Clinical characterization of a proton beam continuous uniform scanning system with dose layer stacking

Area of Science:

• Medical Physics
• Radiation Oncology
• Particle Therapy

Background:

• Clinical proton therapy requires precise beam delivery systems.
• Existing guidance for uniform scanning system characterization is limited.
• The Midwest Proton Radiotherapy Institute implemented a new gantry-based system.

Purpose of the Study:

• To describe the testing and characterization methods for a clinical uniform scanning proton beam delivery system.
• To report the dosimetric characteristics of radiation fields produced by this system.
• To provide guidance for similar system commissioning.

Main Methods:

• Commissioning of a gantry-mounted proton beam delivery system with continuous uniform scanning and dose layer stacking.
• Measurement of transverse and longitudinal dose distributions, penumbra, and absolute dose.
• Utilized multielement ion chamber arrays, small-volume ion chambers, and radiographic films for relative dosimetry.
• Employed calibrated ion chambers, thermoluminescent, and alanine detectors for absolute dose measurements.

Main Results:

• The system delivers proton beams with field sizes up to 30 cm diameter and ranges up to 27 cm in water.
• Dose layer stacking enables spread-out Bragg peaks with uniform modulation up to 15 cm.
• Achieved lateral and longitudinal dose uniformity of 2.5% or better for clinical field sizes and ranges.
• Transverse penumbra widths showed improvement over double scattering techniques.
• Absolute dose measurements agreed within 5% across different detector types.

Conclusions:

• The commissioned uniform scanning proton beam delivery system meets clinical requirements for precise dose distribution.
• The system offers enhanced beam characteristics, including improved penumbra and dose uniformity.
• The reported methods and data serve as a valuable resource for future proton therapy system commissioning.