子宮頸癌高劑量率遙控後荷放射治療機射源校正及品質之確保

Source Calibration and Quality Assurance of High Dose-Rate Remote Afterloading for Cervical Carcinoma Brachytherapy

林招膨(Jao-Perng Lin) ； 劉幕台(Mu-Tai Liu) ； 張東浩(Tung-Hao Chang) ； 黃勝賢(Sheng-Sang Huang) ； 林桂華(Kuei-Hua Lin) ； 陳苑蓉(Yuan-Rong Chen) ； 許智捷(Chih-Chiech Hsu) ； 黃昭源(Chao-Yuan Huang)

《The Changhua Journal of Medicine》 6卷1期 (2000/01) Pp. 25-29

摘要

背景：本文針對子宮頸癌Co-60射源遙控後荷放射治療機，以0.6c.c. Farmer型游離腔在空氣中量測其活度，供比較例行測量活度之依據；並以自製設計之L型尺及CEA底片檢測射源與虛擬射源位置之一致性，建立品質保證課程。同時測量治療機頭之輻射洩漏量，以確保輻射安全。
方法：使用CEA底片以重複曝光方式檢驗射源給予至指定虛擬射源位置之準確性；依AAPM TG-40號建議，以電子計讀器(electronmeter)連接0.6c.c.的套管游離腔(NE 2571和NE 2581)，測量其活度，經溫度、壓力修正後，與原廠提供之活度作比較；另依據原子能委員會規定，近接治療機之安全執行各項守則，並以Victoreen 450P survey meter對治療機頭進行輻射洩漏量的量測。
結果：給予射源位置與各虛擬射源問之誤差準確度在1mm以內；射源活度以 0.6c.c.套管游離腔在距射源20cm處所量得活度誤差可小於3%，並比較所量得之值與原廠之報表數值；治療機頭之輻射漏射量最高點在右側表面處其數值小於0.03mSv/h，滿足美國NRC之要求。一般安全要求亦皆符合安全規範。
結論：射源位置、射源活度之準確性將影響劑量之給予，唯有正確掌握此兩項重點，近接治療之品質才能有所依據。本機為20顆鈷六十射源，位置安排之誤差應要求每週一次檢測，以確保治療品質。

關鍵字

射源活度 ； 射源位置 ； 輻射漏射 ； 近接治療

並列摘要

Background: The quality assurance procedures for Nucletron Selectron Co-60 source brachytherapy machine were performed. The basic items are source strength measurement, source position alignment and head radiation protection ability survey.
Methods: According to the suggestions of AAPM TG-40, 0.6 c.c. Farmer type ionization chambers (NE2571, NE2581) were used to measure the source strength. CEA films were used to check the source position alignment according to the autoradiography method. The head radiation protection ability was surveyed by Victoreen 450P.
Results: The source strength was over estimated from 0.6 c.c. Farmer type ionization chambers (around +1.5%) while the chamber's reading appear under estimated. The source position can be corrected within 1mm and the head radiation protection is satisfied to the NPC and the Council of Atomic Energy's regulation.
Conclusion: The source strength and source position affect the treatment quality greatly. The head protection ability satisfies the regulation and is safe to the staffs. Quality assurance program has been established by our medical physicists.

並列關鍵字

source strength ； source position alignment ； brachytherapy