以移位及數學方法提升PTW 2D Array在放射治療驗證解析度之研究

Using Multiple Acquisition Sequence and Mathematic Theory to Increase PTW 2D-Array Dosimetric Resolution for Patient Specific Dose Verification Quality Assurance

10.6316/TRO/201421(4)317

黃超羣(Chao-Chun Huang)；葉世安(Shyh-An Yeh)；陳清江(Ching-Jiang Chen)；李財福(Tsair-Fwu Lee)；吳嘉明(Jia-Ming Wu)

劑量驗證 ； 強度調控放射治療 ； 二維陣列系統 ； Quality assurance (QA) ； Intensity modulated radiotherapy (IMRT) ； 2D-Array system

放射治療與腫瘤學

21卷4期（2014 / 12 / 01）

317 - 326

繁體中文

目的：在現有PTW-seven29 2D-Array工具下，利用多次移位並結合數學理論，給出一規則性且有效地增加測量解析度的方法，並實際和治療計畫的數值做比較，探討2D Array用在強度調控放射治療(intensity modulated radiotherapy, IMRT)劑量驗證的可行性。材料與方法：PTW-seven29 2D Array為測量工具，並使用15片PTW-RW3 Slab Phantoms在電腦斷層(computed tomography, CT)掃描影像來做劑量分布的模擬計算，射源到固態假體(solid phantom)表面的距離(SSD)為95 cm，表面下5 cm的二維劑量分布當作數值參考值。並紀錄不同移位下的實際測量結果，利用數學原理組合量測數值，以得到不同理論解析度的分布，並討論利用低理論解析度測量結果預測高理論解析度的測量值和實際測量值間的關係，並和治療計畫系統(treatment planning system, TPS)計算結果做Gamma index比較。結果：我們發現利用多次移位確實能有效增加劑量分布的量測解析度，且理論解析度和總量測次數是成正比的關係，也就是假如要獲得4倍理論解析度，則總測量次數為4次，進一步和治療計畫系統的計算結果做Gamma index比較後，認為利用移位4次測量是最有效率且可得到近似於治療計畫的2維劑量分布，當然在時間充足下，移位8次來做測量，能得到較好的結果，但受限游離腔的有限體積，其改善有限。結論：利用組合多次移位2D-Array測量的方式，確實能有效增加測量的解析度並表現出真實劑量分布，在強度調控放射治療(IMRT)劑量驗證上，提供了另一個可行的方法。

Purpose : To investigate the feasibility of using PTW 2D-Array detecting system in IMRT dosimetric quality assurance, we propose a mathematical and efficient method. The method uses the multiple acquisition sequence to increase the resolution. Then the measured results and calculated results are analyzed and compared. Materials and Methods: We use PTW-seven29 2D Array as the detecting system and PTW-RW3 Slab Phantom as solid phantom. With 15 cm-thickness solid phantom and CT images, the dosimetric distribution is calculated by the treatment planning system (TPS). The phantom source surface distance (SSD) is 95 cm and the 2D distribution at the 5 cm depth is as the calculated result. By combining the measured results in different acquisition sequence, we can get the dosimetric distribution in different theory resolution. The relation between the low-resolution and high-resolution results is analyzed. In advance we combine the calculated result to get the Gamma index in different theory resolution. Results: We find that using the multiple acquisition sequence really increases the measured resolution in the 2D-Array detecting system. And the number of measuring times is direct ratio to the theoretic resolution. For example combining the four-times measures in different position can get the fourfold-theory resolution. In comparing the measured results with calculated results, the fourfold-theory resolution is the most efficient and passes the Gamma index test. However using eightfold-theory resolution is better but needs more time in quality assurance. Conclusions: We find that using the multiple acquisition sequence in the 2D-Array detecting system increases the measuring resolution and really is feasible in dosimetric quality assurance.