MR Guidance Research Articles

The Potential of Adjusting Water Bolus Liquid Properties for Economic and Precise MR Thermometry Guided Radiofrequency Hyperthermia

The potential of MR thermometry (MRT) fostered the development of MRI compatible radiofrequency (RF) hyperthermia devices. Such device integration creates major technological challenges and a crucial point for image quality is the water bolus (WB). The WB is located between the patient body and external sources to both couple electromagnetic energy and to cool the patient skin. However, the WB causes MRT errors and unnecessarily large field of view. In this work, we studied making the WB MRI transparent by an optimal concentration of compounds capable of modifying T* relaxation without an impact on the efficiency of RF heating. Three different T* reducing compounds were investigated, namely CuSO, MnCl, and FeO. First, electromagnetic properties and T* relaxation rates at 1.5 T were measured. Next, through multi-physics simulations, the predicted effect on the RF-power deposition pattern was evaluated and MRT precision was experimentally assessed. Our results identified 5 mM FeO solution as optimal since it does not alter the RF-power level needed and improved MRT precision from 0.39 C to 0.09 C. MnCl showed a similar MRT improvement, but caused unacceptable RF-power losses. We conclude that adding FeO has significant potential to improve RF hyperthermia treatment monitoring under MR guidance.

Active tracked intramyocardial catheter injections for regenerative therapy with real-time MR guidance: feasibility in the porcine heart.

The MIGRATE (MrI Guided RegenerAtive ThErapy) consortium is a combined scientific and industrial effort to establish an MRIguided intramyocardial injection platform. By collaborating within the MIGRATE consortium we were able to combine state-of-theart interventional imaging hardware, software, MRI-compatible catheters, and biomaterials. In this pilot study, we demonstrated the feasibility of intramyocardial injections of an MRI-visible biomaterial by interventional MRI using a combination of active tracking and passive visualisation.

Can Ex Vivo Magnetic Resonance Imaging of Rectal Cancer Specimens Improve the Mesorectal Lymph Node Yield for Pathological Examination?

The aim of this study was to use 7 T ex vivo magnetic resonance imaging (MRI) scans to determine the size of lymph nodes (LNs) in total mesorectal excision (TME) specimens and to increase the pathological yield of LNs with MR-guided pathology. Twenty-two fixated TME specimens containing adenocarcinoma were scanned on a 7 T preclinical MRI system with a T1-weighted 3-dimensional gradient echo sequence with frequency-selective lipid excitation (repetition time/echo time, 15/3 milliseconds; resolution, 0.293 mm) and a water-excited 3-dimensional multigradient echo (repetition time, 30 milliseconds; computed echo time, 6.2 milliseconds; resolution, 0.293 mm) pulse sequence.The first series of 11 TME specimens (S1) revealed the number and size of LNs on both ex vivo MRI and histopathology. The second series of 11 TME specimens (S2) was used to perform MR-guided pathology. The number, size, and percentages of yielded LNs of S1 and S2 were compared. In all specimens (22/22), a median number of 34 LNs (interquartile range, 26-34) was revealed on ex vivo MRI compared with 14 LNs (interquartile range, 7.5-21.5) on histopathology (P = 0.003). Mean size of all LNs did not differ between the 2 series (ex vivo MRI: 2.4 vs 2.5 mm, P = 0.267; pathology: 3.6 vs 3.5 mm, P = 0.653). The median percentages of harvested LNs compared with nodes visible on ex vivo MRI per specimen for both series were not significantly different (40% vs 43%, P = 0.718). By using a size threshold of greater than 2 mm, the percentage improved to 71% (S1) and to 78% (S2, P = 0.895). The median number of harvested LNs per specimen did not increase by performing MR-guided pathology (S1, 14 LNs; S2, 20 LNs; P = 0.532). Ex vivo MRI visualizes more LNs than (MR-guided) pathology is able to harvest. Current pathological examination was not further improved by MR guidance. The majority of LNs or LN-like structures visible on ex vivo MRI below 2 mm in size remain unexplained, which warrants a 3-dimensional approach for pathological reconstruction of specimens.

