錐形射束電腦斷層之皮膚劑量測量

Skin Dose Measurements in Cone Beam Computed Tomography

程筠慧(Yun-Hui Cheng) ； 陳俊偉(Chun-Wei Chen) ； 張世宗(Shih-Tsung Chang) ； 陳信雄(Hsin-Hsiung Chen)

《台灣應用輻射與同位素雜誌》 10卷2期 (2014/06) Pp. 803-814

摘要

近年來，影像引導放射線治療（IGRT）是一項嶄新的技術，利用CBCT得到的三維影像（3D）引導到準確的治療位置，同時也接收額外的劑量，而這些額外的劑量對於正常組織誘發癌症的機率也隨機增加。本研究運用直線加速器附設的CBCT對於擬人組織之成人藍道假體測量，利用金氧半場效電晶體（MOSFET）測量頭頸部及胸腔部位各分別五個測量點，取像條件以減少mAs、縮減掃描角度及時間的參數，對於每組減少的參數分別測量皮膚的吸收劑量及影像的可使用的程度。研究結果顯示利用較高的mAs校正比較穩定。本研究顯示掃描張數若是低於343張，影像會因掃描張數不足而使輪廓外觀變形。空間解析度之辨別條件分別為胸腔部位的六組條件 100%、95%、85%、75%、65%、55%，分別得到11 lp/cm、11 lp/cm、10 lp/cm、10 lp/cm、10 lp/cm、9 lp/cm。然而100%至55%的胸腔部位影像並無明顯差異，對於頭頸部100%及95%表面劑量差異不大，胸腔部位100%及55%表面劑量則減少約一倍的劑量，兩者使用自動化影像融合比對的殘差並無明顯差異，本研究顯示取像條件適當的調整，其優點（1）可以減少病人在掃描期間移動。（2）病人接受劑量減少。（3）因病人體型受限於機器可靈活應用。（4）減少影像儲存空間。更加拓展CBCT在臨床上的應用範圍，以供日後臨床使用。

關鍵字

錐狀射束電腦斷層影像 ； 影像引導 ； 影像融合 ； 空間解析度

並列摘要

Image-guided radiation therapy (IGRT) is the new technology of radiotherapy in recent years. Using image-guided positioning system to obtain and verify the accurate treatment position automatically by 3D CBCT. While receiving additional doses, increase the probability of cancer inducement for a random normal tissue. In this study, we use the metal oxide semiconductor field effect transistor (MOSFET) detectors to measure the surface dose in CBCT scans of head &neck and chest locations on an adult tissue equivalent anthropomorphic Rando phantom. There were five measuring points in each location of measurements. By means of reducing mAs, scan angle and scan time, for each set of parameters, we found the skin dose were reducing and images also can be read feasibly. The results show the more stable calibration data were obtained for the higher mAs exposure. The scan number less than 343 images projection will cause the distortion of contour due to insufficient number of projection. Spatial resolution tests were measured in six sets of chest scan conditions 100%, 95%, 85%, 75%, 65%, and 55%, and scored 11 lp/cm, 11 lp/cm, 10 lp/cm, 10 lp/cm, 10 lp/cm, and 9 lp/cm respectively. However, there were no significant differences from 100 %to 55% scan condition for the chest images. For Head and neck scans, the surface dose were similar in 100% and 95%, and surface dose decreased about to the half from 100% to 55% scan conditions for chest location. Both residual comparison was not significant by automatic image fusion. This study shows the advantages in appropriate adjustments of the scan condition:(1) reduce the patient movement probability during the scan, (2) reduces received dose of patients, (3) flexible patient size can be applied, and (4) reduce the image storage space. It also can expand the category of CBCT in clinical application, and provide the reference data to the clinical staffs.

並列關鍵字

Cone-Beam Computed Tomography ； Image-Guided ； Fusion ； Spatial Resolution