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J.B. Ciralsky, S.M. Warden, J.E. Munzenrider, J.A. Adams, S. Mukai; The Use of Gantry Decreases Normal Tissue Exposure in Proton Beam Radiotherapy of Intraocular Retinoblastoma . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2815.
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Proton radiotherapy (PRT) is effective in treating intraocular retinoblastoma (RB). We have treated over 35 patients at the Harvard Cyclotron Laboratory and the Northeast Proton Therapy Center (NPTC) using a lateral (LAT) single beam approach with eye and head immobilization. At NTPC, protons can be delivered via a gantry allowing for varied treatment angles. Theoretically, an anterolateral oblique (ALO) single beam can be used to treat the tumor and decrease normal tissue exposure (Int J Radiation Oncology Biol Phys 6:583). We report treatment of first two cases of RB with ALO single beam protons using the gantry.
Two patients were treated with this approach. Planning CT and treatments were done with the patient lying supine under IV propofol anesthesia, the head immobilized by a custom–molded mask and the eye immobilized in primary position with a corneal suction contact lens. Treatment plans were carried out for LAT and ALO beam angles. Total dose was 46Gy given in 2Gy fractions. Dose–volume histograms for LAT and ALO plans were calculated.
Dose–volume histogram comparisons showed significant decrease in dose to bone and other normal tissues. The planning, setup and treatment by ALO were similar in time and difficulty to those by LAT. In both patients tumors and vitreous or subretinal seeds showed significant regression with no evidence of recurrence. No complication has been seen thus far.
The use of the gantry for PRT of RB allows for reduced radiation to non–target structures. We have shown that this can be done with no increase in effort or risk compared to the LAT approach with good early control of the tumor and seeding. The lower radiation dose to normal tissues should decrease long–term complications such as second malignancies and orbital hypoplasia. PRT utilizing the gantry represents a promising new advancement in the treatment of retinoblastoma.
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