Assessment of Online Adaptive MR-Guided SBRT of Liver Cancers

Online Adaptive Radiotherapy (ART) with daily MR imaging has the potential to improve target coverage by taking into account for anatomical changes during radiotherapy. The purpose of this study is to provide an assessment of potential benefits of online adaptive MRI-Guided Stereotactic Body Radiotherapy (SBRT) for treatment of liver cancer. Five patients with liver cancer who were treated with MR-Guided SBRT were included. Prescription doses ranged between 27-50 Gy in 3-5fx, with the 90%-95% of the PTV covered by 100% of the prescription dose. All patients underwent a planning MRI and setup MRIs prior to each fraction, all acquisitions utilized breath-hold conditions. All SBRT fractions were delivered under MR guidance with cine-MR gating of the gross tumor volume (GTV) based on a modified breath-hold technique. Patients received visual feedback throughout treatment delivery. The planning target volume (PTV) was created by expanding the GTV by 3mm uniform margin. The initial treatment plan was generated using step-and-shoot IMRT and utilized 9-12 beam groups, each beam group consisted of 3 equally spaced Co-60 beams. The electron density (ED) map and contours from planning MR were propagated to daily setup MRI using deformable image registration and were reviewed/edited by the physician. Each adapted plan was obtained by re-optimizing based on the contours on daily setup MRI using the same beam parameters and optimization objectives from the initial MR plan. Non-adaptive plans for each patient were created by recalculating the dose from the initial plan on the daily setup MRI, daily ED map and edited contours. The non-adaptive and adaptive plans were compared using PTV coverage and dose-volume constraints for OARs: duodenum, bowel, stomach, kidneys, and spinal cord. Daily plan adaptation provided increased PTV coverage for 11 of 23 fractions. While 7 fractions required adaptations due to violation of maximum dose constraint for duodenum and 3 fractions required adaptation due to violation of V30Gy <5cc constraint for bowel. Up to 27% decrease in mean dose to liver-GTV was achieved when using daily adaption even though this constraint was satisfied for all fractions. Similarly, up to 28% reduction in maximum cord dose and up to 18% reduction in mean kidney dose was achieved with daily adaptation. Online ART MR-Guided SBRT of liver cancer using daily re-optimization resulted in better target conformity and OAR sparing compared with non-adaptive SBRT. In our experience, adaptation provides the largest benefit when two or more OARs are proximal to the target additionally the larger the intra-fractional motion of the target and OARs the greater the benefit. Significant OAR sparing was still achieved for fractions that did not exceed OAR tolerances. Daily adaptation may allow for PTV dose escalation without compromising OAR sparing as compared to non-adaptive treatments. Further studies are needed to determine the limits to any dose escalation strategy.

Molecular oxygen loading in candidate theranostic droplets stabilized with biocompatible fluorinated surfactants: Particle size effect and application to in situ19F MRI mapping of oxygen partial pressure

