頭頸部放射治療的活體劑量驗證

In Vivo Dose Verification in External Radiotherapy for Head and Neck Patients

王慧娟(Hui-Chuan Wang) ； 羅素花(Su-Hua Lo) ； 董傳中(Chuan-Jong Tung) ； 吳嘉明(Jia-Ming Wu) ； 王重榮(Chong-Jong Wang)陳惠君(Hui-Chun Chen)

《放射治療與腫瘤學》 11卷3期 (2004/09) Pp. 173-184

https://doi.org/10.6316/TRO/200411(3)173

摘要

目的：為了達到放射治療的目的，必須確保處方劑量正確地給予病患。活體劑量驗證為放射治療過程中的最後一道品質保證關卡，它可偵測出個別病患在治療程序上的錯誤，也可評估出特殊治療計畫的病患劑量。本實驗的目的，在於建立鼻咽癌患者之活體劑量驗證程序，研究治療計畫之劑量分布與活體劑量驗證結果的差別，以及比較活體劑量驗證實驗所用之劑量計的優缺點。
材料與方法：本計畫將完整校正後之二極體偵檢器和熱發光劑量計，分別佈置在各個照野中心軸上的射入和射出皮膚位置上，然後將這些劑量計的讀數經過適當的校正與修正參數（包括照野、楔型濾器、與射束阻擋物等）轉換成射入劑量與射出劑量，再利用以固態水假體及游離腔建立的穿透率曲線，推算出病患身體中軸之組織劑量。最後將此實測推算得之中線劑量與處方劑量比較分析其誤差。
結果：以二極體偵檢器與熱發光劑量計分別量測了67個照野，分別屬於20與22位病患。以二極體偵檢器量測活體劑量，結果有8.96%照野的腫瘤劑量大於5%的處方劑量，而所有之劑量誤差都少於10%；以熱發光劑量計度量的結果，有43.28%照野的腫瘤劑量誤差大於5%的處方劑量，大於10%的劑量誤差則有4.47%。
結論：經由本實驗建立一套包括校正劑量計、修正各治療條件、與實際病患量測之完整活體劑量驗證方式，也經由誤差分析，瞭解治療流程中可能發生誤差之程序，在決定治療計畫時應特別注意，以避免劑量誤差，達到品質保證之目的。

關鍵字

活體劑量驗證 ； 二極體偵檢器 ； 熱發光劑量計 ； 品質保證

並列摘要

Purpose : Many national and international associations encourage the extension of in vivo dosimetry as an effective tool for an ultimate check of the treatment in external radiotherapy. In vivo dose measurements will be standardized in the QA procedure to avoid minor errors that might cause severe radiation damage. The aim of this study is to establish an in vivo dose verification procedure for head and neck patients and to ensure that they are treated optimally in radiotherapy.
Materials and Methods : To detect and analyze errors that could affect the therapy, we employed well calibrated diodes and thermoluminescence dosimeters (TLDs) for in vivo dosimetry to trace the dose delivery. The detectors were positioned on the patient’s skin and behind the patient. Then, the entrance or exit dose was measured with appropriate correction factors (taking field size, wedge and block into account), and by combining the two dose mentioned above, the dose inside the patient was obtained using transmission curve. In external radiotherapy for head and neck patients where a very accurate dose delivery to the tumor is required, the experimental and prescribed midline dose values were compared.
Results : From measurements obtained for external radiotherapy for head and neck patients, 8.96% of the diodes measurements showed a discrepancy more than 5% when compared with prescribed dose, while 43.28% was detected from TLDs. Difference of 10% or more were found in 4.47% of the TLDs measurements.
Conclusion : In this study we report on our experience with in vivo dosimetry. It shows that systematic in vivo dosimetry is a valid tool for quality assurance. Cancer centers can define an appropriate action level concerning the deviation between measured and prescribed dose; if the action level is exceeded, treatment parameters have to be checked and generally, in vivo dosimetry has to be repeated until the cause of the deviation is found and, if possible, eliminated.

並列關鍵字

in vivo dosimetry ； diodes ； TLD ； quality assurance