Prog Med Phys.  2014 Mar;25(1):15-22. 10.14316/pmp.2014.25.1.15.

The Output Factor of Small Field in Multileaf Collimator of 6 MV Photon Beams

• Lee HJ
• Choi TJ
• Oh YK
• Jeun KS
• Lee YH
• Kim JH
• Kim OB
• Oh SA
• Kim SK
• Yea JW

• KMID: 1910554
• DOI: http://doi.org/10.14316/pmp.2014.25.1.15

Abstract

The IMRT is proper implement to get high dose deliver to tumor as its shape and selective approach in radiation therapy. Since the IMRT is performed as modulated the radiation fluence by the MLC created the open shapes and its irradiation time, the dose of segment of radiation field effects on the cumulated portal dose. The accurate output factor of small and step shape of segment is important to improve the determination of deliver tumor dose as it is directly proportional to dose. This experiment performed with the 6 MV photon beam of Clinac Ex(Varian) from 3x3 cm2 to 0.5x0.5 cm2 small field size for collimator jaw in MLC free and/or for MLC open field in fixed collimator jaw 10x10 cm2 using the CC01 ion chamber, SFD diode, diamond detector and X-Omat film dosimetry. As results of normalized to the reference field of 10x10 cm2 of MLC, the output factor of 3x3 cm2 showed 0.899+/-0.0106, 0.855+/-0.0106 for 2x2 cm2, 0.764+/-0.0082 for 1x1 cm2 and 0.602+/-0.0399 for 0.5x0.5 cm2. The output factor of MLC open field has shown a maximum 3.8% higher than that of the collimator jaw open field.

Keyword

Small field; Output factor; Film dosimetry

MeSH Terms

Diamond
Film Dosimetry
Jaw
Diamond

Figure

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  Fig. 1. Showing the small field size of MLC in cm for 10×10 cm2 collimator jaw. The pictures showed (a) 1×1 cm2 and (b) 0.5×0.5 cm2 on SAD 100 cm and SPD 95 cm.

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  Fig. 2. Showing the output factors of small fields in 6 MVX rays using the SFD diode, Xomat film, diamond chamber and CC13 ion chamber used for reference output dose. The field size delivered from the collimator jaws in cm for MLC free (a) and the MLC open in collimator jaws set of 10×10 cm2 (b).

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