(Sunday, 7/14/2019) 1:00 PM - 2:00 PM
Room: 301
Purpose: To determine the robustness of using cbDIR of pbMRI to the CT of first HDR fraction with applicators in situ, with the endpoint of generating a high-risk-clinical-target-volume (HRCTV) that can be used for planning purposes.
Methods: Thirty-five patients with locally advanced cervical cancer treated with Tandem and Ovoid (T&O)-based HDR brachytherapy were included. The uterus plus cervix (UPC) structure contoured on pbMRI was deformed using contour-based (cb) and hybrid contour-based (hcb) DIR to the same structure contoured on the CT of first HDR fraction (MIM Software Inc., v6.7 and v6.8). The deformation matrix was used to deform the pbHRCTV, which was then compared with the ground truth HRCTV (gtHRCTV) obtained on the MRI of 1st HDR fraction. Dice Similarity Coefficients (DSC) and Hausdorff Distance (med_HD, max_HD) were used to evaluate the overlap and mismatch at boundaries between the deformed HRCTV and gtHRCTV using both DIR methods. Inter- and intra-user variability was also investigated on a subset of 22 patients and using only cbDIR.
Results: The pbMRI scan was acquired on average 5.9+/-3.8 days before first HDR fraction. Median DSC for UPC was 0.9 (IQR 0.88-0.93) and 0.93 (IQR 0.92-0.94), and for HRCTV was 0.64 (IQR 0.52-0.71) and 0.68 (IQR 0.59-0.72) for cbDIR and hcbDIR, respectively. The median med_HD for UPC was 0.09cm (IQR 0.08-0.1cm) and 0.08cm (IQR 0.06-0.09cm). The median max_HD for HRCTV was 1.37cm (IQR 1.1-2.3cm) and 1.39cm (IQR 1.1-1.6cm) with cbDIR and hcbDIR respectively. The inter-, intra-user, and DSC variability between DIR versions were not statistically significant (p=0.53, p=0.77, p=0.18, respectively).
Conclusion: Contour-based DIR based on uterus/cervix structure is proven to be user independent, improves when hybrid contoured based DIR algorithms are used, and is expected to serve as a good starting point for HRCTV definition for HDR planning in the absence of MRI with applicators in-situ.
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