RESUMO
Very High Energy Electron (VHEE) beams are a promising alternative to conventional radiotherapy due to their highly penetrating nature and their applicability as a modality for FLASH (ultra-high dose-rate) radiotherapy. The dose distributions due to VHEE need to be optimised; one option is through the use of quadrupole magnets to focus the beam, reducing the dose to healthy tissue and allowing for targeted dose delivery at conventional or FLASH dose-rates. This paper presents an in depth exploration of the focusing achievable at the current CLEAR (CERN Linear Electron Accelerator for Research) facility, for beam energies >200 MeV. A shorter, more optimal quadrupole setup was also investigated using the TOPAS code in Monte Carlo simulations, with dimensions and beam parameters more appropriate to a clinical situation. This work provides insight into how a focused VHEE radiotherapy beam delivery system might be achieved.
Assuntos
Elétrons , Método de Monte Carlo , Dosagem Radioterapêutica , Humanos , Aceleradores de Partículas/instrumentação , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia/métodos , Radioterapia de Alta Energia/métodos , Radioterapia de Alta Energia/instrumentaçãoRESUMO
PURPOSE: In this study, a C-series linear accelerator was configured to enable rapid and reliable conversion between the production of conventional electron beams and an ultrahigh-dose-rate (UHDR) electron beamline to the treatment room isocenter for FLASH radiation therapy. Efforts to tune the beam resulted in a consistent, stable UHDR beamline. METHODS AND MATERIALS: The linear accelerator was configured to allow for efficient switching between conventional and modified electron output modes within 2 minutes. Additions to the air system allow for retraction of the x-ray target from the beamline when the 10 MV photon mode is selected. With the carousel set to an empty port, this grants access to the higher current pristine electron beam normally used to produce clinical photon fields. Monitoring signals related to the automatic frequency control system allows for tuning of the waveguide while the machine is in a hold state so a stable beam is produced from the initial pulse. A pulse counting system implemented on an field-programmable gate array-based controller platform controls the delivery to a desired number of pulses. Beam profiles were measured with Gafchromic film. Pulse-by-pulse dosimetry was measured using a custom electrometer designed around the EDGE diode. RESULTS: This method reliably produces a stable UHDR electron beam. Open-field measurements of the 16-cm full-width, half-maximum gaussian beam saw average dose rates of 432 Gy/s at treatment isocenter. Pulse overshoots were limited and ramp up was eliminated. Over the last year, there have been no recorded incidents that resulted in machine downtime due to the UHDR conversions. CONCLUSIONS: Stable 10 MeV UHDR beams were generated to produce an average dose rate of 432 Gy/s at the treatment room isocenter. With a reliable pulse-counting beam control system, consistent doses can be delivered for FLASH experiments with the ability to accommodate a wide range of field sizes, source-to-surface distances, and other experimental apparatus that may be relevant for future clinical translation.
Assuntos
Elétrons , Aceleradores de Partículas , Fótons , Aceleradores de Partículas/instrumentação , Elétrons/uso terapêutico , Fótons/uso terapêutico , Desenho de Equipamento , Dosagem Radioterapêutica , Fatores de Tempo , Radioterapia de Alta Energia/instrumentação , Radioterapia de Alta Energia/métodosRESUMO
Animal models of total-body irradiation (TBI) are used to elucidate normal tissue damage and evaluate the efficacy of medical countermeasures (MCM). The accuracy of these TBI models depends on the reproducibility of the radiation dose-response relationship for lethality, which in turn is highly dependent on robust radiation physics and dosimetry. However, the precise levels of radiation each organ absorbs can change dramatically when different photon beam qualities are used, due to the interplay between their penetration and the natural variation of animal sizes and geometries. In this study, we evaluate the effect of varying the radiation energy, namely cobalt-60 (Co-60); of similar penetration to a 4-MV polyenergetic beam), 6 MV and 15 MV, in the absorbed dose delivered by TBI to individual organs of eight Göttingen minipigs of varying weights (10.3-24.1 kg) and dimensions (17.5-25 cm width). The main organs, i.e. heart, lungs, esophagus, stomach, bowels, liver, kidneys and bladder, were contoured by an experienced radiation oncologist, and the volumetric radiation dose distribution was calculated using a commercial treatment planning system commissioned and validated for Co-60, 6-MV and 15-MV teletherapy units. The dose is normalized to the intended prescription at midline in the abdomen. For each animal and each energy, the body and organ dose volume histograms (DVHs) were computed. The results show that more penetrating photon energies produce dose distributions that are systematically and consistently more homogeneous and more uniform, both within individual organs and between different organs, across all animals. Thoracic organs (lungs, heart) received higher dose than prescribed while pelvic organs (bowel, bladder) received less dose than prescribed, due to smaller and wider separations, respectively. While these trends were slightly more pronounced in the smallest animals (10.3 kg, 19 cm abdominal width) and largest animals (>20 kg, â¼25 cm abdominal width), they were observed in all animals, including those in the 9-15 kg range typically used in MCM models. Some organs received an average absorbed dose representing <80% of prescribed dose when Co-60 was used, whereas all organs received average doses of >87% and >93% when 6 and 15 MV were used, respectively. Similarly, average dose to the thoracic organs reached as high as 125% of the intended dose with Co-60, compared to 115% for 15 MV. These results indicate that Co-60 consistently produces less uniform dose distributions in the Göttingen minipig compared to 6 and 15 MV. Moreover, heterogeneity of dose distributions for Co-60 is accentuated by anatomical and geometrical variations across various animals, leading to different absorbed dose delivered to organs for different animals. This difference in absorbed radiation organ doses, likely caused by the lower penetration of Co-60 and 6 MV compared to 15 MV, could potentially lead to different biological outcomes. While the link between the dose distribution and variation of biological outcome in the Göttingen minipig has never been explicitly studied, more pronounced dose heterogeneity within and between organs treated with Co-60 teletherapy units represents an additional confounding factor which can be easily mitigated by using a more penetrating energy.
