Commissioning of a combined stereoscopic x-ray and surface guided radiotherapy system for performing breath hold gated lung radiotherapy.

backgroundExacTrac Dynamic (ETD) is a novel patient positioning and motion management system for radiation therapy that combines surface guidance, thermal imaging, and stereoscopic x-rays for image guidance. This combination of technology enables both intrafraction monitoring and surface-based breath hold gating capabilities. PURPOSE: 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.

methodsA series of static and dynamic tests were performed using an anthropomorphic thorax phantom placed on a dynamic motion platform. Static tests included localization accuracy and reproducibility, and the impact of reference surface selection on localization. Spatial drift was evaluated during system warmup, during typical treatment session duration, and with changing temperature. Dynamic tests assessed localization accuracy and reproducibility, as well as gating latency. Finally, end-to-end testing of a simulated breath hold lung stereotactic body radiation therapy (SBRT) treatment was performed, with both gated and ungated dose measurements being acquired.

resultsStatic and dynamic localization accuracy averaged less than 1 mm, with reproducibility within 0.4 mm. An optimal Hounsfield Unit (HU) threshold of-700 for the reference surface contour was demonstrated to have the best localization accuracy. The maximum observed spatial drift for all tests was less than 1 mm. Congruence between surface guidance, x-ray imaging, and CBCT were all within 1 mm. Mean beam on and off latency averaged 1023 and 527.1 ms, respectively. End-to-end testing demonstrated less than 1% dose difference between gated and non-gated treatment delivery. The independent ETD systems demonstrated consistent performance across all commissioning tests.

conclusionsAll commissioning tests were within acceptable tolerances published in the AAPM TG-302 report. This study demonstrated that the ETD system is suitable for performing surface-guided breath hold gated lung SBRT treatments.