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    Please use this identifier to cite or link to this item: http://nthur.lib.nthu.edu.tw/dspace/handle/987654321/85131

    Title: Ir-192射源於體腔近接治療之劑量分布研究
    Authors: 吳?暉
    Wu, Chin Hui
    Description: GH029611818
    Date: 2015
    Keywords: 近接治療;徑向劑量函數;非均向函數
    Abstract: 本論文包含兩個部分:(1)近接治療射源192Ir於不同組織之劑量分布,(2)裝療器內含金屬材質對子宮頸癌近接治療劑量分布之影響。
    第二部分是要探討當子宮頸癌患者進行近接治療時,裝療器內含金屬材料對劑量分布造成的影響。192Ir射源單點停留結果顯示,當tandem存在時,MCNPX計算值、測量值與治療計畫計算相對劑量差異在5%以內。當ovoid存在時, MCNPX計算值與測量值相一致,但治療計畫計算值會高估劑量達4倍。這是由於治療計畫系統沒有考慮裝療器中金屬材料所造成的屏蔽效應。192Ir射源多點停留結果顯示,在考慮裝療器存在時,TLD測量值與MCNPX計算值的劑量差異大部分在6%以內,MCNPX與治療計畫計算值相比較,治療計畫計算值會在ICRU直腸與膀胱劑量參考點分別高估58%與50%。本研究結果顯示治療計畫計算值將會因裝療器內含金屬材料而導致劑量分布改變。因此建議治療計畫系統應考量裝療器所造成的屏蔽效應,以確保劑量輸出之準確性。
    This study included two parts: (1) Dose distributions of an 192Ir brachytherapy source in different media ; (2) Influence of metal of the applicator on the dose distribution during brachytherapy. The AAPM TG-43 report provides dose calculation formula and dose parameters for brachytherapy. Although it can be used to evaluate the radiation dose received by the soft tissue, the human organs such as nasopharynx, esophagus, bronchi, lungs and bones are of different densities. AAPM TG-43 does not provide the corresponding dose parameters, therefore, the dose in these tissues can’t be assessed accurately. This may result in tumor recurrence or severe side effects in normal tissues.
    The MCNPX code is used to investigate the 192Ir dose distribution in water, bone and lung tissue. The glass dosimeter measurement was performed to verify the calculation results. It is found that dose rate constant, radial dose function and anisotropy function in water agreed well with previous literatures. The lung dose near the source, however, would be overestimated by up to 12% if water was used as the lung material. The result implies that if tumor is located in lung, the tumor dose will be overestimated if the difference in material density is not taken into consideration. The calculated results from this study could offer as a clinical reference for improving the accuracy of dose delivered for brachytherapy within the patient of lung cancer.
    The 2nd part explores how the metal materials of the applicator influence the dose distribution when performing brachytherapy for cervical cancer. (1) 192Ir source located at a single position: For dose distribution in water with the presence of the tandem, differences among measurement, MCNPX calculation and treatment planning system results are < 5%. For dose distribution in water with the presence of the ovoid, the MCNPX result agrees with the measurement. But the doses calculated from treatment planning system were overestimated by up to a factor of 4. This is due to the shielding effect of the metal materials in the applicator not being considered in the treatment planning system. (2) Multiple 192Ir source dwell positions: When the applicator was used in treatment, the absolute dose difference between the TLD results and the MCNPX simulation results agreed within ~ 6 %. Compared with the MCNPX results, the TPS overestimated the ICRU rectum and bladder reference dose point by 58% and 50%, respectively. This result shows that the dose distribution calculated by TPS would be affected due to the use of applicator containing metal material, which suggests that the TPS result should be modified to take into account the shielding effect of the applicator to ensure the accuracy of the dose delivery.
    URI: http://nthur.lib.nthu.edu.tw/dspace/handle/987654321/85131
    Source: http://thesis.nthu.edu.tw/cgi-bin/gs/hugsweb.cgi?o=dnthucdr&i=sGH029611818.id
    Appears in Collections:[核子工程與科學研究所] 博碩士論文

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