Gafchromic film EBT 對於高能x光與電子之劑量回應關係

dose response of Gafchromic films EBT to high energy x-ray and electron beams

張瀞予(Ching-Yu Chang)

指導教授 ： 張寶樹

高雄醫學大學/健康科學院/醫學放射技術學研究所/碩士(2007年)

https://doi.org/10.6832/KMU.2007.00019

摘要

本實驗目的在探討Gafchromic EBT軟片對於高能x光與電子及單次或分次照射之劑量回應關係。採用Gafchromic EBT軟片(lot no. 34351-05I)，底片規格為 8 英吋 (inch) × 10 英吋，剪裁為20片(5 公分 × 5公分)。利用Varian 2100C直線加速器，SAD (Source Axis Distance)100公分，照野10公分× 10公分，使用x光照射時深度採5 公分，電子射束則是採dmax處，軟片放置在聚苯乙烯假體上。分別使用4、10 MV x光和9、12 MeV電子射束照射，劑量給予採用單次照射四種不同劑量(200, 400,600, 800 cGy)與分次照射劑量(50, 100, 200, 400 cGy)，同時有一張未照射底片作為背景值。測量Gafchromic EBT軟片以不同劑量(50-800 cGy)單次照射後之光密度(OD)值變化，並統計分析其回歸曲線。照射後的Gafchromic EBT軟片皆於24小時後使用Victoreen光密度儀(型號07-424)讀取光密度(OD)值並記錄分析。
結果顯示Gafchromic EBT軟片無能量依存性，同時發現單次照射與分次照射結果之統計分析無顯著差異。實驗不準度分析結果為：劑量給予之系統誤差為0.86-1.24%，底片均勻度為1.5%，光密度儀計讀誤差為2%。Gafchromic EBT軟片經選取50-800 cGy劑量範圍內以任意劑量照射，數據分析之回歸曲線顯示Gafchromic EBT軟片有很好的劑量再現性。Gafchromic EBT軟片的臨床應用廣泛，如用於遠隔治療、近接治療或放射手術的劑量測量，其劑量測量誤差為可接受範圍。
此外, 依據「輻射醫療曝露品質保證標準」規定，使用Gafchromic EBT軟片測量光照野與輻射照野的一致性與中心點之差異，並找出最適合的軟片裁剪尺寸及劑量設定，以實驗來證明其一致性。

關鍵字

劑量回應 ； 光密度 ； 回歸曲線 ； 劑量再現性

並列摘要

The object of this experiment is to confer the dose response of high energy x-ray, electron beams, single or fraction irradiation, and try to find its correlation. Different energy of dose of x-ray and electron beams exposure dividedly collected single and fraction irradiation was made by Varian 2100C accelerator when using the ISP Gafchromic film (RCF) EBT. All the RCF film was read and scanned by digital densitometer after 24 hours. The optic density (OD) value was collected and analyzed. It was using different dose to measure the OD value by single and fraction irradiation.

When random access dose (50-800 cGy) was verified, the reproducibility was acceptable. The result shows that RCF film is out of energy dependence, no apparent difference between single and fraction irradiation, and it can be re-usable by the data analysis.

並列關鍵字

dose response ； optical density ； curvilinear regession ； reproducibility

參考文獻

1. Chiu-Tsao ST, Ho Y, Shankar R, Wang L, Harrison LB. “ Energy dependence of response of new high sensitivity radiochromic films for megavoltage and kilovoltage radiation energies,” Med Phys.32(11):3350-3354(2005)

2. Rink A, Vitkin IA, Jaffray DA. “Characterization and real-time optical measurements of the ionizing radiation dose response for a new radiochromic medium ,”Med Phys.;32(8):2510-2516(2005).

3. W. C. Rőntgen, “Über eine neue Art von Strahlen,” Sitzungsber. Phys.Medi. Gesellsch. Würzburg 1, 132-141 (1885)

4. C. Danciu, B. S. Proimos, J.C. Rosenwald, and B. J. Mijnheer, “Variation of sensitometric curves of radiographic films in highenergy photon beams,” Med. Phy. 28, 966-974(2001)

5. I. J. Yeo, C.-K. C. Wang , and S. E. Burch, “A filtration method for improving film dosimetry in photon radiation therapy,” Med. Phys. 24,1943-1953 (1997)