Clinical Analysis of Rotational-Translational Error Coupling in 3DoF Versus 6DoF CBCT Couch Corrections:A...

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-Guided Therapy

Background:

• Three-degree-of-freedom (3DOF) and six-degree-of-freedom (6DOF) couches improve tumor localization accuracy in radiotherapy.
• The interplay between rotational and translational error corrections requires further clarification for optimizing treatment strategies.

Purpose of the Study:

• To evaluate setup errors in nasopharyngeal carcinoma (NPC), esophageal cancer (EC), and rectal cancer (RC) using cone-beam computed tomography (CBCT).
• To elucidate the coupling between rotational and translational errors to optimize setup correction strategies for 3DOF couches.

Main Methods:

• Cross-sectional study involving 46 NPC, 48 EC, and 23 RC patients.
• Offline registration of pre-treatment CBCT and planning CT images using bony registration in 3DOF and 6DOF modes (1,720 total registrations).
• Analysis of setup errors to investigate the relationship between rotational and translational deviations.

Main Results:

• Significant vertical registration errors were observed in NPC and EC patients (P < 0.05), but not in RC patients (P > 0.05).
• Strong linear correlations were found between 3DOF and 6DOF vector directions (R²NPC = 0.597, R²EC = 0.798, R²RC = 0.781, P<0.01).
• Significant coupling correlations between rotational and translational errors were identified, particularly for NPC (pitch vs. ΔVrt: r = -0.893) and EC (pitch vs. ΔLng: r = 0.544).

Conclusions:

• A site-specific coupling exists between rotational and translational errors in radiotherapy setup.
• Performing site-specific rotational adjustments followed by translation is crucial when rotational errors exceed thresholds.
• This strategy enhances radiotherapy precision and patient safety, especially in non-6DOF couch environments.