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1.
Cancer Radiother ; 24(2): 128-134, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-32224107

RESUMO

PURPOSE: Shielding disks play an important role in intraoperative electron radiation therapy, and different designs are currently used in clinical practice. This paper investigates the dosimetric impact of the shielding disk used during intraoperative electron radiation therapy (IOERT). MATERIALS AND METHODS: This paper focuses on the study of four shielding disks types that have been used in our clinic: Aluminum (Al)/Lead (Pb), PMMA/Copper(Cu)/PMMA, Aluminum (Al)/Copper (Cu) and Aluminum (Al)/Steel with their specific thicknesses. The theoretical study was conducted with the EGSnrc Monte Carlo (MC) code. On the other hand, the measurements were carried out with gafchromic films for the four shielding disks for the same setup inside the water phantom. Finally, a comparison of the simulated and measured PDD curves was performed for the four material combinations. RESULTS: MC simulation and gafchromic measurements illustrated that dose values under the four shielding disks types were close to 0, whereas the backscattering enhancement of the disks were 103% with Al/Pb shielding disk, 102% with Al/Steel shielding disk, 102% with Al/Cu shielding disk, 95% with PMMA/Cu/PMMA shielding disk. The PDDs values of the gafchromic films in front of the disks were: 107%, 105%, 104%, and 94% for the Al/Pb, Al/Steel, Al/Cu, and PMMA/Cu/PMMA disks respectively. CONCLUSIONS: The dose values above and under the shielding disks were acceptable for the four studied shielding types. Demonstrated it is possible to use any of them clinically, while the best shielding disk was the Al/Pb since it has minimum thickness and a small backscatter enhancement.


Assuntos
Elétrons/uso terapêutico , Cuidados Intraoperatórios/instrumentação , Método de Monte Carlo , Órgãos em Risco , Proteção Radiológica/instrumentação , Ligas , Alumínio , Neoplasias da Mama/radioterapia , Cobre , Desenho de Equipamento , Feminino , Coração , Humanos , Cuidados Intraoperatórios/métodos , Pulmão , Aceleradores de Partículas , Imagens de Fantasmas , Dosagem Radioterapêutica , Costelas , Espalhamento de Radiação , Aço
2.
Phys Med ; 67: 100-106, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31704390

RESUMO

PURPOSE: To compare clinical setup using ultrasound (U/S)-delineated target versus computed tomography (CT) virtual simulation using CT-outlined target in breast electron boost. To describe a methodology for electron virtual simulation and collision testing with the treatment planning system (TPS). METHODS: The two techniques were compared in a prospective study on 12 patients, who were treated using a clinical setup. Target definition was performed by both U/S and CT imaging. The U/S-based target was made visible on CT images by placing a radio-opaque wire on U/S skin markings. The dose distribution of the clinical setup was reproduced in the TPS using the actual electron patient treatment parameters. A CT-based TPS virtual simulation/dose optimization was compared to the clinical setup technique. RESULTS: Mean beam aperture was larger by 16.3 cm2 (p = 0.011) for U/S compared to CT-outlined target. Target mean depth difference (CT minus U/S) was 0.03 cm (p = 0.875). Target coverage at depth was adequate in all cases with CT-based simulation while under/overcovering the target at depth by more than 5 mm in 2 out of 12 cases with clinical setup. Mean target V90% was 98.5% (CT-based simulation) and 84.4% (clinical setup). Ipsilateral lung/breast were better spared with CT-based simulation. To date, the methodology for CT virtual simulation was applied on 152 patients and collision was avoided in all cases. CONCLUSIONS: CT-based simulation and target delineation allows for improved definition of the en-face electron field with less amount of normal tissue irradiated while including the entire target with an adequate margin and optimal electron energy.


Assuntos
Neoplasias da Mama/diagnóstico por imagem , Neoplasias da Mama/radioterapia , Elétrons/uso terapêutico , Planejamento da Radioterapia Assistida por Computador/métodos , Tomografia Computadorizada por Raios X , Humanos , Ultrassonografia , Interface Usuário-Computador
3.
Phys Med ; 67: 1-8, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31606657

