|Title:||Dosimetric comparison of intensity modulated stereotactic radiotherapy with different stereotactic techniques for recurrent nasopharyngeal carcinoma|
|Subject:||Hong Kong Polytechnic University -- Dissertations.|
Nasopharynx -- Cancer -- Radiotherapy.
|Department:||Department of Health Technology and Informatics|
|Pages:||vii, 83 leaves : col. ill. ; 30 cm.|
|Abstract:||In Hong Kong, stereotactic radiotherapy has been introduced in the treatment of recurrent nasopharyngeal carcinoma (NPC). Four techniques, including circular arc (CARC), static conformal beam (SmMLC), dynamic conformal arc (mARC) and intensity modulated stereotactic radiotherapy (IMSRT) have been commonly used. The aim of this study was to examine whether the newly developed IMSRT has any dosimetric advantages over the other three techniques. The objectives were to study and compare the dose distribution in the planning target volume (PTV) and organs at risk (OARs) by these four techniques and to assess the influence of tumor size on their dosimetric differences. Thirty-two patients were conveniently selected. They were then divided into two groups: Small PTV size group (<65 cm3) and Large PTV size group (>65 cm3). CT images of these patients were retrieved from stereotactic planning system for contouring and computing treatment plans. Treatment planning of each patient was performed for the four treatment techniques: CARC, SmMLC, mARC and IMSRT. Dose data from dose volume histogram, the conformity and homogeneity indices of PTV and doses to OARs and normal tissue were compared. Results showed that all the four stereotactic techniques delivered adequate doses to PTV. However, only IMSRT, SmMLC and mARC delivered a conformal and homogenous dose to PTV. The conformity and homogeneity in PTV doses were poor in CARC. Each technique could spare some OARs while delivering high doses to other OARs. Among the four techniques, IMSRT spared more OARs. A general trend of larger doses to OARs and more normal tissues irradiated in low dose were resulted in large PTV size group among the four techniques. Based on dose distribution comparison, IMSRT was more optimal to patients with recurrent NPC by delivering a more conformal and homogenous dose to PTV while sparing more OARS among the four techniques.|
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