| Summary: | 碩士 === 高雄醫學大學 === 醫學影像暨放射科學系碩士在職專班 === 103 === Purpose : The aim of this study is to evaluate the skin reaction toxicity for breast cancer patients after intensity modulated radiation therapy (IMRT) and volume modulated arc therapy (VMAT).
Materials and Methods: A spherical polystyrene phantom was adopted to simulate: (1) computed tomography (CT) images in different CT slice thicknesses (1.25, 2.5, 3.75, 5 mm); (2) six shrinkage margins of planned target volumes (PTV0, PTV1,…,PTV5) (total 0-5 mm, 1 mm/step); and (3) the best calculations of PTVs between IMRT and VMAT radiotherapies in order to evaluate the differences of coverage and surface doses. The results of spherical polystyrene phantom simulation were applied to 10 patients with right breast cancers. A dual-arc VMAT [Full SmartArc (FSA) or Partial SmartArc (PSA), 2&;#61616; or 4&;#61616;/arc, y arcs calculated based on every x&;#730; spacing, i.e. FSAy-x&;#61616; or PSAy-x&;#61616; in VMAT)] using computerized therapeutic system Pinnacle3&;#174; SmartArc (SA) and six-field IMRT (coplanar-fixed-angles design: 240&;#61616;, 260&;#61616;, 280&;#61616;, 20&;#61616;, 40&;#61616;, 60&;#61616;), total 8 different treatment planning systems were used in this study. Parameters for the comparisons between the advantages and disadvantages of IMRT and VMAT systems included tumor coverage, conformity index (CI), homogeneity index (HI), and skin surface dose. In total of 92 patients received IMRT and 42 patients received VMAT were analyzed statistically to investigate the severity of dermatitis and skin surface dose.
Results: The mean value of CT slice thickness in 10 breast cancer patients were 3.75 mm, and the average variety in spherical polystyrene phantom simulation were <1%. In different PTVs, PTV5 had the highest tumor dose coverage (up to 98.74%) and the lowest monitor unit (MU) (261). If we used PTV5 as an experimental model, the best CI of PSA2-2&;#61616; and PSA2-4&;#61616; were 1.34 and 1.33, and the best (HI) were 1.06 and 1.06, respectively. In addition, the treatment planning system between radiotherapies in the high dose area (above V40) was IMRT> SA2> SA1, which indicated that VMAT had fewer organ-threatening doses than IMRT did. In summary, the surface dose applied to induce breast cancer patients-associated Grade 2 dermatitis in VMAT system was lower than the dose used in IMRT, and no Grade 3 dermatitis patients were found in VMAT regimen.
Conclusions: This study showed that 5 mm superficial shrinkage of PTV in spherical polystyrene phantom simulation could achieve 95% of PTV coverage as standard requirement and effectively reduce the surface dose of skin. With regard to skin dose-associated PTVs between different radiotherapy systems, we found out that dermatitis, the volume of skin dose, the size of a fraction dose and the amount of total doses were significantly different, i.e. VMAT had a better ability to reduce the severity of skin reaction toxicity.
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