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1.
Radiat Oncol ; 14(1): 67, 2019 Apr 23.
Artigo em Inglês | MEDLINE | ID: mdl-31014356

RESUMO

BACKGROUND: The PRIMO system is a computer software that allows the Monte Carlo simulation of linear accelerators and the estimation of the subsequent absorbed dose distributions in phantoms and computed tomographies. The aim of this work is to validate the methods incorporated in PRIMO to evaluate the deviations introduced in the dose distributions by errors in the positioning of the leaves of the multileaf collimator recorded in the dynalog files during patient treatment. METHODS: The reconstruction of treatment plans from Varian's dynalog files was implemented in the PRIMO system. Dose distributions were estimated for volumetric-modulated arc therapy clinical cases of prostate and head&neck using the PRIMO fast Monte Carlo engine DPM. Accuracy of the implemented reconstruction methods was evaluated by comparing dose distributions obtained from the simulations of the plans imported from the treatment planning system with those obtained from the simulations of the plans reconstructed from the expected leaves positions recorded in the dynalog files. The impact on the dose of errors in the positions of the leaves was evaluated by comparing dose distributions estimated for plans reconstructed from expected leaves positions with dose distributions estimated from actual leaves positions. Gamma pass rate (GPR), a hereby introduced quantity named percentage of agreement (PA) and the percentage of voxels with a given systematic difference (α/Δ) were the quantities used for the comparisons. Errors were introduced in leaves positions in order to study the sensitivity of these quantities. RESULTS: A good agreement of the dose distributions obtained from the plan imported from the TPS and from the plan reconstructed from expected leaves positions was obtained. Not a significantly better agreement was obtained for an imported plan with an increased number of control points such as to approximately match the number of records in the dynalogs. When introduced errors were predominantly in one direction, the methods employed in this work were sensitive to dynalogs with root-mean-square errors (RMS) ≥0.2 mm. Nevertheless, when errors were in both directions, only RMS >1.2 mm produced detectable deviations in the dose. The PA and the α/Δ showed more sensitive to errors in the leaves positions than the GPR. CONCLUSIONS: Methods to verify the accuracy of the radiotherapy treatment from the information recorded in the Varian's dynalog files were implemented and verified in this work for the PRIMO system. Tolerance limits could be established based on the values of PA and α/Δ. GPR 3,3 is not recommended as a solely evaluator of deviations introduced in the dose by errors captured in the dynalog files.


Assuntos
Neoplasias de Cabeça e Pescoço/radioterapia , Método de Monte Carlo , Aceleradores de Partículas/instrumentação , Imagens de Fantasmas , Neoplasias da Próstata/radioterapia , Planejamento da Radioterapia Assistida por Computador/métodos , Software , Humanos , Masculino , Dosagem Radioterapêutica , Radioterapia de Intensidade Modulada/métodos
2.
Radiat Oncol ; 14(1): 70, 2019 Apr 25.
Artigo em Inglês | MEDLINE | ID: mdl-31023340

RESUMO

BACKGROUND: In this study, an external 8 mm thick aluminum target was installed on the upper accessory tray mount of a medical linear accelerator head. The purpose of this study was to determine the effects of the external aluminum target beam (Al-target beam) on the portal image quality by analyzing the spatial and contrast resolutions. In addition, the image resolutions with the Al-target beams were compared with those of conventional 6 megavoltage (MV) images. METHODS: The optimized Al-target beam was calculated using Monte Carlo simulations. To validate the simulations, the percentage depth dose and lateral profiles were measured and compared with the modeled dose distributions. A PTW resolution phantom was used for imaging to assess the image resolution. The spatial resolution was quantified by determining the modulation transfer function. The contrast resolution was determined by a fine contrast difference between the 27 measurement areas. The spatial and contrast resolutions were compared with the those of conventional portal images. RESULTS: The measured and calculated percentage depth dose of the Al-target beam were consistent within 1.6%. The correspondence of measured and modelled profiles was evaluated by gamma analysis (3%, 3 mm) and all gamma values inside the field were less than one. The critical spatial frequencies (f50) of the images obtained with the Al-target beam and conventional imaging beam were 0.745 lp/mm and 0.451 lp/mm, respectively. The limiting spatial frequencies (f10) for the Al-target beam image and the conventional portal image were 2.39 lp/mm and 1.82 lp/mm, respectively. The Al-target beam resolved the smaller and lower contrast objects better than that of the MV photon beam. CONCLUSION: The Al-target beams generated by the simple target installation method provided better spatial and contrast resolutions than those of the conventional 6 MV imaging beam.


