Relative dosimetry with an <scp>MR</scp>‐linac: Response of ion chambers, diamond, and diode detectors for off‐axis, depth dose, and output factor measurements

O'Brien, Daniel; Dolan, James P.; Pencea, S; Schupp, Nicholas; Sawakuchi, Gabriel O.

doi:10.1002/mp.12699

Cited by 63 publications

(74 citation statements)

References 29 publications

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“…The dose deposited at tissue‐air interfaces can increase due to the electron returning effect (ERE), which can also be affected by the surface orientation where the photon beam enters or exits . The dosimetric response of QA devices (especially the detectors used for beam calibration) in magnetic fields have also been studied, focusing mainly on the absolute dose response of the detectors. The effect of the magnetic field on the detectors is demonstrated not only through the trajectory path deflection of the secondary electrons in the medium surrounding and inside the volume of the gas‐filled or solid detector, but also through the change of the intrinsic properties of detectors such as charge carrier versus lattice defect recombination, polarity effect, etc.…”

Section: Introductionmentioning

confidence: 99%

“…For the ionization chamber, however, when the field size is sufficiently larger than the detector's diameter, an additional magnetic field and beam quality correction factor can be applied to the original calibration coefficient, obtained without the magnetic field, to obtain the correct absolute dose calibration in the presence of the magnetic field. The effective point of measurement (EPOM) of the ionization chamber is shifted not only in the beam direction but also laterally, perpendicular to both the beam and the magnetic field direction. According to O'Brien et al, the measured lateral shift in the dose distribution was independent of depth and field size from 2 × 2 cm 2 to 10 × 10 cm 2 .…”

Section: Introductionmentioning

confidence: 99%

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Measurement validation of treatment planning for a MR‐Linac

Chen

Paulson

Ahunbay

et al. 2019

J Applied Clin Med Phys

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Purpose The magnetic field can cause a nonnegligible dosimetric effect in an MR‐Linac system. This effect should be accurately accounted for by the beam models in treatment planning systems (TPS). The purpose of the study was to verify the beam model and the entire treatment planning and delivery process for a 1.5 T MR‐Linac based on comprehensive dosimetric measurements and end‐to‐end tests. Material and methods Dosimetry measurements and end‐to‐end tests were performed on a preclinical MR‐Linac (Elekta AB) using a multitude of detectors and were compared to the corresponding beam model calculations from the TPS for the MR‐Linac. Measurement devices included ion chambers (IC), diamond detector, radiochromic film, and MR‐compatible ion chamber array and diode array. The dose in inhomogeneous phantom was also verified. The end‐to‐end tests include the generation, delivery, and comparison of 3D and IMRT plan with measurement. Results For the depth dose measurements with Farmer IC, micro IC and diamond detector, the absolute difference between most measurement points and beam model calculation beyond the buildup region were <1%, at most 2% for a few measurement points. For the beam profile measurements, the absolute differences were no more than 1% outside the penumbra region and no more than 2.5% inside the penumbra region. Results of end‐to‐end tests demonstrated that three 3D static plans with single 5 × 10 cm2 fields (at gantry angle 0°, 90° and 270°) and two IMRT plans successfully passed gamma analysis with clinical criteria. The dose difference in the inhomogeneous phantom between the calculation and measurement was within 1.0%. Conclusions Both relative and absolute dosimetry measurements agreed well with the TPS calculation, indicating that the beam model for MR‐Linac properly accounts for the magnetic field effect. The end‐to‐end tests verified the entire treatment planning process.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Measurement validation of treatment planning for a MR‐Linac

Chen

Paulson

Ahunbay

et al. 2019

J Applied Clin Med Phys

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“…Some groups have investigated the response of point diodes, diode arrays, and diamond detectors in fields of both orientations and varying strengths. More recently, there have been studies on the effects on relative dosimetry . O’Brien et al examined changes in the relative response for shielded and unshielded diodes, diamond, and three different sized ionization chambers.…”

Section: Introductionmentioning

confidence: 99%

“…More recently, there have been studies on the effects on relative dosimetry. 20,[27][28][29] O'Brien et al 2 examined changes in the relative response for shielded and unshielded diodes, diamond, and three different sized ionization chambers. They concluded that the diodes and diamond were underestimating the lateral shift in profiles characteristic of perpendicular MRI-linacs.…”

Section: Introductionmentioning

confidence: 99%

Experimental characterization of magnetically focused electron contamination at the surface of a high‐field inline MRI‐linac

Roberts¹,

Patterson

Jelen

et al. 2019

Medical Physics

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Purpose The fringe field of the Australian MRI‐linac causes contaminant electrons to be focused along the central axis resulting in a high surface dose. This work aims to characterize this effect using Gafchromic film and high‐resolution detectors, MOSkinTM and microDiamond. The secondary aim is to investigate the influence of the inline magnetic field on the relative dose response of these detectors. Methods The Australian MRI‐linac has the unique feature that the linac is mounted on rails allowing for measurements to be performed at different magnetic field strengths while maintaining a constant source‐to‐surface distance (SSD). Percentage depth doses (PDD) were collected at SSD 1.82 m in a solid water phantom positioned in a low magnetic field region and then at isocenter of the MRI where the magnetic field is 1 T. Measurements for a range of field sizes were taken with the MOSkinTM, microDiamond, and Gafchromic® EBT3 film. The detectors’ relative responses at 1 T were compared to the near 0 T PDD beyond the region of electron contamination, that is, 20 mm depth. The near surface measurements inside the MRI bore were compared among the different detectors. Results Skin dose in the MRI, as measured with the MOSkinTM, was 104.5% for 2.1 × 1.9 cm2, 185.6% for 6.1 × 5.8 cm2, 369.1% for 11.8 × 11.5 cm2, and 711.1% for 23.5 × 23 cm2. The detector measurements beyond the electron contamination region showed agreement between the relative response at 1 T and near 0 T. Film was in agreement with both detectors in this region further demonstrating their relative response is unaffected by the magnetic field. Conclusions Experimental characterization of the high electron contamination at the surface was performed for a range of field sizes. The relative response of MOSkinTM and microDiamond detectors, beyond the electron contamination region, were confirmed to be unaffected by the 1‐T inline magnetic field.

