Received: 14 November 2022

Revised: 21 February 2023

Accepted: 6 March 2023

DOI: 10.1002/acm2.13971

T E C H N I C A L N OT E

Development of a dynamic motion platform with two
independent drive systems for radiotherapy
Masahide Saito1
Hidekazu Suzuki1

Hideyuki Kawakami2
Toshihiro Suzuki1,3
Koji Ueda1
Hikaru Nemoto1
Naoki Sano1

Hiroshi Onishi1
1
Department of Radiology, University of
Yamanashi, Yamanashi, Japan
2

APEX medical Inc., Tokyo, Japan3

Department of Radiology,
Kasugai-CyberKnife Rehabilitation Hospital,
Yamanashi, Japan
Correspondence
Masahide Saito, Department of Radiology,
University of Yamanashi, 1110 Shimokato,Chuo-city, Yamanashi, 409–3898, Japan.
Email: masahides@yamanashi.ac.jp
Funding information
JSPS KAKENHI, Grant/Award Number:
22K15823

Abstract
Background: There are some motion platforms for radiotherapy quality assurance. However, no platform with two drive systems that can move along threeaxes is available.
Purpose: The purpose of this study is to develop a dynamic motion platform
with two drive systems capable of three-axis motion and to evaluate its motion
performance.
Methods: The developed moving platform had two drive systems that use thesame equipment. Each axis of the platform used can support a maximum loadof 10 kg. The motors for moving the platform in each direction are capableof a drive stroke up to 40 mm. The drive speed is 30 mm/s at maximum load
fluctuation. To evaluate the static positional accuracy of this system with anarbitrary input movement, the XYZ position of each axis was measured using acoordinate measuring machine operating from 0 to 40 mm at 10 mm intervals.
In addition, the accuracy of dynamic motion was verified with Sine waveform
inputs of different patterns to the three axes for approximately 60 s, and they
were compared with the resulting detected signals by SyncTrax.
Results: The two drive systems were successfully operated on three axes byusing independent control systems. For static position, the accuracies were
within 0.2 mm, 0.05 mm, and 0.14 mm for lateral, longitudinal, and vertical directions, respectively. For dynamic motion, the mean absolute errors in the X, Y,
and Z axes between the platform inputs and SyncTrax detected signals were0.14 ± 0.10 mm, 0.16 ± 0.12 mm, and 0.16 ± 0.11 mm, respectively.
Conclusions: A new dynamic platform for radiation therapy with two drive systems capable of three-axis motion was developed, and the positional accuracyof the drive axes was confirmed to be less than 0.2 mm.
KEYWORDS
lung cancer, motion phantom, motion tracking, radiotherapy, two drive system

1

INTRODUCTION

For radiotherapy on organs with respiratory movement,
establishing a validation system before administer-ing treatment is crucial. Traditionally, various dynamic
motion platforms and phantoms have been used to evaluate the effects of respiratory movement, including the
CIRS dynamic phantom,1 which simulates the thorax

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the original work is properly cited.
© 2023 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, LLC on behalf of The American Association of Physicists in Medicine.
J Appl Clin Med Phys. 2023;24:e13971.
https://doi.org/10.1002/acm2.13971

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2 of 6and can read any respiratory waveform, thereby allowing the target area to move in three dimensions. The
CIRS platform can also be validated using an individual phantom and a detector.2 QUASER (Modus Medical
Devices) is another device that has been used for quality
assurance of four-dimensional computed tomography(4DCT) scan techniques in multicenters.3 For this device,a new device that can be used under MR has recently
been introduced.4 In addition, Delta4 Hexa-motion has
been developed as a platform for 3D detectors and isused for the verification of moving objects.5
All phantoms are capable of translational three-axis
movement of the target part; however, they are only
capable of the ventral–dorsal one-axis movement of
the surrogate part. For example, the CIRS phantom iscapable of three-axis translation of the target part withrotation, whereas the surrogate part has only one axisof translation. However, there is no phantom with two
drive systems that can move along three axes, that is,no phantom can also move along three axes for thesurrogate part. The development of such phantoms will
enable dynamic verification under more complex surrogate motions. For example, while tracking a tumor using
a gold marker implanted in the body, if the distance
between the tumor and gold marker is large becauseof the migration of the gold marker6,7 and if the tumor
and gold marker movements are slightly different, aphantom with two drive systems that can reproduce
complex movements is necessary for dynamic verification. In addition, for irradiation using external signals
such as surface-guided radiotherapy (SGRT), the position of the body surface may move slightly in any otherdirection apart from the anterior-posterior.8,9 If a phantom takes three-dimensional movement into account,more accurate dynamic verification may be possible inabove situation.
Therefore, in this study, we developed a dynamic
motion platform with two drive systems capable ofthree-axis motion and evaluated its motion performance.

