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Title: TU-AB-BRA-10: Treatment of Gastric MALT Lymphoma Utilizing a Magnetic Resonance Image-Guided Radiation Therapy (MR-IGRT) System: Evaluation of Gating Feasibility

Abstract

Purpose: To evaluate the feasibility of real-time, real-anatomy tracking and gating for gastric lymphoma patients treated with magnetic resonance image-guided radiation therapy (MR-IGRT) Methods: Over the last 2 years, 8 patients with gastric lymphoma were treated with 0.3-T, Co-60 MR-IGRT. Post-treatment analysis of real-time cine imaging in the sagittal plane during each patient’s treatment revealed significant motion of the stomach. While this motion was accounted for with generous PTV margins, the system’s capability for real-time, real-anatomy tracking could be used to reduce treatment margins by gating. However, analysis was needed for the feasibility of gating using only the single available sagittal imaging plane. While any plane may be chosen, if the stomach moves differently where it is not being observed, there may potentially be a mistreatment. To that end, imaging with healthy volunteers was done to ascertain stomach motion over 2–4 min by analyzing multiple parallel sagittal and coronal planes 0.75 cm apart. The stomach was contoured on every slice, and the mean displacement between pairs of contour centroids was used to determine the amount of overall motion. Results: The mean displacement of the centroid in the image plane was 4.3 ± 0.7 mm. The greatest observed motion was moremore » medial with respect to the patient, and less motion laterally, which implies that gating on a plane located closer to MRI isocenter will provide the more conservative scenario as it will turn the radiation delivery off when the stomach is observed to move outside a predetermined boundary. Conclusion: The stomach was observed to move relatively uniformly throughout, with maximum extent of motion closer to where most MRI systems have the best spatial integrity (near isocenter). Analysis of possible PTV margins from the healthy volunteer study (coupled with previous patient data on interfraction volumetric stomach deformation) is pending.« less

Authors:
; ; ; ; ; ;  [1]
  1. Washington University School of Medicine, St. Louis, MO (United States)
Publication Date:
OSTI Identifier:
22653952
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; BIOMEDICAL RADIOGRAPHY; COBALT 60; EVALUATION; IMAGES; LYMPHOMAS; NMR IMAGING; PATIENTS; RADIOTHERAPY; STOMACH

