ESTRO 2024 - Abstract Book

S4018

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

Fig. 2: The absolute displacements over all participants are depicted for all five regions of interest, where the interquartile range is shown as the box and the median is represented by the black line. Intrafraction displacement in the DSPS is determined from scans of both volunteers (n=12) and patients (n=5), while interfraction displacement in the Posicast is determined solely from scans of patients (n=50). Intrafraction displacement was exclusively determined in the DSPS and calculated after three different time intervals: 5, 10, and 30 minutes. The intrafraction displacement after 5 minutes is determined from scans of both volunteers (n=12) and patients (n=5), whereas the intrafraction displacement after 10 and 30 minutes is only determined from scans of volunteers (n=12). Our study showed that the use of DSPS masks led to a significant reduction of the interfraction displacements in all considered regions, except for vertebrae C4-C6, compared to Posicast masks (Fig. 2). For both masks, except for the Posicast in the shoulders region, the median interfraction displacement between weeks and between days was < 3 mm. For the DSPS mask, the median intrafraction displacement was < 2 mm, for all regions and all time intervals. An increase in intrafraction motion was observed with extended time intervals of 30 minutes compared to time intervals of 5 and 10 minutes.

Conclusion:

Our results show that for DSPS Prominent masks, repositioning accuracy and motion reduction was comparable to the Posicast. The DSPS performed slightly better in reducing setup variation but in case online setup correction is used, this is not clinically relevant. Intrafraction motion, which was only available for DSPS Prominent mask, was found to be small, but we observed an increase in intrafraction motion with prolonged time intervals of 30 minutes. This should be taken into consideration when using masks in MR-linac treatments, which typically involve longer treatment durations.

Keywords: positioning systems, MRI; motion

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