Assuntos
Alumínio/química , Elétrons , Processamento de Imagem Assistida por Computador/métodos , Aceleradores de Partículas/instrumentação , Imagens de Fantasmas , Poliestirenos/química , Garantia da Qualidade dos Cuidados de Saúde/normas , Humanos , Método de Monte Carlo , Tomografia Computadorizada por Raios X/métodos
3.
Radiat Oncol ; 14(1): 69, 2019 Apr 25.
Artigo em Inglês | MEDLINE | ID: mdl-31023348

RESUMO

BACKGROUND: To analyze and present the China's national survey on patient-specific IMRT quality assurance (QA). METHODS: A national survey was conducted in all radiotherapy centers in China to collect comprehensive information on status of IMRT QA practice, including machine, technique, equipment, issues and suggestions. RESULTS: Four hundred and three centers responded to this survey, accounting for 56.92% of all the centers implementing IMRT in China. The total number of medical physicists and the total number of patients treated with IMRT annually in these centers was 1599 and 305,000 respectively. All centers implemented measurement-based verification. Point dose verification and 2D dose verification was implemented in 331 and 399 centers, respectively. Three hundred forty-eight centers had 2D arrays, and 52 centers had detector devices designed to measure VMAT beams. EPID and film were used in 78 and 70 centers, respectively. Seventeen and 20 centers used log file and 3D DVH analysis, respectively. One hundred sixty-eight centers performed measurement-based verification not for each patient based on different selection criteria. The techniques and methods varied significantly in both point dose and dose distribution verification, from evaluation metrics, criteria, tolerance limit, and steps to check failed IMRT QA plans. Major issues identified in this survey were the limited resources of physicists, QA devices, and linacs. CONCLUSIONS: IMRT QA was implemented in all the surveyed centers. The practice of IMRT QA varied significantly between centers. An increase in personnel, QA devices and linacs is highly desired. National standard, guideline, regulation and training programs are urgently needed in China for consistent and effective implementation of IMRT QA.


Assuntos
Neoplasias/radioterapia , Aceleradores de Partículas/instrumentação , Garantia da Qualidade dos Cuidados de Saúde/normas , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Intensidade Modulada/normas , China , Humanos , Órgãos em Risco/efeitos da radiação , Dosagem Radioterapêutica , Radioterapia de Intensidade Modulada/métodos , Inquéritos e Questionários
4.
Radiat Oncol ; 14(1): 62, 2019 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-30971273

RESUMO

PURPOSE: To perform quality assurance of non-coplanar, volumetric-modulated arc therapy featuring continuous couch rotation (CCR-VMAT) using a C-arm linear accelerator. METHODS: We planned and delivered CCR-VMAT using the TrueBeam Developer Mode. Treatment plans were created for both a C-shaped phantom and five prostate cancer patients using seven CCR trajectories that lacked collisions; we used RayStation software (ver. 4.7) to this end. Subsequently, verification plans were generated. The mean absolute error (MAE) between the center of an MV-imaged steel ball and the radiation field was calculated using the Winston-Lutz test. The MAEs between planned and actual irradiation values were also calculated from trajectory logs. In addition, correlation coefficients (r values) among the MAEs of gantry angle, couch angle, and multi-leaf collimator (MLC) position, and mechanical parameters including gantry speed, couch speed, MLC speed, and beam output, were estimated. The dosimetric accuracies of planned and measured values were also assessed using ArcCHECK. RESULTS: The MAEs ±2 standard deviations as revealed by the Winston-Lutz test for all trajectories were 0.3 ± 0.3 mm in two dimensions. The MAEs of the gantry, couch, and MLC positions calculated from all trajectory logs were within 0.04°, 0.08°, and 0.02 mm, respectively. Deviations in the couch angle (r = 0.98, p < 0.05) and MLC position (r = 0.86, p < 0.05) increased significantly with speed. The MAE of the beam output error was less than 0.01 MU. The mean gamma passing rate ± 2 SD (range) of the 3%/3 mm, 3%/1 mm, and 5%/1 mm was 98.1 ± 1.9% (95.7-99.6%), 87.2 ± 2.8% (80.2-96.7%), and 96.3 ± 2.8% (93.9-99.6%), respectively. CONCLUSIONS: CCR-VMAT delivered via the TrueBeam Developer Mode was associated with high-level geometric and mechanical accuracy, thus affording to high dosimetric accuracy. The CCR-VMAT performance was stable regardless of the trajectory chosen.


