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Moving Targets in External Versus Internal Motion Tracking

R Holla1,2*, D Khanna1 , (1) Department of Physics, Karunya Institute of Technology and Sciences, Coimbatore - 641 114, India, (2) Department of Medical Physics, Amrita Institute of Medical Sciences, Amrita Vishwa Vidyapeetham, Kochi, India


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To determine the differences in Internal Target Volume (ITV) generated using external and internal motion tracking for moving targets in 4D CT acquisition.

Methods: Two commercially available respiratory gating systems used in this study were AZ-733V Anzai Medical Co.Ltd, Japan (external) and Smart Device-Less 4D,GE Medical Systems, Chicago, USA (internal). The study was performed for target motions in Anterior-Posterior (AP), Lateral, and Superior-Inferior (S-I) directions using CIRS dynamic phantom (Computerized Imaging Reference Systems Inc., Norfolk,USA). Images of the phantom with the target moving in COS4 motion was acquired with different amplitudes of the external surrogate. Maximum Intensity Projection images (MIP) of 10 phase binned image sets were generated. ITVs were delineated on the 4D CT images.

Results: For the target motion in AP direction from 1 mm to 5 mm with 15 mm in S-I direction for all the variable surrogate amplitudes ranging from 5 mm to 25 mm excursions, the absolute volume of the delineated ITV was 11.73 cc ± 0.48 cc for external motion tracking system whereas it was 13.18 cc ± 0.99 cc for internal tracking system with an absolute percent difference of 12.1% ± 3.8%. Whereas for the same motions in lateral directions, the differences were 12.1 cc ± 0.58 cc and 13.3 cc ± 1 cc for both 4D techniques respectively with the absolute percent difference of 10.2% ± 3%. For the target motions with high excursions (≥ 10 mm in S-I, ≥ 3 mm Lateral) differences in the delineated ITVs were statistically significant(P<0.04). However, for low excursions of the target motion, no significant difference in the ITVs were observed (P>0.06).

Conclusion: When the target motion exceeds 3mm in A-P and L-R directions with S-I more than 10mm, external tracking is the choice due to its accuracy in reproducing the absolute target volume.


Gating, Respiration, Target Localization



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