Leipzig Applicators之劑量特性

The Dosimetry Characteristics of Leipzig Applicators

黃英明(Ing-Ming Hwang) ； 郭珍妮(Jenny Que) ； 陳海雯(Helen H.W. Chen) ； 王裕文(Yu-Wen Wang)

《放射治療與腫瘤學》 4卷2期 (1997/06) Pp. 133-137

https://doi.org/10.6316/TRO/199704(2)133

摘要

目的：Leipzig Applicators為Nucletron Micro-selectron^192 lr高劑量率後荷治療機配件之一，依射源之方位可分為直立式及水平式二種型式，又依其口徑大小各可分為一、二及三公分之裝療管。為了解此型裝療管的臨床劑量學特性，本實驗將量測五種特性，分別為：幾何結構、相對輸出、百分深度劑量、等劑量分佈曲線及真實矢狀面輻射洩漏情形。
材料與方法：以高精密度游標尺量取各裝療管之幾何結構。相對輸出則以HN.E.0.03 cc平板型(type:2534)游離腔連接lonex Dosemaster 5590電位計，加上3 mm增建層予以測量，並歸一到在全假體內相等距離所測得的輸出。百分深度劑量及等劑量分佈曲線則以Scanditronix RFA-300水假體連接p-型電子射束半導體偵測器在水中測量而得，輻射洩漏量的測量則於Kodak V-tilm中間，依裝療管之外形挖空，將底片置於裝療管矢狀面，上下各置0.5 cm bolus作增建，以測量真實矢狀面之輻射洩漏量。
結果：水平式裝療管之輸出增加約10%，直立式裝療管則降低約9%。有效射源至表面距離：水平式裝療管為1.93cm，直立式則為1.74cm。直立式裝療管之等劑量分佈曲線中心軸有凹陷情形，水平式裝療管之輻射洩漏量為最高劑量點之30％。位於裝療管的頂部，而直立式之輻射洩漏量為最高劑量點之20%，位於裝療管的側部。
結論：Leipzig applicators由於體積小，適合於一些小範圍皮膚癌，口腔癌。及其他癌症之治療。由測量的結果發現：百分深度劑量可用有效射源至表面距離予以準確估算至20％劑量深度，直立式與水平式裝療管的輸出變化達20%，投予劑量時應特別注意。輻射洩漏量的測量提供使用者了解裝療管的防護能力及熱點所在位置，以供臨床應用時之參考。

關鍵字

近接治療 ； Leipzig Applicator ； 劑量學

並列摘要

Purpose: Leipzig applicators are one kind of accessories of Nucletron (superscript 192)1r High-Dose Rate remote afterloading system. According to the orientation of the source axis in the applicator, it can be divided into two kinds: horizontal and vertical ones. There are three kinds of diameter for each type of applicator: 1, 2 and 3 cm. Five characteristics of the applicator will be measured for clinical application. They are geometric structure, relative output, percent depth dose, isodose curve distributions and real sagittal plane radiation leakage test.
Materials and Methods: High accuracy calipers was used to measure the geometric structure of the applicator The relative outputs were measured with N.E. 0.03 cc. parallel-plate ionization chamber connected to Ionex Dosemaster 2590 in RMI solid phantom with 3 mm build-up layer The outputs were normalized to the dose in full phantom that was measured at the same source-to-chamber distance. The percentage depth dose and isodose curve distributions were measured with Scanditronix RFA300 water phantom connected to p-type electron beam semiconductor chamber The measurement was performed in water along the side Mylar window. The real sagittal plane radiation leakage of the applicator was measured with Kodak V film that was cut according to the shape of the applicator.
Results: The relative outputs of the horizontal type were increased 10%, while the vertical ones were decreased 9%. The effective source-to-surface distance of the horizontal type is equal to 1.93 cm and 1.74 cm for the vertical ones. The isodose curves are attenuated in the central axis of vertical type applicators due to the attenuation from catheter and source tip. The hot spots of the horizontal type applicators are located at the top of the applicator and at the sides for the vertical ones. The leakage is 30% for the horizontal types and 20% for the vertical types.
Conclusion: Leipzig applicators can be used to treat some small volume cancer such as skin cancer, oral cancer and for other dose boost treatment. The dose can be estimated with BSSD to approximately 20% depth accurately. The hot spots of the applicators allow the user to avoid unnecessary exposure.

並列關鍵字

Brachytherapy ； Leipzig applicator ； Dosimetry