Assuntos
Erros Médicos/prevenção & controle , Aceleradores de Partículas/instrumentação , Posicionamento do Paciente/métodos , Imagens de Fantasmas , Neoplasias da Próstata/radioterapia , Garantia da Qualidade dos Cuidados de Saúde/normas , Planejamento da Radioterapia Assistida por Computador/métodos , Humanos , Masculino , Órgãos em Risco/efeitos da radiação , Dosagem Radioterapêutica , Radioterapia de Intensidade Modulada/métodos , Rotação , Software
5.
Zhongguo Yi Liao Qi Xie Za Zhi ; 43(2): 143-145, 2019 Mar 30.
Artigo em Chinês | MEDLINE | ID: mdl-30977617

RESUMO

This study presents an electronic portal imaging devices (EPIDs) based on daily check tool for Linac that is usable for different cancer centers.Several images of open rectangle fields were acquired with EPID and the key items of daily Linac check were derived from the obtained images using an in-house developed automatic analysis software.The experiment results showed that each parameter calculated by this tool is as reliable as the corresponding result measured by the commercial quality assurance devices and its measuring efficiency is much higher.


Assuntos
Eletrônica Médica , Elétrons , Aceleradores de Partículas , Imagens de Fantasmas , Radiometria , Software
6.
Phys Med ; 59: 1-12, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30928056

RESUMO

PURPOSE: The purpose of this work was to develop and validate a multileaf collimator (MLC) model for a TrueBeam™ linac using Geant4 Monte Carlo (MC) simulation kit. METHODS: A Geant4 application was developed to accurately represent TrueBeam™ linac. Pre-computed phase-space file in a plane just above the jaws was used for radiation transport. A Varian 120 leaf Millennium™ MLC was modeled using geometry and material specifications provided by the manufacturer using Geant4 constructs. Leaf characteristics e.g. tongue-groove design, variable thickness, interleaf gap were simulated. The linac model was validated by comparing simulated dose profiles and depth-doses with experimental data using an ionization chamber in water. Dosimetric characteristics of the MLC such as inter- and intra-leaf leakage, penumbra effect, MLC leaf positioning, and dynamic characteristics were also investigated. RESULTS: For the depth dose curves, 99% of the calculated data points agree within 1% of the experimental values for the 4 × 4 cm2 and 10 × 10 cm2 and within 2% of the experimental values for 20 × 20, 30 × 30 and 40 × 40 cm2 jaw defined fields. The cross-plane dose profiles show agreement <2% for depths up to 10 cm and to within 4% beyond 10 cm. MLC dosimetric characterization with MC agree well with film measurements. The rounded leaf penumbra remained constant throughout the range of leaf motion. CONCLUSIONS: The TrueBeam™ linac equipped with 120-leaf MLC was successfully modeled using Geant4. The accuracy of the model was verified by comparing the simulations with experiments. The model may be utilized for independent dose verification and QA of IMRT.


Assuntos
Método de Monte Carlo , Aceleradores de Partículas , Imagens de Fantasmas , Radiometria , Planejamento da Radioterapia Assistida por Computador
7.
Phys Med ; 59: 37-46, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30928064

RESUMO

PURPOSE: To study the sensitivity of an Electronic Portal Imaging Device (EPID) in detecting delivery errors for VMAT lung stereotactic body radiotherapy (SBRT) using the Collapsed Arc method. METHODS: Baseline VMAT plans and plans with errors intentionally introduced were generated for 15 lung SBRT patients. Three types of errors were introduced by modifying collimator angles and multi-leaf collimator (MLC) field sizes (MLCFS) and MLC shifts by ±5, ±2, and ±1° or millimeters. A total of 103 plans were measured with EPID on an Elekta Synergy Linear Accelerator (Agility MLC) and compared to both the original treatment planning system (TPS) Collapsed Arc dose matrix and the no-error plan baseline EPID measurements. Gamma analysis was performed using the OmniPro-I'mRT (IBA Dosimetry) software and gamma criteria of 1%/1 mm, 2%/1 mm, 2%/2 mm, and 3%/3. RESULTS: When the error-introduced EPID measured dose matrices were compared to the TPS matrices, the majority of simulated errors were detected with gamma tolerance of 2%/1 mm and 1%/1 mm. When the error-introduced EPID measured dose matrices were compared to the baseline EPID measurements, all the MLCFS and MLC shift errors, and ±5°collimator errors were detected using 2%/1 mm and 1%/1 mm gamma criteria. CONCLUSION: This work demonstrates the feasibility and effectiveness of the collapsed arc technique and EPID for pre-treatment verification of lung SBRT VMAT plans. The EPID was able to detect the majority of MLC and the larger collimator errors with sensitivity to errors depending on the gamma tolerances.


