Dosimetric Feasibility of Utilizing the ViewRay Magnetic Resonance Guided Linac System for Image-guided Spine Stereotactic Body Radiation Therapy

Redler, Gage; Stevens, Tynan; Cammin, J.; Malin, Martha; Green, Olga; Mutic, Sasa; Pitroda, Sean P.; Aydogan, Bulent

doi:10.7759/cureus.6364

Cited by 10 publications

(17 citation statements)

References 29 publications

(54 reference statements)

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Section: Discussionmentioning

confidence: 99%

“…The MR-guided RT can enable real-time motion monitoring during treatment with cine MRI and it could be an option for spine SBRT as it has been shown that these treatments are dosimetrically feasible. [36][37][38] Overall, the presented approach using periodic triggered kV imaging and visual inspection of projected planning contours versus patient anatomy during spine SBRT treatment delivery provides an effective, non-invasive intrafraction motion monitoring solution, using the built-in functionality of the TrueBeam platform. An important limitation is that the monitoring result is qualitative and depends on observer visual detection capability.…”

Section: Discussionmentioning

confidence: 99%

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Triggered kV Imaging During Spine SBRT for Intrafraction Motion Management

Koo

Nardella

Degnan

et al. 2021

Technol Cancer Res Treat

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Purpose: To monitor intrafraction motion during spine stereotactic body radiotherapy(SBRT) treatment delivery with readily available technology, we implemented triggered kV imaging using the on-board imager(OBI) of a modern medical linear accelerator with an advanced imaging package. Methods: Triggered kV imaging for intrafraction motion management was tested with an anthropomorphic phantom and simulated spine SBRT treatments to the thoracic and lumbar spine. The vertebral bodies and spinous processes were contoured as the image guided radiotherapy(IGRT) structures specific to this technique. Upon each triggered kV image acquisition, 2D projections of the IGRT structures were automatically calculated and updated at arbitrary angles for display on the kV images. Various shifts/rotations were introduced in x, y, z, pitch, and yaw. Gantry-angle-based triggering was set to acquire kV images every 45°. A group of physicists/physicians(n = 10) participated in a survey to evaluate clinical efficiency and accuracy of clinical decisions on images containing various phantom shifts. This method was implemented clinically for treatment of 42 patients(94 fractions) with 15 second time-based triggering. Result: Phantom images revealed that IGRT structure accuracy and therefore utility of projected contours during triggered imaging improved with smaller CT slice thickness. Contouring vertebra superior and inferior to the treatment site was necessary to detect clinically relevant phantom rotation. From the survey, detectability was proportional to the shift size in all shift directions and inversely related to the CT slice thickness. Clinical implementation helped evaluate robustness of patient immobilization. Based on visual inspection of projected IGRT contours on planar kV images, appreciable intrafraction motion was detected in eleven fractions(11.7%). Discussion: Feasibility of triggered imaging for spine SBRT intrafraction motion management has been demonstrated in phantom experiments and implementation for patient treatments. This technique allows efficient, non-invasive monitoring of patient position using the OBI and patient anatomy as a direct visual guide.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Triggered kV Imaging During Spine SBRT for Intrafraction Motion Management

Koo

Nardella

Degnan

et al. 2021

Technol Cancer Res Treat

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“…The system allows to shift the couch and to predict the dose on the anatomy of the day. Moreover, both simple re-optimization or full online-adaptive workflow with dose re-optimization are available [ 5 , 6 ].…”

Section: Introductionmentioning

confidence: 99%

Patient positioning and immobilization procedures for hybrid MR-Linac systems

et al. 2021

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Hybrid magnetic resonance (MR)-guided linear accelerators represent a new horizon in the field of radiation oncology. By harnessing the favorable combination of on-board MR-imaging with the possibility to daily recalculate the treatment plan based on real-time anatomy, the accuracy in target and organs-at-risk identification is expected to be improved, with the aim to provide the best tailored treatment. To date, two main MR-linac hybrid machines are available, Elekta Unity and Viewray MRIdian. Of note, compared to conventional linacs, these devices raise practical issues due to the positioning phase for the need to include the coil in the immobilization procedure and in order to perform the best reproducible positioning, also in light of the potentially longer treatment time. Given the relative novelty of this technology, there are few literature data regarding the procedures and the workflows for patient positioning and immobilization for MR-guided daily adaptive radiotherapy. In the present narrative review, we resume the currently available literature and provide an overview of the positioning and setup procedures for all the anatomical districts for hybrid MR-linac systems.

