全身照射治療的劑量測定與兩側平行對照技術的應用

Application and Dosimetry for Bilateral Opposed Irradiated Technique of Total Body Irradiation

吳簡坤(Jian-Kuen Wu) ； 林盈釧(Ying-Chuan Lin) ； 郭祥吉(Hsiang-Chi Kuo) ； 吳東和(Tung-Ho Wu) ； 黃英強(David Y.C. Huang) ； 陳志成(Jyh-Cheng Chen) ； 蔡玉真(Stella Y.C. Tsai) ； 成佳憲(Jason C.H. Cheng) ； 簡哲民(James Jer-Min Jian)

《放射治療與腫瘤學》 7卷1期 (2000/03) Pp. 27-33

https://doi.org/10.6316/TRO/200007(1)27

摘要

目的：為了能縮短病人接受全身照射治療位置擺設時間及提高每次治療的再現性，規劃躺臥式左右兩側平行對照的放射治療方式來治療骨髓移植病人，並據此方式搭配相關治療輔助設備來執行相關劑量測量及射束數據量工作。
材料與方法：利用小型水假體(35公分(長)×35公分(寬)×37公分(高)側面為麥拉材質的視窗(Mylar window)內置農夫型游離腔(Farmer type0.6cc，PR06C)及蒸餾水並在下面配置昇降平台，可調整適當高度。治療能量還用西門子PRIMUS型直線速器六百萬伏特光子，照野開到最大(離射源100公分處為40×40公分)，準直儀旋轉45度，旋轉臂設在270度等條件下，在距離射源400~500公分之百分深度劑量分佈、劑量剖面、百分深度劑量、補償器及散射屏之衰減因子測量。我們並自己製作昇降床及壓克力散射屏風，如此病人治療時位置的擺設可相對的容易與準確。
結果：離射源400-500公分之百分深度劑量比，以10公分與20公分深度的比值來說，小於0.5%，射束的平坦度在20公分深度下的剖面劑量分佈，在對角線照野長度百分之七十範圍內為±0.5%；由於距離甚遠，輸出劑量除了可用平方反此定律推算，也可依實測值繪製表格以平臨床治療使用，同時因為身體側面不同位置的厚度差異較大，需要製作組織補償器來改善劑量均勻度。至於表面劑量則可用1公分壓克力屏風置於病人前方10公分以達到足夠的治療劑量。
結論：利用頭頸部腫瘤治療普遍使用的左右兩側平行對照的全身照射治療方式，適當的利用病人的手臂取代不易準確擺設的肺部遮檔鉛塊，既不犧牲劑量準確性，且能提高病人治療時的舒適度，雖不算創新，但可提供國內選擇全身照射治療方式的參考。

關鍵字

全身照射治療,骨髓移植,肺部劑量

並列摘要

Purpose: In an attempt to shorten patient setup time and increase setup reproducibility, we developed a supplemental system for a bilateral opposed technique of total body irradiation. We completed the dosimetry study and beam data measurement for clinical application.
Materials and Methods: A small-size water phantom, (35 cm (L) x 35 cm (W) x 37 cm (H? with a lateral Mylar window, built in a farmer type chamber, was used for this measurement. The measurement was performed with 6 MV photon at 270° gantry angle, 45° and 135° collimator angle with maximum field size, and at 400~500 cm source-phantom distance. The measured items were dose rates, beam profiles, percent depth dose, and transmission factors for both tissue compensator and beam spoiler.
Results: The ratio of percent depth doses at 10 cm and 20 cm depth with in 400~500 cm SSD was 0.5%. The flatness of beam profiles was within (5% under the same conditions. The dose output ratios were also measured for clinical treatment. We measured the attenuation coefficient for the compensator material. Besides, we found that a 1 cm thick Lucite screen at 10 cm from the patient was enough to build up the surface dose.
Conclusions: Our bilateral opposed technique for total body irradiation can achieve more comfortable and reproducible levels than that of conventional anterior/posterior technique. There is an advantage of using the arms of patients to shield the lungs, and it can reduce the lung dose effectively. Although this technique is not new, it can be a choice of total body irradiation.

並列關鍵字

Total body irradiation,Bone marrow transplant,Lung dose