Assuntos
Equipamentos e Provisões Elétricas , Neoplasias Pulmonares/diagnóstico por imagem , Planejamento da Radioterapia Assistida por Computador , Erros de Configuração em Radioterapia , Radioterapia de Intensidade Modulada/instrumentação , Humanos , Aceleradores de Partículas , Dosagem Radioterapêutica
8.
Phys Med ; 59: 64-74, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30928067

RESUMO

PURPOSE: The aim of this study is to evaluate the plan delivery accuracy of intensity-modulated radiation therapy (IMRT) by using textural features calculated from fluence maps. METHODS: In total, 202 IMRT plans were generated with the Trilogy (C-series linac) and TrueBeam STx systems. Fluence maps were obtained for each IMRT plan. With the fluence map, six textural features were calculated, namely angular second moment (ASM), inverse difference moment (IDM), contrast, variance, correlation, and entropy (particular displacement distances, d = 1, 5, and 10). To evaluate performances of textural features in predicting IMRT delivery accuracy, Spearman's rank correlation coefficients (rs) were calculated between textural feature values and measures of conventional methods. RESULTS: For Trilogy, correlation (d = 1) showed rs values of -0.764 (p < 0.001) with gamma passing rates of 2%/1 mm and 0.863 (p < 0.001) with multi-leaf collimator (MLC) errors. For TrueBeam STx, variance (d = 10) showed rs values of 0.691 (p < 0.001) with gamma passing rates of 1%/2 mm and -0.585 (p < 0.001) with MLC errors. CONCLUSION: Correlation (d = 1) for Trilogy and variance (d = 10) for TrueBeam STx demonstrated the potential in predicting IMRT delivery accuracy with high correlations to conventional IMRT delivery accuracy measures.


Assuntos
Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Intensidade Modulada , Humanos , Neoplasias/radioterapia , Aceleradores de Partículas , Erros de Configuração em Radioterapia
9.
Phys Med ; 60: 50-57, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31000086

RESUMO

PURPOSE: Measurements and Monte-Carlo simulations were carried out to model the dose distribution of a prototype electron beam linear accelerator (Kinetron LINAC) to determine the dose to organs in small animal irradiations experiments. Dose distributions were simulated using the GATE8.0/Geant4.10.3 Monte-Carlo platform, and measured in air and solid water phantoms using a commercial scintillating screen detector and new EBT-XD Gafchromic films. METHODS: The LINAC is able to produce 4.5 MeV electron beams at dose-rates ranging from Gy/min to thousands of Gy/s, and is used to study the radiobiological effects of very-high dose-rates that have been shown to protect normal tissues from radiation toxicity. Numerical simulations and experimental dosimetric characterisation of this electron accelerator were performed with the Monte-Carlo toolkit and various detectors. Absolute dose distributions in solid water were measured and compared with simulations. Realistic electron irradiation conditions were simulated in voxelised mice CT images. 3D dose distributions and dose-volume histograms in lungs of mice were simulated and analyzed. RESULTS: Measured and calculated depth-dose profiles for several beam configurations (energy and dose-rate) were compared. Beam emittance was validated by comparing measured and calculated beam sizes along the central axis in air: the deviation for all conditions was less than 1 mm. A good agreement was obtained between experimental dose distributions and the results obtained with simulations (<2% dose differences for lateral and depth-dose profiles). CONCLUSIONS: The method presented here, relying on few free parameters, can be adapted to very-high dose-rate electron irradiation to support the analysis of preclinical research experiments.


Assuntos
Aceleradores de Partículas , Animais , Simulação por Computador , Elétrons , Desenho de Equipamento , Pulmão/diagnóstico por imagem , Pulmão/efeitos da radiação , Camundongos , Método de Monte Carlo , Imagens de Fantasmas , Radiometria/instrumentação , Tomografia Computadorizada por Raios X , Água
10.
Med Phys ; 46(5): 1984-1994, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30870581

RESUMO

PURPOSE: Mechanical sag in the radiotherapy linear accelerator gantry and multi-leaf collimator (MLC) carriage effectively causes systematic deviations in the isocenter with respect to gantry angle. To minimize the impact of this error on treatment, a tolerance value of a 1-mm mechanical isocenter shift is commonly accepted for intensity-modulated radiation therapy quality assurance (QA). However, this tolerance value has not been firmly established for volumetric modulated arc therapy (VMAT) treatments. The purpose of this study is therefore to evaluate the impact of gantry and MLC carriage sag on VMAT clinical performance. METHODS: A published dataset of Elekta and Varian sag measurements served as a starting point for the investigation. Typical sag profiles were chosen and modeled as continuous isocenter deviations in three dimensions. The data were then incorporated into existing Digital Imaging and Communications in Medicine protocol, extended for radiotherapy plans via a "beam-splitting" algorithm. Three treatment sites were investigated in parallel: head and neck, prostate, and prostate with surrounding lymph nodes. Monte Carlo-simulated dose distributions were obtained for varying magnifications of the modeled sag. The resulting dose distributions, including that for no error, were compared qualitatively and quantitatively, against multiple metrics. RESULTS: The dose-volume histograms (DVHs) for all plans exhibited a decrease in planning target volume (PTV) dose uniformity with increasing sag magnification, whereas dose to organs at risk exhibited no coherent trend. The prostate plan was shown to be the most vulnerable to mechanical sag across all considered metrics. However, all plans with peak isocenter deviation less than 1 mm were well within typical cutoff points for each metric. CONCLUSIONS: All avenues of investigation presented substantiate the commonly accepted tolerance value of a 1-mm peak isocenter shift in annual linac QA.


