Evaluation of residual abdominal tumour motion in carbon ion gated treatments through respiratory motion modelling

Meschini, Giorgia; Seregni, Matteo; Pella, Andrea; Ciocca, Mario; Fossati, Piero; Valvo, Francesca; Riboldi, Marco; Baroni, Guido

doi:10.1016/j.ejmp.2017.01.009

Cited by 28 publications

(35 citation statements)

References 37 publications

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“…When an imaging representation of the irradiated volume for irregular breathing is lacking, the calculation of dose distribution variations with conventional treatment planning systems (TPS) and Monte Carlo algorithms is infeasible. Motion modeling approaches have been investigated to overcome the lack of imaging data in conventional photon radiotherapy as well as in particle therapy . Nevertheless, these approaches rely on deformable image registration (DIR), which introduces severe uncertainty in low‐contrast region, such as the abdomen …”

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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“…A 4D XCAT phantom of the abdomen was generated simulating a maximum excursion (end‐exhale to end‐inhale) of the diaphragm (superior–inferior direction) and of the chest wall (anterior–posterior direction) of 8.8 and 3.0 mm, respectively. A target was manually delineated in the pancreas, and the resulting motion range was 5.9 mm, comparable to literature values for patients treated with gated carbon ion beams . A 4DCT was obtained with the four respiratory phases (30%‐exhale, end‐exhale, 30%‐inhale, end‐inhale) as those used for treatment planning on patients and it was used to derive the corresponding 4DMRI by means of the digital phantom 4D CoMBAT .…”

Section: Methodsmentioning

confidence: 56%

“…For the abdominal site, motion correlated treatment planning relies on a 4DCT with four respiratory phases: the endexhale, used for plan optimization; the 30%-exhale and 30%inhale, to test the plan against residual motion within the gating window; the end-inhale, to assess the total range of motion. 34,35 The MRI scan was performed on the same day of the 4DCT acquisition. For 4 of the eight patients, two 4DMRI were acquired within the same session.…”

Section: B Patient Datasetmentioning

confidence: 99%

“…A target was manually delineated in the pancreas, and the resulting motion range was 5.9 mm, comparable to literature values for patients treated with gated carbon ion beams. 34 A 4DCT was obtained with the four respiratory phases (30%-exhale, end-exhale, 30%-inhale, end-inhale) as those used for treatment planning on patients and it was used to derive the corresponding 4DMRI by means of the digital phantom 4D CoMBAT. 38 To simulate potential interfraction changes, a reference 3DCT for the virtual 4DCT generation was obtained in correspondence to an end-exhale respiratory phase with a target distance with respect to the ground truth end-exhale CT of 2.2 mm.…”

Section: C Phantom Validationmentioning

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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“…The extended SIFT was tested on lung 4DCT (Fig. , panel A) and applied to abdominal 4DCT data treated with carbon ions, quantifying DIR errors below the voxel resolution. Similarly, a large number of landmarks were also identified for a dense representation in head & neck CT, lung 4DCT, and pelvic MRI by means of improved landmark matching .…”

Section: The Geometric Accuracy Paradigmmentioning

confidence: 99%

“Patient‐specific validation of deformable image registration in radiation therapy: Overview and caveats”

et al. 2018

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Over the last few decades, deformable image registration (DIR) has gained popularity in image-guided radiation therapy for a number of applications, such as contour propagation, dose warping, and accumulation. Although this raises promising perspectives for the improvement of treatment outcomes and quality of radiotherapy clinical practice, the variety of proposed DIR algorithms, combined with the lack of an effective quantitative quality control metric of the registration, is slowing the transfer of DIR into the clinical routine. Recently, a task group (AAPM TG132) report was published outlining the essential aspects of DIR for image guidance in radiotherapy. However, an accurate and efficient patient-specific validation is not yet defined, and appropriate metrics should be identified to achieve the definition of both geometric and dosimetric accuracy. In this respect, the use of a dense set of anatomical landmarks, along with additional evaluations on contours or deformation field analysis, are likely to drive patient-specific DIR validation in clinical image-guided radiotherapy applications to account for geometric inaccuracies. Automatic and efficient strategies able to provide spatial information of DIR uncertainties and to evaluate monomodal and multimodal image registration, as well as to describe homogenous and un-contrasted regions are believed to represent the future direction in DIR validation. But especially in the case of DIR applications for dose mapping and accumulation, the need of accurate patient-specific validation is not only limited to the evaluation of geometric accuracy. In fact, the need to account for dosimetric inaccuracies due to DIR represents another important area in the field of adaptive treatments. Different approaches are currently being investigated to quantify the effect of DIR error on dose analysis, mainly relying on clinically relevant dose metrics, or on the study of deformation field properties for a voxel-by-voxel evaluation. However, novel research is required for the definition of dedicated and personalized measures capable to relate the geometric and dosimetric inaccuracies, thus bearing useful information for a safe use of DIR by clinical end users. In this paper we provide insights on DIR results evaluation on a patient-specific basis, facing the issues of both geometric and dosimetric paradigms. Challenges on DIR validation are overviewed and discussed, in order to push preliminary clinical guidelines forward on this fundamental topic and boost the implementation of more robust and reliable patient-specific evaluation metrics.

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Evaluation of residual abdominal tumour motion in carbon ion gated treatments through respiratory motion modelling

Cited by 28 publications

References 37 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

“Patient‐specific validation of deformable image registration in radiation therapy: Overview and caveats”

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