The Study of Beam Quality of Low Monitor Unit Delivery for Intensity Modulated Radiation Therapy

強度調控放射治療技術低監控單位之射束品質及劑量探討

王國偉(Kuo-Wei Wang) ； 馬漢光(Hon-Kwong Ma) ； 熊敬業(Ching-Yeh Hsiung) ； 林怡君(Yi-Jun Lin) ； 林招膨(Jao-Perng Lin) ； 李桂樑(Kuei-Liang Li) ； 賴源淳(Yuan-Chun Lai)

《台灣應用輻射與同位素雜誌》 7卷2期 (2011/06) Pp. 51-58

https://doi.org/10.29832/TJARI.201106.0001

摘要

IMRT目前已廣泛運用在治療癌症病患身上，但爲了要更達到治療計劃之最適化，以及使正常組織受到的傷害減少，而使照野射束更細化，監控單位更小值；本研究在探討劑量、平坦與對稱性在低的監控單位與高的監控單位下，有何變化與差異性，採用ELEKTA直線加速器來作爲測量，使用0.6cc Farmer ion chamber，將Monitor unit設在1-15、50、100，測其各MU在照野大小分別爲5×5平方公分、10×10平方公分、25×25平方公分的劑量數值，平坦度與對稱性則使用型號爲PTW的二維陣列游離腔(2-D Array ion chamber)，將MU數設在3-15、50、100、150、200，照野大小分別爲5×5平方公分、10×10平方公分、25×25平方公分的情況下量測。結果顯示，低於5MU以下的劑量數值誤差介於0.3%~0.5%之間，尤其是小照野5×5平方公分在低MU時更爲顯著，並且以10MV高能量時小照野不穩定度比大照野來的更加不穩定；對稱與平坦不管是在高低能量監測下，只要是低MU的輸出，都呈現一偏高之不穩定數值，而7MU以上則呈現穩定狀態。建議於臨床上，應盡量避免高能量小照野的產生，一個小照野的最低限值，最好是在5~7MU以上，射束的照射才會趨於穩定狀況，使臨床治療更加理想。

關鍵字

低監控單位 ； 對稱性 ； 平坦性 ； 二維陣列游離腔

並列摘要

IMRT is currently widely used in the treatment of cancer patients; however in order to make the treatment plan more applicable and render less damage to normal tissues, the beams in a field and the monitor units should be made smaller; this study aims to find the changes and difference between lower and higher monitor units in terms of dosage, flatness and symmetry; the measurement is made by using ELEKTA linear accelerator in 0.6cc Farmer ion chamber and setting the monitor unit at 1-15, 50, 100; the dosage in the field of such sizes as 5×5 cm^2、10×10 cm^2、25×25 cm^2 is measured under each of the abovementioned MU; the flatness and symmetry is measured by using PTW 2-D Array ion chamber, where MUs are set at 3-15, 50, 100, 200 and the field size ranges from 5×5 cm^2, 10×10 cm^2 to 25×25 cm^2. The result shows that the error in dosage under 5 MU ranges between 0.3% and 0.5%, which is particularly more significant in the small field of 5×5 cm^2 under low MU and that the small field is much more unstable than the large field when 10MV high energy is input; however, in terms of flatness and symmetry, the output value is a high and unstable number under low MU while it shows a stable status above 7 MU. It is recommended that in clinical practices, the production of small field with high energy should be avoided as much as possible and the lowest limit of a small field be between 5 and 7 MU, because the lighting of the beams is prone to become stable in this range and make the clinical treatment results more ideal.

並列關鍵字

Low monitor units ； Flatness ； Symmetry ； 2-D Array ion chamber