Reconstructed and Real Proton Radiographs for Image-Guidance in Proton Beam Therapy

Abstract

One of the major challenges to proton beam therapy at this time is the uncertainty of the true range of a clinical treatment proton beam as it traverses the various tissues and organs in a human body. This uncertainty necessitates the addition of greater "margins" to the planning target volume along the direction of the beam to ensure safety and tumor target coverage. Proton radiography holds promise as both an image-guidance method for proton beam therapy and as a means of estimating particle beam range in the clinic. In this brief report, we present some of the first real and reconstructed proton radiographs using our particular system. Our qualitative review of these images indicates that this method has excellent potential as a proton radiography-based image guidance system. Based on the encouraging results of our preliminary work, more rigorous and quantitative analyses will be performed shortly and we shall continue to explore the potential of this approach for addressing the particle beam range uncertainty issue.

Figure 1:

A diagram of our proton radiography method showing the two 2D proton detectors (one proximal and one distal to the patient from the beam perspective) along with a residual energy detector. The residual energy detector carries information about both residual range and anatomical information. The latter information can be used to reconstruct an anatomical image that resembles a megavoltage plain x-ray.

Figure 2:

Reconstructed proton radiograph of the chest. Note that the carina, a commonly used anatomical landmark for set-up purposes is seen clearly on this image.

Figure 3:

Right lateral RPR of the head. Note that the air cavities in the paranasal sinuses are readily seen along with relatively easy identification of the sphenoid sinus, epiglottis and uvula. Note also the relative ease of identification of a previous surgical procedure (a Caldwell-Luc antrostomy) draining the maxillary sinus.

Figure 4.

Actual proton radiograph of a frozen tilapia fish. There is a large gas bubble (dark area) seen in the body due to processing and packaging but bones are clearly visible. In future clinical applications, images such as this would be compared to reconstructed x-rays (DRRs) or proton radiographs (RPRs) to set patients up on the treatment table. The quality of this first effort with our method suggests that such future efforts have real potential.