Reconstructed and real proton radiographs for image-guidance in proton beam therapy

Miller, Chelsea; Altoos, Basel; DeJongh, Ethan A.; Pankuch, Mark; DeJongh, Don F.; Rykalin, V.; Ordoñez, C.E.; Karonis, Nicholas T.; Winans, John R.; Coutrakon, G.; Welsh, James S.

doi:10.1007/s13566-019-00376-0

Cited by 17 publications

(13 citation statements)

References 2 publications

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“…While we have evaluated pRad for a pediatric-sized phantom in this study, pRad also works for adult-sized phantoms and larger objects. Although more protons are lost in nuclear interactions and increased multiple scattering will gradually degrade spatial resolution, initial studies indicate the system provides similar WEPL accuracy in thicker objects [29]. Similar precision can be achieved by increasing the number of protons to compensate for the larger range straggling in thicker patients.…”

Section: Discussionmentioning

confidence: 99%

Fast in situ image reconstruction for proton radiography

et al. 2019

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Objective Proton beam therapy is an emerging modality for cancer treatment that, compared to X-ray radiation therapy, promises to provide better dose delivery to clinical targets with lower doses to normal tissues. Crucial to accurate treatment planning and dose delivery is knowledge of the water equivalent path length (WEPL) of each ray, or pencil beam, from the skin to every point in the target. For protons, this length is estimated from relative stopping power based on X-ray Hounsfield units. Unfortunately, such estimates lead to 3 to 4% uncertainties in the proton range prediction. Therefore, protons in the Bragg peak may overshoot (or undershoot) the desired stopping depth in the target causing tissue damage beyond the target volume. Recent studies indicate that tomographic imaging using protons has the potential to provide directly more accurate measurement of RSPs with significantly lower radiation dose than X-rays. We are currently working on a proton radiography system that promises to provide accurate two-dimensional (2D) images of WEPL values for protons that pass through the body. These will be suitable for positioning and range verification in daily treatments. In this study, we demonstrate that this system is capable of rapidly achieving such accurate images in clinically meaningful times. Methods We have developed a software platform to characterize the potential performance of the prototype proton radiography system. We use Geant4 to simulate raw data detected by the device. An especially written software -pRadwas written to process these data as they are received and uses iterative methods to generate radiographs. The software has been designed to generate a radiograph from a few million protons in under a minute after receiving the first proton from the device. We used a head phantom with known chemical compositions that could be modeled quite accurately in Geant4 simulations of proton radiographs. The radiographs are displayed as pixelated WEPL values displayed on a 2D gray scale image of WEPL values. Results Rapid radiograph reconstruction of 3D phantoms using simulated proton pencil beams have been achieved with our software platform. On a modest desktop computer with a single central processing unit (CPU) and a single graphics processing unit (GPU), it takes about 11 s to reconstruct images using iterative linear algorithms to reconstruct a radiograph from 7.6 million protons. For the radiographic reconstructions of the head phantom described here, the mean WEPL errors, in the proton radiograph using a large majority of the pixels in the complete image were less than 1 mm when compared to images obtained without proton scattering and without detector resolution included.

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Section: Discussionmentioning

confidence: 99%

Fast in situ image reconstruction for proton radiography

et al. 2019

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“…Second, i Rad could simultaneously be used for the alignment during patient setup. This application was suggested for proton radiography early on 14 and over the past 10 years, several studies based on irradiations of a few isolated pencil beams called range probes, or on full radiographs using single‐proton tracking were published 15–18 …”

Section: Introductionmentioning

confidence: 99%

Experimental helium‐beam radiography with a high‐energy beam: Water‐equivalent thickness calibration and first image‐quality results