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“…A dosimetria nesses aparelhos é muito importante, pois em qualquer tratamento é necessário que a dose planejada seja igual à dose que será entregue ao paciente (ABAZA, 2016). Os dosímetros que são normalmente utilizados em radioterapia são os dosímetros termoluminescentes (TLDs), câmaras de ionização e filmes radiocrômicos (ALQATHAMI et al, 2016;PAUKSTYTE, S.;URBONAVICIUS, 2017;SCALCHI et al, 2017;ALDELAIJA et al, 2018;HAURI, SCHNEIDER, 2018;O'BRIEN et al, 2018;SINGH et al, 2018). Com o uso dos dois primeiros dosímetros é possível obter informações dosimétricas ponto a ponto, enquanto com o uso dos filmes radiocrômicos é possível obter uma informação bidimensional de dose.…”

Section: Capítulo 1: Introduçãounclassified

Dosimetria gel polimérica usando imagem de ressonância magnética para aplicação em radioterapia

Silva¹

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AgradecimentosPrimeiramente, agradeço à Deus por tudo. Chegar até aqui não foi fácil: desde a graduação foram mais de 10 anos. Foram vários os momentos de lutas, mas a persistência e a fé foram maiores. A vontade de vencer e graças a Sua ajuda, essa luta foi vencida.Muito obrigada! À minha orientadora Profa. Dra. Patrícia Nicolucci. Não posso dizer que você foi "só" uma orientadora. Me lembro perfeitamente da nossa primeira conversa e a amizade foi recíproca desde o primeiro momento. Obrigada pelos ensinamentos, pelas discussões pela parceria, por confiar em mim. Foi uma honra ter sido sua aluna desde o mestrado. Agradeço, diariamente, por ter você no meu caminho e quero ter sua amizade para sempre. Você será, para sempre, o meu espelho e o meu exemplo. Muito obrigada por tudo! Aos meus pais e meu irmão que sempre estiveram ao meu lado, nos momentos de alegria e nos nem tão alegres também. Que foram a minha base, o meu alicerce desde sempre. Essa vitória também é de vocês. Ao Prof Dr John C Gore que me aceitou desde o primeiro momento como aluna em Nashville (EUA), para a realização do meu sonhado doutorado sanduíche na Vanderbilt University, Garrido, obrigada por todas as discussões que tivemos ao longo de todo o trabalho. A ajuda de vocês foi fundamental. Aos meus avós que sempre estiveram me apoiando em cada retorno para casa, muito obrigada. Aos dois avôs e a tia que não estão mais presentes fisicamente aqui, tenho certeza que lá de cima estão felizes por mais essa conquista. Vô Ricardo, vô Avelino e tia Tânia, vocês foram exemplos para mim. Essa conquista também é de vocês. Aos meus tios e primos que carinhosamente me recebiam em todas as voltas para casa, muito obrigada. O carinho e o apoio de vocês fazem a diferença na minha vida. vi À Sandra Andrade que tantas vezes foi meu porto seguro quando diariamente conversava comigo. Obrigada pela sua amizade, pelo apoio que mesmo a distância, fez e faz toda diferença na minha vida. Essa vitória também é sua! Aos amigos que o CIDRA me deu ao longo desses anos: Dra Cassiana, Laurinha, Franciely, Eduardo, Gislaine, Cristiano, Thatiane, Mirko, as duas Fernandas, Camila, Vinicius, Miriã, Matheus, Danny. A batalha foi mais leve, graças ao apoio de vocês. Muito obrigada pela amizade de cada um. Vocês são especiais! À Alice Sancinetti e Mariana Carballeda, que graças a tecnologia que nos aproxima sempre, permite que não perdêssemos o contato. Nós podíamos passar tempo sem nos encontrarmos, mas todas as vezes que nos víamos, era como se revivêssemos os bons tempos que nos encontrávamos diariamente. A amizade e o carinho de vocês são coisas raras! Obrigada por tudo, sempre. Ao Setor de Radioterapia do Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto, em especial ao Físico Leandro Federiche Borges que desde a época do meu mestrado, se prontamente se dispôs a realizar todas as minhas irradiações. Muito obrigada! À Guozhen Luo pelas irradiações na Vanderbilt Clinic e ao Dr. Edvaldo Galhardo pelas irradiações na Medicina de Ribeirão Preto, pela atenção e disponi...

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Relative dosimetry with an MR‐linac: Response of ion chambers, diamond, and diode detectors for off‐axis, depth dose, and output factor measurements

Cited by 63 publications

References 29 publications

Measurement validation of treatment planning for a MR‐Linac

Measurement validation of treatment planning for a MR‐Linac

Experimental characterization of magnetically focused electron contamination at the surface of a high‐field inline MRI‐linac

Dosimetria gel polimérica usando imagem de ressonância magnética para aplicação em radioterapia

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