAR) for cancer induction in 30- and 50-yr-old males and females on the basis of the linear model suggested by the BEIR-VII report. Differential dose-volume histograms derived from patients' three-dimensional (3D) radiotherapy plans were employed to determine the organ equivalent dose (OED) of the brain which was partly exposed to primary radiation. The OED and the relevant LAR for brain cancer development were assessed with the plateau, bell-shaped and mechanistic models. The radiotherapy-induced cancer risks were compared with the lifetime intrinsic risk (LIR) values for unexposed population. RESULTS: The radiation dose range to organs excluded from the treatment volume was 0.1-91.0 mGy for a target dose of 20 Gy. These peripheral organ doses increased the LIRs for cancer development of unexposed 30- and 50-yr-old males up to 1.0% and 0.2%, respectively. The corresponding elevations after radiotherapy of females were 2.0% and 0.4%. The use of nonlinear models gave an OED range of the brain of 482.0-562.5 mGy depending upon the model used for analysis and the patient's gender. The elevation of the LIR for developing brain malignancies after radiotherapy of 30-yr-old males and females reached to 13.3% and 16.6%, respectively. The corresponding increases after orbital irradiation at the age of 50 yr were 6.7% and 8.3%. CONCLUSIONS: The level of the LIR increase attributable to radiation therapy for GO varied widely by the organ under examination and the age and gender of the exposed subject. This study provides the required data to quantify the elevation of these baseline cancer risks following orbital irradiation.


Assuntos
Oftalmopatia de Graves/radioterapia , Neoplasias Induzidas por Radiação/etiologia , Fótons/efeitos adversos , Fótons/uso terapêutico , Neoplasias Encefálicas/etiologia , Método de Monte Carlo , Órgãos em Risco/efeitos da radiação , Dosagem Radioterapêutica , Medição de Risco
7.
Radiat Prot Dosimetry ; 180(1-4): 338-341, 2018 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-29036696

RESUMO

The microdosimetric variance-covariance method was used to study the stray radiation fields from the photon therapy facility at the Technical University of Denmark and the scanned proton therapy beam at the Skandion Clinic in Uppsala, Sweden. Two TEPCs were used to determine the absorbed dose, the dose-average lineal energy, the dose-average quality factor and the dose equivalent. The neutron component measured by the detectors at the proton beam was studied through Monte Carlo simulations using the code MCNP6. In the photon beam the stray absorbed dose ranged between 0.3 and 2.4 µGy per monitor unit, and the dose equivalent between 0.4 and 9 µSv per monitor unit, depending on beam energy and measurement position. In the proton beam the stray absorbed dose ranged between 3 and 135 µGy per prescribed Gy, depending on detector position and primary proton energy.


Assuntos
Fótons/efeitos adversos , Prótons/efeitos adversos , Proteção Radiológica/métodos , Radiometria/métodos , Radioterapia/efeitos adversos , Radioterapia/instrumentação , Simulação por Computador , Humanos , Método de Monte Carlo
8.
Med Phys ; 44(11): 5660-5666, 2017 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-28905394

RESUMO

PURPOSE: The purpose of this study was to quantify the relative neutron damage induced in CIEDs from clinical 18 MV photon beams for varying field sizes, depths, and off axis distances. METHODS AND MATERIALS: Damage was assessed using silicon damage response functions and ICRP neutron dose conversion factors in MCNPX. Particular attention was devoted to the modelling of the Varian 2100C/D linear accelerator to ensure accurate contamination neutron spectra. Neutron dose, fluence and relative damage to CIEDs was calculated. RESULTS: CIED damage from neutrons is related to the neutron dose rather than the neutron fluence. As field size increases, the region of high damage probability extends to a greater distance beyond the edge of the field than with smaller fields. At a distance greater than 50 cm or from the central axis or a depth deeper than 10 cm, the probability of damage is less than 10% of the central axis damage probability for all field sizes. CONCLUSIONS: Clinically, increasing the depth or the distance from the central axis to the CIED will reduce the probability of damage from neutrons. Care must be taken when treating large fields as the overall probability of damage increase as does the distance the higher probability of damage extends beyond the field edge.