et al. 2022

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A clinical implementation of ion-beam radiography (iRAD) is envisaged to provide a method for on-couch verification of ion-beam treatment plans. The aim of this work is to introduce and evaluate a method for quantitative waterequivalent thickness (WET) measurements for a specific helium-ion imaging system for WETs that are relevant for imaging thicker body parts in the future. Methods: Helium-beam radiographs (𝛼Rads) are measured at the Heidelberg Ion-beam Therapy Center with an initial beam energy of 239.5 MeV/u. An imaging system based on three pairs of thin silicon pixel detectors is used for ion path reconstruction and measuring the energy deposition (dE) of each particle behind the object to be imaged. The dE behind homogeneous plastic blocks is related to their well-known WETs between 280.6 and 312.6 mm with a calibration curve that is created by a fit to measured data points. The quality of the quantitative WET measurements is determined by the uncertainty of the measured WET of a single ion (single-ion WET precision) and the deviation of a measured WET value to the well-known WET (WET accuracy). Subsequently, the fitted calibration curve is applied to an energy deposition radiograph of a phantom with a complex geometry. The spatial resolution (modulation transfer function at 10 % -MTF 10% ) and WET accuracy (mean absolute percentage difference-MAPD) of the WET map are determined. Results: In the optimal imaging WET-range from ∼280 to 300 mm, the fitted calibration curve reached a mean single-ion WET precision of 1.55 ± 0.00%. Applying the calibration to an ion radiograph (iRad) of a more complex WET distribution, the spatial resolution was determined to be MTF 10% = 0.49 ± 0.03 lp/mm and the WET accuracy was assessed as MAPD to 0.21 %. Conclusions: Using a beam energy of 239.5 MeV/u and the proposed calibration procedure, quantitative 𝛼Rads of WETs between ∼280 and 300 mm can be measured and show high potential for clinical use. The proposed approach with the resulting image qualities encourages further investigation toward the clinical application of helium-beam radiography.

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“…The ability to directly measure accurate RSP maps would also enable pCT to be used for cross‐calibration of x‐ray CT systems 5 . Further, pCT enables proton radiography (pRad), which has the potential to provide a fast and efficient check of patient setup and integrated range along the beam's eye view just before treatment 6,7 . A comparison of a pRad with a digitally reconstructed radiograph (DRR) based on projections through the three‐dimensional (3D) RSP map used for treatment planning can reveal discrepancies from range uncertainties as well as other sources such as changes in anatomical consistency and patient misalignment.…”

Section: Introductionmentioning

confidence: 99%

A comparison of proton stopping power measured with proton CT and x‐ray CT in fresh postmortem porcine structures

DeJongh

Rykalin

et al. 2021

Medical Physics

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Purpose: Currently, calculations of proton range in proton therapy patients are based on a conversion of CT Hounsfield units of patient tissues into proton relative stopping power. Uncertainties in this conversion necessitate larger proximal and distal planned target volume margins. Proton CT can potentially reduce these uncertainties by directly measuring proton stopping power. We aim to demonstrate proton CT imaging with complex porcine samples, to analyze in detail three-dimensional regions of interest, and to compare proton stopping powers directly measured by proton CT to those determined from x-ray CT scans. Methods: We have used a prototype proton imaging system with single proton tracking to acquire proton radiography and proton CT images of a sample of porcine pectoral girdle and ribs, and a pig's head. We also acquired close in time x-ray CT scans of the same samples and compared proton stopping power measurements from the two modalities. In the case of the pig's head, we obtained x-ray CT scans from two different scanners and compared results from high-dose and low-dose settings. Results: Comparing our reconstructed proton CT images with images derived from x-ray CT scans, we find agreement within 1% to 2% for soft tissues and discrepancies of up to 6% for compact bone. We also observed large discrepancies, up to 40%, for cavitated regions with mixed content of air, soft tissue, and bone, such as sinus cavities or tympanic bullae. Conclusions:Our images and findings from a clinically realistic proton CT scanner demonstrate the potential for proton CT to be used for low-dose treatment planning with reduced margins. K E Y W O R D Sdigitally reconstructed radiograph, iterative algorithm, proton computed tomography, proton imaging, proton radiography, relative stopping power 7998

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Reconstructed and real proton radiographs for image-guidance in proton beam therapy

Cited by 17 publications

References 2 publications

Fast in situ image reconstruction for proton radiography

Fast in situ image reconstruction for proton radiography

Experimental helium‐beam radiography with a high‐energy beam: Water‐equivalent thickness calibration and first image‐quality results

A comparison of proton stopping power measured with proton CT and x‐ray CT in fresh postmortem porcine structures

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