本研究主要是探討電子式照野影像裝置的影像解析度與多葉式準直儀的空間解析度、強度調控能力和物理特性。實驗使用自製分別為0.1、0.125、0.167、0.2、0.25、0.33、0.5和1 lp / mm之線對假體 (line-pair phantom)來測量電子式照野影像裝置的影像解析度，並使用Slide window技術創造之動態多葉式準直儀線對模式來測量多葉式準直儀的空間解析度和強度調控能力，並且對多葉式準直儀的物理特性做測量與探討。結果顯示利用調制轉移函數之方法求出空間解析度，可以對於電子式高能呈像裝置之影像品質作量化數據顯示。另外，動態多葉式準直儀在執行劑量強度調控時，其劑量平坦度會受動態多葉式準直儀之誤差容許值的嚴謹程度和劑量率不同的影響。且劑量率越高其暴露時間越短，但是其葉片位置誤差均方根也越大，因此劑量率與容許誤差值和葉片速度之間的考量也是執行強度調控放射治療時使用動態式多葉式準直儀之重要考量。在臨床上，通常都設定為2mm的誤差容許值和不超過400MU/min的劑量率。而測出多葉式準直儀的空間解析度和強度解析度，或許可以提供做為臨床強度調控放射治療在執行"Sliding Window"技術時，產生多重劑量分布調控時最小限度之參考。

The objective of this theist is to study (1) the image resolution of an electronic portal image devices (EPID), (2)the physical characteristic of the dynamic multileaf collimator(DMLC)and the relationship between DMLC’s spatial resolution and intensity modulated capability. The materials of the experiment are (1) in house made line-pair phantom with 0.1,0.125,0.167,0.2,0.25,0.33,0.5 lp/mm respectively, (2) a DMLC created line pair template with sliding window technique. The line-pair phantom is designed as an objective phantom from which we can utilize modulation transfer function (MTF) method to quantify the image resolution of an EPID, we compared with the other test pattern and the results show consistent. The inspection on the physical characteristic of DMLC shows that the dosimetry precision by DMLC is strongly affacted by the leaves’ traveling stability, which is again affected by leaves’ tolerance setting. The results show that higher dose rate may shorter the exposure time in the expense of higher root mean square error (RMS) of the leave position. However, too tight tolerance setting (<1mm) would induce beam hold off, which cased overall dose error especially when low MU is setting. Clinically, a trade off between dosimetry accuracy and treatment is to use 2mm tolerance setting for DMLC and no more than 400 MU/min dose rate. From our line pair template we test the least spatial resolution and intensity resolution of two DMLC system. We expect these results would provide a reference for a clinical planar an idea of reachable dose gradient, which is the key point in an intensity modulated radiation treatment (IMRT).

參考文獻
1、 R Mohan, “Field shaping for three-dimensional conformal radiation therapy and multileaf collimator,” Seminars in Radiation Oncology, 5: 86-99, 1995.
2、 IJ Das, GE Desobry, SW Mcneeley, EC Cheng and TE Schultheiss, “Beam characteristics of a retrofitted double-focused multileaf collimator,” Med. Phys. 25: 1676-1684, 1998.
3、 WD Powlis, AR Smith, E Cheng, JM Galvin, F Villari, P Bloch and MM Kilgerman, “Initiation of multileaf collimator conformal radiation therapy,” Int. J. Radiat. Oncol., Biol., Phys. 25: 171-179, 1993.
4、 JM Galvin, AR Smith, and B Lally, “Characterization of a multi-leaf collimator system,” Int. J. Radiat. Oncol., Biol., Phys. 25: 181-192, 1993.
5、 JR Palta, DK Yeung, and V Frouhar, “Dosimetric considerations for a multileaf collimator system,” Med. Phys. 23: 1219-1224, 1996.
6、 JM Boone, T Yu, and JA Seibert, “Sinusoidal modulation analysis for optical system MTF measurements,” Med. Phys. 23: 1955-1963, 1996.
7、 H Fujita, D Tsia, T Itoh, K Doi, J Morishita, K Ueda, and A Ohtsuka, “A simple method for determining the modulation transfer function in digital radiograph,” IEEE Trans. Med. Image. 11: 34-39, 1992.
8、 S Webb, "The physics of three-dimensional radiation therapy," IOP Publishing Ltd. 218-241, 1993.
9、 S Webb, "The physics of conformal radiotherapy," IOP Publishing Ltd. 176-220, 1997.
10、 T LoSasso and GJ Kutcher, "Multileaf collimation versus alloy blocks: analysis of geometric accuracy," Int. J. Radiation Oncology Biol. Phys. 32: 499-506, 1995.
11、 JM Galvin, AR Smith, and B Lally, “Characterization of a multi-leaf collimator system,” Int. J. Radiat. Oncol., Biol., Phys. 25: 181-192, 1993.
12、 TJ Jordan and PC Williams, "The design and performance characteristics of a multi-leaf collimator," Phys. Med. Biol. 39: 231-251, 1994.
