ESTRO 2024 - Abstract Book

S4280

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

(3) The fraction of time during simulated RPM gate-ON where the internal marker centroid CC position was outside the optimal internal gating level defined from the planning CT was 12.8 ± 11.2% (> 0 mm out), 6.1 ± 6.5% (> 1 mm) and 2.4 ± 3.3% (> 2 mm), see example in Fig. 1.

Table 1. Cranio-caudal motion during 4DCT and pre-treatment CBCT

4DCT (mm)

CBCT individual cycles (mm)

CBCT total motion range (mm)

CC motion (mean ± SD)

Full motion

11.9 ± 4.5

14.6 ± 4.4

17.9 ±4.3

Within 50th percentile

4.5 ± 2.6

4.3 ± 1.8

5.1 ± 1.8

Difference full motion vs. 4DCT

-

3.1 ± 3.6

6.1 ±3.7

Difference 50th percentile vs. 4DCT

-

0.0± 2.1

1.5 ±1.7

Conclusion:

Valuable verification data were retrospectively extracted from CBCT projections. Real-time implementation is feasible.

(1) Due to motion blurring, online manual marker match was uncertain but acceptable errors typically below 2mm (maximum 3.1 mm) were observed.

(2) Respiratory exhale gating with a 50% duty cycle markedly reduced both motion amplitude and motion variation.

(3) Acceptable consistency between external and internal gating windows was observed with only limited motion occurring outside the intended internal 50% gating level during external gate-ON.