[en] Aim: This work presents evaluations of the absorbed dose by 'in vitro' blood cultures when mixed with ¹⁵³Sm solutions of different concentrations. Although ¹⁵³Sm is used as radiopharmaceutical mainly due to its beta emission, which is short-range radiation, it also emits gamma radiation which has a longer-range penetration. Therefore it turns to be a difficult task to determine the absorbed dose by small samples where the infinite approximation is no longer valid. Materials and Methods: MCNP-4C (Monte Carlo N - Particle transport code) has been used to perform the evaluations. It is not a deterministic code that calculates the value of a specific quantity solving the physical equations involved in the problem, but a virtual experiment where the events related to the problems are simulated and the concerned quantities are tallied. MCNP also stands out by its possibilities to specify geometrically any problem. However, these features, among others, turns MCNP in a time consuming code. The simulated problem consists of a cylindrical plastic tube with 1.5 cm internal diameter and 0.1cm thickness. It also has 2.0 cm height conic bottom end, so that the represented sample has 4.0 ml ( consisted by 1 ml of blood and 3 ml culture medium). To evaluate the energy deposition in the blood culture in each ¹⁵³Sm decay, the problem has been divided in 3 steps to account to the β- emissions (which has a continuum spectrum), gammas and conversion and Auger electrons emissions. Afterwards each emission contribution was weighted and summed to present the final value. Besides this radiation 'fragmentation', simulations were performed for many different amounts of ¹⁵³Sm solution added to the sample. These amounts cover a range from 1μl to 0.5 ml. Results: The average energy per disintegration of ¹⁵³Sm is 331 keV [1]. Gammas account for 63 keV and β-, conversion and Auger electrons account for 268 keV. The simulations performed showed an average energy deposition of 260 keV/Bq.s that represents 79 % of available energy. The axial dose distribution mapping shows also a great difference between gamma radiation and charged radiation deposition patterns. While the gamma radiation energy deposition is clearly sensitive to the holder shape, charged radiation shows this dependence only in the vicinity of the sample itself. However, as the charged radiation accounts for almost all the energy deposited in the sample, the dose distribution over the sample can be regarded as homogeneous, although its value be dependent of the amount of ¹⁵³Sm solution added. Conclusion: This work shows that an infinite medium approach to estimate the amount of deposited energy is not valid to systems of the order of mm-cm. It supplies a way to provide a precise value for the absorbed dose and also its gradient distribution