Sains Malaysiana 51(4)(2022): 1229-1244

http://doi.org/10.17576/jsm-2022-5104-22

The Occurred Error in Microdosimetry Calculations while Using Water Instead of the Body Organs in Proton Therapy and a New Formula for an Estimate of the Statistical Uncertainty of Microdosimetric Quantities

(Ralat Berlaku dalam Pengiraan Mikrodosimetri semasa Menggunakan Air Bukan Organ Badan dalam Terapi Proton dan Formula Baharu untuk Anggaran Ketidakpastian Statistik Kuantiti Mikrodosimetrik)

SOMAYEH JAHANFAR & HOSSEIN TAVAKOLI-ANBARAN^*

Faculty of Physics and Nuclear Engineering, Shahrood University of Technology, Shahrood, Iran

Diserahkan: 4 Jun 2021/Diterima: 26 Ogos 2021

Abstract

In many experimental and simulation researches, water phantom is used instead of most body organs. Therefore, in this study, we replaced the water phantom instead of some organs to calculate its effect on the proton stopping-power, and range and the consequence of deposited energy and microdosimetric spectra in small sites. Some organs such as the spleen, thyroid, pancreas, prostate, testis, and ovaries are considered. We calculated the proton stopping-power in these organs using the SRIM code. Then using these results, we wrote a program in the programming language of Fortran and computed the proton range and deposited energy in two sites of 1 and 100 micron. Also, using the Geant4-10-4 code, we simulated these sites and obtained microdosimetric spectra of protons at 1 and 5MeV energies. In order to compare different states, the frequency-mean lineal energy, dose-mean lineal energy, these statistical uncertainties and absorb dose in each case were calculated and reported. Also, we estimated the statistical uncertainty of quantities with a new formula. We observed that using water instead of the organs causes a significant error in the calculations of the range and the maximum relative difference percentage of 18% and 22% in deposited energy in 1 and 100 micron sites, respectively. These differences depend on the energy of the incident proton, organ, and size site. Also, this replacement changes microdosimetric spectra, the location, and intensity of the Bragg's peak. The percent difference of location and intensity of the Bragg's peak for water instead of the spleen is -8.66 and 13.42%, respectively. Therefore, using water instead of the body organs in microdosimetry calculations is not recommended.

Keywords: Body organs and water; microdosimetry; proton range and stopping power; proton therapy; statistical uncertainty

Abstrak

Dalam banyak penyelidikan uji kaji dan simulasi, fantom air digunakan sebagai ganti kebanyakan organ tubuh. Oleh itu, dalam kajian ini, kami menggantikan fantom air dan bukannya beberapa organ untuk menghitung kesannya pada daya berhenti proton dan julat serta akibat daripada tenaga dan spektrum mikrodosimetri yang tersimpan di lokasi kecil. Beberapa organ seperti limpa, tiroid, pankreas, prostat, testis dan ovari dipertimbangkan. Kami menghitung daya berhenti proton pada organ-organ ini menggunakan kod SRIM. Kemudian, menggunakan hasil ini, kami menulis sebuah program dalam bahasa pengaturcaraan Fortran dan menghitung julat proton dan menyimpan tenaga di dua lokasi antara 1 dan 100 mikron. Juga, menggunakan kod Geant4-10-4, kami mensimulasi lokasi ini dan memperoleh spektrum mikrodosimetri proton pada tenaga 1 dan 5MeV. Untuk membandingkan keadaan yang berlainan, tenaga linear frekuensi-min, tenaga garis lurus-dosis, ketidakpastian statistik ini dan penyerap dos dalam setiap kes dihitung dan dilaporkan. Kami juga menganggarkan ketidaktentuan statistik kuantiti dengan formula baru. Kami memerhatikan bahawa penggunaan air sebagai ganti organ telah menyebabkan ralat yang ketara dalam pengiraan julat dan peratusan perbezaan relatif maksimum 18% dan 22% tenaga yang tersimpan masing-masing di lokasi 1 dan 100 mikron. Perbezaan ini bergantung pada tenaga proton, organ dan ukuran saiz lokasi. Juga, penggantian ini mengubah spektrum mikrodosimetri, lokasi dan keamatan puncak Bragg. Perbezaan peratus lokasi dan keamatan puncak Bragg untuk air dan bukannya limpa masing-masing adalah -8.66 dan 13.42%. Oleh itu, penggunaan air bukan organ tubuh dalam pengiraan mikrodosimetri tidak digalakkan. 

Kata kunci: Julat proton dan daya berhenti; ketidaktentuan statistik; mikrodosimetri; organ badan dan air; terapi proton

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^*Pengarang untuk surat-menyurat; email: tavakoli.anbaran@gmail.com