Deformable 3D dosimetry of MRI-tracking radiotherapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Anatomical motion during breathing can lead to inaccurate radiation dose delivery.
• Magnetic Resonance Imaging-linear accelerators (MRI-linacs) enable real-time imaging for motion compensation.
• Risks exist in MRI-guided tracking radiotherapy due to potential lag or unaddressed organ deformation.

Purpose of the Study:

• To evaluate the feasibility and accuracy of polymer gel dosimetry for assessing radiation dose in moving and deforming targets within MRI-guided radiotherapy.
• To investigate the impact of compression on polymer gel dose response.
• To validate the tracking performance of an MRI-linac using gel and film dosimetry.

Main Methods:

• Spherical polymer gel phantoms were compressed to assess deformation effects on dose response.
• End-to-end experiments were conducted on a prototype MRI-linac using moving and breathing anthropomorphic phantoms with gel dosimeters.
• Radiochromic film dosimeters were used for secondary validation of dose profiles.

Main Results:

• Compression did not significantly affect the dose response of the polymer gels.
• Gel dosimetry measurements closely matched film dosimetry results in both tracked and non-tracked scenarios.
• End-to-end experiments demonstrated improved dose conformity with MRI-guided tracking radiotherapy.

Conclusions:

• Deformable 3D gel dosimeters are suitable for evaluating the geometric accuracy of tracked treatments on MRI-linacs.
• Polymer gel dosimetry offers a high-resolution 3D dose profile for moving and deforming targets.
• Care must be taken to address oxygen inhibition effects at the edges of gel dosimeters in anthropomorphic phantoms.