Assessing a set of optimal user interface parameters for intensity-modulated proton therapy planning

Area of Science:

• Medical Physics
• Radiation Oncology
• Particle Therapy

Background:

• Spot-scanned proton therapy offers precise dose delivery.
• Optimizing treatment planning parameters is crucial for maximizing therapeutic benefit and minimizing side effects.
• Understanding the impact of dose grid resolution and spot spacing is essential for accurate proton therapy planning.

Purpose of the Study:

• To determine optimal treatment planning parameters for spot-scanned proton therapy.
• To establish the minimal necessary dose grid resolution for accurate proton therapy planning.
• To evaluate the impact of spot spacing on dose homogeneity and conformity.

Main Methods:

• Treatment plans were calculated using varying parameters and dose grid resolutions in a homogeneous phantom.
• Three cubic targets of different sizes (8, 64, 244 cm³) were used.
• Dose profiles, homogeneity, and conformity were analyzed for single-beam proton delivery.

Main Results:

• Comparable dose homogeneity and conformity were achieved when spot layer distance approximated Bragg peak width and lateral spot distance was within 2x spot sigma.
• Larger spot layer distances increased the homogeneity index significantly, especially for larger targets.
• A dose grid resolution of 2-3 mm is necessary to accurately capture steep dose gradients, with maximum deviations below 3% for resolutions up to 6 mm.

Conclusions:

• Optimal spot-scanned proton therapy planning involves specific spot spacing and dose grid resolution.
• Longitudinal spot separation within the Bragg peak width and lateral separation up to 2x spot sigma are adequate for homogeneous phantoms.
• A dose grid resolution of 2-3 mm is critical for precise dose gradient resolution in intensity-modulated proton therapy (IMPT).