Citation Formats

Mazur, T, Gach, H, Chundury, A, Fischer-Valuck, B, Huang, J, Thomas, M, and Green, O. TU-AB-BRA-10: Treatment of Gastric MALT Lymphoma Utilizing a Magnetic Resonance Image-Guided Radiation Therapy (MR-IGRT) System: Evaluation of Gating Feasibility. United States: N. p., 2016. Web. doi:10.1118/1.4957420.
Mazur, T, Gach, H, Chundury, A, Fischer-Valuck, B, Huang, J, Thomas, M, & Green, O. TU-AB-BRA-10: Treatment of Gastric MALT Lymphoma Utilizing a Magnetic Resonance Image-Guided Radiation Therapy (MR-IGRT) System: Evaluation of Gating Feasibility. United States. doi:10.1118/1.4957420.
Mazur, T, Gach, H, Chundury, A, Fischer-Valuck, B, Huang, J, Thomas, M, and Green, O. Wed . "TU-AB-BRA-10: Treatment of Gastric MALT Lymphoma Utilizing a Magnetic Resonance Image-Guided Radiation Therapy (MR-IGRT) System: Evaluation of Gating Feasibility". United States. doi:10.1118/1.4957420.
@article{osti_22653952,
title = {TU-AB-BRA-10: Treatment of Gastric MALT Lymphoma Utilizing a Magnetic Resonance Image-Guided Radiation Therapy (MR-IGRT) System: Evaluation of Gating Feasibility},
author = {Mazur, T and Gach, H and Chundury, A and Fischer-Valuck, B and Huang, J and Thomas, M and Green, O},
abstractNote = {Purpose: To evaluate the feasibility of real-time, real-anatomy tracking and gating for gastric lymphoma patients treated with magnetic resonance image-guided radiation therapy (MR-IGRT) Methods: Over the last 2 years, 8 patients with gastric lymphoma were treated with 0.3-T, Co-60 MR-IGRT. Post-treatment analysis of real-time cine imaging in the sagittal plane during each patient’s treatment revealed significant motion of the stomach. While this motion was accounted for with generous PTV margins, the system’s capability for real-time, real-anatomy tracking could be used to reduce treatment margins by gating. However, analysis was needed for the feasibility of gating using only the single available sagittal imaging plane. While any plane may be chosen, if the stomach moves differently where it is not being observed, there may potentially be a mistreatment. To that end, imaging with healthy volunteers was done to ascertain stomach motion over 2–4 min by analyzing multiple parallel sagittal and coronal planes 0.75 cm apart. The stomach was contoured on every slice, and the mean displacement between pairs of contour centroids was used to determine the amount of overall motion. Results: The mean displacement of the centroid in the image plane was 4.3 ± 0.7 mm. The greatest observed motion was more medial with respect to the patient, and less motion laterally, which implies that gating on a plane located closer to MRI isocenter will provide the more conservative scenario as it will turn the radiation delivery off when the stomach is observed to move outside a predetermined boundary. Conclusion: The stomach was observed to move relatively uniformly throughout, with maximum extent of motion closer to where most MRI systems have the best spatial integrity (near isocenter). Analysis of possible PTV margins from the healthy volunteer study (coupled with previous patient data on interfraction volumetric stomach deformation) is pending.},
doi = {10.1118/1.4957420},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = {Wed Jun 15 00:00:00 EDT 2016},
month = {Wed Jun 15 00:00:00 EDT 2016}
}
  • Purpose: To describe the design and characteristics of a novel linac-based MRI guided radiation therapy system that addresses RF and magnetic field interference and that can be housed in conventional radiotherapy vaults. Methods: The MR-IGRT system will provide simultaneous MR imaging combined with both simple (3D) and complex (IMRT, SBRT, SRS) techniques. The system is a combination of a) double-donut split solenoidal superconducting 0.345T MRI; and b) a 90 cm isocenter ring-gantry mounted 6MV, flattening filter-free linac coupled with a stacked doubly-focused multileaf collimator with 4 mm resolution. A novel RF shielding and absorption technology was developed to isolate themore » beam generating RF emissions from the MR, while a novel magnetic shielding sleeve system was developed to place the magnetic field-sensitive components in low-magnetic field regions. The system design produces high spatial resolution radiation beams with state-of-the art radiation dose characteristics and simultaneous MR imaging. Results: Prototype testing with a spectrum analyzer has demonstrated complete elimination of linac RF inside the treatment room. The magnetic field inside of the magnetic shielding was well below the specification, allowing the linear accelerator to operate normally. A novel on-gantry shimming system maintained < 25 ppm magnetic field homogeneity over a 45 cm spherical field of view for all gantry angles. Conclusion: The system design demonstrates the feasibility coupling a state-of-the art linac system with a 0.345T MRI, enabling highly conformal radiation therapy with simultaneous MR image guidance. S. Mutic’s employer (Washington University) has grant with ViewRay; D. Low is former ViewRay scientific advisory board member (ended October 2015); T. Chmielewski, G. Fought, M. Hernandez, I. Kawrakow, A. Sharma, S. Shvartsman, J. Dempsey are employees of ViewRay with stock options (Dempsey has leadership role and Dempsey/Kawrakow have stock).« less
  • Purpose: The aim of this work was to measure the influences of the Lorentz force (electron return effect) on secondary electron transport in the presence of a low magnetic field produced in a commercial MR-IGRT system using a custom heterogeneous phantom. Methods: A commercial MR-IGRT system has been commissioned in our department. The system combines real-time imaging using a split-bore 0.35-T MRI and three Co-60 heads, each collimated with a doubly-focused MLC. The integrated treatment planning system uses a Monte-Carlo algorithm that models the magnetic field effects on scattered electrons. During commissioning, a custom heterogeneity phantom was designed to acquiremore » ionization chamber and film measurements. The 30 cm cubic phantom consists of two waterfilled annuli, each containing a central region that simulates a 6 cm cubic lung tumor using polystyrene embedded in cork. Film may be placed inbetween the halves, and small-volume ionization chambers may be placed in different positions to measure dose to the tumor and near interfaces where the electron return effect is expected. The treatment planning system was used to create open-field and IMRT treatment plans on a CT scan of the phantom. Plans were delivered to the phantom, and radiographic film and ionization chamber measurements were obtained. Results: The mean ionization chamber measured dose ratio for 27 measurements for 5 plans was 0.993 ± 0.027. Lateral profile film measurements confirm that the electron-return-effect is observable, producing local dose variations of less than 10% over 5 mm with 0.35 T magnetic field for single field treatment plans. The effect becomes negligible for opposing-field and IMRT treatments. Conclusion: A heterogeneous phantom for measurement of the electron-return-effect has been designed. Ionization chamber and film measurements made with the phantom indicate that the dosimetric effect is minimal, and the treatment planning system predicts dose reasonably well for complex heterogeneous scenarios.« less