RESUMO

PURPOSE: To study the dosimetric properties of electron arc beams delivered by photon-beam multi-leaf collimators (pMLC) in electron modulated arc therapy (EMAT) for postmastectomy chest wall treatments. METHODS: Using the Monte Carlo method, we simulated a 2100EX Varian linear accelerator and verified the beam models in a water tank. Dosimetric characterizations were performed on cylindrical water phantoms of elliptical bases with various field sizes, arc ranges and source-to-surface distances (SSDs) for 6, 9 and 12 MeV beam energy. RESULTS: The arc beam has a higher bremsstrahlung dose than the static beam at the isocenter due to crossfire, but choosing a field size greater than 5 cm effectively reduces the bremsstrahlung dose. The depths of the 90% maximum dose located at 1.7, 2.8 and 4.1 cm for 6, 9 and 12 MeV, respectively, are similar to those of the static beams and independent of the field size and arc range. CONCLUSION: Based on the study, we recommend using the 5 cm field width for electron arc beams considering both bremsstrahlung dose at the isocenter and the arc profile penumbra. To ensure sufficient PTV edge coverage, we recommend a field length extension of at least 4 cm from PTV's edge for all beam energies and an arc extension of around 7°, 5°, and 5° for beam energies 6, 9, and 12 MeV, respectively. These dosimetric characterizations are the basis of pMLC-delivered EMAT treatment planning for postmastectomy chest wall patients.


Assuntos
Elétrons/uso terapêutico , Mastectomia , Método de Monte Carlo , Fótons , Radiometria , Parede Torácica/efeitos da radiação , Aceleradores de Partículas
4.
Phys Med ; 64: 188-194, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31515019

RESUMO

The main challenge in electron external beam radiation therapy with clinical accelerators is the absence of integrated systems to form irregular fields. The current approach to provide conformal irradiation is to use additional metallic shaping blocks, with inefficient and expensive workflows. This work presents a simple method to form therapeutic electron fields using 3D printed samples. These samples are manufactured by fused deposition modeling, which can affect crucial properties, such as material homogeneity, due to the presence of residual air-filled cavities. The applicability of this method was therefore investigated with a set of experiments and Monte Carlo simulations aimed at determining the electron depth dose distribution in polymer materials. The results show that therapeutic electron beams with energies 6-20 MeV can be effectively absorbed using these polymeric samples. The model developed in this study provides a way to assess the dose distribution in such materials and to calculate the appropriate thickness of polymer samples for therapeutic electron beam formation. It is shown that for total absorption of 6 MeV electron beams the material thickness should be at least 4 cm, while this value should be at least 8 cm for 12 MeV and 11 cm for 20 MeV, respectively. The results can be used to further develop 3D printing procedures for medical electron beam profile formation, allowing the creation of a collimator or absorber with patient-specific configuration using rapid prototyping systems, thus contributing to improve the accuracy of dose delivery in electron radiotherapy within a short manufacturing time.


Assuntos
Elétrons/uso terapêutico , Método de Monte Carlo , Polímeros , Estudos de Viabilidade , Humanos , Aceleradores de Partículas , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador
5.
Phys Med ; 64: 81-88, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31515039

RESUMO

In this work we have created and commissioned a Monte Carlo model of 6FFF Varian TrueBeam linear accelerator using BEAMnrc. For this purpose we have experimentally measured the focal spot size and shape of three Varian TrueBeam treatment units in 6FFF modality with a slit collimator and several depth dose and lateral beam profiles in a water phantom. The Monte Carlo model of a 6FFF TrueBeam machine was implemented with a primary electron source commissioned as a 2D Gaussian with Full Width Half Maximum selected by comparison of simulated and measured narrow beam profiles. The energy of the primary electron beam was optimized through a simultaneous fit to the measured beam depth dose profiles. Special attention was paid to evaluation of uncertainties of the selected Monte Carlo source parameters. These uncertainties were calculated by analysing the sensitivity of the commissioning process to changes in both primary beam size and energy. Both experimental and Monte Carlo commissioned focus size values were compared and found to be in excellent agreement. The commissioned Monte Carlo model reproduces within 1% accuracy the dose distributions of radiation field size from 3 cm × 3 cm to 15 cm × 15 cm.


Assuntos
Elétrons/uso terapêutico , Método de Monte Carlo , Radioterapia , Imagens de Fantasmas , Doses de Radiação , Dosagem Radioterapêutica , Reprodutibilidade dos Testes
6.
Phys Med ; 66: 29-35, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31550531

