| Author: | Yeung, Fung Yung Adela |
| Title: | A dosimetric study : comparison of volumetric-modulated arc (VMAT) and hybrid-arc (HA) to central neck region in radiation therapy of nasopharyngeal carcinoma |
| Advisors: | Wu, Vincent (HTI) |
| Degree: | M.Sc. |
| Year: | 2018 |
| Subject: | Hong Kong Polytechnic University -- Dissertations Nasopharynx -- Cancer -- Radiotherapy Radiation dosimetry |
| Department: | Department of Health Technology and Informatics |
| Pages: | 104 pages : color illustrations |
| Language: | English |
| Abstract: | Our oncology centre has used volumetric-modulated arc (VMAT or RA) radiation therapy as the standard of treatment for nasopharyngeal carcinoma since 2011, and nearly 300 cases have been treated. Dysphagia and swallowing dysfunctions are long-term side-effects from radiation treatments and may progressively deteriorate for years post-treatments, which have a great impact on the quality of life for cancer survivors of NPC. The aim of this study was to assess the dosimetric effects of two planning methods - HybridArc (HA) and RA-with-flattening-filter-free beams (RA-FFF) - as compared to the RapidArc method that have been used since 2011. The comparisons focused on the larynx, the normal tissues on the lower central neck region, the spinal cord, and the pharyngeal-esophagus. A total of 36 patients was recruited and divided into two groups according to their N-staging. Their CT data were retrospectively re-planned with the two methods. All re-plans were evaluated based on their dose-volume histograms, visual inspections of isodose distribution in the treatment planning system, of their dosimetric performance of the target dose, dose constraints to the organs-at-risk, and normal tissue spread. The statistical analysis was done by the Multivariate Analysis of Variance (MANOVA). The significance level was p < 0.05. All the re-plans met the acceptance for PTV dose coverage and OARs sparing as the clinical plans. For the laryngeal dose, HA was able to reduce the volumes receiving V16, V20, V25, and V30 by 3.73%, 7.23%, 14.82%, and 17.27%, while RA-FFF averaged to 1.55%. For the normal tissues in the central neck region, HA was able to decrease the volumes receiving V13, V20, V26, and V30 by 95%, 79%, 59%, and 41%, while RA-FFF averaged to 0.41%. For spinal cord and the pharyngeal-esophagus, volumes receiving V12 and V13 and V23 and V30 respectively also decreased significantly in HA plans and RA-FFF plans. MUs were on average 12 % and 33 % more in HA and RA-FFF respectively, while beam-on times were 64 % more in HA and was 0.78 % less in RA-FFF. In general, HA and RA-FFF plans were comparable plans to RA plans, and they were able to spare dose to the larynx and the normal tissues in the lower neck region than RA plans. |
| Rights: | All rights reserved |
| Access: | restricted access |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| 991022173537703411.pdf | For All Users (off-campus access for PolyU Staff & Students only) | 2.1 MB | Adobe PDF | View/Open |
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