Assuntos
Relação Dose-Resposta à Radiação , Porco Miniatura , Irradiação Corporal Total , Abdome/anatomia & histologia , Abdome/efeitos da radiação , Absorção de Radiação , Animais , Tamanho Corporal , Peso Corporal , Radioisótopos de Cobalto , Raios gama , Masculino , Modelos Animais , Especificidade de Órgãos , Aceleradores de Partículas , Pelve/anatomia & histologia , Pelve/efeitos da radiação , Fótons , Decúbito Ventral , Doses de Radiação , Tolerância a Radiação , Teleterapia por Radioisótopo/instrumentação , Planejamento da Radioterapia Assistida por Computador , Radioterapia de Alta Energia/instrumentação , Ombro/anatomia & histologia , Ombro/efeitos da radiação , Suínos , Porco Miniatura/anatomia & histologia , Tomografia Computadorizada por Raios XRESUMO
PURPOSE: Treating deep-seated bulky tumors with traditional single-field Cerrobend GRID-blocks has many limitations such as suboptimal target coverage and excessive skin toxicity. Heavy traditional GRID-blocks are a concern for patient safety at various gantry-angles and dosimetric detail is not always available without a GRID template in user's treatment planning system. Herein, we propose a simple, yet clinically useful multileaf collimator (MLC)-based three-dimensional (3D)-crossfire technique to provide sufficient target coverage, reduce skin dose, and potentially escalate tumor dose to deep-seated bulky tumors. MATERIALS/METHODS: Thirteen patients (multiple sites) who underwent conventional single-field cerrobend GRID-block therapy (maximum, 15 Gy in 1 fraction) were re-planned using an MLC-based 3D-crossfire method. Gross tumor volume (GTV) was used to generate a lattice pattern of 10 mm diameter and 20 mm center-to-center mimicking conventional GRID-block using an in-house MATLAB program. For the same prescription, MLC-based 3D-crossfire grid plans were generated using 6-gantry positions (clockwise) at 60° spacing (210°, 270°, 330°, 30°, 90°, 150°, therefore, each gantry angle associated with a complement angle at 180° apart) with differentially-weighted 6 or 18 MV beams in Eclipse. For each gantry, standard Millenium120 (Varian) 5 mm MLC leaves were fit to the grid-pattern with 90° collimator rotation, so that the tunneling dose distribution was achieved. Acuros-based dose was calculated for heterogeneity corrections. Dosimetric parameters evaluated include: mean GTV dose, GTV dose heterogeneities (peak-to-valley dose ratio, PVDR), skin dose and dose to other adjacent critical structures. Additionally, planning time and delivery efficiency was recorded. With 3D-MLC, dose escalation up to 23 Gy was simulated for all patient's plans. RESULTS: All 3D-MLC crossfire GRID plans exhibited excellent target coverage with mean GTV dose of 13.4 ± 0.5 Gy (range: 12.43-14.24 Gy) and mean PVDR of 2.0 ± 0.3 (range: 1.7-2.4). Maximal and dose to 5 cc of skin were 9.7 ± 2.7 Gy (range: 5.4-14.0 Gy) and 6.3 ± 1.8 Gy (range: 4.1-11.1 Gy), on average respectively. Three-dimensional-MLC treatment planning time was about an hour or less. Compared to traditional GRID-block, average beam on time was 20% less, while providing similar overall treatment time. With 3D-MLC plans, tumor dose can be escalated up to 23 Gy while respecting skin dose tolerances. CONCLUSION: The simple MLC-based 3D-crossfire GRID-therapy technique resulted in enhanced target coverage for de-bulking deep-seated bulky tumors, reduced skin toxicity and spare adjacent critical structures. This simple MLC-based approach can be easily adopted by any radiotherapy center. It provides detailed dosimetry and a safe and effective treatment by eliminating the heavy physical GRID-block and could potentially provide same day treatment. Prospective clinical trial with higher tumor-dose to bulky deep-seated tumors is anticipated.