ObjectivePerfluorocarbon nano- and micron-sized emulsions are a new field of investigation in cancer treatment due to their ability to be used as imaging contrast agents, or as delivery vectors for pharmaceuticals. They also demonstrated capability to enhance the efficiency of high intensity focused ultrasound thermo-therapy. In the context of new biomedical applications we investigated perfluorooctyl bromide (PFOB) theranostic droplets using 19F NMR. Each droplet contains biocompatible fluorinated surfactants composed of a polar Tris(hydroxymethyl)aminomethane head unit and hydrophobic perfluorinated tail (abbreviated as F-TAC). The influence of the droplet size on the oxygen loading capacity was determined from longitudinal relaxation (T1) data of 19F NMR signal. Material and methodsLiquid PFOB and five samples of PFOB droplets of average diameter 0.177, 0.259, 1.43, 3.12 and 4.53 µm were tested with different oxygen levels. A dedicated gas exchange system was validated to maintain steady state oxygen concentrations, including a spatial gradient of oxygen concentration. A prototyped transmit-receive switchable 19F/1H quadrature coil was integrated on a 3 T clinical scanner. The coil is compatible with focused ultrasound sonication for future application. A spectroscopy FID inversion-recovery (IR) sequence was used to measure the T1 value per sample and per value of equilibrium oxygen pressure. Pixel wise, spatial T1 mapping was performed with magnetization prepared 2D gradient echo sequences in tissue mimicking gels doped with theranostic droplets. ResultsExperimental data indicated that the longitudinal relaxation rate of 19F signal of the investigated theranostic droplets depended approximately linearly on the oxygen level and its slope decreased with the particle size according to a second order polynomial over the investigated range. This semi-empirical model was derived from general thermodynamics and weak electrostatic forces theory and fitted the experimental data within 0.75% precision. The capacity of oxygen transportation for the described theranostic droplets tended to that of pure PFOB, while micron-sized droplets lost up to 50% of this capacity. In a specific setup producing a steady state gradient of oxygen concentration, we demonstrated spatial mapping of oxygen pressure gradient of 6 kPa/mm with 1 mm in-plane resolution. ConclusionThe size-tunable PFOB theranostic droplets stabilized with F-TAC surfactants could be characterized by 19F MRI in a clinical setup readily compatible with interventional in vivo studies under MR guidance. Current precision and spatial resolution of T1 mapping are promising. A potential challenge for further in vivo studies is the reduction of the imaging time.

Chondrosarcoma radiotherapy with helical delivery and analysis of MR guidance

Chondrosarcoma radiotherapy with helical delivery and analysis of MR guidance

Stormram 4: An MR Safe Robotic System for Breast Biopsy

Suspicious lesions in the breast that are only visible on magnetic resonance imaging (MRI) need to be biopsied under MR guidance with high accuracy and efficiency for accurate diagnosis. The aim of this study is to present a novel robotic system, the Stormram 4, and to perform preclinical tests in an MRI environment. Excluding racks and needle, its dimensions are 72 × 51 × 40 mm. The Stormram 4 is driven by two linear and two curved pneumatic stepper motors. The linear motor is capable of exerting 63 N of force at a pressure of 0.65 MPa. In an MRI environment the maximum observed stepping frequency is 30 Hz (unloaded), or 8 Hz when full force is needed. The Stormram 4’s mean positioning error is 0.73 ± 0.47 mm in free air, and 1.29 ± 0.59 mm when targeting breast phantoms in MRI. Excluding the off-the-shelf needle, the robot is inherently MR safe. The robot is able to accurately target lesions under MRI guidance, reducing tissue damage and risk of false negatives. These results are promising for clinical experiments, improving the quality of healthcare in the field of MRI-guided breast biopsies.

Erratum to: Greater occipital nerve infiltration under MR guidance: Feasibility study and preliminary results.

The original version of this article, published on 12 July 2017, unfortunately contained mistakes. The following corrections have therefore been made in the original.

The Positive Outcome of MRI-Guided Vacuum Assisted Core Needle Breast Biopsies Is Not Influenced by a Prior Negative Targeted Second-Look Ultrasound

