کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
8250625 | 1533397 | 2016 | 7 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
The influence of field size and off-axis distance on photoneutron spectra of the 18Â MVÂ Siemens Oncor linear accelerator beam
دانلود مقاله + سفارش ترجمه
دانلود مقاله ISI انگلیسی
رایگان برای ایرانیان
کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
فیزیک و نجوم
تشعشع
پیش نمایش صفحه اول مقاله
چکیده انگلیسی
At present, high energy electron linear accelerators (LINACs) producing photons with energies higher than 10Â MeV have a wide use in radiotherapy (RT). However, in these beams fast neutrons could be generated, which results in undesired contamination of the therapeutic beams. These neutrons affect the shielding requirements in RT rooms and also increase the out-of-field radiation dose to patients. The neutron flux becomes even more important when high numbers of monitor units are used, as in the intensity modulated radiotherapy. Herein, to evaluate the exposure of patients and medical personnel, it is important to determine the full radiation field correctly. A model of the dual photon beam medical LINAC, Siemens ONCOR, used at the University Hospital Centre of Osijek was built using the MCNP611 code. We tuned the model according to measured photon percentage depth dose curves and profiles. Only 18Â MV photon beams were modeled. The dependence of neutron dose equivalent and energy spectrum on field size and off-axis distance in the patient plane was analyzed. The neutron source strength (Q) defined as a number of neutrons coming from the head of the treatment unit per x-ray dose (Gy) delivered at the isocenter was calculated and found to be 1.12Â ÃÂ 1012 neutrons per photon Gy at isocenter. The simulation showed that the neutron flux increases with increasing field size but field size has almost no effect on the shape of neutron dose profiles. The calculated neutron dose equivalent of different field sizes was between 1 and 3Â mSv per photon Gy at isocenter. The mean energy changed from 0.21Â MeV to 0.63Â MeV with collimator opening from 0Â ÃÂ 0Â cm2 to 40Â ÃÂ 40Â cm2. At the 50Â cm off-axis the change was less pronounced. According to the results, it is reasonable to conclude that the neutron dose equivalent to the patient is proportional to the photon beam-on time as suggested before. Since the beam-on time is much higher when advanced radiotherapy techniques are used to fulfill high conformity demands, this makes the neutron flux determination even more important. We also showed that the neutron energy in the patient plane significantly changes with field size. This can introduce significant uncertainty in dosimetry of neutrons due to strong dependence of the neutron detector response on the neutron energy in the interval 0.1-5Â MeV.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Radiation Measurements - Volume 93, October 2016, Pages 28-34
Journal: Radiation Measurements - Volume 93, October 2016, Pages 28-34
نویسندگان
Hrvoje BrkiÄ, Ana IvkoviÄ, Mladen KasabaÅ¡iÄ, Marina Poje Sovilj, Slaven JurkoviÄ, Damir Å timac, Otmar Rubin, Dario Faj,