Determination of Integral Depth Dose in Proton Pencil Beam Using Plane-parallel Ionization Chambers

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Proton therapy utilizes pencil beam scanning for precise dose delivery.
• Accurate dosimetry is essential for effective proton therapy.
• Detector characteristics influence the accuracy of dose measurements.

Purpose of the Study:

• To determine integral depth-dose curves in proton pencil beam scanning.
• To assess the geometric collection efficiency of various detector diameters.
• To compare different ionization chambers for proton dosimetry.

Main Methods:

• Utilized the Varian ProBeam Compact spot scanning system.
• Acquired integral depth-dose curves using 8-cm and 15-cm PTW Bragg peak chambers, a 12-cm IBA Giraffe chamber, and an 8-cm PTW PeakFinder.
• Compared geometric collection efficiency using a 15-cm chamber as the reference detector.

Main Results:

• The 15-cm PTW Bragg peak chamber (34089) yielded the highest integral depth-dose curves.
• PTW 34089 demonstrated superior geometric collection efficiency compared to other detectors.
• Increased detector diameter correlated with improved collection efficiency.

Conclusions:

• Larger plane-parallel ionization chambers enhance geometric collection efficiency.
• This improvement is particularly significant at intermediate depths and high-energy proton beams.
• Optimizing detector size is key for accurate proton dosimetry.