Poster - Thur Eve - 34: Evaluation of 4DCT on the GE lightspeed RT16 using a respiratory motion phantom

This study encompasses several quality assurance tests performed during the commissioning of the 4DCT technique on the GE Lightspeed RT16 CT scanner for SBRT at the Cancer Centre of Southeastern Ontario. The main purpose is to assess geometric position and volumetric delineation accuracy. A limited assessment of the image quality and dose was performed.

The Quasar Respiratory Motion with a modified cylindrical moving insert was used. Clinically relevant breathing motion patterns analyzed were: sinusoidal with amplitudes of 5 and 15 mm, and periods of 3 s and 6 s; and a typical respiratory breathing motion of amplitude of 10 mm and period of 4 s.

Couch position errors were ≤ 1mm for maximum inspiration (Ph 0%) and expiration (Ph 50%) phases. errors were greater for mid-phases, the largest being 8.1 mm (Ph 20%) for the typical respiratory pattern. MIP volume deviations ranged from -0.3 to -3.2 cm³ ; the greater deviations corresponding to larger amplitudes and shorter periods, where image distortion is also more severe. SUP and INF position error of MIP on coronal views for the lung window and level used in our centre ranged from -0.07 to 1.4 mm and from -0.04 to 1 mm on the SUP and INF direction respectively. The dose from a 4DCT acquisition was 2.8 times higher than in a free breading scan, while the noise was comparable.

Although higher doses are obtained, 4DCT is a sufficiently accurate approach that could be used safely to account for breathing motion.