這項研究的目的是了解兩種演算法模擬治療床衰減和實測的差異，並驗證治療床衰減對患者劑量驗證的影響。我們用兩種光子能量6 MV及10 MV，針對治療床頭部(head)、骨盆部(pelvis)及兩個支撐架，共進行了八種治療床衰減測量。我們還使用Delta假體對頭頸部和攝護腺病例進行了驗證。對於頭頸部情況，對於在電腦模擬中，治療角度完全由0射入情況下，筆形光束卷積(pencil-beam convolution，PBC)及均向異性分析算法(anisotropic analytical algorithm，AAA)模擬的與實測一致性最高，尤其AAA的驗證結果，用劑量差異(dose deviation，DD)，距離一致(distance to agreement，DTA)和伽瑪指標(gamma index)幾乎相同。在治療床未列入模擬的情況下，與真實測量情況不同，AAA的劑量驗證真實反映糟糕的結果，頭頸部的DD，DTA和gamma指數分別為74.4％，99.3％和89％。對於攝護腺病例，相應的值分別為56.2％，95.1％和92.4％。我們建議電腦模擬應盡速加入模擬治療床功能。另外，建議劑量驗證(dose verification)同時使用三個指標，DD，DTA和伽瑪指標(gamma index)，進行劑量驗證。

The aim of this study was to understand the difference between the measured and calculated irradiation attenuations obtained using two algorithms and to identify the influence of couch attenuation on patient dose verification. We performed eight tests of couch attenuation with two photon energies, two longitudinal couch positions, and two rail positions. The couch attenuation was determined using a radiation treatment planning system. The measured and calculated attenuations were compared. We also performed 12 verifications of head-and-neck and rectum cases by using a Delta phantom. The dose deviation (DD), distance to agreement (DTA), and gamma index of pencil-beam convolution (PBC) verifications were nearly the same. The agreement was least consistent for the anisotropic analytical algorithm (AAA) without the couch for the head-and-neck case, in which the DD, DTA, and gamma index were 74.4%, 99.3%, and 89%, respectively; for the rectum case, the corresponding values were 56.2%, 95.1%, and 92.4%. We suggest that dose verification should be performed using the following three metrics simultaneously: DD, DTA, and the gamma index.

1. Marcel van Herk, “Errors and margins in radiotherapy”, Semin Radiat Oncol. 2004;14(1):52-64.
2. Rasmus Bokrantz, Albin Fredriksson, “Scenario-based radiation therapy margins for patient setup, organ motion, and particle range uncertainty”, Phys Med Biol. 2017;62(4):1342-1357.
3. Yuji Kurosawa , Hitoshi Ishikawa, Yoshihiko Hoshino, eta., “Intra-fractional set-up and organ motion errors in intensity-modulated radiation therapy for prostate cancer”, Nihon Hoshasen Gijutsu Gakkai Zasshi. 2012;68(3):290-8.
4. Sumin Zhou, Xiaofeng Zhu, Mutian Zhang, eta., “Estimation of internal organ motion-induced variance in radiation dose in non-gated radiotherapy”, Phys Med Biol. 2016;61(23):8157-8179.
5. Arezoo Modiri, Pouya Sabouri, Xuejun Gu , eta., “Inversed-Planned Respiratory Phase Gating in Lung Conformal Radiation Therapy”, Int J Radiat Oncol Biol Phys. 2017;99(2):317-324.
6. Seyed Ali Mirzapour, Thomas R Mazur, H Harold Li, Ehsan Salari, eta., “Technical Note: Cumulative dose modeling for organ motion management in MRI-guided radiation therapy”, Med Phys. 2021;48(2):597-604.
7. James G Mechalakos, Margie A Hunt, Nancy Y Lee, eta., “Using an onboard kilovoltage imager to measure setup deviation in intensity-modulated radiation therapy for head-and-neck patients”, J Appl Clin Med Phys. 2007;8(4):28-44.
8. Lei Fu, Harold Perera, Xiao Ying, Yan Yu, “Importance of CBCT setup verification for optical-guided frameless radiosurgery”, J Appl Clin Med Phys. 2014;15(3):4487.
