A Phantom Validation of Deep Inspiration Breath Hold with Triggered Imaging for Stereotactic Body Radiotherapy of Mobile Tumors In the Thorax and Abdomen
Abstract
Purpose
Deep inspiration breath hold (DIBH) using surface guidance can be useful as a motion management strategy but for high dose, steep gradient modalities such as SBRT, it is important to compliment it with active motion management using triggered imaging of the internal target. In this study, we designed and validated a phantom study that accomplished this.
Methods
Surface guided radiotherapy (SGRT) from LAP LUNA 3D and Triggered Imaging from Varian TrueBeam were utilized. A cosine trajectory with a 1cm amplitude and a DIBH amplitude of 2cm with a 20s breath hold was programed for a lung phantom target trajectory representative of a DIBH patient on the CIRS motion platform. At CT simulation, the primary image and reference breath-hold surface were acquired. The target fiducial was contoured and a Triggered-Fiducial-1mm contour generated, namely the contoured fiducial with a 1mm margin. A 2-arc VMAT plan was generated and delivered on the Varian TrueBeam. Initial setup was with respect to breath-hold CBCT which was then verified using surface guidance. Triggered imaging was set with image acquisition every 45 degrees. To ensure that a triggered image is acquired at the beginning of each breath-hold, beam off, rather than beam hold was implemented each time the BH duration elapsed before the planned MU could be delivered.
Results
Initial setup using BH CBCT agreed well when compared with setup using SGRT DIBH to within 0.04cm, 0.04cm, -0.11cm in the vertical, longitudinal, and lateral directions and -0.3deg, 0.2deg, and -1.0deg in yaw, pitch and roll respectively. The entire treatment was delivered successfully with the acquired triggered images showing the visible fiducial always inside the Triggered-Fiducial-1mm contour and the SGRT parameters within threshold throughout.
Conclusion
The presented phantom validation has enabled us to successfully treat our first liver SBRT patient utilizing DIBH complemented with triggered imaging.