Tumor Trailing for Liver SBRT on the MR-Linac

Fast, Martin F.; Schoot, A. Van de; Lindt, Tessa N. van de; Carbaat, C.; Heide, Uulke A. van der; Sonke, Jan‐Jakob

doi:10.1016/j.ijrobp.2018.09.011

Cited by 66 publications

(59 citation statements)

References 46 publications

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“…[19][20][21] Balanced steady-state free precession (bSSFP) is used in all aspects of MR-IGRT including simulation, patient setup/alignment, and real-time tracking. 22,23 Four-dimensional (4D) GRE MRI is being used in body RT treatment planning to reduce dose errors caused by organ motion. 24 Poor field homogeneity also causes peak broadening that degrades fat saturation used with both GRE and spin echo MRI, and affects the sensitivity of MRS. 25 As suggested by AAPM Report No.…”

Section: B B 0 Field Homogeneity and Mri Qualitymentioning

confidence: 99%

B₀ field homogeneity recommendations, specifications, and measurement units for MRI in radiation therapy

et al. 2020

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Purpose: The purpose is: (a) Relate magnetic resonance imaging (MRI) quality recommendations for radiation therapy (RT) to B 0 field homogeneity; (b) Evaluate manufacturer specifications of B 0 homogeneity for 34 commercial whole-body MRI systems based on the MRI quality recommendations and RT application; (c) Measure field homogeneity in five commercial MRI systems and one commercial MRI-Linac used in RT and compare the results with their B 0 homogeneity specifications. Methods: Magnetic resonance imaging quality recommendations for spatial integrity, image blurring, fat saturation, and null banding in RT were developed based on the literature. Guaranteed (maximum) and typical B 0 field homogeneity specifications for various diameter spherical volumes (DSVs) were provided by GE, Philips, Siemens, and Canon. For each system, the DSV that conforms to each MRI quality recommendation and anatomical RT application was estimated based on the manufacturer specifications. B 0 field homogeneity was measured on six MRI systems including Philips (1.5 T), Siemens (1.5 and 3 T), and ViewRay MRI (0.35 T) systems using 24 and 35 cm DSV spherical phantoms. Two measurement techniques were used: (a) MRI using phase contrast field mapping to measure peak-to-peak (pk-pk), volume root mean square (VRMS), and standard deviation (SD); and (b) Magnetic resonance (MR) spectroscopy by acquiring a volumetric free induction decay (FID) to measure full width at half maximum (FWHM). The measurements were used to assess: (a) conformance with the manufacturer specifications; and (b) the relationship between the various field homogeneity measurement units. Measurements were made with and without gradient shimming (gradshim) or second-order active shimming. Multiple comparisons, analysis of variance (ANOVA), and Pearson correlations were performed to assess the dependence of pk-pk, VRMS, SD, and FWHM measurements of field homogeneity on shim volume, level of shim, and MRI system. Results: For a 40 cm DSV, the B 0 homogeneity specifications ranged from 0.35 to 5 ppm (median = 0.75 ppm) VRMS for 1.5 T systems and 0.2 to 1.4 ppm (median = 0.5 ppm) VRMS for 3 T systems. The usable DSVs ranged from 16 to 49 cm (median = 35 cm) based on the image quality recommendations and the manufacturer specifications. There was general compliance between the six measured field homogeneities and manufacturer specifications although signal dephasing was observed in two systems at < 35 cm DSV. The relationships between pk-pk, VRMS, SD, and FWHM varied based on MRI system, shim volume, and quality of shim. However, VRMS and SD measurements were highly correlated. Conclusions: The delineation of the diseased lesion from organs at risk is the main priority for RT. Therefore, field homogeneity performance for RT must minimize image blurring and image artifacts (null bands and signal dephasing) while optimizing spatial integrity and fat saturation. Based on the specifications and recommendations for field homogeneity, some MRI systems are not well suited to meet the stri...

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Section: B B 0 Field Homogeneity and Mri Qualitymentioning

confidence: 99%

B₀ field homogeneity recommendations, specifications, and measurement units for MRI in radiation therapy

et al. 2020

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“…However, due to the spatial confinement of the MRI‐bore and because of the anterior MRI coil, the arms‐up setup is more constrained on the MR‐linac, with the arms being forced fully above the head. This arms‐up position can be difficult to maintain for sustained periods of time, with on‐table times expected in excess of 30 min …”

Section: Introductionmentioning

confidence: 99%

Investigating the impact of patient arm position in an MR‐linac on liver SBRT treatment plans

