Technical evaluation of a laser-based optical surface scanning system for prospective and retrospective breathing adapted computed tomography

Abstract

Background. For breathing adapted radiotherapy, the same motion monitoring system can be used for imaging and triggering of the accelerator.

Purpose. To evaluate a new technique for prospective gated computed tomography (CT) and four-dimensional CT (4DCT) using a laser based surface scanning system (Sentinel^™, C-RAD, Uppsala, Sweden). The system was compared to the AZ-733V respiratory gating system (Anzai Medical, Tokyo, Japan) and the Real-Time Position Management System (RPM^™) (Varian Medical Systems, Palo Alto, CA, USA).

Material and methods. Temporal accuracy was evaluated using a moving phantom programmed to move a platform along trajectories following a sin⁶(ωt) function with amplitudes from 6 to 20 mm and periods from 2 to 5 s during 120 s while the motion was recorded. The recorded data was Fourier transformed and the peak area at the fundamental and harmonic frequencies compared to data generated using the same sinusoidal function. For verification of the 4DCT reconstruction process, the phantom was programmed to move along a sinusoidal trajectory. Ten phase series were reconstructed. The distance from the couch to the platform was measured in each image. By fitting the function sin(ωt-φ) to the values measured in the images corresponding to each slice, the phase of each image was verified.

Results and conclusion. In the recorded data, the peak area at the fundamental frequency covered on average 104 ± 4%, 102 ± 4% and 91 ± 27% of the peak area in the generated data for the Sentinel^™, RPM^™ and AZ-733V systems, respectively. All systems managed to resolve both harmonic frequencies. The second experiment showed that all images were sorted into the correct series using breathing data recorded by each system. The systems generated very similar results, however, it is preferable to use the same system both for imaging and treatment.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.