ESTRO 2024 - Abstract Book

S3754

Physics - Image acquisition and processing

ESTRO 2024

registration accuracy was assessed by comparing the absolute shifts obtained from CT and sCT-based registrations. Wilcoxon tests were performed for comparing the matching modalities.

Results:

The study involved 58 intracerebral PTVs, with 34 lesions treated with 1-5 fractions in stereotactic [27Gy (Min-Max: 12Gy-35Gy)] and 24 receiving standard fractionation [40Gy (Min-Max: 23.4Gy-60Gy)]. The analysis reported in Table1 showed a median relative dose difference between the D mean values calculated on CT and those on sCT of -0.27% [IQ range: -0.61%;-0.01%] for PTVs and -0.16% [IQ range: -0.48%; 0.11%] for GTVs. No median dose differences were found for OARs. The most notable D mean differences in the targets (-2.5%) were obtained in a case where part of the body was not reconstructed and the PTV was in the same slice of artifact (Figure1). The mean±standard deviation of the differences between CT-CBCT and sCT-CBCT co-registrations along vertical, longitudinal, and lateral axes were -0.04±0.78mm, 0.13±0.57mm, and 0.17±0.91mm, respectively. Along rotational axes, the differences were -0.17°±0.4° (pitch), 0.01°±0.21° (rotation), and 0.0°±0.16° (roll). Statistical analysis indicated that there were no significant differences in the three translational axes between CT-CBCT and sCT-CBCT co registrations (p-values: 0.549, 0.217, and 0.415, respectively). However, a statistically significant difference was observed for pitch (p-value=0.023), even though the median difference of 0.1° was considered no clinically significant. No differences were found for rotation and roll (p-values: 0.746 and 0.865, respectively).

Table 1: The median and quartile range of the relative dose differences for both targets and OARs.

Figure 1: On the left panel the CT, while on the right the reconstructed sCT displaying a significant hole in the body due to the lack of signal from the metal implant in MRI acquisition. The lesion (red contour) is located within the same region as the artifact.

Conclusion: