Radiochromic film is a good dosimeter choice for patient QA for complex treatment techniques because of its near tissue equivalency, high spatial resolution and established method of use. Commercial scanners are typically used for film dosimetry, with Epson scanners being the most common. Radiochromic film dosimetry is not straightforward having some well-defined problems which must be considered, one of the main ones being the Lateral Response Artefact (LRA) effect. Previous studies showed that the contributing factors to LRA are from the structure of the active ingredients of the film and the components and construction of the flatbed scanner. This study investigated the effect of the scanner lens on the LRA effect, as part of a wider investigation of scanner design effects and uncertainties. Gafchromic EBT3 films were irradiated with 40 × 40 cm2 field size 6 MV beams. Films were analysed using images captured by a Canon 7D camera utilising 18 mm, 50 mm and 100 mm focal length lenses compared to images scanned with a conventional Epson V700 scanner. The magnitude of the LRA was observed to be dependent on the focal length of the lens used to image the film. A substantial reduction in LRA was seen with the use of the 50 mm and 100 mm lenses, by factors of 3–5 for the 50 mm lens and 4–30 for the 100 mm lens compared to conventional desktop scanner techniques. This is expected to be from the longer focal length camera lens system being able to collect more light from distant areas compared to the scanner-based system. This provides an opportunity to design film dosimetry systems that minimise this artefact.

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Radiochromic film is a good dosimeter choice for patient QA for complex treatment techniques because of its near tissue equivalency, very high spatial resolution and established method of use. Epson scanners are widely used for film dosimetry. Previous studies reported that different components in the construction of flatbed scanners introduce light polarisation which is responsible for enhancing the Lateral Response Artefact (LRA) effect. The purpose of this study is to investigate the contribution of the scanner bed and mirror system of EPSON flatbed scanners to this effect. EBT3 films were irradiated with 40x40cm2 field size in 6 MV beams. Films were analysed using images captured by a Canon 7D camera utilising a 50mm focal length lens to evaluate the polarization introduced by various combinations of mirrors making up the mirror system. An EPSON V700 scanner is used to investigate the effect of the scanner bed. The magnitude of polarization introduced by the mirror system is found to be up to 14%, whereas the path length effect, from the difference in refractive index of film and scanner bed, is found to be insignificant (at less than 2%).