Abstract
The purpose of this study was to assess the performance of structure‐guided deformable image registration (SG‐DIR) relative to rigid registration and DIR using TG‐132 recommendations. This assessment was performed for image registration of treatment planning computed tomography (CT) and magnetic resonance imaging (MRI) scans with Primovist® contrast agent acquired post stereotactic body radiation therapy (SBRT). SBRT treatment planning CT scans and posttreatment Primovist® MRI scans were obtained for 14 patients. The liver was delineated on both sets of images and matching anatomical landmarks were chosen by a radiation oncologist. Rigid registration, DIR, and two types of SG‐DIR (using liver contours only; and using liver structures along with anatomical landmarks) were performed for each set of scans. TG‐132 recommended metrics were estimated which included Dice Similarity Coefficient (DSC), Mean Distance to Agreement (MDA), Target Registration Error (TRE), and Jacobian determinant. Statistical analysis was performed using Wilcoxon Signed Rank test. The median (range) DSC for rigid registration was 0.88 (0.77–0.89), 0.89 (0.81–0.93) for DIR, and 0.90 (0.86–0.94) for both types of SG‐DIR tested in this study. The median MDA was 4.8 mm (3.7–6.8 mm) for rigid registration, 3.4 mm (2.4–8.7 mm) for DIR, 3.2 mm (2.0–5.2 mm) for SG‐DIR where liver structures were used to guide the registration, and 2.8 mm (2.1–4.2 mm) for the SG‐DIR where liver structures and anatomical landmarks were used to guide the registration. The median TRE for rigid registration was 7.2 mm (0.5–23 mm), 6.8 mm (0.7–30.7 mm) for DIR, 6.1 mm (1.1–20.5 mm) for the SG‐DIR guided by only the liver structures, and 4.1 mm (0.8–19.7 mm) for SG‐DIR guided by liver contours and anatomical landmarks. The SG‐DIR shows higher liver conformality as per TG‐132 metrics and lowest TRE compared to rigid registration and DIR in Velocity AI software for the purpose of registering treatment planning CT and post‐SBRT MRI for the liver region. It was found that TRE decreases when liver contours and corresponding anatomical landmarks guide SG‐DIR.
Highlights
Stereotactic Body Radiation Therapy (SBRT) is an ablative technique characterized by the high dose delivered in one to five fractions with either the same or greater biologically effective dose as conventional radiotherapy.[1]
There was a significant difference between the two types of structure‐guided deformable image registration (SG‐DIR) and rigid registration (P = 0.001), as well as between rigid and DIR (P = 0.005), and between SG‐DIRliver+landmarks and DIR (P = 0.007) with respect to Dice Similarity Coefficient (DSC)
This study evaluated the performance of SG‐DIR for the liver structure and its internal segments with respect to rigid registration and DIR in Velocity AI software
Summary
Stereotactic Body Radiation Therapy (SBRT) is an ablative technique characterized by the high dose delivered in one to five fractions with either the same or greater biologically effective dose as conventional radiotherapy.[1]. Child‐Pugh score is often utilized in order to evaluate the liver dysfunction using several markers of liver injury including biochemical and clinical, the use as a predictor for the risk of radiation‐induced liver damage is arbitrary and somewhat limited as it does not provide any regional‐volumetric information on compromised liver function. Gadolinium‐ethoxybenzyl‐diethylenetriamine pentaacetic acid (Gd‐EOB‐DTPA) is an MRI contrast agent known as Primovist® (Bayer Pharma AG, Berlin, Germany) that is taken up by hepatocytes, and as a result the assessment of the intensity of liver parenchyma can be correlated to the liver dysfunction.[11] Following contrast administration, Primovist® is distributed into the vascular space during arterial and portal venous phases; subsequently it is taken up by the hepatocytes during the hepatobiliary phase, where an enhancement can be observed on delayed images. Liver parenchyma can be correlated to the liver dysfunction based on decreased signal intensity.[12]
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