Evaluating Proton Dose and Associated Range Uncertainty Using Daily Cone-Beam CT.

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Science

Background:

• Proton therapy offers precise dose delivery, but accurate range determination is crucial.
• Cone-beam CT (CBCT) is increasingly used for image guidance in proton therapy.
• Evaluating range uncertainties from CBCT is essential for ensuring treatment accuracy.

Purpose of the Study:

• To quantitatively assess range uncertainties in proton dose calculations using daily CBCT images compared to conventional CT.
• To validate the accuracy of CBCT-based range and dose calculations using a measurement-based technique.
• To determine the suitability of CBCT for daily dose validation in proton therapy.

Main Methods:

• Developed a measurement-based technique to evaluate range uncertainties.
• Created intensity-modulated proton therapy (IMPT) plans for head and thorax phantoms.
• Measured dose distributions using a 2D ion chamber array and compared them with CT and CBCT calculations.
• Recalculated IMPT plans for a thymoma patient on multiple CBCT and CT datasets.

Main Results:

• Head phantom: CBCT range uncertainty was 1.2% vs. 0.5% for CT.
• Thorax phantom: CBCT range uncertainty was 2.1% vs. 0.8% for CT.
• Thymoma patient: Breath-hold uncertainty caused up to 8 mm anatomy change, impacting dose calculation.

Conclusions:

• The developed measurement-based method is sensitive for evaluating range uncertainties.
• CBCT-based dose calculations show acceptable accuracy for daily validation in specific proton therapy cases.
• CBCT can be a valuable tool for adaptive proton therapy planning and quality assurance.