目的：本研究的目的是比較螺旋光子刀（Tomotherapy）以及使用傳統的直線加速器進行的全腦及脊髓照射計畫的劑量學參數材料與方法：本研究納入了三個接受全腦及脊髓照射的病人族群。所有患者皆為成年男性和身體擺位為仰臥姿勢，並以10mm為掃瞄厚度取得電腦斷層掃描資料，再設計成三維順形放射線治療和螺旋光子刀計劃。計劃靶區（PTV）的設計劑量為32 Gy。劑量均勻性指數（DHI），順形指數（CI），以及一些物理學參歡用於比較上述兩種治療方式。結果：在V95%（體積百分比接受至少95%的設計劑量）的計劃靶區體積－腦（PTV－B）在所有的六個計劃皆為100%。平均V95%的計畫靶區體積－脊髓（PTV-S）在三維順形放射線治療和螺旋光子刀計劃分別為98.7%和100%。計劃靶區體積－腦（PTV-B）的平均最大劑量在三維順形放射線治療是高於螺旋光子刀計劃（37.4 Gy/117%和33.6 Gy/105%）。計劃靶區體積－脊髓（PTV-S）的對PTV-S的平均最大劑量在三維順形放射線治療也是高於螺旋光子刀計劃（50.8Gy/159%和33 Gy/103%）。計劃靶區體積－腦（PTV-B）的平均劑量均勻性指數顯示也有顯著差異（3D CRT vs. Tomo: 1.17 vs. 1.05，p= 0.009）。計劃靶區體積－脊髓（PTV-S）的劑量分佈在螺艇光子刀計劃更均勻（DHI: 1.03 vs. 1.59，p= 0.0047）。計畫靶區體積－腦（PTV-B）的順形指數（CI）在兩種計劃方式並無顯著差異（3D CRT vs. Tomo: 0.76 vs. 0.74，P > 0.05）。計劃靶區體積－脊髓（PTV-S）的順形指數（CI）在螺旋光子刀計劃則是優於三維順形放射線治療（0.47 vs. 0.2，p<0.05）。螺旋光子刀計劃減少大部份危及器官（OAR）的平均最大劑量，除了雙邊腎臟（Tomo vs. 3D CRT: 14.8 Gy vs. 3.8 Gy）。結論：對全腦及脊髓照射治療而言，因為沒有照野相接的問題，使用螺旋光子刀（Tomotherapy）比直線加速器簡單而方便。在螺旋光子刀計劃可以得到優於三維順形放射線治療的劑量參數（DHI and CI）。使用螺旋光子刀可以減少危及器官（OAR）的劑量，可能有助於減少晚期效應。

Purpose: The aim of this study is to compare dosimetric parameters of TomoTherapy (Tomo) and 3D conformal radiotherapy (3D CRT) for craniospinal irradiation (CSI). Materials & Methods: Three patients requiring CSI treatments were enrolled. All patients were adult males and treated in the supine position. Computed tomography (CT) scans with 10mm slice thickness were acquired for both the 3D CRT and Tomo plans. The prescribed dosage of the planning target volume (PTV) was 32 Gy. Dose homogeneity index (DHI), conformal index (CI), and physical parameters were used to compare the differences between the two treatment modalities. Results: The V95% (volume of receiving at least 95% of prescribed dose) of planning target volume-brain (PTV-B) was 100% for six plans. The mean V95% of planning target volume-spine (PTV-S) were 98.7% and 100% for 3D CRT and Tomo plans, respectively. The mean Dmax (maximal dose) of PTV-B was higher on 3D CRT than on Tomo (37.4 Gy/117% vs. 33.6 Gy/105%). The mean Dmax of PTV-S on 3D CRT was much higher than that on Tomo (50.8 Gy/159% vs. 33 Gy/103%). The mean DHI of PTV-B showed significant differences between CRT (1.17) and Tomo (1 .05), p= 0.009. The dose distribution of PTV-S planned by Tomo was more homogenous than that planned by 3D CRT (mean DHI 1.03 vs. 1.59, p= 0.0047). There were no significant differences in the mean CI of PTV-B on CRT (0.76) and Tomo (0.74), p> 0.05. The mean CI of PTV-S of Tomo was better than that of 3D CRT (0.47 vs. 0.2, p< 0.05). There were decreases in all Dmax of organs at risk (OARs) in the Tomo group except for bilateral kidneys (Tomo vs. 3D CRT: 14.8 Gy vs. 3.8 Gy). Conclusion: Tomo is simpler than linear accelerator for CSI because there is no junction between treatment fields. The dosimetric parameters of DHI and CI are superior in the Tomo group. Decreased OAR dose via Tomo may be helpful for minimizing the long-term latent effect.