- 學位論文
二維輻射探測器劑量轉換與校正因子之研究
An investigation of ionizing radiation to dose conversion and its calibration factors for a proprietary 2D Pad detector
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摘要
隨著科技業的蓬勃發展，現今醫療儀器產業日新月異，放射遠隔治療透過快速且精確的電腦運算以及精密的儀器設備，可以將輻射劑量準確的投擲於病灶處並且有效的降低腫瘤周圍正常組織的輻射劑量，以達到保存正常組織之目的；然而在此不容差錯的情況下，導致了輻射劑量的驗證與安全問題變得更加繁瑣且關鍵；本論文主要目的為使用自製研發之輻射探測器(Pad detector)置於輻射源下進行量測，將量測所得之輻射游離計數，經由理論公式計算，轉換為輻射劑量單位；並且根據現有的劑量議定書之內容規範所提及會使游離腔讀出數值產生影響之項目進行校正。本研究中主要針對環境溫度壓力、再結合效應與空氣克馬校正項目進行校正；利用不同的實驗或者是透過Geant4程式模擬，得到不同的校正因子，將各個因素所導致游離訊號產生的差異進行校正；將此三種影響因子對於Pad detector之量測訊號進行修正後，比較Pad detector之量測計數與我國游離輻射標準實驗室所提供之量測數據，其相較後發現經過校正的Pad detector之量測數據與國家標準實驗室之量測結果差異<5%。並且透過持續追蹤Pad detector於同一Co60射源下的量測結果，除了可以觀察Co60射源自然衰減的情況之外，本研究同時利用衰減公式將每次實驗之量測結果回推至射源強度一致的情況下，比較每次實驗量測之差異<0.4%。
並列摘要
Modern external radiotherapy with photon beams takes advantage of computers, sophisticated algorithms and precise mechanics in order to let the damage close to the tumor while sparing normal tissue. Because of the accurate technique, it becomes more crucial for verification and safety issues. In this study we present the results of dosimetric evaluation of a two- dimensional Pad detector with the objective of its implementation for quality assurance in National Radiation Standard Laboratory (NRSL). The radiation dose conversion of the count reading on Pad detector is performed by means of formula and certain correction for the effect on reading of dosimeter according to the specification of the content of the dose protocols. To proceed with the correction, this research is mainly aimed at environmental temperature and pressure correction, recombination correction, and air Kerma calibration. Experiments and Geant4 simulation are designed to find recombination correction and air Kerma calibration, respectively to correct the difference in output readings between reference and user’s condition. The results show that this detector can be used for 2D dosimetry of beams. The difference of corrected statistic in this study is under 5% compared to the reference statistic provided by NRSL. Four measurements at different time of the same Co60 radiation source using the Pad detector are performed over a period of 43 days. The natural decay of Co60 source can be clearly observed from the measurements. After converting the readings of Pad detector to the same source strength by the decay formula of Co60, it is found that the difference among the four experimental measurements is < 0.4%.
參考文獻
[2] S. Webb, "Intensity Modulated Radiation Therapy," in IOPP, Bristol, 2000.
[3] Amerio et al., "Dosimetric characterization of a large area pixel-segmented ionization chamber," Medical Physics, pp. 414-420, 2 February 2004.
[4] C. Brusasco et al., "Strip ionization chambers as 3-D detector for hadrontherapy," Nucl. Instrum. Methods Phys., p. 499–512, 1997.
[6] C.Brusasco et al., "Strip ionization chambers as 3-D detector for hadrontherapy," Medical Physics, p. 499–512, 1997.
[7] BuccioliniM, Buonamici F B and CasatiM, “Verification of IMRT fields by film dosimetry,” Med. Phys., pp. 161-8, 2004.