title: Optimization of Couch Modeling in the Change of Dose Calculation Methods and Their Versions.
abstract: In external radiotherapy, the X-ray beam passes through the treatment couch, leading to the dose reduction by the attenuation of the couch. As a method to compensate for the reduction, radiation treatment planning systems (RTPS) support virtual couch function, namely "couch modeling method". In the couch modeling method, the computed tomography (CT) numbers assigned to each structure should be optimized by comparing calculations to measurements for accurate dose calculation. Thus, re-optimization of CT numbers will be required when the dose calculation algorithm or their version changes. The purpose of this study is to evaluate the calculation accuracy of the couch modeling method in different calculation algorithms and their versions. The optimal CT numbers were determined by minimizing the difference between measured transmission factors and calculated ones. When CT numbers optimized by Anisotropic Analytical Algorithm (AAA) Ver. 8.6 were used, the maximum and the mean difference of transmission factor were 5.8% and 1.5%, respectively, for Acuros XB (AXB) Ver. 11.0. However, when CT numbers optimized by AXB Ver. 11.0 were used, they were 2.6% and 0.6%, respectively. The CT numbers for couch structures should be optimized when changing dose calculation algorithms and their versions. From the comparison of the measured transmission to calculation, it was found that the CT numbers had high accuracy.
authors.affiliation: Division of Clinical Radiology Service, Kyoto University Hospital.
authors.forename: Junichi
authors.initials: J
authors.lastname: Kuwahara
authors.forename: Manabu
authors.initials: M
authors.lastname: Nakata
authors.forename: Takahiro
authors.initials: T
authors.lastname: Fujimoto
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Nakamura
authors.forename: Makoto
authors.initials: M
authors.lastname: Sasaki
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Tsuruta
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Yano
authors.forename: Kyoji
authors.initials: K
authors.lastname: Higashimura
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hiraoka
mesh_terms: D000465:Algorithms; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D013679:Technology, Radiologic; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*