This paper investigates the ability of Polarimetric SAR Tomography (PolTomSAR), performed at P-band, to retrieve Above-Ground-Biomass (AGB) over dense tropical forests. PolTomSAR techniques allow an accurate estimation of the backscattered power distribution in the vertical direction. A first tomographic biomass estimator, relating AGB to the backscattered power in the higher part of the vegetation is analyzed through a Random-Volume-over-Ground (RVoG) analytical description of a forest profile. A PolTom-RVoG derivation of the power backscattered by the upper vegetation layer is performed as an integration of the reflectivity along the volume vertical structure. This integration is carried out over a domain fixed by TomSAR resolution and tree height, leading to a novel and accurate ABG estimator. The proposed techniques are applied to P-Band data acquired over the Paracou data site on French Guiana in 2009, in the frame of the European Space Agency (ESA) TropiSAR campaign.