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Journal articles on the topic 'MRI-linear accelerator'

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Author: Grafiati

Published: 10 December 2022

Last updated: 28 January 2023

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1

Liney, G. P., B. Whelan, B. Oborn, M. Barton, and P. Keall. "MRI-Linear Accelerator Radiotherapy Systems." Clinical Oncology 30, no. 11 (November 2018): 686–91. http://dx.doi.org/10.1016/j.clon.2018.08.003.

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2

Crijns, S. P. M., J. G. M. Kok, J. J. W. Lagendijk, and B. W. Raaymakers. "Towards MRI-guided linear accelerator control: gating on an MRI accelerator." Physics in Medicine and Biology 56, no. 15 (July 13, 2011): 4815–25. http://dx.doi.org/10.1088/0031-9155/56/15/012.

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3

Randall, James W., Nikhil Rammohan, Indra J. Das, and Poonam Yadav. "Towards Accurate and Precise Image-Guided Radiotherapy: Clinical Applications of the MR-Linac." Journal of Clinical Medicine 11, no. 14 (July 13, 2022): 4044. http://dx.doi.org/10.3390/jcm11144044.

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Advances in image-guided radiotherapy have brought about improved oncologic outcomes and reduced toxicity. The next generation of image guidance in the form of magnetic resonance imaging (MRI) will improve visualization of tumors and make radiation treatment adaptation possible. In this review, we discuss the role that MRI plays in radiotherapy, with a focus on the integration of MRI with the linear accelerator. The MR linear accelerator (MR-Linac) will provide real-time imaging, help assess motion management, and provide online adaptive therapy. Potential advantages and the current state of these MR-Linacs are highlighted, with a discussion of six different clinical scenarios, leading into a discussion on the future role of these machines in clinical workflows.

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4

Graham, J., G. Redler, K. DeLozier, H. H. M. Yu, D. E. Oliver, and S. A. Rosenberg. "Dosimetric Feasibility of HA-WBRT With an MRI-Guided Linear Accelerator." International Journal of Radiation Oncology*Biology*Physics 111, no. 3 (November 2021): e511-e512. http://dx.doi.org/10.1016/j.ijrobp.2021.07.1403.

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5

Blinde, S., A. S. R. Mohamed, A. Al-Mamgani, K. Newbold, I. Karam, J. R. Robbins, D. Thomson, N. Raaijmakers, C. D. Fuller, and C. Terhaard. "Interobserver Variation in the International MRI Linear Accelerator Oropharyngeal Carcinoma Delineation Study." International Journal of Radiation Oncology*Biology*Physics 100, no. 5 (April 2018): 1362. http://dx.doi.org/10.1016/j.ijrobp.2017.12.143.

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6

Bol, G. H., S. Hissoiny, J. J. W. Lagendijk, and B. W. Raaymakers. "Fast online Monte Carlo-based IMRT planning for the MRI linear accelerator." Physics in Medicine and Biology 57, no. 5 (February 21, 2012): 1375–85. http://dx.doi.org/10.1088/0031-9155/57/5/1375.

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7

Wang, Michael H., Anthony Kim, Mark Ruschin, Hendrick Tan, Hany Soliman, Sten Myrehaug, Jay Detsky, et al. "Comparison of Prospectively Generated Glioma Treatment Plans Clinically Delivered on Magnetic Resonance Imaging (MRI)-Linear Accelerator (MR-Linac) Versus Conventional Linac: Predicted and Measured Skin Dose." Technology in Cancer Research & Treatment 21 (January 2022): 153303382211246. http://dx.doi.org/10.1177/15330338221124695.

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Introduction: Magnetic resonance imaging-linear accelerator radiotherapy is an innovative technology that requires special consideration for secondary electron interactions within the magnetic field, which can alter dose deposition at air–tissue interfaces. As part of ongoing quality assurance and quality improvement of new radiotherapy technologies, the purpose of this study was to evaluate skin dose modelled from the treatment planning systems of a magnetic resonance imaging-linear accelerator and a conventional linear accelerator, and then correlate with in vivo measurements of delivered skin dose from each linear accelerator. Methods: In this prospective cohort study, 37 consecutive glioma patients had treatment planning completed and approved prior to radiotherapy initiation using commercial treatment planning systems: a Monte Carlo-based algorithm for magnetic resonance imaging-linear accelerator or a convolution-based algorithm for conventional linear accelerator. In vivo skin dose was measured using an optically stimulated luminescent dosimeter. Results: Monte Carlo-based magnetic resonance imaging-linear accelerator plans and convolution-based conventional linear accelerator plans had similar dosimetric parameters for target volumes and organs-at-risk. However, magnetic resonance imaging-linear accelerator plans had 1.52 Gy higher mean dose to air cavities ( P < .0001) and 1.10 Gy higher mean dose to skin ( P < .0001). In vivo skin dose was 14.5% greater for magnetic resonance imaging-linear accelerator treatments ( P = .0027), and was more accurately predicted by Monte Carlo-based calculation ( ρ = 0.95, P < .0001) versus convolution-based ( ρ = 0.80, P = .0096). Conclusion: This is the first prospective dosimetric comparison of glioma patients clinically treated on both magnetic resonance imaging-linear accelerator and conventional linear accelerator. Our findings suggest that skin doses were significantly greater with magnetic resonance imaging-linear accelerator plans but correlated better with in vivo measurements of actual skin dose from delivered treatments. Future magnetic resonance imaging-linear accelerator planning processes are being designed to account for skin dosimetry and treatment delivery.

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8

Woodings, Simon J., J. H. Wilfred Vries, Jan M. G. Kok, Sara L. Hackett, Bram Asselen, Johanna J. Bluemink, Helena M. Zijp, et al. "Acceptance procedure for the linear accelerator component of the 1.5 T MRI‐linac." Journal of Applied Clinical Medical Physics 22, no. 8 (July 17, 2021): 45–59. http://dx.doi.org/10.1002/acm2.13068.

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9

Williams, C. L., E. Huynh, J. Campbell, J. Penney, S. Boyle, I. Usta, E. Neubauer Sugar, et al. "Initial Experience With Online Adaptive Radiotherapy Workflows on an MRI-guided Linear Accelerator." International Journal of Radiation Oncology*Biology*Physics 108, no. 3 (November 2020): e348. http://dx.doi.org/10.1016/j.ijrobp.2020.07.2327.

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10

Carlone, M., M. Lamey, S. Steciw, B. Burke, and B. Fallone. "TH-C-L100J-02: Study of RF Interference Between a Linear Accelerator and MRI." Medical Physics 34, no. 6Part22 (June 2007): 2621. http://dx.doi.org/10.1118/1.2761640.

