Effect of multileaf collimator-defined segment size on S(c)

Medical Physics
P Alaei, P D Higgins

Abstract

Tertiary multileaf collimators (MLCs) in certain linear accelerators have been found to influence the factor S(c). This effect on S(c) is often ignored at the time of commissioning and beam data collection since the scatter/output factors are usually measured with the MLCs retracted. This may be a negligible effect for majority of conventional radiotherapy portals since the jaws are set to conform with MLCs as closely as possible. In the case of IMRT treatments, however, the jaw is often set at a fixed size, and the MLCs form the segments, or control points, of each beam, thus the difference between MLC and jaw settings may be significant. The authors quantified the magnitude of this scatter difference for various field sizes defined by MLCs and jaws and characterized the variation in this scatter with MLC and jaw settings. They measured S(c) and S(c,p) factors for square fields (apertures) of different sizes for jaw settings from 10 x 10 to 36 x 36 cm2. The data indicate that the larger the difference between MLC-defined aperture and jaw settings, the more significant the difference between the output factors. The authors fitted curves to the MLC output factors for any given jaw size in order to parametrize this aperture effec...Continue Reading

References

Jan 15, 1997·International Journal of Radiation Oncology, Biology, Physics·M K Yu, R S Sloboda
Jan 22, 1998·Physics in Medicine and Biology·P D HigginsA S Ahuja
Jul 18, 2002·Physics in Medicine and Biology·M Saiful HuqJames M Galvin
Sep 21, 2004·Medical Physics·Dietmar GeorgMikael Karlsson
Oct 19, 2004·Medical Physics·Timothy C ZhuMike Bieda
Apr 21, 2005·Medical Physics·James C L ChowAndrew Alexander
Aug 11, 2006·Medical Physics·P D Higgins, P Alaei
Dec 10, 2009·Medical Physics·Timothy C ZhuUNKNOWN AAPM Therapy Physics Committee Task Group 74

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Citations

Apr 29, 2014·Physica Medica : PM : an International Journal Devoted to the Applications of Physics to Medicine and Biology : Official Journal of the Italian Association of Biomedical Physics (AIFB)·Lucas Nonato de OliveiraLinda V E Caldas
Dec 24, 2019·Nihon Hoshasen Gijutsu Gakkai zasshi·Takahide HayakawaRyuta Sasamoto
Jul 25, 2019·Australasian Physical & Engineering Sciences in Medicine·So-Yeon ParkSang-Tae Kim

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