Proton Radiotherapy Decreases Incidence of Radiation-Induced Second Malignant Neoplasms Compared to Photon Radiotherapy in Patients With Retinoblastoma.

Retinoblastoma is the most common primary intraocular neoplasm in children. Use of radiotherapy has decreased due to the incidence of second malignant neoplasms (SMNs). In our study, photon (n = 42) and proton (n = 66) radiotherapy cohorts had median follow-up of 28.7 and 18.2 years, respectively. The majority of patients (74%) had bilateral disease at diagnosis. Proton radiotherapy is associated with significantly lower cumulative incidence of in-field SMNs (0% vs. 11.1% at 15 years, p = 0.005), with three additional cases occurring > 20 years after photon radiotherapy. These findings suggest that when radiotherapy is indicated for patients with bilateral retinoblastoma, proton radiotherapy should be considered when feasible.