RESUMO

PURPOSE: To clarify the physical characteristics of a newly developed real time variable shape rubber containing tungsten (STR) with changes in heat and estimate its shielding abilities against electron beams and γ-rays from 192Ir. METHODS: Dynamic mechanical analysis for the STR (density = 7.3 g/cm3) was conducted at a frequency of 1.0 Hz in the temperature range of -60 °C to 60 °C. We evaluated tanδ, defined as the ratio (E″/E') between the storage modulus (E') and loss modulus (E″). The transmission rates were measured against 6- and 12-MeV electron beams and the percentage depth dose and lateral dose profile were compared with low-melting alloy (LMA). For the shielding rate of 192Ir against γ-rays, measurement data and Monte Carlo simulation data were obtained with STR thickness ranging from 1.0 mm to 16.0 mm. RESULTS: At 36 °C, the tanδ value was 0.520, while at 60 °C, this value was 1.016. For 6- and 12-MeV electron beams, the transmission rates decreased with increasing STR thickness and reached plateaus at approximately 1.0% and 4.0% with STR thickness of >7.0 and >12.0 mm, respectively. The dose distributions were almost equal to those for LMA. Against γ-rays, the thickness of STR that obtained a 50% attenuation rate for 192Ir was 5.804 mm. The Monte Carlo calculation results were 2.6% higher on average than the measurement results. CONCLUSION: The STR can be changed shape in real time at 60 °C and maintains its shape at body temperatures. It has adequate shielding abilities against megavoltage electron beams and γ-rays from 192Ir.


Assuntos
Braquiterapia/efeitos adversos , Elétrons/efeitos adversos , Proteção Radiológica/instrumentação , Borracha , Tungstênio , Elétrons/uso terapêutico , Temperatura , Fatores de Tempo
7.
Phys Med ; 66: 36-44, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31550532

RESUMO

PURPOSE: An EGSnrc based electron model was developed and validated for an Elekta Synergy® 160-leaf Agility™ linear accelerator. It was able to reproduce measured central axis (CAX) percentage depth dose (PDD) curves and off-axis profiles (OAPs) within 2%/2 mm, and relative output factors (ROFs) within 3%. METHODS: BEAMnrc component modules were used to model the accelerator accurately according to vendor supplied specifications. The electron beam focal spot size and input energy spectrum were determined through their effects on electron CAX PDDs and OAPs as benchmarked against water tank data. Phase space files were used as source input in DOSXYZnrc water phantom simulations. Dose distributions were calculated for six electron nominal energies, 11 field sizes and two source-to-surface distances. RESULTS: The full width at half maximum of the focal spot (assuming a Gaussian intensity distribution) was determined to be 1.50 mm. An asymmetrical input electron energy spectrum with a low-energy tail produced good agreement with measured data and solved the match in the build-up (BU) region for all electron energies used in this study. CONCLUSIONS: The improved input electron spectra for the electron model could predict dose distributions within 2%/2 mm of measured data. The model's success is embedded in the asymmetrical energy spectrum which provided a valuable free parameter which, by fine adjustment, improved the match in the BU region of dose distributions. Furthermore, focal spot parameters could be determined by means of iterative simulations.


Assuntos
Elétrons/uso terapêutico , Método de Monte Carlo , Humanos , Aceleradores de Partículas , Imagens de Fantasmas
8.
Phys Med ; 65: 150-156, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31473502

RESUMO

PURPOSE: The aim of this work is to improve the potential bleeding detection during intraoperative radiotherapy with linac polymethyl methacrylate applicators (PMMA), based on one previously developed. The improvements carried out have been focused on: i) minimizing the impact of the detector on the visual through the plastic applicators and ii) avoiding the asymmetry in the detection capability when the applicator is tilted. METHODS: Simulations have been made to select the geometry that provides a reduced visual impact on the applicator as well as allowing an independent response with the tilting angle of the applicator. A low-noise circuit for signal conditioning has been developed. Measurements have been made on three setups: 10 cm, 7 cm and 4 cm applicator diameters, 0° and 45° tilted. RESULTS: The detector has a visibility through the applicator greater than 50%. Due to the geometry, optimal detection is ensured regardless of its orientation when the applicator is tilted. It is possible to detect the presence of fluid well below the typical perturbing fluid depth established by the clinic (1-1.5 cm). CONCLUSIONS: The detector can distinguish the presence of around 0.5 cm of fluid depth while showing a high visual field through the PMMA applicators and providing a measure that does not depend on the detector orientation when the applicator is tilted. The prototype is ready for its industrialization by embedding it into the applicator for clinical use. The detector would have a significant impact on both the quality assurance and the outcome of the treatment.


Assuntos
Elétrons/uso terapêutico , Hemorragia/diagnóstico , Radioterapia , Hemorragia/etiologia , Período Intraoperatório , Aceleradores de Partículas
9.
Med Phys ; 46(10): 4314-4323, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31332792

