光子射束下使用碳纖呼吸調控版於不同照野大小及機頭入射角度之衰減效應

目的：碳纖呼吸調控板可用來抑制因病人呼吸起伏造成之器官移動，然而若其對於放射治療射束之衰減過大，在病患對位時若有誤差，將會大幅影響治療之劑量準確性。本研究之主要目的為評估碳纖呼吸調控板對於放射治療射束之衰減效應。材料與方法：藉由碳纖呼吸調控板的CT值來預測其各個結構之電子密度極可能造成的衰減程度。使用Varian iX直線加速器測量在6 MV及10 MV光子射束下碳纖呼吸調控板在不同機頭入射角度的衰減因子。測量時使用碳纖呼吸調控板直接加壓固態水假體，置入PTW 0.6cc農夫型游離腔測量不同照野大小之衰減因子，並用成對t檢定進行分析。利用Gafchromic EBT3軟片量測二維的加壓組件衰減。結果：在固態水假體的量測中，機頭角度300度至60度幾乎沒有衰減；在機頭角度165度至195度時，小照野在不同光子能量的平均衰減約為25.17%及20.21%（6 MV及10 MV），大照野的平均衰減約為23.53%及19.20%；在其他機頭入射角度時，小照野的平均衰減約為9.51%及7.31%，大照野的平均衰減約為8.57%及6.84%。無論是大照野或高能量，其衰減因子都有顯著降低（p＜ 0.01）。結論：衰減效應會隨著光子能量增加與照野增加而隨之減少。碳纖呼吸調控板能夠有效地並較舒適地減少呼吸造成的器官位移，但還是要顧慮可能造成的衰減效應。若腫瘤恰巧被碳纖呼吸調控板遮蔽，應盡量避免使用調控板，或以治療計畫系統計算其衰減效應。

關鍵字

碳纖呼吸調控板；衰減效應；照野；機頭角度

並列摘要

Purpose: The Carbon Fiber Respiratory Control Board (CFRCB) (Blessing-Cathay Corp.) was used to suppress the organ motions due to respiratory. The attenuation effects of CFRCB will affect the dose accuracy in radiation treatment plans. The purpose of this study is to evaluate the attenuation effects with different measurement field sizes and gantry angle due to the Carbon Fiber Respiratory Control Board. Materials and Methods: The CT numbers of CFRCB would be analyzed to predict the electron density and attenuation of each components. The attenuation factors of CFRCB were measured with rotated gantry angles in 6 MV and 10 MV using a Varian iX Linac machine. In the measurements, the CFRCB compressed from anterior (gantry= 180°) to the center of plastic water phantoms. A PTW 30013 0.6cc farmer chamber was placed in plastic water phantoms and measured with different field sizes. The attenuation factors would be calculated and compared between different field sizes and photon energy with paired t-test. The Gafchromic EBT3 films replaced the farmer chamber to perform the attenuation of the compressor in 2D. Results: In phantom attenuation measurements, there were no attenuation effects in gantry angle 300° to 60° (posterior). In gantry angle 165° to 195° (anterior), the mean attenuations were 25.17% vs 20.21% (in 6 MV vs 10 MV) in smaller field size 10 x 10 cm^2, and 23.53% vs 19.20% in larger field size. In the other gantry angles, the mean attenuations were 9.51% vs 7.31% (in 6 MV vs 10 MV) in smaller field size, and 8.57% vs 6.84% in larger field size. In larger field size and higher photon energy, the attenuation factors were significantly decrease (p＜ 0.01).The largest attenuation of the compressor was in diameter 1cm of beam center, that is the position of the screw. The attenuation due to the respiratory suppression plate was lower than the attenuation of the screw, but it should also be concerned. Conclusions: The attenuation effects were decrease when measured with higher energy, larger field size. Therefore, CFRCB can control and decrease the respiratory motions efficiently and comfortably, but the attenuation effect should be considered. When the tumor targets are blocked by CFRCB, the CFRCB should not be used in treatment or the attenuation effects must be calculated by the planning system.

並列關鍵字

Carbon Fiber Respiratory Control Board (CFRCB) ； Attenuation effects ； Field size ； Gantry angle

國際替代計量

光子射束下使用碳纖呼吸調控版於不同照野大小及機頭入射角度之衰減效應

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