Comparison of a static conformal technique and the arc circular field technique in the stereotactic radiotherapy of head and neck lesions

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Comparison of a static conformal technique and the arc circular field technique in the stereotactic radiotherapy of head and neck lesions

 

Author: Tang, Pik-kei Peggy
Title: Comparison of a static conformal technique and the arc circular field technique in the stereotactic radiotherapy of head and neck lesions
Degree: M.Sc.
Year: 2001
Subject: Brain -- Cancer -- Radiotherapy
Nasopharynx -- Cancer -- Radiotherapy
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Optometry and Radiography
Pages: ix, 88, [19] leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1569104
URI: http://theses.lib.polyu.edu.hk/handle/200/583
Abstract: In the last twenty years, stereotactic radiotherapy, as a non-invasive technique, was widely used in the treatment of brain lesions as well as tumors in head and neck regions. Different types of tertiary collimation systems are used in stereotactic radiotherapy. This dissertation aims to explore the utilization of cylindrical collimation arc therapy and mini multi-leaf collimation (MMLC) static conformal therapy in the treatment of brain lesions and Nasopharyngeal Carcinoma (NPC) recurrences. Seventeen NPC recurrence and eleven brain lesion retrospective cases were selected. Target contours and critical organs were defined by oncologists. Two computer planning systems, the Xknife and the Xplan, were used. The former was used to design a set of 3- or 5- arcs plans involving a single isocenter with a cylindrical collimator. The latter involved static beams and the MMLC to conform a high radiation dose region to the target. 5- and 7- static beams plans were made for each case. Dose conformity and dose homogeneity of the target volume, doses to critical organs, tissue density correction effect and the number of beam effect were compared for both techniques. A spherical target volume was defined in a head phantom and computer planning for this target was performed. One treatment plan involved isocentric five arcs irradiation with a cylindrical collimator. Another treatment plan involved isocentric five static beams irradiation with the MMLC. Then the two treatments were separately delivered. A 6X6cm2 radiochromic film was embedded in the phantom at the isocentre. Dose profiles along x- and y- axes and a planar dose distribution through the centre of the target volume were measured from the film. Agreement between dose distribution measured by the radiochromic film with a 671 nm wavelength film reader and computer plans was acceptable. Computer planning results indicated that the MMLC performed a better dose conformity and contributed lesser doses to vital organs than the cylindrical collimation system for the treatment of NPC recurrences. Both techniques produced similar results for the treatment of brain lesions. The correction of tissue densities was recommended for the planning of NPC recurrence cases. Increasing the number of static beams from 5 to 7 did not significantly affect the dose conformity to the target and doses to critical organs.

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