9. Joseph Fodor 3rd, John C Breneman, Michael A Lamba, et al., “Modification of a linear accelerator table top for non-coplanar conformal brain radiotherapy”, Med Dosim. Spring 1998;23(1):27-9.
10. Sandra C Vieira, Robert S J P Kaatee, Maarten L P Dirkx, et al., “Two-dimensional measurement of photon beam attenuation by the treatment couch and immobilization devices using an electronic portal imaging device”, Med Phys. 2003;30(11):2981-7.
11. Zhihui Hu, Jianrong Dai, Liang Li, et al., “Evaluating and modeling of photon beam attenuation by a standard treatment couch”, J Appl Clin Med Phys. 2011;12(4):3561.
12. Christopher F Njeh, Jason Parker, Joseph Spurgin, et al., “A validation of carbon fiber imaging couch top modeling in two radiation therapy treatment planning systems: Philips Pinnacle3 and BrainLAB iPlan RT Dose”, Radiat Oncol. 2012;7:190.
13. Mikoto Tamura, Hajime Monzen, Kenji Matsumoto, et al., “Reduction of Potential Risk for Skin Toxicity in Megavoltage Radiotherapy Using a Novel Rigid Couch”, In Vivo. May-Jun 2018;32(3):531-536.
14. Asma Sheykhoo, Sara Abdollahi, Mohammad Hadi Hadizadeh Yazdi, et al., “Effects of Siemens TT-D carbon fiber table top on beam attenuation, and build up region of 6 MV photon beam”, Rep Pract Oncol Radiother. Jan-Feb 2017;22(1):19-28.
15. Heng Li, Andrew K Lee, Jennifer L Johnson, “Characterization of dose impact on IMRT and VMAT from couch attenuation for two Varian couches”, Appl Clin Med Phys. 2011;12(3):3471.
16. Stephen McCormack, Jennifer Diffey, Andrew Morgan, “The effect of gantry angle on megavoltage photon beam attenuation by a carbon fiber couch insert”, Med Phys. 2005;32(2):483-7.
17. W Kenji Myint, Malgorzata Niedbala, David Wilkins, et al., “Investigating treatment dose error due to beam attenuation by a carbon fiber tabletop”, J Appl Clin Med Phys. 2006;7(3):21-7.
18. Daniela Wagner and Hilke Vorwerk, “Treatment Couch Modeling in the Treatment Planning System Eclipse”, J Cancer Sci Ther. 2011;3, 188–193.
19. David W Smith, Damianos Christophides, Christopher Dean, et al., “Dosimetric characterization of the iBEAM evo carbon fiber couch for radiotherapy”, Med Phys. 2010;37(7):3595-606.
20. Chun-Yen Yu, Wen-Tsae Chou, Yi-Jen Liao, et al., “Impact of radiation attenuation by a carbon fiber couch on patient dose verification” Sci Rep. 2017;7:43336.
21. Ruohui Zhang, Yulan Gao, Wenwen Bai, “Quantification and comparison the dosimetric impact of two treatment couch model in VMAT” J Appl Clin Med Phys. 2018;19(1):10-16.
22. Omemh Bawazeer, Sisira Herath, Sivananthan Sarasanandarajah, et al., “A simple and efficient method to measure beam attenuation through a radiotherapy treatment couch and immobilization devices”, Australas Phys Eng Sci Med. 2019;42(4):1183-1189.
23. T Sedaghatian, M Momennezhad, S H Rasta, et al., “An Update of Couch Effect on the Attenuation of Megavoltage Radiotherapy Beam and the Variation of Absorbed Dose in the Build-up Region”, J Biomed Phys Eng. 2017;7(3):279-288.
24. Jan K.H. Seppälä and Jarmo A.J. Kulmala, “Increased beam attenuation and surface dose by different couch inserts of treatment tables used in megavoltage radiotherapy”, J Appl Clin Med Phys. 2011;12(4):3554.
25. Zhihui Hu, Jianrong Dai, Liang Li, et al., “Evaluating and modeling of photon beam attenuation by a standard treatment couch”, J Appl Clin Med Phys. 2011; 12(4): 139–146.
26. K Shioiri, M Kurooka, S Yoshino, W Maehana, et al., “Accuracy of Dose Attenuation Correction for a 6D Carbon Fiber Treatment Couch Using a Virtual Couch Technique Integrated into a Treatment Planning System”, Med Phys. 2012;39(6Part13):3758.
