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Characterization of the Megavoltage Cone-Beam Computed Tomography (MV-CBCT) System on Halcyon(TM) for IGRT: Image Quality Benchmark, Clinical Performance, and Organ Doses
Purpose: The Varian Halcyon includes an ultrafast 6 MV flattening filter free (FFF) cone-beam computed tomography (MV-CBCT). Although a kV-CBCT add-on is available, in the basic configuration MV is used for image guided radiotherapy (IGRT). We characterized the MV-CBCT imager in terms of reproducibi...
Autores principales: | , , , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
Frontiers Media S.A.
2019
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6582256/ https://www.ncbi.nlm.nih.gov/pubmed/31249808 http://dx.doi.org/10.3389/fonc.2019.00496 |
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author | Malajovich, Irina Teo, Boon-Keng Kevin Petroccia, Heather Metz, James M. Dong, Lei Li, Taoran |
author_facet | Malajovich, Irina Teo, Boon-Keng Kevin Petroccia, Heather Metz, James M. Dong, Lei Li, Taoran |
author_sort | Malajovich, Irina |
collection | PubMed |
description | Purpose: The Varian Halcyon includes an ultrafast 6 MV flattening filter free (FFF) cone-beam computed tomography (MV-CBCT). Although a kV-CBCT add-on is available, in the basic configuration MV is used for image guided radiotherapy (IGRT). We characterized the MV-CBCT imager in terms of reproducibility, linearity, field of view (FOV) dependence, detectability of soft-tissue, and the effect of metal implants. The performance of the MV-CBCT in the clinic, including resulting dose to organs, is also discussed herein. Methods: A Gammex phantom was scanned using a Halcyon MV-CBCT and a 120 kVp Siemens Definition Edge CT. Mean and standard deviation of Hounsfield Units (HUs) for different electron density relative to water ([Formula: see text]) inserts were extracted. Doses to clinical patients due to MV-CBCT are calculated within Eclipse during treatment planning. Results: A stable and near-linear HU-to- [Formula: see text] curve was obtained using the MV-CBCT. As the scan length increased from 10 to 28cm, the linearity of curve improved while the mean HUs decreased by 30%. All soft tissue inserts in the Gammex phantom were distinguishable. A crescent artifact affected HU measurements by up to 40 HUs. Soft-tissue contrast was sufficient for clinical online image-guidance in the low dose (5 MU) mode. Mean doses per fraction to organs-at-risk (OARs) were as high as 6 cGy for head and neck, 5 cGy for breast, and 4 cGy for pelvis patients. Metal rods did not affect HU values or introduce noticeable artifacts. Conclusions: Halcyon's MV-CBCT has sufficient soft tissue contrast for IGRT and lacks metal-induced artifacts. Even though the absolute HU values vary with phantom size and scanning length, the HU-to- [Formula: see text] conversions are linear and stable day-to-day. In clinical cases, highest tissue doses from MV-CBCT ranged from 2-7cGy per fraction for various treatment sites, which could be significant for some organs at risk. Dose to out-of-treatment-field organs can be limited by reducing the scan length definition during planning and using the low dose mode. The high quality imaging mode did not provide material advantages over the low dose mode. Adequate IGRT was successfully delivered to multiple tumor sites using MV-CBCT. |
format | Online Article Text |
id | pubmed-6582256 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2019 |
publisher | Frontiers Media S.A. |
record_format | MEDLINE/PubMed |
