Analytical expressions for Diffuse Optical Tomography are generally limited to simple geometries such as a diffusive slab, a sphere or a cylinder. Imaging of tissues however involves solutions for diffuse media with complex boundaries, in which case the use of numerical methods is directed. Herein we consider analytical solutions of the diffusion equation for complex boundaries based on the Kirchhoff approximation, as a time-efficient surrogate of numerical methods. We examine the performance of the approximation as a function of the shape and size of the outer boundary assuming a compressed breast geometry and demonstrate that the accuracy of the calculation is not reduced compared to numerical approaches.