systems depending on the starting position and movement pattern. Therefore, it is necessary to verify theinterference situation of each axis before use.
Figure 1a presents an overview of the developed
dynamic motion platform. It is characterized by two drive
systems that use the same equipment. The weight ofthe system is 13.4 kg and it is connected to a computer for operation. Each axis of the platform supports
a maximum load of 10 kg. ZABER LMR050A-T3 (Zaber
Technologies Inc., Vancouver, Canada) was used as
the motor for the X-(lateral) and Y-(longitudinal), and
ZABER VSR40A-T3 (Zaber Technologies Inc., Vancouver, Canada) was used as the motor for the Z-axis. Bothmotors were capable of a drive stroke of up to 40 mm,
and the drive speed was 30 mm/s at maximum load fluctuation. Figure 1b shows an overview of the softwaredeveloped to read arbitrary waveforms in CSV format
for the two drive systems. The software works well on
Windows 10 or 11. Static movement is also possible, andany waveform can be continuously read. Arbitrary start
positions can be entered for each axis, and functionalities such as start, pause, and stop can be manuallycontrolled. Respiratory waveforms are displayed in theupper and lower rows for each of the axes, respectively (Figure 1b upper row:Stage-1,Figure 1b lower row:
Stage-2).

2

MATERIALS AND METHODS

2.2

2.1

Dynamic motion platform

We have developed a dynamic motion platform with two
drive systems that is capable of three-axis motion andcan also read arbitrary waveforms. The platform canuse basic mathematical waveforms (Sin and Cos waveforms) and signals extracted from humans at 0.03 ms
intervals. However, these waveforms must be preparedby the user as comma-separated value (CSV) files, andthese files can be loaded up to about 10 h. For singledrive system movements, movements up to ±40 mm canbe realized for all three axes. However, for two drive system movements, the larger the movement, the greater
the possibility of interference between the two drive

Areas of Expertise
THExternal
beamphotons: Motion
management—interfraction
THExternal
beamphotons: Motion
management—intrafraction
TH- External beam- photons: cyberknife
TH- External beam- photons: extracranialstereotactic/SBRT

Static positioning evaluation

This study entailed the verification of the basic positional
behavior of the two drive systems. The measurement
points are shown in Figure 2. A structurally defined
point on the fixed part of Stage 1 was set as themeasurement origin, and the measurement points on
the movable parts of Stage 1 and Stage 2 wereset as M1 and M2, respectively. For M1 and M2, theXYZ position of each axis was measured using acoordinate measuring machine (CRYSTA-PLUS M544,
developed by Mitutoyo, Kanagawa, JAPAN) that operated from 0 to 40 mm at 10 mm intervals. The
measurement accuracy was less than 10 µm in all
directions. Further details are mentioned in the white
paper.10

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2.3

SAITO ET AL.

Dynamic positioning evaluation

In this study, the accuracy of the dynamic movementof the drive system was verified using SyncTraX® FX4(Shimadzu, Kyoto, Japan). SyncTraX® FX4 is the new
system used for tracking irradiation,11 and in recent
years, some technical12,13 and clinical14 evidences havevalidated its efficacy. In this verification, the driving accuracy of only one of the drive systems was tested(Stage-1 only), assuming that both drive systems in theplatform are equivalent in their accuracy because they
have a similar structure. Here, dynamic drive accuracy
was verified by inputting typical sine waveforms with different patterns to all the three axes for approximately
60 s and comparing them with the results detected by
SyncTrax. Three metal markers were placed on the platform and position accuracy was checked on the X-ray
image of the SyncTraX system with a detection cycle ofapproximately 60−70 ms.

