Setup error analysis in helical tomotherapy based image-guided radiation therapy treatments.

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Accurate patient positioning is crucial in helical tomotherapy for effective cancer treatment.
• Setup margins are essential to account for systematic and random errors during radiation delivery.

Purpose of the Study:

• To investigate the adequacy of clinical setup margins for various anatomical sites treated with helical tomotherapy.
• To compare calculated margins with clinically used margins to identify potential discrepancies.

Main Methods:

• Analysis of 2686 megavoltage computed tomography images from 102 patients across brain, head and neck, pelvis, lung, and craniospinal irradiation (CSI) sites.
• Calculation of systematic and random errors in translational and rotational directions using the van Herk formula.
• Comparison of calculated setup margins with established clinical margins for each site.

Main Results:

• Clinical margins were adequate for brain, head and neck (H and N), and lung sites.
• Longitudinal margins for brain patients were slightly out of tolerance (0.7 mm).
• Pelvic and CSI sites showed discrepancies, with calculated margins exceeding clinical allowances in certain directions, indicating potential undercoverage.

Conclusions:

• Current clinical setup margins are sufficient for H and N, lung, and brain treatments.
• Helical tomotherapy treatments for pelvis and CSI require re-evaluation of setup margins to ensure adequate coverage and patient safety.
• Site-specific margin adjustments may be necessary to optimize treatment accuracy.