基于蒙特卡羅計算的伽瑪刀劑量學研究
發(fā)布時間：2018-08-19 11:29
【摘要】：論文以我國自行研制并已投入臨床使用的LunaTM-260全身伽瑪刀治療機為對象,研究了該伽瑪刀單源和多源的靜態(tài)聚焦的劑量學特性。目的,建立Luna伽瑪刀的蒙特卡羅劑量計算模型,模擬計算伽瑪刀劑量學參數。解決Luna伽瑪刀在臨床使用中單源的百分深度劑量(PDD)、組織最大劑量比(TMR)、射野離軸比(OAR)及輸出因子等劑量學參數無法測量的問題,并將蒙卡計算結果與治療計劃系統(tǒng)的數據比較,對驗證伽瑪刀治療的劑量準確性進行驗證。 課題涉及伽瑪刀機頭的幾何建模、膠片劑量計的實驗測量、蒙特卡羅程序的模擬計算等工作。論文介紹并論述了目前伽瑪刀計劃系統(tǒng)的劑量計算模型及優(yōu)缺點以及蒙特卡羅方法的基本原理。著重論述了Luna伽瑪刀計劃系統(tǒng)采用的TMR-OAR劑量計算模型,涉及到的一些劑量學參數,討論了蒙特卡羅程序MCNP4C對開展本研究的可行性和實用性。詳述了基于Luna伽瑪刀的機頭結構、材料和尺寸,以及放射源的特征的MCNP劑量計算模型的幾何建模。并通過與測量數據的比較來驗證計算模型的正確性,基于所建劑量計算模型開展伽瑪刀單源和多源聚焦的劑量學研究。伽瑪刀的實驗測量采用Gafchromic EBT2新型膠片劑量計。 研究方法：通過建立伽瑪刀劑量計算模型,分別計算單源和多源射束所有準直器在30cm×30cm×30cm水模體中的劑量參數和在直徑16cm的伽瑪刀專用有機玻璃球模中的等劑量分布。 結果：模擬計算了luna伽瑪刀6種準直器(4mm×4mm、8mm×8mm、14mm×14mm、14mm×20mm、14mm×40mm、14mm×60mm)單源和多源的在水模中的0.5cm、5cm及10cm深度出處的百分深度劑量及離軸比；計算了在專用測量球模中的等劑量分布曲線。在水模0.5cm深度處4、5、6號準直器的射野離軸比計算結果不好；5cm和10cm處的計算結果比較理想。根據百分深度劑量與組織最大劑量比的關系,由百分深度劑量數據得到組織最大劑量比的值。將單源方模中的組織最大劑量比的計算結果、計劃系統(tǒng)中的原始數據(測量數據)及標準的組織最大劑量比曲線進行了比較：計算結果與標準曲線符合的較好,與TPS中數據(測量)有一定誤差,最大誤差不超過5%。對于l號準直器在0—5cm深度范圍計算值比測量值大,5—15cm深度范圍計算值與測量值基本一致,大于15cm的深度計算值比測量值��；對于其余的5個準直器計算值與測量值一致,測量值大于計算值,誤差為2%-5%。單源方模中5cm深度處射野離軸比的比較結果：射野內的數值符合的較好,射野外的數值相差較大。每個準直器取其焦點處的劑量作為標準值,以6號準直器最為標準歸一計算了6個準直器的輸出因子,將其與測量結果比較。1號準直器相差較大(大于10%),其余均小于3%。 結論：所建立的蒙特卡羅計算模型很好地驗證了單源射野的百分深度劑量(PDD)、組織最大劑量比(TMR)、射野離軸比(OAR)及輸出因子,計算結果與測量結果在誤差范圍(5%)內符合的很好；同時,對于多源聚焦的劑量分布特點進行了研究,給出luna伽瑪刀的焦點劑量分布。研究結果表明所建立的luna伽瑪刀蒙特卡羅劑量計算模型可以用于其劑量學參數的驗證,很好地解決了單源劑量學參數無法測量的問題,同時對于伽瑪刀的臨床上計劃設計和劑量計算起到一定的指導性作用。本工作為伽瑪刀今后研究工作奠定了基礎。
[Abstract]:The dosimetric characteristics of single-source and multi-source static focusing of LunaTM-260 gamma knife were studied. Objective To establish a Monte Carlo dosimetric model of Luna gamma knife and simulate the dosimetric parameters of Luna gamma knife. The dosimetric parameters such as PDD, TMR, OAR and output factor can not be measured. The results of Monte Carlo simulation were compared with the data of treatment planning system to verify the dose accuracy of gamma knife therapy.
The subject involves the geometric modeling of gamma knife head, the experimental measurement of film dosimeter and the simulation calculation of Monte Carlo program. The paper introduces and discusses the dose calculation model, advantages and disadvantages of the current gamma knife planning system and the basic principle of Monte Carlo method. The TMR-OAR used in Luna gamma knife planning system is emphatically discussed. The feasibility and practicability of the Monte Carlo program MCNP4C for this study are discussed. The geometric modeling of the MCNP dose calculation model based on Luna gamma knife is described in detail, including the structure, material and size, and the characteristics of the radiation source. Based on the correctness of the calculation model, single-source and multi-source focused gamma knife dosimetry was carried out. Gafchromic EBT2 film dosimeter was used in the experimental measurement of gamma knife.