RESUMO

PURPOSE: We investigated the impact on computed tomography (CT) image quality and photon, electron, and proton head-and-neck (H&N) radiotherapy (RT) dose calculations of three CT metal artifact reduction (MAR) approaches: A CT-based algorithm (oMAR Philips Healthcare), manual water override, and our recently presented, Magnetic Resonance (MR)-based kerMAR algorithm. We considered the following three hypotheses: I: Manual water override improves MAR over the CT- and MR-based alternatives; II: The automatic algorithms (oMAR and kerMAR) improve MAR over the uncorrected CT; III: kerMAR improves MAR over oMAR. METHODS: We included a veal shank phantom with/without six metal inserts and nine H&N RT patients with dental implants. We quantified the MAR capabilities by the reduction of outliers in the CT value distribution in regions of interest, and the change in particle range and photon depth at maximum dose. RESULTS: Water override provided apparent image improvements in the soft tissue region but insignificantly or negatively influenced the dose calculations. We however found significant improvements in image quality and particle range impact, compared to the uncorrected CT, when using oMAR and kerMAR. kerMAR in turn provided superior improvements in terms of high intensity streak suppression compared to oMAR, again with associated impacts on the particle range estimates. CONCLUSION: We found no benefits of the water override compared to the rest, and tentatively reject hypothesis I. We however found improvements in the automatic algorithms, and thus support for hypothesis II, and found the MR-based kerMAR to improve upon oMAR, supporting hypothesis III.


Assuntos
Artefatos , Neoplasias de Cabeça e Pescoço/diagnóstico por imagem , Neoplasias de Cabeça e Pescoço/radioterapia , Imagem por Ressonância Magnética , Metais , Tomografia Computadorizada por Raios X , Elétrons/uso terapêutico , Humanos , Fótons/uso terapêutico , Terapia com Prótons , Estudos Retrospectivos
10.
Brachytherapy ; 18(5): 651-657, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31235444

RESUMO

PURPOSE: To report the recurrence rates after single-fraction intraoperative electron radiotherapy (IOERT) in patients with early-stage breast cancer treated on a single institution prospective Phase I/II protocol at a community hospital. Results were retrospectively analyzed according to suitability criteria from the updated American Society for Radiation Oncology (ASTRO) consensus statement for accelerated partial breast irradiation (APBI). METHODS AND MATERIALS: Patients over 40 years with early-stage invasive or in situ breast cancer (<2.5 cm and node negative) were enrolled. IOERT 2100 cGy was delivered during breast conservation surgery, and patients were followed up for a median of 3 years (0.8-6.5 years) to determine toxicity and recurrence rates. RESULTS: Single-fraction IOERT was performed in 215 cases (6 bilateral treatments, 196 patients) with 13 patients receiving whole-breast radiation (WBR) after IOERT for adverse pathologic features. Of 202 cases of IOERT without WBR, 89 patients experienced an ipsilateral breast tumor recurrence (IBTR) giving a cumulative incidence of 3.96%. When the ASTRO APBI suitability criteria were applied, the IBTR rate was significantly lower for suitable patients vs. cautionary or unsuitable patients (1.6% vs. 3.4% vs. 21.0%, p = 0.0002). 3-year progression-free survival after IOERT alone was 93.4%. For patients who received standard WBR (4500-5040 cGy) after IOERT, no Grade 3 or 4 toxicities (acute or late) occurred and all patients are disease-free. CONCLUSIONS: Single-fraction IOERT results in a low rate of IBTR when strictly adhering to ASTRO criteria for APBI suitability. Standard dose WBR for unfavorable pathologic results after 2100 cGy IOERT is well tolerated.


Assuntos
Neoplasias da Mama/radioterapia , Elétrons/uso terapêutico , Adulto , Idoso , Braquiterapia/métodos , Neoplasias da Mama/patologia , Neoplasias da Mama/cirurgia , Feminino , Hospitais Comunitários , Humanos , Mastectomia Segmentar/métodos , Pessoa de Meia-Idade , Recidiva Local de Neoplasia , Estadiamento de Neoplasias , Seleção de Pacientes , Estudos Prospectivos , Radioterapia Adjuvante/métodos , Estudos Retrospectivos
11.
Phys Med ; 61: 94-102, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31151586

RESUMO

PURPOSE: To assess the capability of different types of detectors to measure relative output factors (OF) at high dose per pulse by comparison with alanine dosimeters, which are independent of dose rate. METHODS: Measurements were made in 9 MeV and 7 MeV electron beams produced by a Novac7 accelerator for intraoperative radiotherapy. Applicators with diameter of 10-7-6-5 and 4 cm were used. The dose per pulse varied from about 30 mGy, for the 10 cm reference applicator, to about 70 mGy, for the 4 cm applicator. Five types of plane-parallel ionization chambers (PTW Advanced Markus, Markus and Roos, IBA PPC40 and PPC05), two types of silicon diodes (PTW 60017 and IBA EFD3G) and a PTW 60019 microDiamond were considered. For the ionization chambers, correction factors for ion recombination effects were determined for each applicator using a modified two-voltage-analysis method that includes the free-electron component. RESULTS: Reference OF values were determined by alanine dosimeters with a standard combined uncertainty of 0.8%. Deviations from the reference OFs were generally within 1.5% for all the detectors, hence within the 95% confidence interval of alanine measurements. Larger deviations of up to about 2% obtained in a few cases are consistent with a 0.7% long-term reproducibility of OF measurements. CONCLUSIONS: Comparison with alanine measurements demonstrated that all the detectors considered in this work can be used to measure OFs in high dose-per-pulse electron beams with an accuracy better than 2%, provided that appropriate corrections for ion recombination effects are applied when using ionization chambers.


