The impact of secondary fragments on the image quality of helium ion imaging

Volz, Lennart; Piersimoni, Pierluigi; Bashkirov, V.; Brons, Stephan; Collins-Fekete, Charles-Antoine; Johnson, R. P.; Schulte, R.; Seco, Joao

doi:10.1088/1361-6560/aadf25

Cited by 25 publications

(54 citation statements)

References 70 publications

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“…In recent studies, the RSP accuracy achieved by some of these prototypes has been reported to be better than 1.6% for three inserts (Esposito et al 2018) and 1.39% for seven inserts (Giacometti et al 2017). For the same seven inserts, Volz et al (2018) achieved accuracy better than 1% using helium ions with a 30 pCT prototype. An alternative for obtaining RSP images of high accuracy is dual energy X-ray CT (DECT) (Yang et al 2010), where several studies (Hünemohr et al 2013, Bourque et al 2014, Hudobivnik et al 2016, Möhler et al 2016, Han et al 2016, Taasti et al 2016, Lalonde et al 2017, Saito & Sagara 2017b, Almeida et al 2018 have 35 demonstrated the potential of reaching an RSP accuracy of about 1%.…”

Section: Introductionmentioning

confidence: 99%

Experimental comparison of proton CT and dual energy x-ray CT for relative stopping power estimation in proton therapy

et al. 2019

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Proton computed tomography (pCT) has been proposed as an alternative to X-ray computed tomography (CT) for acquiring relative to water stopping power (RSP) maps used for proton treatment planning dose calculations. In parallel, it has been shown that dual energy X-ray CT (DECT) improves RSP accuracy when compared to conventional single energy X-ray CT. This study aimed at directly comparing the RSP accuracy of both modalities using phantoms scanned at an advanced prototype pCT scanner and a state-of-the-art DECT scanner. Two phantoms containing 13 tissue-mimicking inserts of known RSP were scanned at the pCT phase II prototype and a latest generation dual-source DECT scanner (Siemens SOMATOM Definition FORCE). RSP accuracy was compared by mean absolute percent error (MAPE) over all inserts. A highly realistic Monte Carlo (MC) simulation was used to gain insight on pCT image artifacts which degraded MAPE. MAPE was 0.55% for pCT and 0.67% for DECT. The realistic MC simulation agreed well with pCT measurements (MAPE = 0.69%).

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Section: Introductionmentioning

confidence: 99%

Experimental comparison of proton CT and dual energy x-ray CT for relative stopping power estimation in proton therapy

et al. 2019

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“…[7][8][9] X-ray CT images are typically not acquired in treatment position and not prior to every treatment fraction, in order to keep treatment time short and imaging dose low enough that they do not compromise the dose benefit of proton therapy. 10 Direct imaging of RSP using proton computed tomography (pCT) [11][12][13][14][15][16] has been proposed to increase accuracy and to allow for a frequent, dose efficient acquisition in treatment position. Accuracies achievable with current prototypes are comparable to state-of-the art clinical dual energy x-ray CT. 7,[17][18][19] A further reduction of imaging dose can be achieved by modulating the imaging fluence field during the acquisition and thereby achieving a task-specific image quality.…”

