Proton Beam Therapy in the Treatment of Periorbital Malignancies

Abstract

Purpose: Periorbital tumor location presents a significant challenge with 3-dimensional conformal radiation therapy or intensity modulated radiation therapy due to high tumor dose needed in the setting of close proximity to orbital structures with lower tolerance. Proton beam therapy (PBT) is felt to be an effective modality in such cases due to its sharp dose gradient.

Materials and methods: We reviewed our institutional PBT registry and identified 17 patients with tumor epicenters within 2 cm of the eye and optic apparatus treated with passive scatter PBT with comparison volumetric arc therapy plans available. Maximum and mean doses to organs at risk of interest, including optic nerves, optic chiasm, lens, eye ball, pituitary, cochlea, lacrimal gland, and surrounding brain, were compared using the paired Wilcoxon signed rank test. Overall survival was determined using the Kaplan-Meier method.

Results: Median age was 67. Median follow-up was 19.7 months. Fourteen patients underwent upfront resection and received postoperative radiation and 3 received definitive radiation. One patient received elective neck radiation, 2 underwent reirradiation, and 3 had concurrent chemotherapy. There was a statistically significant reduction in mean dose to the optic nerves and chiasm, brain, pituitary gland, lacrimal glands, and cochlea as well as in the maximum dose to the optic nerves and chiasm, pituitary gland, lacrimal glands, and cochlea with PBT. The 18-month cumulative incidence of local failure was 19.1% and 1-year overall survival was 80.9%.

Conclusion: Proton beam therapy resulted in significant dose reductions to several periorbital and optic structures compared with volumetric arc therapy. Proton beam therapy appears to be the optimal radiation modality in such cases to minimize risk of toxicity to periorbital organs at risk.

Keywords: cochlea; optics; periorbital; pituitary; proton.

Figure 1.

Local control of patients with periorbital tumors treated with PBT. Abbreviation: PBT, proton beam therapy.

Figure 2.

Overall survival of patients with periorbital tumors treated with PBT. Abbreviation: PBT, proton beam therapy.

Figure 3.

Axial, sagittal, and coronal cross-sections taken from the VMAT plan of a representative patient. The CTV is shaded in teal, the brainstem is shaded in light green, and ipsilateral optic nerve is shaded in red. The 95% isodose line is shown in red, 50% isodose line in blue, 25% isodose line in green, and 10% isodose line in orange. Abbreviations: CTV, clinical target volume; VMAT, volumetric arc therapy.

Figure 4.

Axial, sagittal, and coronal cross-sections taken from the PBT plan of a representative patient. The CTV is shaded in teal, the brainstem is shaded in light green, and ipsilateral optic nerve is shaded in red. The 95% isodose line is shown in red, 50% isodose line in blue, 25% isodose line in green, and 10% isodose line in orange. Abbreviations: CTV, clinical target volume; PBT, proton beam therapy.

Figure 5.

Digital subtraction images that were generated to show differences in integral dose. Positive percentages indicate areas where VMAT delivered higher dose while negative percentages indicate areas where PBT delivered higher dose. Abbreviations: PBT, proton beam therapy; VMAT, volumetric arc therapy.