MRI-guidance for motion management in external beam radiotherapy: current status and future challenges

Paganelli, Chiara; Whelan, Brendan; Peroni, M.; Summers, Paul; Fast, Martin F.; Lindt, T. Van de; McClelland, Jamie R.; Eiben, Björn; Keall, Paul J.; Lomax, Tony; Riboldi, Marco; Baroni, Guido

doi:10.1088/1361-6560/aaebcf

Cited by 103 publications

(136 citation statements)

References 191 publications

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“…The 4D magnetic resonance imaging (4DMRI) technique is a valuable alternative to 4DCT for capturing respiratory motion variability, as it allows one to acquire data over multiple breathing cycles without exposing the patient to ionizing radiation. [6][7][8][9][10] The variability of breathing induced motion has been reported to be significant. 11,12 This is a critical issue in particle therapy, as it introduces uncertainty in target localization and tissue density within the beam path with respect to the planning scenario.…”

Section: Introductionmentioning

confidence: 99%

Validation of a model for physical dose variations in irregularly moving targets treated with carbon ion beams

et al. 2019

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Purpose In particle therapy, conventional treatment planning systems rely on an imaging representation of the irradiated region to compute the dose. For irregular breathing, when an imaging dataset describing the actual motion is not available, a different approach for dose estimation is needed. To this aim, we validate a method for the estimation of physical dose variations in gated carbon ion treatments, providing also a demonstration of the feasibility of physical dose metrics to assess the method performance. Finally, we describe a sample use case, in which this method is used to assess plan robustness with respect to undetected irregular tumor motion. Methods The method entails the definition of a patient‐ and beam‐specific water equivalent depth (WED) space, the simulation of motion as a translation equal to tumor displacement, and the reconstruction of the altered dose. We validated the approach using four‐dimensional computed tomographies (4DCTs) and clinical plans in 12 patients, treated with respiratory gated carbon ion beams at the National Centre for Oncological Hadrontherapy (Pavia, Italy). Using the end‐exhale CT and dose distribution as a reference, the physical dose delivered at the end‐inhale tumor position was estimated and compared to the ground‐truth dose recalculation on the end‐inhale CT. Biologically effective and physical dose variations between the plan and the recalculation were compared as well. As a use case, we evaluated dose changes caused by simulated irregular tumor motion, that is, linear and nonlinear baseline shifts and/or amplitude variations with hysteresis. Results The ratio between biologically effective and physical equivalent uniform dose (EUD) variations due to end‐exhale to end‐inhale motion was less than one for 96% of investigated structures. In the validation study, we found a median error corresponding to a 14% EUD overestimation for the tumor and 4% EUD underestimation for a subgroup of organs at risk, together with a high EUD variation due to motion [median 352% EUD variation between end‐exhale and end‐inhale doses in the planning tumor volume (PTV)]. Considering relevant dose‐volume histogram (DVH) metrics, the median difference between estimated and ground truth doses was ≤ 4%. Gamma analysis between estimated and recalculated dose distributions resulted in a pass rate > 80% for 83% of the target volumes. For the two patients selected for the sample use case, a patient‐specific assessment of the method performance was performed on the 4DCT and it was possible to relate EUD variations of both tumor and organs at risk to the simulated target motion. Conclusions The physical dose distribution was found to be more sensitive to motion with respect to the biologically effective one, suggesting the suitability of the physical dose metrics for the WED‐space method validation. We showed that the method can compensate for intra‐fractional tumor motion with proper accuracy in the selected patient group, although its use is recommended when limited deformations are expected....

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Section: Introductionmentioning

confidence: 99%

Validation of a model for physical dose variations in irregularly moving targets treated with carbon ion beams

et al. 2019

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“…15 Four-dimensional magnetic resonance imaging (4DMRI) was recently made available to capture respiratory motion variability as a way to complement and support 4DCT. [16][17][18][19] MRI combines exquisite soft tissue contrast and radiation-free imaging, thus allowing multiple repeated acquisitions, 19,20 but it is not suitable for computing the treatment dose.…”

