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KMID : 1164220180300010129
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Journal of Korean Society for Radiotherapeutic Technology
2018 Volume.30 No. 1 p.129 ~ p.138
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Comparison and Evaluation of radiotherapy plans by multi leaf collimator types of Linear accelerator
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Lim Ji-Hye
Chang Nam-Joon
Seok Jin-Yong
Jung Yun-Ju
Won Hui-Su
Jung Hae-Yoon
Choi Byeong-Don
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Abstract
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Purpose : An aim of this study was to compare the effect of multi leaf collimator(MLC) types for high dimension radiotherapy in treatment sites used clinically.
Material and Method : 70 patients with lung cancer, spine cancer, prostate cancer, whole pelvis, head and neck, breast cancer were included in this study. High definition(HD) MLC of TrueBeam STx (Varian Medical system, Palo Alto, CA) and millenium(M) MLC of VitalBeam (Varian Medical system, Palo Alto, CA) were used. Radiotherapy plans were performed for each patient under same treatment goals with Eclipse (Version 13.7, Varian Palo Alto USA, CA). To compare the indicators of the radiotherapy plans, planning target volume(PTV) coverage, conformity index(CI), homogeneity index(HI), and clinical indicators for each treatment sites in normal tissues were evaluated. To evaluate low dose distribution, V30 % values were compared according to MLC types. Additionally, length and volume of targets for each treatment sites were investigated.
Result : In stereotatictic body radiotherapy(SBRT) plan for lung, the average value of PTV coverage was reduced by 0.52 % with HD MLC. With SBRT plan using HD MLC for spine, the average value of PTV coverage decreased by 0.63 % and maximum dose decreased by 1.13 %. In the test of CI and HI, the values in SBRT plan with HD MLC for spine were 1.144, 1.079 and the values using M MLC were 1.160, 1.092 in SBRT plan for lung, The dose evaluation of critical organ was reduced by 1.48 % in the ipsilateral lung mean dose with HD MLC. In prostate cancer volumetric modulated arc therapy(VMAT) with HD MLC, the mean dose and the V30 of bladder and the mean dose and the V25 of rectum were reduced by 0.53 %, 1.42 %, 0.97 %, and 0.69 %, respectively (p<0.05). The average value of heart mean dose was reduced by 0.83 % in breast cancer VMAT with M MLC. Other assessment indices for treatment sites showed no significant difference between treatment plans with two types of MLC.
Conclusion : Using HD MLC had a positive impact on the PTV coverage and normal tissue sparing in usually short or small targets such as lung and spine SBRT and prostate VMAT. But, there was no significant difference in targets with long and large such as lung, head and neck, and whole pelvis for VMAT.
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KEYWORD
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High definition MLC, Millenium MLC, Stereotatic body radiation therapy, Volumetric modulated arc radiotherapy
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