Assuntos
Neoplasias/radioterapia , Órgãos em Risco/efeitos da radiação , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Alta Energia/instrumentação , Radioterapia de Alta Energia/métodos , Humanos , Prognóstico , Dosagem Radioterapêutica , Estudos RetrospectivosRESUMO
Electron dosimetry can be performed using cylindrical chambers, plane-parallel chambers, and diode detectors. The finite volume of these detectors results in a displacement effect which is taken into account using an effective point of measurement (EPOM). Dosimetry protocols have recommended a shift of 0.5 rcav for cylindrical chambers; however, various studies have shown that the optimal shift may deviate from this recommended value. This study investigated the effect that the selection of EPOM shift for cylindrical chamber has on percentage depth dose (PDD) curves. Depth dose curves were measured in a water phantom for electron beams with energies ranging from 6 to 18 MeV. The detectors investigated were of three different types: diodes (Diode-E PTW 60017 and SFD IBA), cylindrical (Semiflex PTW 31010, PinPoint PTW 31015, and A12 Exradin), and parallel plate ionization chambers (Advanced Markus PTW 34045 and Markus PTW 23343). Depth dose curves measured with Diode-E and Advanced Markus agreed within 0.2 mm at R50 except for 18 MeV and extremely large field size. The PDDs measured with the Semiflex chamber and Exradin A12 were about 1.1 mm (with respect to the Advanced Markus chamber) shallower than those measured with the other detectors using a 0.5 rcav shift. The difference between the PDDs decreased when a Pinpoint chamber, with a smaller cavity radius, was used. Agreement improved at lower energies, with the use of previously published EPOM corrections (0.3 rcav ). Therefore, the use of 0.5 rcav as an EPOM may result in a systematic shift of the therapeutic portion of the PDD (distances < R90 ). Our results suggest that a 0.1 rcav shift is more appropriate for one chamber model (Semiflex PTW 31010).
Assuntos
Algoritmos , Elétrons/uso terapêutico , Imagens de Fantasmas , Garantia da Qualidade dos Cuidados de Saúde/normas , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Alta Energia/instrumentação , Desenho de Equipamento , Humanos , Método de Monte Carlo , Dosagem Radioterapêutica , ÁguaRESUMO
Conventional radiotherapy is mainly applied by linear accelerators. Although linear accelerators provide dual (electron/photon) radiation beam modalities, both of them are intrinsically produced by a megavoltage electron current. Modern radiotherapy treatment techniques are based on suitable devices inserted or attached to conventional linear accelerators. Thus, precise control of delivered beam becomes a main key issue. This work presents an integral description of electron beam deflection control as required for novel radiotherapy technique based on convergent photon beam production. Theoretical and Monte Carlo approaches were initially used for designing and optimizing device´s components. Then, dedicated instrumentation was developed for experimental verification of electron beam deflection due to the designed magnets. Both Monte Carlo simulations and experimental results support the reliability of electrodynamics models used to predict megavoltage electron beam control.
Assuntos
Elétrons/uso terapêutico , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Alta Energia/métodos , Simulação por Computador , Humanos , Método de Monte Carlo , Aceleradores de Partículas , Imagens de Fantasmas , Fótons/uso terapêutico , Planejamento da Radioterapia Assistida por Computador/instrumentação , Planejamento da Radioterapia Assistida por Computador/estatística & dados numéricos , Radioterapia de Alta Energia/instrumentação , Radioterapia de Alta Energia/estatística & dados numéricosRESUMO
AAPM Report 142 recommends and the State of Ohio requires that the imaging dose be quantified in radiotherapy applications. Using the TG51 dose calibration protocol for MV Imaging dose measurement requires knowledge of the kQ parameter for the beam quality and the ionization chamber type under investigation. The %dd(10)x of the Varian TrueBeam 2.5 MV imaging beam falls outside the range of the available data for the calculation of the kQ value. Due to the similarities of the 2.5 MV imaging beam and the 60 Co beam, we and others made the assumption that kQ = 1.0 in TG51 calculations. In this study, we used the TG21 and TG51 calibration protocols in conjunction to validate that kQ = 1.0 for the 2.5 MV imaging beam using a PTW 30013 farmer chamber. Standard measurements for TG51 absolute dosimetry QA were performed at 100 cm SSD, 10 cm depth, 10 × 10 field size, delivering 100 Monitor Units to a waterproof Farmer Chamber (PTW TN30013) for both 2.5 and 6 MV. Both the TG21 and TG51 formalisms were used to calculate the dose to water per MU at dmax (Dw /MU) for the 6 MV beam. The calculated outputs were 1.0005 and 1.0004 cGy/MU respectively. The TG21 formalism was then used to calculate (Dw /MU) for the 2.5 MV imaging beam. This value was then used in the TG51 formalism to find kQ for the 2.5 MV imaging beam. A kQ value of 1.00 ± 0.01 was calculated for 2.5 MV using this method.
