1. Physica Medica 32 (2016) 1570–1574 報告人：王俊淵
Method of evaluating respiratory induced organ motion by vector volume histogram
Physica Medica 32 (2016) 1570–1574
報告人：王俊淵

2. Outline Introduction Methods and materials Results Discussion
Conclusions

3. Introduction
Respiratory induced organ motion is an important issue in radiotherapy treatment planning of the thoracic and upper abdominal regions.
It produces the greatest movement in the caudal-cranial (CC) direction because the most important muscle used in inhalation is the diaphragm.
Here, we propose a novel method for evaluating respiratory organ motion using DIR.
This work presents a quantitative method that evaluates the vector with the location of pixels inside each organ.
We also measured respiratory organ motion from the displacement of the centroid of the organ in two phases.

4. Methods and materials
We used the 4D CT datasets of the five patients from the DIR website (
The 4D CT images were acquired over the entire thorax and upper abdomen at 2.5 mm slice spacing using a General Electric Discovery ST PET/CT scanner (GE Medical Systems, Waukesha, WI).
The voxel dimension was mm.
We used the end-expiration and end-inspiration phases of the 4D CT image sets.
We focused on the lung, esophagus, stomach, spinal cord, and liver in this study.

5. Methods and materials
The vector field is defined as the deformation vector field (DVF).
The calculated DVF was exported via a script.
DVFs consist of DVFLR (left-right), DVFAP (anterior-posterior), and DVFCC separates files.
Each DVF value was calculated as an absolute value.
The vector volume histogram (VVH) calculation approach is a concept similar to that of the dose volume histogram (DVH).
The motion vector is a three-dimensional array defining the location of each pixel.
Vectors on each direction are stored in separate arrays.

6. Methods and materials 3D-DVF is calculated by
In comparison, the VVH for each organ is calculated by evaluating the number of magnitude values in the organ.
The following motion indices were used to evaluate the respiratory motion:
Lmax (mm): Largest motion extent within the organ.
L2% (mm):2%of the volume of the organ has moved more than L2%.
V10 mm (%): the relative volume of organ moving more than 10 mm.
Organ motion extent using the centroid method was defined as the absolute difference of coordinates of the end-expiration phase and end-inspiration phase.

11. Discussion
In most previous investigations, the magnitudes of the tumor and organ motions were simply calculated using the centroid or edge coordinates of the contour drawn on each phase.
In our study, we demonstrated the feasibility of using DIR to evaluate organ motion.
Our proposed method can provide a valuable indicator of respiratory induced organ deformation during respiration, which previously has not received sufficient evaluation because only the motion of the centroid or edge of the organ was used.
A deformation grid of 2.5*2.5*2.5 mm and image voxel size of 0.97*0.97*2.5 mm was used in this study.
Therefore, the accuracy of our analysis may be limited by the spatial resolution.

12. Discussion
In our study, organ motion using the centroid method was smaller than Lmax using VVH.
Currently, visual inspection of the DVF distribution using DIR is the primary means of examining the spatial characteristics of deformation.
This inspection is time consuming and unable to provide objective, quantified metrics.
VVH can be used as a means of finding the existence of large organ motion features within structures of interest.
Our proposed vector volume method was used instead of point vectors at arbitrary positions such as the centroid or edge.
Additionally, the VVH method using DIR makes it possible to evaluate not only intra-fractional organ motion, but also inter-fractional organ motion using cone-beam computed tomography (CBCT) with DIR.

13. Discussion
Our proposed method of VVH using DIR can be applied to evaluate all phases of the respiratory organ motion.
The use of the entire lung and liver failed to assess the variability of organ segments (e.g. lung upper, middle, and lower lobes).
The VVH and centroid methods were not compared in detail because the main purpose of this study is to propose a novel quantitative method for evaluating respiratory organ motion using DIR.

14. Conclusions
We introduced a method of evaluating respiratory induced organ motion using DIR.
Our proposed VVH method could be easily used for the volumetric evaluation of respiratory induced organ motion.
Moreover, the method of VVH proposes to extend the methodology to inter-fractional motion using CBCT with DIR.