spelling | pubmed-65822562019-06-27 Characterization of the Megavoltage Cone-Beam Computed Tomography (MV-CBCT) System on Halcyon(TM) for IGRT: Image Quality Benchmark, Clinical Performance, and Organ Doses Malajovich, Irina Teo, Boon-Keng Kevin Petroccia, Heather Metz, James M. Dong, Lei Li, Taoran Front Oncol Oncology Purpose: The Varian Halcyon includes an ultrafast 6 MV flattening filter free (FFF) cone-beam computed tomography (MV-CBCT). Although a kV-CBCT add-on is available, in the basic configuration MV is used for image guided radiotherapy (IGRT). We characterized the MV-CBCT imager in terms of reproducibility, linearity, field of view (FOV) dependence, detectability of soft-tissue, and the effect of metal implants. The performance of the MV-CBCT in the clinic, including resulting dose to organs, is also discussed herein. Methods: A Gammex phantom was scanned using a Halcyon MV-CBCT and a 120 kVp Siemens Definition Edge CT. Mean and standard deviation of Hounsfield Units (HUs) for different electron density relative to water ([Formula: see text]) inserts were extracted. Doses to clinical patients due to MV-CBCT are calculated within Eclipse during treatment planning. Results: A stable and near-linear HU-to- [Formula: see text] curve was obtained using the MV-CBCT. As the scan length increased from 10 to 28cm, the linearity of curve improved while the mean HUs decreased by 30%. All soft tissue inserts in the Gammex phantom were distinguishable. A crescent artifact affected HU measurements by up to 40 HUs. Soft-tissue contrast was sufficient for clinical online image-guidance in the low dose (5 MU) mode. Mean doses per fraction to organs-at-risk (OARs) were as high as 6 cGy for head and neck, 5 cGy for breast, and 4 cGy for pelvis patients. Metal rods did not affect HU values or introduce noticeable artifacts. Conclusions: Halcyon's MV-CBCT has sufficient soft tissue contrast for IGRT and lacks metal-induced artifacts. Even though the absolute HU values vary with phantom size and scanning length, the HU-to- [Formula: see text] conversions are linear and stable day-to-day. In clinical cases, highest tissue doses from MV-CBCT ranged from 2-7cGy per fraction for various treatment sites, which could be significant for some organs at risk. Dose to out-of-treatment-field organs can be limited by reducing the scan length definition during planning and using the low dose mode. The high quality imaging mode did not provide material advantages over the low dose mode. Adequate IGRT was successfully delivered to multiple tumor sites using MV-CBCT. Frontiers Media S.A. 2019-06-12 /pmc/articles/PMC6582256/ /pubmed/31249808 http://dx.doi.org/10.3389/fonc.2019.00496 Text en Copyright © 2019 Malajovich, Teo, Petroccia, Metz, Dong and Li. http://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. |
spellingShingle | Oncology Malajovich, Irina Teo, Boon-Keng Kevin Petroccia, Heather Metz, James M. Dong, Lei Li, Taoran Characterization of the Megavoltage Cone-Beam Computed Tomography (MV-CBCT) System on Halcyon(TM) for IGRT: Image Quality Benchmark, Clinical Performance, and Organ Doses |
title | Characterization of the Megavoltage Cone-Beam Computed Tomography (MV-CBCT) System on Halcyon(TM) for IGRT: Image Quality Benchmark, Clinical Performance, and Organ Doses |
title_full | Characterization of the Megavoltage Cone-Beam Computed Tomography (MV-CBCT) System on Halcyon(TM) for IGRT: Image Quality Benchmark, Clinical Performance, and Organ Doses |
title_fullStr | Characterization of the Megavoltage Cone-Beam Computed Tomography (MV-CBCT) System on Halcyon(TM) for IGRT: Image Quality Benchmark, Clinical Performance, and Organ Doses |
title_full_unstemmed | Characterization of the Megavoltage Cone-Beam Computed Tomography (MV-CBCT) System on Halcyon(TM) for IGRT: Image Quality Benchmark, Clinical Performance, and Organ Doses |
title_short | Characterization of the Megavoltage Cone-Beam Computed Tomography (MV-CBCT) System on Halcyon(TM) for IGRT: Image Quality Benchmark, Clinical Performance, and Organ Doses |
title_sort | characterization of the megavoltage cone-beam computed tomography (mv-cbct) system on halcyon(tm) for igrt: image quality benchmark, clinical performance, and organ doses |
topic | Oncology |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6582256/ https://www.ncbi.nlm.nih.gov/pubmed/31249808 http://dx.doi.org/10.3389/fonc.2019.00496 |
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