- 學位論文
使用ArcCHECK評估碳纖維治療床對高能光子射束衰減的影響
The Evaluation of the MV photon beam Attenuated by a Carbon Fiber Couch through the ArcCHECK
摘要
本研究的目的是利用一個二極體劑量計(ArcCHECK)，並評估它在強度調控放射治療(IMRT)中的品質保證的使用結果。以往在治療計劃系統(TPS)沒有考慮治療床在放射劑量上的影響，並且傳統強度調控放射治療計劃的QA常規都僅是在固定機架角度進行，而最近一些研究已經發現治療床在治療計劃中並不能忽視。 本研究主要分成二部份:第一部份為利用經校正後的游離腔(ion chamber)來測量治療床所造成劑量的衰減，並且找出其與測量角度、能量及照野大小之間的依存性。同時依照實際治療床的尺寸及密度，在Pinnacle3 TPS中建立一臨床碳纖維治療床模版(couch model)，並將實際測量結果和治療計畫系統(使用創建的治療床模版)計算結果進行比較分析。 本研究目標希望能探討兩者的差異性(驗證治療床模版劑量修正的準確性)。第二部份將驗證後的碳纖維治療床的模版導入臨床患者治療計畫，重新再行運算，並將該計畫再運算結果複製到ArcCHECK中。複製至ArcCHECK時，完全依照治療計畫計算時的所有射束照野及採用實際治療角度位置來執行照射及測量，再將劑量測量值與計算值相互比較。最後分析治療計畫有無治療床模版在IMRT QA的量測結果。 第一階段使用所設計的治療床模版驗證臨床劑量，發現在能量6 MV時不同射束角度造成衰減的差異性在-2.6 %～1.9 %。而能量10 MV則在-0.2 %～2.5 %。兩者的差異性均在± 3 %以內。電腦治療計劃在沒有couch model條件修正下，通過率測試結果(γ≤1)在92.6%〜97.1%間。而在有加入couch model 條件下，通過率測試結果(γ≤1)在94.3%〜98.2%間。再以配對t檢驗(paired t-test)對通過率結果進行統計分析， 發現二者在統計學上具有顯著差異(p < 0.05)。顯示出有加入couch model 條件下能有較佳及較能符合實際劑量的驗證結果。在本研究中已經將couch model成功加入TPS並加以驗證。總體而言，我們建議治療射束若有後斜位的方向時，必須要在治療計劃將couch model加入計算。另外，由我們比較的測量結果顯示ArcCHECK，可以適用於臨床IMRT QA的驗證。
並列摘要
The goal of this study is to evaluate the ArcCHECK device with a diode detector and use it in the routine quality assurance (QA) of Intensity-Modulated Radiation Therapy (IMRT). In the beginning, we did not consider the treatment couch in the Treatment Planning Systems (TPS). Traditionally, the IMRT plans QA were performed with fixed gantry angles. However, some studies had shown that the treatment couch cannot be neglected in the treatment planning. This study includes two steps. First, we measured the couch attenuation with an ion chamber with different setups of gantry angle, energy and field size. At the same time we established a couch model into Pinnacle3 TPS according to the size and density of the actual treatment couch. After that, the measured dose and treatment planning calculated dose (include couch model) was compared and analyzed. Second, the validated couch model was introduced into the TPS and all the plans were recalculated. Then all the setups of the recalculated plan were introduced into a phantom for the QA of IMRT, which was performed by a new device. The ArcCHECK measured dose and the planned dose was also compared. The IMRT QA results between with couch model and without couch model in TPS were analyzed. Then the paired t-test between the gamma passing rates with or without couch model built in the TPS was also performed. For the validation of couch model in TPS, the attenuation differences are between -2.6% and 1.9% for 6 MV photon beam. For 10 MV photon beam, the differences are between -0.2% and 2.5%. All differences were within 3%. The results of the second step demonstrated that the gamma passing rates were located between 92.6% and 97.1% without couch model built in the TPS. The gamma passing rate is higher and located between 94.3% and 98.2%, where the couch model was built in the TPS. The p-value of the t-test is less than 0.05 standing for statistically significant, which shows that the couch model built in the TPS do have better results. In summary, the couch model included in the treatment planning is recommended for all treatments, and the ArcCHECK is demonstrated to be suitable for clinical QA verification of IMRT.