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11

Bol, G. H., S. Hissoiny, J. J. W. Lagendijk, and B. W. Raaymakers. "OC-0553 FAST MONTE-CARLO BASED IMRT PLANNING FOR THE MRI LINEAR ACCELERATOR (MRL)." Radiotherapy and Oncology 103 (May 2012): S221. http://dx.doi.org/10.1016/s0167-8140(12)70892-7.

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12

Brand, Nicole, Stefan Pojtinger, Savas Tsitsekidis, Daniela Thorwarth, and Oliver S. Dohm. "Experimental analysis of correction factors for reference dosimetry in a magnetic field." Current Directions in Biomedical Engineering 3, no. 2 (September 7, 2017): 803–5. http://dx.doi.org/10.1515/cdbme-2017-0170.

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AbstractToday, hybrid systems of linear accelerator and MRI scanner are clinically available. Therefore it is important to investigate the feasibility of reference dosimetry with ionization chambers in the presence of a magnetic field and determine correction factors. In this work, correction factors under various conditions that influence the chamber response were experimentally investigated, using a conventional 6 MV linear accelerator together with a stand-alone magnet. We found that the correction factor for a PTW31010 ionization chamber ranges from 0.9873 to 1.009 depending on the magnetic field strength, magnetic field orientation and magnetic field size. The phantom material also does have an influence on the measured signal. Therefore, reference dosimetry with ionization chambers in the presence of a magnetic field is feasible, but requires dedicated correction factors, which depend on the experimental setup.

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13

Huber, Peter E., Hans Hawighorst, Martin Fuss, Gerhard van Kaick, Michael F. Wannenmacher, and Juergen Debus. "Transient enlargement of contrast uptake on MRI after linear accelerator (linac) stereotactic radiosurgery for brain metastases." International Journal of Radiation Oncology*Biology*Physics 49, no. 5 (April 2001): 1339–49. http://dx.doi.org/10.1016/s0360-3016(00)01511-x.

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14

Charaghvandi, K. R., T. van't Westeinde, S. Yoo, A. C. Houweling, A. Rodrigues, H. M. Verkooijen, M. E. P. Philippens, B. van Asselen, J. K. Horton, and H. J. G. D. van den Bongard. "Single dose partial breast irradiation using an MRI linear accelerator in the supine and prone treatment position." Clinical and Translational Radiation Oncology 14 (January 2019): 1–7. http://dx.doi.org/10.1016/j.ctro.2018.09.001.

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15

Mao, W., and G. Wang. "TU-H-BRA-05: A System Design for Integration of An Interior MRI and a Linear Accelerator." Medical Physics 43, no. 6Part36 (June 2016): 3769. http://dx.doi.org/10.1118/1.4957627.

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16

Llorente, Ricardo, Benjamin O. Spieler, James Victoria, Cristiane Takita, Raphael Yechieli, John C. Ford, Karen Brown, Michael A. Samuels, and Eric A. Mellon. "MRI-guided stereotactic ablative radiation therapy of spinal bone metastases: a preliminary experience." British Journal of Radiology 93, no. 1105 (January 2020): 20190655. http://dx.doi.org/10.1259/bjr.20190655.

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Objective: MRI provides clear visualization of spinal cord, tumor, and bone for patient positioning and verification during MRI-guided radiotherapy (MRI-RT). Therefore, we wished to evaluate spine stereotactic ablative radiotherapy (SABR) feasibility with MRI-RT. Given dosimetric limitations of first generation Co-60 MRI-RT, we then evaluated improvements by newer linear accelerator (linac) MRI-RT. Methods: Nine spinal metastases were treated with Co-60 MRI-RT. Seven received a single 16 Gy fraction, and two received three fractions totaling 24 or 30 Gy. After replanning with linac MRI-RT software, comparisons of organ at risk and dose spillage objectives between Co-60 and linac plans were performed. Results: Spinal cord and cauda equina dose constraints were met in all Co-60 cases. Treatments were delivered successfully with real-time imaging during treatment and no treatment-related toxicities. While limits for dose spillage into surrounding soft tissues were not achieved due to the limitations of the Co-60 system, this could be corrected with linac MRI-RT delivery. Conclusions: MRI-RT SABR of spinal metastases is feasible with Co-60 MRI-RT. Dose delivery is improved by linac MRI-RT. Advances in knowledge: This is the first report of MRI-RT for SABR of spinal metastases. The enhanced visualization of anatomy by MRI may facilitate RT dose escalation for spine SABR.

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17

Kwong, Forrest, Daphne B. Scarpelli, Ramon F. Barajas, Debra Monaco, James A. Tanyi, Shearwood McClelland, and Jerry J. Jaboin. "Resolution of Radiation-Induced Necrosis in Arteriovenous Malformation with Bevacizumab: A Case Report and Review of Current Literature." Case Reports in Neurology 13, no. 2 (May 27, 2021): 297–304. http://dx.doi.org/10.1159/000513560.

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Stereotactic radiosurgery (SRS) is a proven treatment modality for inoperable arteriovenous malformations (AVMs). However, the rate of radiation-induced necrosis (RIN) is as high as 10%. A 6-year-old female patient presented with severe headache, emesis, and syncope, and workup revealed a Spetzler-Martin grade 4 AVM with intraventricular hemorrhage and hydrocephalus. The patient underwent a right frontal ventriculostomy followed by a linear accelerator-based SRS of 16.9 Gy. At 19 years, she developed progressive neurological symptoms. Diagnostic magnetic resonance imaging (MRI) revealed a recurrent parietal AVM nidus. We delivered the linear accelerator-based SRS of 18.5 Gy to the AVM nidus. Within 9 months, she experienced episodic headaches and left-sided weakness and spasticity; symptoms were initially managed with dexamethasone. Follow-up MRI was notable for edema and nondetectable blood flow, consistent with RIN and AVM obliteration. The second course of steroids did not provide the symptom control. Persistent RIN was noted on MRI, and she had stigmata of steroid toxicity (centripetal obesity, depression, and sleep disorder). Two infusions of bevacizumab (5 mg/kg) were administered concurrently with a tapering dose of dexamethasone. The patient noted a near immediate improvement in her headaches, and 2 months following the second bevacizumab infusion, she reported a near-complete resolution of her symptoms and displayed improved ambulation. The development of RIN remains a noteworthy concern post-SRS of AVMs. While steroids aid with initial management of RIN, for persistent and recurrent symptoms, bevacizumab infusions serve as a viable treatment course, with the added benefit of reducing the likelihood of adverse effects resulting from prolonged steroid therapy.

