Proton Beam Irradiation for Treatment of Experimental Human Retinoblastoma

Abstract

Proton beam irradiation was used to treat human retinoblastoma (Y-79 cell line) grown subcutaneously in the athymic "nude" mouse. Thirty-four tumors were included in the experimental groups, of which twenty-three were irradiated and eleven served as controls. Tumors were irradiated with protons produced at the 160 megavolts Harvard cyclotron. The dose delivered to the tumor ranged from 7.5 to 27.5 proton gray in a single treatment, and 25.0 proton gray delivered in two fractions separated by 24 hours. Reduction of tumor growth was significantly greater than controls (p less than 0.001) with treatment doses greater than or equal to 17.5 proton gray. Histologic examination revealed a marked decrease of mitotic activity in all specimens examined 48 hours after treatment at these higher doses. Total regression without evidence of remaining malignant cells was noted in three tumors treated at 17.5 proton gray or above. Our results indicate that human retinoblastoma in a murine host, with a tumor mass similar to that seen in a clinical setting, is sensitive to radiation by high energy protons.

Treatment of Retinoblastoma: The Role of External Beam Radiotherapy

“… 10 Animal RB tumors also showed significantly greater radiosensitivity than control tumors at doses of 17.5 proton Gray (cobalt gray equivalent, CGE) or above. 11 Moreover, successful treatment outcomes were observed when low dose radiotherapy, ranging from 24-36 Gy, was administered as the primary treatment 12 13 14 or as salvage treatment after chemotherapy, 15 16 suggesting that there is a subset of RBs that are exceptionally sensitive to radiation.…”

Subconjunctival Carboplatin in Retinoblastoma<subtitle>Impact of Tumor Burden and Dose Schedule</subtitle>

“…6,7 More recent treatment options in the management of retinoblastoma (including external beam radiotherapy, episcleral plaque radiotherapy, cryotherapy, laser photoablation, and systemic chemotherapy) offer the potential of sight preservation. [8][9][10] External beam radiotherapy has played a prominent role in the treatment of retinoblastoma, especially in children with a germline Rb mutation predisposing them to bilateral eye involvement. [11][12][13] Although the efficacy of ionizing radiation treatment has been demonstrated, this therapeutic modality is associated with such complications as fa-cial deformities, cataract, and radiation retinopathy and an increased incidence of second tumors.…”