SU-E-J-65: Feasibility Study of Backscatter Imaging for Image-Guided Radiotherapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Technology

Background:

• Accurate tracking of lung tumors during external beam radiation therapy is crucial but limited by current techniques.
• Existing methods struggle with 2D motion, real-time imaging during treatment, axial motion, or increased patient radiation dose.
• Utilizing naturally scattered radiation offers a potential solution to overcome these limitations.

Purpose of the Study:

• To investigate the feasibility of using photon scatter for in situ imaging during external beam radiation delivery.
• To assess the potential of scatter imaging for real-time tumor motion tracking in lung cancer patients.

Main Methods:

• A prototype imager was developed using a Trilogy Linac, pinhole collimator, and computed radiography (CR) plate.
• Two phantoms (solid water and cerrobend) were irradiated with a 6MV beam at 45° and 90° gantry angles.
• Image quality was assessed using contrast-to-noise ratios (CNR) and photon dose was measured with optically-stimulated luminescent (OSLD) detectors.

Main Results:

• Higher contrast-to-noise ratios (CNR) were achieved at a 90° gantry orientation (14.8-18.3) compared to 45° (1.5-5.3).
• The measured CNR at 90° satisfied the Rose criteria for image detectability (CNR > 3-5).
• Image quality is expected to meet detectability criteria with reduced radiation output (200MU) and improved noise reduction strategies.

Conclusions:

• Preliminary findings confirm the feasibility of scatter imaging for in situ monitoring during radiation therapy.
• Further research will focus on developing tomosynthesis imaging capabilities.
• Improving image quality through enhanced shielding and multi-pinhole collimators is planned for future investigations.