Section: Introductionmentioning

confidence: 99%

Virtual 4DCT from 4DMRI for the management of respiratory motion in carbon ion therapy of abdominal tumors

et al. 2020

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Purpose To evaluate a method for generating virtual four‐dimensional computed tomography (4DCT) from four‐dimensional magnetic resonance imaging (4DMRI) data in carbon ion radiotherapy with pencil beam scanning for abdominal tumors. Methods Deformable image registration is used to: (a) register each respiratory phase of the 4DMRI to the end‐exhale MRI; (b) register the reference end‐exhale CT to the end‐exhale MRI volume; (c) generate the virtual 4DCT by warping the registered CT according to the obtained deformation fields. A respiratory‐gated carbon ion treatment plan is optimized on the planning 4DCT and the corresponding dose distribution is recalculated on the virtual 4DCT. The method was validated on a digital anthropomorphic phantom and tested on eight patients (18 acquisitions). For the phantom, a ground truth dataset was available to assess the method performances from the geometrical and dosimetric standpoints. For the patients, the virtual 4DCT was compared with the planning 4DCT. Results In the phantom, the method exhibits a geometrical accuracy within the voxel size and Dose Volume Histograms deviations up to 3.3% for target V95% (mean dose difference ≤ 0.2% of the prescription dose, gamma pass rate > 98%). For patients, the virtual and the planning 4DCTs show good agreement at end‐exhale (3% median D95% difference), whereas other respiratory phases exhibit moderate motion variability with consequent dose discrepancies, confirming the need for motion mitigation strategies during treatment. Conclusions The virtual 4DCT approach is feasible to evaluate treatment plan robustness against intra‐ and interfraction motion in carbon ion therapy delivered at the abdominal site.

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“…1 This motion can be substantial, is patient-specific, difficult to predict, can be irregular and change from one day to another. [2][3][4][5][6][7][8] Intrafractional motion, defined as any motion induced by physiological processes occurring within a treatment session such as breathing, and interfractional changes occurring between treatment sessions need to be accounted for in the planning and delivery process. 9 To address intrafractional changes, passive and active motion management techniques have been developed over the last decades.…”

Section: Introductionmentioning

confidence: 99%

“…The movement of lung tumors has been investigated with two-dimensional (2D) cine-MRI, which Medical Physics, 47 (4), April 2020 enables the repeated acquisition of temporally resolved images of arbitrary duration with high soft tissue contrast without delivering dose to the patient. 5,6 Several studies have investigated intrafractional and interfractional changes with 2D cine-MRI. 6,[30][31][32][33][34][35] Cai et al 36 showed that the characterization of lung tumor motion with temporally resolved MRI is more representative than with 4D-CT, mainly due to improved statistics through longer acquisition times.…”

Section: Introductionmentioning

confidence: 99%

“…5,6 Several studies have investigated intrafractional and interfractional changes with 2D cine-MRI. 6,[30][31][32][33][34][35] Cai et al 36 showed that the characterization of lung tumor motion with temporally resolved MRI is more representative than with 4D-CT, mainly due to improved statistics through longer acquisition times. 22 Hence, temporally resolved MRI can help to refine the ITV definition for treatment planning.…”

Section: Introductionmentioning

confidence: 99%

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Real‐time 4DMRI‐based internal target volume definition for moving lung tumors

et al. 2020

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PTVs were smaller than the ITV-based PTVs. While the SE was high for patients with small breathing pattern variations, changes of the median breathing amplitudes in different imaging sessions led to inferior SE values for the mid-ventilation PTV for one patient. In contrast, PTV 5% r and PTV 10% r showed higher SE values with a higher robustness against interfractional changes, at the cost of larger target volumes. Conclusions:The results indicate that rt-4DMRI could be valuable for the definition of target volumes based on the GTV POP to achieve a higher robustness against interfractional changes than feasible with today's 4D-CT-based target definition concepts.

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MRI-guidance for motion management in external beam radiotherapy: current status and future challenges

Abstract: PK is a stakeholder in SeeTreat, a start-up company to commercialize intellectual property generated through NHMRC program grant APP1036075 "The Australian MRI-Linac program".

Cited by 103 publications

References 191 publications

Validation of a model for physical dose variations in irregularly moving targets treated with carbon ion beams

Validation of a model for physical dose variations in irregularly moving targets treated with carbon ion beams

Virtual 4DCT from 4DMRI for the management of respiratory motion in carbon ion therapy of abdominal tumors

Real‐time 4DMRI‐based internal target volume definition for moving lung tumors

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