A novel method for delineation of oral mucosa for radiotherapy dose–response studies
Identifieur interne : 001962 ( Pmc/Corpus ); précédent : 001961; suivant : 001963A novel method for delineation of oral mucosa for radiotherapy dose–response studies
Auteurs : Jamie A. Dean ; Liam C. Welsh ; Sarah L. Gulliford ; Kevin J. Harrington ; Christopher M. NuttingSource :
- Radiotherapy and Oncology [ 0167-8140 ] ; 2015.
Abstract
There is currently no standard method for delineating the oral mucosa and most attempts are oversimplified. A new method to obtain anatomically accurate contours of the oral mucosa surfaces was developed and applied to 11 patients. This is expected to represent an opportunity for improved toxicity modelling of oral mucositis.
Url:
DOI: 10.1016/j.radonc.2015.02.020
PubMed: 25779721
PubMed Central: 4641317
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<record><TEI><teiHeader><fileDesc><titleStmt><title xml:lang="en">A novel method for delineation of oral mucosa for radiotherapy dose–response studies</title><author><name sortKey="Dean, Jamie A" sort="Dean, Jamie A" uniqKey="Dean J" first="Jamie A." last="Dean">Jamie A. Dean</name><affiliation><nlm:aff id="af005">Joint Department of Physics at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, UK</nlm:aff></affiliation></author><author><name sortKey="Welsh, Liam C" sort="Welsh, Liam C" uniqKey="Welsh L" first="Liam C." last="Welsh">Liam C. Welsh</name><affiliation><nlm:aff id="af010">Head and Neck Unit, The Royal Marsden NHS Foundation Trust, London, UK</nlm:aff></affiliation></author><author><name sortKey="Gulliford, Sarah L" sort="Gulliford, Sarah L" uniqKey="Gulliford S" first="Sarah L." last="Gulliford">Sarah L. Gulliford</name><affiliation><nlm:aff id="af005">Joint Department of Physics at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, UK</nlm:aff></affiliation></author><author><name sortKey="Harrington, Kevin J" sort="Harrington, Kevin J" uniqKey="Harrington K" first="Kevin J." last="Harrington">Kevin J. Harrington</name><affiliation><nlm:aff id="af010">Head and Neck Unit, The Royal Marsden NHS Foundation Trust, London, UK</nlm:aff></affiliation></author><author><name sortKey="Nutting, Christopher M" sort="Nutting, Christopher M" uniqKey="Nutting C" first="Christopher M." last="Nutting">Christopher M. Nutting</name><affiliation><nlm:aff id="af010">Head and Neck Unit, The Royal Marsden NHS Foundation Trust, London, UK</nlm:aff></affiliation></author></titleStmt><publicationStmt><idno type="wicri:source">PMC</idno><idno type="pmid">25779721</idno><idno type="pmc">4641317</idno><idno type="url">http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4641317</idno><idno type="RBID">PMC:4641317</idno><idno type="doi">10.1016/j.radonc.2015.02.020</idno><date when="2015">2015</date><idno type="wicri:Area/Pmc/Corpus">001962</idno><idno type="wicri:explorRef" wicri:stream="Pmc" wicri:step="Corpus" wicri:corpus="PMC">001962</idno></publicationStmt><sourceDesc><biblStruct><analytic><title xml:lang="en" level="a" type="main">A novel method for delineation of oral mucosa for radiotherapy dose–response studies</title><author><name sortKey="Dean, Jamie A" sort="Dean, Jamie A" uniqKey="Dean J" first="Jamie A." last="Dean">Jamie A. Dean</name><affiliation><nlm:aff id="af005">Joint Department of Physics at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, UK</nlm:aff></affiliation></author><author><name sortKey="Welsh, Liam C" sort="Welsh, Liam C" uniqKey="Welsh L" first="Liam C." last="Welsh">Liam C. Welsh</name><affiliation><nlm:aff id="af010">Head and Neck Unit, The Royal Marsden NHS Foundation Trust, London, UK</nlm:aff></affiliation></author><author><name sortKey="Gulliford, Sarah L" sort="Gulliford, Sarah L" uniqKey="Gulliford S" first="Sarah L." last="Gulliford">Sarah L. Gulliford</name><affiliation><nlm:aff id="af005">Joint Department of Physics at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, UK</nlm:aff></affiliation></author><author><name sortKey="Harrington, Kevin J" sort="Harrington, Kevin J" uniqKey="Harrington K" first="Kevin J." last="Harrington">Kevin J. Harrington</name><affiliation><nlm:aff id="af010">Head and Neck Unit, The Royal Marsden NHS Foundation Trust, London, UK</nlm:aff></affiliation></author><author><name sortKey="Nutting, Christopher M" sort="Nutting, Christopher M" uniqKey="Nutting C" first="Christopher M." last="Nutting">Christopher