- 學位論文
評估三種不同放射治療技術之全腦及脊髓照射劑量比較與誘發二次癌症危險度分析
Retrospective evaluation on dosimetric comparison and secondary cancers risks for three techniques on cranio-spinal irradiation
摘要
目的：本研究目的主要比較三維順形放射治療技術(three dimension conformal radiation therapy, 3D-CRT)、強度調控放射治療(intensity modulation radiation therapy, IMRT)及體積調控弧形放射治療(volumetric-modulated arc therapy, VMAT)三種技術治療劑量的差異；並利用器官等效劑量（organ equivalent dose, OED）分析建立二次癌症的風險評估模型，以得到額外絕對危險度(Excess absolute risk, EAR)。 材料與方法：選取2010-03至2016-02間接受全腦脊髓照射(craniospinal irradiation, CSI)治療的5位病患做為研究對象。規劃3D-CRT、IMRT及VMAT三種不同之治療計畫，利用腫瘤包覆率、順形指標(conformity index, CI)、勻稱指標(homogeneity index, HI)及特定器官之劑量等四項指標以評估治療計畫之優劣。將治療計畫所得之劑量體積直方圖(dose-volume histogram, DVH)資料輸出，執行器官等效劑量（OED）之參數計算，建立額外絕對危險度(EAR)之三種模型，用以評估因放射治療所誘發之二次癌症機率。 結果：以VMAT治療技術之計畫靶體積之V95%之腫瘤劑量包覆率高達99.26%，為最高。VMAT治療技術之順形指標(CI)為1.17；勻稱指標(HI)為1.08，為最佳。VMAT較3D-CRT及IMRT顯著的減少特定危急器官之平均劑量。在額外絕對危險度(EAR)評估結果中顯示，在全腦脊隨照射中引起小腸(small intestine)二次癌症之額外絕對危險度為每萬人中大於50人，其中以3D-CRT之治療技術評估結果為最高；肺部(lungs)二次癌症之額外絕對危險度為每萬人中大於30人，以VMAT之治療技術評估結果為最高。在肝臟及口腔二次癌症之額外絕對危險度為每萬人中小於10人以內，機率極低。 結論：本研究為首篇針對全腦脊髓照射(CSI)三種不同之技術進行劑量學之差異比較，並建立台灣本地接受CSI放射治療患者二次癌症危險度參數，提供臨床治療規劃之二次癌症危險度參考指標。
並列摘要
Purpose : The study aims to perform dosimetric comparison of treatment plans for 3D conformal radiation therapy (3D-CRT)、intensity modulation radiation therapy (IMRT)、volumetric-modulated arc therapy (VMAT)，and evaluated the secondary cancers rick of three techniques for cranio-spinal irradiation. Materials and Methods: Ten patients were enrolled from 2010 to 2016, the prescription was 36 Gy in 20 fraction. Differences in plans were evaluated using Wilcoxon signed rank tests for various dosimetric parameters for the target volumes and normal tissue. The relative organ equivalent dose (OED) concept was applied in three dose-risk scenarios: a linear response model, a plateau response and an organ specific linear-exponential response and excess absolute risk (EAR) was calculated. Results: VMAT technique improved normal tissue sparing while also providing more homogeneous target coverage than 3D-CRT and IMRT for CSI patients. The VMAT of PTV V95% coverage was 99.26%, was the highest; CI were 1.17; HI1.08, for the best. In the EAR to assess the results we have seen in the small intestine caused by CSI (Small intestine) secondary additional absolute risk of cancer per million people in more than fifty (per 1.0000/per year, 3D-CRT to treat the results of the assessment of the highest; EAR of lungs was more than thirty (per 1.0000/per year), VMAT was the highest. In the liver and oral additional absolute risk of secondary cancers per million people within less than 10 people, the probability is very low. Conclusions: This was first study to compare on dosimetric parameters of three techniques of craniospinal irradiation, and the establishment of the EAR parameters in Taiwan. Our study aims to serve as reference when CSI implementation is considered. VMAT treatments achieved better PTV homogeneity and reduced maximum dose to normal tissues. The result of EAR offer estimation for CSI patient’s secondary malignance carcinoma risks of three techniques.