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“…22 For example, the feasibility of spine SBRT was demonstrated in several recent studies. 23,24 Similar to spine SBRT, brain SRS requires highly conformal dose distributions and high dose gradients to spare organs-atrisk and/or reduce the volume of normal brain tissue irradiated. A recent study by Wen et al investigated the feasibility of performing cranial SRS with the ViewRay MR-linac.…”

Section: Introductionmentioning

confidence: 99%

“…The combination of the decreased beam penumbra and double‐stacked double‐focused MLC (0.415‐cm‐effective width) reduced the minimum available field size and enabled more conformal treatments 22 . For example, the feasibility of spine SBRT was demonstrated in several recent studies 23,24 . Similar to spine SBRT, brain SRS requires highly conformal dose distributions and high dose gradients to spare organs‐at‐risk and/or reduce the volume of normal brain tissue irradiated.…”

Section: Introductionmentioning

confidence: 99%

Dosimetric feasibility of brain stereotactic radiosurgery with a 0.35 T MRI‐guided linac and comparison vs a C‐arm‐mounted linac

et al. 2020

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Purpose MRI is the gold‐standard imaging modality for brain tumor diagnosis and delineation. The purpose of this work was to investigate the feasibility of performing brain stereotactic radiosurgery (SRS) with a 0.35 T MRI‐guided linear accelerator (MRL) equipped with a double‐focused multileaf collimator (MLC). Dosimetric comparisons were made vs a conventional C‐arm‐mounted linac with a high‐definition MLC. Methods The quality of MRL single‐isocenter brain SRS treatment plans was evaluated as a function of target size for a series of spherical targets with diameters from 0.6 cm to 2.5 cm in an anthropomorphic head phantom and six brain metastases (max linear dimension = 0.7‐1.9 cm) previously treated at our clinic on a conventional linac. Each target was prescribed 20 Gy to 99% of the target volume. Step‐and‐shoot IMRT plans were generated for the MRL using 11 static coplanar beams equally spaced over 360° about an isocenter placed at the center of the target. Couch and collimator angles are fixed for the MRL. Two MRL planning strategies (VR1 and VR2) were investigated. VR1 minimized the 12 Gy isodose volume while constraining the maximum point dose to be within ±1 Gy of 25 Gy which corresponded to normalization to an 80% isodose volume. VR2 minimized the 12 Gy isodose volume without the maximum dose constraint. For the conventional linac, the TB1 method followed the same strategy as VR1 while TB2 used five noncoplanar dynamic conformal arcs. Plan quality was evaluated in terms of conformity index (CI), conformity/gradient index (CGI), homogeneity index (HI), and volume of normal brain receiving ≥12 Gy (V12Gy). Quality assurance measurements were performed with Gafchromic EBT‐XD film following an absolute dose calibration protocol. Results For the phantom study, the CI of MRL plans was not significantly different compared to a conventional linac (P > 0.05). The use of dynamic conformal arcs and noncoplanar beams with a conventional linac spared significantly more normal brain (P = 0.027) and maximized the CGI, as expected. The mean CGI was 95.9 ± 4.5 for TB2 vs 86.6 ± 3.7 (VR1), 88.2 ± 4.8 (VR2), and 88.5 ± 5.9 (TB1). Each method satisfied a normal brain V12Gy ≤ 10.0 cm3 planning goal for targets with diameter ≤2.25 cm. The mean V12Gy was 3.1 cm3 for TB2 vs 5.5 cm3, 5.0 cm3 and 4.3 cm3, for VR1, VR2, and TB1, respectively. For a 2.5‐cm diameter target, only TB2 met the V12Gy planning objective. The MRL clinical brain plans were deemed acceptable for patient treatment. The normal brain V12Gy was ≤6.0 cm3 for all clinical targets (maximum target volume = 3.51 cm3). CI and CGI ranged from 1.12–1.65 and 81.2–88.3, respectively. Gamma analysis pass rates (3%/1mm criteria) exceeded 97.6% for six clinical targets planned and delivered on the MRL. The mean measured vs computed absolute dose difference was −0.1%. Conclusions The MRL system can produce clinically acceptable brain SRS plans for spherical lesions with diameter ≤2.25 cm. Large lesions (>2.25 cm) should be treated with a linac capable of delivering noncoplan...

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Dosimetric Feasibility of Utilizing the ViewRay Magnetic Resonance Guided Linac System for Image-guided Spine Stereotactic Body Radiation Therapy

Cited by 10 publications

References 29 publications

Triggered kV Imaging During Spine SBRT for Intrafraction Motion Management

Triggered kV Imaging During Spine SBRT for Intrafraction Motion Management

Patient positioning and immobilization procedures for hybrid MR-Linac systems

Dosimetric feasibility of brain stereotactic radiosurgery with a 0.35 T MRI‐guided linac and comparison vs a C‐arm‐mounted linac

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