27. I B Mihaylov1, P Corry, Y Yan, et al., “Modeling of carbon fiber couch attenuation properties with a commercial treatment planning system”, Phys. 2008;35(11):4982-8.
28. Guangjun Li, Sen Bai, Nianyong Chen, “Evaluation of the sensitivity of two 3D diode array dosimetry systems to setup error for quality assurance (QA) of volumetric‐modulated arc therapy (VMAT)”, J Appl Clin Med Phys. 2013; 14(5): 13–24.
29. William Neil Duggar, Alex Nguyen, Jason Stanford, et al., “Modeling treatment couches in the Pinnacle treatment planning system: Especially important for arc therapy”, Med Dosim. Spring 2016;41(1):34-41.
30. M Geurts, J Gonzalez, P Serrano-Ojeda, “Longitudinal study using a diode phantom for helical tomotherapy IMRT QA”, Med Phys. 2009;36(11):4977-83.
31. James L Bedford, Young K Lee, Philip Wai, “Evaluation of the Delta4 phantom for IMRT and VMAT verification”, Phys Med Biol. 2009;54(9):N167-76.
32. Vladimir Feygelman, Kenneth Forster, Daniel Opp, “Evaluation of a biplanar diode array dosimeter for quality assurance of step-and-shoot IMRT”, J Appl Clin Med Phys. 2009;10(4):64-78.
33. Varatharaj Chandraraj, Sotirios Stathakis, Ravikumar Manickam, “Comparison of four commercial devices for RapidArc and sliding window IMRT QA”, J Appl Clin Med Phys. 2011;12(2):3367.
34. Lukasz Szczurek, Robert Juszkat, Jolanta Szczurek, et al., “Pre-treatment 2D and 3D dosimetric verification of volumetric arc therapy. A correlation study between gamma index passing rate and clinical dose volume histogram”, PLoS One. 2019;14(8):e0221086.
35. Jinling Yi, Ce Han, Xiaomin Zheng, et al., “Individual volume‐based 3D gamma indices for pretreatment VMAT QA”, J Appl Clin Med Phys. 2017; 18(3): 28–36.
36. Nesrin Dogan, Ivaylo Mihaylov, Yan Wu, et al., “Monte Carlo dose verification of prostate patients treated with simultaneous integrated boost intensity modulated radiation therapy”, Radiat Oncol. 2009;4:18.
37. Ellen E Wilcox, George M Daskalov, George Pavlonnis 3rd, et al., “Dosimetric verification of intensity modulated radiation therapy of 172 patients treated for various disease sites: comparison of EBT film dosimetry, ion chamber measurements, and independent MU calculations”, Med Dosim. Winter 2008;33(4):303-9.
38. M Hussein, C H Clark, A Nisbet, “Challenges in calculation of the gamma index in radiotherapy - Towards good practice”, Phys Med. 2017;36:1-11.
39. Shinichi Nakayama, Hajime Monzen, Yuuichi Oonishi, et al., “A novel method for dose distribution registration using fiducial marks made by a megavoltage beam in film dosimetry for intensity-modulated radiation therapy quality assurance”, Phys Med. 2015;31(4):414-9.
40. Stewart J Becker, Wes Culberson, Ryan Flynn, “Collision indicator charts for gantry-couch position combinations for Siemens ONCOR and Elekta Infinity linacs”, J Appl Clin Med Phys. 2013;14(5):278-83.
41. M S Muthuswamy, “A method of beam-couch intersection detection”, Med Phys. 1999;26(2):229-35.
42. Sandra C Vieira, Robert S J P Kaatee, Maarten L P Dirkx, et al., “Two-dimensional measurement of photon beam attenuation by the treatment couch and immobilization devices using an electronic portal imaging device”, Med Phys. 2003;30(11):2981-7.
43. Andrew H Buckle, “An algorithm for detection of couch-beam intersection”, Med Dosim. 2005;30(2):65-8.
44. 鄭因絢，林坤生，何志偉等，”瓦里安碳纖維治療床之衰減及射束與治療床的幾何關係”，放射治療與腫瘤學 2006；13(1):47 – 56。