M. Nutting</name><affiliation><nlm:aff id="af010">Head and Neck Unit, The Royal Marsden NHS Foundation Trust, London, UK</nlm:aff></affiliation></author></analytic><series><title level="j">Radiotherapy and Oncology</title><idno type="ISSN">0167-8140</idno><idno type="eISSN">1879-0887</idno><imprint><date when="2015">2015</date></imprint></series></biblStruct></sourceDesc></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract" xml:lang="en"><p>There is currently no standard method for delineating the oral mucosa and most attempts are oversimplified. A new method to obtain anatomically accurate contours of the oral mucosa surfaces was developed and applied to 11 patients. This is expected to represent an opportunity for improved toxicity modelling of oral mucositis.</p></div></front><back><div1 type="bibliography"><listBibl><biblStruct><analytic><author><name sortKey="Schwartz, D L" uniqKey="Schwartz D">D.L. Schwartz</name></author><author><name sortKey="Hutcheson, K" uniqKey="Hutcheson K">K. Hutcheson</name></author><author><name sortKey="Barringer, D" uniqKey="Barringer D">D. Barringer</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Sanguineti, G" uniqKey="Sanguineti G">G. Sanguineti</name></author><author><name sortKey="Gunn, G B" uniqKey="Gunn G">G.B. Gunn</name></author><author><name sortKey="Parker, B C" uniqKey="Parker B">B.C. Parker</name></author><author><name sortKey="Endres, E J" uniqKey="Endres E">E.J. Endres</name></author><author><name sortKey="Zeng, J" uniqKey="Zeng J">J. 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<front><journal-meta><journal-id journal-id-type="nlm-ta">Radiother Oncol</journal-id><journal-id journal-id-type="iso-abbrev">Radiother Oncol</journal-id><journal-title-group><journal-title>Radiotherapy and Oncology</journal-title></journal-title-group><issn pub-type="ppub">0167-8140</issn><issn pub-type="epub">1879-0887</issn><publisher><publisher-name>Elsevier Scientific Publishers</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="pmid">25779721</article-id><article-id pub-id-type="pmc">4641317</article-id><article-id pub-id-type="publisher-id">S0167-8140(15)00112-7</article-id><article-id pub-id-type="doi">10.1016/j.radonc.2015.02.020</article-id><article-categories><subj-group subj-group-type="heading"><subject>Deliniation of Oral Mucosa</subject></subj-group></article-categories><title-group><article-title>A novel method for delineation of oral mucosa for radiotherapy dose–response studies</article-title></title-group><contrib-group><contrib contrib-type="author"><name><surname>Dean</surname><given-names>Jamie A.</given-names></name><email>jamie.dean@icr.ac.uk</email><xref rid="af005" ref-type="aff">a</xref><xref rid="cor1" ref-type="corresp">⁎</xref></contrib><contrib contrib-type="author"><name><surname>Welsh</surname><given-names>Liam C.</given-names></name><xref rid="af010" ref-type="aff">b</xref></contrib><contrib contrib-type="author"><name><surname>Gulliford</surname><given-names>Sarah L.</given-names></name><xref rid="af005" ref-type="aff">a</xref></contrib><contrib contrib-type="author"><name><surname>Harrington</surname><given-names>Kevin J.</given-names></name><xref rid="af010" ref-type="aff">b</xref></contrib><contrib contrib-type="author"><name><surname>Nutting</surname><given-names>Christopher M.</given-names></name><xref rid="af010" ref-type="aff">b</xref></contrib></contrib-group><aff id="af005"><label>a</label>Joint Department of Physics at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, UK</aff><aff id="af010"><label>b</label>Head and Neck Unit, The Royal Marsden NHS Foundation Trust, London, UK</aff><author-notes><corresp id="cor1"><label>⁎</label>Corresponding author at: Joint Department of Physics at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London SM2 5NG, UK. <email>jamie.dean@icr.ac.uk</email></corresp></author-notes><pub-date pub-type="pmc-release"><day>1</day><month>4</month><year>2015</year></pub-date><pmc-comment> PMC Release delay is 0 months and 0 days and was based on .</pmc-comment>