PurposeThe study sought to investigate the outcome of breast magnetic resonance–guided biopsies as a function of the indication for magnetic resonance imaging (MRI), the MRI features of the lesions, and the performance or not of a targeted second-look ultrasound (SLUS) prior breast MRI-guided biopsy. MethodsWe identified 158 women with MRI-detected breast lesions scheduled for MRI-guided biopsy (2007-2013). Patient demographics, performance of targeted SLUS, imaging characteristics, and subsequent pathology results were reviewed. ResultsThree biopsies were deferred, and 155 lesions were biopsied under MRI guidance (155 women; median age 55.14 years; range 27-80 years). Ninety-eight women underwent a SLUS prior to the MRI-guided biopsy (63%). Of the 155 biopsied lesions, 23 (15%) were malignant, 106 (68%) were benign, and 26 (17%) were high risk. Four of 15 surgically excised high-risk lesions were upgraded to malignancy (27%). Most of the biopsied lesions corresponded to non–mass-like enhancement (81%, 126 of 155) and most of the biopsies (52%, 81 of 155) were performed in a screening context. No demographic or MRI features were associated with malignancy. No differences were noted between the 2 subgroups (prior SLUS vs no prior SLUS) except for the presence of a synchronous carcinoma associated with a likelihood of targeted SLUS before MRI-guided biopsy (P = .001). ConclusionA negative SLUS does not influence the pathology outcome of a suspicious lesion biopsied under MR guidance.

Fast online replanning for interfraction rotation correction in prostate radiotherapy.

To enable fast online replanning for prostate radiotherapy with the inclusion of interfraction rotations and translations and investigate the possibility for margin reduction via this regime. Online daily replanning for a 35-fraction treatment for five prostate cases is simulated while accounting for anatomical transformations derived from fiducial marker data available in our clinic. Two online replanning strategies were simulated, compensating for: (a) rotation-only in combination with a couch shift and (b) both translation and rotation without a couch shift. They were compared against our current clinical protocol consisting of a single offline plan used over all fractions with daily couch repositioning (translations only). For every patient, the above methods were generated for several planning margins (0-8 mm with 2 mm increments) in order to assess the performance of online replanning in terms of target coverage and investigate the possible dosimetric benefit for the organs at risk. The daily DVHs for each treatment strategy were used for evaluation and the non tumor integral dose (NTID) for the different margins was calculated in order to quantify the overall reduction of the delivered energy to the patient. Our system is able to generate a daily automated prostate plan in less than 2 min. For every patient, the daily treatment plans produce similar dose distributions to the original approved plan (average CTV D99 relative difference: 0.2%). The inclusion of both shifts and rotations can be effectively compensated via replanning among all planning margins (average CTV D99 difference: 0.01 Gy between the two replanning regimes). Online replanning is able to maintain target coverage among all margins, while - as expected - the conventional treatment plan is increasingly affected by the interfraction rotations as the margins shrink (average CTV D99 decrease: 0.2 Gy at 8 mm to 2.9 Gy at 0 mm margin). The possible gain in total delivered energy to the patient was quantified by the decreased NTID ranging from 12.6% at 6 mm to 32.9% at 0 mm. We demonstrate that fast daily replanning can be utilized to account for daily rotations and translations based on the daily positioning protocol. A daily plan can be generated from scratch in less than 2 min making it suitable for online application. Given the large magnitude of prostate rotation around the LR axis, online correction for daily rotations can be beneficial even for the clinical 8 mm margin and could be utilized for treatments with small margin reduction mainly limited then by anatomical deformations and intrafraction motion. Our online replanning pipeline can be used in future treatments with online MR guidance that can lead to further safe reduction of the planning margins.

Greater occipital nerve infiltration under MR guidance: Feasibility study and preliminary results.

