Scatter imaging during lung stereotactic body radiation therapy characterized with phantom studies

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Image Guidance

Background:

• Stereotactic body radiation therapy (SBRT) requires precise tumor targeting.
• Markerless tracking of lung tumors during SBRT is challenging.
• Scatter imaging utilizes scattered photons to create images of the treated volume.

Purpose of the Study:

• To evaluate scatter imaging for markerless lung tumor tracking during SBRT.
• To assess image quality and tracking accuracy in static and dynamic phantom studies.

Main Methods:

• A scatter-imaging camera with a CsI flat-panel detector and pinhole collimator was used.
• Phantoms with simulated lung tumors (2.1-3.0 cm) were irradiated with megavoltage photons.
• Tumor position was tracked during sinusoidal motion in open-field, DCA, and VMAT deliveries.

Main Results:

• Anatomical features were identifiable with a contrast-to-noise ratio of 4.4 for a 2.1 cm tumor at 10 MU.
• Tracking accuracy showed root-mean-square errors of 0.8 mm (open field), 1.2 mm (DCA), and 2.9 mm (VMAT).
• Tracking precision reached sub-millimeter levels, though modulation impacted accuracy.

Conclusions:

• Scatter imaging is a promising technique for markerless lung tumor tracking in SBRT.
• It can provide quality images at low, clinically relevant doses (10 MU) without additional imaging dose.
• The technique demonstrates potential for precise tumor localization during radiation therapy.