鼻咽癌強度調控放射治療計劃之品保監測探討

The Study of Quality Assurance for Intensity Modulated Radiation Therapy Planning System of Nasopharyngeal Carcinoma

林怡君(Yi-Jun Lin) ； 賴源淳(Yuan-Chun Lai) ； 林招膨(Jao-Perng Lin) ； 李桂樑(Kuei-Liang Li) ； 康惠傑(Hui-Chieh Kang) ； 林大全(Ta-Chung Lin)

《台灣應用輻射與同位素雜誌》 7卷1期 (2011/03) Pp. 15-21

https://doi.org/10.29832/TJARI.201103.0003

摘要

強度調控放射治療(Intensity modulation radiation therapy, IMRT)目前已廣泛運用在治療癌症病患身上，放射治療的目的就是要使腫瘤接受更高劑量，而旁邊正常組織接受到較少劑量，而爲了要達到治療計劃更適化，計劃中難免會出現低監控單位，但根據文獻指出小監控單位對於劑量輸出是不穩定的，對於臨床使用者應該將監控單位設置在多少(Monitor unit, MU)以下才是對於計劃系統和臨床IMRT品質保證才是最佳的；本研究採用五位鼻咽癌病患，使用Philip Pinnacle3 version 7.6c治療計劃系統，將計劃系統最低限制MU設置2~10九種狀況的治療計劃，利用ELEKTA SYNERGY直線加速器輸出電腦治療計劃系統的劑量分佈，再以二維陣列式游離腔來監測分析，比對治療計劃系統的劑量分佈與實際測量劑量分佈誤差，在95%的計劃靶體積下是否超過3%，並觀察每一個計劃裡的順形指數(Conformity Index, CI)、劑量同質性指標(Homogeneity Index, HI)和總和目標值(Composite Objective Value, COV)，來判斷計劃的品質好壞；結果顯示腫瘤治療範圍較大的病患，改變其最低設定監控單位MU數，則有明顯的點劑量不及格率，以監控單位設置最小值在2-3MU，最大值8-9MU的點劑量不及格率最高，而大部分的病患則在7MU相對於其他MU數點劑量誤差則是最小的，而每個照野數平均最小設定值皆在5MU以上，少部分的則會在5MU以下。因此，假使使用在臨床上的治療可建議把最低監控單位數值設定在7MU，達到電腦計劃系統與臨床使用的劑量誤差性最小。

關鍵字

低監控單位 ； 鼻咽癌 ； 順形指數 ； 劑量同質性指標 ； 總和目標值

並列摘要

In recent years, IMRT has been implemented in clinical practice. The basic aim of radiotherapy is to deliver a high dose to target volume are while sparing the adjacent organs at risk for achieving the planning system and the lowest of normal tissue of IMRT. Then make the field of beam become the lowest. The monitor unit must be small. It has been reported that dose delivery not stability by using the low monitor units. How much MU should be set is the best of planning system and the QA of IMRT. A total of five IMRT plans with NPC cancer were performed with the Philip Pinnacle3 version 7.6c planning system. We set the low monitor units from 2 to 10, and using the ELEKTA SYNERGY to output the dose distribution of computer planning system. And then, using the 2-D Diode array ion chamber to comparison between the distributions of planning system and measured in the clinic. The Local% Difference is within 3% of planned target volume. Evaluation of quality assurance to observe the Conformity Index, Homogeneity Index, Composite Objective Value for every one planning system. In this result, patients have the effect to change the monitor units of the large tumor. The point dose fail to pass highest for the monitor units set on the 2-3 or 8-9. And almost the segment number per field, the segment number is larger than 5, only segment under the 5. So the low segment may delivery monitor unit of 7 in the clinic.

並列關鍵字

Low monitor units ； NPC ； Conformity index ； Homogeneity index ； Composite objective value