Unintended Consequences of Proton Beam Radiation for Sinonasal Malignancies

Introduction: Proton beam radiation (PBR) carries a theoretical advantage of a narrow Bragg peak and improved relative biological effectiveness (RBE) for treatment of sinonasal cancer. The goals of this retrospective review are to report local control rates and to describe unintended but common biological tissue effects.

Methods: This is a retrospective case series report of all 29 patients from a single rhinology practice that received PBR for sinonasal malignancy from 2003 to 2016. Adverse tissue effects associated with PBR were analyzed: including skin/brow changes, epiphora, blindness, frontal lobe radiological change, osteoradionecrosis, and radiation induced secondary tumor. The post-PBR magnetic resonance imaging (MRI) frontal lobe transformations were graded as described in the literature.

Results: Adjuvant PBR was associated with a local control rate of 89.6% for a mean follow-up of 58.7 months, 96.4% nasal crusting, 77.8% epiphora, 53.6% intranasal synechiae requiring lysis, 48% with radiation-induced frontal lobe changes, 22.2% eyebrow loss, 6.9% blindness, 3.4% with radiation-induced malignancy. The average time to initial MRI brain findings was 31.0 months. 58.3% of those subjects had worsening over time, with an average time to final change of 58.6 months from PBR. The average final MRI grade for those subjects with changes was 3.33 out of 4. 13.8% had osteoradionecrosis an average of 46.3 months after PBR completion.

Conclusions: PBR appears to be an important tool in adjuvant treatment of sinonasal malignancies with a high rate of local control. There is limited information about the short and long term sequelae of this treatment modality in this patient population. Of particular interest is the radiological findings on the frontal lobe after therapy. Although these findings do not appear to have a neurological measurable ramification a better understanding of this presentation becomes relevant for patient education, patient management, and to prevent unnecessary brain biopsies.