Dosimetric Impact of Using a Virtual Couch Shift for Online Correction of Setup Errors for Brain Patients on an Integrated High-Field Magnetic Resonance Imaging Linear Accelerator


      To quantify the dosimetric impact of using virtual couch shift (VCS) for correcting setup errors in glioblastoma multiforme (GBM) patients treated on a magnetic resonance imaging (MRI)-linac.

      Methods and Materials

      Six GBM patients treated with 60 Gy (30 fractions) were selected for this simulation study. For each case, 2 reference plans were generated in the MRL treatment planning system: With (WIB) and with no (NOB) MRI B field present. Subsequently, 2-mm, 4-mm, and 6-mm translational errors were simulated and corrected for using a VCS method based on shift-only, warm start segment weight (SWO), and segment weight and shape (SSO) optimization. The resulting distributions were compared with the reference plan using planning target volume (PTV) homogeneity index (HI), conformity index (CI), organs at risk (OAR) maximum dose (D0.01cc), and OAR median dose (D50). A simulated 30-fraction treatment was constructed to evaluate the cumulative effect of daily corrections. Feasibility and workflow for correcting rotations were also assessed.


      All reference plans were deemed clinically acceptable with respect to PTV and OAR objectives. The difference in HI (ΔHI) between corrected and reference was not statistically significant between WIB and NOB (P=.89). The average ΔHI was +0.8%, −0.1%, and −1.0% for shift-only, SWO, and SSO, respectively, with a statistically significant difference (P<.001) for shift-only versus SWO and SSO. The CI remained unchanged (mean ΔCI = −0.01) between the corrected and reference plans, with no statistically significant dependence on magnetic field presence, correction method, or shift magnitude or orientation. The brainstem D50 on average decreased with SWO and SSO; however, D0.01cc increased by a median value of 1.2%, 1.9%, and 2.0% for shift-only, SWO, and SSO, respectively. For other OARs, D0.01cc decreased using SWO or SSO. For the simulated treatment and rotational corrections, similar trends were measured.


      For translational errors in brain MRI-linac radiation therapy, the VCS method is an acceptable correction strategy, but caution must be used in particular for serial organs where maximum doses are most relevant. The effect of the magnetic field on relative changes between corrected versus reference plans is not clinically relevant.
      To read this article in full you will need to make a payment
      ASTRO Member Login
      ASTRO Members, full access to the journal is a member benefit. Use your society credentials to access all journal content and features.
      One-time access price info
      • For academic or personal research use, select 'Academic and Personal'
      • For corporate R&D use, select 'Corporate R&D Professionals'

      Purchase one-time access:

      Already a print subscriber? Claim online access
      Already an online subscriber? Sign in
      Institutional Access: Sign in to ScienceDirect


