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KMID : 1164220140260020257
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Journal of Korean Society for Radiotherapeutic Technology
2014 Volume.26 No. 2 p.257 ~ p.264
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Experimental investigation of the photoneutron production out of the high-energy photon fields at linear accelerator
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Kim Yeon-Soo
Yoon In-Ha
Bae Sun-Myeong
Kang Tae-Young
Back Geum-Mun
Kim Sung-Hwan
Nam Uk-Won
Lee Jae-Jin
Park Yeong-Sik
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Abstract
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Purpose : Photoneutron dose in high-energy photon radiotherapy at linear accelerator increase the risk for secondary cancer. The purpose of this investigation is to evaluate the dose variation of photoneutron with different treatment method, flattening filter, dose rate and gantry angle in radiation therapy with high-energy photon beam (E≥8MeV).
Materials and Methods : TrueBeam STxTM(Ver1.5, Varian, USA) and Korea Tissue Equivalent Proportional Counter (KTEPC) were used to detect the photoneutron dose out of the high-energy photon field. Complex Patient plans using Eclipse planning system (Version 10.0, Varian, USA) was used to experiment with different treatment technique(IMRT, VMAT), condition of flattening filter and three different dose rate. Scattered photoneutron dose was measured at eight different gantry angles with open field (Field size : 5 X 5 cm).
Results : The mean values of the detected photoneutron dose from IMRT and VMAT were 449.7μ㏜, 2940.7μ㏜. The mean
values of the detected photoneutron dose with Flattening Filter(FF) and Flattening Filter Free(FFF) were measured as 2940.7μ㏜, 232.0μ㏜. The mean values of the photoneutron dose for each test plan (case 1, case 2 and case 3) with FFF at the three different dose rate (400, 1200, 2400 MU/min) were 3242.5μ㏜, 3189.4μ㏜, 3191.2μ㏜ with case 1, 3493.2μ㏜, 3482.6μ㏜,
3477.2μ㏜ with case 2 and 4592.2μ㏜, 4580.0μ㏜, 4542.3μ㏜ with case 3, respectively. The mean values of the photoneutron
dose at eight different gantry angles ( 0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°) were measured as 3.2μ㏜, 4.3μ㏜, 5.3μ㏜,
11.3μ㏜, 14.7μ㏜, 11.2μ㏜, 3.7μ㏜, 3.0μ㏜ at 10MV and as 373.7μ㏜, 369.6μ㏜, 384.4μ㏜, 423.6μ㏜, 447.1μ㏜, 448.0μ㏜,
384.5μ㏜, 377.3μ㏜ at 15MV.
Conclusion : As a result, it is possible to reduce photoneutron dose using FFF mode and VMAT method with TrueBeam
STxTM. The risk for secondary cancer of the patients will be decreased with continuous evaluation of the photoneutron dose.
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KEYWORD
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photoneutron, LINAC, KTEPC
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