Vestibular schwannomas are benign nerve sheath tumors that develop from vestibular nerves in the cerebellopontine angle. Although benign, they may cause serious symptoms, comprising hearing loss, tinnitus, and balance disturbance. Larger tumors may cause facial paresis, facial numbness or pain, elevated intracranial pressure and compression of the brain stem. In large and growing tumors, current treatment options include surgical resection and photon radiotherapy. Conventional photon radiotherapy has a high tumor control rate (90-95%). However, over 40% of the patients suffer from hearing loss after photon radiotherapy. Facial paresis, vertigo, and tinnitus also occur. In addition there is a risk of impacting on cognitive functioning and induction of secondary tumors. Proton radiotherapy potentially reduces the radiotherapeutical risk while maintaining a high tumor control rate. As the majority of vestibular schwannoma patients present between the 3rd and 5th decade in life, a reduction of side effects, including long-term sequelae of photon radiotherapy is very relevant.

The research aims to:

• Elucidate the potential of current proton radiotherapy strategies in vestibular schwannoma patients, and identify patient subgroups that would benefit most.
• Compare proton with photon radiotherapy in vestibular schwannoma patients.

The radiotherapy modalities will be compared in two ways: by comparing radiotherapy plans and by prospectively comparing matched cohorts of vestibular schwannoma patients receiving photon and proton radiotherapy. In this prospective cohort study, tumor control and side effects will be assessed as well as quality of life and cost-effectiveness

• Predict the response of vestibular schwannomas to proton and photon radiotherapy. Advanced pre- and post-irradiation (functional) MR imaging will be compared with pre- and post- treatment outcomes. Focus will be on the tumor itself and organs at risk (i.e. cochlea, vestibular organ, trigeminal and facial nerves, brainstem, and brain).

HollandPTC-Varian 2018

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