Room: Exhibit Hall | Forum 5
Purpose: This work aims to verify appropriateness of target volume margin by evaluating inter- and intra-fraction positional variation in visual-guided breath-hold stereotactic body radiation therapy (SBRT) for small hepatocellular carcinoma (HCC).
Methods: Considering reproducibility in actual treatment, we chose expiration breath-holding technique for liver SBRT treatment. The liver patient underwent 2D sim, 3D CT sim (4-time scanning after injecting contrast agent), and treatment after setup with breath-hold CBCT. After CBCT matching, our protocol is to acquire fluoroscopy imaging around internal marker (liver dome or seed marker) before and after the treatment. It compares the placement of internal marker at the same fraction with pre- and post-treatment fluoroscopy imaging, and across the different fractions to investigate intra- and inter-fractional positional variation, presumably corresponding to ITV and PTV margin, respectively. We comprehended 26 liver patients treated by SBRT for this study, which were analyzed and assessed through offline review in Varian Eclipse treatment planning system.
Results: From what we observed, the diaphragm movement tends to be well correlated with the external marker movement from the baseline. To be specific, the positional variation of the diaphragm was measured as 1.5 mm Â± 1.4 mm in the inter-fractional variation and 3.2 mm Â± 2.7 mm in the inter-fractional variation. With 95% confidence interval, the inter-fractional variation ranged from 1.0 mm to 2.0 mm, and inter-fractional variation had 2.1 to 4.2mm, which both criteria did not exceed the ITV and PTV margins except only 1 patient case.
Conclusion: This work demonstrated the relevance of visual-guided expiration breath-hold liver SBRT treatment with respect to margin determination by analyzing the placements of internal marker with fluoroscopy imaging on intra- and inter-fractional basis.