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Patient-Specific Quality Assurance in a Multileaf Collimator-Based CyberKnife System Using the Planar Ion Chamber Array

 Jeongmin Yoon  ;  Eungman Lee  ;  Kwangwoo Park  ;  Jin Sung Kim  ;  Yong Bae Kim  ;  Ho Lee 
 Korean Journal of Medical Physics (의학물리), Vol.29(2) : 59-65, 2018 
Journal Title
 Korean Journal of Medical Physics (의학물리) 
Issue Date
CyberKnife ; MLC ; Patient-specific quality assurance ; Octavius 1000SRS
This paper describes the clinical use of the dose verification of multileaf collimator (MLC)-based CyberKnife plans by combining the Octavius 1000SRS detector and water-equivalent RW3 slab phantom. The slab phantom consists of 14 plates, each with a thickness of 10 mm. One plate was modified to support tracking by inserting 14 custom-made fiducials on surface holes positioned at the outer region of 10×10 cm2. The fiducial-inserted plate was placed on the 1000SRS detector and three plates were additionally stacked up to build the reference depth. Below the detector, 10 plates were placed to avoid longer delivery times caused by proximity detection program alerts. The cross-calibration factor prior to phantom delivery was obtained by performing with 200 monitor units (MU) on the field size of 95×92.5 mm2. After irradiation, the measured dose distribution of the coronal plane was compared with the dose distribution calculated by the MultiPlan treatment planning system. The results were assessed by comparing the absolute dose at the center point of 1000SRS and the 3-D Gamma (g) index using 220 patient-specific quality assurance (QA). The discrepancy between measured and calculated doses at the center point of 1000SRS detector ranged from −3.9% to 8.2%. In the dosimetric comparison using 3-D g-function (3%/3 mm criteria), the mean passing rates with g-parameter ≤ 1 were 97.4%±2.4%. The combination of the 1000SRS detector and RW3 slab phantom can be utilized for dosimetry validation of patient-specific QA in the CyberKnife MLC system, which made it possible to measure absolute dose distributions regardless of tracking mode.
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1. College of Medicine (의과대학) > Dept. of Radiation Oncology (방사선종양학교실) > 1. Journal Papers
Yonsei Authors
Kim, Yong Bae(김용배) ORCID logo https://orcid.org/0000-0001-7573-6862
Kim, Jinsung(김진성) ORCID logo https://orcid.org/0000-0003-1415-6471
Lee, Eung Man(이응만)
Lee, Ho(이호) ORCID logo https://orcid.org/0000-0001-5773-6893
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