13、 IJ Das, GE Desobry, SW Mcneeley, EC Cheng and TE Schultheiss, “Beam characteristics of a retrofitted double-focused multileaf collimator,” Med. Phys. 25: 1676-1684, 1998.
14、 L Brester, GS Magcras and R Mohan, "Automatic generation of beam apertures," Med. Phys. 20: 1337-1342, 1993.
15、 TJ LoSasso , CS Chui, GJ Kutcher, et al, "The use of a multi -leaf collimator for conformal radiotherapy of carcinomas of the prostates and nasopharynx," Int. J. Radiat. Oncol. Biol. Phys. 25: 161-170, 1993.
16、 B Rosner, "Fundamentals of biostatistics," Wadsworth Publishing Company, 419-423, 1995.
17、 DJ Convery, ME Roscobloom, "The generation of intensity-modulated fields for conformal radiotherapy by dynamic collimation" Phys. Med. Biol. 37: 1359-1374, 1992.
18、 T Bortfeld, DI Kahler, TJ Waldron, et al, "X-ray field compensation with multileaf collimators," Int. J. Radiat. Oncol. Biol. Phys. 28: 723-730, 1994.
19、 SV Spirou, CS Chui, "Generation of arbitrary flounce profiles by dynamic jaws or collimators," Med. Phys. 21: 1031-1041, 1994.
20、 MC Kirby and PC Williams, "Measurement possibilities using an electronic portal imaging devices," Radiotherapy and Oncology, 29: 237-243, 1993.
21、 R Rajapakshe, K Luchka, and S Shalev, "A quality control test for electronic portal imaging devices," Med. Phys. 23: 1237-1244, 1996.
22、 GJ Kutcher, L Coia, M Gillin, WF Hanson, S Leibel, RJ Morton, JR Palta, JA Purdy, LE Reinstein, GK Sevensson, M Weller, and L Wingfield, "Comprehensive QA for radiation oncology: Report of AAPM Radiation Therapy Committee Task Group 40," Med. Phys. 21: 581-618, 1994.
23、 CJ Kazmark, CS Nunan, and E Tanabe, "Medical Linear Accelerators", New York, McGraw-Hill, 1993.
24、 D Greene and PC Williams, "Linear Accelerators for Radiation Therapy", Second Edition, Institute of Physics Publishing, 1997.
25、 JA Purdy and G Starkscball, "A Practical Guide to 3-D Planning and Conformal Radiation Therapy," Advanced Medical Publishing, 257-277, 1999.
26、 IA Cunningham and BK Reid, "Signal and noise in modulation transfer function determinations using the slit, wire, and edge techniques," Med. Phy. 19: 1037-1044, 1992.
27、 IA Cunningham and A Fenster, "A method for modulation transfer function determination from edge profiles with correction for finite-element differentiation," Med. Phys. 14: 533-537, 1987.
28、 T Falco and BG Fallone, "Characteristics of metal-plate/film detectors at therapy energies. I. Modulation transfer function," Med. Phys. 25: 2455-2461, 1998.
29、 G Pang and JA Rowlands, "Electronic portal imaging with an avalanche-multiplication-based video camera," Med. Phys. 27: 676-684, 2000.
30、 莊克士編著，"醫學影像物理學"，合記圖書出版社，425 - 439，1998。
31、 AB Wolbarst, "Physic of Radiology," Prentice-Hall International, 206-216, 1993.
32、 JM Boone, T Yu, and JA Seibert, "Sinusoidal modulation analysis for optical system MTF measurements," Med. Phys. 23: 1955-1963, 1996.
33、 WR Hendee and R Ritenour, "Medical Imaging Physics," Mosby Year Book, 455-459, 1992.
34、 P Sprawls, "Physical principles of medical imaging," An Aspen publication, 256-259, 1987.
35、 JA Purdy and G Starkscball, "A Practical Guide to 3-D Planning and Conformal Radiation Therapy," Advanced Medical Publishing, 257-277, 1999.
36、 吳世法著，“近代成象技術與圖象處理"，國防科技圖書出版社，35-43，1997.
37、 HK Huang, "Picture Archiving and Communication System in Biomedical Imaging," VCH Publishers Inc, 9-37, 1996.
38、 RT Droege and RL Morin, "A practical method to measure the MTF of CT scanners," Med. Phys. 9: 758-760, 1982.
39、 P Xia, P Geis, P Xing, C Ma, D Findley, K Forster, and A Boyer, "physical characteristics of a miniature multileaf collimator," Med. Phys. 26: 65-70, 1999.
40、 R Roberts, "Short communication：Portal imaging with film-cassette combinations：what film should we use ?" Br. J. Radiol. P.70-71, 1996.
41、 CW Cheng, IJ Das, "Dosimetry of high energy photon and electron beams with CEA films," Med. Phys. 23: 1225-1232, 1996.
42、 CS Chui, S Spirou, and T LoSasso, "Testing of dynamic multileaf collimation," Med. Phys. 23: 635-641, 1996.