現今臨床胸腔腫瘤放射治療計畫，是以結構性放射治療計畫(Anatomic Treatment Planning)製作方式製作，使用電腦斷層模擬攝影影像或電腦斷層模擬攝影影像與診斷影像或功能性造影影像之影像融合影像作為定義腫瘤、重要組織及危急器官之圈選，其中，在肺組織定義及肺部區域放射劑量的評估，是以整個肺區作為一個器官考量結構，給予適當劑量體積限制參數，降低整個肺區域的輻射劑量分布，但是並無考慮肺功能的部分，且針對肺功能較佳的區域，並無特別考量此區域所接受之輻射劑量多寡。本研究使用四維電腦斷層影像與影像形變對位法定義高肺功能肺區(Functional Lung Regions)，製作功能性放射治療計畫(Functional Treatment Planning)。收集臨床11例胸腔腫瘤病患四維電腦斷層影像，採用最大吸氣(Maximum End-Inhale)及最大吐氣(Maximum End-Exhale)兩組相位電腦斷層影像，使用光流法(Optical Flow Method)之形變影像對位技術(Deformable Image Registration)，計算出肺組織的最大呼吸運動變化量功能性肺區影像；(1)回溯性的探討一般傳統結構性強度調控放射治療計畫中，高肺功能肺區所接受的輻射劑量分布情形。(2)製作功能性強度調控放射治療計畫，並與結構性強度調控放射治療計畫做比較，比較兩者計畫對於腫瘤劑量的包覆性與均勻性之差異與肺部劑量體積參數百分比及平均肺劑量(V5%、V20%、MLD)。結果發現功能性強度調控放射治療計畫在腫瘤劑量的部分，因降低功能性肺區輻射劑量，而些微犧牲腫瘤的順形度與均勻度，但是皆在臨床可接受範圍內；在周圍的正常組織及危急器官部分，降低功能性肺區之輻射劑量，會導致肺以外周圍的其他器官輻射劑量略微增加，但是皆在耐受劑量體積限制標準內。
In current practice of thoracic cancer radiotherapy, the difference in pulmonary function was not considered when generating treatment plans. Lung volumes are deemed equally when placing radiation beams in planning. The primary purpose of this study was to evaluate the radiation dose of IMRT treatment plans on highly functional lung volumes by incorporation of functional lung imaging using 4D-CT for thoracic cancer patients. Eleven patients who had non-trivial but stable respiration motion and were available for 4D simulation schedule received 4D radiotherapy simulation and were included in this retrospective study. With deformation calculated by deformable image registration among 4D-CT image sets, pulmonary ventilation can be defined as the fractional volume change in respiration. The 3D dose distributions of IMRT plans were overlapped with the 3D ventilation distributions and analyzed. The ventilation difference of the left and right lungs can be seen on the corresponding ventilation image. Lower ventilation around lung tumor region was also observed. For the cases of small target volumes (planned target volume < 400 cc, 6 cases in total), all V5(%), V20(%) and the mean lung dose (MLD) values for the highly functional regions, top 20%, 30% and 40% ventilation, were lower than the values for the total lung. For the cases of large target volumes, two out of five cases had higher V5(%) and V20(%) values for the highly functional regions compared with total lung. The present study has demonstrated the evaluation of radiation dose of IMRT treatment plans with incorporation of functional lung imaging from 4D-CT for thoracic cancer patients. Radiation treatments affect functional lung volumes more seriously on larger tumors than small tumors. Thus it is more critical to arrange radiation beams for functional lung sparing for patients with large tumors.
