Feasibility of MRI-only treatment planning for proton therapy in brain and prostate cancers: Dose calculation accuracy in substitute CT images

Koivula, Lauri; Wee, Leonard; Korhonen, Juha

doi:10.1118/1.4958677

Cited by 69 publications

(87 citation statements)

References 56 publications

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“…There is also interest in using MR imaging alone, without a corresponding pre-treatment computed tomography (CT) exam, for both photon and proton radiation therapy planning[6,9,10]. A major technical challenge in utilizing MRI lies in determining the geometric accuracy of the tissues that are to be targeted or avoided during radiation therapy.…”

Section: Introductionmentioning

confidence: 99%

Image-based gradient non-linearity characterization to determine higher-order spherical harmonic coefficients for improved spatial position accuracy in magnetic resonance imaging

Weavers

Tao

Trzasko

et al. 2017

Magnetic Resonance Imaging

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Purpose Spatial position accuracy in magnetic resonance imaging (MRI) is an important concern for a variety of applications, including radiation therapy planning, surgical planning, and longitudinal studies of morphologic changes to study neurodegenerative diseases. Spatial accuracy is strongly influenced by gradient linearity. This work presents a method for characterizing the gradient non-linearity fields on a per-system basis, and using this information to provide improved and higher-order (9th vs 5th) spherical harmonic coefficients for better spatial accuracy in MRI. Methods A large fiducial phantom containing 5229 water-filled spheres in a grid pattern is scanned with the MR system, and the positions all the fiducials are measured and compared to the corresponding ground truth fiducial positions as reported from a computed tomography (CT) scan of the object. Systematic errors from off-resonance (i.e., B0) effects are minimized with the use of increased receiver bandwidth (±125 kHz) and two acquisitions with reversed readout gradient polarity. The spherical harmonic coefficients are estimated using an iterative process, and can be subsequently used to correct for gradient non-linearity. Test-retest stability was assessed with five repeated measurements on a single scanner, and cross-scanner variation on four different, identically-configured 3T wide-bore systems. Results A decrease in the root-mean-square error (RMSE) over a 50 cm diameter spherical volume from 1.80 mm to 0.77 mm is reported here in the case of replacing the vendor’s standard 5th order spherical harmonic coefficients with custom fitted 9th order coefficients, and from 1.5mm to 1mm by extending custom fitted 5th order correction to the 9th order. Minimum RMSE varied between scanners, but was stable with repeated measurements in the same scanner. Conclusions The results suggest that the proposed methods may be used on a per-system basis to more accurately calibrate MR gradient non-linearity coefficients when compared to vendor standard corrections.

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Section: Introductionmentioning

confidence: 99%

Image-based gradient non-linearity characterization to determine higher-order spherical harmonic coefficients for improved spatial position accuracy in magnetic resonance imaging

Weavers

Tao

Trzasko

et al. 2017

Magnetic Resonance Imaging

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show abstract

“…An important finding reported was that the number of tissue grades defined impacted the dosimetry match with the reference CT dose plans. In more recent work by Koivula et al, 26 the feasibility of using MRI for both brain and prostate cancers has also been studied. In this work substitute CT datasets were generated by transforming the intensity values of in-phase MR images to Hounsfield units with a dual model HU conversion technique to enable heterogeneous tissue representation.…”