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18

Raaymakers, A., B. Raaymakers, and J. Lagendijk. "322 Simulation and validation of an Elekta SL linear accelerator and CT-data implementation in GEANT4 for the virtual prototyping of the MRI-accelerator." Radiotherapy and Oncology 76 (September 2005): S147—S148. http://dx.doi.org/10.1016/s0167-8140(05)81298-8.

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19

Meijers, L. T. C., S. J. Hoogcarspel, A. N. T. J. Kotte, C. N. N. Nomden, G. G. Sikkes, I. H. Kiekebosch, E. N. Groot de, et al. "OC-0163: Online workflow for the First-in-Man study on bone metastases at the MRI-linear accelerator." Radiotherapy and Oncology 123 (May 2017): S83—S84. http://dx.doi.org/10.1016/s0167-8140(17)30606-0.

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20

Wojcieszynski, A. P., P. M. Hill, S. A. Rosenberg, C. R. Hullett, Z. E. Labby, B. R. Paliwal, M. W. Geurts, et al. "A Dosimetric Comparison of MRI-Guided Cobalt-60 to Linear Accelerator--Based Stereotactic Ablative Radiation Lung Cancer Plans." International Journal of Radiation Oncology*Biology*Physics 93, no. 3 (November 2015): E588. http://dx.doi.org/10.1016/j.ijrobp.2015.07.2049.

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21

Bol, G., S. Hissoiny, J. Lagendijk, and B. Raaymakers. "WE-G-BRCD-08: Virtual Couch Shift (VCS) by Online Plan Re-Optimization for the MRI Linear Accelerator." Medical Physics 39, no. 6Part28 (June 2012): 3966. http://dx.doi.org/10.1118/1.4736185.

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22

Rammohan, Nikhil, James W. Randall, and Poonam Yadav. "History of Technological Advancements towards MR-Linac: The Future of Image-Guided Radiotherapy." Journal of Clinical Medicine 11, no. 16 (August 12, 2022): 4730. http://dx.doi.org/10.3390/jcm11164730.

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Image-guided radiotherapy (IGRT) enables optimal tumor targeting and sparing of organs-at-risk, which ultimately results in improved outcomes for patients. Magnetic resonance imaging (MRI) revolutionized diagnostic imaging with its superior soft tissue contrast, high spatiotemporal resolution, and freedom from ionizing radiation exposure. Over the past few years there has been burgeoning interest in MR-guided radiotherapy (MRgRT) to overcome current challenges in X-ray-based IGRT, including but not limited to, suboptimal soft tissue contrast, lack of efficient daily adaptation, and incremental exposure to ionizing radiation. In this review, we present an overview of the technologic advancements in IGRT that led to MRI-linear accelerator (MRL) integration. Our report is organized in three parts: (1) a historical timeline tracing the origins of radiotherapy and evolution of IGRT, (2) currently available MRL technology, and (3) future directions and aspirations for MRL applications.

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23

Sahgal, Arjun, Lijun Ma, Eric Chang, Almon Shiu, David A. Larson, Normand Laperriere, Fang-Fang Yin, et al. "Advances in Technology for Intracranial Stereotactic Radiosurgery." Technology in Cancer Research & Treatment 8, no. 4 (August 2009): 271–80. http://dx.doi.org/10.1177/153303460900800404.

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Stereotactic radiosurgery (SRS) refers to a single radiation treatment delivering a high dose to an intra-cranial target localized in three-dimensions by CT and/or MRI imaging. Traditionally, immobilization of the patient's head has been achieved using a rigid stereotactic head frame as the key step in allowing for accurate dose delivery. SRS has been delivered by both Cobalt-60 (Gamma Knife®) and linear accelerator (linac) technologies for many decades. The focus of this review is to highlight recent advances and major innovations in SRS technologies relevant to clinical practice and developments allowing for non-invasive frame SRS.

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24

Willigenburg, Thomas, Daan M. de Muinck Keizer, Max Peters, An Claes, Jan J. W. Lagendijk, Hans C. J. de Boer, and Jochem R. N. van der Voort van Zyp. "Evaluation of daily online contour adaptation by radiation therapists for prostate cancer treatment on an MRI-guided linear accelerator." Clinical and Translational Radiation Oncology 27 (March 2021): 50–56. http://dx.doi.org/10.1016/j.ctro.2021.01.002.

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25

Farjam, Reza, Himanshu Nagar, Xi Kathy Zhou, David Ouellette, Silvia Chiara Formenti, and J. Keith DeWyngaert. "Deep learning‐based synthetic CT generation for MR‐only radiotherapy of prostate cancer patients with 0.35T MRI linear accelerator." Journal of Applied Clinical Medical Physics 22, no. 8 (June 28, 2021): 93–104. http://dx.doi.org/10.1002/acm2.13327.

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26

Ahmad, S., A. Sarfehnia, M. Paudel, A. Sahgal, S. Hissoiny, and B. Keller. "SU-E-T-203: Comparison of a Commercial MRI-Linear Accelerator Based Monte Carlo Dose Calculation Algorithm and Geant4." Medical Physics 42, no. 6Part15 (June 2015): 3378–79. http://dx.doi.org/10.1118/1.4924564.

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27

Marciscano, Ariel E., Jonathan P. S. Knisely, Himanshu Nagar, Andrew Brandmaier, Ryan T. Pennell, Michael Speiser, Sungheon G. Kim, et al. "SPIN-02 LEVERAGING AN MRI-GUIDED LINEAR ACCELERATOR PLATFORM FOR POST-OPERATIVE STEREOTACTIC BODY RADIATION THERAPY (SBRT) OF SPINAL METASTASES." Neuro-Oncology Advances 4, Supplement_1 (August 1, 2022): i11. http://dx.doi.org/10.1093/noajnl/vdac078.043.

