Full metadata record
DC FieldValueLanguage
dc.contributorDepartment of Health Technology and Informaticsen_US
dc.contributor.advisorWu, Vincent (HTI)-
dc.creatorLam, Cho Pan-
dc.identifier.urihttps://theses.lib.polyu.edu.hk/handle/200/9749-
dc.languageEnglishen_US
dc.publisherHong Kong Polytechnic University-
dc.rightsAll rights reserveden_US
dc.titleDosimetric influences and reproducibility of flexed neck and extended neck set‐up positions in helical tomotherapy of nasopharyngeal carcinomaen_US
dcterms.abstractBackground: Patients with nasopharyngeal carcinoma (NPC) treated with Helical Tomotherapy (HT) are commonly positioned in an extended neck (EN) or a flexed neck (FN) position. The two set-up positions may have different dosimetric influences to the HT plans and to the reproducibility HT treatments. Objectives: To investigate possible dosimetric differences of EN and FN set-up positions, especially in intracranial structures and to investigate the reproducibility of the setup in the neck regions of these two set-up positions throughout the treatment course. Method: Twenty NPC patients with various disease stages from each set-up group, treated with HT from 2014 to 2016, were conveniently recruited. All organs-at-risk (OARs) were re-contoured and the nasopharyngeal target volumes were standardized. Forty HT plans were re-computed using the same target dose prescription and OARs constraints. Conformity Index (CI), Homogenity Index (HI), maximum, minimum, mean doses of the targets and the maximum and mean doses of OARs were compared. Apart from HT re-planning, past daily megavoltage computed tomography (MVCT) images of each patient were retrieved and re-registered with the matching focus on the clivus. Set-up errors on the cervical level of C4 and C7 were obtained and compared between two groups.en_US
dcterms.abstractResults: The CI of PTV-NP in FN group was significantly higher than that of EN group (p<0.05), while the CIs of both neck targets in FN group were significantly smaller than those of EN group (p <0.05). All target volumes of FN group had significantly higher HI values than those of EN group with all p < 0.05. For OARs in FN group, both cerebellum and hippocampus received significantly lower maximum and mean doses and the temporal lobes received significant lower mean doses. In contrast, all optic structures, brainstem, spinal cord and parotid glands received higher doses in FN group. For set-up errors calculation, the systematic errors at C4 level in FN groups were larger than that in EN group in all translational directions. The systematic errors in FN group on both C4 and C7 level were larger in both superoinferior(SI) and anteroposterior(AP) directions than those in EN group. For random errors, they were similar except in AP direction, both C4 and C7 level in EN group deviated more than those in FN group. Conclusion: FN position was beneficial in reducing the received radiation doses to cranial structures including cerebellum, temporal lobes and hippocampus and thus minimize chronic neurocognitive impairments as side effects of HT treatment of NPC. On the contrary, FN position at the same time might increase radiation dose to optic structures and was more prone to greater deviations in SI and AP directions. Hence, reducing target margin near optic structures, applying planning organ-at-risk volume to the optic structures and modifying the FN set-up devices would improve the performance of FN position in dosimetric outcome and reproducibility. Otherwise, suppressing radiation dose to cerebellum, hippocampus and temporal lobes should be considered in an EN setting to minimize late complications to these structures.en_US
dcterms.extentix, 77 pages : color illustrationsen_US
dcterms.isPartOfPolyU Electronic Thesesen_US
dcterms.issued2018en_US
dcterms.educationalLevelM.Sc.en_US
dcterms.educationalLevelAll Masteren_US
dcterms.LCSHHong Kong Polytechnic University -- Dissertationsen_US
dcterms.LCSHNasopharynx -- Cancer -- Radiotherapyen_US
dcterms.LCSHRadiation dosimetryen_US
dcterms.LCSHRadiotherapy -- Positioningen_US
dcterms.accessRightsrestricted accessen_US

Files in This Item:
File Description SizeFormat 
991022173538103411.pdfFor All Users (off-campus access for PolyU Staff & Students only)2.76 MBAdobe PDFView/Open


Copyright Undertaking

As a bona fide Library user, I declare that:

  1. I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
  2. I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
  3. I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.

By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.

Show simple item record

Please use this identifier to cite or link to this item: https://theses.lib.polyu.edu.hk/handle/200/9749