Room: AAPM ePoster Library
Purpose: The developed proton-tissue-equivalent materials (ProTEMs) have the proton relative-stopping power of corresponded human tissue. To evaluate the scattering powers of ProTEMs, measured lateral profiles of single spot for the pencil-beam-scanning (PBS) protons are compared with Monte Carlo (MC) simulations using ICRP reference human tissue compositions.
Methods: The lateral scattering power for ProTEMs; soft tissue, bone, and lung, are investigated by measuring lateral profiles of PBS protons at no air gaps from the beam exit over five energies. A 5.0cm thick block with 10cmx10cm cross-section was manufactured for each ProTEM. The 2D images were acquired by using the Lynx optical dosimeter, located at the beam isocenter. Extracted 1D profiles in two directions were analyzed by a Gaussian fit for obtaining the spot-size. The MC simulations with the corresponded human issue for each irradiated ProTEM were conducted by using the PHITS code. The source model for its initial spot size and energy spectra used MC code was first commissioned to properly reproduce in-air spot-size passing no material and a 5.0cm water. The commissioned source model was then used to simulate the measured spot-size by using the reference human tissue of each ProTEM.
Results: Both measured and computed spot-sizes decrease as a function of energy for three ProTEMs. Measured spot-sizes of irradiated all ProTEMs are within 0.1mm with respect to the calculated ones for all energies. Large spot sizes are generated by both ProTEM and reference bone in comparison with water, while small size was seen for ProTEM and reference lung tissues.
Conclusion: The trend of spot-size of measured profiles for each ProTEMs is within 2% to calculated spot-size of corresponded human tissue that indicates the each ProTEM has similar scattering power that its corresponded human tissue. Further study on the trend of spot-size as a function of air-gap will be conducted.