Assuntos
Modelos Teóricos , Imagens de Fantasmas , Monitoramento de Radiação/instrumentação , Monitoramento de Radiação/métodos , Radioterapia de Alta Energia/instrumentação , Radioterapia de Alta Energia/métodos , Calibragem , Elétrons , Humanos , Fótons , Radiometria/métodosRESUMO
BACKGROUND: A comprehensive evaluation of the current national and regional radiotherapy capacity in Austria with an estimation of demands for 2020 and 2030 was performed by the Austrian Society for Radiation Oncology, Radiobiology and Medical Radiophysics (ÖGRO). MATERIALS AND METHODS: All Austrian centers provided data on the number of megavoltage (MV) units, treatment series, fractions, percentage of retreatments and complex treatment techniques as well as the daily operating hours for the year 2014. In addition, waiting times until the beginning of radiotherapy were prospectively recorded over the first quarter of 2015. National and international epidemiological prediction data were used to estimate future demands. RESULTS: For a population of 8.51 million, 43 MV units were at disposal. In 14 radiooncological centers, a total of 19,940 series with a mean number of 464 patients per MV unit/year and a mean fraction number of 20 (range 16-24) per case were recorded. The average re-irradiation ratio was 14%. The survey on waiting times until start of treatment showed provision shortages in 40% of centers with a mean waiting time of 13.6 days (range 0.5-29.3 days) and a mean maximum waiting time of 98.2 days. Of all centers, 21% had no or only a limited ability to deliver complex treatment techniques. Predictions for 2020 and 2030 indicate an increased need in the overall number of MV units to a total of 63 and 71, respectively. CONCLUSION: This ÖGRO survey revealed major regional differences in radiooncological capacity. Considering epidemiological developments, an aggravation of the situation can be expected shortly. This analysis serves as a basis for improved public regional health care planning.
Assuntos
Acessibilidade aos Serviços de Saúde/tendências , Necessidades e Demandas de Serviços de Saúde/estatística & dados numéricos , Necessidades e Demandas de Serviços de Saúde/tendências , Radioterapia/estatística & dados numéricos , Radioterapia/tendências , Sociedades Médicas , Áustria , Fracionamento da Dose de Radiação , Previsões , Acessibilidade aos Serviços de Saúde/estatística & dados numéricos , Humanos , Radioterapia/instrumentação , Radioterapia de Alta Energia/instrumentação , Radioterapia de Alta Energia/estatística & dados numéricos , Radioterapia de Alta Energia/tendências , Retratamento/instrumentação , Retratamento/tendências , Listas de EsperaRESUMO
The aim of this test study is to check whether boron nitride (BN) might be applied as a detector material in high-energy photon-beam dosimetry. Boron nitride exists in various crystalline forms. Hexagonal boron nitride (h-BN) possesses high mobility of the electrons and holes as well as a high volume resistivity, so that ionizing radiation in the clinical range of the dose rate can be expected to produce a measurable electrical current at low background current. Due to the low atomic numbers of its constituents, its density (2.0 g cm-3) similar to silicon and its commercial availability, h-BN appears as possibly suitable for the dosimetry of ionizing radiation. Five h-BN plates were contacted to triaxial cables, and the detector current was measured in a solid-state ionization chamber circuit at an applied voltage of 50 V. Basic dosimetric properties such as formation by pre-irradiation, sensitivity, reproducibility, linearity and temporal resolution were measured with 6 MV photon irradiation. Depth dose curves at quadratic field sizes of 10 cm and 40 cm were measured and compared to ionization chamber measurements. After a pre-irradiation with 6 Gy, the devices show a stable current signal at a given dose rate. The current-voltage characteristic up to 400 V shows an increase in the collection efficiency with the voltage. The time-resolved detector current behavior during beam interrupts is comparable to diamond material, and the background current is negligible. The measured percentage depth dose curves at 10 cm × 10 cm field size agreed with the results of ionization chamber measurements within ±2%. This is a first study of boron nitride as a detector material for high-energy photon radiation. By current measurements on solid ionization chambers made from boron nitride chips we could demonstrate that boron nitride is in principle suitable as a detector material for high-energy photon-beam dosimetry.
Assuntos
Compostos de Boro/química , Teste de Materiais , Fótons/uso terapêutico , Radiometria/instrumentação , Radiometria/métodos , Radioterapia de Alta Energia/instrumentação , Diamante/química , Elétrons , Reprodutibilidade dos Testes , Silício/químicaRESUMO
Water-equivalent plastics are frequently used in dosimetry for experimental simplicity. This work evaluates the water-equivalence of novel water-equivalent plastics specifically designed for light-ion beams, as well as commercially available plastics in a clinical high-energy carbon-ion beam. A plastic- to-water conversion factor [Formula: see text] was established to derive absorbed dose to water in a water phantom from ionization chamber readings performed in a plastic phantom. Three trial plastic materials with varying atomic compositions were produced and experimentally characterized in a high-energy carbon-ion beam. Measurements were performed with a Roos ionization chamber, using a broad un-modulated beam of 11 × 11 cm2, to measure the plastic-to-water conversion factor for the novel materials. The experimental results were compared with Monte Carlo simulations. Commercially available plastics were also simulated for comparison with the plastics tested experimentally, with particular attention to the influence of nuclear interaction cross sections. The measured [Formula: see text] correction increased gradually from 0% at the surface to 0.7% at a depth near the Bragg peak for one of the plastics prepared in this work, while for the other two plastics a maximum correction of 0.8%-1.3% was found. Average differences between experimental and numerical simulations were 0.2%. Monte Carlo results showed that for polyethylene, polystyrene, Rando phantom soft tissue and A-150, the correction increased from 0% to 2.5%-4.0% with depth, while for PMMA it increased to 2%. Water-equivalent plastics such as, Plastic Water, RMI-457, Gammex 457-CTG, WT1 and Virtual Water, gave similar results where maximum corrections were of the order of 2%. Considering the results from Monte Carlo simulations, one of the novel plastics was found to be superior in comparison with the plastic materials currently used in dosimetry, demonstrating that it is feasible to tailor plastic materials to be water-equivalent for carbon ions specifically.
