A clustering approach to 4D MRI retrospective sorting for the investigation of different surrogates

Meschini, Giorgia; Paganelli, Chiara; Gianoli, Chiara; Summers, Paul; Bellomi, Massimo; Baroni, Guido; Riboldi, Marco

doi:10.1016/j.ejmp.2019.02.003

Cited by 17 publications

(23 citation statements)

References 33 publications

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“…The 4DCT depicts an average respiratory cycle and is representative of the irradiated volume in the case of regular respiratory pattern. 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 …”

Section: Introductionmentioning

confidence: 99%

“…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%

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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%

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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“…It should be noted that the 4DCT and 4DMRI spatial resolutions were chosen, respectively, according to the clinical practice and as a trade-off between spatial and temporal resolution to obtain sufficient anatomical detail and proper motion description. 36,43 The spatial resolution of the used imaging data affects the DIR accuracy and, therefore, it is put forward as the minimum acceptable uncertainty in the virtual 4DCT method. The major limitation of the present study is the restricted field of view of the 4DMRI and of the derived virtual 4DCT (12.5 cm in the right-left direction).…”

Section: Discussionmentioning

confidence: 99%

“…The imaged volume consisted of 25 sagittal slices, including a limited field of view of 12.5 cm in the right–left direction; for each slice 30 frames were acquired (TR/TE: 228.07 ms/1.5 ms; α: 33°; scan matrix: 256 × 256 pixels with spacing of 1.33 × 1.33 mm; slice thickness of 5 mm; acquisition time: 310 ms/slice with 25 slices × 30 frames; k‐space percentage sampling: 65%; acceleration factor: 2 with a generalized auto‐calibrating partially parallel acquisition using 16 auto‐calibration lines). The 4DMRI was retrospectively reconstructed by means of a previously published and validated algorithm based on clustering and image‐based multi‐dimensional surrogates …”

Section: Methodsmentioning

confidence: 99%

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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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Time‐resolved MRI for off‐line treatment robustness evaluation in carbon‐ion radiotherapy of pancreatic cancer

et al. 2022

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In this study, we investigate the use of magnetic resonance imaging (MRI) for the clinical evaluation of gating treatment robustness in carbonion radiotherapy (CIRT) of pancreatic cancer. Indeed, MRI allows radiation-free repeated scans and fast dynamic sequences for time-resolved (TR) imaging (cine-MRI), providing information on inter-and intra-fraction cycle-to-cycle variations of respiratory motion. MRI can therefore support treatment planning and verification, overcoming the limitations of the current clinical standard, that is, four-dimensional computed tomography (4DCT), which describes an "average" breathing cycle neglecting breathing motion variability. Methods: We integrated a technique to generate a virtual CT (vCT) from 3D MRI with a method for 3D reconstruction from 2D cine-MRI, to produce TR vCTs for dose recalculations. For eight patients, the method allowed evaluating inter-fraction variations at end-exhale and intra-fraction cycle-to-cycle variability within the gating window in terms of tumor displacement and dose to the target and organs at risk. Results:The median inter-fraction tumor motion was in the range 3.33-12.16 mm, but the target coverage was robust (-0.4% median D 95% variation). Concerning cycle-to-cycle variations, the gating technique was effective in limiting tumor displacement (1.35 mm median gating motion) and corresponding dose variations (-3.9% median D 95% variation). The larger exposure of organs at risk (duodenum and stomach) was caused by inter-fraction motion, whereas intra-fraction cycle-to-cycle dose variations were limited. Conclusions: This study proposed a method for the generation of TR vCTs from MRI, which enabled an off -line evaluation of gating treatment robustness and suggested its feasibility to support treatment planning of pancreatic tumors in CIRT.

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A clustering approach to 4D MRI retrospective sorting for the investigation of different surrogates

Cited by 17 publications

References 33 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

Time‐resolved MRI for off‐line treatment robustness evaluation in carbon‐ion radiotherapy of pancreatic cancer

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