Assuntos
Neoplasias de Cabeça e Pescoço/radioterapia , Linfonodos/efeitos da radiação , Aceleradores de Partículas/instrumentação , Neoplasias da Próstata/radioterapia , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Intensidade Modulada/instrumentação , Equipamentos e Provisões Elétricas , Humanos , Masculino , Método de Monte Carlo , Dosagem Radioterapêutica
11.
J Appl Clin Med Phys ; 20(4): 99-105, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30883010

RESUMO

PURPOSE: Beam matching occurs on all linacs to some degree and when two are more are matched to each other, patients are able to be transferred between machines. Quality assurance of plans can also be performed "distributively" on any of the matched linacs. The degree to which machines are matched and how this translates to like delivery of plans has been the focus of a number of studies. This concept has not yet been explored for stereotactic techniques which require a higher degree of accuracy. This study proposes beam matching criteria which allows for the distributive delivery and quality assurance of stereotactic body radiotherapy (SBRT) plans. METHOD: Two clinically relevant and complex volumetric modulated arc therapy (VMAT) SBRT spine and lung plans were chosen as benchmarking cases. These were delivered on nine previously beam matched linacs with quality assurance performed through ArcCheck and film exposure in the sagittal plane. Measured doses were compared to their treatment planning system predictions through gamma analysis at a range of criteria. RESULTS: Despite differences in beam match parameters and variations in small fields, all nine linacs produced accurate deliveries with a tight deviation in the population sample. Pass rates were well above suggested tolerances at the recommended gamma criterion. Film was able to detect dose errors to a greater degree than ArcCheck. CONCLUSION: Distributive quality assurance and delivery of stereotactic ablative radiotherapy treatments amongst beam matched linacs is certainly feasible provided the linacs are matched to a strict protocol like that suggested in this study and regular quality assurance is performed on the matched fleet. Distributive quality assurance and delivery of SBRT provides the possibility of efficiency gains for physicists as well as treatment staff.


Assuntos
Neoplasias Pulmonares/cirurgia , Aceleradores de Partículas/instrumentação , Garantia da Qualidade dos Cuidados de Saúde/normas , Radiocirurgia/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Intensidade Modulada/métodos , Neoplasias da Coluna Vertebral/cirurgia , Estudos de Viabilidade , Humanos , Órgãos em Risco/efeitos da radiação , Dosagem Radioterapêutica , Técnicas Estereotáxicas
12.
J Appl Clin Med Phys ; 20(4): 106-114, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30889312

RESUMO

PURPOSE: To characterize the stacked and staggered dual-layer multileaf collimator (MLC) on the HalcyonTM system. METHODS: The novel MLC assembly was reviewed and compared to the widely used MillenniumTM 120-leaf MLC system. We investigated the MLC positioning stability over 70 days using Machine Performance Check (MPC) data. We evaluated the leaf transmission, penumbra, leaf end effect, and leaf edge effect. Leaf transmission through distal, proximal, and both MLC layers was measured with a Farmer chamber, by comparing an open and a closed field. Leaf penumbra was measured using film for three different MLC-defined field sizes. The leaf end effect was measured with sweeping gap fields of varying gap sizes defined by the distal MLC. The leaf edge effect was evaluated using the Electronic Portal Imaging Device (EPID) for the different banks, gantry positions, and collimator angles. Point dose measurements for 10 test plans were compared to dose predictions of two dose calculation model versions. RESULTS: From MPC data, the largest measured MLC positioning accuracy deviation was within 0.1 mm. The proximal MLC exhibited greater deviations compared to the distal MLC. The distal-and-proximal-combination had reduced inter-leaf and intra-leaf transmission compared to delivery with distal-only. The measured leaf transmission was 0.41% for distal-only, 0.40% for proximal-only, and negligible for distal-and-proximal-combination. The leaf end penumbra was wider compared to the leaf edge penumbra. The leaf end effect was measured to be -0.2 mm. The leaf edge effect showed minimal bank, gantry position, and collimator angle dependence. However, a systematic deviation between measurements and treatment planning system handling of the leaf edge effect was observed. The discrepancy between the measured and predicted dose in the 10 test plans improved with the latest version of the dose calculation algorithm. CONCLUSION: The characteristics of the stacked and staggered dual-layer MLC on the HalcyonTM system were presented.


