Presentation of a matrix-based method to calculate dose distribution in brachytherapy with photon-emitting sources

The report of the task group number 43(TG-43) of AAPM has been known as the most common method to obtain the dose distribution around brachytherapy sources. The error caused by independent obtaining and rounding and combinational error caused by algebraic operations of each TG-43 dosimetry parameters increase the total error in the calculation of the dose distribution around the brachytherapy sources. The aim of the present study is to present and evaluate a matrix-based approach for simplifying and reducing calculation errors.

In this study, the simulation method with MCNPX code was used to obtain the dose distribution. Four sources were simulated, and the dose matrix around these sources was obtained. Finally, the dose distribution obtained from the matrix-based method was compared with the dose distribution obtained from the method of TG-43 report.

There is little difference between the values obtained from the two methods in some points. Absolute mean differences between the values obtained by these two methods were 1.4% for the ⁶⁰Co, 3.52% for the ¹³⁷Cs, 2.67% for the ¹⁹²Ir, and 2.42% for the ¹⁰³Pd sources. The advantage of the matrix-based method is its simple computing process and less computation time.

Considering that the comparison of brachytherapy sources is not raised in calculations of treatment planning systems and also considering the more uncertainty in the calculation of the dose distribution in TG-43 method, it is recommended that dose distribution obtained from matrix-based method be used as input for treatment planning systems.