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Abstract PURPOSE/OBJECTIVE(S) Post-operative spine SBRT presents unique clinical challenges. Spinal hardware produces CT and high-field strength MRI artifacts that obscure visualization of the spinal cord and unresected disease. Existing workflows incorporate additional invasive procedures with CT myelogram and quality control for these procedures can introduce uncertainty into SBRT planning. Reducing metallic imaging artifact with a low-field strength (0.35 T) MRI integrated into a MR-Linac (MRL) may facilitate superior visualization of the spinal cord, improved target delineation and treatment localization. The primary objective is to determine the feasibility of MRL-based simulation workflow to facilitate MR-guided post-operative spine SBRT without the need for CT myelogram or CT-based target delineation. MATERIALS/METHODS A single-institution, single-arm interventional feasibility study is planned. A total of 10 patients who underwent surgical resection of solid tumor spinal metastases with an indication for post-operative SBRT will be enrolled and undergo radiation planning and treatment on a MRL platform that combines a 6MV Linac and 0.35 T on-board MRI system. Enrolled subjects will undergo CT and MR simulation followed by standard-of-care post-operative spine SBRT and follow-up spine imaging every 3 months. RESULTS The primary endpoint is feasibility of MR-guided post-operative spine SBRT without CT myelogram. Feasibility is defined as > 70% of participants with clinically acceptable visualization/delineation as determined by blinded dual neuroradiologist review for clinically acceptable visualization/delineation of organs-at-risk (OARs) and target volume(s). Exploratory endpoints involve radiation dosimetry analysis of OARs and target volumes as well as documenting the use of adaptive planning. Radiation site progression-free survival will be recorded at 6-months after SBRT. CONCLUSION If feasible, an MRL-based workflow for post-operative spine SBRT represents a patient-centric approach to improve efficiency, minimize treatment delays, and avoid invasive procedures that may improve clinical management of solid tumor spinal metastases.

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28

Dayarian, Iman, Timothy C. Y. Chan, David Jaffray, and Teo Stanescu. "A mixed-integer optimization approach for homogeneous magnet design." TECHNOLOGY 06, no. 02 (June 2018): 49–58. http://dx.doi.org/10.1142/s2339547818500036.

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Magnetic resonance imaging (MRI) is a powerful diagnostic tool that has become the imaging modality of choice for soft-tissue visualization in radiation therapy. Emerging technologies aim to integrate MRI with a medical linear accelerator to form novel cancer therapy systems (MR-linac), but the design of these systems to date relies on heuristic procedures. This paper develops an exact, optimization-based approach for magnet design that 1) incorporates the most accurate physics calculations to date, 2) determines precisely the relative spatial location, size, and current magnitude of the magnetic coils, 3) guarantees field homogeneity inside the imaging volume, 4) produces configurations that satisfy, for the first time, small-footprint feasibility constraints required for MR-linacs. Our approach leverages modern mixed-integer programming (MIP), enabling significant flexibility in magnet design generation, e.g., controlling the number of coils and enforcing symmetry between magnet poles. Our numerical results demonstrate the superiority of our method versus current mainstream methods.

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29

Tadic, T., and BG Fallone. "Poster - Thurs Eve-08: Passive shimming optimization of a permanent magnet structure for a prototype coupled MRI-medical linear accelerator." Medical Physics 35, no. 7Part2 (July 2008): 3403. http://dx.doi.org/10.1118/1.2965927.

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30

Zapata, I., R. Magallon, M. I. Garcia-Berrocal, R. Moleron, M. Veiras, F. J. Valcarcel, C. A. Regueiro, J. Romero, L. Nuñez, and A. de la Torre. "MRI Initial Changes are Correlated with Long-term Outcome: A Single-institution Experience with Linear Accelerator Radiosurgery For Vestibular Schwannomas." International Journal of Radiation Oncology*Biology*Physics 72, no. 1 (September 2008): S222—S223. http://dx.doi.org/10.1016/j.ijrobp.2008.06.684.

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31

Nan, Jiaofen, Nannan Zong, Qiqiang Chen, Liangliang Zhang, Qian Zheng, and Yongquan Xia. "A Structure Design Method for Reduction of MRI Acoustic Noise." Computational and Mathematical Methods in Medicine 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/6253428.

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The acoustic problem of the split gradient coil is one challenge in a Magnetic Resonance Imaging and Linear Accelerator (MRI-LINAC) system. In this paper, we aimed to develop a scheme to reduce the acoustic noise of the split gradient coil. First, a split gradient assembly with an asymmetric configuration was designed to avoid vibration in same resonant modes for the two assembly cylinders. Next, the outer ends of the split main magnet were constructed using horn structures, which can distribute the acoustic field away from patient region. Finally, a finite element method (FEM) was used to quantitatively evaluate the effectiveness of the above acoustic noise reduction scheme. Simulation results found that the noise could be maximally reduced by 6.9 dB and 5.6 dB inside and outside the central gap of the split MRI system, respectively, by increasing the length of one gradient assembly cylinder by 20 cm. The optimized horn length was observed to be 55 cm, which could reduce noise by up to 7.4 dB and 5.4 dB inside and outside the central gap, respectively. The proposed design could effectively reduce the acoustic noise without any influence on the application of other noise reduction methods.

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32

Matsuo, Takayuki, Tomohiro Okunaga, Kensaku Kamada, Tsuyoshi Izumo, Nobuyuki Hayashi, and Izumi Nagata. "Long-term follow-up results of linear accelerator-based radiosurgery for vestibular schwannoma using serial three-dimensional spoiled gradient-echo MRI." Journal of Clinical Neuroscience 22, no. 2 (February 2015): 320–25. http://dx.doi.org/10.1016/j.jocn.2014.06.100.

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33

Tseng, C. L., W. Eppinga, E. Seravalli, E. Brand, S. Hackett, M. E. Ruschin, Y. K. Lee, M. van Vulpen, and A. Sahgal. "Dosimetric Feasibility of the Hybrid Magnetic Resonance Imaging (MRI)-Linear Accelerator System for Brain Metastases: The Impact of the Magnetic Field." International Journal of Radiation Oncology*Biology*Physics 96, no. 2 (October 2016): E628. http://dx.doi.org/10.1016/j.ijrobp.2016.06.2201.

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34

Wojcieszynski, Andrzej P., Patrick M. Hill, Stephen A. Rosenberg, Craig R. Hullett, Zacariah E. Labby, Bhudatt Paliwal, Mark W. Geurts, et al. "Dosimetric Comparison of Real-Time MRI-Guided Tri-Cobalt-60 Versus Linear Accelerator-Based Stereotactic Body Radiation Therapy Lung Cancer Plans." Technology in Cancer Research & Treatment 16, no. 3 (February 7, 2017): 366–72. http://dx.doi.org/10.1177/1533034617691407.

