Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_19_3302 - Vector Volume Histogram: New Method to Evaluate Deformed Organ Motion

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Vector Volume Histogram: New Method to Evaluate Deformed Organ Motion
H. Miura1,2, S. Ozawa1,2, Y. Doi1, M. Kenjou1,2, M. Nakao1, and Y. Nagata1,2; 1Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan, 2Department of Radiation Oncology, Institute of Biomedical & Health Science, Hiroshima University, Hiroshima, Japan

Purpose/Objective(s): Published organ motion data have been collected from measurements of a limited number of points within the organ, the centroid, or the edge of the organ. These approaches does not consider to the organ deformation. Deformable image registration (DIR) is method for deforming the anatomy of one image set to another, and it is widely used in the field of radiation therapy. We propose a novel quantitative method for evaluating deformed organ motion using DIR. This work presents a quantitative method that evaluates the vector with the location of pixels inside each organ.

Materials/Methods: Two phases from a 4-dimensional computed tomography (4D-CT) dataset at maximum inspiration and expiration were each taken from five patients. The left and right lungs, esophagus, stomach, spinal cord, and liver in the end-expiration phase were manually contoured by a radiation oncologist. The hybrid deformable registration algorithm of RayStation treatment planning system (TPS) was used to deform from end-expiration to end-inspiration phase, and calculated the deformation vector field (DVF). DVFs consist of DVFRL (right-left), DVFAP (anterior-posterior), and DVFSI (superior-inferior) as separate files. Vectors on each direction are stored in separate arrays. Exported DVF data was converted as the Digital Imaging and Communications in Medicine-Radiation Therapy (DICOM RT). The modified DICOM-RT file was then imported into the RayStation TPS. We calculated vector volume histogram (VVH) and Lmax (maximum absolute vector of the organ) to evaluate the each vector for each organ motion. The 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. We also measured respiratory organ motion from the position of the organ centroid in two phases.

Results: VVH enabled us to find the absolute distance and volume of the organ contributing to motion points on the curve. 3D vectors for left and right lungs using VVH (Lmax) were 20.8. ± 5.4 mm and 24.3 ± 5.7 mm, respectively. 3D vectors for left and right lungs using centroid method were 12.7 ± 3.1 mm and 14.5 ± 4.2 mm, respectively. Organ motion using the centroid method was smaller than Lmax using VVH. Other organs were also a similar trend. The evaluation of the centroid method has only one point value, so volumetric organ motion evaluation is impossible. VVH can be used as a means of finding the existence of large organ motion features within structures of interest.

Conclusion: Our proposed VVH method could be easily used for the volumetric evaluation of deformed organ motion.

Author Disclosure: H. Miura: None. Y. Doi: None. M. Kenjou: None.

Hideharu Miura, PhD


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TU_19_3302 - Vector Volume Histogram: New Method to Evaluate Deformed Organ Motion

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