Session Item

An in-bore surface scanning system to monitor patients in the closed-bore linac Halcyon (Varian Medical Systems) has recently become available, AlignRT InBore (VisionRT Ltd.). We treated 4 patients in deep-inspiration breath-hold (DIBH) and assessed inter and intra fraction motion and workflow efficiency.

Four left-sided breast cancer patients were treated in DIBH on Halcyon using a triple partial arc VMAT technique with simultaneous integrated boost (SIB) for 21 fractions. Setup was performed with the ceiling mounted AlignRT system and patients were shifted into the Halcyon bore. A manual switch to the AlignRT InBore system was required for our research system. At the treatment isocenter, AlignRT InBore monitored the breast surface and patients performed video-coached breath-holds, figure 1. Delivery was manually interrupted when the patients left the breath-hold window (± 3mm, 3°). Portal images were acquired during delivery using framegrabber hardware and software (iTools, Varian Medical Systems) at gantry angle 130°. Inter fraction, intra fraction and intra-breath-hold motion were extracted from surface, CBCT and portal image data. The efficiency of the surface guided workflow was assessed by collecting setup time, time at the isocenter and total fraction duration from both AlignRT as Record and Verify timestamp information.

A total of 64 complete fractions were available for analysis. Inter fraction systematic (Σ) and random (σ) setup errors were Σ =1.0mm,  σ =1.2  mm for the AP, Σ =1.3mm, σ =1.8 mm for the SI and Σ =1.1mm, σ =1.7 mm for the LR axis. The mean intra fraction errors were 0.0 ± 1.0 mm for the “AP” axis (linear combination of the AP and LR component) and 0.4 ± 1.0 mm for the SI axis as detected on portal images, see figure 2. Intra-breath-hold motion was limited to median 1 mm for the AP, 1.3mm for the SI and 0.6 mm for the LR axis. Median total fraction duration was 10 min 1 sec which includes a mean 2 minutes of idle time (figure 1) to switch from the patient setup to the InBore AlignRT system. A median 5 min 15 sec was spent at the treatment isocenter (including CBCT acquisition, position verification and VMAT delivery). 92% of all fractions were completed in 4 breath-holds of mean 25 sec duration.

Full surface guided DIBH workflows using both AlignRT for patient setup as AlignRT InBore  on the Halcyon linac proved efficient with good inter and intra fraction reproducibility.