Assuntos
Elétrons/uso terapêutico , Doses de Radiação , Aceleradores de Partículas , Radiometria , Dosagem Radioterapêutica , Reprodutibilidade dos Testes
12.
Radiother Oncol ; 139: 34-39, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31174897

RESUMO

PURPOSE: Preclinical studies using a new treatment modality called FLASH Radiotherapy (FLASH-RT) need a two-phase procedure to ensure minimal uncertainties in the delivered dose. The first phase requires a new investigation of the reference dosimetry lying outside the conventional metrology framework from national metrology institutes but necessary to obtain traceability, repeatability, and stability of irradiations. The second consists of performing special quality assurance procedure prior to irradiation. MATERIALS AND METHODS: The Oriatron eRT6 (PMB-Alcen, France) is an experimental high dose-per-pulse linear accelerator, delivering a 6 MeV pulsed electron beam with mean dose-rates, ranging from a few Gy/min up to thousands of Gy/s. Absolute dosimetry is investigated with alanine, thermo-luminescent dosimeters (TLD) and radiochromic films as well as an ionization chamber for relative stability. The beam characteristic and dosimetry are prepared for three different setups. RESULTS: A cross-check between alanine, films and TLD revealed a dose agreement within 3% for dose-rates between 0.078 Gy/s and 1050 Gy/s, showing that these dosimeters are suitable for absolute dosimetry for FLASH-RT. In absence of appropriate setup dependent corrections, active dosimetry can reveal dose deviations up to 15% of the prescribed dose. These differences reduce to less than 3% when our dosimetric procedure is applied. CONCLUSION: We developed procedures to accurately irradiate biological models. Our method is based on validated absolute dosimeters and extends their use to routine FLASH irradiations. We reached an agreement of 3% between the delivered and prescribed dose and developed the requirements needed for workflows of preclinical and clinical studies.


Assuntos
Elétrons/uso terapêutico , Humanos , Modelos Biológicos , Aceleradores de Partículas , Dosagem Radioterapêutica
13.
Med Phys ; 46(8): 3378-3384, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31173366

RESUMO

PURPOSE: This work is aimed at studying the feasibility of reducing stray x-ray contamination of therapeutic electron beams used in Intraoperative Radiation Therapy (IOERT) through improvements in the design of the dual foil beam forming system. METHODS: We assess the validity of a known method for designing the primary scattering foil. To this end, we perform, for the first time, a systematic computational study of the performance of beam forming systems equipped with primary scattering foils of different thicknesses, including a foil designed according to the currently used method. In this study, we further develop and apply a recently proposed method for optimization of dual foil systems. RESULTS: For each of the considered primary foils, a secondary foil that minimizes the stray x-ray contamination was designed under additional conditions on the clinically acceptable therapeutic range and flatness of off-axis dose profile. For comparison, we also designed secondary foils that enable the production of the best flattened beams irrespective of x-ray contamination and therapeutic range. CONCLUSIONS: By means of a comparative analysis, we demonstrated that currently employed design methods do not lead to an optimal solution in terms of stray x-ray contamination and therapeutic range. It is further demonstrated that, in comparison to older designs, reduction in x-ray contamination exceeding 30% may be expected in a system designed using the novel method developed here. Such a reduction is beneficial for IOERT delivered in a regular, unshielded operating room.


Assuntos
Elétrons/uso terapêutico , Método de Monte Carlo , Radioterapia/instrumentação , Espalhamento de Radiação , Desenho de Equipamento , Período Intraoperatório , Raios X
14.
J Appl Clin Med Phys ; 20(7): 78-86, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31183970