        • Lagendijk J.J.
        • Raaymakers B.W.
        • Raaijmakers A.J.
        • et al.
        MRI/linac integration.
        Radiother Oncol. 2008; 86: 25-29
        • Raaymakers B.W.
        • Lagendijk J.J.
        • Overweg J.
        • et al.
        Integrating a 1.5 T MRI scanner with a 6 MV accelerator: Proof of concept.
        Phys Med Biol. 2009; 54: N229-N237
        • Mahdavi S.R.
        • Esmaeeli A.D.
        • Pouladian M.
        • et al.
        Breast dosimetry in transverse and longitudinal field MRI-linac radiotherapy systems.
        Med Phys. 2015; 42: 925-936
        • Stam M.K.
        • van Vulpen M.
        • Barendrecht M.M.
        • et al.
        Dosimetric feasibility of MRI-guided external beam radiotherapy of the kidney.
        Phys Med Biol. 2013; 58: 4933-4941
        • van Heijst T.C.
        • den Hartogh M.D.
        • Lagendijk J.J.
        • et al.
        MR-guided breast radiotherapy: Feasibility and magnetic-field impact on skin dose.
        Phys Med Biol. 2013; 58: 5917-5930
        • McPartlin A.J.
        • Li X.A.
        • Kershaw L.E.
        • et al.
        MRI-guided prostate adaptive radiotherapy: A systematic review.
        Radiother Oncol. 2016; 119: 371-380
        • Menten M.J.
        • Fast M.F.
        • Nill S.
        • et al.
        Lung stereotactic body radiotherapy with an MR-linac: Quantifying the impact of the magnetic field and real-time tumor tracking.
        Radiother Oncol. 2016; 119: 461-466
        • Bol G.H.
        • Lagendijk J.J.
        • Raaymakers B.W.
        Virtual couch shift (VCS): Accounting for patient translation and rotation by online IMRT re-optimization.
        Phys Med Biol. 2013; 58: 2989-3000
        • Mohan R.
        • Zhang X.
        • Wang H.
        • et al.
        Use of deformed intensity distributions for on-line modification of image-guided IMRT to account for interfractional anatomic changes.
        Int J Radiat Oncol Biol Phys. 2005; 61: 1258-1266
        • Rijkhorst E.J.
        • Lakeman A.
        • Nijkamp J.
        • et al.
        Strategies for online organ motion correction for intensity-modulated radiotherapy of prostate cancer: Prostate, rectum, and bladder dose effects.
        Int J Radiat Oncol Biol Phys. 2009; 75: 1254-1260
        • Ludlum E.
        • Mu G.
        • Weinberg V.
        • et al.
        An algorithm for shifting MLC shapes to adjust for daily prostate movement during concurrent treatment with pelvic lymph nodes.
        Med Phys. 2007; 34: 4750-4756
        • Ahunbay E.E.
        • Ates O.
        • Li X.A.
        An online replanning method using warm start optimization and aperture morphing for flattening-filter-free beams.
        Med Phys. 2016; 43: 4575
        • Ates O.
        • Ahunbay E.E.
        • Moreau M.
        • et al.
        Technical note: A fast online adaptive replanning method for VMAT using flattening filter free beams.
        Med Phys. 2016; 43: 2756
        • Thompson C.M.
        • Weston S.J.
        • Cosgrove V.C.
        • et al.
        A dosimetric characterization of a novel linear accelerator collimator.
        Med Phys. 2014; 41: 031713
        • Ahmad S.B.
        • Sarfehnia A.
        • Paudel M.R.
        • et al.
        Evaluation of a commercial MRI Linac based Monte Carlo dose calculation algorithm with GEANT4.
        Med Phys. 2016; 43: 894-907
        • Murray L.J.
        • Cosgrove V.
        • Lilley J.
        • et al.
        Developing a class solution for prostate stereotactic ablative body radiotherapy (SABR) using volumetric modulated arc therapy (VMAT).
        Radiother Oncol. 2014; 110: 298-302
        • Wu Q.
        • Mohan R.
        • Niemierko A.
        • et al.
        Optimization of intensity-modulated radiotherapy plans based on the equivalent uniform dose.
        Int J Radiat Oncol Biol Phys. 2002; 52: 224-235
        • Kataria T.
        • Sharma K.
        • Subramani V.
        • et al.
        Homogeneity index: An objective tool for assessment of conformal radiation treatments.
        J Med Phys. 2012; 37: 207-213
        • Yoon M.
        • Park S.Y.
        • Shin D.
        • et al.
        A new homogeneity index based on statistical analysis of the dose-volume histogram.
        J Appl Clin Med Phys. 2007; 8: 9-17
        • Shaw E.
        • Kline R.
        • Gillin M.
        • et al.
        Radiation Therapy Oncology Group: Radiosurgery quality assurance guidelines.
        Int J Radiat Oncol Biol Phys. 1993; 27: 1231-1239
        • Seibert T.M.
