ESTRO 2024 - Abstract Book

S4141

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

ESTRO 2024

diaphragm; and the shortest distance to the chest wall and the lung lobe containing the tumor, if it was located in the lungs.

Results:

The distribution of the margin required for 95% target coverage is plotted in Fig. 1, and the details are summarized in Table 1. The median for all directions was found to be less than 0.5 mm. The absolute value of the 95th percentile varied from 0.836 to 2.316 mm. This implied that to achieve 95% target coverage, 95% of patients needed a margin of approximately 2.32 mm in the SI direction. In the lateral direction, a margin of 0.88 mm was necessary and in the AP direction, a margin of 1.50 mm was necessary.

For 99% target coverage, the margins needed to cover 95% of patients in the SI, lateral and AP directions were approximately 2.79, 1.10 and 1.75 mm, respectively (Table 1).

Margin expansions were correlated with the distance to the diaphragm, with larger prediction errors occurring closer to the diaphragm. The p-value is statistically significant. The fitted slope for inferior and superior margin expansion and the perpendicular distance to the diaphragm is 0.064 mm/cm and 0.009 mm/cm respectively. It implied that for target closer to diaphragm, extra margin might be added in the SI direction. Interfractional changes were larger when lesions were closer to the diaphragm.