使用磁振造影影像於腦腫瘤放射治療計畫系統中劑量計算之依據

Using MRI for Dose Calculation in Radiation Treatment Planning System of Brain Tumor

林廉鈞(Lien-Chung Lin)

指導教授 ： 莊克士

國立清華大學/原子科學院/生醫工程與環境科學系/碩士(2007年)

摘要

本研究目的在評估以影像（MRI）為基礎之電腦治療計畫，其臨床上之可行性。許多學者指出，3D順行放射治療（3DCRT）及強度調控放射治療（IMRT）在一合理副作用的前提下，可大大提高腫瘤控制率；然而，當劑量相對增加時，對於腫瘤位置、大小及準確的劑量給予就顯得十分重要。我們知道，對於軟組織的對比及腫瘤的圈選，MRI可提供更多的資訊及影像品質相較於電腦斷層影像（CT）；但是，由於MRI的像素灰階強度與組織電子密度無強烈關係存在，也就是影像中缺乏電子密度的資訊，所以無法應用於現今治療計畫中劑量之計算。為了解決這個問題，本研究首先使用模糊C-means分群法（FCM）將MRI分割成數個典型的組織，之後在指定各組織合理之CT值，將這張帶有CT值資訊的影像視為目標影像（Target image），再以非線性轉換方法中的人工類神經網路（ANNs），藉由反覆訓練，找出MRI與目標影像之最佳的映射關係，如此，便可透過網路將MRI轉換成HCT（Homemade CT）影像，而此HCT影像就是單由MRI影像轉換而成且帶有CT值資訊的影像。實驗結果顯示，在不同角度、能量及照野大小下，經由治療計畫運算，HCT影像與真正電腦斷層影像之劑量差異皆在2％以內，且與全部當做均質水的影像相比，HCT影像亦提供了更準確的劑量分佈；此外，HCT影像也可重建出模擬定位中之數位重建放射影像（DRR）。

關鍵字

磁振造影 ； 腦腫瘤 ； 放射治療計畫 ； 劑量計算

並列摘要

The purpose of this work is to evaluate the practicality of a treatment planning method based only on magnetic resonance imaging (MRI) for radiotherapy. Many investigators have demonstrated that dose escalation with three-dimensional conformal radiation therapy (3DCRT) and intensity-modulated radiation therapy (IMRT) potentially increases the tumor control rate while keeping complication risk at a reasonable level. As dose levels are increased, the precise information of target location and size and the accuracy of dose delivery become crucial. Magnetic resonance imaging (MRI) provides superior image quality for soft-tissue delineation over computed tomography (CT) and is widely used for target and organ delineation in radiotherapy for treatment planning. The main drawback of this modality for treatment planning is the lack of electron density information in the MR images. In this study, we segment two sets MRI images of brain by FCM (fuzzy c-means clustering) method as a target image. To overcome the limitation of MRI in dose calculation, we assigned electron density values to typical anatomical structures. We use the non-linear convert method (Artificial Neural Networks) to transform MRI to Homemade CT (HCT) images. Our results show that the dose differences between HCT images and real CT images are within ±2% in different depths, photon energy, and field sizes. Compared with the homogeneous images, HCT-based treatment planning revealed the more accurate dose and dose distribution. In addition, HCT images can also provide DRR (digitally reconstructed radiograph) for radiography simulation.

並列關鍵字

MRI ； Brain Tumor ； Radiation Treatment Planning(RTP) ； Dose Calculation

參考文獻

treatment planning of gliomas Med. Phys. 33 32-40

treatment planning? Br. J. Radiol. 73 229-33

prostate IMRT Int. J. Radiat. Oncol. Biol. Phys. 60 636-47

Vaidyanathan M, Hall L O, Thatcher R W and Silbiger M L

1995 MRI segmentation: methods and applications Magn.