  Massive star formation occurs in the interior of giant molecular clouds (GMC)
and proceeds through many stages. In this work, we focus on massive young
stellar objects (MYSOs) and Ultra-Compact HII regions (UCHII), where the former
are enshrouded in dense envelopes of dust and gas, which the latter have begun
dispersing. By selecting a complete sample of MYSOs and UCHII from the Red MSX
Source (RMS) survey data base, we combine Planck and IRAS data and build their
Spectral Energy Distributions (SEDs). With these, we estimate the physical
properties (dust temperatures, mass, luminosity) of the sample. Because the RMS
database provides unique solar distances, it also allows investigating the
instantaneous Star Formation Efficiency (SFE) as a function of Galactocentric
radius. We find that the SFE increase between 2 and 4.5 kpc, where it reaches a
peak, likely in correspondence of the accumulation of molecular material at the
end of the Galactic bar. It then stays approximately constant up to 9 kpc,
after which it linearly declines, in agreement with predictions from
extragalactic studies. This behavior suggests the presence of a significant
amount of undetected molecular gas at R$_G$ $>$ 8 kpc. Finally we present
diagnostic colors that can be used to identify sites of massive star formation.
