Evaluation of Dosimetic Characteristics of Electronic Portal Imaging Device (EPID) for Flattening Filter Free (FFF) Beams

Objective: To evaluatethe dosimetric characteristics of electronics portal imaging device (EPID) for 6 and 10 megavoltage(MV) of flattening filter-free (FFF) beams.Material and Method: The EPID characteristicsfor FFF beams have been evaluated as follows; saturation with sourcedetector-distance (SDD), saturation with dose rate, dose linearity response with monitor unit (MU), and the scatterd radiation with field size.Results: The saturation of signal was not occurred at 150 cm and 180 cm SDD for 6 and 10 MV of FFF beams, respectively. When the signals were measured with optimal SSD according to vendor suggestion (150 cm and 180 cm), the standard deviation for all dose rate were ±1.35 and ±1.64 CU for 6 and 10 MV of FFF beams,respectively. The dose linearity response showed that EPID has a good linearity response between signals and MU forthe both of 6 and 10 MV of FFF beams. The results of scatterd radiation with field size were found that FFF beams have different respose from flattening filter (FF) beams with the highest differences of 5.50% and 6.78% for 6 and 10 MV of FFF beams, respectively.Conclusion: EPID has a good characteristic for FFF beams, and an extended SSD can be used to reduce the satured signal effects in FFF beams.

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Dosimetric Characterization of the Dual Layer MLC System for an O-Ring Linear Accelerator

Technology in Cancer Research & Treatment ◽

10.1177/1533033819883641 ◽

2019 ◽

Vol 18 ◽

pp. 153303381988364 ◽

Cited By ~ 1

Author(s):

Michele M. Kim ◽

Douglas Bollinger ◽

Chris Kennedy ◽

Wei Zou ◽

Ryan Scheuermann ◽

...

Keyword(s):

Linear Accelerator ◽

Multileaf Collimator ◽

Electronic Portal Imaging Device ◽

Imaging Device ◽

Portal Imaging ◽

Electronic Portal Imaging ◽

Flattening Filter Free ◽

Flattening Filter ◽

Dosimetric Leaf Gap

The Halcyon is Varian’s latest linear accelerator that offers a single 6X flattening-filter-free beam with a jawless design that features a new dual layer multileaf collimator system with faster speed and reduced transmission. Dosimetric characteristics of the dual layer multileaf collimator system including transmission, dosimetric leaf gap, and tongue and groove effects were measured. Ionization chambers, diode arrays, and an electronic portal imaging device were used to measure various multileaf collimator characteristics. Transmission through both multileaf collimator banks was found to be 0.008%, while the distal and proximal banks alone had transmission values of 0.4%. The penumbra was slightly sharper for fields using only the distal multileaf collimator bank but found to be largely independent of leaf position with values between 2.7 to 3.0 mm at dmax for the combined multileaf collimator banks. The dosimetric leaf gap was measured for the proximal and distal multileaf collimator banks both individually and together and found to have values of −0.216 mm, −0.225 mm, and 0.964 mm, respectively. Measurements of dosimetric leaf gap at the leaf edge and midline were also performed. Tongue and groove effects were investigated with both the electronic portal imaging device and a 2-dimensional array of diodes.

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Enhance dynamic wedge verification by using electronic portal imaging device

Chiang Mai Medical Journal ◽

10.12982/cmumedj.2021.16 ◽

2021 ◽

Vol 60 (2) ◽

Author(s):

N Saiyo ◽

◽

S Thongsawad ◽

P Changphong ◽

T Khotsawan ◽

...

Keyword(s):

Beam Profile ◽

Field Size ◽

Electronic Portal Imaging Device ◽

Imaging Device ◽

Portal Imaging ◽

Output Factor ◽

Electronic Portal Imaging ◽

Treatment Planning Systems ◽

Dynamic Wedge ◽

The Difference

Objectives The purpose of this study was to verify the 80% enhanced dynamic wedge (EDW) beam profile using an electronic portal imaging device (EPID). Methods This study investigated symmetric and asymmetric field sizes using a 6 MV photon beam. Verification of the wedge output factor with an 80% beam profile was performed by comparing EPID measurements and treatment planning systems (TPS) calculations in both symmetric and asymmetric field sizes at different wedge angles (15, 30, 45, and 60 degrees). Results For the symmetric field size, the average difference between the measured and calculated beam profile was less than 2% (range 0.57-1.12%). For the asymmetric field size, the difference was also less than 2% (range 0.3-0.52%). Conclusion This study indicates that EPID can be used to verify the 80% enhanced dynamic wedge beam profile at different field sizes and wedge angles. The difference in beam profiles was less than 2% which is in accordance with AAPM TG no.142 recommendations.

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