Room: AAPM ePoster Library
New parallel plate ionisation chambers with large radii are commercially available for capturing most of the radial dose in the proton beam; this is known as Bragg peak chamber. The aim of this work is to quantify the dose correction factors of two commercially available chambers at different depth in a water phantom using Monte Carlo simulation.
The Monte Carlo simulation is performed with GEANT4 and two Bragg peak chambers are used in the simulation - IBA Stingray and PTW TN34070. The materials and the dimensions of the chambers are publicly available. The chambers are placed at various depth in a water phantom in step of 1 centimetre during the simulation. The dose correction factor, defined as the ratio of the dose scored in the chamber to the dose scored in an infinitely wide detector, are scored across the depth. The proton gantry was previously simulated and validated with Hitachi's beam data. The dose correction factor was calculated for 220 MeV protons, both in the presence and absence of range shifter.
Our preliminary result shows that both chambers do capture at least 98% of the radial dose for 220 MeV protons across all depths. The correction factor increases with increasing depth as the secondary electrons are more energetic when the protons first entered the water phantom. IBA stingray results in a noisier data and result due to a smaller chamber depth of 1 mm compared to 2 mm for TN34070.
Both chambers do not require correction factor for high energy proton beam of 220 MeV and the data collected can be input into Treatment Planning System right away. Similar analysis will be performed for all energies and more chambers in future work.