Assuntos
Sistema Cardiovascular , Método de Monte Carlo , Nêutrons/efeitos adversos , Fótons/efeitos adversos , Próteses e Implantes , Aceleradores de Partículas , Fótons/uso terapêutico , Doses de Radiação
9.
J Neurooncol ; 135(3): 521-528, 2017 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-28825228

RESUMO

As proton radiotherapy (RT) remains a limited resource, predictive estimates of the potential reduction in adverse treatment-related outcomes compared to photon RT could potentially help improve treatment selection. The aim of this study was to predict the magnitude of the neurocognitive and hearing deficits associated with proton and photon RT for children with brain tumors. The existing RT plans for 50 children treated with photon intensity modulated RT were compared with generated intensity modulated proton RT plans. The proton and photon RT dose distribution was used to estimate the Full Scale Intelligence Quotient (IQ) via a Monte Carlo model and the probability of hearing loss per ear, based on previously published dose-risk relationships. Compared to photon plans, the mean brain dose was found to be reduced in all proton plans, translating into a gain of [Formula: see text] IQ points for the whole cohort at 5 years post-RT for dose regimens of 54 Gy, or [Formula: see text] IQ points for dose regimens of 59.4 Gy, where the errors shown represent statistical and systematic uncertainties. The probability of hearing loss ≥20 dB per ear was less for proton versus photon RT: overall (9 ± 4) versus (17 ± 6)%, respectively, based on dose regimens of 54 Gy, and (13 ± 5) versus (23 ± 9)% for dose regimens of 59.4 Gy. Proton RT is thus expected to reduce the detrimental effect of RT upon IQ and hearing as compared to photon RT for pediatric brain tumors.


Assuntos
Neoplasias Encefálicas/radioterapia , Disfunção Cognitiva/diagnóstico , Disfunção Cognitiva/etiologia , Diagnóstico por Computador , Perda Auditiva/diagnóstico , Perda Auditiva/etiologia , Encéfalo/efeitos da radiação , Neoplasias Encefálicas/complicações , Neoplasias Encefálicas/diagnóstico , Criança , Pré-Escolar , Diagnóstico por Computador/métodos , Relação Dose-Resposta à Radiação , Seguimentos , Humanos , Testes de Inteligência , Método de Monte Carlo , Fótons/efeitos adversos , Fótons/uso terapêutico , Prognóstico , Terapia com Prótons/efeitos adversos , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador , Radioterapia de Intensidade Modulada/efeitos adversos
10.
Appl Radiat Isot ; 123: 32-35, 2017 May.
Artigo em Inglês | MEDLINE | ID: mdl-28214683

RESUMO

One of the major causes of secondary malignancies after radiotherapy treatments are peripheral doses, known to increase for some newer techniques (such as IMRT or VMAT). For accelerators operating above 10MV, neutrons can represent important contribution to peripheral doses. This neutron contamination can be measured using different passive or active techniques, available in the literature. As far as active (or direct-reading) procedures are concerned, a major issue is represented by their parasitic photon sensitivity, which can significantly affect the measurement when the point of test is located near to the field-edge. This work proposes a simple method to estimate the unwanted photon contribution to these neutrons. As a relevant case study, the use of a recently neutron sensor for "in-phantom" measurements in high-energy machines was considered. The method, called "Dual Energy Photon Subtraction" (DEPS), requires pairs of measurements performed for the same treatment, in low-energy (6MV) and high energy (e.g. 15MV) fields. It assumes that the peripheral photon dose (PPD) at a fixed point in a phantom, normalized to the unit photon dose at the isocenter, does not depend on the treatment energy. Measurements with ionization chamber and Monte Carlo simulations were used to evaluate the validity of this hypothesis. DEPS method was compared to already published correction methods, such as the use of neutron absorber materials. In addition to its simplicity, an advantage of DEPs procedure is that it can be applied to any radiotherapy machine.


