Calculation of air-kerma strength and dose rate constant for new BEBIG 60Co HDR brachytherapy source: an EGSnrc Monte Carlo study M. Anwarul Islam, Medical Physicist SQUARE Hospitals Ltd, Bangladesh anwar.amch@yahoo.com

1. Dr. Mir Md. Akramuzzaman 1 , G.A. Zakaria 2 , G.H. Hartmann 3 1 Department of Physics, Jahangirnagar University, Savar, Dhaka, Bangladesh. 2 Gummersbach Academic Teaching Hospital, University of Cologne, Germany. 3 Department of Medical Physics in Radiotherapy, German Cancer Research Center, Heidelberg, Germany. M. Anwarul Islam Department of Physics Jahangirnagar University Calculation of air-kerma strength and dose rate constant for new BEBIG 60 Co HDR brachytherapy source: an EGSnrc Monte Carlo study

4. Monte Carlo Procedure Filtering Apply physical/ statistical law/ theory Group of Random Events Analysis Apply Physical Law/theory Apply Boundary Condition Apply Statistical Law Apply Probability theory

9. BEBIG 60 Co HDR source models Real geometry of the source Model geometry of the source

10. Monte Carlo input of source model Sagittal Section Fig: Equal sagittal section for Monte Carlo source input

11. TG-43 Formalism General 2D formalism The general, two-dimensional ~2D dose-rate equation from the TG-43 protocol is retained , Where, = dose rate at the point (r, θ )

12. Fig: Coordinate system used for brachytherapy dosimetry calculations TG-43 Formalism

13. Using Formula for fluence calculation And finally, S k /A = 2 × K΄ air (d) × d 2 Where, is the total air-kerma at the distance, d and the unit is Gy/Photon is the photon fluence per unit energy and it’s unit MeV -1 cm -2 is the mass energy absorption coefficient and it’s unit cm 2 gm -1 E i is the energy spectrum and Δ E is the energy bin size The factor 1.602×10 -10 is required to convert K air (d) from MeV gm -1 into Gy S k /A is the air-kerma strength per unit source activity. The unit is μ Gym2h-1.Bq-1 or UBq-1 D = 100 cm according to the TG-43 formalism

15. Dose calculation formula The user-code DOSRZnrc is used to calculate, D photons where D photons is the total dose by photons S k /A is air-kerma strength per source activity into [U Bq-1] is the true dose rate per unit air-kerma strength for 60 Co source in [cGy h-1 U-1]

16. Phantom Model

17. Geometric Preview Window Calculated point

18. Tissue basis absorbed dose calculation Some body equivalent tissues (shows in table below) are simulated to investigate the relative absorbed dose with different distances in respective tissue phantom and also in vacuum phantom with 5 cm distance. Tissue basis density table 1.04 1.0 1.12 0.92 0.26 1.06 1.02 1.85 1.00 Density g/cm 3 Testese Soft tissue Muscle Adipose tissue Lung Blood Breast Com bone Water Tissue

19. Results Energy fluence vs. Spectrum

20. Calculated 60 Co fluence data (MeV-1 cm-2)

21. Calculated 60 Co fluence data (MeV-1 cm-2)

22. Calculated 60 Co fluence data (MeV-1 cm-2)

23. Air-kerma strength Article Air-kerma strength Per unit source activity (c Gy.cm 2 .h -1 .Bq -1 ) This work 3.035×10 -7 ±0.15% T. Palani Selvam et al.(2010), India 3.04×10 -7 ±0.05%

24. Dose Rate Constant Article Dose rate constant, Λ (cGy h -1 U -1 ) This work 1.097 ± 0.12% T. Palani Selvam et al.(2010), India 1.086 ± 0.06%

25. Tissue basis relative absorbed dose

26. Relative absorbed dose with distance Lung Comp. bone