Effect of patient setup errors on simultaneously integrated boost head and neck IMRT treatment plans

Area of Science:

• Radiation Oncology
• Medical Physics
• Clinical Dosimetry

Background:

• Head-and-neck cancer treatment often utilizes simultaneous integrated boost-intensity-modulated radiation therapy (SIB-IMRT).
• Accurate dose delivery is critical for treatment efficacy and minimizing toxicity.
• Setup errors can significantly impact dose delivery in radiation therapy.

Purpose of the Study:

• To determine dose delivery errors resulting from random and systematic setup errors in head-and-neck SIB-IMRT.
• To assess the dosimetric impact of various simulated setup error magnitudes.

Main Methods:

• Re-evaluated dose distributions from 24 head-and-neck SIB-IMRT patients.
• Simulated random setup errors (sigma = 1, 3, 5 mm) and systematic errors (Sigma = 1.5, 3.0 mm).
• Evaluated dose to GTV, CTV, nodes, cord, and parotid, with and without a 3-mm PTV margin.

Main Results:

• SIB-IMRT plans were more sensitive to systematic than random setup errors.
• Systematic errors (Sigma = 3.0 mm) caused >3% dose error in 50% of plans.
• Combined errors (sigma = Sigma = 3.0 mm) led to >3% dose error in over 50% of plans.
• A 3-mm PTV margin reduced >5% dose deviations to 5.4% of plans.

Conclusions:

• Reducing systematic setup errors is essential for improving head-and-neck SIB-IMRT accuracy.
• Evaluating dose using PTVs improves agreement with target doses under simulated setup errors.
• PTV margins may be smaller for SIB-IMRT head-and-neck patients compared to 3D-CRT.