Extrapolated surface dose measurements using a NdFeB magnetic deflector for 6 MV x-ray beams

Damrongkijudom, Nuanpen; Butson, Martin J; Rosenfeld, Anatoly B.

doi:10.1007/bf03178409

Cited by 5 publications

(2 citation statements)

References 9 publications

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“…Film dosimeters offer permanent records of the ionizing dose distribution measured at high resolutions with the evident advantages of being 2D detectors. Due to the high-atomic-number material constituents, silver halide films are traditionally used; however, these films have the disadvantage of pronounced energy dependence (Damrongkijudom et al, 2007;Palm et al, 2004). This could introduce systematic errors for most usual treatment plans (Arjomandy et al, 2010;Rath et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Wiener filter applied with a multi-channel method for EBT2 film dosimetry

Chang

2016

Engineering Computations

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Purpose – EBT2 film, a convenient quality assurance (QA) tool with high 2D dosimetry resolution, has been widely used in the dosimetry application of radiation therapy with lots of benefits especially its self-development, water equivalent, energy independent and high spatial resolution. However, the higher inhomogeneity between the pixels of EBT2 image, needed to be averaged out according to the traditional method, but it could sacrifice the spatial resolution. To solve this problem, the purpose of this paper is to introduce a Wiener filter (WF) technique applied with a multi-channel (MC) method. Design/methodology/approach – The EBT2 film was calibrated by using the percentage depth dose method combined with the WF technique and a MC method. Then the calculated film doses were compared with the measurement doses by the edge detector with the water phantom. Findings – With high spatial resolution to be 0.2 mm, the results demonstrate that the EBT2 film calibration through both of the WF technique and MC method has higher accuracy (within 2 percent) and lower uncertainty. Originality/value – A new technique of WF with MC method was presented to calibrate the dosimetry system of EBT2 film. With high spatial resolution (0.2 mm), the studies show that the combination of WF technique with MC method can have high accuracy with low noises to calibrate EBT2 film. This method can also be applied to all the QAs of treatment planning of radiation therapy by using the EBT2 film.

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Section: Introductionmentioning

confidence: 99%

Wiener filter applied with a multi-channel method for EBT2 film dosimetry

Chang

2016

Engineering Computations

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“…Many of these changes can be attributed to variations in electron contamination and phantom scatter. Large variations are observed for changes in beam parameters such as field size, the use of beam modifying devices and the beam angle of incidence (Butson et al 1996, Zhu and Palta 1998, Hounsell and Wilkinson 1999, Damrongkijudom et al 2007 or for changes in the material which may be in a direct or indirect path of the radiation beam in question. It has been shown that the skin dose can be adequately measured with the EBT Gafchromic, radiochromic film (Devic et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Megavoltage x-ray skin dose variation with an angle using grid carbon fibre couch tops

Butson

Cheung

2007

Phys. Med. Biol.

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It is well known that a skin dose from high-energy x-ray radiation varies with the angle of beam incidence or the presence of a radiotherapy linear accelerator couch top material. This note investigates changes produced to the skin dose from a Varian carbon fibre grid couch top at differing angles of incidence for 6 MV x-rays as is often the case clinically. Results have shown that the skin dose can easily be measured using an EBT Gafchromic film whereby the delivered skin dose can be quantified to a high level of spatial resolution, not easily achieved with other skin dose detectors. Results have shown a significant increase in the skin dose specifically at the point of a cross-sectional carbon fibre grid. Values in % of the skin dose increased from approximately 27% (an open area within a 10 cm x 10 cm field) up to 55% (same field size) at the centre of the carbon fibre mesh strip (0 degrees incidence). This is compared to 19% of the skin dose for an open field of a 10 cm x 10 cm beam without the couch material present. At larger angles similar effects occur with values changing from 52% to 75% (60 degrees , 10 cm x 10 cm) in the open area and under the grid, respectively. This produces a wave effect for the skin dose. The average skin dose magnitude increases with the angle of incidence of the beam, ranging from 37.5% to 66% from 0 degrees to 60 degrees (10 x 10 cm), respectively. The symmetric wave nature of the skin dose profile skews to deliver an increased dose on the posterior side of the carbon fibre grid as the angle of incidence increases. Simulated fractional dose delivery on a phantom has shown that over 30 fractions the wave nature of the delivered skin dose is minimized due to the random nature of most patient positioning on the treatment couch. However, some variations are still present as the ratio of the open to grid area is approximately 4:1 and the dose spread is not necessarily completely averaged during a typical fractionated radiotherapy treatment. As such, if the treatment type results in a more rigorously positioned patient on the treatment couch, the wave nature of skin dose delivery may need to be taken into account.

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Evaluation of the magnitude of EBT Gafchromic film polarization effects

Butson

Cheung

2009

Australas. Phys. Eng. Sci. Med.

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Gafchromic EBT film, has become a main dosimetric tools for quantitative evaluation of radiation doses in radiation therapy application. One aspect of variability using EBT Gafchromic film is the magnitude of the orientation effect when analysing the film in landscape or portrait mode. This work has utilized a > 99% plane polarized light source and a non-polarized diffuse light source to investigate the absolute magnitude of EBT Gafchromic films polarization or orientation effects. Results have shown that using a non-polarized light source produces a negligible orientation effect for EBT Gafchromic film and thus the angle of orientation is not important. However, the film exhibits a significant variation in transmitted optical density with angle of orientation to polarized light producing more than 100% increase, or over a doubling of measured OD for films irradiated with x-rays up to dose levels of 5 Gy. The maximum optical density was found to be in a plane at an angle of 14 degrees +/- 7 degrees (2 SD) when the polarizing sheet is turned clockwise with respect to the film. As the magnitude of the orientation effect follows a sinusoidal shape it becomes more critical for alignment accuracy of the film with respect to the polarizing direction in the anticlockwise direction as this will place the alignment of the polarizing axes on the steeper gradient section of the sinusoidal pattern. An average change of 4.5% per 5 degrees is seen for an anticlockwise polarizer rotation where as the effect is 1.2% per 5 degrees for an clockwise polarizer rotation. This may have consequences to the positional accuracy of placement of the EBT Gafchromic film on a scanner as even a 1 degree alignment error can cause an approximate 1% error in analysis. The magnitude of the orientation effect is therefore dependant on the degree of polarization of the scanning light source and can range from negligible (diffuse LED light source) through to more than 100% or doubling of OD variation with a fully linear polarized light source.

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Extrapolated surface dose measurements using a NdFeB magnetic deflector for 6 MV x-ray beams

Cited by 5 publications

References 9 publications

Wiener filter applied with a multi-channel method for EBT2 film dosimetry

Wiener filter applied with a multi-channel method for EBT2 film dosimetry

Megavoltage x-ray skin dose variation with an angle using grid carbon fibre couch tops

Evaluation of the magnitude of EBT Gafchromic film polarization effects

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