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Purpose: Magnetic resonance imaging–guided radiation therapy has entered clinical practice at several major treatment centers. Treatment of early-stage non-small cell lung cancer with stereotactic body radiation therapy is one potential application of this modality, as some form of respiratory motion management is important to address. We hypothesize that magnetic resonance imaging–guided tri-cobalt-60 radiation therapy can be used to generate clinically acceptable stereotactic body radiation therapy treatment plans. Here, we report on a dosimetric comparison between magnetic resonance imaging–guided radiation therapy plans and internal target volume–based plans utilizing volumetric-modulated arc therapy. Materials and Methods: Ten patients with early-stage non-small cell lung cancer who underwent radiation therapy planning and treatment were studied. Following 4-dimensional computed tomography, patient images were used to generate clinically deliverable plans. For volumetric-modulated arc therapy plans, the planning tumor volume was defined as an internal target volume + 0.5 cm. For magnetic resonance imaging–guided plans, a single mid-inspiratory cycle was used to define a gross tumor volume, then expanded 0.3 cm to the planning tumor volume. Treatment plan parameters were compared. Results: Planning tumor volumes trended larger for volumetric-modulated arc therapy–based plans, with a mean planning tumor volume of 47.4 mL versus 24.8 mL for magnetic resonance imaging–guided plans ( P = .08). Clinically acceptable plans were achievable via both methods, with bilateral lung V20, 3.9% versus 4.8% ( P = .62). The volume of chest wall receiving greater than 30 Gy was also similar, 22.1 versus 19.8 mL ( P = .78), as were all other parameters commonly used for lung stereotactic body radiation therapy. The ratio of the 50% isodose volume to planning tumor volume was lower in volumetric-modulated arc therapy plans, 4.19 versus 10.0 ( P < .001). Heterogeneity index was comparable between plans, 1.25 versus 1.25 ( P = .98). Conclusion: Magnetic resonance imaging–guided tri-cobalt-60 radiation therapy is capable of delivering lung high-quality stereotactic body radiation therapy plans that are clinically acceptable as compared to volumetric-modulated arc therapy–based plans. Real-time magnetic resonance imaging provides the unique capacity to directly observe tumor motion during treatment for purposes of motion management.

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Joseph, J., J. R. Adler, R. S. Cox, and S. L. Hancock. "Linear accelerator-based stereotaxic radiosurgery for brain metastases:the influence of number of lesions on survival." Journal of Clinical Oncology 14, no. 4 (April 1996): 1085–92. http://dx.doi.org/10.1200/jco.1996.14.4.1085.

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PURPOSE To evaluate the influence of the number of brain metastases on survival after stereotaxic radiosurgery and factors that affect the risk of delayed radiation necrosis after treatment. MATERIALS AND METHODS Between March 1989 and December 1993, 120 consecutive patients underwent linear accelerator-based stereotaxic radiosurgery for brain metastases identified by computed tomography (CT) or magnetic resonance imaging (MRI) scans. The influence of various clinical factors on outcome was assessed using Kaplan-Meier plots of survival from the date of radiosurgery, and univariate and multivariate analyses. RESULTS The median survival time was 32 weeks. Progressive brain metastases, both local and regional, caused 25 of 104 deaths. Patients with two metastases (n = 30) or a solitary metastasis (n = 70) had equivalent actuarial survival times (P = .07; median, 37 weeks; maximum, 211+ weeks). Patients treated to three or more metastases (n = 20) had significantly shorter survival times (P < .002; median, 14 weeks; maximum, 63 weeks). Prognostic factors associated with prolonged survival included a pretreatment Karnofsky performance status > or = 70% and fewer than three metastases. Delayed radiation necrosis at the treated site developed in 20 patients and correlated with prior or concurrent delivery of whole-brain irradiation and the logarithm of the tumor volume. CONCLUSION Survival duration is equivalent for patients with one or two brain metastases and is similar to that reported for patients with a solitary metastasis managed by surgical resection and whole-brain irradiation. Survival after radiosurgery for three or more metastases was similar to that reported for whole-brain irradiation.

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Low, D., S. Mutic, S. Shvartsman, T. Chmielewski, G. Fought, A. Sharma, and J. Dempsey. "TU-H-BRA-02: The Physics of Magnetic Field Isolation in a Novel Compact Linear Accelerator Based MRI-Guided Radiation Therapy System." Medical Physics 43, no. 6Part36 (June 2016): 3768. http://dx.doi.org/10.1118/1.4957624.

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Dolera, Mario, Luca Malfassi, Simone Pavesi, Silvia Marcarini, Massimo Sala, Giovanni Mazza, Nancy Carrara, Sara Finesso, and Gaetano Urso. "Stereotactic Volume Modulated Arc Radiotherapy in Canine Meningiomas: Imaging-Based and Clinical Neurological Posttreatment Evaluation." Journal of the American Animal Hospital Association 54, no. 2 (March 1, 2018): 77–84. http://dx.doi.org/10.5326/jaaha-ms-6488.

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ABSTRACT A prospective study to assess high-dose hypofractionated volume modulated arc radiotherapy feasibility and efficacy in canine meningiomas was conducted. Thirty-nine patients with encephalic and spinal meningiomas assumed from MRI findings were recruited and received high-dose hypofractionated volumetric modulated arc radiotherapy by a linear accelerator equipped with an external beam modulator micro-multileaf collimator and an XVI cone beam computed tomography system. The prescribed mean dose was 33 Gy in five fractions. The treatment feasibility was tested through planned and delivered dose agreement checks. Regular clinical examinations were performed during and after irradiation time, with regard to mentation, deambulation, cranial nerve dysfunction, and seizures. Serial MRI exams were done 60 days after irradiation and after 4, 6, 12, 18, and 24 mo. Volumetric disease reduction criteria implemented with clinical neurological systematic evaluation were adopted to assess the course and to categorize patients’ responses. Complete and partial responses were observed on the whole in 65.5% of alive patients 24 mo after irradiation. Two-yr overall and disease-specific survival rates were 74.3% and 97.4%, respectively, and the putative radiotoxic effects were found to be few and slight.

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Richter, Sebastian, Stefan Pojtinger, David Mönnich, Oliver S. Dohm, and Daniela Thorwarth. "Influence of a transverse magnetic field on the dose deposited by a 6 MV linear accelerator." Current Directions in Biomedical Engineering 3, no. 2 (September 7, 2017): 281–85. http://dx.doi.org/10.1515/cdbme-2017-0058.

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AbstractAn integrated system of a linear accelerator and a magnetic resonance imaging (MRI) device may provide real-time imaging during radiotherapy treatments. This work investigated changes affecting the dose deposition caused by a magnetic field (B-field) transverse to the beam direction by means of Monte Carlo simulations. Two different phantoms were used: A water phantom (Ph1) and a water-air phantom (Ph2) with a 4-2-4 cm water-air-water cross section. Dose depositions were scored for B-field values of 0 T, 0.35 T, 0.5 T, 1.5 T, 3 T and 5 T. Beams were based on a precalculated photon spectrum taken from an earlier simulated Elekta 6 MV FFF accelerator. All lateral profiles in Ph1 showed a Lorentz force driven shift w.r.t. the B-field strength, presenting a steeper penumbra in the shift's direction. Depositions were shifted up to 0.3 cm for 5 T, showing a constant central axis plateau-dose or an increase by 2.3 % for small fields. Depth-dose curves in Ph1 showed a shift of the dose maximum towards the beam entrance direction for increasing B-field of up to 1.1 cm; the maximum dose was increased by 6.9 %. In Ph2, an asymmetric dose increase by up to 36.9 % was observed for 1.5 T at the water-air boundary, resulting from the electron return effect (ERE). In our scenario, B-field dependent dose shifts and local build-ups were observed, which consequently affect the resulting dose distribution and need to be considered in magnetic resonance guided radiotherapy treatment planning.

