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Investigation of the Feasibility of Collimating the Proton Pencil Beams for Integrated Depth Dose Measurement

A Darafsheh

A Darafsheh*, W Nie , E Diffenderfer , Y Xie , B Teo , A Kassaee , UNIVERSITY OF PENNSYLVANIA, Philadelphia, Pennsylvania


SU-I-GPD-T-144 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To study the feasibility of using a collimator to reduce the spot size of proton therapy pencil beams in order to measure the integrated percent depth dose using a multi-layer ionization chamber (MLIC) device (Zebra, IBA) having smaller diameter (2.5 cm diameter) collection area compared with standard Bragg peak chambers (12 cm diameter).

Methods: Experimental measurements were performed using the MLIC with and without collimation of the beam (energies in the range 100-210 MeV) using a different collimators with various sizes and materials including aluminum and brass. The measurements were compared with a standard Bragg peak chamber. Monte Carlo (MC) simulations were performed using TOPAS (GEANT 4) to mimic the geometry of the experiments.

Results: The MLIC measurements with collimation do not show the typical integrated percent depth dose (PPD) measurements with Bragg peak chambers for various beam energies and beam collimations, in agreement with MC simulations. This results for most part shows PDDs that resembles measurements along the central axis with small area chambers. This signifies the fact that the collimation of the beam would affect the beam characteristic emanated from proton machine gantry nozzle due to multiple scattering within the collimator and the scattering at the collimator.

Conclusion: Our preliminary results indicate that beam collimation using simple block geometry would reduce the beam size but alters its characteristics (scattering components) from the original beam and hence does not replace the need to use the Bragg peak chambers.

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