Assuntos
Carbono/química , Modelos Teóricos , Imagens de Fantasmas , Plásticos/química , Radioterapia de Alta Energia/instrumentação , Água/química , Humanos , Método de Monte Carlo , Radiometria/métodos , Radioterapia de Alta Energia/normasRESUMO
Out-of-field doses from radiotherapy can cause harmful side effects or eventually lead to secondary cancers. Scattered doses outside the applicator field, neutron source strength values, and neutron dose equivalents have not been broadly investigated for high-energy electron beams. To better understand the extent of these exposures, we measured out-of-field dose characteristics of electron applicators for high-energy electron beams on two Varian 21iXs, a Varian TrueBeam, and an Elekta Versa HD operating at various energy levels. Out-of-field dose profiles and percent depth-dose curves were measured in a Wellhofer water phantom using a Farmer ion chamber. Neutron dose was assessed using a combination of moderator buckets and gold activation foils placed on the treatment couch at various locations in the patient plane on both the Varian 21iX and Elekta Versa HD linear accelerators. Our findings showed that out-of-field electron doses were highest for the highest electron energies. These doses typically decreased with increasing distance from the field edge but showed substantial increases over some distance ranges. The Elekta linear accelerator had higher electron out-of-field doses than the Varian units examined, and the Elekta dose profiles exhibited a second dose peak about 20 to 30 cm from central-axis, which was found to be higher than typical out-of-field doses from photon beams. Electron doses decreased sharply with depth before becoming nearly constant; the dose was found to decrease to a depth of approximately E(MeV)/4 in cm. With respect to neutron dosimetry, Q values and neutron dose equivalents increased with electron beam energy. Neutron contamination from electron beams was found to be much lower than that from photon beams. Even though the neutron dose equivalent for electron beams represented a small portion of neutron doses observed under photon beams, neutron doses from electron beams may need to be considered for special cases.
Assuntos
Elétrons , Nêutrons , Aceleradores de Partículas , Imagens de Fantasmas , Radiometria/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Alta Energia/métodos , Algoritmos , Humanos , Fótons , Radiometria/instrumentação , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador/instrumentação , Radioterapia de Alta Energia/instrumentação , ÁguaRESUMO
PURPOSE: Synchrotron microbeam radiation therapy (MRT) is based on the spatial fractionation of the incident, highly focused synchrotron beam into arrays of parallel microbeams, typically a few tens of microns wide and depositing several hundred grays. This irradiation modality was shown to have a high therapeutic impact on tumors, especially in intracranial locations. However, mechanisms responsible for such a property are not fully understood. METHODS AND MATERIALS: Thanks to recent progress in dosimetry, we compared the effect of MRT and synchrotron broad beam (BB) radiation therapy delivered at comparable doses (equivalent to MRT valley dose) on tumor growth control and on classical radiobiological functions by histologic evaluation and/or transcriptomic analysis. RESULTS: MRT significantly improved survival of rats bearing 9L intracranial glioma compared with BB radiation therapy delivered at a comparable dose (P<.001); the efficacy of MRT and BB radiation therapy was similar when the MRT dose was half that of BB. The greater efficacy of MRT was not correlated with a difference in cell proliferation (Mki67 and proliferating cell nuclear antigen) or in transcriptomic stimulation of angiogenesis (vascular endothelial growth factor A or tyrosine kinase with immunoglobulin-like and epidermal growth factor-like domains 2) but was correlated with a higher cell death rate (factor for apoptosis signals) and higher recruitment of macrophages (tyrosine kinase with immunoglobulin-like and epidermal growth factor-like domains 1 and CD68 transcripts) a few days after MRT. CONCLUSIONS: These results show the superiority of MRT over BB radiation therapy when applied at comparable doses, suggesting that spatial fractionation is responsible for a specific and particularly efficient tissue response. The higher induction of cell death and immune cell activation in brain tumors treated by MRT may be involved in such responses.
