Some chemotherapy drugs contain a high Z element in their structure that can be used for tumour dose enhancement in radiotherapy. In the present study, dose enhancement factors (DEFs) by cisplatin and titanocene dichloride agents in brachytherapy were quantified based on Monte Carlo simulation. Six photon emitting brachytherapy sources were simulated and their dose rate constant and radial dose function were determined and compared with published data. Dose enhancement factor was obtained for 1, 3 and 5 % concentrations of cisplatin and titanocene dichloride chemotherapy agents in a tumour, in soft tissue phantom. The results of the dose rate constant and radial dose function showed good agreement with published data. Our results have shown that depending on the type of chemotherapy agent and brachytherapy source, DEF increases with increasing chemotherapy drug concentration. The maximum in-tumour averaged DEF for cisplatin and titanocene dichloride are 4.13 and 1.48, respectively, reached with 5 % concentrations of the agents, and 125I source. Dose enhancement factor is considerably higher for both chemotherapy agents with 125I, 103Pd and 169Yb sources, compared to 192Ir, 198Au and 60Co sources. At similar concentrations, dose enhancement for cisplatin is higher compared with titanocene dichloride. Based on the results of this study, combination of brachytherapy and chemotherapy with agents containing a high Z element resulted in higher radiation dose to the tumour. Therefore, concurrent use of chemotherapy and brachytherapy with high atomic number drugs can have the potential benefits of dose enhancement. However, more preclinical evaluations in this area are necessary before clinical application of this method.

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