Respiratory Motion Management For Radiation Therapy

Date(s) - 06/25/2015
2:00 pm - 5:00 pm

Ashley Smith, PhD candidate

Radiotherapy motion management is important when tumor movement is present due to respiration.  One approach to motion management is respiratory gating, which synchronizes radiation delivery with respiration.  A temperature based respiration sensor was developed that does not require abdominal movement like commonly used external markers.  The sensor tracks breathing cycles by measuring the temperature of inspiratory and expiratory air, so it can be used with forced shallow breathing (FSB) or thermoplastic body mask immobilization.  The temperature sensor was used to track breathing cycles for five volunteers using FSB, and compared to simultaneously recorded signals from an external marker.  Temperature sensor performance was tested in CT, MR, and linear accelerator environments.  The sensor effect on image quality was evaluated for CT and MR.

The temperature sensor successfully recorded breathing cycles for all volunteers, while the external marker had one failure.  Temperature sensor signal in CT and MR environments was similar to background signal; however it is recommended the sensor be placed outside the linear accelerator radiation field.  Temperature signals were obtained without deterioration of CT or MR images.  These results indicate this device is suitable for respiratory gating, and an improvement to external markers.

Another approach to motion management is to use flattening filter free (FFF) beams to reduce beam on time, which aids in breath hold techniques and reduces changes over time in breathing patterns.  The interplay effect with FFF beams was investigated using an ionization chamber array on a moving platform to simulate respiratory motion.  Measured dose distributions were compared to planned dose for patient plans using gamma analysis and percent of pixels within 5% and 10% of planned dose.  The impact of the interplay effect was observed on dose distributions; however deviations were not influenced by high FFF dose rate.  FFF plans were also evaluated for lateral targets with homogeneity and conformality indices to compare central and off-axis geometry (OAG).  It was shown FFF beams can be used in OAG without dosimetric compromise.

This research contributed to respiratory management techniques with an improvement to respiratory gating sensors and by verifying FFF has a role in motion management.