Assuntos
Neoplasias Encefálicas/radioterapia , Irradiação Craniana/métodos , Glioma/radioterapia , Hipofracionamento da Dose de Radiação , Radioterapia Conformacional/métodos , Síncrotrons/instrumentação , Animais , Neoplasias Encefálicas/patologia , Linhagem Celular Tumoral , Relação Dose-Resposta à Radiação , Feminino , Glioma/patologia , Humanos , Masculino , Radioterapia de Alta Energia/instrumentação , Radioterapia de Alta Energia/métodos , Ratos , Ratos Endogâmicos F344 , Resultado do Tratamento , Carga Tumoral/efeitos da radiaçãoRESUMO
In a radiotherapy facility, safety in areas next to the treatment room can be of concern when irradiating downward due to oblique x-ray transmission through the floor and/or walls, especially in areas immediately adjacent or underground. Even when there is no basement underneath, a usual conservative solution is to build a thick concrete slab as the base for the treatment room. Of course, this implies deeper soil excavation and higher associated costs. As a convenient alternative, the limiting walls can be buried a certain depth below floor level to shield oblique, downward irradiation. Besides, for space considerations, laminated barriers are usually employed, and some additional shielding to the floor may be required (L-shaped barriers). In this work, the author introduces an analytical method for calculating the required wall penetration below floor level or, alternatively, the additional floor shielding for L-shaped barriers, taking into account in either case the attenuation properties of the earth underneath the vault. Interestingly, the required penetration depth for a given wall barrier (primary or secondary), relative to a reference thickness, is only a function of basic attenuation data. Likewise, for a laminated, lead-concrete barrier, the required dimensions depend on the relative amount of lead used for the wall and on the corresponding attenuation data. The shielding design criteria developed in this work to protect underground nearby sites is conservative in nature, yet it yields optimal shield dimensions for wall footing and for wall-floor shielding, avoiding the need to construct oversized concrete slab floors.
Assuntos
Desenho Assistido por Computador , Materiais de Construção/efeitos da radiação , Arquitetura de Instituições de Saúde/instrumentação , Arquitetura de Instituições de Saúde/métodos , Proteção Radiológica/instrumentação , Radioterapia de Alta Energia/instrumentação , Argentina , Desenho de Equipamento , Análise de Falha de Equipamento , Doses de Radiação , Monitoramento de Radiação/métodos , Proteção Radiológica/métodos , Radioterapia de Alta Energia/métodosRESUMO
PURPOSE: Online verification and 3D dose reconstruction on daily patient anatomy have the potential to improve treatment delivery, accuracy and safety. One possible implementation is to recalculate dose based on online fluence measurements with a transmission detector (TD) attached to the linac. This study provides a detailed analysis of the influence of a new TD on treatment beam characteristics. METHODS: The influence of the new TD on surface dose was evaluated by measurements with an Advanced Markus Chamber (Adv-MC) in the build-up region. Based on Monte Carlo simulations, correction factors were determined to scale down the over-response of the Adv-MC close to the surface. To analyze the effects beyond dmax percentage depth dose (PDD), lateral profiles and transmission measurements were performed. All measurements were carried out for various field sizes and different SSDs. Additionally, 5 IMRT-plans (head & neck, prostate, thorax) and 2 manually created test cases (3×3cm(2) fields with different dose levels, sweeping gap) were measured to investigate the influence of the TD on clinical treatment plans. To investigate the performance of the TD, dose linearity as well as dose rate dependency measurements were performed. RESULTS: With the TD inside the beam an increase in surface dose was observed depending on SSD and field size (maximum of +11%, SSD = 80cm, field size = 30×30cm(2)). Beyond dmax the influence of the TD on PDDs was below 1%. The measurements showed that the transmission factor depends slightly on the field size (0.893-0.921 for 5×5cm(2) to 30×30cm(2)). However, the evaluation of clinical IMRT-plans measured with and without the TD showed good agreement after using a single transmission factor (γ(2%/2mm) > 97%, δ±3% >95%). Furthermore, the response of TD was found to be linear and dose rate independent (maximum difference <0.5% compared to reference measurements). CONCLUSIONS: When placed in the path of the beam, the TD introduced a slight, clinically acceptable increase of the skin dose even for larger field sizes and smaller SSDs and the influence of the detector on the dose beyond dmax as well as on clinical IMRT-plans was negligible. Since there was no dose rate dependency and the response was linear, the device is therefore suitable for clinical use. Only its absorption has to be compensated during treatment planning, either by the use of a single transmission factor or by including the TD in the incident beam model.
Assuntos
Neoplasias/radioterapia , Aceleradores de Partículas/instrumentação , Radiometria/instrumentação , Planejamento da Radioterapia Assistida por Computador/instrumentação , Radioterapia de Alta Energia/instrumentação , Transdutores , Desenho de Equipamento , Análise de Falha de Equipamento , Humanos , Assistência Centrada no Paciente , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador/métodos , Reprodutibilidade dos Testes , Espalhamento de Radiação , Sensibilidade e Especificidade , Raios XRESUMO
The purpose of this work was to experimentally investigate the out-of-field dose in a water phantom, with several high energy electron beams used in external beam radiotherapy (RT). The study was carried out for 6, 9, 12, and 18 MeV electron beams, on three different linear accelerators, each equipped with a specific applicator. Measurements were performed in a water phantom, at different depths, for different applicator sizes, and off-axis distances up to 70 cm from beam central axis (CAX). Thermoluminescent powder dosimeters (TLD-700) were used. For given cases, TLD measurements were compared to EBT3 films and parallel-plane ionization chamber measurements. Also, out-of-field doses at 10 cm depth, with and without applicator, were evaluated. With the Siemens applicators, a peak dose appears at about 12-15 cm out of the field edge, at 1 cm depth, for all field sizes and energies. For the Siemens Primus, with a 10 × 10 cm(²) applicator, this peak reaches 2.3%, 1%, 0.9% and 1.3% of the maximum central axis dose (Dmax) for 6, 9, 12 and 18 MeV electron beams, respectively. For the Siemens Oncor, with a 10 × 10 cm(²) applicator, this peak dose reaches 0.8%, 1%, 1.4%, and 1.6% of Dmax for 6, 9, 12, and 14 MeV, respectively, and these values increase with applicator size. For the Varian 2300C/D, the doses at 12.5 cm out of the field edge are 0.3%, 0.6%, 0.5%, and 1.1% of Dmax for 6, 9, 12, and 18 MeV, respectively, and increase with applicator size. No peak dose is evidenced for the Varian applicator for these energies. In summary, the out-of-field dose from electron beams increases with the beam energy and the applicator size, and decreases with the distance from the beam central axis and the depth in water. It also considerably depends on the applicator types. Our results can be of interest for the dose estimations delivered in healthy tissues outside the treatment field for the RT patient, as well as in studies exploring RT long-term effects.
