Comparison of the hypothetical (57)Co brachytherapy source with the (192)Ir source.
OBJECTIVE
The (57)Co radioisotope has recently been proposed as a hypothetical brachytherapy source due to its high specific activity, appropriate half-life (272 days) and medium energy photons (114.17 keV on average). In this study, Task Group No. 43 dosimetric parameters were calculated and reported for a hypothetical (57)Co source.


METHODS
A hypothetical (57)Co source was simulated in MCNPX, consisting of an active cylinder with 3.5 mm length and 0.6 mm radius encapsulated in a stainless steel capsule. Three photon energies were utilized (136 keV [10.68%], 122 keV [85.60%], 14 keV [9.16%]) for the (57)Co source. Air kerma strength, dose rate constant, radial dose function, anisotropy function, and isodose curves for the source were calculated and compared to the corresponding data for a (192)Ir source.


RESULTS
The results are presented as tables and figures. Air kerma strength per 1 mCi activity for the (57)Co source was 0.46 cGyh(-1) cm 2 mCi(-1). The dose rate constant for the (57)Co source was determined to be 1.215 cGyh(-1)U(-1). The radial dose function for the (57)Co source has an increasing trend due to multiple scattering of low energy photons. The anisotropy function for the (57)Co source at various distances from the source is more isotropic than the (192)Ir source.


CONCLUSIONS
The (57)Co source has advantages over (192)Ir due to its lower energy photons, longer half-life, higher dose rate constant and more isotropic anisotropic function. However, the (192)Ir source has a higher initial air kerma strength and more uniform radial dose function. These properties make (57)Co a suitable source for use in brachytherapy applications.
Biomedical Engineering and Medical Physics Department, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Mohammad Taghi Bahreyni
MT
Toossi
Biomedical Engineering and Medical Physics Department, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Mahdi
M
Ghorbani
Biomedical Engineering and Medical Physics Department, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Atefeh
A
Rostami
Faculty of Medicine, North Khorasan University of Medical Sciences, Bojnurd, Iran.
Mohsen
M
Khosroabadi
Medical Physics and Medical Engineering Department, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
Sara
S
Khademi
Comprehensive Cancer Centers of Nevada, Las Vegas, Nevada, USA.
Courtney
C
Knaup
192Ir; 57Co; Monte Carlo simulation; TG-43 dosimetric parameters; hypothetical source
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