<pub-date pub-type="ppub"><month>4</month><year>2015</year></pub-date><volume>115</volume><issue>1</issue><fpage>63</fpage><lpage>66</lpage><history><date date-type="received"><day>11</day><month>7</month><year>2014</year></date><date date-type="rev-recd"><day>2</day><month>2</month><year>2015</year></date><date date-type="accepted"><day>5</day><month>2</month><year>2015</year></date></history><permissions><copyright-statement>© 2015 The Authors</copyright-statement><copyright-year>2015</copyright-year><license license-type="CC BY" xlink:href="http://creativecommons.org/licenses/by/4.0/"><license-p>This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).</license-p></license></permissions><abstract><p>There is currently no standard method for delineating the oral mucosa and most attempts are oversimplified. A new method to obtain anatomically accurate contours of the oral mucosa surfaces was developed and applied to 11 patients. This is expected to represent an opportunity for improved toxicity modelling of oral mucositis.</p></abstract><kwd-group><title>Keywords</title><kwd>Contouring</kwd><kwd>Delineation</kwd><kwd>Oral mucosa</kwd><kwd>Oral mucositis</kwd><kwd>Dose–response</kwd></kwd-group></article-meta></front><body><p>Mucositis of the oral mucosa is a common and important acute toxicity in head and neck radiotherapy warranting efforts to mitigate its severity and impact on patients. It may result in reduced quality of life due to pain, dysphagia <xref rid="b0005" ref-type="bibr">[1]</xref>, <xref rid="b0010" ref-type="bibr">[2]</xref>, <xref rid="b0015" ref-type="bibr">[3]</xref>, weight loss and aspiration <xref rid="b0020" ref-type="bibr">[4]</xref>, <xref rid="b0025" ref-type="bibr">[5]</xref>. These effects can result in patients being hospitalised and missing treatment fractions <xref rid="b0030" ref-type="bibr">[6]</xref>, compromising locoregional control <xref rid="b0035" ref-type="bibr">[7]</xref>, <xref rid="b0040" ref-type="bibr">[8]</xref>. Mucositis is also frequently the dose-limiting toxicity in dose escalation and accelerated fractionation regimens, designed to improve tumour control <xref rid="b0045" ref-type="bibr">[9]</xref>, <xref rid="b0050" ref-type="bibr">[10]</xref>, <xref rid="b0055" ref-type="bibr">[11]</xref>, and has been implicated in causing ‘late’ toxicity <xref rid="b0060" ref-type="bibr">[12]</xref>, <xref rid="b0065" ref-type="bibr">[13]</xref>, <xref rid="b0070" ref-type="bibr">[14]</xref>, <xref rid="b0075" ref-type="bibr">[15]</xref>.</p><p>Heterogeneous dose distributions are delivered to the mucosa with intensity-modulated radiotherapy (IMRT), allowing the oral mucosa to be partially spared <xref rid="b0080" ref-type="bibr">[16]</xref>. However, the development and grade of mucositis is challenging to predict. If a relationship between the dose distribution and toxicity is established, it may be possible to reduce oral mucositis, by means of a treatment planning intervention. Few dose–response studies have been performed for oral mucositis. The complex shape of the mucosal surface, coupled with the fact that it is poorly visualised on computed tomography (CT) are challenges to accurate delineation. Previous oral mucosa dose–response studies <xref rid="b0080" ref-type="bibr">[16]</xref>, <xref rid="b0085" ref-type="bibr">[17]</xref>, <xref rid="b0090" ref-type="bibr">[18]</xref> have reduced the complex shape of the oral mucosa surfaces to a solid oral cavity volume. Clinical experience suggests that dose–area effects may influence mucositis severity. Characterising the dose delivered to the surfaces of the oral mucosa is necessary to properly study the dose–response relationship. A method of obtaining the dose distribution delivered to the oral mucosa surfaces would, therefore, represent an important advance in attempts to model and, thereby, reduce oral mucositis.</p><p>The primary aim of this study was to develop CT-based delineation guidelines to contour the surfaces of the oral mucosa in an anatomically realistic manner. The secondary aim was to establish the worth of the new contouring approach for dose–response studies by assessing the magnitude of the differences in dose metrics extracted from treatment plans using the new, more realistic approach, and previously used contouring techniques.</p><sec id="s0005"><title>Materials and methods</title><sec id="s0010"><title>Patients</title><p>Treatment plans of 11 head and neck radiotherapy patients treated at our institution between 2006 and 2013 were included in the study. The patients had oral cavity contours (OCC) generated using our previous method <xref rid="b0085" ref-type="bibr">[17]</xref> (based on the oral mucosa definition described by Eisbruch et al. <xref rid="b0095" ref-type="bibr">[19]</xref>), and these were used for comparison of the dose distributions extracted using our new technique for obtaining mucosal surface contours (MSC). This cohort incorporated a range of primary disease sites (oropharynx, hypopharynx and nasopharynx), two different CT scanners and included edentulous and dentate patients, eight of whom had dental implants.