بررسی عوامل اثرگذار بر طیف انرژی فوتون دستگاه شتاب‌دهنده‌ی خطی MV 18 واریان مدل C/D2100

نویسندگان

دانشگاه بیرجند

10.22052/8.1.2

چکیده

رادیوتراپی یکی از روش‌های درمانی پرکاربرد در درمان سرطان می‌باشد. با توجه به وابستگی مستقیم نتایج محاسبات دز به انرژی باریکه، شناخت دقیق از طیف انـرژی فوتون دستگـاه‌های شتاب‌دهنـده‌ی خطی درمـانی ضروری است. در این مطالعه دستگـاه شتاب‌دهنـده‌ی خطی واریان مدلC/D 2100، با انرژی فوتون MV 18، با استفاده از کد مونت‌کارلوی MCNPX 2.6.0 شبیه‌سازی شده است. سپس با استفاده از نتایج تجربی مقادیر بهینه‌ی انرژی و پهنای باریکه‌ی الکترونی به‌ترتیبMeV  5/18 و cm 14/0 محاسبه شد. در ادامه چگونگی تأثیر عمق فانتوم، فاصله‌ی چشمه تا سطح فانتوم، انداز‌ه‌ی میدان، هندسه اجزاء تشکیل‌دهنده سر شتاب‌دهنده و جنس فیلتر مسطح‌کننده بر طیف فوتون این دستگاه مورد بررسی قرار گرفت. نتایج نشان داد که با افزایش عمق درون فانتوم و فاصله‌ی چشمه تا سطح، در انرژی‌های بالا، فراوانی‌ها در طیف فوتون به‌صورت نمایی کاهش می‌یابد. همچنین تغییر جنس فیلتر مسطح‌کننده با توجه به عدد اتمی آن سبب تغییر در فراوانی طیف فوتون می‌شود به‌طوری که تغییر جنس فیلتر از آهن به آلومینیوم به دلیل کاهش سطح مقطع جذب فوتون، فراوانی طیف فوتون را 6/31% افزایش داد. همچنین هریک از اجزاء سر شتاب‌دهنده به دلیل جنس و هندسه خاص تأثیر متفاوتی بر طیف فوتون دارد به‌طوری که کلیماتور اولیه بیشترین و MLC کمترین تأثیر را بر میانگین انرژی نشان دادند. افزایش اندازه‌ میدان از cm2‌ 5⨯5 به cm2‌40⨯40 به دلیل پراکندگی از کلیماتور و فانتوم باعث افزایش فراوانی طیف فوتون به میزان 3/28% شد.

کلیدواژه‌ها

عنوان مقاله [English]

Investigations of parameters affecting the photon energy spectra of an 18 MV Varian 2100C/D linear accelerator

نویسندگان [English]

  • samira razghandi
  • Keyhandokht Karimi Shahri
  • Mohammad Mahdi Firoozabadi
چکیده [English]

Radiotherapy using linear accelerators is known as an effective modality for cancer treatment. The photons energy of treatment beams significantly affect the dose distribution. Therefore, it is important to accurately evaluate the photon energy spectra. In this study, MCNPX Monte Carlo code (version 2.6.0) was used to simulate an 18 MV photon beam of a Varian 2100C/D linear accelerator. By matching computed and measured percent depth and profile doses, the optimum values of mean energy and full width at half maximum (FWHM) of the radial distribution of beam were found to be 18.5 MeV and 0.14 cm, respectively. The simulation was also used to investigate the impact of parameters, such as depth, source-to-surface distances (SSD), field size, flattening filter material and geometry of treatment head components on the photon spectra. The results showed that the photon spectra were decreased as an exponential function by increasing depth in phantom and SSD. Results also indicated that the photon spectra depend on the Z of the flattening filter materials. Photon spectra for low-Z materials, such as Al, were significantly increased (up to 31.6%) in comparison with using the original material due to the decrease in the photon absorption cross-section. Each component of the linac head has a different effect on the photon spectrum due to its material and special shape. Based on the obtained results, primary collimator and MLC have, respectively, maximum and minimum effect on the mean energy of photons. Moreover, photon spectra were changed considerably with field size. Change in the photon spectra up to 28.3% was obtained when using 40 × 40 cm2 field size compared to the 5 × 5 cm2 because of the increased scatter from the collimator and the phantom.

کلیدواژه‌ها [English]

  • MCNPX Monte Carlo
  • Varian linear accelerator
  • Photon spectra

مراجع

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