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Brandy C. Hayden, BS; Timothy G. Murray, MD; Nicole Cicciarelli; Ingrid U. Scott, MD, MPH; Anastassia Alexandridou, MD; Eleut Hernandez, LAT; Xiaodong Wu, PhD; Arnold M. Markoe, MD; William Feuer, MS; Lilia Fulton, BA; Joan M. O'Brien, MD

Arch Ophthalmol. 2002;120:353-359.

Objective  To determine the in vivo efficacy of hyperfractionated external beam radiation therapy (EBRT) in comparison with standard daily EBRT in a murine model of heritable retinoblastoma.

Methods  Two hundred twenty eyes from 6-week-old simian virus-40 large T-antigen–positive mice were treated with a total dose of EBRT ranging from 10-76 Gy (1000 to 7600 rad). One hundred ten eyes underwent EBRT administered in 2.0-Gy (200-rad) fractions once per day. Forty-two eyes received hyperfractionated EBRT administered in 1.2-Gy (120-rad) fractions twice per day, while 48 eyes received EBRT twice daily in fractions of 5.0 Gy (500 rad). Twenty eyes served as untreated controls. All eyes were obtained for histopathologic examination and graded positive if any tumor was present.

Results  A dose-dependent inhibition of ocular tumor was observed for EBRT in these transgenic retinoblastoma mice. The tumor control dose for 50% of eyes (TCD₅₀) treated with 2.0 Gy fractions of EBRT was 45 Gy (4500 rad) when treatments were administered once daily. A significant increase in tumor control was observed when treatments were administered twice per day at fractions of 1.2 Gy, resulting in a TCD₅₀ of 33 Gy (3300 rad) (P = .003). A further increase in tumor control was observed when twice-daily EBRT was administered in 5.0 Gy fractions resulting in a TCD₅₀ of 28 Gy (2800 rad).

Conclusions  Hyperfractionated EBRT safely and effectively controls intraocular retinoblastoma in this transgenic animal model. Use of hyperfractionation allows for a reduction in total radiation delivered dose, while shortening the total treatment time.

Clinical Relevance  This treatment approach may be applicable in the management of pediatric retinoblastoma by maintaining excellent tumor control, while reducing treatment-associated complications.

From the Bascom Palmer Eye Institute, Department of Ophthalmology (Mss Hayden and Cicciarelli, Drs Murray, Scott, Alexandridou, and Markoe, and Messrs Hernandez and Feuer), and Department of Radiation/Oncology, Sylvester Comprehensive Cancer Center (Drs Murray, Wu, and Markoe), University of Miami, Miami, Fla; and Department of Ophthalmology, University of California, San Francisco (Ms Fulton and Dr O'Brien).

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