To assess the feasibility of greater occipital nerve (GON) intermediate site infiltration with MRI guidance. Eleven consecutive patients suffering from chronic refractory cranio-facial pain who underwent 16 GON infiltrations were included in this prospective study. All of the procedures were performed on an outpatient basis in the research facility of our institution, with a 1.5T scanner. The fatty space between inferior obliquus and semispinalis muscles at C1-C2 level was defined as the target. Technical success was defined as the ability to accurately inject the products at the target, assessed by post-procedure axial and sagittal proton density-weighted sequences. Clinical success was defined as a 50% pain decrease at 1month. Technical success was 100%. GON was depicted in 6/11 cases on planning MRI sequences. Mean duration of procedure was 22.5min (range 16-41). Clinical success was obtained in 7/11 included patients (63.6%) with a mean self-reported improvement of 78%. Interventional MR-guidance for GON infiltration is a feasible technique offering similar results to an already established effective procedure. It may appear as a useful tool in specific populations, such as young patients and repeat infiltrations, and should be considered in these settings. • MR guidance for GON infiltration is a feasible technique. • Preliminary results are in agreement with other guidance modalities. • MR guidance may be seen as a useful tool in specific populations. • Specific populations include young patients and repeat infiltrations. • Target patients may also include patients with potentionally previously reported complications (torticollis).

Capacitive Micromachined Ultrasound Transducers for Interstitial High-Intensity Ultrasound Therapies.

Capacitive micromachined ultrasound transducers (CMUTs) exhibit several potential advantages over conventional piezo technologies for use in therapeutic ultrasound (US) devices, including ease of miniaturization and integration with electronics, broad bandwidth (>several megahertz), and compatibility with magnetic resonance imaging (MRI). In this paper, the electroacoustic performance of CMUTs designed for interstitial high-intensity contact US (HICU) applications was evaluated and the feasibility of generating US-induced heating and thermal destruction of biological tissues was studied. One-dimensional CMUT linear arrays as well as a prism-shaped 2-D array composed of multiple 1-D linear arrays mounted on a cylindrical catheter were fabricated. The electromechanical and acoustic characteristics of the CMUTs were first studied at low intensity. Then, the acoustic output during continuous wave (CW) driving was studied while varying the bias voltage ( VDC ) and driving voltage ( VAC ). US heating was performed in tissue-mimicking gel phantoms under infrared (IR) or MR-thermometry monitoring. Acoustic intensities compatible with thermal ablation were obtained by driving the CMUTs in the collapse-snapback operation mode ( [Formula: see text]). Hysteresis in the acoustic output was observed with varying VDC . IR- and MR-thermometry monitoring showed directional US-induced heating patterns in tissue-mimicking phantoms (frequency: 6-8 MHz and exposure time: 60-240 s) extending over 1.5-cm depth from the CMUT surface. Irreversible thermal damage was produced in turkey breast tissue samples ( [Formula: see text]). Multidirectional US-induced heating was also achieved in 3-D with the CMUT catheter. These studies demonstrate that CMUTs can be integrated into HICU devices and be used for heating and destruction of tissue under MR guidance.

Magnetic Resonance Imaging-Guided Transplantation of Neural Stem Cells into the Porcine Spinal Cord

Background: Cell-based therapies are a promising treatment option for traumatic, tumorigenic and degenerative diseases of the spinal cord. Transplantation into the spinal cord is achieved with intravascular, intrathecal, or direct intraparenchymal injection. The current standard for direct injection is limited by surgical invasiveness, difficulty in reinjection, and the inability to directly target anatomical or pathological landmarks. The objective of this study was to present the proof of principle for minimally invasive, percutaneous transplantation of stem cells into the spinal cord parenchyma of live minipigs under MR guidance. Methods: An MR-compatible spine injection platform was developed to work with the ClearPoint SmartFrame system (MRI Interventions Inc.). The system was attached to the spine of 2 live minipigs, a percutaneous injection cannula was advanced into the spinal cord under MR guidance, and cells were delivered to the cord. Results: A graft of 2.5 × 10⁶ human (n = 1) or porcine (n = 1) neural stem cells labeled with ferumoxytol nanoparticles was transplanted into the ventral horn of the spinal cord with MR guidance in 2 animals. Graft delivery was visualized with postprocedure MRI, and characteristic iron precipitates were identified in the spinal cord by Prussian blue histochemistry. Grafted stem cells were observed in the spinal cord of the pig injected with porcine neural stem cells. No postoperative morbidity was observed in either animal. Conclusion: This report supports the proof of principle for transplantation and visualization of pharmacological or biological agents into the spinal cord of a large animal under the guidance of MRI.

