Complications after Proton Beam Therapy to Skull Base Tumors: Case Series

Background: Skull base tumors, such as chordomas (CD) and chondrosarcomas (CS), are pathological entities that require multimodality therapy, including surgery and radiation therapy (RT). Among the available modalities of RT, proton beam therapy (PBT) has been progressively more used in the past few years to treat CD and CS, due to greater accessibility, advances in programming technique using pencil beam scanning, and the theoretical biophysical advantages of the protons over the photons. However, complications associated with PBT of skull base tumors have been incompletely described.

Objective: To describe and discuss the outcomes of CD and CS treated with surgery and PBT, and to ascertain associated posttreatment complications of PBT.

Methods: A retrospective medical records analysis of patients with CD and CS who underwent surgery and PBT between July 2010 and July 2018 was conducted. Overall, 47 patients were found and included in this study. Data were collected regarding the time between the surgery and the beginning of the PBT, as well as the period between the completion of PBT and the observation of complications. Data were also collected regarding previous radiotherapy modalities utilized, amount of radiation received, localization of the tumor, and previous treatment at other institutions. Magnetic resonance images (MRI) were also reviewed to assess fluid-attenuated inversion recovery (FLAIR) changes, as well as signs of ischemia in the brain, labyrinth, and the cochlea.

Results: We found minor complications after PBT in this case series of patients. These included: six cases of spontaneous CSF leak necessitating surgical treatment, of which four required a second procedure; one case of osteoradionecrosis of the skull base; one case of refractory dizziness, treated medically; one case of hearing loss. There were also MRI changes: in the labyrinth; in the temporal lobes FLAIR changes with aphasia.

Conclusion: CD and CS are complex tumors of the SB usually treated with multimodality therapy, including PBT, which is increasingly used in such cases. As demonstrated in the present study, we found some complications associated with PBT. However, due to the retrospective nature of the study and the small sample size, a causal relationship cannot be established. Nevertheless, these findings may contribute to developing awareness about what to expect concerning posttreatment complications and potentially contribute to the establishment of preventive measures.

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