91 patients aged 15 to 40 years with stages I and II classical Hodgkin Lymphoma treated with proton therapy (n=48) or photon radiotherapy (n=43) were reviewed in this study. 12 patients experienced progression including 4 occurred out-of-field, 2 occurred in-field, and 6 experienced both in- and out-of-field. This study reported no significant difference in 2-year PFS among adolescent and young adult (AYA) patients by radiotherapy dose received (≥ 30 Gy, 91%; < 30 Gy, 86%; P = .82), nor by radiotherapy modalities (proton, 94%; photon, 83%; P = .07). However, the authors recommend the use of proton therapy in AYA patients for whom it provides a clear dosimetric benefit.