- 期刊
電子射束遮擋照野之劑量特性
Dosimetery Characteristics of Cerrobend Blocked Electron Beams
摘要
目的：本研究以CERROBEND鉛合金，針對CL-2100CD直線加速器開壁式各限光筒尺寸，製成邊長以1cm為級數變化之正方形遮檔塊，測量在射源至皮膚表面為 100 cm時，各縮小照野之百分深度劑量曲線，以觀察並探討縮小照野面積的百分深度劑量曲線變化之情形及臨床應注意的事項。 材料與方法：以CERROBEND鉛合金，依各限光筒尺寸製作邊長以1cm為級數之正方形中空遮擋塊，依次置於Varian CL－210OCD直線加速器電子限光筒底部，以Nucletron三度空問水假體連接Scanditronix p型半導體偵測器，測暈各檔塊照野電子射束能量分別為6，9，12，16，20 Mev射束之百分深度劑量曲線，觀察各能量各照野之最高劑量點(D(下標 max))，90%，80%劑量點之深度，及電子束射程(Rp)之變化情形。 結果：最高劑量點(D(下標 max))，90%，80%劑量點深度之變化情形為：當照野面積縮小到1x1cm^2時，所有能量射東之最高劑量點皆位於0.5~0.8cm之間，不論限光筒大小為何，90%劑量點深度的變化情形為：6 MeV從照野3x3cm^2, 9MeV從4.5x4.5cm^2，12 MeV從6x6cm^2，16 MeV從8x8cm^2，20 MeV則從10.5xl0.5cm^2以下開始降低。 結論：臨床上以不規則形CERROBEND鉛合金執行小照野電子射束治療時，其最高劑量點，90%，80%劑量點之深度將會變小，因此，臨床上在決定射束能量時，若照野面積小於各能量、各劑量的降低點時，應先注意治療擋塊之大小，查得其90%，80%劑量點深度，再決定能量。
並列摘要
Purpose: The percentage depth dose changes of high energy electron beams generated from Varian CL2100C/D linear accelerator collerated with various sizes of cutout blocks were measured at 100cm source-to-surface distance. The clinical significance was discussed. Materials and Methods: CERROBEND cutout blocks were made for open-wall MLC type applicators. The step size of the square cutout is 1 cm. The percentage depth dose curve were scanned with Nucletron 3-D water phantom system connected with Scanditronix p-type semiconductor chamber. The electron energies were ranged from 6, 9, 12, 16 and 20 MeV. The depths of D(subscript max), D90, D80 and R(subscript p) were measured to observed its variation with cutout size. Results: The depths of D(subscript max) were located at 0.5 to 0.8cm at the cutout size equal to 1x1 cm^2 for all energies. The decrement points of the four parameters for each energy were the same in all cone sizes. The decrement cutout sizes were 3x3 cm^2 for 6 MeV, 4.5x4.5 cm^2 for 9 MeV, 6x6 cm^2 for 12 MeV 8x8 cm^2 for 16 MeV and 10.5x10.5 cm^2 for 20 MeV. Conclusions: The depth of 90% and 80% depth dose will shift to surface direction when the irradiate area was decreased. It is mentioned clinically that the 90% depth should be examined before energy selection for tumor treatment.