RESUMO

PURPOSE: We report the first cervical cancer cases treated with interstitial electronic brachytherapy (eBT) at our hospital and compare them with plans made with high-dose-rate interstitial brachytherapy based on Ir192 (HDR-BT). MATERIALS AND METHODS: Eight patients with cervical cancer were treated with the Axxent eBT device (Xoft, Inc.). Planning was with magnetic resonance imaging and computed tomography following the recommendations of the EMBRACE protocol. The dosimetry parameters of organs at risk (OAR) were evaluated for the bladder, rectum, and sigmoid colon (D2cc, D1cc, and D0.1cc). In addition, the V150 and V200 of irradiated tissue were compared for both eBT and HDR-BT. All patients received intensity-modulated external beam radiation therapy with a regimen of 23 sessions of 2 Gy followed by four sessions of 7 Gy of eBT performed over 2 weeks (two sessions followed by another two sessions a week later) following the EMBRACE recommendations. Each of the eight patients was followed to assess acute toxicity associated with treatment. RESULTS: The doses reaching OAR for eBT plans were lower than for HDR-BT plans. As for acute toxicity associated with eBT, very few cases of mucositis were detected. No cases of rectal toxicity and one case with grade 1 urinary toxicity were detected. The results at 1 month are equally good, and no relapses have occurred to date. CONCLUSIONS: The first results of treatment with the Axxent eBT device are promising, as no recurrences have been observed and toxicity is very low. eBT is a good alternative for treating cervical cancer in centers without access to conventional HDR.


Assuntos
Braquiterapia/métodos , Elétrons/uso terapêutico , Recidiva Local de Neoplasia/radioterapia , Planejamento da Radioterapia Assistida por Computador/métodos , Neoplasias do Colo do Útero/radioterapia , Adulto , Idoso , Feminino , Humanos , Pessoa de Meia-Idade , Órgãos em Risco/efeitos da radiação , Prognóstico , Dosagem Radioterapêutica , Estudos Retrospectivos
15.
J Appl Clin Med Phys ; 20(6): 184-193, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31120615

RESUMO

The RayStation treatment planning system implements a Monte Carlo (MC) algorithm for electron dose calculations. For a TrueBeam accelerator, beam modeling was performed for four electron energies (6, 9, 12, and 15 MeV), and the dose calculation accuracy was tested for a range of geometries. The suite of validation tests included those tests recommended by AAPM's Medical Physics Practice Guideline 5.a, but extended beyond these tests in order to validate the MC algorithm in more challenging geometries. For MPPG 5.a testing, calculation accuracy was evaluated for square cutouts of various sizes, two custom cutout shapes, oblique incidence, and heterogenous media (cork). In general, agreement between ion chamber measurements and RayStation dose calculations was excellent and well within suggested tolerance limits. However, this testing did reveal calculation errors for the output of small cutouts. Of the 312 output factors evaluated for square cutouts, 20 (6.4%) were outside of 3% and 5 (1.6%) were outside of 5%, with these larger errors generally being for the smallest cutout sizes within a given applicator. Adjustment of beam modeling parameters did not fix these calculation errors, nor does the planning software allow the user to input correction factors as a function of field size. Additional validation tests included several complex phantom geometries (triangular nose phantom, lung phantom, curved breast phantom, and cortical bone phantom), designed to test the ability of the algorithm to handle high density heterogeneities and irregular surface contours. In comparison to measurements with radiochromic film, RayStation showed good agreement, with an average of 89.3% pixels passing for gamma analysis (3%/3mm) across four phantom geometries. The MC algorithm was able to accurately handle the presence of irregular surface contours (curved cylindrical phantom and a triangular nose phantom), as well as heterogeneities (cork and cortical bone).


Assuntos
Algoritmos , Elétrons/uso terapêutico , Método de Monte Carlo , Imagens de Fantasmas , Planejamento da Radioterapia Assistida por Computador/métodos , Osso e Ossos/diagnóstico por imagem , Mama/diagnóstico por imagem , Feminino , Humanos , Pulmão/diagnóstico por imagem , Nariz/diagnóstico por imagem , Aceleradores de Partículas , Doses de Radiação , Software
16.
J Vis Exp ; (147)2019 05 03.
Artigo em Inglês | MEDLINE | ID: mdl-31107434

RESUMO

A methodology is described to generate an isotopically pure 229Th ion beam in the 2+ and 3+ charge states. This ion beam enables one to investigate the low-lying isomeric first excited state of 229Th at an excitation energy of about 7.8(5) eV and a radiative lifetime of up to 104 seconds. The presented method allowed for a first direct identification of the decay of the thorium isomer, laying the foundations to study its decay properties as prerequisite for an optical control of this nuclear transition. High energy 229Th ions are produced in the α decay of a radioactive 233U source. The ions are thermalized in a buffer-gas stopping cell, extracted and subsequently an ion beam is formed. This ion beam is mass purified by a quadrupole-mass separator to generate a pure ion beam. In order to detect the isomeric decay, the ions are collected on the surface of a micro-channel plate detector, where electrons, as emitted in the internal conversion decay of the isomeric state, are observed.