</p></sec><sec id="s0015"><title>Structure definition</title><p>The MSC were defined as a 3 mm thick wall of tissue based on work by Ueno et al. measuring the oral mucosal thickness at multiple sites in five cadavers using a reamer method <xref rid="b0100" ref-type="bibr">[20]</xref>. They measured a mean thickness of 3.12 ± 1.43 mm. The outlined MSC included the following surfaces: buccal mucosa, buccal gingiva, gingiva proper, lingual gingiva, lingual frenulum, alveolar mucosa, labial mucosa, labial gingiva, labial frenulum, mucosal surface of the floor of mouth, mucosal surface of the tongue anterior to the terminal sulcus, and the mucosal surface of the hard palate. The superior extent was defined to be the superior border of the labial mucosa of the upper lip anteriorly, the roof of the palate posteriorly and the superior extent of the buccal mucosa laterally. The inferior extent was formed by the inferior border of the labial mucosa of the lower lip anteriorly, the surface of the tongue posteriorly and the inferior extents of the floor of mouth mucosa and buccal mucosa laterally. The lateral extents of the buccal mucosa formed the lateral borders. The anterior border followed the alveolar mucosa and the posterior extent of the hard palate formed the posterior border (<xref rid="f0005" ref-type="fig">Fig. 1</xref>).</p></sec><sec id="s0020"><title>Structure delineation</title><p>Structure delineation was performed, by a head and neck radiation oncologist (LW), using the RayStation version 4.0 treatment planning system (RaySearch Laboratories AB, Stockholm, Sweden). The majority of contouring was performed on coronal slices as the main axis of the structure runs in the anterior–posterior direction. Using the coronal plane is beneficial in being able to capture the arch of the palate and the superior, inferior and lateral extents of the buccal mucosa. Sagittal views were useful in establishing the position of the posterior border and axial views aided in contouring the mucosa of the retromolar trigone. The MSC were initially delineated as a single line and, once complete, expanded to a 3 mm annulus. The delineation process was semi-automated using atlas-based segmentation (described in the <xref rid="s0065" ref-type="sec">Supplementary Material</xref>).</p></sec><sec id="s0025"><title>Comparison of geometries</title><p>The geometries of the OCC and MSC structures were compared by measuring the volumes of these structures and the volumes of their overlap with the primary planning target volume (PTV). To gain an appreciation of the difference in the surface areas of the OCC and MSC structures, an ‘OCC surface’ was defined as a 3 mm annulus extending inwards from the outer surface of the OCC. The volumes of these ‘surface’ structures were then compared to the MSC volumes.</p></sec><sec id="s0030"><title>Comparison of dose distributions</title><p>Comparisons of the dose distributions to the oral mucosa extracted using the MSC method and the OCC method previously used at our institution were performed. Neither set of contours was used for treatment plan optimisation. All doses are quoted as the equivalent dose in 2 Gy fractions with an α/β ratio of 10 <xref rid="b0105" ref-type="bibr">[21]</xref>.</p><p>As a result of the sparsity of dose–response studies for oral mucosal toxicity, there is currently a lack of strong evidence on the importance of specific dose–volume parameters for mucositis outcomes. Clinical experience suggests that mucositis is a ‘parallel’ type toxicity. Therefore, mean dose, which incorporates information from every dose level, is a useful descriptor of the dose distribution and so was chosen for quantitative dosimetric comparisons. Maximum dose is included in the <xref rid="s0065" ref-type="sec">Supplementary Material</xref> for completeness.