F I G U R E 1 Interface of the dynamic motion platform. (a)Platform constructed with motion Stages 1 and 2. (b) Softwaredeveloped for importing waveforms.

3

RESULTS AND DISCUSSION

The actual movement of the dynamic platform is
described in video 1. The two drive systems were successfully operated on three axes by using independent
control systems. Tables 1 and 2 show the driving accuracy results for Stages 1 and 2, respectively. The verticalaxis represents the measurement value obtained by thecoordinate measuring machine, and the horizontal axis
represents the set movement amount of the platform.
For the X-axis, the accuracy was within 0.2 mm when
the platform moved from 0 to 40 mm. However, it wasalso moved systematically with respect to the Y-axis, byapproximately 0.13 mm as the X-axis moved. Solely for
the Y-axis, the same accuracy of 0.05 mm or lower was
confirmed; however, the X-axis was driven with accuracies of 0.08 mm each as the Y-axis moved. As regards
the Z-axis an accuracy of 0.14 mm or lower, with almost
no movement of the other axes, was achieved. The
aforementioned characteristics were common to Stage
1 and Stage 2.
The results of the dynamic movement verificationis shown in Figure 3: Figure 3a is the respiratory
waveform input to the dynamic platform, Figure 3bis the signal detected by SyncTrax, and Figure 3cis the difference between the two waveforms. The
mean absolute errors in the X, Y, and Z axes were0.14 ± 0.10, 0.16 ± 0.12, and 0.16 ± 0.11 mm,
respectively.
Figure 4 shows the coordinate systems employedin this study. The gray lines denote the exact coordinate system, and the black lines show the coordinate system of the platform. The results indicatethat the X-Y plane was slightly tilted while maintaining a right angle. However, because the magnitude of movement on the Y-axis was approximately
0.15 mm when the platform was moved 10 mm on the
X-axis.
As a comparison with other commercially available products in terms of accuracy, Table 3 shows
the accuracy values of the CIRS phantom, QUASAR
phantom and our platform. The accuracy achievedin this study is confirmed to be comparable to thatof available products. However, it should be kept inmind that these measurement conditions are slightly
different.
It should be noted that the maximum speed of ourplatform is 30 mm/s. Therefore, it is difficult to reproduce
conditions such coughing; it is suitable for verification only under free-breathing conditions. Furthermore,
direct irradiation of approximately 500 Gy to the platformbody (circuit board) may cause system malfunctions.
Therefore, especially during non-coplanar beam validation, caution must be used to avoid exposure to large
amounts of radiation.

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3 of 6

4 of 6F I G U R E 2 Details of the moving platform
structure. (a) Top and (b) front views. The
measurement points are denoted as M1 andM2 based on the origin point in (a).

TA B L E 1

Result of the driving accuracy for Stage 1.

TA B L E 2Result of the driving accuracy for Stage 2.

