利用電腦斷層影像評估金屬假牙對頭頸部放射治療劑量計算之影響

The Use of Computed Tomography for Evaluation of the Dose Calculation Effect in the Presence of Metallic Dental Prostheses on Head and Neck Radiotherapy

林煒柔(Wei-Jou Lin) ； 黃安潔(An-Jie Huang) ； 胡志忠(Chih-Chung Hu) ； 黃國明(Guo-Ming Huang) ； 吳簡坤(Jian-Kuen Wu) ； 成佳憲(Chia-Hsien Cheng)

《台灣應用輻射與同位素雜誌》 7卷3期 (2011/09) Pp. 101-109

https://doi.org/10.29832/TJARI.201109.0001

摘要

為探討頭頸癌患者的植入式金屬假牙對放射治療劑量計算的影響，本研究使用仟伏特級電腦斷層影像(kilovoltage computed tomography, kVCT)與百萬伏特級電腦斷層影像(megavoltage computed tomography, MVCT)製作電腦治療計畫，比較兩者的劑量計算結果，分析在不同實驗分組下的差異。使用RANDO(上标 ®)Phantom及特製的鈦合金假牙模擬病患植入金屬假牙的情形，以不同的金屬假牙數目為實驗分組條件，各別取得kVCT與MVCT影像。治療計畫參數設定為直線加速器6MV光子能量下，照野12cm×12cm，給予正向與側向角度的4種射束組合，並於影像上設定劑量計算點分別代表治療靶區及危急器官。劑量計算結果顯示：金屬假牙數目越多，kVCT與MVCT的劑量計算結果差異越大，在多達全口的金屬假牙條件下得到最大差異(5.9%)；當射束為正向角度直接穿透金屬假牙本體時，會比側向射束未穿透金屬本體而僅穿透金屬假影的劑量計算差異來的大；且鄰近金屬假牙的治療靶區，差異也最明顯。從實際量測結果可看出，在病患有大量金屬假牙且無法拔除的情況下，使用kVCT製作治療計畫存在劑量計算不準確性；臨床上，可由較無假影、且訂定金屬物質CT值與電子密度較為準確的MVCT影像進行比對和修正，以減少治療計畫的劑量計算誤差。

關鍵字

金屬假牙 ； 仟伏特級電腦斷層影像 ； 百萬伏特級電腦斷層影像 ； 電腦治療計畫 ； 放射治療劑量計算

並列摘要

This study is to investigate the dose calculation effect in the presence of metallic dental prostheses on head and neck radiotherapy. Kilovoltage computed tomography (kVCT) and megavoltage computed tomography (MVCT) were used in treatment plan to compare the dosimetric difference with different settings. The presence of dental implant was simulated with the RANDO(superscript ®) Phantom and dental prostheses which were made of Titanium alloy. kVCT and MVCT images were obtained with different number of metallic dental prostheses to generate treatment plans, which were designed in linear accelerator 6MV photon energy, field size 12cm×12cm, four groups of beam directions, and dose calculation points representing the target region and organs at risk (OAR). The results indicated that the increase of number of metallic dental prostheses resulted in more dose difference. The most significant difference (5.9%) was from full-mouth metallic dental prostheses. The dose calculation inaccuracy was more from the metal material itself than from metal artifact. The most significant point dose difference was in the target region close to dental prostheses. With metallic dental prostheses, dose calculation inaccuracy was shown in treatment plan by use of kVCT. In addition, MVCT had more precise density estimation for metal prostheses. MVCT-based plan with more accurate dose calculation can correct dose difference in kVCT plan.

並列關鍵字

Metallic dental prostheses ； Kilovoltage computed tomography ； Megavoltage computed tomography ； Treatmeant planning ； Dose calculation