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KMID : 1164220180300010073
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Journal of Korean Society for Radiotherapeutic Technology
2018 Volume.30 No. 1 p.73 ~ p.81
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Evaluation of the Usefulness for VMAT of multiple brain metastasis using jaw tracking
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Kim Tae-Won
Yoo Soon-Mi
Jeon Soo-Dong
Yoon In-Ha
Back Geum-Mun
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Abstract
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Purpose : The aims of this study were to compare and assess the effectiveness of Volumetric Modulated Arc Therapy(VMAT) using jaw tracking(JT) and fixed jaw(FJ) in radiation therapy of multiple brain metastasis.
Methode and material : Among the patients with Multiple Brain Metastasis treated with jaw tracking, 10 patients with more than 6 tumors and with the size of radiation field 14 × 14 cm2 or more were included. Each Treatment plans with jaw tracking(JT) and fixed jaw(FJ) was established with Eclipse (Ver. 13.6 Varian, USA). Gamma Index (3 mm, 3 % confidence interval - 95 %) and maximum dose difference were measured with an electronic portal imaging device(EPID). The Dmax and Dmean of Organ At Risk(OAR) were assessed and compared, and the Conformity Index(CI) and Homogeneity Index(HI) were evaluated.
Result : Evaluating jaw tracking(JT) and fixed jaw(FJ) outcomes, in all cases, Gamma Index met the permissible standard of 3 mm, 3 % confidence intervals of 95 %. The maximum dose difference value from the areas with leaf end transmission was measured at a maximum of 98.4 % and an average of 43.6 % in clockwise(CW), and 67.9 % and 41.0 % for each in Counter-Clockwise(CCW). With jaw tracking, the maximum value of Dmax for each normal organ in OAR decreased in 15.36 %~74.59 % with the average value decreasing in 2.84 %~39.80 %. The maximum value of Dmean in OAR decreased in 27.90 %~65.23 %, with the average value decreasing in 7.70 %~ 41.71 %. No change has been found in Conformity Index and Homogeneity Index values.
Conclusion : When Jaw tracking is used in treating patients with multiple brain metastasis with VMAT, the unnecessary
exposure due to leakage and transmission of radiation in unspecified areas was reduced, without affecting the dose distribution of the planning target volume(PTV), and the availability of radiation therapy with lower doses in normal organs is expected.
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KEYWORD
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jaw tracking, fixed jaw, VMAT
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