利用影像導引定位系統分析鼻咽癌患者在放射治療中的擺位誤差

The Application of ExactTrac X-ray Positioning System to Analyze the Setup Error in Radiotherapy for Nasopharyngeal Cancer Patients

康誠麟(Chen-Lin Kang) ； 陳文凱(Wen-Kai Chen) ； 蔡正祥(Cheng-Hsiang Tasi) ； 張軒銘(Hsuan-Ming Chang) ； 廖宗義(Tzung-Yi Liao) ； 阮國榮(Kuo-Jung Juan)

《中華放射線技術學雜誌》 32卷1期 (2008/06) Pp. 65-71

https://doi.org/10.30045/CJRT.200806.0009

摘要

在放射治療過程中，患者的擺位誤差(setup errors)是影響精確治療的關鍵因素，越是精確的放射治療，對照射部位準確性要求越高。本研究針對使用諾力刀(Novalis)治療機治療的鼻咽癌患者，用其搭配影像導引定位系統(ExactTrac X-ray positioning system)將X-ray和治療計畫中的數位重組影像(Digital Reconstructed Radiography, DRR)進行校正比對，測定患者的擺位誤差。擺位誤差可主要分爲系統誤差(Systematic error)和隨機誤差(Random error)，系統誤差可能在患者治療前就已存在，隨機誤差可能是來自每日治療時的擺位誤差或者病患呼吸，器官移動所引起的。收集共25名使用即時影像定位系統的患者資料來分析擺位偏差，三維各軸的平移誤差，所測得平均位移分別爲1.24 mm、1.05 mm、1.67 mm。Σ值分別爲0.84 mm、0.41 mm、1.03 mm。σ值分別爲0.41 mm、0.28 mm、0.42 mm。等中心點的三維平均位移向量(3D Vector)爲2.33 mm。藉著所測得的擺位誤差，利用國外文獻所提出計畫靶體積(Planning Target Volume, PTV)設定方法，來分析外擴邊緣的大小，最後評估在本科治療的鼻咽癌患者，PTV外擴邊緣減少至3 mm是可行的。

關鍵字

擺位誤差 ； 系統誤差 ； 隨機誤差 ； 三維平均位移向量

並列摘要

In the process of radiotherapy, the setup error of a patient is the key factor affecting the precision of therapy. Higher radiation accuracy is required for more precise radiotherapy. The current study is designed to investigate setup errors of nasopharyngeal cancer patients treated with Novalis, coupled with ExactTrac X-ray positioning system, to compare X-ray images with Digital Reconstructed Radiography (DRR) in the treatment planning system.
Setup error could majorly be divided into systematic error and random error. Systematic error could exist before the treatment, and random error may result from the setup error in daily treatment or the movement of internal organs along with respiration.
We collected twenty-five patients and used the ExactTrac X-ray positioning system to analyze the setup data. The mean translation of each dimension in X, Y, Z was 1.24 mm, 1.05 mm, and 1.67 mm, respectively. The standard deviations of systematic error (Σ) was 0.84 mm, 0.41 mm, and 1.03 mm, respectively. The σ was 0.41 mm, 0.28 mm, 0.42 mm. The 3D vector was 2.33 mm in isocenter. We checked the setup errors with the settings of planning target volume (PTV) mentioned in the literature to analyze the setup error the size of margin.
The final results revealed it was feasible to decrease the PTV margin (M(subscript PTV)) to 3 mm in treating our patients of nasopharyngeal cancer.

並列關鍵字

Setup Error ； Systematic Error ； Random Error ； 3D Vector