Analysis of the interplay effect in lung stereotactic ablative radiation therapy based on both breathing motion and plan characteristics

Asmaa M. Ali, Jason B. Greenwood*, Mohammad Varasteh , Sergio Esteve, Prakash Jeevanandam, Fabian Göpfert, Denise M. Irvine, Alan R. Hounsell, Conor K. McGarry

*Corresponding author for this work

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Stereotactic ablative radiotherapy (SABR) is susceptible to challenges for tumours affected by intrafraction organ motion. This study aims to investigate the effect of breathing characteristics and plan complexity on the interplay effect.

A patient-specific interplay effect evaluation was performed using in-house software with an alpha version of the treatment planning verification software Verisoft (PTW-Freiburg, Germany) on VMAT plans. The OCTAVIUS 4D phantom was used to acquire the static dose distribution, and the simulation approach was utilised to generate the moving dose distribution. The influence of plan complexity, PTV size, number of breaths, and motion amplitudes on the interplay effect were examined. The dose distribution of two extreme phases—end-inhale and end-exhale—was considered using the gamma criteria of 2%/2 mm for the interplay effect evaluation.

A strong correlation was found between the motion amplitude (p < 0.001) and the NBs (p < 0.001) with the gamma-passing rate. No correlation was found between the gamma-passing rate and the PTV size or plan complexity.

The simulation tool allowed the analysis of a large number of breathing traces, demonstrating how free-breathing patients, suspected of high interplay, could be selected for other motion management solutions. The simulated cases showed strong interplay effects for long breathing periods with extended motion amplitudes in a small group of patients.

Original languageEnglish
Article numbere75
Number of pages11
JournalJournal of Radiotherapy in Practice
Publication statusPublished - 21 Sept 2023


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