Daily quality assurance, system and procedure-specific commissioning of a bore-based optical surface imaging system...

This study aimed to commission the AlignRT inBore system in Ethos/Halcyon linear accelerator (Linac) systems for surface-guided radiotherapy (SGRT), including developing a soft collision quality assurance (QA) to pass daily AlignRT QA without daily calibration, ensuring compatibility between SGRT and image-guided radiotherapy (IGRT) setups, establishing a baseline performance in AlignRT motion monitoring, and enabling breast DIBH SGRT using manual beam gating with timing accuracy assessment.

The AlignRT inBore system contains three ceiling-mounted camera pods for SGRT setup at the simulation isocenter (sim-ISO), and two ring-mounted camera sets on the spring-supported bore cover for motion monitoring at treatment ISO (txt-ISO), after iterative cone-beam computed tomography (iCBCT) setup. The commissioning includes confirming the ring cameras are outside the radiation fields, verifying IEC coordinate consistency between SGRT and IGRT, and ensuring the compatibility of AlignRT daily QA with collision QA. A dot-array plate was used for SGRT calibration and daily QA at both ISO positions. A soft collision check method was developed to minimize the bore-cover displacement by (1) triggering the collision alarm from the rear side, distant from the front ring cameras, and (2) reproducing the rear bore-cover position by marking before the collision check. Clinical staff were trained for the new daily QA procedure, and the average period between calibrations was calculated over the past 12 months. Additionally, the application-specific breast DIBH SGRT procedure was commissioned through an end-to-end test with manual gating, which was retrospectively evaluated for timing accuracy.

The AlignRT inBore camera ring was moved 2 cm away from the iCBCT field toward the bore front, and the IEC 61217 coordinate system yields consistent SGRT and IGRT setups. AlignRT inBore daily QA can pass using the soft collision procedure without daily calibration, with an average calibration period of 2 weeks, as ad-hoc calibrations are required after open-bore services. The manual gating accuracy is found to be 0.6s ± 0.2s, which can be further reduced if the beam can be proactively turned off before coaching patients to relax from a DIBH.

The commissioning of the AlignRT inBore systems was successfully implemented, including developing and implementing the soft collision QA without daily calibration for 2 weeks, updating inBore camera position (2 cm to the bore front), ensuring SGRT-IGRT couch-shift consistency, establishing a baseline performance (< 0.2 mm drift), and allowing SGRT applications on Ethos/Halcyon systems. The application-specific breast DIBH SGRT procedure with manual beam gating is also commissioned with a new retrospective timing analysis for assessing gating accuracy (0.6s ± 0.2s).