MRI-guided laser interstitial thermal therapy for the treatment of low-grade gliomas in children: a case-series review, description of the current technologies and perspectives.

Pediatric low-grade gliomas (LGGs) account for approximately half of all pediatric central nervous system tumors. The low-grade gliomas' first line of treatment is gross total resection. However, when gross total resection is not possible, options for adjuvant therapy are limited. MRI-guided laser ablation (magnetic resonance-guided laser interstitial thermal therapy (MRgLITT)) offers a new option for treatment in selected cases. We present a description of the current MRgLITT technology and an exemplary case-series review of our experience in its use in LGGs. A 19-month-old male was referred to the pediatric neurosurgery clinic with an incidental left temporal lesion discovered on a prenatal ultrasound. An MRI of the brain revealed a diffuse mesial temporal lesion. Electroencephalogram (EEG) showed generalized activity arising from the lesion. The patient underwent a navigation-guided biopsy then, two bolts were secured to the skull, and laser ablation was performed with intraoperative MR guidance. Pathology was consistent with ganglioglioma. Follow-up images 13months after ablation showed a significant volumetric reduction in size of the tumor. It is important to achieve maximal resection of low-grade gliomas in children, lessening the need for adjuvant chemotherapy and radiotherapy, while minimizing the length of hospital stay and disruption to the child's life. Of our nine LGGs patients treated with this technology, six had undergone previous surgery and MRgLITT proved itself to be a safe surgical treatment option to achieve further cytoreduction. While most of the cases are pilocytic astrocytomas, the location of the tumors was surgically challenging. Eight of the nine cases required a single trajectory-laser-while our case example requires two lasers. Only a case of a midbrain-thalamic tumor presented a post-ablation significant brain edema as perioperative complication [1]. Eight of the nine tumors did not require any coadjuvant therapy or further surgical treatment to date. MRIgLITT is a successful option for treatment for selected de novo or recurrent low-grade gliomas in children. It can be combined with other therapies offering the advantages of a minimally invasive procedure. LITT may be added to the current pediatric neuro-oncology protocols, but larger prospective series are needed to show the effectiveness of LITT and to standardize indications and protocols.

SU‐F‐J‐225: Histology Study of MR Guided Pulsed Focused Ultrasound On Treatment of Prostate Cancer in Vivo

Purpose:Our previous study demonstrated significant tumor growth delay in the mice treated with pulsed high intensity focused ultrasound (pHIFU). The purpose of this study is to understand the cell killing mechanisms of pHIFU.Methods:Prostate cancer cells (LNCaP), were grown orthotopically in 17 nude mice. Tumor‐bearing mice were treated using pHIFU with an acoustic power of 25W, pulse width 100msec and 300 pulses in one sonication under MR guidance. Mutiple sonications were used to cover the whole tumor volume. The temperature (less than 40 degree centigrade in the focal spot) was monitored using MR thermometry. Animals were euthanized at pre‐determined time points (n=2) after treatment: 0 hours; 6 hrs; 24 hrs; 48 hrs; 4 days and 7 days. Two tumorbearing mice were used as control. Three tumor‐bearing mice were treated with radiation (RT, 2 Gy) using 6 MV photon beams. RT treated mice were euthanized at 0 hr, 6 hrs and 24 hrs. The tumors were processed for immunohistochemical (IHC) staining for PARP (a surrogate of apoptosis). A multispectral imaging analysis system was used to quantify the expression of PARP staining. Cell apoptosis was calculated based on the PARP expression level using the DAB analysis software.Results:Our data showed that PARP related apoptosis peaked at 48 hrs and 7 days in pHIFU treated mice, which is comparable to that for the RT group at 24 hrs. The preliminary results from this study were consistent with our previous study on tumor growth delay using pHIFU.Conclusion:Our results demonstrated that non‐thermal pHIFU increased apoptotic tumor cell death through the PARP related pathway. MR guided pHIFU may have a great potential as a safe, noninvasive treatment modality for cancer therapy. This treatment modality may synergize with PARP inhibitors to achieve better therapeutic result.

