A study of Winston–Lutz test on two different electronic portal imaging devices and with low energy imaging

Abstract

Stereotactic radiosurgery requires sub-millimetre accuracy in patient positioning and target localization. Therefore, verification of the linear accelerator (linac) isocentre and the laser alignment to the isocentre is performed in some clinics prior to the treatment using the Winston-Lutz (W-L) test with films and more recently with images obtained using the electronic portal imaging devices (EPID). The W-L test is performed by acquiring EPID images of a radio-opaque ball of 6 mm diameter (the W-L phantom) placed at the isocentre of the linac at various gantry and table angles, with a predefined small square or circular radiation beam. In this study, the W-L test was performed on two linacs having EPIDs of different size and resolution, viz, a TrueBeam™ linac with aS1000 EPID of size 40 × 30 cm(2) with 1024 × 768 pixel resolution and an EDGE™ linac having an EPID of size 43 × 43 cm(2) with pixel resolution of 1280 × 1280. In order to determine the displacement of the radio-opaque ball centre from the radiation beam centre of the W-L test, an in-house MATLAB™ image processing code was developed using morphological operations. The displacement in radiation beam centre at each gantry and couch position was obtained by determining the distance between the radiation field centre and the radio-opaque ball centre for every image. Since the MATLAB code was based on image processing that was dependent on the image contrast and resolution, the W-L test was also compared for images obtained with different beam energies. The W-L tests were performed for 6 and 8 MV beams on the TrueBeam™ linac and for 2.5 and 6 MV beams on the EDGE™ linac with a higher resolution EPID. It was observed that the images obtained with the EPID of higher resolution resulted in same accuracy in the determination of the displacement between the centres of the radio-opaque ball and the radiation beam, and significant difference was not observed with images acquired with different energies. It is concluded that the software based on morphological operations provided an accurate estimation of the displacement of the ball centre from the radiation beam center.

Rapid detection of Escherichia coli using bacteriophage-induced lysis and image analysis

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The impact of isocentric shifts on delivery accuracy during the irradiation of small cerebral targets—Quantification and possible corrections

“…A common method to assess mechanical imperfections affecting the isocenter is the Winston‐Lutz (WL) test. First developed in 1988 using radiochromic films, 8 the method has become more wide‐spread after the establishment of portal imaging made the method less tedious to use 9‐12 . Images of a ball‐bearing phantom in the radiation beam are acquired at several gantry, collimator, and table angles.…”

Detecção Automática do Teste de Winston-Lutz em Filmes Radiocrômicos

“…Radiocirurgia estereotáxica (SRS, Stereotactic radiosurgery) é uma técnica de radioterapia utilizada no tratamento de tumores cerebrais inacessíveis à cirurgia, bem como em leitos cirúrgicos após cirurgias com ressecção parcial. SRS também é utilizada nos tratamentos de doenças benignas como malformação arteriovenosa, e funcionais como a neuralgia do trigêmeo (1)(2)(3). SRS é uma técnica altamente precisa para entrega de altas doses em um pequeno volume alvo, utilizando alto gradiente de dose a fim de poupar tecidos sadios adjacentes 4 .…”

“…SRS é uma técnica altamente precisa para entrega de altas doses em um pequeno volume alvo, utilizando alto gradiente de dose a fim de poupar tecidos sadios adjacentes 4 . Como toda a dose de prescrição de tratamento geralmente é administrada em uma única sessão durante o tratamento de SRS, exige-se alta precisão na localização e entrega de dose, necessitando de exatidão submilimétrica no posicionamento do paciente e na localização do alvo (1)(2)(3)(4)(5)(6).…”