</p></sec></sec><sec id="s0035"><title>Results</title><sec id="s0040"><title>Structure delineation</title><p>An anatomically realistic delineation of the oral mucosa was achieved in all patients (<xref rid="f0005" ref-type="fig">Fig. 1</xref> shows a representative example case). Eight of the 11 patients had streak artefacts on their CT scans due to dental implants. These increased the uncertainty as to the exact location of the mucosal surface where it was obscured by artefact. Whilst the artefacts greatly hinder mucosal contouring on axial slices, in the coronal and sagittal planes following the shape of the mucosa allowed the position of obscured mucosa to be manually imputed with relative ease. The volumes of the OCC, OCC surface and MSC for each patient, and the overlap volume of the OCC, OCC surface and MSC with the primary PTV are shown in <xref rid="s0065" ref-type="sec">Table 1 in the Supplementary Material</xref>.</p></sec><sec id="s0045"><title>Dose comparison</title><p>Using the MSC delineation method led to differences in the dose distributions (<xref rid="s0065" ref-type="sec">Fig. 1 in the Supplementary Material</xref> shows a representative example case) and dose–volume histograms compared with the OCC method (<xref rid="f0010" ref-type="fig">Fig. 2</xref>). The median (and range) of the reduction in the mean mucosal dose when the MSC contours were used was 28.7% (12.8–84.5%) (The individual values for all of the patients are shown in <xref rid="s0065" ref-type="sec">Tables 2 and 3 in the Supplementary Material</xref>). The locations of the maximum doses, as obtained using the OCC method, were either in the musculature of the tongue or floor of mouth, within the PTV. These are not included in the MSC volumes.</p></sec></sec><sec id="s0050"><title>Discussion</title><p>In this work we have demonstrated that it is possible to delineate the oral mucosa of head and neck radiotherapy patients as an anatomically realistic mucosal surface structure on planning CT scans, rather than as an anatomically unrealistic solid organ.</p><p>There is a large difference in the geometry of the MSC, compared with the OCC (<xref rid="f0005" ref-type="fig">Fig. 1</xref> and <xref rid="s0065" ref-type="sec">Supplementary Material Table 1</xref>). The majority of the volume difference represents the volume of the musculature of the tongue and floor of mouth, which are not included in the MSC. The volumes of the MSC structures are greater than those of the corresponding OCC surface structures in all cases, indicating that the MSC structures exhibit larger surface areas. These volume differences translate into large differences in the characterisations of the oral mucosal dose distributions, particularly at intermediate dose levels (<xref rid="f0010" ref-type="fig">Fig. 2</xref> and <xref rid="s0065" ref-type="sec">Supplementary Material Fig. 1</xref>).</p><p>Reductions in the mean mucosal doses with the MSC method were demonstrated for all patients, when compared with the OCC method. The differences in these dose metrics between the two contouring techniques are due to greater overlap between the primary PTV and the OCC than the MSC (<xref rid="s0065" ref-type="sec">Table 1 in the Supplementary Material</xref>). The other major source of differences in the dose metrics is due to the MSC extending laterally, away from the high dose region (which tends to be medially concentrated for the primary disease sites of patients in the study), relative to the OCC, which are centrally confined. The findings of Narayan et al. <xref rid="b0110" ref-type="bibr">[22]</xref> give us reason to believe that the magnitudes of the differences in the mean doses found between the two oral mucosa outlining methods would be clinically significant in terms of predicting mucosal toxicity outcomes and, therefore, would also influence radiotherapy planning interventions aimed at reducing mucosal toxicity.</p><p>Few attempts to extract dose distributions for the oral mucosa have previously been carried out. Sanguineti et al. defined the oral mucosa as a single solid volume encompassing the oral cavity (including buccal mucosa), oropharynx and hypopharynx <xref rid="b0080" ref-type="bibr">[16]</xref>. Werbrouck et al. contoured the oral cavity volume, including the buccal mucosa, but excluded the air within the cavity <xref rid="b0090" ref-type="bibr">[18]</xref>. van de Water et al. studied the dose–response of the oral mucosa for xerostomia <xref rid="b0115" ref-type="bibr">[23]</xref>, rather than mucositis. They divided the oral mucosa into smaller substructures in an attempt to establish which substructures, if any, are most radiosensitive for xerostomia-related endpoints. A limitation of this approach is that it does not allow for dose–area effects of the entire mucosa to be assessed robustly.