Retinoblastoma--comparative analysis of external radiotherapy techniques, including an IMRT technique.
OBJECTIVE
To compare the numerous external radiotherapy (RT) techniques for the treatment of retinoblastoma, 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
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 >or=20 Gy), vitreous, optic nerve, lacrimal gland (volume that received a dose of >or=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 >or=20 Gy in the orbit, followed by the IMRT technique. The IMRT technique also achieved the lowest volume that received a dose of >or=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.


CONCLUSIONS
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.
Reisner
Márcio Lemberg
ML
Department of Radiation Oncology, Hospital Universitário Clementino Fraga Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil. mreisner@uol.com.br
Viégas
Célia Maria Pais
CM
Grazziotin
Rachele Zanchet
RZ
Santos Batista
Delano Valdivino
DV
Carneiro
Túlio Meneses
TM
Mendonça de Araújo
Carlos Manoel
CM
Marchiori
Edson
E
D002675:Child, Preschool; D006801:Humans; D007765:Lacrimal Apparatus / Q000528:radiation effects; D007908:Lens, Crystalline / Q000528:radiation effects; D009900:Optic Nerve / Q000528:radiation effects; D011832:Radiation Injuries / Q000517:prevention & control; D011878:Radiotherapy / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D015203:Reproducibility of Results; D012160:Retina / Q000528:radiation effects; D019572:Retinal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D012175:Retinoblastoma / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D014057:Tomography, X-Ray Computed; D014822:Vitreous Body / Q000528:radiation effects