This study from the MGH group analyzed brain volume change in two matched groups of patients with WHO grade 2-3 gliomas treated with either PRT (n = 17) or XRT (n = 17). Brain volume change was measured as ventricular volume expansion in the tumor free hemisphere (contralateral to RT target) as a proxy indicator of brain volume loss. This study reported significant ventricular volume increases in the contra-lesional hemisphere in both groups at two years post-RT, with greater volume change observed in XRT (26.55%) vs. PRT (12.03%) (p = 0.048). This study suggests progressive brain volume loss following cranial irradiation, with greater severity after XRT vs. PRT. Radiation-induced brain volume loss appears to be associated with measurable cognitive changes on an individual level.