AbstractID: 6988 Title: Respiratory Gated Radiation Therapy with Active Breathing
Control
There are two approaches for reducing margin for respiratory motion. With active
breathing control (ABC), patient’s breathing is continuously monitored with a flow
meter. A valve is activated to temporarily suspend breathing as the patient is instructed
to reach a pre-defined lung volume. Breath-hold is typically applied at a moderately
large lung volume to reduce the irradiated lung mass, and for 10 sec or more to improve
operation efficiency. With ABC, the tumor and organs are immobilized such that a
margin of ~3mm, can be used. Unfortunately, patients who cannot repeatedly hold their
breath for 10 sec or more are not suitable for the procedure. In the respiratory gating
approach, the patient breathes freely and the motion of surface markers is monitored by
infra-red cameras as a surrogate respiratory signal. Radiation is turned on only when the
respiratory signal is within a pre-defined gating window. As a result, the patient is not
discomforted by lengthy breath-hold. However, verbal coaching is needed to minimize
the variability of the breathing pattern, and without immobilization, a margin of ~5 mm is
used. It is clear that the combination of ABC and respiratory gating offers an improved
approach. Organ motion can be immobilized at any lung volume even when the patient
can only maintain breath-hold for 4 to 5 sec. The combined approach is being tested in
conjunction with a Elekta machine with new radiation gating capability. Dosimetric
results will be presented.
Supported in part by NCI CA76182 and Elekta Oncology Systems.