  • Purpose: To compare depth-dose and surface-dose measurements without and with the magnetic field in a 0.3T MR image-guided Co-60 treatment unit using MOSFET dosimeters. Methods: MOSFET dosimeters (Best Medical Canada, model TN-502RDH-10) were placed in a solid water phantom at 5cm depth with 8cm backscatter (with the MOSFET wires in different orientations to the couch long axis) and also on the surface of an 8cm solid water phantom. The phantoms were placed in an MR image-guided Co-60 treatment machine at an SAD of 105cm to the MOSFETs. Dose measurements were performed between 50 and 200cGy at 5cm depth in amore » 10.5cm × 10.5cm radiation field without the magnetic field (during a machine maintenance period) and with the nominal magnetic field of 0.3T. The dose linearity was measured at 5cm depth with an orthogonal field and the angular dose dependence was measured on the surface with an orthogonal field and oblique fields at +60 degrees and −60 degrees. Results: The measured MOSFET readings at 5cm depth were linear with dose with slopes of (2.97 +/− 0.01) mV/cGy and (3.01 +/− 0.02) mV/cGy without and with the magnetic field, respectively. No statistically significant difference was found. The surface dose measurements, however, were lower by 6.4% for the AP field (2.3 σ) with magnetic field, 4.9% for the −60 degree field (1.4 σ), and 0.4% different for the +60 degree field (0.2 σ). Conclusion: There is no statistically significant difference in the dose at depth without and with the magnetic field and different orientations of the MOSFET wires. There is a statistically significant difference for the surface dose due to the influence of the magnetic field on secondary electrons from head-scatter and the build-up region in certain field orientations. Clinical surface-dose dosimetry in a magnetic field should apply asymmetric angle-dependent corrections.« less
  • Purpose: To test the radiation delivery robustness of the first MR-IGRT system using a commercial cylindrical diode array detector (ArcCHECK) and an ionization thimble chamber (Exradin A18). Methods: The MR-IGRT system is composed of three evenly spaced Co-60 sources on a rotating gantry located between two magnet halves. The collimator for each source consists of 30 doubly-focused leaf pairs that allow the system to deliver both conformal and intensity modulated (IMRT) treatment plans. The system's delivery robustness was tested over a span of 6 months from September 2013 through February 2014. This was achieved by repeatedly delivering 10 patient plans.more » These plans consisted of 2 conformal prostates, 2 IMRT prostates, 2 IMRT head and neck, 2 IMRT breast, 1 IMRT pancreas, and 1 IMRT bladder. The plans were generated with the system's treatment planning software. Once the plans were generated, quality assurance plans were created on a digital ArcCHECK dataset. The ArcCHECK used for testing was specially designed to be MR-compatible by moving the power supply outside of the magnetic field. The A18 ionization chamber was placed in a custom plastic plug insert in the center of the ArcCHECK. Gamma analysis was used with the ArcCHECK for relative dose evaluating both 3%/3mm and 2%/2mm. Absolute point dose was compared between ion chamber measurement and treatment plan. Results: The ArcCHECK passing rate remained constant over the 6 month period. The average passing rate for 3%/3mm and 2%/2mm analysis was 98.6% ± 0.7 and 88.8% ± 2.9, respectively. The ion chamber measurements showed little variation with an average percent difference between planned dose verses measured dose of 0.9% ± 0.7. Conclusion: Minimal differences were noted in the delivery of the 10 patient plans. Over a period that included acceptance testing, commissioning, and clinical deliveries, the MR-IGRT system remained consistent in radiation delivery.« less
  • Purpose: To test the sensitivity of the quality assurance (QA) tools actively used on a clinical MR-IGRT system for potential delivery errors. Methods: Patient-specific QA procedures have been implemented for a commercially available Cobalt-60 MR-IGRT system. The QA tools utilized were a MR-compatible cylindrical diode-array detector (ArcCHECK) with a custom insert which positions an ionization chamber (Exradin A18) in the middle of the device, as well as an in-house treatment delivery verification program. These tools were tested to investigate their sensitivity to delivery errors. For the ArcCHECK and ion chamber, a baseline was established with a static field irradiation tomore » a known dose. Variations of the baseline were investigated which included rotated gantry, altered field size, directional shifts, and different delivery time. In addition, similar variations were tested with the automated delivery verification program that compared the treatment parameters in the machine delivery logs to the ones in the plan. To test the software, a 3-field conformal plan was generated as the baseline. Results: ArcCHECK noted at least a 13% decrease in passing rate from baseline in the following scenarios: gantry rotation of 1 degree from plan, 5mm change in field size, 2mm lateral shift, and delivery time decrease. Ion chamber measurements remained consistent for these variations except for the 5 second decrease in delivery time scenario which resulted in an 8% difference from baseline. The delivery verification software was able to detect and report the simulated errors such as when the gantry was rotated by 0.6 degrees, the beam weighting was changed by a percent, a single multileaf collimator was moved by 1cm, and the dose was changed from 2 to 1.8Gy. Conclusion: The results show that the current tools used for patient specific QA are capable of detecting small errors in RT delivery with presence of magnetic field.« less