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Comparing the Performance of Different Types of Proton Imaging Set-Ups Following a Newly Derived Expression for the Most Likely Path

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N Krah

N Krah1*, I Rinaldi1 , (1) Institute of Nuclear Physics of Lyon, France


TU-C3-GePD-JT-3 (Tuesday, August 1, 2017) 10:30 AM - 11:00 AM Room: Joint Imaging-Therapy ePoster Theater

Purpose: To derive a compact analytical expression for the most likely path (MLP) for different types ofproton imaging set-ups (PIS) and to compare these in terms of intrinsic spatial resolution.

Methods: Multiple Coulomb scattering causes protons to traverse matter on non straight stochastic trajectories leading to spatial blurring in proton imaging. The MLP is a statistical estimate of proton trajectories based on information about position and angle of the protons before entering and after exiting the imaged volume. We have extended and devised the mathematical framework of the MLP. We have introduced a cone beam system of reference to account for the beam geometry. We have further added expressions to describe the uncertainty on the proton position and angle. We solved convolution integrals analytically. We use the average width of the uncertainty envelope around the MLP as a quantitative figure of merit for the intrinsic spatial resolution. Based on this, we compare typical types of PIS.

Results: The spatial resolution of a PIS with passive field and pixel detector is only 5 times lower compared to single tracking device, provided the protons' entry and exit angles are measured accurately. For an uncertainty of +/- 1 degree, single tracking is comparable to a set-up combining pencil beam scanning (PBS) and a pixel detector. PBS in combination with a range telescope is limited by beam spot size for thinner phantoms (<20 cm), but comparable to a passive field coupled to a pixel detector for thick (>20 cm) phantoms.

Conclusion: The derived expression for the MLP is compact and easy to implement numerically. Through numerical parameters in the expression, different kinds of PIS can conveniently be analyzed without the need to re-derive any formulae. The comparison study helps select an appropriate PIS depending on the requirements on spatial and water equivalent thickness resolution.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by a postdoc fellowship of the German Academic Exchange Service (DAAD).

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