Section: C Existing Literature In Mrptmentioning

confidence: 99%

Future of medical physics: Real‐time MRI‐guided proton therapy

et al. 2017

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With the recent clinical implementation of real-time MRI-guided x-ray beam therapy (MRXT), attention is turning to the concept of combining real-time MRI guidance with proton beam therapy; MRIguided proton beam therapy (MRPT). MRI guidance for proton beam therapy is expected to offer a compelling improvement to the current treatment workflow which is warranted arguably more than for x-ray beam therapy. This argument is born out of the fact that proton therapy toxicity outcomes are similar to that of the most advanced IMRT treatments, despite being a fundamentally superior particle for cancer treatment. In this Future of Medical Physics article, we describe the various software and hardware aspects of potential MRPT systems and the corresponding treatment workflow. Significant software developments, particularly focused around adaptive MRI-based planning will be required. The magnetic interaction between the MRI and the proton beamline components will be a key area of focus. For example, the modeling and potential redesign of a magnetically compatible gantry to allow for beam delivery from multiple angles towards a patient located within the bore of an MRI scanner. Further to this, the accuracy of pencil beam scanning and beam monitoring in the presence of an MRI fringe field will require modeling, testing, and potential further development to ensure that the highly targeted radiotherapy is maintained. Looking forward we envisage a clear and accelerated path for hardware development, leveraging from lessons learnt from MRXT development. Within few years, simple prototype systems will likely exist, and in a decade, we could envisage coupled systems with integrated gantries. Such milestones will be key in the development of a more efficient, more accurate, and more successful form of proton beam therapy for many common cancer sites.

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“…Proton CT offers the potential to directly determine the proton SPR (Schulte and Penfold, 2012) but currently lacks a clinical implementation as a number of challenges await its development (including numerous small-angle scatterings due to Coulomb interactions and high energy requirements to penetrate the body for imaging) (Li et al, 2006). Recently, magnetic resonance imaging (MRI) images converted to pseudoCT or syntheticCT (sCT) scans have been proposed as a reasonable alternative to SECT (Edmund et al, 2014;Koivula et al, 2016;Rank et al, 2013a;Rank et al, 2013b) for SPR determination. In the case of the prior work of sCT to SPR conversion, the efforts have been to simulate kV SECT images and not necessarily to increase the information content beyond SECT and/or improve the accuracy of SPR determination relative to kV SECT.…”

Section: Introductionmentioning

confidence: 99%

Determination of mean ionization potential using magnetic resonance imaging for the reduction of proton beam range uncertainties: theory and application

Sudhyadhom¹

2017

Phys. Med. Biol.

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Accurate determination of mean ionization potential (Im) has the potential to reduce range uncertainty based margins and therefore allow for more focal treatments in proton radiotherapy. Many methods have been proposed to reduce uncertainty in Im and stopping power ratios (SPR) each with varying degrees of accuracy and issues. In this work, we present on a simple parameterized model to determine Im in human biological tissue, which allows for computation of patient-specific Im at the voxel level using magnetic resonance imaging (MRI). The model requires the measurement of three parameters by MRI with only two parameters, mass percent water content and mass percent hydrogen content in organic molecules, required for the special case of soft tissues. The accuracy of this Im determination method was evaluated in available "standard" (ICRU Report #44) human tissues. The sensitivity of this Im determination method to in-vivo perturbations was also tested by calculating the effect of 10% variations of the experimentally measurable parameters on Im and SPR. For the human tissues modeled in this work, a high level of accuracy with low susceptibility to perturbations in measurement error was achieved in the prediction of Im. Root-mean-square errors (RMSE) in Im were within 0.77% and 1.8% for both soft and bony tissues and were 0.09% and 0.2% for soft and bony tissues SPR, respectively, assuming knowledge of electron density.Proof of principle MR measurements and model-based computations of Im and SPR were taken in phantom for a series of hydrogenous solutions and compared against expected Im and SPR calculations from known elemental composition. MR determined Im and SPR values in a known composition solution were determined to within 5% and 0.52%, respectively. We present on a novel model to accurately calculate mean ionization potential from measurements acquirable by MRI and show feasibility in phantom.

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Feasibility of MRI-only treatment planning for proton therapy in brain and prostate cancers: Dose calculation accuracy in substitute CT images

Abstract: This study demonstrates that proton therapy dose calculations on heterogeneous sCTs are in good agreement with plans generated with standard planning CT. An MRI-only based RTP workflow is feasible in IMPT for brain tumors and prostate cancers.

Cited by 69 publications

References 56 publications

Image-based gradient non-linearity characterization to determine higher-order spherical harmonic coefficients for improved spatial position accuracy in magnetic resonance imaging

Image-based gradient non-linearity characterization to determine higher-order spherical harmonic coefficients for improved spatial position accuracy in magnetic resonance imaging

Future of medical physics: Real‐time MRI‐guided proton therapy

Determination of mean ionization potential using magnetic resonance imaging for the reduction of proton beam range uncertainties: theory and application

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