2017 - Advancing Surface Based Breath Hold Gated Lung Radiotherapy: Commissioning of a Combined Stereoscopic X-ray and Surface Guided Motion Management System
Presenter(s)
G. C. Baltz, and S. M. Kirsner; Scripps Cancer Center, San Diego, CA
Purpose/Objective(s): A stereotactic X-ray tool is a novel radiotherapy motion management system that integrates surface guidance, thermal imaging, and stereoscopic X-ray imaging. This combination of technologies enables both surface-based intrafraction monitoring and breath hold gating, which can improve target localization compared to conventional gating methods. The purpose of this study was to use the American Association of Physicists in Medicine (AAPM) TG-302 framework to commission two independent ETD systems for performing breath hold gated lung radiotherapy.
Materials/Methods: A series of static and dynamic tests listed in Table 1 were performed using an anthropomorphic thorax phantom placed on a dynamic motion platform. Static tests evaluated localization accuracy and reproducibility compared to CBCT, as well as the impact of reference surface generation on localization. Spatial drift was evaluated during system warmup, typical treatment session duration, and with changing phantom temperature. Dynamic tests were performed with the phantom simulating a breath hold motion pattern and assessed localization accuracy and reproducibility. Finally, end-to-end testing of a simulated breath hold lung stereotactic body radiation therapy (SBRT) treatment was conducted, with both gated and ungated dose measurements being acquired.
Results: The results of the commissioning tests are summarized in Table 1. Static and dynamic localization accuracy both averaged less than 1 mm, with reproducibility within 0.3 mm. An optimal Hounsfield Unit (HU) threshold of -700 for the reference surface contours was demonstrated to provide the best localization accuracy. The maximum spatial drift observed for all tests was less than 1 mm. Congruence among surface guidance, X-ray imaging, and CBCT was within 1 mm. End-to-end testing demonstrated less than a 1% difference between gated and ungated treatment delivery. Both independent ETD systems showed consistently uniform performance across all commissioning tests.
Conclusion: All commissioning tests met the acceptable tolerances outlined in the AAPM TG-302 report. This study demonstrated the ETD system is suitable for performing surface guided based breath hold gated lung SBRT treatments.
Abstract 2017 - Table 1| Static Tests | Results |
| Localization Accuracy | Surface=0.9 mm, X-ray=0.9 mm, CBCT=0.7 mm |
| Localization Reproducibility | 0.3 mm |
| Localization Accuracy vs Reference Surface Selection | Lowest residual error for -700 HU threshold. Agreement of CBCT and X-ray within 0.2 mm |
| Spatial Drift During System Warmup | Maximum Drift of 0.8 mm over 40 mins |
| Spatial Drift During Treatment | Maximum Drift of 0.9 mm over 30 mins |
| Spatial Drift vs Phantom Temperature | Drift < 0.6 mm within 3°C temperature change |
| Dynamic Tests | |
| Localization Accuracy and Reproducibility | 0.3 ± 0.2 mm |
| End-To-End Gated Dose Measurement | Gated dose within 0.9% of ungated |