Cone Beam Computed Tomography (CBCT)-Based Online Adaptive Radiotherapy for Patients With Metal Implants: An...

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Technology

Background:

• Metal implants (MIs) often exclude patients from cone beam computed tomography (CBCT)-based online adaptive radiotherapy (oART) due to imaging artifact concerns.
• This exclusion limits access to innovative radiotherapy technologies for patients with MIs.

Purpose of the Study:

• To evaluate the institutional experience and feasibility of using an oART workflow in patients with MIs.
• To assess dose accuracy and on-couch treatment time in patients undergoing oART with MIs.
• To investigate the impact of metal artifacts (MAs) on treatment planning and auto-contouring.

Main Methods:

• Retrospective analysis of eight patients (five with MIs, three without) treated on the Ethos system.
• Implementation of dosimetric avoidance through MIs during treatment planning.
• Evaluation of MA override necessity using 3D gamma analysis and dose metrics (Dmax, Dmin, Dmean).
• Assessment of AI-based auto-contouring performance using Dice Similarity Coefficient (DSC) and Maximum Hausdorff Distance (MHD).

Main Results:

• Dosimetric avoidance achieved clinically acceptable plan quality for MIs.
• No significant dose distribution differences were found with or without MA overrides, suggesting overrides are often unnecessary.
• MI and CBCT artifacts impacted auto-contouring but did not impede oART delivery feasibility.
• Contouring times were comparable between patients with and without MIs.
• Good agreement was observed between auto-contoured and manually edited structures, except for the bladder.

Conclusions:

• The proposed workflow demonstrates the feasibility of CBCT-based oART for patients with MIs.
• Institutional experience supports the use of oART in this patient population.
• Further validation may be needed to meet institutional standards and policies.