Systematic set-up errors for IMRT in the head and neck region: effect on dose distribution

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Intensity-modulated radiation therapy (IMRT) may be more sensitive to patient positioning errors than conventional treatments.
• Concerns exist regarding the impact of systematic set-up errors on IMRT dose distributions.

Purpose of the Study:

• Evaluate the International Commission on Radiation Units and Measurements (ICRU) method for systematic set-up errors in IMRT.
• Compare the effects of the ICRU method on dose distribution in IMRT versus conventional treatments.

Main Methods:

• Applied ICRU-defined planning margins to clinical target volumes and spinal cords for three head and neck patients.
• Simulated set-up errors in six IMRT and three conventional treatment plans.
• Analyzed the impact of set-up errors on dose distribution using physical dose parameters.

Main Results:

• The ICRU method demonstrated satisfactory performance for both IMRT and conventional treatments.
• No significant difference was observed in the effectiveness of the ICRU method between the two treatment techniques.
• Target volume sensitivity to set-up errors depends on treatment plan quality; critical organ effects depend on dose gradient sharpness.

Conclusions:

• The ICRU method for managing set-up errors is generally effective for IMRT and conventional radiotherapy.
• Plan quality and dose gradient steepness influence the impact of set-up errors on target and organs at risk.
• The ICRU method presents challenges for incorporating adjacent organs at risk with parallel structures.