Intensity-modulated radiation therapy for children with intraocular retinoblastoma: Potential sparing of the bony orbit

Aims: We have evaluated the potential for intensity-modulated radiation therapy (IMRT) to reduce dose to surrounding normal tissues in children with retinoblastoma confined to the globe of the eye. Materials and methods: Treatment planning computed tomography (CT) scans from five children were used for comparison of four radiotherapy techniques to treat the eye. IMRT, conformal, anterior-lateral photon and en face electron plans were generated using the Corvus (NOMOS) and PLUNC treatment planning systems. Doses to surrounding critical structures were compared after normalisation of target coverage. Results: The IMRT treatment technique allowed the greatest sparing of the surrounding bony orbit, with an average of 60% of the ipsilateral bony orbit treated above 20 Gy and 48% treated above 24 Gy when 45 Gy is prescribed to the globe. IMRT techniques reduced dose to the surrounding bony orbit by more than one-third compared with anterior-lateral photon and electron techniques, and by 23% compared with conformal techniques. The application of IMRT also reduced dose to other surrounding normal tissues, including the temporal lobe and contralateral orbit. Conclusion: IMRT shows potential for protecting normal tissues in patients requiring external beam radiation therapy for retinoblastoma.