Additive manufacturing (AM) is emerging as an effective manufacturing technology that benefits the medical field with its ease of quickly realizing complex designs. Brachytherapy is a process to cure cancer patients through a high dose rate of gamma radiation. This work aimed at AM-based development of multi-channel vaginal and penile brachytherapy applicators for selectively treating cancer cells in a direction sideways to the applicator rather than the uniform radiation dose possible around the conventional applicator used in cancer treatment. An analytical model was proposed to predict the maximum surface temperature on applicators during Ir-192 source radiation. Also, the predicted values of multi-physics-based finite element method simulation were experimentally validated using a thermal imaging camera. Thermal imaging is a non-contact measurement that is found superior to the brachytherapy scale to position radioactive sources inside the applicator. Experimentally examined multi-channel applicator shows dosimetry advantage in effective radiation control and shows promise of curing cancerous cells with minimal effects on normal cells.