建構立體定位放射手術計畫之評估模組： 針對多發性腦瘤之治療計畫技術比較

Biological plan evaluation for stereotactic radiosurgery: a comparison between single isocenter and multiple isocenter techniques

李孟秦(Meng-Chin Lee)

指導教授 ： 蔡惠予

國立清華大學/原子科學院/核子工程與科學研究所/碩士(2020年)

摘要

立體定位放射手術(SRS)為多發性顱內轉移腫瘤主要的治療方式，但針對多個病灶使用多等中心點(multiple isocenter)技術製作治療計畫耗時且臨床操作效率低，病人長時間滯留在治療床也造成安全性的疑慮。近年來嘗試使用單等中心點(single isocenter)治療計畫不僅加速臨床效率也能有不錯的病灶劑量分布與治療效果，然而，單等中心點技術容易發生病灶外的劑量洩漏及散溢的現象，潛在著對危急器官的輻射生物效應，目前尚未有文獻探討此議題。另外，隨著診斷技術提升，能夠及早發現病灶及早治療，延長了病人的存活時間，因此在放射治療領域開始重視散射及洩漏劑量誘發正常組織二次癌症的風險。本研究目的即針對立體定位放射手術之兩種技術治療計畫比較生物效應與風險之差異，並建構一套完整的生物性治療計畫評估系統及操作平台。
評估對象取自美國休士頓衛理公會醫院(Houston Methodist Hospital)患有多發性腦腫瘤的案例資料，再分別以多等中心點及單等中心點技術建立兩種治療計畫。其中生物效應的評估以腫瘤控制率(TCP)和正常組織併發症機率(NTCP)模型，並結合Schneider發表之輻射誘發癌症風險模型做計算。從抓取DICOM資訊到模型計算分析，本研究使用MATLAB來建立完整的生物性治療計畫評估系統。
研究結果發現在大多數案例中，兩技術之腫瘤控制率較無明顯差異，而部分器官之正常組織併發症機率和誘發癌症風險與病灶數量、病灶分佈的位置距離以及兩種技術之計畫設計有關，因此仍需個別探討各生物模型之評估結果，以利臨床有更完善的計畫評估。然而單等中心點技術在整體的生物性評分模型(UCFCP)計算下，有近似甚至優於多等中心點技術的趨勢，病灶數目越多分數差越顯著。因此針對多發性腦瘤使用單等中心點技術不僅能提高治療效率，也有良好的物理劑量與合理的生物性評估表現。

關鍵字

立體定位放射手術 ； 單等中心點 ； 生物性治療計畫評估 ； 輻射誘發癌症風險

並列摘要

Volumetric modulated arc therapy (VMAT) is commonly employed for stereotactic radiosurgery (SRS) treatment delivery. Especially the single isocenter techniques were introduced to multiple intracranial lesions for reducing the treatment time in recent years. The plan quality indices of single isocenter compared to multiple isocenter have been proposed, however, there has some potential biological effects in single isocenter. Therefore, the aim of this study is using biological model to compare single isocenter and multiple isocenter treatment plans and establishing the biological evaluation program for SRS plans.
Both multiple-isocenter and single-isocenter stereotactic treatment plans were created and exported by Varian Eclipse (Varian Medical Systems, Palo Alto, CA) treatment planning system for each multiple brain metastasis case. For defined critical organs in medium and high-dose regions, Schneider’s organ equivalent dose (OED) model was used, and the parameters of life attributable risk (LAR) for cancer risk assessment were according to the BEIR VII report. The biological effect models include the tumor control probability (TCP) and the normal tissue complication probability (NTCP) with parameters that are applicable for SRS.
An in-house MATLAB program imported DICOM and DICOM RT files from Eclipse planning system and all models were calculated by this program to establish a complete treatment plan evaluation system. The results show that the secondary cancer risk of critical organs was higher for most single isocenter plans, and the comparison of NTCP was not significantly different between the two types of plans. However, some multiple isocenter plans got worse TCP. Because those values were depending on lesion locations, we used the uncomplicated and cancer-free control probability (UCFCP) model which proposed by the Sánchez-Nieto to score the plans, and most single isocenter plans got a higher score.
The shortened treatment time of single isocenter plans improves efficiency and patient tolerance. However, there is still a biological effect difference between these two techniques, even if they give a similar physical dosimetric performance. This work gave the comprehensive system of biological evaluation for SRS plan to evaluate case by case that could give a help for choosing plan or re-optimization.

並列關鍵字

Stereotactic Radiosurgery Single Isocenter ； Radiation-induced Cancer ； Tumor Control Probability ； Normal Tissue Complication Probability

參考文獻

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