SU‐F‐J‐17: Patient Localization Using MRI‐Guided Soft Tissue for Head‐And‐Neck Radiotherapy: Indication for Margin Reduction and Its Feasibility

Purpose:On‐board MRI provides superior soft‐tissue contrast, allowing patient alignment using tumor or nearby critical structures. This study aims to study H&amp;N MRI‐guided IGRT to analyze inter‐fraction patient setup variations using soft‐tissue targets and design appropriate CTV‐to‐PTV margin and clinical implication.Methods:282 MR images for 10 H&amp;N IMRT patients treated on a ViewRay system were retrospectively analyzed. Patients were immobilized using a thermoplastic mask on a customized headrest fitted in a radiofrequency coil and positioned to soft‐tissue targets. The inter‐fraction patient displacements were recorded to compute the PTV margins using the recipe: 2.5∑+0.7σ. New IMRT plans optimized on the revised PTVs were generated to evaluate the delivered dose distributions. An in‐house dose deformation registration tool was used to assess the resulting dosimetric consequences when margin adaption is performed based on weekly MR images. The cumulative doses were compared to the reduced margin plans for targets and critical structures.Results:The inter‐fraction displacements (and standard deviations), ∑ and σ were tabulated for MRI and compared to kVCBCT. The computed CTV‐to‐PTV margin was 3.5mm for soft‐tissue based registration. There were minimal differences between the planned and delivered doses when comparing clinical and the PTV reduced margin plans: the paired t‐tests yielded p=0.38 and 0.66 between the planned and delivered doses for the adapted margin plans for the maximum cord and mean parotid dose, respectively. Target V95 received comparable doses as planned for the reduced margin plans.Conclusion:The 0.35T MRI offers acceptable soft‐tissue contrast and good spatial resolution for patient alignment and target visualization. Better tumor conspicuity from MRI allows soft‐tissue based alignments with potentially improved accuracy, suggesting a benefit of margin reduction for H&amp;N radiotherapy. The reduced margin plans (i.e., 2 mm) resulted in improved normal structure sparing and accurate dose delivery to achieve intended treatment goal under MR guidance.

SU‐F‐J‐110: MRI‐Guided Single‐Session Simulation, Online Adaptation, and Treatment

Purpose:To develop a combined simulation and treatment workflow for MRI‐guided radiation therapy using the ViewRay treatment planning and delivery system.Methods:Several features of the ViewRay MRIdian planning and treatment workflows are used to simulate and treat patients that require emergent radiotherapy. A simple “pre‐plan” is created on diagnostic imaging retrieved from radiology PACS, where conformal fields are created to target a volume defined by a physician based on review of the diagnostic images and chart notes. After initial consult in radiation oncology, the patient is brought to the treatment room, immobilized, and imaged in treatment position with a volumetric MR. While the patient rests on the table, the pre‐plan is applied to the treatment planning MR and dose is calculated in the treatment geometry. After physician review, modification of the plan may include updating the target definition, redefining fields, or re‐balancing beam weights. Once an acceptable treatment plan is finalized and approved, the patient is treated.Results:Careful preparation and judicious choices in the online planning process allow conformal treatment plans to be created and delivered in a single, thirty‐minute session. Several advantages have been identified using this process as compared to conventional urgent CT simulation and delivery. Efficiency gains are notable, as physicians appreciate the predictable time commitment and patient waiting time for treatment is decreased. MR guidance in a treatment position offers both enhanced contrast for target delineation and reduction of setup uncertainties. The MRIdian system tools designed for adaptive radiotherapy are particularly useful, enabling plan changes to be made in minutes. Finally, the resulting plans, typically 6 conformal beams, are delivered as quickly as more conventional AP/PA beam arrangements with comparatively superior dose distributions.Conclusion:The ViewRay treatment planning software and delivery system can accommodate a fast simulation and treatment workflow.

