ESTRO 2024 - Abstract Book

S3105

Physics - Autosegmentation

ESTRO 2024

(Hero Imaging AB, Umeå, Sweden) [4]. We calculated the Dice Similarity Coefficient (DSC) as a measure of overlap. Using the true positive and true negative pixels of a segmented image (defined by histopathology), we also calculated a pixel-based sensitivity and specificity measure for the individual lesion. For each segmentation algorithm we thus had one measure per lesion, which we summarized by calculating the median values for the DSC, sensitivity, and specificity measures. The Wilcoxon matched-pairs signed rank test was used for comparison between methods. All statistical analyses were performed using SPSS 28.0 (IBM Corp, Armonk, NY, USA), with the significance level set at 0.05.

Results:

The gross tumor volumes (GTVs) obtained from lower SUV values, for example SUV=2 exhibited higher median sensitivity (93%), indicating greater coverage of the histopathology volume. However, the mentioned SUV value also leads to low median specificity (55%) and DSC of 0.13. This is due to the overestimation of volume, which when applied to radiotherapy could lead to increased exposure of healthy tissues. For both the absolute and relative threshold methods, the obtained GTVs from cut-off value of SUV 4.5, SUV max 40% and SUV max 50% showed no statistically significant differences compared to the reference volume. The derived GTVs from the adaptive threshold method demonstrated the median sensitivity of 78%, specificity of 79% and DSC value of 0.29, where the GTV was statistically significantly larger than the GTV of histopathology. Our results indicate that the adaptive threshold method may not be the best approach for precisely defining intraprostatic lesions. In the multi-level Otsu threshold method, the GTV obtained from Otsu2 had a median sensitivity of 61% and the specificity and DSC of this method were 85% and 0.37, respectively. When compared to the reference volume, the GTV derived from this method demonstrated a significant difference. GTV Otsu3 showed the median sensitivity of 29%, specificity of 96% and DSC of 0.35. Although GTV Otsu2 displayed higher sensitivity and DSC, it had lower specificity values in comparison with GTV Otsu3 . Additionally, there was no statistically significant difference between the GTV Otsu3 and the reference volume. More detailed information about the methods can be found in table1.