PTW 2D-Array於強度調控放射治療及體積調控弧形治療劑量驗證之經驗分享

The IMRT and VMAT QA Experience Using PTW 2D-Array

洪照雄(Chao-Hsiung Hung) ； 劉國基(Kuo-Chi Liu) ； 陳弘政(Hung-Cheng Chen) ； 黃英強(David Y. C. Huang) ； 賴家玄(Chia-Hsuan Lai) ； 陳妙芬(Miao-Fen Chen) ； 陳文政(Wen-Cheng Chen)

《放射治療與腫瘤學》 20卷1期 (2013/03) Pp. 41-48

https://doi.org/10.6316/TRO/201320(1)41

摘要

目的：本研究之主要目的是在評估強度調控放射治療技術（Intensity-modulated radiation therapy; IMRT）和體積調控弧形放射治療技術（Volumetric Modulated Arc Therapy; VMAT）之放射治療劑量給予準確性。材料與方法：利用具有729個游離腔之PTW 2D-ARRAY和Octavius假體進行強度調控放射治療技術（Intensity-modulated radiation therapy; IMRT）及體積調控弧形放射治療技術（Volumetric Modulated Arc Therapy; VMAT）之二維劑量分布量測。農夫型游離腔和固態水假體之劑量驗證系統則用來量測單點之絕對劑量。在本研究中選取了19個強度調控放射治療病患及8個體積調控弧形放射治療病患之治療計劃進行劑量量測，其中強度調控放射治療計劃均在旋轉臂角度為0度時進行劑量量測分析，而體積調控弧形放射治療技術則採用其原來弧形放射治療角度進行劑量量測實驗。但是，由於PTW 2D-ARRAY有角度依存性之問題存在，因此針對體積調控弧形放射治療技術而言，在進行二維劑量分析時，必須給予一劑量修正因子。二維劑量分布之評估方法採用Gamma-index method，使用之評估標準劑量誤差小於3%且距離誤差小於3毫米。結果：在旋轉臂角度介於90度至270度之間時PTW 2D-ARRAY會有明顯之角度依存性存在，尤其是在角度為90度和270度時更為明顯，而此時入射角度與量測平面平行。實驗結果顯示，當旋轉臂角度為90度和270度時，6 MV光子射束之加馬因子（gamma factor）分別為 13.1%和22.3%，而10 MV光子射束之加馬因子（gamma factor）分別為 31.7%和 37.2%。點劑量之量測結果，所有27個病患之點劑量平均誤差分析結果為 -1.0%±1.0%。二維劑量驗證分析結果，19個強度調控放射治療病患治療計劃之平均加馬因子（mean gamma factor）為 98.3%±2.1%，而8個體積調控弧形放射治療病患之治療計劃在給予角度依存性校正因子修正後之平均加馬因子（mean gamma factor）為 95.6±2.6%，而修正因子介於 1.007至 1.040之間。結論：PTW 2D-ARRAY應用在量測固定角度的強度調控放射治療之可達到較佳的結果，但是在應用於測量體積調控弧形放射治療技術之劑量準確性時，因為有角度依存性使其應用上受到限制。我們建議在使用 PTW 2D-ARRAY量測體積調控弧形放射治療二維劑量分布時，必須針對每個治療計劃施予角度依存性校正因子，才能得到更準確的測量結果。

關鍵字

強度調控放射治療技術 ； 體積調控弧形放射治療技術 ； 角度依存性

並列摘要

Purpose: The purpose of this study was to evaluate the accuracy of dose delivery in IMRT and VMAT.Method and Materials: The PTW 2D-ARRAY consists of 729 vented ionization chambers with a dedicated phantom called Octavius were used to acquire the 2D dose distributions for the IMRT and VMAT plans. One limitation of the PTW 2D-ARRAY is the significant angular dependency, so we had measured the correction factors for VMAT plans. Another dosimetry system consists of a farmer type ion chamber (Wellhofer FC-65P) and solid water phantom was used to measure the selected point dose. Total of 19 IMRT and 8 VMAT plans were included in this study. IMRT plans were verified with perpendicular deliveries at 0 degree gantry angle. VMAT plans were measured with actual treatment arcs, and then the corrections were applied after the measurements. We performed gamma comparison with 3% and 3mm criteria to evaluate the results of all 2D dose maps.Results: The significant angular dependences of PTW 2D-ARRAY were showed at the measured gantry angle between 90 to 270 degrees, especially at both 90 and 270 degrees, which was parallel with the measured plane of PTW 2D-ARRAY. The gamma factors of the gantry angle 90 and 270 were 13.1% and 22.3% for 6 MV photon beam and 31.7% and 37.2% for 10 MV photon beam.The mean point doses variation between each measurements and treatment plans in all IMRT/VMAT QA was -1.0% +/-1.0 % (mean +/- std). The mean gamma factor of IMRT QA was 98.3%+/- 2.1%. And the mean gamma factor in the full-arc VMAT QA was 95.6+/-2.6% after applied acorrection factor range from 1.007 to 1.040. Therefore, the 2D dose maps showed great agreements in all IMRT/VMAT QA.Conclusions: PTW 2D-ARRAY has better performance in static angle IMRT, but has limitations caused by angular dependences in VMAT QA. We suggest a correction factor should be applied to every measured points of 2D dose maps when using PTW 2D-ARRAY for a full-arc VMAT QA.

並列關鍵字

Intensity-modulated radiation therapy ； Volumetric Modulated Arc Therapy ； Angular dependences