学位の種別:課程博士University of Tokyo(東京大学

SAOTOME NAOYA

早乙女 直也

UTokyo Repository

論文の内容の要旨  
論文題目  Four-dimensional dose calculation using in-treatment  
cone beam computed tomography and  
linear accelerator log data 
（治療中コーンビーム断層画像と医療用加速器の  
動作記録を用いた４次元線量分布計算) 
氏名  早乙女直也  
 
With recent developments, the record and verification system for high-precision 
radiotherapy during dose delivery plays an important role in quality control and 
assurance. An investigation of robust techniques for actual dose verification is currently 
one of the active areas of research in radiation therapy. The aim of this study is to 
develop a reliable technique of in vivo dosimetry for a moving target based on 
in-treatment data. This thesis is composed of 3 parts; (1) the analysis of log data in the 
state-of-the-art digital linear accelerator (LINAC) using an electric portal imaging 
device (EPID); (2) the analysis of the density-override method in dose calculation; and 
(3) the study of the four-dimensional (4D) dose calculation based on the 2 other studies 
outlined above.  
After the introduction, in Chapter 2, the position of the multi-leaf collimator 
(MLC) recorded in the log data is analyzed by using the EPID. From the comparison, 
the difference was 0.88 ± 0.93 mm. As an estimate of the dose difference, an 
approximately 1-mm difference of MLC position does not effectively affect the dose 
distribution for the delivery of volumetric modulated arc therapy (VMAT). This result 
justified the use of the log data for actual dose verification. 
In Chapter 3, the influence of the image quality in the dose calculation is discussed. Due 
to image degradation, it is well known that use of cone-beam computed tomography 
(CBCT) for dose calculation yields a large uncertainty in dose distribution. In this thesis, 
the method that utilizes the information of the anatomical mean densities inside the 
region of interest (ROI) obtained by the treatment planning computed tomography (CT) 
is employed. Applying the ROI mapping method to the same planning CT as in the 
original plan for 3 lung cancer patients, the accuracy of the ROI mapping method was 
within 1.2%. 
In Chapter 4, the 4D dose calculation with the ROI mapping method was 
performed by use of the in-treatment 4D CBCT and LINAC log data, both of which 
were acquired during treatment. In a study using a moving phantom, 4D dose 
calculation well reproduced the measurement in comparison with the 3D dose 
calculation. Actual dose distributions for three lung cancer patients with this technique 
were compared with those of the plan. A small but significant dose difference between 
the 3D and 4D calculations was observed for the case of large target traveling. In 
addition, day-to-day fluctuation of the delivered dose was observed for all the patients. 
The importance of in vivo dosimetry for a moving target is apparent. The present 
technique and the findings of this study will contribute to maintain the quality of 
high-precision radiation therapy. 
 
 


治療中コーンビーム断層画像と医療用加速器の動作記録を用いた4次元線量分布計算

https://repository.dl.itc.u-tokyo.ac.jp/?action=repository_action_common_download&item_id=6974&item_no=1&attribute_id=14&file_no=2

治療中コーンビーム断層画像と医療用加速器の動作記録を用いた4次元線量分布計算

Abstract

Similar works

Full text

Available Versions

UTokyo Repository