Assuntos
Algoritmos , Neoplasias/radioterapia , Aceleradores de Partículas/instrumentação , Imagens de Fantasmas , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Intensidade Modulada/instrumentação , Humanos , Órgãos em Risco/efeitos da radiação , Radiometria , Dosagem Radioterapêutica , Radioterapia de Intensidade Modulada/métodos
13.
Radiat Res ; 191(5): 447-459, 2019 05.
Artigo em Inglês | MEDLINE | ID: mdl-30849023

RESUMO

To identify modifications to amino acids that are directly induced by ionizing radiation, free amino acids and 3-residue peptides were irradiated using a linear accelerator (Linac) radiotherapy device. Mass spectrometry was performed to detail the relative sensitivity to radiation as well as identify covalent, radiation-dependent adducts. The order of reactivity of the 20 common amino acids was generally in agreement with published literature except for His (most reactive of the 20) and Cys (less reactive). Novel and previously identified modifications on the free amino acids were detected. Amino acids were far less reactive when flanked by glycine residues in a tripeptide. Order of reactivity, with GVG most and GEG least, was substantially altered, as were patterns of modification. Radiation reactivity of amino acids is clearly and strongly affected by conversion of the α-amino and α-carboxyl groups to peptide bonds, and the presence of neighboring amino acid residues.


Assuntos
Aminoácidos/química , Elétrons/uso terapêutico , Aceleradores de Partículas , Peptídeos/química , Radioterapia/instrumentação
14.
Med Phys ; 46(5): 2347-2355, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30838680

RESUMO

PURPOSE: MR-guided radiation therapy (RT) offers unparalleled soft tissue contrast for localization and target tracking. However, MRI distortions may be detrimental to high precision RT. This work characterizes the gradient nonlinearity (GNL) and total distortions over the first year of clinical operation of a 0.35T MR-linac. METHODS: For GNL characterization, an in-house large field of view (FOV) phantom (60 × 42.5 × 55 cm3 , >6000 spherical landmarks) was configured and scanned at four timepoints with forward/reverse read polarities (Gradient Echo sequence, FA/TR/TE = 28°/30 ms/6 ms). GNL was measured in Anterior-Posterior (AP), Left-Right (LR), and Superior-Inferior (SI) frequency-encoding directions based on deviation of the auto-segmented landmark centroids between rigidly registered MR and CT images and assessed based on radial distance from magnet isocenter. Total distortion was assessed using a 30 × 30 cm2 grid phantom oriented along the cardinal axes over >1 year of operation. RESULTS: The scanner's spatial integrity within the first ~10 months was stable (maximum total distortion variation = 10/6/8%, maximum distortion = 1.41/0.99/1.56 mm in Axial/Coronal/Sagittal planes, respectively). GNL distortions measured during this time period <10 cm from isocenter were (-0.74, 0.45), (-0.67, 0.53), and (-0.86, 0.70) mm in AP/LR/SI directions. In the 10-20 cm range, <1.5% of the distortions exceeded 2 mm in the AP and LR axes while <4% of the distortions exceeded 2 mm for SI. After major repairs and magnet re-shim, detectable changes were observed in total and GNL distortions (20% reduction in AP and 36% increase in SI direction in the 20-25 cm range). Across all timepoints and axes, 38-53% of landmarks in the 20-25 cm range were displaced by >1 mm. CONCLUSIONS: GNL distortions were negligible within a 10 cm radius from isocenter. However, in the periphery, non-negligible distortions of up to ~7 mm were observed, which may necessitate GNL corrections for MR-IGRT for treatment sites distant from magnet isocenter.


Assuntos
Imagem por Ressonância Magnética/instrumentação , Aceleradores de Partículas , Processamento de Imagem Assistida por Computador , Dinâmica não Linear , Imagens de Fantasmas , Planejamento da Radioterapia Assistida por Computador , Radioterapia Guiada por Imagem
15.
Radiat Res ; 191(5): 460-465, 2019 05.
Artigo em Inglês | MEDLINE | ID: mdl-30896280

RESUMO

Evaluation of the characteristics of accelerator-based thermal neutron fields is recognized as an important issue when discussing the effectiveness of boron neutron capture therapy (BNCT). In this study, we propose that the radiation chemical yield (G value) of hydroxyl radicals (Goh•) can be considered a universal parameter for the description of the accelerator-based thermal neutron field. The Goh• of the 10B(n,α)7Li reaction was quantitatively evaluated using an aqueous coumarin-3-carboxylic acid (3CCA) solution, and was discriminated from that of contaminations (i.e., γ rays and fast neutrons). The Goh• of the 10B(n,α)7Li reaction was 0.107 ± 0.004 OH•/100 eV, which is almost equivalent to that exposed to α particles with an energy of 6.0 MeV. Since the Goh• of γ rays from a 60Co source is 2.03 ± 0.05 OH•/100 eV, this lower value suggests that indirect action by the 10B(n,α)7Li reaction is not dominant in BNCT. However, our results indicate that one can assess the 60Co equivalent dose of the 10B(n,α)7Li reaction in water from the Goh• derived using aqueous 3CCA solution in the accelerator-based thermal neutron field.