Assuntos
Elétrons/uso terapêutico , Íons/metabolismo
17.
Phys Med Biol ; 64(12): 125025, 2019 06 21.
Artigo em Inglês | MEDLINE | ID: mdl-31035267

RESUMO

Surface dosimetry is required for ensuring effective administration of total skin electron therapy (TSET); however, its use is often reduced due to the time consuming and complex nature of acquisition. A new surface dose imaging technique was characterized in this study and found to provide accurate, rapid and remote measurement of surface doses without the need for post-exposure processing. Disc-shaped plastic scintillators (1 mm thick × 15 mm [Formula: see text]) were chosen as optimal-sized samples and designed to attach to a flat-faced phantom for irradiation using electron beams. Scintillator dosimeter response to radiation damage, dose rate, and temperature were studied. The effect of varying scintillator diameter and thickness on light output was evaluated. Furthermore, the scintillator emission spectra and impact of dosimeter thickness on surface dose were also quantified. Since the scintillators were custom-machined, dosimeter-to-dosimeter variation was tested. Scintillator surface dose measurements were compared to those obtained by optically stimulated luminescence dosimeters (OSLD). Light output from scintillator dosimeters evaluated in this study was insensitive to radiation damage, temperature, and dose rate. Maximum wavelength of emission was found to be 422 nm. Dose reported by scintillators was linearly related to that from OSLDs. Build-up from placement of scintillators and OSLDs had a similar effect on surface dose (4.9% increase). Variation among scintillator dosimeters was found to be 0.3 ± 0.2%. Scintillator light output increased linearly with dosimeter thickness (~1.9 × /mm). All dosimeter diameters tested were able to accurately measure surface dose. Scintillator dosimeters can potentially improve surface dosimetry-associated workflow for TSET in the radiation oncology clinic. Since scintillator data output can be automatically recorded to a patient medical record, the chances of human error in reading out and recording surface dose are minimized.


Assuntos
Elétrons/uso terapêutico , Dosimetria por Luminescência Estimulada Opticamente/instrumentação , Dosimetria por Luminescência Estimulada Opticamente/métodos , Imagens de Fantasmas , Contagem de Cintilação/instrumentação , Neoplasias Cutâneas/radioterapia , Algoritmos , Humanos , Dosagem Radioterapêutica , Neoplasias Cutâneas/patologia
18.
Radiother Oncol ; 139: 23-27, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31010709

RESUMO

For decades the field of radiation oncology has sought to improve the therapeutic ratio through innovations in physics, chemistry, and biology. To date, technological advancements in image guided beam delivery techniques have provided clinicians with their best options for improving this critical tool in cancer care. Medical physics has focused on the preferential targeting of tumors while minimizing the collateral dose to the surrounding normal tissues, yielding only incremental progress. However, recent developments involving ultra-high dose rate irradiation termed FLASH radiotherapy (FLASH-RT), that were initiated nearly 50 years ago, have stimulated a renaissance in the field of radiotherapy, long awaiting a breakthrough modality able to enhance therapeutic responses and limit normal tissue injury. Compared to conventional dose rates used clinically (0.1-0.2 Gy/s), FLASH can implement dose rates of electrons or X-rays in excess of 100 Gy/s. The implications of this ultra-fast delivery of dose are significant and need to be re-evaluated to appreciate the fundamental aspects underlying this seemingly unique radiobiology. The capability of FLASH to significantly spare normal tissue complications in multiple animal models, when compared to conventional rates of dose-delivery, while maintaining persistent growth inhibition of select tumor models has generated considerable excitement, as well as skepticism. Based on fundamental principles of radiation physics, radio-chemistry, and tumor vs. normal cell redox metabolism, this article presents a series of testable, biologically relevant hypotheses, which may help rationalize the differential effects of FLASH irradiation observed between normal tissue and tumors.


Assuntos
Neoplasias Hepáticas/radioterapia , Protocolos Clínicos , Tomografia Computadorizada de Feixe Cônico/métodos , Elétrons/uso terapêutico , Marcadores Fiduciais , Humanos , Movimento , Radiobiologia/métodos , Dosagem Radioterapêutica , Fatores de Tempo
19.
Phys Med ; 60: 37-43, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31000084

