(Wednesday, 8/1/2018) 10:00 AM - 10:30 AM
Room: Exhibit Hall | Forum 5
Purpose: To assess the setup uncertainty in hypofractionated liver radiation treatment using automatic image registration-based image guidance and to estimate PTV margins in the absence of in-room CT imaging.
Methods: A total of 917 pre-treatment daily in-room CT images were collected from 69 patients that received hypofractionated radiation therapy to the liver with inspiration breath-hold technique. For each treatment, the daily CT was initially aligned to the planning CT using automatic image registration based on the anatomical traits of the liver. After the initial alignment, manual shift corrections were determined based on a visual inspection of the two CTs, and the corrections were applied to shift the patient to the attending physician-approved treatment position. By taking this final position as the gold-standard setup, systematic and random uncertainties in the initial automatic setup were quantified. These uncertainties were then used to deduce the margins.
Results: The median composite initial setup uncertainty was 1.1 mm (0-24.3 mm), and 38 % of treatment fractions required a manual shift correction of 3 mm or greater. The systematic uncertainty was 1.5, 1.1, and 2.4 mm in the anterior-posterior (AP), left-right (LR), and superior-inferior (SI) direction, respectively. The random uncertainty was 2.2, 1.9, and 2.2 mm in the AP, LR, and SI direction, respectively. The recommended PTV margins to be used in the absence of in-room CT imaging was 5.3, 3.5, and 5.1 mm in the AP, LR, and SI direction, respectively.
Conclusion: This study confirms that manual shift correction based on soft-tissue alignment is significant in the treatment of the abdominal region. The study emphasizes the benefit of in-room CT imaging, especially for dose escalation and normal tissue sparing for hypofractionated liver radiation therapy, by demonstrating that in-room CT contributes to PTV margin reduction by 4 to 5 mm.
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