- 期刊
Quality Assurance Schedule and Practical Experience with Helical Tomotherapy
多模式螺旋斷層放射治療儀的品質保證排程與實際經驗
摘要
目的：我們提出一個多模式螺旋斷層放射治療儀的品質保證(QA)排程並且分享此一最先進機器的品質保證實際經驗。在台灣，根據游離輻射防護法（第17條第三項），依照醫療曝露品質保證作業的規定，在一個放射治療部門裡，必須為每一治療儀器訂定品質保證處理程序來確保治療品質，其中須包括每天、每月、每年一次的項目並須定期實施。多模式螺旋斷層放射治療儀於2003年在麥迪遜威州大學發展後量產；為提供病患高品質服務，我們阮綜合醫院在2006年4月安裝此一最先進機器，因而在南台灣遙遙領先其他醫院。在這項研究中，我們提出在我們部門內執行的品質保證排程，此一排程遵循了AAPM TG-40的原則但也包含一些嶄新的項目，反映出此一最先進機器設備和傳統的直線加速器之間的差別。 材料與方法：本研究擬訂了一套遵循AAPM TG-40原則的品質保證處理程序，比較了多模式螺旋斷層放射治療儀和Elekta-Precise直線加速器之間的品質保證實施效率，其中完整地包括了每天、每月、每年一次的QA項目。在多模式螺旋斷層放射治療儀方面，其品質保證計畫的實施使用一特別設計製作的勻稱圓柱型實體模擬水假體，來作一系列的實際記錄量測。此專用水假體是被分成兩半的圓柱體其直徑為30厘米、長為18厘米，因此X光片可以在作實際記錄量測時被放在他們之間。為了執行劑量參數和修正係數的量測，在多模式螺旋斷層放射治療儀方面使用Standard Imaging公司製造的三支Exradin-A1SL游離腔和一組TomoEletrometer計讀器；而在Elekta-Precise直線加速器上使用了一支0.6 cc PTW TM30013農夫型游離腔和PTW T0008電子電量計讀器。於年度射束品質量測方面，使用一組多模式螺旋放射治療儀專用的電子電量量測系統(TEMS)配合一套二維射束分析掃描儀(TomoScanner)，與另一套PTW-Freiburg MP3-S射束分析水假體系統，來執行個別機器的射束勻稱性數據掃描圖(profile)量測，並檢測分析射束數據掃描圖是否與接機驗收時一樣。 結果：多模式螺旋斷層放射治療儀的品質保證測量方法是一嶄新的觀念，我們利用將近一年的實際測量資料統計，可以得到多模式螺旋斷層放射治療儀除了在品質保證測量時間上比Elekta-Precise直線加速器短且有效率外，其劑量輸出誤差值亦比Elekta-Precise直線加速器低。在每月品保實施時間上約少2小時、每年品保實施時間約少10小時，而在每日品保實施時間上則約略相當。在劑量輸出統計方面，每日劑量輸出誤差在1%內的約佔總比率的75%，誤差在1-2%以內的約佔18.75%，誤差在2-3%以內的約佔6.25%。且在每月的劑量輸出穩定性上表現都在1%以內。 結論：本研究的結論可歸納如下：首先，依實際測量資料統計結果在例行的品質保證測量時間上多模式螺旋斷層放射治療儀比直線加速器較有效率。再者，由於多模式螺旋斷層放射治療儀機器的本質結構特性，有些品質保證測量項目不須實施，如在機械方面不須要做旋轉臂、治療床、準直儀之品質保證測量校正工作，所以在例行的品質保證測量工作上較為簡單；此外因多模式螺旋斷層放射治療儀只有單一光子射束(6MV)，而沒有電子射束所以在品質保證量測上不須測量電子射束，因而簡化許多程序，但電子射束的特性可以由不同的小射束(beamlet)組合來達到相同的效果。由於多模式螺旋斷層放射治療儀的實際臨床記錄相對較短，所以當有更進一步的品質保證測量實際操作經驗被獲得後，可能發現有一些品質保證項目應該在不同的期間被適時修正，或者須增添一些新的品質保證項目才能使整個品質保證排程更臻於完善。
並列摘要
Purpose: We present a quality assurance (QA) schedule for the Hi-Art Helical Tomo-Therapy unit and share our QA practical experience with this state-of-the-art machine. According to the Ionizing Radiation Protection Act (Article. 17, item 3), the regulation of medical exposure QA in Taiwan has to include daily, monthly, and annual items in the schedule for every treatment machine in a radiation oncology department. The Hi-Art Helical Tomo-Therapy unit was developed at the University of Wisconsin-Madison in 2003. We installed a new system at Yuan's General Hospital to take the lead in South- Taiwan in April 2006. In this study, we present the QA schedule that is performed in our department, which follows the principles of AAPM TG-40 but contains some novel components, reflecting the differences between the Hi-Art device and conventional linear accelerators. Materials and Methods: We compared the efficiency of the daily, monthly, and annual QA programs in our department with Hi-Art Helical Tomo-Therapy unit and an Elekta-Precise linear accelerator with a standard QA schedule. We followed the principles of AAPM TG-40. For tomotherapy, the QA program included a series of measurements that were recorded in a specially fabricated, cylindrically symmetric Virtual Water phantom. This was designed specifically for commissioning the Helical Tomo-Therapy unit and QA. The phantom is 30cm in diameter, 18cm long, and is divided into two halves, such that film may be placed between them. To perform the measurements of the dosimetry parameters and correction factors, three EXRADIN-A1SL ion chambers and a Standard Imaging-TomoEletrometer were used for the Helical Tomo-Therapy unit, and a 0.6CC PTW TM30013 Farmer chamber with PTW T0008 Eletrometer was used for the Elekta-Precise linear accelerator. For the beam quality measurements, the dedicated TomoTherapy electrometer measurement system (TEMS) along with a two-dimensional radiation beam analyzer (TomoScanner) and a PTW-Freiburg MP3-S therapy beam analyzer water phantom system were performed the scanning for the beam symmetrical profiles assessment for the corresponding machine respectively. Results: The lengths of time required for daily QA program was almost the same for the two machines. However, the monthly and annual programs were more efficient for the Hi-Art Helical TomoTherapy, saving 2 hours and 10 hours compared to the Elekta-Precise linear accelerator, respectively. The statistical data collected over the past 10 months show that the time spent for the TomoTherapy was less, and the tolerance value was lower than that of the Elekta-Precise linear accelerator; the output error of daily QA was within ±1% for 75% of the data, within ±2% for 18.75% of the data, and within +3% for the remaining 6.25% of the data, and the dose output error value for the monthly QA was less than ±1%. Conclusions： The following conclusions can be drawn from this study. First, the time needed for the QA schedule for the Hi-Art Helical TomoTherapy is less than that required for routine work with a linear accelerator. Due to the TomoTherapy machine intrinsic characteristics, some mechanical items, such as the gantry, the couch angle, the collimator etc., do not need to be checked. Additionally, no electron beam verification is needed but the same beam effect can be formed from the different beamlets of the machine. Nonetheless, Helical TomoTherapy has a relatively short clinical track record and, as further operational experience is gained, it may be found that some QA items will need to be modified and some additional tests may need to be developed for completeness of the QA schedule.