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Lamb, J., D. Low, S. Mutic, S. Shvartsman, T. Chmielewski, G. Fought, A. Sharma, and J. Dempsey. "TU-H-BRA-01: The Physics of High Power Radiofrequency Isolation in a Novel Compact Linear Accelerator Based MRI Guided Radiation Therapy System." Medical Physics 43, no. 6Part36 (June 2016): 3768. http://dx.doi.org/10.1118/1.4957623.

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Banla, L. I., E. S. Paulson, D. Wittman, D. Schott, P. Knechtges, A. Li, C. J. Schultz, B. A. Erickson, and W. A. Hall. "Methodology and Feasibility of Acquiring Pancreatic Diffusion Weighted Imaging (DWI) Using A Linear Accelerator Equipped with a 1.5 Magnetic Resonance Imaging (MRI) System." International Journal of Radiation Oncology*Biology*Physics 105, no. 1 (September 2019): S28—S29. http://dx.doi.org/10.1016/j.ijrobp.2019.06.436.

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Sung, Soo-Yoon, Sea-Won Lee, Ji Hyung Hong, Hye Jin Kang, So Jung Lee, Myungsoo Kim, Ji-Hoon Kim, and Yoo-Kang Kwak. "Linear Tumor Regression of Rectal Cancer in Daily MRI during Preoperative Chemoradiotherapy: An Insight of Tumor Regression Velocity for Personalized Cancer Therapy." Cancers 14, no. 15 (August 1, 2022): 3749. http://dx.doi.org/10.3390/cancers14153749.

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Objective: Neoadjuvant chemoradiotherapy (CCRT) is current standards of care for locally advanced rectal cancer. The precise and thorough investigation of a tumor during the full course of CCRT by means of daily MRI can provide an idea on real-time treatment sensitivity in addition to tumor biology. Tumor volumetry from daily MRI during CCRT may allow patient-driven treatment decisions. Material and Methods: Patients diagnosed with cT3-4 and/or cN+ rectal adenocarcinoma undergoing preoperative CCRT with capecitabine on the pelvis up to 50 Gy in 25 daily fractions from November 2018 to June 2019 were consecutively included. Rectal tumor volume was uniformly measured by a single physician (YKK) in daily 0.35T MRI obtained with MR-guided linear accelerator. Primary endpoint was to assess the pattern of tumor volume regression throughout the full course of CCRT using daily registration MRI. Secondary endpoint was to assess the effect of tumor regression velocity on disease-free survival (DFS). Tumor regression velocity (cc) per fraction of each patient was calculated using the simple regression analysis of tumor volumes from fraction 1 to fraction 25. Results: Twenty patients were included. Daily tumor volumetry demonstrated linear tumor regression during CCRT. The tumor regression velocity of all 20 patients was 2.40 cc per fraction (R2 = 0.93; p < 0.001). The median tumor regression velocity was 1.52 cc per fraction. Patients with tumor regression velocity ≥ 1.52 cc per fraction were grouped as rapid regressors (N = 9), and those with tumor regression velocity < 1.52 cc per fraction were grouped as slow regressors (N = 11). Rapid regressors had greater tumor regression velocity (4.58 cc per fraction) compared to that of slow regressors (0.78 cc per fraction) with statistical significance (p < 0.001). The mean DFS of rapid regressors was 36.8 months, numerically longer than the 31.9 months of slow regressors (p = 0.400) without statistical significance. Rapid regressors had numerically superior DFS rate compared to slow regressors without statistical significance. The 2-year DFS was 88.9% for rapid regressors and 72.7% for slow regressors, respectively (p = 0.400). Conclusion: This study is the first observation of linear tumor regression in daily MRI during the preoperative CCRT of locally advanced rectal cancer. Daily tumor regression velocity discriminated DFS, although without statistical significance. This study with a phenomenal approach is hypothesis-generating. Nevertheless, the potential of CCRT from therapeutics to a newer level, the “theranostics”, has been inceptively suggested. Further validation studies for the value of daily tumor volumetry on treatment decisions are warranted.

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Kooreman, Ernst S., Max Tanaka, Leon C. ter Beek, Femke P. Peters, Corrie A. M. Marijnen, Uulke A. van der Heide, and Petra J. van Houdt. "T1ρ for Radiotherapy Treatment Response Monitoring in Rectal Cancer Patients: A Pilot Study." Journal of Clinical Medicine 11, no. 7 (April 2, 2022): 1998. http://dx.doi.org/10.3390/jcm11071998.

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Quantitative MRI has the potential to produce imaging biomarkers for the prediction of early response to radiotherapy treatment. In this pilot study, a potential imaging biomarker, the T1ρ relaxation time, is assessed for this purpose. A T1ρ sequence was implemented on a 1.5 T MR-linac system, a system that combines an MRI with a linear accelerator for radiation treatment. An agar phantom with concentrations of 1–4% w/w was constructed for technical validation of the sequence. Phantom images were assessed in terms of short-term repeatability and signal-to-noise ratio. Twelve rectal cancer patients, who were treated with 5 × 5 Gy, were imaged on each treatment fraction. Individual changes in the T1ρ values of the gross tumor volume (GTV) showed an increase for most patients, although a paired t-test comparing values in the GTV from the first to the last treatment fraction showed no statistically significant difference. The phantom measurements showed excellent short-term repeatability (0.5–1.5 ms), and phantom T1ρ values corresponded to the literature values. T1ρ imaging was implemented successfully on the MR-linac, with a repeatability comparable to diagnostic systems, although clinical benefit in terms of treatment response monitoring remains to be demonstrated.

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Demiral, Selcuk, Murat Beyzadeoglu, Ferrat Dincoglan, and Omer Sager. "Assessment of Target Volume Definition for Radiosurgery of Atypical Meningiomas with Multimodality Imaging." Journal of Hematology and Oncology Research 3, no. 4 (April 14, 2020): 14–21. http://dx.doi.org/10.14302/issn.2372-6601.jhor-20-3293.

