pmp Progress in Medical Physics Progress in Medical Physics 2508-4445 2508-4453 Korean Society of Medical Physics 10.14316/pmp.2014.25.1.15 pmp-25-15 Original Article The Output Factor of Small Field in Multileaf Collimator of 6 MV Photon Beams LeeHo Joon ∗ ChoiTae-Jin ∗ OhYoung Kee † JeunKyung Soo † LeeYong Hee † KimJin Hee † KimOk Bae † OhSe An † KimSung Kyu † YeaJi Woon ‡ Department of Radiation Oncology, Daegu Catholic University Medical Center, Daegu, Korea Keimyung University Dongsan Medical Center, Daegu, Korea Youngnam University Medical Center, Daegu, Korea Correspondence:Young Kee Oh (ykoh@dsmc.or.kr) Tel: 82-53-250-7683, Fax: 82-53-250-7984 32014 1732014 251 1522 11022014 13032014 Copyright © 2014 Korean Society of Medical Physics 2014 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 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 3×3 cm2 to 0.5×0.5 cm2 small field size for collimator jaw in MLC free and/or for MLC open field in fixed collimator jaw 10×10 cm2 using the CC01 ion chamber, SFD diode, diamond detector and X-Omat film dosimetry. As results of normalized to the reference field of 10×10 cm2 of MLC, the output factor of 3×3 cm2 showed 0.899±0.0106, 0.855±0.0106 for 2×2 cm2, 0.764±0.0082 for 1×1 cm2 and 0.602±0.0399 for 0.5×0.5 cm2. The output factor of MLC open field has shown a maximum 3.8% higher than that of the collimator jaw open field.

 Small field Output factor Film dosimetry REFERENCES Klein EE Hanley J Bayouth J Task Group 142 report: Quality assurance of medical accelerators Med Phys 369 41974212 2009 Barbosa NA Rosa LAR Development of a phantom for dose distribution verification in Stereotactic Radiosurgery Physica Medica 29 461469 2013 Thomas SJ Eaton DJ Equivalent squares for small field dosimetry The British Journal of Radiology. 81 897901 2008 Choi TJ Kim JH Kim OB Development of a New Radiotherapy Technique using the Quasi-conformation Method J Korean Soc Ther Radiol 92 343350 1991 Kenichiro Hasumi, Yukimasa Aoki, Ryuko Wantanabe, Dean L Mann Clinical respondse of advanced cancer patients to cellular immunotherapy and intensity-modulated radiation therapy Oncoimmunology 210 2013 Cadman P Sidhul NPS Ibbott G Nelson A Dosimetric considerations for validation of sequential IMRT process with a commercial treatment planning system Phys Med Biol 47 30013010 2002 Alfonso R Andreo P Capote R A new formalism for reference dosimetry of small and nonstandard fields Medical Physics 35 51795186 2008 Francescon P Cora S Cavedon C Total scatter factors of small beams: A multidetector and Monte Carlo study Medical Physics 30 341347 2003 Oh SA Kang MK Study of the Penumbra for High-energy Photon Beams with GafchromaticTM EBT2 Journal of the Korean Physical Society 6011 19731976 2012 Varian medical system. Eclipse Algorithms Reference Guide. p43-45 2009 Francisco SD Günther HH Javier P Uncertainty estimation in intensity-modulated radiotherapy absolute dosimetry verification Int J Radiation Oncology Biol Phys 681 301310 2007 Alfonso R Andreo P Capote R A new formalism for reference dosimetry of small and nonstandard fields Medical Physics 35 51795186 2008 Das IJ Ding GX Ahnesjo A Small fields: Nonequilibrium radiation dosimetry Medical Physics 35 206215 2008 Followill DS Kry SF Qin L The Radiological Physics Center's standard dataset for small field size output factors Journal of Applied Clinical Medical Physics 135 282289 2012 Scott AJD Nahum AE Fenwick JD Using a Monte Carlo model to predict dosimetric properties of small radiotherapy photon fields Medical Physics 35 46714684 2008 Das IJ Ding GX Ahnesjo A Small fields: Nonequilibrium radiation dosimetry Medical Physics 35 206215 2008 Gavin CS Steve W Narinder PS Experimental small field 6 MV output ratio analysis for various diode detector and accelerator combinations Radiotherapy and Oncology 100 429435 2011 Duggan DM Coffey CW II Small Photon Field Dosimetry for Stereotactic Radiosurgery Medical Dosimetry 233 153159 1998 Klein DM Tailor RC Measuring output factors of small fields formed by collimator jaws and multileaf collimator using plastic scintillation detectors Med Phys 3710 55415549 2010 Kim JO Siebers JV Keall PJ A Monte Carlo study of radiation transport through multileaf collimators Med Phys 2812 24972506 2001 Figures and Tables

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.

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).

The averaged output factors obtained as function of the collimator field size for the MLC free.

  Jaw field (cm2) Output factor∗
MLC free 10×10 1.000±0.0000
5×5 0.920±0.0100
3×3 0.866±0.0093
2×2 0.830±0.0096
1×1 0.741±0.0022
0.5×0.5 0.550±0.0240

The averaged output factors were delivered from the CC01 ion chamber, SFD diode chamber, diamond chamber and Xomat film dosimetry.

The averaged output factors obtained as function of the MLC field size for the Collimator 10×10 cm2.

  MLC field (cm2) Output factor∗
JAW 10×10 cm2 10×10 1.000±0.0000
5×5 0.955±0.0035
3×3 0.899±0.0106
2×2 0.855±0.0106
1×1 0.764±0.0082
0.5×0.5 0.602±0.0399

The averaged output factors were delivered from the CC01 ion chamber, SFD diode chamber, diamond chamber and Xomat film dosimetry.

Comparison the output factors of experiments to that of derivered' from TPS.

  Jaw field (r) TPS∗ MUGy CBSF (r) Dnorm (X,Y)10 TMR∗∗ (r,10) TPS OPF Experiment
OPF diff (%)
MLC free 10×10 126 1.000 1.000 0.775 1.000 1.000 0.0%
5×5 139 0.979 0.887 0.737 0.949 0.955 －0.6%
3×3 146 0.950 0.820 0.707 0.942 0.899 4.8%
2×2 154 0.930 0.761 0.689 0.915 0.855 7.0%
1×1 180 0.909 0.636 0.662 0.815 0.764 6.7%
0.5×0.5 - - - - - 0.602 -

TPS∗ MUGy represents MU for 1 Gy at 10 cm depth in a given jaw field(r) and TMR∗∗ was derivered from PBC modeling in Eclipse TPS.