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Detector comparison for small field output factor measurements in flattening filter free photon beams.

Lechner, W*; Palmans, H; Solkner, L*; Grochowska, P*; Georg, D* (2013) Detector comparison for small field output factor measurements in flattening filter free photon beams. Radiother. Oncol., 109 (3). pp. 356-360.

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Abstract

Purpose: The applicability of various detectors for small field dosimetry and whether there are differences in the detector response when irradiated with FF- and FFF-beams was investigated.
Materials and methods: Output factors of 6 and 10 MV FF- and FFF-beams were measured with 14 different online detectors using field sizes between 10 x 10 and 0.6 x 0.6 cm^2 at a depth of 5 cm of water in isocentric conditions. Alanine pellets with a diameter of 5 and 2.5 mm were used as reference dosimeters for field sizes down to 1.2 x 1.2 and 0.6 x 0.6 cm^2, respectively. The ratio of the relative output measured with the online detectors to the relative output measured with alanine was evaluated (referred to as dose response ratio).
Results: The dose response ratios of two different shielded diodes measured with 10 MV FF-beams deviated substantially by 2-3% compared to FFF-beams at a field size of 0.6 x 0.6 cm^2. This difference was less pronounced for 6MV FF- and FFF-beams. For all other detectors the dose response ratios of FF- and FFFbeams showed no significant difference.
Conclusion: The dose response ratios of the majority of the detectors agreed within the measurement uncertainty when irradiated with FF- and FFF-beams. Of all investigated detectors, the microDiamond and the unshielded diodes would require only small corrections which make them suitable candidates for small field dosimetry in FF- and FFF-beams.

Item Type: Article
Keywords: Flattening filter free, Output factors, Small fields, FFF, Alanine
Subjects: Ionising Radiation
Ionising Radiation > Dosimetry
Identification number/DOI: 10.1016/j.radonc.2013.10.022
Last Modified: 02 Feb 2018 13:14
URI: http://eprintspublications.npl.co.uk/id/eprint/6058

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