Assuntos
Terapia por Captura de Nêutron de Boro/instrumentação , Cumarínicos/química , Radical Hidroxila/química , Aceleradores de Partículas , Ácidos Bóricos/química , Radioquímica , Soluções
16.
J Cancer Res Ther ; 15(Supplement): S103-S109, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30900630

RESUMO

Objective: Undesired neutron contamination imposed to patients during treatment is among the main factors increasing the risk of secondary cancer in radiotherapy. This additional undesirable dose is due to neutron contamination production in high-energy accelerators. In this study, neutron contamination is investigated in the presence of wedge and block in 15 MV photon fields of Siemens Primus linear accelerator. Materials and Methods: Neutron production by 30°, 45°, and 60° wedges and cerrobend block was investigated. Measurements were conducted in a 10 cm × 10 cm field at the source to -surface distance of 100 cm at 0.5, 2, 3, and 4 cm depths of a 30 cm × 30 cm × 30 cm Perspex phantom using the CR-39 passive film detectors. Chemical etching was performed using sodium hydroxide solution with 6.25 M concentration as the etchant at 85°C for 3 h. Results: The neutron dosimetry results reveal that the presence of wedge and block increases the neutron contamination. However, the 45° wedge is most effective in producing neutron contamination. The results also show that the fast neutron contamination is lower in the steeper depths. Conclusion: The presence of a wedge in a therapeutic high-energy photon field is a source of neutron contamination and may be of concern regarding clinical aspects. The results of this study show that superficial tissues such as skin will incur higher fast neutron contamination than the deep tissues.


Assuntos
Nêutrons Rápidos/efeitos adversos , Fótons , Dosagem Radioterapêutica , Dosimetria Fotográfica/instrumentação , Aceleradores de Partículas , Imagens de Fantasmas , Polietilenoglicóis/química , Dosímetros de Radiação , Radiometria/instrumentação
17.
J Cancer Res Ther ; 15(Supplement): S110-S114, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30900631

RESUMO

Aim: The aim of this study is to investigate the effect of scattering and differential attenuation on dose profile of 6 MV photon beam in the presence of cadmium (Cd)-free compensator which has been used in compensator-based intensity-modulated radiotherapy. Materials and Methods: Totally, 10 slabs of Cd-free compensator having thicknesses ranging from 2.4 to 61.4 mm have been prepared. Dose profiles have been taken using computer-controlled radiation field analyzer for five field sizes from 30 mm × 30 mm to 200 mm × 200 mm and at three depths in water phantom. Off-axis dose variation (ODV) has been measured with off-axis percentage depth dose scan and with ion chamber by measuring point dose at two diagonal points with respect to dose at central axis point in a plane and at three depths. Results: A decrease in beam flatness has been observed with increase in compensator thickness and depth in phantom. ODV has been found to increase with compensator thickness. Selective beam hardening has been observed due to differential attenuation from compensator. Point dose measurements show approximately 20% and 23% underdose region at 70 and 106 mm off-axis diagonal point, respectively, as compared to dose at central axis point for a field size of 200 mm × 200 mm at a depth of 15 mm, with 30.2-mm slab thickness. Significant increase in scattered penumbra has been observed with field size and thickness of compensator due to increase in scattered photon. Conclusions: The presence of compensator changes photon beam mean energy along the cross-section resulted in decreased beam flatness and increased scattering. This may lead to overestimation of dose along off-axis within radiation field if change in flatness is not taken into account and more exposure to healthy tissues in penumbral region due to large-angle scattering.


Assuntos
Fótons , Radioterapia de Intensidade Modulada/instrumentação , Espalhamento de Radiação , Ligas , Aceleradores de Partículas , Imagens de Fantasmas , Dosagem Radioterapêutica , Água/química
18.
J Cancer Res Ther ; 15(Supplement): S115-S122, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30900632

RESUMO

Aim of Study: The aim of this study is to evaluate some dosimetry parameters such as uniformity, surface dose, and max depth dose with thermoluminescent dosimetry (TLD) and EBT3 film in total skin electron beam therapy (TSEBT). Methods: Stationary and rotary methods were set on Varian linear accelerator, Clinac 2100C. To create a radiation field large enough (168 cm × 60 cm) and uniform, the source skin distance was set 400 cm. Electron beam energy was 6 MeV. The skin dose values were obtained in 21 different points on the phantom surface. Results: The results of dose uniformity in stationary technique were obtained as 10% and 2.6% by TLDs and 6% and 2.3% by films in longitudinal axis and transverse axis, respectively. The measurements at rotational technique by TLDs at the referred conditions showed a homogeneous total field with intensity variation of 10% in the longitudinal axis and 4% at horizontal axis. Conclusion: Based on the results of this study, stationary techniques are preferred for TSEBT. The main advantage of rotational techniques is reducing the time of treatment. The results also demonstrate that TLD should be routinely used in TSEBT treatment. Due to the high sensitivity of radiochromic films, this type of film was suitable for a wide therapeutic field. Comprehensive treatment to Rando phantom showed that the uniformity is better at the trunk than in the mobile parts of the body; the soles of the feet, perineum region, and scalp vertex should be treated in boost.


