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. 2019 Jul;20(7):128-134.
doi: 10.1002/acm2.12667. Epub 2019 Jun 20.

Development of twist-correction system for radiotherapy of head and neck cancer patients

Hidetoshi Shimizu  1   2 , Koji Sasaki  2 , Takahiro Aoyama  1 , Shigeru Matsushima  3 , Taiki Isomura  1 , Hiroshi Fukuma  4 , Hiroyuki Tachibana  1 , Takeshi Kodaira  1
Affiliations

Development of twist-correction system for radiotherapy of head and neck cancer patients

Hidetoshi Shimizu et al. J Appl Clin Med Phys. 2019 Jul.

Abstract

To propose a concept for correcting the twist between the head and neck and the body frequently occurring in radiotherapy patients and to develop a prototype device for achieving this. Furthermore, the operational accuracy of this device under no load was evaluated. We devised a concept for correcting the twist of patients by adjustment of the three rotation (pitch, roll, and yaw) angles in two independent plates connected by a joint (fulcrum). The two plates (head and neck plate and body plate) rotate around the fulcrum by adjusting screws under each of them. A prototype device was created to materialize this concept. First, after all adjusting screws were set to the zero position, the rotation angle of each plate was measured by a digital goniometer. Repeatability was evaluated by performing 20 repeated measurements. Next, to confirm the rotational accuracy of each plate of the prototype device, the calculated rotation angles for 20 combinations of patterns of traveled distances of the adjusting screws were compared with those measured by the digital goniometer and cone-beam computed tomography (CT). The repeatability (standard deviation: SD) of the pitch, roll, and yaw angles of the head and neck plate was 0.04°, 0.05°, and 0.03°, and the repeatability (SD) of the body plate was 0.05°, 0.04°, and 0.04°, respectively. The mean differences ± SD between the calculated and measured pitch, roll, and yaw angles for the head and neck plate with the digital goniometer were 0.00 ± 0.06°, -0.01 ± 0.06°, and -0.04 ± 0.04°, respectively. The differences for the body plate were -0.03 ± 0.04°, 0.03 ± 0.05°, and 0.02 ± 0.05°, respectively. Results of the cone-beam CT were similar to those of the digital goniometer. The prototype device exhibited good performance regarding the rotational accuracy and repeatability under no load. The clinical implementation of this concept is expected to reduce the residual error of the patient position due to the twist.

Keywords: 6DoF; IMRT; head and neck; twist-correction.

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Conflict of interest statement

No conflict of interest.

Figures

Figure 1
Figure 1
The prototype of the twist‐correction device: (a) and (b) the positions of the angle‐adjusting screws (HNS, HNR, HNL, BR, BL, and BI), (c) an inferior‐side view, (d) a right‐side view, and (e) the joint (fulcrum) of the head and neck (HN) plate and the body plate
Figure 2
Figure 2
Enlarged image of the two types of adjusting screws: (a) and (b). The arrows show the scale on the surface of the screw
Figure 3
Figure 3
Relationship between the rotation angle and the traveled distance of the adjusting screw: (a) pitch, (b) roll, and (c) yaw angles
Figure 4
Figure 4
Photograph of the cubic phantoms installed to confirm the rotational accuracy of the prototype device by Varian cone‐beam computed tomography imaging system. The tungsten sphere of 1 mm at diameter was inserted into each acrylic cube
Figure 5
Figure 5
The differences between the calculated and measured rotation angles in the combinations of 20 patterns for the adjusting screws: (a) for the HN plate with the digital goniometer, (b) for the body plate with the digital goniometer, (c) for the HN plate with cone‐beam computed tomography, and (d) for the body plate with the cone‐beam computed tomography
See this image and copyright information in PMC

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