Proton therapy has been increasing over the past several years, with several new treatment facilities being built in Europe, Japan and the United States. In this work, analytical and Monte Carlo tools were combined to model the passively scattered neurosurgery treatment beamline of the Harvard Cyclotron Laboratory (Cambridge, MA). The predicted three-dimensional dose distributions agree with actual measurements to within 0.1 mm for all quantities considered in central-axis depth-dose curve and to within 2.1 mm for all quantities considered in the absorbed dose cross-field profile. The predicted neutron dose equivalent per therapeutic absorbed dose, H/D, was calculated at various locations representing clinically significant anatomical sites. Under typical treatment conditions, the average ratio of predicted-to-measured H/D is 1.8 in the gonadal region (50 cm from isocentre) and 3.4 in the thyroid region (21 cm from isocentre). The global ratio of predicted-to-measured H/D is 2.6.