doi:10.1016/j.ijrobp.2006.09.057 PHYSICS CONTRIBUTION RETINOBLASTOMA— COMPARATIVE ANALYSIS OF EXTERNAL RADIOTHERAPY TECHNIQUES, INCLUDING AN IMRT TECHNIQUE MÁRCIO LEMBERG REISNER, M.D.,* CÉLIA MARIA PAIS VIÉGAS, M.D., M.SC., PH.D., † RACHELE ZANCHET GRAZZIOTIN, M.D., † DELANO VALDIVINO SANTOS BATISTA, M.S., ‡ TÚLIO MENESES CARNEIRO, M.D., CARLOS MANOEL MENDONÇA DE ARAÚJO, M.D., PH.D., † AND EDSON MARCHIORI, M.D., PH.D. § Departments of *Radiation Oncology and § Department of Radiology, Hospital Universitário Clementino Fraga Filho, Universidade Federal do Rio de Janeiro; † Department of Radiation Oncology and ‡ Division of Medical Physics, Department of Radiation Oncology, Instituto Nacional de Câncer, Rio de Janeiro, Brazil Purpose: To compare the numerous external radiotherapy (RT) techniques for the treatment of retinoblas- toma, as well as an intensity-modulated RT (IMRT) technique. The latter was elaborated to evaluate the potential dose reduction in the surrounding tissue, as well as the potential avoidance of subdosage in the ora serrata retinae. Methods and Materials: A 2-year-old patient with unilateral retinoblastoma underwent CT. With the aid of an ophthalmologist, the ocular structures were delimited, and 13 techniques described in published reports were reproduced on three-dimensional planning software and identified according to their authors. A technique with four noncoplanar fields using IMRT was also elaborated. These techniques were compared according to the dose to the ora serrata retinae, lens, orbit (volume that received a dose of >20 Gy), vitreous, optic nerve, lacrimal gland (volume that received a dose of >34 Gy), and cornea and according to their ease of reproducibility. Results: The techniques that attained the therapeutic dose to the ora serrata retinae were the IMRT technique and the techniques of Haye, Cassady, Cormack, and al-Beteri. The Cormack technique had the lowest volume that received a dose of >20 Gy in the orbit, followed by the IMRT technique. The IMRT technique also achieved the lowest volume that received a dose of >34 Gy (14%) in the lacrimal gland. The Abramson/McCormick/Blach, Cassady, Reese, and Schipper techniques were the easiest to reproduce and the Chin the most complex. Conclusion: Retinoblastoma treatment with IMRT has an advantage over the other techniques, because it allows for the greatest reduction of dose to the orbit and lacrimal gland, while maintaining the therapeutic dose to the ora serrata retinae and vitreous. © 2007 Elsevier Inc. Retinoblastoma, External beam radiotherapy, Intensity-modulated radiotherapy, Planning comparison, Orbit deformities. INTRODUCTION Retinoblastoma is the most common intraocular malignant tumor of early childhood. It is also the second most common in every age group, after choroidal melanoma (1). Its inci- dence is rare, ranging from 1 in every 14,000 born alive to 1 in every 34,000, and representing only 1% of all pediatric tumors (2, 3). Despite the use of new treatment options, such as photo- coagulation (4–7), cryotherapy (8, 9), plaque therapy (10– 15), new chemotherapy combinations (16 –19), and even thermochemotherapy (20, 21), external beam radiotherapy (RT) has had an important role and is still one of the most effective therapies. The proximity between the retina and the other structures of the visual system, which are sensitive to radiation, poses a challenge for RT planning. The lens is located 1–2 mm anterior to the ora serrata retinae and has a tolerance dose of 12 Gy when conventionally fractionated treatments are pre- scribed (22, 23). Because the retina must receive about Reprint requests to: Márcio Lemberg Reisner, M.D., Rua Kobe 60, Barra da Tijuca, Rio de Janeiro, RJ, Brazil CEP 22631-410. Tel: (+55) 21-3325-6544; Fax: (+55) 21-3325-6482; E-mail: mreisner@ uol.com.br M. L. Reisner, R. Z. Grazzition, and T. M. Carneiro were formerly Residents at the Department of Radiation Oncology, Instituto Nacional de Câncer, Rio de Janeiro, Brazil. T.M. Car- neiro, M.D., is now at the Department of Radiation Oncology, Hospital Aristides Maltes, Salvador, Brazil. Conflict of interest: none. Acknowledgments—We thank the Instituto Nacional de Câncer, Salyk, and Simone Reisner for their support. Received May 8, 2006, and in revised form Sept 20, 2006. Accepted for publication Sept 21, 2006. Int. J. Radiation Oncology Biol. Phys., Vol. 67, No. 3, pp. 933–941, 2007 Copyright © 2007 Elsevier Inc. Printed in the USA. All rights reserved 0360-3016/07/$–see front matter 933