The transformative effect of oxygen on conventional x-ray radiotherapy has long been known, with the presence of molecular oxygen boosting treatment efficacy multi-fold. This effect is present too in charged particle therapy, but the boosting potential decreases with increasing linear energy transfer of the incident radiation. With particle modalities such as proton therapy becoming common-place and emerging technologies like carbon-ion therapy on the horizon, it is pertinent to address the additive dose boost gained from molecular oxygen with high energy radiation, and the implications of this for dose planning. This work establishes an empirical model for oxygen enhancement across the radiotherapy energy spectrum, and discusses implications of this for therapy.