On the interplay effect for moving targets treated with the CyberKnife static tracking system. (October 2021)

• Record Type: Journal Article
• Authors: Zeverino, Michele; Jia, Yihan; Charosky, Leo; Bourhis, Jean; Bochud, Francois O.; Moeckli, Raphael
• Is Part Of: Physica medica. Volume 90(2021)
• Page Start: 30
• Page End: 39
• Publication Date: 2021-10
• Subjects: Interplay effect -- CyberKnife static tracking technique -- Lung SBRT -- Gafchromic EBT3; Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2021.08.016
• Languages: English
• ISSNs: 1120-1797

Abstract

Highlights: The Monitor Unit per beam has an impact on the interplay effect in CK treatments. The interplay effect was observed for both small and large respiration motions. The ITV approach does not always guarantee an optimal GTV coverage. Large Monitor Unit per beam allows for an optimal GTV coverage. Abstract: 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.