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Study of tissue heterogeneity in the received dose of rat cervical spinal cord region in homogenous phantom and real sample by thermoluminescence dosimetry

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Objectives: To investigate the effect of heterogeneity in the cervical spinal cord region of rat on the received dose of orthovoltage x- ray a homogeneous phantom was designed. Methods: Using liquid nitrogen,a frozen sample of the animal was produced suitable for simulating living tissues especially the cervical spinal cord region . For the reason of reproducibility, a jig was used .Dosimeter used was a rod shaped thermoluminesance dosimetry (TLD) chips with the diameter of 1mm and length of 6mm. TLD was used as the equivalent for the spinal cord both in the formed spinal canal of the homogeneous phantom and frozen sample in the cervical region. The x-ray generating device was a radiotherapeutic x-ray system with relative stability of <3% and filament current intensity of 19mA in potential of 200 Kv (HVL= 1.5mmCu). The reader device was a Hardshow TLD reader model 3500 with the heating accuracy of ±1°C. We took advantage of various dosimetry protocols including American association of physical medicine (AAPM) report TG-61,2001, dosimetry protocol in radiobiology by zotelief et al, 2001, NSC-report 3, TR-IAEA, 277 protocol and also reports by ICRU-23, 24, 30, 48. Results: Statistical calculations using SPSS for the T-Test on the resulting doses in the confidence interval of 3.5% showed no significant difference between the two groups. Conclusion: In the normal fields in radiobiological issues and in the spectrum of orthovoltage energies used, a normal accuracy in calculations could be accepted. However, in the regions where there is no equilibrium in the charged particle and where microdosimetry is concerned the results are not to be crucially applied.


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