Groot, C. de (2014) The estimation of visual impairment after head and neck radiotherapy. thesis, Medicine.
Full text available on request.Abstract
Purpose: The purpose of this thesis is twofold: first, to analyse visual impairment in patients treated with radiotherapy for tumours adjacent the optic pathway, and to relate dose-volume histogram (DVH) parameters of optic structures to development of these visual deficits. Second, to evaluate current delineation and study delineation, based on a new guideline, of optic structures and analyse differences in DVH’s between these structures. Methods and Materials: Between 2007 and 2013, 66 patients with tumours of the nasopharynx, nasal cavity, paranasal sinuses and skull-base were treated with curative intent, and received either definitive or postoperative (chemo)radiation using CT-planned radiotherapy. Patients were followed for at least 6 months after radiotherapy. Dosimetric parameters of the optic nerves, optic chiasm and optic tracts were derived from DVHs of both the original contours of the radiotherapy planning and the study contours according to the developed guideline. Results: The median follow-up period was 31.5 months. Severe visual impairment occurred in 3.5% of cases. On average, maximum equivalent doses in 2-Gy fractionating (EQD2) to all optic structures were significantly higher for patients with any visual complication (mild to severe) (51,5 Gy) versus patients without complications (30.2 Gy, p=0,027). Of all optic structures, 22% received a maximum EQD2 exceeding the dose constraint of 56 Gy. The possibility of severe visual deficits increased remarkably when mean and maximum EQD2 doses exceeded 75 Gy and 65 Gy, respectively. The median chiasmal volume was 0.35cm³ (SD 0.05 cm³) and 0.64 cm³ (SD 0.38 cm³) for study an original contours, respectively. The average Dice and Jaccard coefficient were 0.18 (range, 0.00-0.61) and 0.11(range, 0.00-0.41). Among all original and study contours, mean and maximum doses to all structures were significantly different. Conclusions: The results of this study suggest that currently used dose constraints to optic structures (Dmax <55-60 Gy) might be conservative since no severe visual impairment occurred when maximum EQD2 was <65 Gy. Poor consistency and accuracy in delineation of original optic structures for treatment planning was found, the use of a delineation guideline and fused MR-CT images in this study significantly improved these measures.
| Item Type: | Thesis (Thesis) |
|---|---|
| Supervisor name: | Steenbakkers, Dr. R.J.M. and Bijl, Dr. H.P. |
| Faculty: | Medical Sciences |
| Date Deposited: | 25 Jun 2020 10:57 |
| Last Modified: | 25 Jun 2020 10:57 |
| URI: | https://umcg.studenttheses.ub.rug.nl/id/eprint/1778 |
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