        • White N.S.
        • Kim G.Y.
        • et al.
        Distortion inherent to magnetic resonance imaging can lead to geometric miss in radiosurgery planning.
        Pract Radiat Oncol. 2016; 6: e319-e328
        • Watanabe Y.
        • Han E.
        Image registration accuracy of GammaPlan: A phantom study.
        J Neurosurg. 2008; 109: 21-24
        • Demol B.
        • Boydev C.
        • Korhonen J.
        • et al.
        Dosimetric characterization of MRI-only treatment planning for brain tumors in atlas-based pseudo-CT images generated from standard T1-weighted MR images.
        Med Phys. 2016; 43: 6557
        • Yu H.
        • Lee Y.
        • Ruschin M.
        • et al.
        Mo-f-campus-j-04: Tissue segmentation-based MR electron density mapping method for MR-only radiation treatment planning of brain.
        Med Phys. 2015; 42: 3574
        • Uh J.
        • Merchant T.E.
        • Li Y.
        • et al.
        MRI-based treatment planning with pseudo CT generated through atlas registration.
        Med Phys. 2014; 41: 051711
        • Raaymakers B.W.
        • de Boer J.C.
        • Knox C.
        • et al.
        Integrated megavoltage portal imaging with a 1.5 T MRI linac.
        Phys Med Biol. 2011; 56: N207-N214
        • Chen G.P.
        • Ahunbay E.
        • Li X.A.
        Technical note: Development and performance of a software tool for quality assurance of online replanning with a conventional linac or MR-linac.
        Med Phys. 2016; 43: 1713
        • Tsien C.
        • Gomez-Hassan D.
        • Ten Haken R.K.
        • et al.
        Evaluating changes in tumor volume using magnetic resonance imaging during the course of radiotherapy treatment of high-grade gliomas: Implications for conformal dose-escalation studies.
        Int J Radiat Oncol Biol Phys. 2005; 62: 328-332
        • Kim T.G.
        • Lim do H.
        Interfractional variation of radiation target and adaptive radiotherapy for totally resected glioblastoma.
        J Korean Med Sci. 2013; 28: 1233-1237
        • Raaijmakers A.J.
        • Raaymakers B.W.
        • Lagendijk J.J.
        Integrating a MRI scanner with a 6 MV radiotherapy accelerator: Dose increase at tissue-air interfaces in a lateral magnetic field due to returning electrons.
        Phys Med Biol. 2005; 50: 1363-1376
        • Raaijmakers A.J.
        • Raaymakers B.W.
        • van der Meer S.
        • et al.
        Integrating a MRI scanner with a 6 MV radiotherapy accelerator: Impact of the surface orientation on the entrance and exit dose due to the transverse magnetic field.
        Phys Med Biol. 2007; 52: 929-939
        • Raaijmakers A.J.
        • Raaymakers B.W.
        • Lagendijk J.J.
        Magnetic-field-induced dose effects in MR-guided radiotherapy systems: Dependence on the magnetic field strength.
        Phys Med Biol. 2008; 53: 909-923
        • Bol G.H.
        • Lagendijk J.J.
        • Raaymakers B.W.
        Compensating for the impact of non-stationary spherical air cavities on IMRT dose delivery in transverse magnetic fields.
        Phys Med Biol. 2015; 60: 755-768
        • Chen X.
        • Prior P.
        • Chen G.P.
        • et al.
        Technical note: Dose effects of 1.5 T transverse magnetic field on tissue interfaces in MRI-guided radiotherapy.
        Med Phys. 2016; 43: 4797
        • Uilkema S.
        • van der Heide U.
        • Sonke J.J.
        • et al.
        A 1.5 T transverse magnetic field in radiotherapy of rectal cancer: Impact on the dose distribution.
        Med Phys. 2015; 42: 7182-7189
        • Tseng C.L.
        • Eppinga W.
        • Seravalli E.
        • et al.
        Dosimetric feasibility of the hybrid magnetic resonance imaging (MRI)-linear accelerator system for brain metastases: The impact of the magnetic field.
        Int J Radiat Oncol Biol Phys. 2016; 96: E628


      Commenting Guidelines

      To submit a comment for a journal article, please use the space above and note the following:

      • We will review submitted comments as soon as possible, striving for within two business days.
      • This forum is intended for constructive dialogue. Comments that are commercial or promotional in nature, pertain to specific medical cases, are not relevant to the article for which they have been submitted, or are otherwise inappropriate will not be posted.
      • We require that commenters identify themselves with names and affiliations.
      • Comments must be in compliance with our Terms & Conditions.
      • Comments are not peer-reviewed.