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一种描述无均整器光子束特性的方法
符贵山, 王谦, 陈佳赟, 张可, 闫玲玲, 戴建荣
国家癌症中心/中国医学科学院北京协和医学院肿瘤医院放疗科,北京 100021;
A method of describing the characteristics of flattening filter-free photon beam
Fu Guishan, Wang qian, Chen Jiayun, Zhang Ke, Yan Lingling, Dai Jianrong
Department of Radiation Oncology,National Cancer Center/Cancer Hospital,Chinese Academy of Medical Sciences,Peking Union Medical College,Beijing 100021,China;
Abstract： Objective To establish a novel method of describing the off-axis ratio (OAR) characteristics of the flattening filter-free (FFF) beam. Methods The OAR curves at a depth of 1.5,5,10 and 20 cm were measured for Varian Edge,Elekta VersaHD and Tomotherapy using the water tank. The second derivatives of the OAR in the positive and negative directions were calculated. The center of the line connecting the maximum and minimum second derivatives was defined as the field edge. The distance between the left and right field edges was defined as the dosimetric field size. The OAR curve within the 80% of dosimetric field size was fitted using the gaussian function and the fitting parameters were adopted to describe the shape of OAR. Results The calculated field size error was less than 0.11 cm and the central axis position error was less than 0.05 cm. The fitting correlation coefficient was greater than 0.998.The fitting maximum error of OAR curve did not significantly alter with the depth, whereas slightly increased over the increased field size. The maximum error for a field size of 10,20,30 and 40 cm was 0.49%,0.67%,1.25% and 2.52%,respectively. Conclusions A method which can independently and accurately describe the OAR characteristics of FFF photon beam is established for the first time,which can calculate the field size of FFF beam and fit the OAR curve of FFF beam using the gaussian function.
Fu Guishan,Wang qian,Chen Jiayun et al. A method of describing the characteristics of flattening filter-free photon beam[J]. Chinese Journal of Radiation Oncology, 2019, 28(1): 52-56.
[1] Brien P,Gillies B,Schwartz M,et al. Radiosurgery with unflattened 6-MV photon beams[J].Med Phys, 2013,18(3):519-521. [2] Fu WH,Dai JR,Hu YM,et al. Delivery time comparison for intensity-modulated radiation therapy with/without flattening filter:a planning study[J].Phys Med Biol,2004,49(8):1535-1547. [3] Cashmore J,The characterization of unflattened photon beams from a 6 MV linear accelerator[J].Phys Med Biol,2008,53(7):1933-1946.DOI:10.1088/0031-9155/53/7/009. [4] Georg D,Knöös T,McClean B.Current status and future perspective of flattening filter free photon beams[J].Med Phys,2011,38(3):1280-1293. [5] Stevens SW,Rosser KE,Bedford JL.A 4 MV flattening filter-free beam:commissioning and application to conformal therapy and volumetric modulated arc therapy[J].Phys Med Biol,2011,56(13):3809-3824.DOI:10.1088/0031-9155/56/13/005. [6] Fu GS,Li MH,Song YX,et al. A dosimetric evaluation of flattening filter-free volumetric modulated arc therapy in nasopharyngeal carcinoma[J].J Med Phys,2014,39(3):150-155.DOI:10.4103/0971-6203.139003. [7] Murray LJ,Thompson CM,Lilley J,et al. Radiation-induced second primary cancer risks from modern external beam radiotherapy for early prostate cancer:impact of stereotactic ablative radiotherapy (SABR),volumetric modulated arc therapy (VMAT) and flattening filter free (FFF) radiotherapy[J].Phys Med Biol,2015,60(3):1237-1257. [8] Pönisch F,Titt U,Vassiliev O,et al. Properties of unflattened photon beams shaped by a multileaf collimator[J].Med Phys,2006,33(6):1738-1746. [9] Pichandi A,Kadirampatti M, Amalraj J,et al. Analysis of physical parameters and determination of inflection point for Flattening Filter Free beams in medical linear accelerator[J].Rep Pract Oncol Radiother,2014,19(5):322-331.DOI:10.1016/j.rpor.2014.01.004. [10] Fogliata A.Definition of parameters for quality assurance of flattening filter free (FFF) photon beams in radiation therapy[J].Med Phys,2012,39(10):6455-6464.DOI:10.1118/1.4754799. [11] Fogliata A,Fleckenstein J,Schneider F,et al. Flattening filter free beams from TrueBeam and Versa HD units:Evaluation of the parameters for quality assurance. Med Phys[J].2016,43(1):205.DOI:10.1118/1.4938060. [12] Klein E,Hanley J,Bayouth J,et al. Task Group 142 report:Quality assurance of medical accelerators[J].Med. Phys,2009(36):4197-212. [13] Balog J,Soisson E.Helical Tomotherapy quality assurance[J].Int J Radiat Oncol Biol Phys,2008,71(1 Suppl):S113-117.DOI:10.1016/j.ijrobp.2007.10.001.
2019, Vol. 28 
