Purpose: Accurate patient-specific absorbed dose estimation is important for radionuclide therapy, but its routine clinical use is limited by the high computational cost of full Monte Carlo simulations. Voxel S value (VSV)-based convolution methods are efficient, but their accuracy may decrease in heterogeneous media, especially for short-range electrons. This study presents a practical hybrid dose calculation framework for I-131 therapy to balance accuracy and efficiency. Methods: In the proposed framework, electron transport was simulated using Monte Carlo methods, whereas photon dose was calculated by convolution with pre-calculated VSV kernels. Total absorbed dose was obtained by voxel-wise summation of electron and photon contributions. Photon VSV accuracy was first validated against MIRD Pamphlet No. 17 data. The hybrid method was then evaluated in heterogeneous phantoms with different material densities and in a clinical post-therapy SPECT/CT dataset. Results: The photon VSV agreed well with the MIRD Pamphlet No. 17 reference data. In heterogeneous media, the hybrid method improved dose estimation in low-density regions compared with the conventional VSV approach and showed close agreement with full Monte Carlo simulation. In the patient study, computation time was reduced by about sevenfold while improved dosimetric accuracy was maintained in regions where the conventional VSV method showed larger deviations. Conclusions: The proposed hybrid framework provides an efficient strategy for voxel-level dose estimation in I-131 therapy, improving accuracy in heterogeneous media while substantially reducing computation time. It may support personalized internal dosimetry when integrated with quantitative imaging and time-integrated activity estimation.