Assuntos
Nêutrons Rápidos , Fótons , Radiometria/métodos , Dosagem Radioterapêutica , Simulação por Computador , Nêutrons Rápidos/efeitos adversos , Humanos , Método de Monte Carlo , Neoplasias Induzidas por Radiação/etiologia , Segunda Neoplasia Primária/etiologia , Imagens de Fantasmas , Fótons/efeitos adversos , Radiometria/instrumentação , Radiometria/estatística & dados numéricos , Radioterapia de Intensidade Modulada/efeitos adversos , Espalhamento de Radiação
11.
Biomed Res Int ; 2016: 7319843, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-26977413

RESUMO

A novel treatment modality termed energy modulated photon radiotherapy (EMXRT) was investigated. The first step of EMXRT was to determine beam energy for each gantry angle/anatomy configuration from a pool of photon energy beams (2 to 10 MV) with a newly developed energy selector. An inverse planning system using gradient search algorithm was then employed to optimize photon beam intensity of various beam energies based on presimulated Monte Carlo pencil beam dose distributions in patient anatomy. Finally, 3D dose distributions in six patients of different tumor sites were simulated with Monte Carlo method and compared between EMXRT plans and clinical IMRT plans. Compared to current IMRT technique, the proposed EMXRT method could offer a better paradigm for the radiotherapy of lung cancers and pediatric brain tumors in terms of normal tissue sparing and integral dose. For prostate, head and neck, spine, and thyroid lesions, the EMXRT plans were generally comparable to the IMRT plans. Our feasibility study indicated that lower energy (<6 MV) photon beams could be considered in modern radiotherapy treatment planning to achieve a more personalized care for individual patient with dosimetric gains.


Assuntos
Neoplasias/radioterapia , Fótons/uso terapêutico , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Intensidade Modulada/métodos , Criança , Feminino , Humanos , Masculino , Método de Monte Carlo , Neoplasias/patologia , Fótons/efeitos adversos , Radiometria , Dosagem Radioterapêutica , Radioterapia de Intensidade Modulada/efeitos adversos
13.
Phys Med Biol ; 61(2): 683-95, 2016 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-26716718

RESUMO

The goal of this work was to determine the scattered photon dose and secondary neutron dose and resulting risk for the sensitive fetus from photon and proton radiotherapy when treating a brain tumor during pregnancy. Anthropomorphic pregnancy phantoms with three stages (3-, 6-, 9-month) based on ICRP reference parameters were implemented in Monte Carlo platform TOPAS, to evaluate the scattered dose and secondary neutron dose and dose equivalent. To evaluate the dose equivalent, dose averaged quality factors were considered for neutrons. This study compared three treatment modalities: passive scattering and pencil beam scanning proton therapy (PPT and PBS) and 6-MV 3D conformal photon therapy. The results show that, for 3D conformal photon therapy, the scattered photon dose equivalent to the fetal body increases from 0.011 to 0.030 mSv per treatment Gy with increasing stage of gestation. For PBS, the neutron dose equivalent to the fetal body was significantly lower, i.e. increasing from 1.5 × 10(-3) to 2.5 × 10(-3) mSv per treatment Gy with increasing stage of gestation. For PPT, the neutron dose equivalent of the fetus decreases from 0.17 to 0.13 mSv per treatment Gy with the growing fetus. The ratios of dose equivalents to the fetus for a 52.2 Gy(RBE) course of radiation therapy to a typical CT scan of the mother's head ranged from 3.4-4.4 for PBS, 30-41 for 3D conformal photon therapy and 180-500 for PPT, respectively. The attained dose to a fetus from the three modalities is far lower than the thresholds of malformation, severe mental retardation and lethal death. The childhood cancer excessive absolute risk was estimated using a linear no-threshold dose-response relationship. The risk would be 1.0 (95% CI: 0.6, 1.6) and 0.1 (95% CI: -0.01, 0.52) in 10(5) for the 9-month fetus for PBS with a prescribed dose of 52.2 Gy(RBE). The increased risks for PPT and photon therapy are about two and one orders of magnitude larger than that for PBS, respectively. We can conclude that a pregnant woman with a brain tumor could be treated with pencil beam scanning with acceptable risks to the fetus.


