Comparison of the gross target volume of lung cancer based on three dimensional CT and four dimensional CT in stereotactic body radiation therapy

比較接受立體定位軀體放射治療之肺癌病人利用3DCT與4DCT下之腫瘤體積

何秀雯(Hsiu-wen Ho) ； 林裕為(Mark Lin) ； 林立青(Li-ching Lin) ； 郭珍妮(Jenny Guo)

《放射治療與腫瘤學》 25卷2期 (2018/06) Pp. 139-150

https://doi.org/10.6316/TRO.201806_25(2)0008

摘要

Purpose: Stereotactic body radiation therapy (SBRT) is widely used as therapy for localized lung cancer or metastases. Four-dimensional computed tomography (4DCT) is the most common technique used to estimate the internal motion of lung cancer tumors. The purpose of this study was to observe tumor motion with 4DCT image in SBRT patients. Materials and Methods: This study was a retrospective analysis. From September 2008 to March 2016; forty patients with proven pathology for lung cancer or pulmonary metastasis, treated with stereotactic body radiotherapy were included in this study. All patients underwent three dimensional (3D) and four dimensional (4D) CT scans. GTV_(3D) and GTV_(4D) were created from 3D and 4DCT scanning, respectively. The volume, position and other tumor parameters, included matching index (MI) and degree of inclusion (DI) between GTV_(3D) and GTV_(4D) were also compared in this study. Results: The tumor motion measured by comparison of different 4DCT phases was highest for the CC direction (mean 0.65 cm, median 0.40 cm, range 0.10 - 2.70 cm). The next highest was for the AP direction (mean 0.24 cm, median 0.20 mm, range 0 - 0.90 cm) then the LR direction (mean 0.15 cm, median 0.10 cm, range 0 - 0.40 cm). The mean motion vector was 0.44 ± 0.21 cm, 0.73 ± 0.45 cm and 1.35 ± 0.81 cm in upper, middle and lower lobes, respectively. This shows that tumors located in the lower lobe of the lung exhibited the greatest amount of motion, and the magnitude was usually greatest along the CC axis. The MI and DI in the lower lobe was significantly different from the upper and middle lobes (p ＜ 0.05). No clinical or anatomic factors were identified as being related to the magnitude of the tumor excursion, except for lobe location (p= 0.005). Conclusion: Respiration induced tumor motion is an important issue in high precision SBRT. Using 4DCT information can greatly improve the target definition for lung cancer. The respiratory management technique is necessary for middle and lower lung lobes tumors in our study according to The AAPM Task Group 76 report [11]. The tumor motion in all patients was anisotropic, the amplitude was significantly larger in the CC direction than in AP and LR directions. To avoid the target missing and reduce the normal tissue irradiated. The anisotropic margins of ITV were more appropriate than isotropic margin in lung tumor. The tumor movement in lower lobe tumors is obviously greater than in the upper and middle lobes, especially where tumors are adhered to the chest wall and diaphragm. The greater margin in the CC direction especially for lower lobe tumors should be added. To account the internal motions which arise from breathing, the 4DCT is necessary for lung tumor especially in SBRT patients.

關鍵字

Stereotactic body radiation therapy (SBRT) ； Four-dimensional computed tomography (4DCT) ； Lung cancer

並列摘要

目的：立體定位軀體放射治療是一種廣泛應用在局部肺腫瘤的治療技術，而四維電腦斷層掃描影像可提供肺腫瘤在病人體內隨呼吸移動的有效工具。本研究目的旨在分析本院利用四維電腦斷層掃描影像在立體定位軀體放射治療可提供的有效資訊。材料與方法：本研究涵蓋自2008年9月至2016年3月在本院接受立體定位軀體放射線治療的40位原發性或轉移肺腫瘤病人。所有病人皆有執行三維及四維電腦斷層掃描定位並由其中影像產生兩種GTV（GTV_(3D)與GTV_(4D)）。紀錄並比較個別GTV之體積、座標與其他腫瘤靶體積分析因子。結果：以四維電腦斷層掃描影像分析可知腫瘤移動幅度以病人頭腳方向最為顯著，平均移動結果在病人前後、左右及頭腳方向分別為0.24 cm（median 0.20 cm, range 0-0.90 cm）、0.15cm（median 0.10 cm, range 0-0.40 cm）及0.65 cm（median 0.40 cm, range 0.10-2.70 cm）。分析移動幅度與腫瘤位置關係發現，其個別平均移動向量在上、中與下肺葉分別為0.44±0.21 cm, 0.73±0.45 cm與1.35±0.81 cm。結果顯示位於下肺葉腫瘤具有最大移動幅度，並且在頭腳方向最為顯著。MI與DI數值在下肺葉腫瘤明顯大於中上肺葉腫瘤。而分析個別移動預測因子發現，移動幅度僅與腫瘤在肺葉位置具有統計學上的顯著相關性。結論：呼吸引起的腫瘤位移在立體定位軀體放射治療病人是極為重要的考量。利用四維電腦斷層影像可提供有效的臨床計畫靶體積參考資訊。根據AAPM Task Group 76報告建議對照本研究結果顯示，呼吸調控技術對於中下肺葉腫瘤有其必要性。且腫瘤在體內位移為非均向性（anisotropic），頭腳方向的位移量顯然大於其他兩個方向。位於下肺葉的腫瘤特別是與橫膈膜相連者，其移動幅度明顯大於中上肺葉腫瘤。因此對於考量病人體內位移對腫瘤位置影響時，加上非均向性的病人體內位移範圍才能正確將劑量集中在腫瘤並減少正常組織接受到的劑量。特別是對於接受高劑量低分次的立體定位軀體放射治療病人而言，可有效評估腫瘤移動的4DCT是必要的工具。

並列關鍵字

立體定位軀體放射治療 ； 四維電腦斷層影像 ； 肺癌