Magnitude of
movement [mm]Measured value [mm]Move axis
X

YZ

Magnitude of
movement [mm]Measured value [mm]Move axis
X

Y

Z

0

X-axis

0.000

0.000

0.000

0

X-axis

0.000

0.000

Y-axis

0.000

0.000

0.000

Y-axis

0.000

0.000

0.000

Z-axis

0.000

0.000

0.000

Z-axis

0.000

0.000

0.000

X-axis

9.938

0.090

0.000

Y-axis−0.138

9.964

0.000

Z-axis

0.000

0.000

10.102

X-axis20.009

0.221

0.000

10

20

30

40

X-axis10.189

0.133

0.000

Y-axis0.018

10.0070.000

Z-axis−0.0020.009

10.132

X-axis20.196

0.261

0.000

Y-axis

−0.09419.9490.000

Y-axis−0.30819.9300.000

Z-axis−0.0060.010

20.113Z-axis−0.0040.002

20.095

X-axis30.147

0.416

0.000

Y-axis−0.26830.0190.000

Z-axis−0.0070.031

30.132

X-axis40.149

0.509

0.000

Y-axis−0.38040.017

Z-axis−0.010

0.040

10

0.000

20

X-axis

29.961

0.293

0.000

Y-axis−0.39629.9700.000

Z-axis−0.0120.018

30.091

X-axis

39.986

0.466

0.000

0.000

Y-axis−0.54339.9310.000

40.133Z-axis−0.0190.046

40.084The phantom developed in this study may be usedin the following practical cases. Examples of typicalplatform uses are shown in Figure 5. First, Figure 5ashows one example to simulate the movements of agold marker and tumor inside the body. This phantom
may be useful for verification of tumor tracking whenthe marker cannot be implanted at the intended position (i.e., locations away from the tumor, or locations that
do not seem to correlate with movement, etc.). In addition, Figure 5b shows another example to simulate themovements of the body surface and tumor; however, thebody surface has a particularly complex motion not only

30

40

in the anterior-posterior direction, but in various otherdirections as well.
One limitation of this study is that it does not consider the effects of the installation and fixing accuracyof the actual installation jig or the effects of the load
capacity (up to 10 kg, according to the specifications).
Further, specific verification regarding rotational movements was not performed. Therefore, in actual use, theaccuracy achieved may be worse than the results presented herein, and further verification according to thesetting conditions will be necessary.

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SAITO ET AL.

F I G U R E 3 Results of dynamic movement verification: (a) platform input values (in X, Y, and Z directions). (b) SyncTrax detection signals ineach direction. (c) Difference between them.

TA B L E 3 Comparison of the driving accuracy of our platform
with those of other motion phantom.
Motion phantom

Accuracy

CIRS dynamic motion
phantom1±0.10 mm (Motion Accuracy)

QUASAR™ MRI4D
Motion Phantom2±0.25 mm (Motion Precision, [alongZ-axis])Our platform±0.20 mm (Static and Motion Accuracy[average value], X, Y, Z-axis)

4

CONCLUSION

A novel dynamic platform for radiation therapy having
two drive systems and capable of three-axis motion wasdeveloped in this study; the positional accuracy of thedrive axes was confirmed to be less than 0.2 mm.

F I G U R E 4 Coordinate system used in this study. The grayarrows show the actual measurement coordinates, and the blackarrows show the platform coordinates. The red dashed line shows
the systematic shift in the Y-direction when the platform was moved
10 mm in the X-direction.

AU T H O R C O N T R I B U T I O N S
Study conception and design: Masahide Saito, Hideyuki
Kawakami, Naoki Sano, and Hiroshi Onishi. Acquisitionof data: Masahide Saito, Hideyuki Kawakami, Toshihiro Suzuki, Hidekazu Suzuki, and Koji Ueda. Analysis
and interpretation of data: Masahide Saito, Hideyuki

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5 of 66 of 6F I G U R E 5 Examples of the platform use:(a) Example to simulate the movement of agold marker inside the body and the
movement of a tumor. (b) Example to simulate
the movement of the body surface and the
movement of a tumor.

Kawakami and Hikaru Nemoto. Drafting of manuscript:
M.S., and Hiroshi Onishi. Critical revision: Masahide
Saito, Hideyuki Kawakami Naoki Sano, and Hiroshi
Onishi.
AC K N OW L E D G M E N T S
This work was supported by JSPS KAKENHI Grant
Number 22K15823.
C O N F L I C T O F I N T E R E S T S TAT E M E N T
This study was supported by joint research with APEX
Medical Inc. and Hamano Engineering.
DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available from the corresponding author upon reasonable
request.
ORCID
Masahide Saito
https://orcid.org/0000-0002-8636-4045
Toshihiro Suzuki
https://orcid.org/0000-0003-0414-5218
Hikaru Nemoto
https://orcid.org/0000-0001-6540-2906

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S U P P O R T I N G I N F O R M AT I O N
Additional supporting information can be found online
in the Supporting Information section at the end of thisarticle.

How to cite this article: Saito M, Kawakami H,
Suzuki T, et al. Development of a dynamic motion
platform with two independent drive systems forradiotherapy. J Appl Clin Med Phys.
2023;24:e13971.
https://doi.org/10.1002/acm2.13971

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