ESTRO 2023 - Abstract Book

S1651

Digital Posters

ESTRO 2023

Vertebral column shifts were generally small and were uncorrelated to target shifts ( ρ =0.4566). The median T0 to T_CBCT0 time was 133s [52;1478]. The median resting time of fractions with target shifts below and above 3mm was 143s [52;1478] and 119s [65;405], respectively. A tendency towards smaller intra-fraction target shifts is seen with longer patient resting time (see Figure 2).

Except for a few outliers, when the resting time is at least 3min30sec all intra-fractional target shifts are below 4mm, corresponding to the total PTV margin. Conclusion For some lesions, large intra-fractional shifts are observed. For most lesions, this can be reduced by allowing a longer patient resting time. Except for a few outliers (see Figure 2), a resting time above 3min30s leads to intra-fractional target shifts below 4mm. The observed target shifts were uncorrelated to the shifts of the vertebra.