Section: Introductionmentioning

confidence: 99%

An optimization algorithm for dose reduction with fluence‐modulated proton CT

et al. 2020

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Purpose: Fluence-modulated proton computed tomography (FMpCT) using pencil beam scanning aims at achieving task-specific image noise distributions by modulating the imaging proton fluence spot-by-spot based on an object-specific noise model. In this work, we present a method for fluence field optimization and investigate its performance in dose reduction for various phantoms and image variance targets. Methods: The proposed method uses Monte Carlo simulations of a proton CT (pCT) prototype scanner to estimate expected variance levels at uniform fluence. Using an iterative approach, we calculate a stack of target variance projections that are required to achieve the prescribed image variance, assuming a reconstruction using filtered backprojection. By fitting a pencil beam model to the ratio of uniform fluence variance and target variance, relative weights for each pencil beam can be calculated. The quality of the resulting fluence modulations is evaluated by scoring imaging doses and comparing them to those at uniform fluence, as well as evaluating conformity of the achieved variance with the prescription. For three different phantoms, we prescribed constant image variance as well as two regions-of-interest (ROI) imaging tasks with inhomogeneous image variance. The shape of the ROIs followed typical beam profiles for proton therapy. Results: Prescription of constant image variance resulted in a dose reduction of 8.9% for a homogeneous water phantom compared to a uniform fluence scan at equal peak variance level. For a more heterogeneous head phantom, dose reduction increased to 16.0% for the same task. Prescribing two different ROIs resulted in dose reductions between 25.7% and 40.5% outside of the ROI at equal peak variance levels inside the ROI. Imaging doses inside the ROI were increased by 9.2% to 19.2% compared to the uniform fluence scan, but can be neglected assuming that the ROI agrees with the therapeutic dose region. Agreement of resulting variance maps with the prescriptions was satisfactory. Conclusions: We developed a method for fluence field optimization based on a noise model for a real scanner used in pCT. We demonstrated that it can achieve prescribed image variance targets. A uniform fluence field was shown not to be dose optimal and dose reductions achievable with the proposed method for FMpCT were considerable, opening an interesting perspective for image guidance and adaptive therapy.

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“…The goal of this work was to investigate the effect of such events on the accuracy of pCT with the prototype detector developed by the US pCT collaboration (Bashkirov et al 2016a, Johnson et al 2017 in Monte Carlo simulations. We investigate the performance of the usual 3 σ WEPL filter and assess the potential of using the ∆E-E filtering technique recently proposed to identify nuclear fragmentation events in helium ion CT (HeCT) with the scanner energy/range detector (Volz et al 2018) to identify nuclear interaction events in pCT.…”

Section: Introductionmentioning

confidence: 99%

Improving single-event proton CT by removing nuclear interaction events within the energy/range detector

Volz¹,

Piersimoni²,

Johnson³

et al. 2019

Phys. Med. Biol.

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Improving single-event proton CT by removing nuclear interaction events within the energy/range detector. Permalink https://escholarship.org/uc/item/5rg9r6rw Journal Physics in medicine and biology, 64 (15) Abstract. Data filtering is crucial for accurate relative stopping power (RSP) reconstruction in proton CT (pCT). In this work, we assess different filters and their performance for the US pCT collaboration prototype pCT system in Monte Carlo (MC) simulations. The potential of using the recently proposed ∆E-E filter for removing nuclear interactions that occurred in the energy/range detector of the pCT system is investigated.Full pCT scans were acquired with the TOPAS MC simulated version of the prototype scanner that comprises two tracking detectors and a 5 stage energy/range detector. An ideal water cylinder and a water cylinder with 5 tissue inserts were investigated. Before image reconstruction, a 3 σ WEPL filter was applied as the only filter, or in addition to filters acting on the energy deposit in each of the energy detector stages, as done currently with the prototype. The potential of the ∆E-E filter that was recently proposed for helium imaging was assessed. The results were compared to simulations for which nuclear interactions were disabled representing ground truth.The 3 σ WEPL filter alone was not sufficient to filter out all nuclear interaction events and systematic fluctuations in the form of ring artifacts were present in the pCT reconstructed images. Applying energy filters currently used with the device prior to the 3 σ WEPL filter only slightly improved the image quality. A 2 σ WEPL filter improved the mean RSP accuracy, but could not

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The impact of secondary fragments on the image quality of helium ion imaging

Cited by 25 publications

References 70 publications

Experimental comparison of proton CT and dual energy x-ray CT for relative stopping power estimation in proton therapy

Experimental comparison of proton CT and dual energy x-ray CT for relative stopping power estimation in proton therapy

An optimization algorithm for dose reduction with fluence‐modulated proton CT

Improving single-event proton CT by removing nuclear interaction events within the energy/range detector

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