• Simulation: Uncertainty in residual range is dominated by intrinsic fluctuations through water.. • Due to fluctuations in energy loss, the protons arrive at the detector with a range r
Trang 1Dependence of pulse height on range:
Approximately linear (from a convolution of light yield with photon collection efficiency)
• Simulation:
Uncertainty in residual range is dominated by intrinsic fluctuations through water
• Due to fluctuations in energy loss, the
protons arrive at the detector with a range resolution of 2-2.5 mm
• Perfect Detector:
Resolution determined only by Intrinsic
fluctuations through water
• Range reconstruction uses total energy output
as well as position-weighted outputs
• Plot shows one quadrant of 20x20x10
cm detector
• The intrinsic resolution from the water is
approximately 2.5 mm
Proton Residual Range Reconstruction and Impact on Dose to the Target Object in a Proton Imaging System
Purpose: Proton radiography would be the most direct method of image guidance for proton therapy We aimed to develop a high-performance, low-cost proton radiography system based on
well-established fast scintillator technology We also aimed to achieve the lower dose to the patient, relative to equivalent x-ray images, that is possible with proton imaging This dose advantage relies
on a precise reconstruction of the residual ranges of individual protons traversing the patient, and a strategy to maintain low residual range during the scan
Methodology: We have developed an algorithm to reconstruct proton residual range with our proton imaging system We tested this algorithm with simulated data, and compared simulated data
with test beam data from our actual detector We also used simulations to understand the effect of residual range on dose to the patient
Results: We find that for protons traversing 20 cm (water-equivalent) of material, our detector achieves a residual range resolution, for individual protons, dominated by the intrinsic range
fluctuations through the material Therefore, as individual protons are averaged to form the image, the intrinsic fluctuations are the major factor in the total dose to the patient We also find that the
dose to the patient is lower for lower residual ranges
E DeJongh, F DeJongh, V Rykalin ProtonVDA Inc
J Welsh Stritch School of Medicine Loyola University - Chicago
M Pankuch Northwestern Medicine Chicago Proton Center
quantized from RF accelerator system
are single proton events
two-proton events
from protons sitting on a tail of a proton 10 nsec earlier
fall below 0.06V
Transverse position from two position-weighted Range detector outputs
Northwestern:
Scanning pencil beam at ultra-low intensity
0 0.5 1 1.5 2 2.5 3 3.5
Residual Range (cm)
Calculation, for a fixed final residual range resolution in image:
• Vertical axis: Relative dose to target object
• Horizontal axis: Residual range
Includes nuclear effects
Simulation of uncertainty on reconstruction of transverse position
of track
Determines final image sharpness
Real