Assuntos
Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Alta Energia/métodos , Elétrons/uso terapêutico , Desenho de Equipamento , Dosimetria Fotográfica , Humanos , Aceleradores de Partículas , Imagens de Fantasmas , Radiometria/instrumentação , Radiometria/métodos , Planejamento da Radioterapia Assistida por Computador/estatística & dados numéricos , Radioterapia de Alta Energia/instrumentação , Radioterapia de Alta Energia/estatística & dados numéricos , Dosimetria Termoluminescente , ÁguaRESUMO
PURPOSE: In this work, the authors describe an electron sealed water calorimeter (ESWcal) designed to directly measure absorbed dose to water in clinical electron beams and its use to derive electron beam quality conversion factors for two ionization chamber types. METHODS: A functioning calorimeter prototype was constructed in-house and used to obtain reproducible measurements in clinical accelerator-based 6, 9, 12, 16, and 20 MeV electron beams. Corrections for the radiation field perturbation due to the presence of the glass calorimeter vessel were calculated using Monte Carlo (MC) simulations. The conductive heat transfer due to dose gradients and nonwater materials was also accounted for using a commercial finite element method software package. RESULTS: The relative combined standard uncertainty on the ESWcal dose was estimated to be 0.50% for the 9-20 MeV beams and 1.00% for the 6 MeV beam, demonstrating that the development of a water calorimeter-based standard for electron beams over such a wide range of clinically relevant energies is feasible. The largest contributor to the uncertainty was the positioning (Type A, 0.10%-0.40%) and its influence on the perturbation correction (Type B, 0.10%-0.60%). As a preliminary validation, measurements performed with the ESWcal in a 6 MV photon beam were directly compared to results derived from the National Research Council of Canada (NRC) photon beam standard water calorimeter. These two independent devices were shown to agree well within the 0.43% combined relative uncertainty of the ESWcal for this beam type and quality. Absorbed dose electron beam quality conversion factors were measured using the ESWcal for the Exradin A12 and PTW Roos ionization chambers. The photon-electron conversion factor, kecal, for the A12 was also experimentally determined. Nonstatistically significant differences of up to 0.7% were found when compared to the calculation-based factors listed in the AAPM's TG-51 protocol. General agreement between the relative electron energy dependence of the PTW Roos data measured in this work and a recent MC-based study are also shown. CONCLUSIONS: This is the first time that water calorimetry has been successfully used to measure electron beam quality conversion factors for energies as low as 6 MeV (R50=2.25 cm).
Assuntos
Absorção de Radiação , Calorimetria/instrumentação , Elétrons/uso terapêutico , Radiometria/instrumentação , Radioterapia de Alta Energia/instrumentação , Água/química , Algoritmos , Calorimetria/métodos , Simulação por Computador , Desenho de Equipamento , Análise de Falha de Equipamento , Modelos Químicos , Radiometria/métodos , Radioterapia de Alta Energia/métodos , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
A high-energy photon beam that is more than 10 MV can produce neutron contamination. Neutrons are generated by the [γ,n] reactions with a high-Z target material. The equivalent neutron dose and gamma dose from activation products have been estimated in a LINAC equipped with a 15-MV photon beam. A Monte Carlo simulation code was employed for neutron and photon dosimetry due to mixed beam. The neutron dose was also experimentally measured using the Optically Stimulated Luminescence (OSL) under various conditions to compare with the simulation. The activation products were measured by gamma spectrometer system. The average neutron energy was calculated to be 0.25 MeV. The equivalent neutron dose at the isocenter obtained from OSL measurement and MC calculation was 5.39 and 3.44 mSv/Gy, respectively. A gamma dose rate of 4.14 µSv/h was observed as a result of activations by neutron inside the treatment machine. The gamma spectrum analysis showed (28)Al, (24)Na, (54)Mn and (60)Co. The results confirm that neutrons and gamma rays are generated, and gamma rays remain inside the treatment room after the termination of X-ray irradiation. The source of neutrons is the product of the [γ,n] reactions in the machine head, whereas gamma rays are produced from the [n,γ] reactions (i.e. neutron activation) with materials inside the treatment room. The most activated nuclide is (28)Al, which has a half life of 2.245 min. In practice, it is recommended that staff should wait for a few minutes (several (28)Al half-lives) before entering the treatment room after the treatment finishes to minimize the dose received.