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Objective Meningiomas are most common intracranial benign tumors comprising around one third of all intracranial neoplasms, and typically have benign and indolent nature with slow-growing behaviour. Benign meningiomas are slow growing tumors typically following an indolent disease course. Nevertheless, atypical or anaplastic meningiomas may follow a more aggressive disease course with invasion of critical structures and recurrences. In the current study, we evaluate the incorporation of magnetic resonance imaging (MRI) for radiosurgery treatment planning of atypical meningiomas. Materials and Methods Atypical meningioma radiosurgery target volume determination with and without incorporation of MRI has been evaluated. Ground truth target volume used as the reference has been outlined by the board-certified group of radiation oncologists after comprehensive assessment, thorough collaboration and consensus. Results Target volume definition by use of Computed Tomography (CT)-only imaging and by CT-MR fusion based imaging has been comparatively evaluated in this study for linear accelerator (LINAC)-based radiosurgical management of atypical meningioma. Ground truth target volume defined by the board-certified radiation oncologists after detailed evaluation, collaboration, colleague peer review and consensus has been found to be identical to target determination by use of CT-MR fusion based imaging. Conclusion Despite significant progress in neurosurgical techniques over the years, complete surgical resection may not be feasible in the presence of meningiomas located at eloquent brain areas in close association with important neurovascular structures. RT may have a role in multidisciplinary management of meningiomas. Incorporation of MRI into treatment planning for radiosurgery of atypical meningiomas may improve target definition despite the need for further supporting evidence.

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Raaijmakers, A., B. Raaymakers, and J. Lagendijk. "227 Dose distribution in a patient anatomy for an integrated MRI-linear accelerator system: boosting the dose around air cavities using the magnetic field." Radiotherapy and Oncology 76 (September 2005): S109—S110. http://dx.doi.org/10.1016/s0167-8140(05)81204-6.

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Komiyama, T., H. Onishi, M. Nagata, M. Hori, K. Kuriyama, S. Tanaka, M. Sano, et al. "Documentary of inter and intra-fractional prostate motion using self-moving CT scanner combined with linear accelerator, and cine-MRI: what moves the prostate." International Journal of Radiation Oncology*Biology*Physics 54, no. 2 (October 2002): 261. http://dx.doi.org/10.1016/s0360-3016(02)03510-1.

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De Deene, Yves. "Radiation Dosimetry by Use of Radiosensitive Hydrogels and Polymers: Mechanisms, State-of-the-Art and Perspective from 3D to 4D." Gels 8, no. 9 (September 19, 2022): 599. http://dx.doi.org/10.3390/gels8090599.

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Gel dosimetry was developed in the 1990s in response to a growing need for methods to validate the radiation dose distribution delivered to cancer patients receiving high-precision radiotherapy. Three different classes of gel dosimeters were developed and extensively studied. The first class of gel dosimeters is the Fricke gel dosimeters, which consist of a hydrogel with dissolved ferrous ions that oxidize upon exposure to ionizing radiation. The oxidation results in a change in the nuclear magnetic resonance (NMR) relaxation, which makes it possible to read out Fricke gel dosimeters by use of quantitative magnetic resonance imaging (MRI). The radiation-induced oxidation in Fricke gel dosimeters can also be visualized by adding an indicator such as xylenol orange. The second class of gel dosimeters is the radiochromic gel dosimeters, which also exhibit a color change upon irradiation but do not use a metal ion. These radiochromic gel dosimeters do not demonstrate a significant radiation-induced change in NMR properties. The third class is the polymer gel dosimeters, which contain vinyl monomers that polymerize upon irradiation. Polymer gel dosimeters are predominantly read out by quantitative MRI or X-ray CT. The accuracy of the dosimeters depends on both the physico-chemical properties of the gel dosimeters and on the readout technique. Many different gel formulations have been proposed and discussed in the scientific literature in the last three decades, and scanning methods have been optimized to achieve an acceptable accuracy for clinical dosimetry. More recently, with the introduction of the MR-Linac, which combines an MRI-scanner and a clinical linear accelerator in one, it was shown possible to acquire dose maps during radiation, but new challenges arise.

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Young, C., R. Summerfield, M. Schwartz, P. O'Brien, and R. Ramani. "Radiosurgery for Arteriovenous Malformations: the University of Toronto Experience." Canadian Journal of Neurological Sciences / Journal Canadien des Sciences Neurologiques 24, no. 2 (May 1997): 99–105. http://dx.doi.org/10.1017/s0317167100021405.

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ABSTRACT:Background:From July 1989 to February 1996, 130 patients underwent sterotactic radiosurgery. We report the results of the first 50 patients eligible for a minimum of three years of follow-up.Methods:Twenty women and 30 men, (mean age: 37.5 years) were treated by dynamic rotation on a 6 MV linear accelerator. Prior treatment was embolization in seventeen, surgery in three and embolization and surgery in six. All had DSA and enhanced CT scanning, while some had MRI. Forty-seven treatments used a single isodose. Restricting eloquent normal tissue to 15 Gy, margin doses (at 50 - 90% isodose) were 12 Gy (one patient); 15 Gy (sixteen patients); 20 Gy (31 patients); 25 Gy (two patients). Maximum diameters were: <1.5 cm (12 patients); < 2.0 cm (nine patients); < 2.5 cm (twelve patients); < 3.0 cm (thirteen patients; 3.0 cm (four patients).Results:Forty-five patients were evaluable at three years, with thirty-nine having angiography. Twenty-five had angiographically confirmed obliterations; two had parenchymal AVMs obliterated but with residual dural components; four had MRI evidence of obliteration (refused angiography). One patient acutely had a seizure; one patient (with hemorrhages, resection, and embolizations preceding two applications of radiosurgery, separated by 3.5 years) had worsening of memory.Conclusions:Our uncorrected (five patients unevaluable at three years) and corrected angiographically confirmed obliteration rates are 54% and 60% respectively. Our follow-up (98% accounting of cohort; 78% angiographic rate) and explicit derivation of denominators help delineate the efficacy of radiosurgery at these doses.

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McClelland, Shearwood, Ulysses Gardner, Mark Langer, and Kevin Shiue. "RADT-43. TREATMENT OF RETROPERITONEAL LEIOMYOSARCOMA BRAIN METASTASES WITH STEREOTACTIC RADIOSURGERY." Neuro-Oncology 22, Supplement_2 (November 2020): ii190—ii191. http://dx.doi.org/10.1093/neuonc/noaa215.796.

