| Summary: | 碩士 === 元培醫事科技大學 === 醫學影像暨放射技術系碩士班 === 104 === Tomotherapy just as computer tomography scanning administered dose delivery, so there are several special parameters set in the treatment planning, respectively according to the field width (FW), modulation factor (MF) and pitch. This study examines the relationship between these parameters and their influence on the quality of the nasopharyngeal cancer treatment plans and their execution time on Tomotherapy. Target volumes and organ at risk (OAR) volumes were delineated on a computerized tomography of a phantom (RANDO® Alderson). Maintaining the weightings of each volume, treatment plans were optimized with a different combination of planning parameters (FW = 1, 2.5, 5 cm. MF =1.0 ~ 5.0 in step at 0.2). Background a key aspect of treatment planning is the coverage of the PTV by the 95% isodose. 63 different plans in terms of FW and MF were prepared. Each plan was analyzed for dose distribution, treatment time, delivery quality assurance and ripple effect.
The results show that using the field width of 1cm can more significantly reduce the of the critical organ doses received (p <0.0001). The ratio between treatment time with different field widths, when treatment time at 5 cm was 1, 1.8 and 4 times at widths of 2.5 cm and 1 cm respectively. Analysis of the quality of the obtained treatment plans allows one to specify the lower limit of the optimum MF for the nasopharyngeal cancer at the level of 2.0. And analysis of individual treatment plan time execution allows one to specify the upper limit of the optimal MF factor at the level of 2.8, 3.0 and 3.4, in the FW = 1, 2,5, 5 cm. Field width could lead to change in treatment time. Combination of small field width and small pitch yielded better planning quality, and increase in treatment time. Treatment time could be shortened with combination of large field width, at expense of increased dose to longitudinal directions.
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