Prog Med Phys.  2013 Jun;24(2):85-91.

Development of Video Image-Guided Setup (VIGS) System for Tomotherapy: Preliminary Study

• Kim JS
• Ju SG
• Hong CS
• Jeon J
• Son K
• Shin JS
• Shin E
• Ahn SH
• Han Y
• Choi DH

Abstract

At present, megavoltage computed tomography (MVCT) is the only method used to correct the position of tomotherapy patients. MVCT produces extra radiation, in addition to the radiation used for treatment, and repositioning also takes up much of the total treatment time. To address these issues, we suggest the use of a video image-guided setup (VIGS) system for correcting the position of tomotherapy patients. We developed an in-house program to correct the exact position of patients using two orthogonal images obtained from two video cameras installed at 90degrees and fastened inside the tomotherapy gantry. The system is programmed to make automatic registration possible with the use of edge detection of the user-defined region of interest (ROI). A head-and-neck patient is then simulated using a humanoid phantom. After taking the computed tomography (CT) image, tomotherapy planning is performed. To mimic a clinical treatment course, we used an immobilization device to position the phantom on the tomotherapy couch and, using MVCT, corrected its position to match the one captured when the treatment was planned. Video images of the corrected position were used as reference images for the VIGS system. First, the position was repeatedly corrected 10 times using MVCT, and based on the saved reference video image, the patient position was then corrected 10 times using the VIGS method. Thereafter, the results of the two correction methods were compared. The results demonstrated that patient positioning using a video-imaging method (41.7+/-11.2 seconds) significantly reduces the overall time of the MVCT method (420+/-6 seconds) (p<0.05). However, there was no meaningful difference in accuracy between the two methods (x=0.11 mm, y=0.27 mm, z=0.58 mm, p>0.05). Because VIGS provides a more accurate result and reduces the required time, compared with the MVCT method, it is expected to manage the overall tomotherapy treatment process more efficiently.

Keyword

Tomotherapy; Image guidance; Patient positioning

MeSH Terms

Humans
Hydrazines
Immobilization
Patient Positioning
Hydrazines

Figure

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  Fig. 1. Comparison of treatment process using (a) MVCT and (b) VIGS (Video Image-Guided Setup). The treatment process is shown for the typical patient using the first video image obtained after the MVCT correction as a reference image.

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  Fig. 2. In the closed-tomotherapy gantry, two cameras that meet at right angles are installed to take the patient's orthogonal image. It is important to install the cameras so that they do not block the slit through which radiation is emitted.

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  Fig. 3. The GUI program for the camera calibration. The empty couch image (anterior-posterior image) with 4 holes is acquired with the camera 1 (on Fig. 2) and in-house made fixed pattern on gantry ring image is also capture with the camera 2 (on Fig. 2). With pre-known distance between holes, the calibration program calculates the spatial transformation between original image and each calibration image and defines the number of pixels on the distance in millimeters per pixel for the correction.

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  Fig. 4. The GUI program that corrects the patient position using two orthogonal video images. Fully automatic registration and a manual procedure are available. Both registration procedures were programmed using Matlab.

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