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Abstract INTRODUCTION Retroperitoneal leiomyosarcoma is a relatively rare disease, with infrequent metastatic spread to the CNS. We present the first report of radiosurgical treatment of this disease. METHODS A 49-year-old woman developed leiomyosarcoma of the inferior vena cava and retroperitoneum with lung metastases on diagnosis. Following multiple courses of systemic and operative treatment, she developed a tender ulcerating mass in the left upper maxillary incisor associated with numbness along the upper gum, lip, and premaxillary area. CT revealed a 3.0 cm left posterior alveolar ridge gum lesion with bone invasion, for which she elected to undergo palliative radiation therapy (30 Gy in 10 fractions). Due to potential maxillary nerve involvement altering the intended radiation therapy treatment fields, an orbit/face MRI was performed to better delineate the lesion. On this MRI, two frontal lobe lesions were visualized; subsequent dedicated brain MRI revealed a total of five metastases (0.9 cm right superior frontal gyrus, 0.9 cm left middle frontal gyrus, 0.9 cm right postcentral gyrus, 0.7 cm right occipital, and 1.6 cm left occipital). Consequently, the decision was made to treat the brain metastases with linear accelerator (LINAC) stereotactic radiosurgery (SRS) to allow simultaneous treatment of the maxillary lesion and brain metastases. RESULTS A single CT simulation was performed for her intracranial and extracranial disease, using the Encompass face mask to allow for simultaneous head immobilization and optimal SRS targeting accuracy. LINAC SRS was delivered simultaneously during maxillary lesion radiation therapy to all five lesions (22 Gy to the 80% isodose line) in a single fraction with a 0.2 cm planning target volume (PTV) margin for each lesion. CONCLUSIONS The first reported case of metastatic retroperitoneal leiomyosarcoma brain metastases treated with SRS demonstrates the flexibility of LINAC (rather than Gamma Knife) SRS in allowing for simultaneous treatment of intracranial and extracranial metastatic disease.

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Dalyai, Richard, Robert M. Starke, Nohra Chalouhi, Thana Theofanis, Christopher Busack, Pascal Jabbour, L. Fernando Gonzalez, Robert Rosenwasser, and Stavropoula Tjoumakaris. "Smoking is a negative predictor of arteriovenous malformation posttreatment obliteration: analysis of vascular risk factors in 774 patients." Neurosurgical Focus 37, no. 3 (September 2014): E3. http://dx.doi.org/10.3171/20145.focus14121.

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Object Cigarette smoking has been well established as a risk factor in vascular pathology, such as cerebral aneurysms. However, tobacco’s implications for patients with cerebral arteriovenous malformations (AVMs) are controversial. The object of this study was to identify predictors of AVM obliteration and risk factors for complications. Methods The authors conducted a retrospective analysis of a prospectively maintained database for all patients with AVMs treated using surgical excision, staged endovascular embolization (with N-butyl-cyanoacrylate or Onyx), stereotactic radiosurgery (Gamma Knife or Linear Accelerator), or a combination thereof between 1994 and 2010. Medical risk factors, such as smoking, abuse of alcohol or intravenous recreational drugs, hypercholesterolemia, diabetes mellitus, hypertension, and coronary artery disease, were documented. A multivariate logistic regression analysis was conducted to detect predictors of periprocedural complications, obliteration, and posttreatment hemorrhage. Results Of 774 patients treated at a single tertiary care cerebrovascular center, 35% initially presented with symptomatic hemorrhage and 57.6% achieved complete obliteration according to digital subtraction angiography (DSA) or MRI. In a multivariate analysis a negative smoking history (OR 1.9, p = 0.006) was a strong independent predictor of AVM obliteration. Of the patients with obliterated AVMs, 31.9% were smokers, whereas 45% were not (p = 0.05). Multivariate analysis of obliteration, after controlling for AVM size and location (eloquent vs noneloquent tissue), revealed that nonsmokers were more likely (0.082) to have obliterated AVMs through radiosurgery. Smoking was not predictive of treatment complications or posttreatment hemorrhage. Abuse of alcohol or intravenous recreational drugs, hypercholesterolemia, diabetes mellitus, and coronary artery disease had no discernible effect on AVM obliteration, periprocedural complications, or posttreatment hemorrhage. Conclusions Cerebral AVM patients with a history of smoking are significantly less likely than those without a smoking history to have complete AVM obliteration on follow-up DSA or MRI. Therefore, patients with AVMs should be strongly advised to quit smoking.

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Cummings, Michael, Paul Youn, Derek P. Bergsma, Kenneth Y. Usuki, Kevin Walter, Manju Sharma, Paul Okunieff, Michael C. Schell, and Michael T. Milano. "Single-Fraction Radiosurgery Using Conservative Doses for Brain Metastases: Durable Responses in Select Primaries With Limited Toxicity." Neurosurgery 83, no. 3 (August 12, 2017): 437–44. http://dx.doi.org/10.1093/neuros/nyx427.

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Abstract BACKGROUND Optimal doses for single-fraction stereotactic radiosurgery (SRS) in the treatment of brain metastases are not well established. Our institution utilized conservative dosing compared to maximum-tolerated doses from the Radiation Therapy Oncology Group 90-05 Phase I study. OBJECTIVE To report individual lesion control (LC) from conservative single-fraction doses and determine factors affecting LC. METHODS From 2003 to 2015, patients who underwent linear accelerator-based single-fraction SRS for cerebral/cerebellar metastases and receiving at least 1 follow-up magnetic resonance imaging (MRI) were identified. Lesion response was assessed by a size-based rating system and modified “Response Assessment in Neuro-Oncology Brain Metastases” (RANO-BM) criteria. RESULTS Among 188 patients with 519 lesions, median survival was 13.1 mo; median follow-up time with MRI was 9.6 mo per course. Median tumor-periphery dose was 15 Gy (range: 7.5-20.7). Median lesion volume was 0.5 cc and diameter was 9 mm (range: 2-45). Concordance between RANO-BM and size-based system was 93%. Crude 1-yr LC was 80%, 73%, 56%, and 38% for lesions 1 to 10, 11 to 20, 21 to 30, >31 mm, respectively. On multivariate analysis, increased size, melanoma and colorectal histology, and progression after whole brain radiation therapy predicted worse LC. When excluding lesions treated as a boost, dose was a significant predictor of LC in multivariate models (hazard ratio 0.89, P = .01). Symptomatic radiation necrosis occurred in 10 lesions in 10 patients. CONCLUSION Histology predicts LC after conservative SRS doses with evidence of a dose–response relationship. Conservative single-fraction SRS doses confer minimal toxicity and acceptable control in certain subgroups (breast cancer, <5 mm), with suboptimal control in larger lesions and in combination with whole brain radiation therapy.

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