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We present an updated cosmic-ray mass composition analysis in the energyrange $10^{16.8}$ to $10^{18.3}$ eV from 334 air showers measured with theLOFAR radio telescope, and selected for minimal bias. In this energy range, theorigin of cosmic rays is expected to shift from galactic to extragalacticsources. The analysis is based on an improved method to infer the depth ofmaximum $X_{\rm max}$ of extensive air showers from radio measurements and airshower simulations.  We show results of the average and standard deviation of $X_{\rm max}$ versusprimary energy, and analyze the $X_{\rm max}$-dataset at distribution level toestimate the cosmic ray mass composition. Our approach uses an unbinned maximumlikelihood analysis, making use of existing parametrizations of $X_{\rmmax}$-distributions per element. The analysis has been repeated for three mainmodels of hadronic interactions.  Results are consistent with a significant light-mass fraction, at best fit$23$ to $39$ $\%$ protons plus helium, depending on the choice of hadronicinteraction model. The fraction of intermediate-mass nuclei dominates. Thisconfirms earlier results from LOFAR, with systematic uncertainties on $X_{\rmmax}$ now lowered to 7 to $9$ $\mathrm{g/cm^2}$.  We find agreement in mass composition compared to results from Pierre AugerObservatory, within statistical and systematic uncertainties. However, in linewith earlier LOFAR results, we find a slightly lower average $X_{\rm max}$. Thevalues are in tension with those found at Pierre Auger Observatory, but agreewith results from other cosmic ray observatories based in the Northernhemisphere.

Depth of shower maximum and mass composition of cosmic rays from 50 PeV to 2 EeV measured with the LOFAR radio telescope