Assuntos
Neoplasias Encefálicas/radioterapia , Feto/efeitos da radiação , Terapia com Prótons/efeitos adversos , Radioterapia Conformacional/efeitos adversos , Feminino , Humanos , Imagens de Fantasmas , Fótons/efeitos adversos , Fótons/uso terapêutico , Gravidez , Prótons/efeitos adversos
14.
Appl Radiat Isot ; 105: 11-14, 2015 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-26218451

RESUMO

Examination of physical interactions of photons in materials is a significant subject for buildup factor studies. In most of the buildup calculations, by default, coherent (Rayleigh) scattering is ignored and the Compton scattering is modeled by free-electron Klein-Nishina formula with "simple physics" treatment. In this work, photon buildup factors are calculated for many different cases including "detailed physics" by taking into account coherent and bound-electron Compton scatterings with the Monte Carlo code, MCNP5, and the results are compared with the literature values. They are computed for point isotropic photon sources up to depths of 20 mean free paths and at the three photon energies most widely used (0.06, 0.6 and 6MeV). Calculations are made for both finite and infinite homogeneous ordinary water media. It is concluded that Coherent scattering is very dominant at low energies and for deep penetrations and assumed physical approximation (simple/detailed, finite/infinite) is the critical point for determining shielding material dimensions. After all, it can be stated that all parametric assumptions should be clearly given and indicated in the tabulation of photon buildup factors.


Assuntos
Raios gama/efeitos adversos , Proteção Radiológica/estatística & dados numéricos , Fenômenos Biofísicos , Humanos , Modelos Biológicos , Método de Monte Carlo , Fótons/efeitos adversos , Radiometria/estatística & dados numéricos , Espalhamento de Radiação
15.
PLoS One ; 9(6): e99831, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24919099

RESUMO

The risk of internal exposure to 137Cs, 134Cs, and 131I is of great public concern after the accident at the Fukushima-Daiichi nuclear power plant. The relative biological effectiveness (RBE, defined herein as effectiveness of internal exposure relative to the external exposure to γ-rays) is occasionally believed to be much greater than unity due to insufficient discussions on the difference of their microdosimetric profiles. We therefore performed a Monte Carlo particle transport simulation in ideally aligned cell systems to calculate the probability densities of absorbed doses in subcellular and intranuclear scales for internal exposures to electrons emitted from 137Cs, 134Cs, and 131I, as well as the external exposure to 662 keV photons. The RBE due to the inhomogeneous radioactive isotope (RI) distribution in subcellular structures and the high ionization density around the particle trajectories was then derived from the calculated microdosimetric probability density. The RBE for the bystander effect was also estimated from the probability density, considering its non-linear dose response. The RBE due to the high ionization density and that for the bystander effect were very close to 1, because the microdosimetric probability densities were nearly identical between the internal exposures and the external exposure from the 662 keV photons. On the other hand, the RBE due to the RI inhomogeneity largely depended on the intranuclear RI concentration and cell size, but their maximum possible RBE was only 1.04 even under conservative assumptions. Thus, it can be concluded from the microdosimetric viewpoint that the risk from internal exposures to 137Cs, 134Cs, and 131I should be nearly equivalent to that of external exposure to γ-rays at the same absorbed dose level, as suggested in the current recommendations of the International Commission on Radiological Protection.


Assuntos
Exposição Ambiental/análise , Raios gama/efeitos adversos , Lesões por Radiação/diagnóstico , Radioisótopos/efeitos adversos , Transporte Biológico/efeitos da radiação , Efeito Espectador/efeitos da radiação , Núcleo Celular/efeitos da radiação , Tamanho Celular/efeitos da radiação , Elétrons/efeitos adversos , Exposição Ambiental/efeitos adversos , Humanos , Método de Monte Carlo , Centrais Nucleares , Fótons/efeitos adversos , Probabilidade , Doses de Radiação , Liberação Nociva de Radioativos , Radiometria/métodos
16.
Med Phys ; 41(4): 043901, 2014 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-24694161

