Treatment plans optimization for contrast-enhanced synchrotron stereotactic radiotherapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy

Background:

• Synchrotron stereotactic radiotherapy (SSRT) utilizes high-Z elements and monochromatic X-rays for localized tumor dose enhancement.
• Iodine-enhanced SSRT, using iodinated contrast agents, has been successfully developed and is progressing to clinical trials.

Purpose of the Study:

• To investigate the impact of contrast agent type, beam quality, irradiation geometry, and beam weighting on SSRT treatment plans.
• To optimize SSRT treatment planning for enhanced efficacy and reduced side effects.

Main Methods:

• Theoretical dosimetry simulations using the MCNPX particle transport code on an idealized head phantom.
• Investigation of various contrast agents (iodine, gadolinium, gold), beam qualities (monochromatic synchrotron, polychromatic tube, linear accelerator), and irradiation geometries.
• Optimization of beam weighting and application to patient-specific CT data.

Main Results:

• An 80 keV monochromatic X-ray beam offers a good compromise for iodine-enhanced SSRT, yielding a dose enhancement factor of approximately 2 with superior bone sparing compared to lower energies.
• Monochromatic X-rays significantly reduce bone dose compared to polychromatic X-rays from conventional tubes.
• Iodine-enhanced SSRT demonstrates superior sparing of healthy brain tissue versus high-energy treatments, and beam weighting optimization improves plans for off-centered tumors.

Conclusions:

• Realistic clinical plans for low-energy monochromatic X-ray contrast-enhanced radiotherapy are feasible.
• This approach is suitable for initial clinical trials targeting brain metastases with homogeneous iodine uptake.