Assuntos
Elétrons , Dosimetria Fotográfica , Pele/efeitos da radiação , Dosimetria Termoluminescente , Humanos , Modelos Biológicos , Neoplasias/radioterapia , Aceleradores de Partículas , Posicionamento do Paciente , Imagens de Fantasmas , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador/métodos
19.
J Cancer Res Ther ; 15(1): 204-210, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30880779

RESUMO

Purpose: The aim of the present study was to compare the positional accuracy of varian's exact-arm (E-arm) and retractable-arm (R-arm) supporting electronic portal imaging device (EPID) systems (amorphous silicon flat-panel detector) using the intensity-modulated radiotherapy (IMRT) graticule phantom. Materials and Methods: The known shifts of 0.5, 1.0, and 1.5 cm were introduced to the given phantom in longitudinal, lateral, and vertical directions, respectively, with respect to treatment couch of medical linear accelerator. The experiment was repeated for different gantry angle and varying source to imager distances (SIDs). The images were acquired for each shift at varying SIDs and beam orientations for both EPID supporting systems. The corresponding shifts obtained from treatment planning system (TPS) were recorded and compared. Results: The known (expected) and observed (recorded from TPS) shifts obtained for different beam angles (namely, 0°, 90°, 180°, and 270° for anterior, left lateral, posterior, and right-lateral portal images, respectively) in the longitudinal, lateral, and vertical direction at varying SID were compared. The maximum shift in the observed value from the expected one was 3 and 2 mm, respectively, out of the all beam configuration for R-arm and E-arm. These shifts were randomly observed for all imager position and beam orientation. Conclusion: The IMRT graticule phantom is an effective tool to check the mechanical characteristic and consistency of different EPID supporting arms. The effect of EPID sag due to gravity (gantry and treatment couch) was not significant for detection of shift in patient's position. The E-arm support EPID has better mechanical stability and accuracy in detection of patient's position than that of R-arm.


Assuntos
Equipamentos e Provisões Elétricas , Posicionamento do Paciente/instrumentação , Radioterapia de Intensidade Modulada/instrumentação , Humanos , Neoplasias/radioterapia , Aceleradores de Partículas , Imagens de Fantasmas , Radiometria , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador/instrumentação , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Intensidade Modulada/métodos
20.
J Cancer Res Ther ; 15(1): 216-222, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30880781

RESUMO

Aim: The purpose of this study is to measure radiation leakage of Siemens Primus Plus and Siemens Artiste linear accelerators in electron mode and to compare the leakage level with that recommended by the International Electrotechnical Commission (IEC) standard. Materials and Methods: In this assessment, Siemens Primus Plus linear accelerator with 10 cm × 10 cm, 15 cm × 15 cm, and 25 cm × 25 cm applicators was used. The radiation leakage in lateral and vertical directions was measured for Siemens Primus Plus and Siemens Artiste linear accelerators. Results: Data derived from radiation leakage measurement for Siemens Primus Plus and Siemens Artiste linear accelerators in lateral direction from the field edge and in vertical direction from the applicator were reported. The radiation leakage data were then compared with the IEC standard to evaluate in-air field leakage. Conclusion: Comparing the radiation leakage level from fields with the IEC standard for two applicators, the maximum that was occurred for 12 MeV electron beam and applicator size of 10 cm × 10 cm in Siemens Artiste linear accelerator was 2.3%, which is less than the IEC's recommended limit of 10%. It is concluded that the leakage amount is much less than the specified limit and that both of the linear accelerators have high level of safety. Considering the measurement stage, it also needs to be noted that the beam angle affected the radiation leakage level from field edge, and in 25° angle, it is higher than in 0° angle. Comparing radiation leakage from the right side of the field for the two linear accelerators, the amount of leakage for Siemens Primus Plus linear accelerator is more than Siemens Artiste linear accelerator.


Assuntos
Elétrons/efeitos adversos , Neoplasias Induzidas por Radiação/prevenção & controle , Aceleradores de Partículas/normas , Elétrons/uso terapêutico , Humanos , Neoplasias Induzidas por Radiação/etiologia , Imagens de Fantasmas , Dosagem Radioterapêutica/normas
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