RESUMO

PURPOSE: To provide a method for calculating the transmission of any broad photon beam with a known energy spectrum in the range of 20-1090 keV, through concrete and lead, based on the superposition of corresponding monoenergetic data obtained from Monte Carlo simulation. METHODS: MCNP5 was used to calculate broad photon beam transmission data through varying thickness of lead and concrete, for monoenergetic point sources of energy in the range pertinent to brachytherapy (20-1090 keV, in 10 keV intervals). The three parameter empirical model introduced by Archer et al. ["Diagnostic x-ray shielding design based on an empirical model of photon attenuation," Health Phys. 44, 507-517 (1983)] was used to describe the transmission curve for each of the 216 energy-material combinations. These three parameters, and hence the transmission curve, for any polyenergetic spectrum can then be obtained by superposition along the lines of Kharrati et al. ["Monte Carlo simulation of x-ray buildup factors of lead and its applications in shielding of diagnostic x-ray facilities," Med. Phys. 34, 1398-1404 (2007)]. A simple program, incorporating a graphical user interface, was developed to facilitate the superposition of monoenergetic data, the graphical and tabular display of broad photon beam transmission curves, and the calculation of material thickness required for a given transmission from these curves. RESULTS: Polyenergetic broad photon beam transmission curves of this work, calculated from the superposition of monoenergetic data, are compared to corresponding results in the literature. A good agreement is observed with results in the literature obtained from Monte Carlo simulations for the photon spectra emitted from bare point sources of various radionuclides. Differences are observed with corresponding results in the literature for x-ray spectra at various tube potentials, mainly due to the different broad beam conditions or x-ray spectra assumed. CONCLUSIONS: The data of this work allow for the accurate calculation of structural shielding thickness, taking into account the spectral variation with shield thickness, and broad beam conditions, in a realistic geometry. The simplicity of calculations also obviates the need for the use of crude transmission data estimates such as the half and tenth value layer indices. Although this study was primarily designed for brachytherapy, results might also be useful for radiology and nuclear medicine facility design, provided broad beam conditions apply.


Assuntos
Braquiterapia/métodos , Método de Monte Carlo , Proteção Radiológica/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Braquiterapia/efeitos adversos , Fótons/efeitos adversos , Fótons/uso terapêutico
17.
Radiat Environ Biophys ; 53(3): 525-33, 2014 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-24659413

RESUMO

This paper presents a biophysical model of radiation-induced cell death, implemented as a Monte Carlo code called BIophysical ANalysis of Cell death and chromosome Aberrations (BIANCA), based on the assumption that some chromosome aberrations (dicentrics, rings, and large deletions, called ''lethal aberrations'') lead to clonogenic inactivation. In turn, chromosome aberrations are assumed to derive from clustered, and thus severe, DNA lesions (called ''cluster lesions,'' or CL) interacting at the micrometer scale; the CL yield and the threshold distance governing CL interaction are the only model parameters. After a pilot study on V79 hamster cells exposed to protons and carbon ions, in the present work the model was extended and applied to AG1522 human cells exposed to photons, He ions, and heavier ions including carbon and neon. The agreement with experimental survival data taken from the literature supported the assumptions. In particular, the inactivation of AG1522 cells was explained by lethal aberrations not only for X-rays, as already reported by others, but also for the aforementioned radiation types. Furthermore, the results are consistent with the hypothesis that the critical initial lesions leading to cell death are DNA cluster lesions having yields in the order of *2 CL Gy-1 cell-1 at low LET and*20 CL Gy-1 cell-1 at high LET, and that the processing of these lesions is modulated by proximity effects at the micrometer scale related to interphase chromatin organization. The model was then applied to calculate the fraction of inactivated cells, as well as the yields of lethal aberrations and cluster lesions, as a function of LET; the results showed a maximum around 130 keV/lm, and such maximum was much higher for cluster lesions and lethal aberrations than for cell inactivation.


