Spirometer-guided breath-hold breast VMAT verified with portal images and surface tracking

Background and purpose: Fast rotating closed-bore gantry linacs are ideally suited for breath-hold treatments due to reduced imaging and delivery times. We evaluated the reproducibility and stability of spirometer-guided breath-hold breast treatments, using intra-bore surface monitoring and portal imaging on Halcyon (Varian Medical Systems). Materials and methods: Seven left-sided breast cancer patients were treated in breath-hold using the SDX spirometer (Dyn'R) with an integrated boost volumetric arc protocol on Halcyon. A dual depth-camera surface scanning system monitored the left breast. The interfraction, intrafraction and intrabreath-hold motion was determined in the anterior-posterior (AP) and superior-inferior (SI) direction. Portal images (PI), acquired at a tangential gantry angle were manually registered to the planning-CT to determine inter- and intrafraction breath-hold errors for the SI and tangential-anterior-posterior (AP) axis. Correlations between PI and surface imaging deviations were investigated. To evaluate workflow efficiency, the total time and the number of breath-holds were recorded. Results: Systematic and random variability of breath-hold amplitude was below 0.7 mm for the AP and below 1.2 mm for the SI component as detected by surface monitoring (N = 130). Systematic and random errors retrieved from portal images (N = 140) were below 1.2 mm for the AP and 2.1 mm for SI axis. A limited correlation was found between PI and surface monitoring deviations for both the SI and AP axes (R-2 = 0.27/0.38, p < 0.01). 75% of fractions were completed using four breath-holds and 82% within 10 min. Conclusion: Surface imaging indicated spirometer-guided breath-hold VMAT breast radiotherapy can be accurately and quickly performed on a closed-bore gantry linac. Intra-bore surface scanning proved a valuable technique for monitoring breathing motion in closed-bore systems. (C) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

This study evaluated the reproducibility and stability of breath-hold breast treatments on a closed-bore gantry linac, showing minimal systematic and random variability in breath-hold amplitude. There was a limited correlation between portal images and surface monitoring deviations.