et al. 2019

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Purpose The superior soft‐tissue contrast offered by the integrated magnetic resonance imaging (MRI) of the Unity MR‐linac compared to the x‐ray‐based image guidance on conventional linacs potentially allows for liver stereotactic body radiation therapy (SBRT) without the need for implanted markers or other surrogates. On conventional linacs, liver SBRT patients are typically positioned with their arms above their heads (arms‐up) to minimize exposure to healthy tissue. However, the spatial confinement of the MRI‐bore and increased treatment delivery times can make the arms‐up position straining. Therefore, we assessed the plan quality for MR‐linac treatment plans with the patient in the arms‐up and in the arms‐down position. Additionally, we compared the MR‐linac plans with clinically used arms‐up treatment plans made for a conventional linac. Methods Fifteen consecutively treated patients with oligometastatic liver disease were included in this retrospective study. For each patient, a planning computed tomography (CT) with delineations, a diagnostic MRI, and a 3 × 20 Gy dual‐arc volumetric modulated arc therapy (VMAT) plan, which was used to treat the patient in an arms‐up position on the conventional linac, were available. For the MR‐linac, 15‐beam step‐and‐shoot intensity‐modulated radiation therapy (IMRT) plans were created for four patient positioning scenarios: arms‐up, mimicking current clinical practice; arms‐down, with treatment beams avoiding the arms on the entrance side; arms‐through, arms are down but not avoided, and right‐arm‐up; only the right arm is up and the left arm is avoided on the entrance side. Resulting treatment plans were compared. Bonferroni‐corrected two‐sided Wilcoxon signed‐ranks tests were used to assess statistical significance (P < 0.05). Results No significant differences were found in gross tumour volume (GTV) coverage (D2%, D50%, and D98%) or liver sparing (liver‐GTV V<15normalGy) between the clinical plans and any of the MR‐linac plans. The median target conformity [exterior V40%/planning target volume (PTV)] was significantly better in the clinical plans (5.8) than in the MR‐linac scenarios (arms‐down: 6.6, arms‐up/right‐arm‐up: 6.2, arms‐through: 6.3). No MR‐linac plan violated any additional organ‐at‐risk (OAR) constraint that was not already violated in the clinical plans. In the arms‐down scenario a significantly increased median spinal cord D1% (14.5 Gy) was detected compared to the clinical setup (7.2 Gy). For the arms‐down (arms‐through) scenario, the median left arm D1% was 1.5 (2.7) Gy, the median right arm D1% was 5.8 (22.7) Gy, and the median right arm V20Gy was 0.0 (14.7) cc. These differences were statistically significant. For the right‐arm‐up scenario, the median left arm D1% (2.3 Gy) and V5Gy (0.0) were not significantly different compared to the arms‐down scenario. Conclusions Mimicking the current clinical practice by treating patients in the arms‐up/right‐arm‐up position on the MR‐linac leads to plans which are dosimetrically very similar to the convention...

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“…Future studies on tumor volume delineation based on PET/MRI may bene t from more advanced technology such as MR-linac, novel radioactive tracers and 4D-PET. For example, studies are ongoing to investigate the impact of MR-linac on liver SBRT planning [31,32,33]. On conventional linacs, based on X-ray-based image guidance, liver lesions are often poor or invisible in this pattern of images; thus, the injection of contrast material, or the implantation of markers is needed address this issue.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of Hybrid PET/MRI for Gross Tumor Volume (GTV) Delineation in Liver Cancer Radiotherapy

Zhang

et al. 2020

Preprint

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Background: Hybrid 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/magnetic resonance imaging (PET/MRI) has been increasingly incorporated into the practice of radiation oncologists since it contains both anatomical and biological data and may bring about personalized radiation plans for each patient. The objective of this study was to evaluate the feasibility of gross tumor volume (GTV) delineation from hybrid PET/MRI compared with that from current-practice MRI during radiotherapy planning in patients with liver cancer. Methods: Twelve patients (eighteen lesions) with liver cancer were enrolled in this study. We chose one of the most popular delineating methods—the visual method—in this study, and three physicians delineated the target volume of each lesion from MRI, PET, and hybrid PET/MRI images. The difference and correlation of GTV values obtained by MRI, PET and hybrid PET/MRI were subjected to statistical analysis. In addition, the Dice similarity coefficient (DSC) was calculated to assess the spatial overlap. GTV-MRI was set as a reference. Results: Most GTV-PET/MRI (83%) and 50% of GTV-PET were larger than the reference GTV-MRI. Statistical analysis revealed that GTV-PET/MRI (p=0.021) diverged statistically significantly from the reference GTV-MRI. In contrast, GTV-PET (p=0.266) was not significantly different from GTV-MRI. GTV-PET (r=0.991, p<0.001) and GTV-PET/MRI (r=0.997, p<0.001) were significantly related to GTV-MRI. The average DSC value between GTV-MRI and GTV-PET was 0.45 (range 0–0.90) and that between GTV-MRI and GTV-PET/MRI was 0.76 (range 0.43–0.90). Conclusions: With the database used, PET/MRI-based target volume delineation for liver cancer is feasible. The larger GTV-PET/MRI may allow adequate irradiation of the diseased tissue and improved treatment effect.

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Tumor Trailing for Liver SBRT on the MR-Linac

Cited by 66 publications

References 46 publications

B₀ field homogeneity recommendations, specifications, and measurement units for MRI in radiation therapy

B₀ field homogeneity recommendations, specifications, and measurement units for MRI in radiation therapy

Investigating the impact of patient arm position in an MR‐linac on liver SBRT treatment plans

Evaluation of Hybrid PET/MRI for Gross Tumor Volume (GTV) Delineation in Liver Cancer Radiotherapy

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Tumor Trailing for Liver SBRT on the MR-Linac

Cited by 66 publications

References 46 publications

B0 field homogeneity recommendations, specifications, and measurement units for MRI in radiation therapy

B0 field homogeneity recommendations, specifications, and measurement units for MRI in radiation therapy

Investigating the impact of patient arm position in an MR‐linac on liver SBRT treatment plans

Evaluation of Hybrid&nbsp;PET/MRI&nbsp;for Gross Tumor Volume (GTV) Delineation in Liver Cancer Radiotherapy

Contact Info

Product

Resources

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B₀ field homogeneity recommendations, specifications, and measurement units for MRI in radiation therapy

B₀ field homogeneity recommendations, specifications, and measurement units for MRI in radiation therapy

Evaluation of Hybrid PET/MRI for Gross Tumor Volume (GTV) Delineation in Liver Cancer Radiotherapy