WE‐H‐207B‐02: MR‐Driven RT Planning

In recent years, steady progress has been made towards the implementation of MRI in external beam radiation therapy for processes ranging from treatment simulation to in‐room guidance. Novel procedures relying mostly on MR data are currently implemented in the clinic. This session will cover topics such as (a) commissioning and quality control of the MR in‐room imagers and simulators specific to RT, (b) treatment planning requirements, constraints and challenges when dealing with various MR data, (c) quantification of organ motion with an emphasis on treatment delivery guidance, and (d) MR‐driven strategies for adaptive RT workflows. The content of the session was chosen to address both educational and practical key aspects of MR guidance. Learning Objectives: Good understanding of MR testing recommended for in‐room MR imaging as well as image data validation for RT chain (e.g. image transfer, filtering for consistency, spatial accuracy, manipulation for task specific); Familiarity with MR‐based planning procedures: motivation, core workflow requirements, current status, challenges; Overview of the current methods for the quantification of organ motion; Discussion on approaches for adaptive treatment planning and delivery.T. Stanescu ‐ License agreement with Modus Medical Devices to develop a phantom for the quantification of MR image system‐related distortions.; T. Stanescu, N/A

WE‐H‐207B‐04: Strategies for Adaptive RT

In recent years, steady progress has been made towards the implementation of MRI in external beam radiation therapy for processes ranging from treatment simulation to in‐room guidance. Novel procedures relying mostly on MR data are currently implemented in the clinic. This session will cover topics such as (a) commissioning and quality control of the MR in‐room imagers and simulators specific to RT, (b) treatment planning requirements, constraints and challenges when dealing with various MR data, (c) quantification of organ motion with an emphasis on treatment delivery guidance, and (d) MR‐driven strategies for adaptive RT workflows. The content of the session was chosen to address both educational and practical key aspects of MR guidance. Learning Objectives: Good understanding of MR testing recommended for in‐room MR imaging as well as image data validation for RT chain (e.g. image transfer, filtering for consistency, spatial accuracy, manipulation for task specific); Familiarity with MR‐based planning procedures: motivation, core workflow requirements, current status, challenges; Overview of the current methods for the quantification of organ motion; Discussion on approaches for adaptive treatment planning and delivery.T. Stanescu ‐ License agreement with Modus Medical Devices to develop a phantom for the quantification of MR image system‐related distortions.; T. Stanescu, N/A

WE‐H‐207B‐00: MRgRT

In recent years, steady progress has been made towards the implementation of MRI in external beam radiation therapy for processes ranging from treatment simulation to in‐room guidance. Novel procedures relying mostly on MR data are currently implemented in the clinic. This session will cover topics such as (a) commissioning and quality control of the MR in‐room imagers and simulators specific to RT, (b) treatment planning requirements, constraints and challenges when dealing with various MR data, (c) quantification of organ motion with an emphasis on treatment delivery guidance, and (d) MR‐driven strategies for adaptive RT workflows. The content of the session was chosen to address both educational and practical key aspects of MR guidance. Learning Objectives: Good understanding of MR testing recommended for in‐room MR imaging as well as image data validation for RT chain (e.g. image transfer, filtering for consistency, spatial accuracy, manipulation for task specific); Familiarity with MR‐based planning procedures: motivation, core workflow requirements, current status, challenges; Overview of the current methods for the quantification of organ motion; Discussion on approaches for adaptive treatment planning and delivery.T. Stanescu ‐ License agreement with Modus Medical Devices to develop a phantom for the quantification of MR image system‐related distortions.; T. Stanescu, N/A