AbstractID: 7844 Title: Evaluation of internal lung motion for gated therapy using magnetic resonance
imaging (MRI)
In a commercial respiratory-gating system, the position of an external skin marker was
used to synchronize radiation treatment with respiration. The aim of this research was to
test the correlation of motions between the marker and internal lung or tumor motion.
Magnetic resonance (MR) imaging was chosen for this aim because of the greater
temporal resolution and flexibility of imaging plane compared to X-ray CT. MR images
were acquired along sagittal planes using a fast-gradient-echo sequence with ~0.5s/image
and 100 images per cine-image series. An image registration algorithm was developed to
track the movement of pulmonary vessels as a surrogate for the lung motion in the
anterior/posterior (AP) and superior/inferior (SI) directions. Another algorithm was
developed to track the AP motion of the skin surface at different locations along the SI
direction. The correlation between the vessel tracks with the skin-surface motion were
tested at each skin location. Results showed the vessels’ motions correlated with the
skin surface motion. However, the degree and uncertainty of the correlation depended on
vessel and skin marker locations. Skin movement at the most inferior locations near the
umbilicus had the strongest correlation with the vessel motion. In addition, the
relationship between the skin surface movement and vessel motion may change
depending on breathing pattern. A range of vessel positions could be associated with one
single skin surface position, implying that margins for the tumor motion may not be
reduced significantly even with the gating technique.
Research partially supported by Varian Medical Systems.