</p><p>Analysis of the treatment plans showed that the maximum doses reported using the OCC method were located within the musculature of the tongue or the floor of mouth in regions close to or within the PTV. Therefore, no treatment planning intervention to reduce doses to these regions would be possible without also compromising local disease control. However, most of the oral mucosa surface lies outside the PTV and, hence, it should be possible to achieve clinically feasible dose-sparing across at least some of these regions. To this end, we suggest that characterising the oral mucosa dose distribution using our new anatomically realistic approach would provide meaningful dose information that would allow for the modification of treatment plans in an attempt to reduce mucosal toxicity.</p><p>We recognise that, within many radiotherapy treatment planning systems, it is not currently possible to perform contouring in the coronal and sagittal planes or to construct an atlas for semi-automated structure segmentation. Whilst contouring solely in the axial plane would be possible by viewing the axial contours in the coronal and sagittal planes before editing them in the axial plane, this would be inefficient. We recommend that treatment planning system vendors make these features available in the future, as they are necessary to accurately contour structures with complex shapes.</p><p>The method we have developed for oral mucosal surface outlining provides a means of obtaining a more anatomically representative characterisation of the dose distribution delivered to the oral mucosa surfaces than has previously been achieved. 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Water</surname><given-names>T.A.</given-names></name><name><surname>Bijl</surname><given-names>H.P.</given-names></name><name><surname>Westerlaan</surname><given-names>H.E.</given-names></name><name><surname>Langendijk</surname><given-names>J.A.</given-names></name></person-group><article-title>Delineation guidelines for organs at risk involved in radiation-induced salivary dysfunction and xerostomia</article-title><source>Radiother Oncol</source><volume>93</volume><year>2009</year><fpage>545</fpage><lpage>552</lpage><pub-id pub-id-type="pmid">19853316</pub-id></element-citation></ref></ref-list><sec id="s0065" sec-type="supplementary-material"><label>Appendix A</label><title>Supplementary data</title><p><supplementary-material content-type="local-data" id="m0005"><caption><title>Supplementary Material</title><p>Tables and figures.</p></caption><media xlink:href="mmc1.docx"></media></supplementary-material></p></sec><ack id="ak005"><title>Acknowledgments</title><p>This work was supported by the <funding-source id="gp005">Engineering and Physical Sciences Research Council, Cancer Research UK Programme</funding-source> Grant A13407 and <funding-source id="gp010">NHS</funding-source> funding to the NIHR Biomedical Research Centre at The Royal Marsden and ICR. We wish to thank Alex Dunlop, Dualta McQuaid, Simeon Nill and Uwe Oelfke for general support.</p></ack><fn-group><fn id="s0060" fn-type="supplementary-material"><label>Appendix A</label><p>Supplementary data associated with this article can be found, in the online version, at <ext-link ext-link-type="doi" xlink:href="10.1016/j.radonc.2015.02.020" id="ir0005">http://dx.doi.org/10.1016/j.radonc.2015.02.020</ext-link>.</p></fn></fn-group></back><floats-group><fig id="f0005"><label>Fig. 1</label><caption><p>CT scan of a head and neck radiotherapy patient with the OCC (top) and MSC (bottom) shown in green. The OCC representation reduces the complex shape of the mucosal wall to a simplified solid volume, whereas the MSC structure is represented as a mucosal surface and, as such, represents a more anatomically realistic description of the oral mucosa.</p></caption><graphic xlink:href="gr1"></graphic></fig><fig id="f0010"><label>Fig. 2</label><caption><p>Median dose–volume histograms for the oral mucosa for the 11 patients using the OCC (dashed line) and MSC (solid line) delineation approach. The shaded areas represent the ranges. The darker shaded area shows the overlap between the ranges.</p></caption><graphic xlink:href="gr2"></graphic></fig></floats-group></pmc></record>Pour manipuler ce document sous Unix (Dilib)
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