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Updated: Oct 20, 2025
Dynamic Lung Tumor Tracking for Stereotactic Ablative Body Radiation Therapy
Published on: June 7, 2015
On the interplay effect for moving targets treated with the CyberKnife static tracking system
Michele Zeverino1, Yihan Jia2, Leo Charosky1
1Institute of Radiation Physics, Lausanne University Hospital and Lausanne University, Lausanne, Switzerland.
Purpose:
To assess the interplay effect amplitude between different planned MU distributions and respiratory patterns in the CyberKnife system when treating moving targets with static tracking technique.
Methods:
Small- and Large-Respiratory Motions (SRM and LRM) differing in amplitude and frequency were simulated in a semi-anthropomorphic dynamic thorax phantom. The interplay effect was evaluated for both respiration motions in terms of GTV coverage and conformity for three plans designed with an increasing range of MU per beam (small, medium and large). Each plan was delivered three times changing the initial beam-on phase to assess the inter-fraction variation. Dose distributions were measured using radiochromic films placed in the GTV axial and sagittal planes.
Results:
Generally, SRM plans gave higher GTV coverage and were less dependent on beam-on phases than LRM plans. For SRM (LRM) plans, the GTV coverage ranged from 95.2% to 99.7% (85.9% to 99.8%). Maximum GTV coverage was found for large MU plans in SRM and for small MU plans in LRM. Minimum GTV coverage was found for medium MU plans for both SRM and LRM. For SRM plans, dose conformity decreased with increasing MU range while the variation was reduced for LRM plans. Large MU plans reduced the inter-fraction variation for SRM and LRM.
Conclusions:
We confirmed the interplay effect between target motion and beam irradiation time for CyberKnife static tracking. Plans with large MU per beam improved the GTV coverage for small motion amplitude and the inter-fraction dose variation for large motion amplitude.
