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. 2012 Nov;39(11):6957-67.
doi: 10.1118/1.4758064.

Implementation and experimental results of 4D tumor tracking using robotic couch

I Buzurovic  1 , Y Yu, M Werner-Wasik, T Biswas, P R Anne, A P Dicker, T K Podder
Affiliations

Implementation and experimental results of 4D tumor tracking using robotic couch

I Buzurovic et al. Med Phys. 2012 Nov.

Abstract

Purpose: This study presents the implementation and experimental results of a novel technique for 4D tumor tracking using a commercially available and commonly used treatment couch and evaluates the tumor tracking accuracy in clinical settings.

Methods: Commercially available couch is capable of positioning the patient accurately; however, currently there is no provision for compensating physiological movement using the treatment couch in real-time. In this paper, a real-time couch tracking control technique is presented together with experimental results in tumor motion compensation in four dimensions (superior-inferior, lateral, anterior-posterior, and time). To implement real-time couch motion for tracking, a novel control system for the treatment couch was developed. The primary functional requirements for this novel technique were: (a) the treatment couch should maintain all previous∕normal features for patient setup and positioning, (b) the new control system should be used as a parallel system when tumor tracking would be deployed, and (c) tracking could be performed in a single direction and∕or concurrently in all three directions of the couch motion (longitudinal, lateral, and vertical). To the authors' best knowledge, the implementation of such technique to a regular treatment couch for tumor tracking has not been reported so far. To evaluate the performance of the tracking couch, we investigated the mechanical characteristics of the system such as system positioning resolution, repeatability, accuracy, and tracking performance. Performance of the tracking system was evaluated using dosimetric test as an endpoint. To investigate the accuracy of real-time tracking in the clinical setting, the existing clinical treatment couch was replaced with our experimental couch and the linear accelerator was used to deliver 3D conformal radiation therapy (3D-CRT) and intensity modulated radiation therapy (IMRT) treatment plans with and without tracking. The results of radiation dose distribution from these two sets of experiments were compared and presented here.

Results: The mechanical accuracies were 0.12, 0.14, and 0.18 mm in X, Y, and Z directions. The repeatability of the desired motion was within ±0.2 mm. The differences of central axis dose between the 3D-CRT stationary plan and two tracking plans with different motion trajectories were 0.21% and 1.19%. The absolute dose differences of both 3D tracking plans comparing to the stationary plan were 1.09% and 1.20%. Comparing the stationary IMRT plan with the tracking IMRT plan, it was observed that the central axis dose difference was -0.87% and the absolute difference of both IMRT plans was 0.55%.

Conclusions: The experimental results revealed that the treatment couch could be successfully used for real-time tumor tracking with a high level of accuracy. It was demonstrated that 4D tumor tracking was feasible using existing couch with implementation of appropriate tracking methodology and with modifications in the control system.

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Figures

Figure 1
Figure 1
Schematic view of ELEKTA Precise Table™: (a) and (b) Internal isometric view, (c) System model: vertical movement in s direction is achieved by motor installed in the holder A. Tabletop movement in ξ and η directions are achieved by two motors sitting bellow the tabletop.
Figure 2
Figure 2
Functional elements of tumor tracking control system; DF: digital filter; SR = ZOH signal reconstruction; DAC: digital to analog converter. The ZOH, or zero-order-hold, represents the effect of the sampling process, where the motor command is updated once per sampling period. The DAC or D-to-A converter converts a 16-bit number to an analog voltage.
Figure 3
Figure 3
(a) The decomposed tumor centroid, (b) couch, and (c) tumor relative motions in absolute coordinate system in the tracking mode. Data show one representative case for breathing cycle of 6 s in X, Y, and Z directions. The trajectories represent real patient tumor motion.
Figure 4
Figure 4
(a) Control system integration parts, (b) ELEKTA Precise Table™ robotic treatment couch—experimental setup with reference coordinate system.
Figure 5
Figure 5
(a) Installation of the encoder to vertical lift motor. Inset shows the adapter and holder for encoder. (b) Installation of the encoder for longitudinal couch motion (X direction). Inset represents the encoder mounting to the existing motor.
Figure 6
Figure 6
(a) Experimental setup: Sun Nuclear programmable 4D phantom on the top of the couch, (b) The metal plate with the hole was fixed on the top of the 4D phantom.
Figure 7
Figure 7
Experimental setup of the tumor motion compensation system.
Figure 8
Figure 8
Couch motion in X and Y direction for the tumor tracking test.
Figure 9
Figure 9
Comparison of the stationary plan with the tracking plan (a) inplane profile, (b) crossplane profile, (c) passing criteria is critical in the high gradient region, (d) 3D dose profile for both plans. Circles denote the dose differences within 1%; stars/crosses denote dose differences higher and lower than 1% for the specific profile.
Figure 10
Figure 10
Comparison of the IMRT plan with the tracking plan (a) inplane profile, (b) crossplane profile, (c) diagonal profile. Circles denote the dose differences within 1%; stars/crosses denote dose differences higher and lower than 1% for the specific profile.
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