Objective
To determine the efficacy of low-dose "salvage" external beam radiationtherapy (EBRT) following failed subconjunctival carboplatin chemotherapy ina murine model of heritable retinoblastoma.
Methods
Eighty-four eyes from 8-week-old, simian virus 40, T-antigen–positivemice were treated with 6 serial subconjunctival carboplatin injections (100µg/25 µL). At 12 weeks of age, 64 eyes received EBRT for a totaldose of 480 (4.8 Gy), 1200 (12.0 Gy), 1560 (15.6 Gy), or 3000 (30.0 Gy) rad.Twenty eyes received no additional therapy following subconjunctival carboplatininjections. Ten eyes received a total dose EBRT of only 3000 rad. Eight eyesreceived subconjuctival injections of only an isotonic sodium chloride solution.Ten eyes served as untreated controls.
Main Outcome Measures
Eyes were enucleated at 20 weeks to assess the presence of tumor onhistopathological examination.
Results
Salvage therapy using low-dose EBRT was able to reestablish tumor controlin a dose-dependent manner. Increasing the EBRT dose to 3000 rad resultedin 100% tumor control. The dose-dependent curves were significantly differentbetween the treatment groups—EBRT alone vs salvage EBRT after receivingsubconjunctival carboplatin injections (P<.001).
Conclusion
Low-dose hyperfractionated salvage EBRT following failed primary subconjunctivalcarboplatin chemotherapy is efficacious in the treatment of retinoblastomain this animal model.
Clinical Relevance
Salvage EBRT using a reduced total radiation dose could be associatedwith a radiation-related treatment enhancement in pediatric retinoblastoma.