Assuntos
Nêutrons , Radioterapia de Alta Energia/instrumentação , Método de Monte Carlo , Doses de RadiaçãoRESUMO
Microbeam radiation therapy (MRT) is an irradiation modality for therapeutic purposes which uses arrays of collimated quasi parallel microbeams, each up to 100 µm wide, to deliver high radiation doses. Several studies have reported the extraordinary tolerance of normal tissues to MRT irradiation; conversely, MRT has been shown to be highly efficient on tumor growth control. The original and most widely developed application of MRT, yet in the preclinical phase, consists in using spatially fractionated X-ray beams issued from a synchrotron radiation source in the treatment of brain tumors. More recently, MRT has been tested in successful pioneering assays to reduce or interrupt seizures in preclinical models of epilepsy. The MRT concept has also been extended to proton therapy. The development of MRT towards its clinical implementation is presently driven by an EU-supported consortium of laboratories from 16 countries within the COST Action TD1205 (SYRA3). The results of the first SYRA3 workshop on "Radiation Therapy with Synchrotron Radiation: Achievements and Challenges" held in Krakow (Poland) during March 25-26 2014 are summarized in this issue with an overview presented in this paper. The papers reflect the multidisciplinary international activities of SYRA3. The topics covered in this focus issue include medical physics aspects, pre-clinical studies, clinical applications, and an industrial perspective; finally an outlook towards future prospects of compact sources and proton microbeams.
Assuntos
Fracionamento da Dose de Radiação , Terapia com Prótons/tendências , Radiocirurgia/tendências , Radioterapia de Alta Energia/tendências , Radioterapia Guiada por Imagem/tendências , Síncrotrons , Terapia com Prótons/instrumentação , Radiocirurgia/instrumentação , Dosagem Radioterapêutica , Radioterapia de Alta Energia/instrumentação , Radioterapia Guiada por Imagem/instrumentaçãoRESUMO
PURPOSE: Microplanar X-ray beams (microbeams) originated by synchrotron sources have been delivered to the visual brain cortex regions in rodents to create microscopically narrow lesions. The effects of microbeams mimic those generated by microsurgical subpial transections (also known as multiple subpial transections) but are obtained in a low-invasive way. METHODS: Image-guided atlas-based microbeam cortical transections have been generated on seven 1 month-old Wistar rats. An array of 10 parallel beams of 25 microns in thickness and spaced of 200 micron center-to-center was centered on the visual cortex and deposited an incident dose of 600 Gy. RESULTS: The procedure was well tolerated by rats. After recovery, rats showed regular behavior, no sign of gross visual impairment and regular weight gain. After 3 months, rats were sacrificed and brains histologically examined. Cortical transections resembling those obtained through a surgical incision were found over the irradiated region. Remarkable sparing of the cortical columns adjacent to the transections was observed. No sign of radionecrosis was evident at least at this time point. CONCLUSIONS: The visual brain cortex transected by synchrotron-generated microbeams showed an incision-like path of neuronal loss while adjacent non irradiated columns remained intact. These preliminary findings, to be further investigated also using other techniques, suggest that microbeam radiosurgery can affect the cortex at a cellular level providing a potential novel and attractive tool to study cortical function.
Assuntos
Neoplasias Encefálicas/radioterapia , Fracionamento da Dose de Radiação , Microcirurgia/métodos , Radiocirurgia/métodos , Radioterapia de Alta Energia/instrumentação , Córtex Visual/cirurgia , Animais , Desenho de Equipamento , Masculino , Radioterapia de Alta Energia/métodos , Ratos , Ratos Wistar , Síncrotrons/instrumentação , Resultado do Tratamento , Córtex Visual/patologiaRESUMO
Stereotactic Synchrotron Radiotherapy (SSRT) and Microbeam Radiation Therapy (MRT) are both novel approaches to treat brain tumor and potentially other tumors using synchrotron radiation. Although the techniques differ by their principles, SSRT and MRT share certain common aspects with the possibility of combining their advantages in the future. For MRT, the technique uses highly collimated, quasi-parallel arrays of X-ray microbeams between 50 and 600 keV. Important features of highly brilliant Synchrotron sources are a very small beam divergence and an extremely high dose rate. The minimal beam divergence allows the insertion of so called Multi Slit Collimators (MSC) to produce spatially fractionated beams of typically â¼25-75 micron-wide microplanar beams separated by wider (100-400 microns center-to-center(ctc)) spaces with a very sharp penumbra. Peak entrance doses of several hundreds of Gy are extremely well tolerated by normal tissues and at the same time provide a higher therapeutic index for various tumor models in rodents. The hypothesis of a selective radio-vulnerability of the tumor vasculature versus normal blood vessels by MRT was recently more solidified. SSRT (Synchrotron Stereotactic Radiotherapy) is based on a local drug uptake of high-Z elements in tumors followed by stereotactic irradiation with 80 keV photons to enhance the dose deposition only within the tumor. With SSRT already in its clinical trial stage at the ESRF, most medical physics problems are already solved and the implemented solutions are briefly described, while the medical physics aspects in MRT will be discussed in more detail in this paper.