Assuntos
Modelos Biológicos , Morte Celular/efeitos da radiação , Núcleo Celular/efeitos da radiação , Sobrevivência Celular/efeitos da radiação , Fibroblastos/citologia , Fibroblastos/efeitos da radiação , Íons Pesados/efeitos adversos , Hélio/efeitos adversos , Humanos , Método de Monte Carlo , Fótons/efeitos adversos
18.
Radiat Prot Dosimetry ; 162(4): 469-77, 2014 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-24435911

RESUMO

In case of internal contamination due to long-lived actinides by inhalation or injection pathway, a major portion of activity will be deposited in the skeleton and liver over a period of time. In this study, calibration factors (CFs) of Phoswich and an array of HPGe detectors are estimated using skull and knee voxel phantoms. These phantoms are generated from International Commission of Radiation Protection reference male voxel phantom. The phantoms as well as 20 cm diameter phoswich, having 1.2 cm thick NaI (Tl) primary and 5cm thick CsI (Tl) secondary detector and an array of three HPGe detectors (each of diameter of 7 cm and thickness of 2.5 cm) are incorporated in Monte Carlo code 'FLUKA'. Biokinetic models of Pu, Am, U and Th are solved using default parameters to identify different parts of the skeleton where activity will accumulate after an inhalation intake of 1 Bq. Accordingly, CFs are evaluated for the uniform source distribution in trabecular bone and bone marrow (TBBM), cortical bone (CB) as well as in both TBBM and CB regions for photon energies of 18, 60, 63, 74, 93, 185 and 238 keV describing sources of (239)Pu, (241)Am, (238)U, (235)U and (232)Th. The CFs are also evaluated for non-uniform distribution of activity in TBBM and CB regions. The variation in the CFs for source distributed in different regions of the bones is studied. The assessment of skeletal activity of actinides from skull and knee activity measurements is discussed along with the errors.


Assuntos
Fótons/efeitos adversos , Monitoramento de Radiação/estatística & dados numéricos , Elementos da Série Actinoide/efeitos adversos , Elementos da Série Actinoide/farmacocinética , Carga Corporal (Radioterapia) , Simulação por Computador , Humanos , Articulação do Joelho/anatomia & histologia , Articulação do Joelho/efeitos da radiação , Limite de Detecção , Masculino , Modelos Biológicos , Método de Monte Carlo , Exposição Ocupacional , Imagens de Fantasmas , Radiometria , Crânio/anatomia & histologia , Crânio/efeitos da radiação
19.
Europace ; 16(4): 612-6, 2014 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-23933852

RESUMO

AIMS: Radiotherapy (RT) for malignancies can harm pacemakers (PMs) and implantable cardioverter-defibrillators (ICDs). There is some evidence that, besides cumulative dose, the damaging radiation effects increase with beam energy. The aim of this study was to determine whether modern PMs and ICDs are more sensitive to high-energy than to low-energy photon beams. METHODS AND RESULTS: Two groups of unused PMs and explanted ICDs (five PMs and one ICD in each) were subjected to irradiations in a phantom with 6 and 18 megavolt (MV) photons, respectively. The devices were exposed to radiation at doses of 2 gray (Gy) daily to simulate two clinical scenarios with the PM/ICD in the RT field. A cumulative dose of 150 Gy was given to each device, corresponding to approximately twice the therapeutic dose. In the 6 MV group, one episode of PM malfunction was detected after reaching 150 Gy. In the 18 MV group, a total of 14 episodes of malfunction were detected starting at 30 Gy in all five PMs. No episodes appeared in the ICD, at the respective treatment groups. This corresponded to a hazard ratio of 9.11 [∼95% confidence interval (CI): 1.04-79.69] by Cox regression analysis between the two groups. In a repeated measures logistic regression model comparing the incidence rate of malfunctions, the odds ratio was 18.29 (∼95% CI: 1.52-219.41). CONCLUSION: Photon beam energy plays a considerable role in inducing implantable cardiac device malfunctions. Low-energy RT may be safer in PM/ICD patients despite relatively high radiation dose to the device.


Assuntos
Desfibriladores Implantáveis , Falha de Equipamento , Marca-Passo Artificial , Radioterapia de Alta Energia/efeitos adversos , Desenho de Equipamento , Análise de Falha de Equipamento , Modelos Logísticos , Teste de Materiais , Análise Multivariada , Razão de Chances , Fótons/efeitos adversos , Modelos de Riscos Proporcionais , Dosagem Radioterapêutica , Medição de Risco , Fatores de Risco
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