Research methods: By establishing gamma knife dose calculation model, the dose parameters of all collimators of single source and multi-source beam in 30 cm 65507
Results: The percentile depth doses and off-axis ratios of 6 kinds of Luna gamma knife collimators (4 mm 4 mm, 8 mm 8 mm, 14 mm 14 mm, 14 mm 65 According to the relationship between the percentage depth dose and the maximum dose ratio of tissue, the maximum dose ratio of tissue can be obtained from the percentage depth dose data. Comparing the measured data with the standard tissue maximum dose ratio curve, the calculated results are in good agreement with the standard curve, and the maximum error is less than 5% with the TPS data. The calculated depth at 15 cm is smaller than the measured value, and the measured value is larger than the calculated value for the remaining 5 collimators, with an error of 2%-5%. The comparison of the off-axis ratio of the field at the depth of 5 cm in a single source square model shows that the values in the field are in good agreement with those in the field, and the values in the field are quite different. The output factors of the six collimators were normalized by using collimator No. 6 as the standard value. The difference between collimator No. 1 and the measured results was larger (more than 10%) and the rest was less than 3%.
CONCLUSION: The Monte Carlo calculation model validates the PDD, TMR, OAR and output factor of single source radiation field. The calculated results are in good agreement with the measured results within the error range (5%). The results show that the Monte Carlo dose calculation model of Luna gamma knife can be used to validate the dosimetric parameters of Luna gamma knife. It can solve the problem that single source dosimetric parameters can not be measured. It also plays a guiding role in clinical planning and dose calculation of Luna gamma knife. This work lays the foundation for future research work of gamma knife.
【學位授予單位】：中國人民解放軍軍事醫(yī)學科學院
【學位級別】：博士
【學位授予年份】：2012
【分類號】：R142
本文編號：2191525
[Abstract]:The dosimetric characteristics of single-source and multi-source static focusing of LunaTM-260 gamma knife were studied. Objective To establish a Monte Carlo dosimetric model of Luna gamma knife and simulate the dosimetric parameters of Luna gamma knife. The dosimetric parameters such as PDD, TMR, OAR and output factor can not be measured. The results of Monte Carlo simulation were compared with the data of treatment planning system to verify the dose accuracy of gamma knife therapy.
The subject involves the geometric modeling of gamma knife head, the experimental measurement of film dosimeter and the simulation calculation of Monte Carlo program. The paper introduces and discusses the dose calculation model, advantages and disadvantages of the current gamma knife planning system and the basic principle of Monte Carlo method. The TMR-OAR used in Luna gamma knife planning system is emphatically discussed. The feasibility and practicability of the Monte Carlo program MCNP4C for this study are discussed. The geometric modeling of the MCNP dose calculation model based on Luna gamma knife is described in detail, including the structure, material and size, and the characteristics of the radiation source. Based on the correctness of the calculation model, single-source and multi-source focused gamma knife dosimetry was carried out. Gafchromic EBT2 film dosimeter was used in the experimental measurement of gamma knife.
Research methods: By establishing gamma knife dose calculation model, the dose parameters of all collimators of single source and multi-source beam in 30 cm 65507
Results: The percentile depth doses and off-axis ratios of 6 kinds of Luna gamma knife collimators (4 mm 4 mm, 8 mm 8 mm, 14 mm 14 mm, 14 mm 65 According to the relationship between the percentage depth dose and the maximum dose ratio of tissue, the maximum dose ratio of tissue can be obtained from the percentage depth dose data. Comparing the measured data with the standard tissue maximum dose ratio curve, the calculated results are in good agreement with the standard curve, and the maximum error is less than 5% with the TPS data. The calculated depth at 15 cm is smaller than the measured value, and the measured value is larger than the calculated value for the remaining 5 collimators, with an error of 2%-5%. The comparison of the off-axis ratio of the field at the depth of 5 cm in a single source square model shows that the values in the field are in good agreement with those in the field, and the values in the field are quite different. The output factors of the six collimators were normalized by using collimator No. 6 as the standard value. The difference between collimator No. 1 and the measured results was larger (more than 10%) and the rest was less than 3%.
CONCLUSION: The Monte Carlo calculation model validates the PDD, TMR, OAR and output factor of single source radiation field. The calculated results are in good agreement with the measured results within the error range (5%). The results show that the Monte Carlo dose calculation model of Luna gamma knife can be used to validate the dosimetric parameters of Luna gamma knife. It can solve the problem that single source dosimetric parameters can not be measured. It also plays a guiding role in clinical planning and dose calculation of Luna gamma knife. This work lays the foundation for future research work of gamma knife.
【學位授予單位】：中國人民解放軍軍事醫(yī)學科學院
【學位級別】：博士
【學位授予年份】：2012
【分類號】：R142
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