RESUMO

INTRODUCTION: Single fraction nature of intraoperative radiotherapy highly demands a quality assurance procedure to qualify both beam setup and treatment delivery. The aim of this study is to evaluate the treatment setup during breast intraoperative electron radiotherapy (IOERT) and in-vivo dose delivery verification. MATERIALS AND METHODS: Twenty-five breast cancer patients were enrolled and setup verification for each case was performed using C-arm imaging. The received dose by surface and distal end of target was measured by EBT2 film. The significance level of difference between obtained dosimetry results and predicted ones was evaluated by the T statistical test. RESULTS: Acquired C-arm images in two different oblique views revealed any misalignment between the applicator and shielding disk. The mean difference between the measured surface dose and expected one was 1.8% ±â€¯1.2 (p = 0.983) while a great disagreement, 11.1% ±â€¯1.5 (p < 0.001), was observed between the measured distal end dose and expected one. This discrepancy is mainly correlated to the backscattering effect from the shielding disk. Target depth nonuniformities can also contribute to this remarkable difference. CONCLUSION: Employing the intraoperative imaging for IOERT setup verification can considerably improve the treatment quality. Therefore, it is suggested to implement this imaging procedure as a part of treatment quality assurance. Favorable agreement between the predicted and measured surface doses demonstrates the applicability of EBT2 film for dose delivery verification. The results of in-vivo dosimetry showed that the electron backscattering from employed shielding disk can affect the received dose by the distal end of tumor bed.


Assuntos
Neoplasias da Mama/radioterapia , Neoplasias da Mama/cirurgia , Elétrons/uso terapêutico , Dosimetria in Vivo/métodos , Cirurgia Assistida por Computador , Mama/diagnóstico por imagem , Mama/cirurgia , Neoplasias da Mama/diagnóstico por imagem , Carcinoma/diagnóstico por imagem , Carcinoma/radioterapia , Carcinoma/cirurgia , Terapia Combinada/métodos , Fluoroscopia/métodos , Humanos , Período Intraoperatório , Melhoria de Qualidade , Dosímetros de Radiação , Dosagem Radioterapêutica , Espalhamento de Radiação
20.
Int J Radiat Oncol Biol Phys ; 104(4): 877-884, 2019 07 15.
Artigo em Inglês | MEDLINE | ID: mdl-30926576

RESUMO

PURPOSE: To evaluate locoregional control and outcome after mastectomy in patients treated with postmastectomy highly conformal electron radiation therapy (PMERT) with bolus compared with patients treated by highly conformal photon radiation therapy (PMPhRT) without bolus in the adjuvant setting of nonmetastatic breast cancer. METHODS AND MATERIALS: We studied women undergoing PMRT without immediate reconstruction for breast cancer before 2012 in 2 sites of our hospital using 2 different techniques. All patients received 50 Gy in 25 fractions. Patients previously treated by neoadjuvant chemotherapy were excluded. RESULTS: Among the 807 patients, 583 received PMERT and 224 received PMPhRT. The median follow-up was 64 months. Patients in the PMERT group had a median age of 52.7 years (range, 26-91 years), 6.9% were triple-negative, 16.3% were HER2-positive, and 58.6% had multifocal lesions. Patients in the PMPhRT group had a median age of 56.4 years (28-89), 8.5% were triple negative, 12.9% were HER2-positive, and 55.8% had multifocal lesions. Lymph node involvement was observed in 66% and 72.8% of cases (P = .07) treated with PMERT and PMPhRT, respectively. No significant difference in overall survival was observed between the 2 groups (hazard ratio [HR], 1.2; 95% CI, 0.67-2.13; P = .54). The risk of locoregional recurrence, estimated using the Fine-Gray method, was significantly higher with PMPhRT than with PMERT (subdistribution HR, 3.62; 95% CI, 1.07-12.3; P = .04), corresponding to a 5-year LRR rate of 0.53% (95% CI, 0-1.12%) for PMERT and 2.52% (95% CI, 0.05%-4.6%) for PMPhRT. CONCLUSIONS: A higher risk of local recurrence was observed in the PMPhRT without bolus group compared with the PMERT with bolus group. Prospective randomized trials are needed to confirm these findings.


Assuntos
Neoplasias da Mama/radioterapia , Neoplasias da Mama/cirurgia , Elétrons/uso terapêutico , Mamoplastia , Recidiva Local de Neoplasia , Fótons/uso terapêutico , Radioterapia Conformacional/métodos , Adulto , Idoso , Idoso de 80 Anos ou mais , Neoplasias da Mama/química , Neoplasias da Mama/mortalidade , Fracionamento da Dose de Radiação , Elétrons/efeitos adversos , Feminino , Humanos , Excisão de Linfonodo , Linfonodos/patologia , Irradiação Linfática , Mastectomia , Pessoa de Meia-Idade , Fótons/efeitos adversos , Cuidados Pós-Operatórios , Lesões por Radiação/patologia , Radioterapia Adjuvante , Radioterapia Conformacional/efeitos adversos , Estudos Retrospectivos , Pele/efeitos da radiação
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