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Stereotactic Radiosurgery and Radiotherapy for Lateral Skull Tumors
Built from Haynes-Glasscock-Shambaugh Surgery of the Ear, Seventh Edition
What’s inside
9 sections · 110 slides
Overview
- Scope of this topic
History and radiobiology
- Origins of stereotactic radiosurgery
- From X-ray to the cobalt Gamma Knife
- Current share of vestibular schwannoma practice
- Radiobiology of stereotactic radiosurgery
Methods of delivery
- Principle of Gamma Knife delivery
- Shots and dose shaping
- Gamma Knife Perfexion unit
- Gamma Knife Perfexion specifications
- Gamma Knife Icon unit
- Gamma Knife Icon and mask-based delivery
- Gamma Knife treatment unit and couch
- CyberKnife: LINAC-based radiosurgery
- CyberKnife system components
- Advantages of robotic arm delivery
- Medical linear accelerator in a treatment room
- Choosing between Gamma Knife and CyberKnife
Vestibular schwannoma: patient selection
- Framework for modality selection
- Patient factors in treatment planning
- Psychological effect of the tumour
- Axial MRI of a cerebellopontine angle schwannoma
- Tumour size limits for radiosurgery
- Subtotal resection with adjuvant radiosurgery
- Effect of tumour location on outcome
- Vestibular symptoms and the translabyrinthine option
- Radiation-associated tumours and malignant transformation
Gamma Knife technique
- Gamma Knife treatment workflow
- Objectives of stereotactic frame placement
- Centring the frame on the tumour
- Pin technique and frame fixation
- Collision checks before treatment
- Skull geometry verification
- Fiducial boxes and stereotactic coordinates
- Fiducial materials and their pitfalls
- CT and MRI in Gamma Knife planning
- Contoured cochlea, labyrinth, brainstem and tumour
- Dose evolution for vestibular schwannoma
- The 50% isodose line
- Contouring structures at risk
- Manual and inverse planning
- Plan evaluation: coverage and dose limits
- Plan optimisation and export
- Model treatment plan for a left vestibular schwannoma
Outcomes after radiosurgery
- Principles of surveillance imaging
- Patterns of tumour response after radiosurgery
- Timing the diagnosis of treatment failure
- Loss of central enhancement after treatment
- Duration of surveillance after radiosurgery
- Mechanisms of hearing loss after radiosurgery
- Predictors of favourable hearing outcome
- Why hearing preservation rates are disputed
- AAO-HNS hearing guidelines
- Gardner-Robertson scale
- Long-term hearing decline after radiosurgery
- Progressive hearing loss across all modalities
- Facial nerve injury after radiosurgery
- Dose and facial nerve outcome
- Hemifacial spasm after radiosurgery
- Mechanisms of hydrocephalus after radiosurgery
- Rates of hydrocephalus by tumour size
- Management of post-radiosurgical hydrocephalus
- Tinnitus after treatment
- Timing of intervention in small tumours
- Evidence for up-front radiosurgery
- Unresolved question of treatment timing
Special considerations
- Behaviour of cystic vestibular schwannoma
- Radiation-induced cystic change
- Outcomes of radiosurgery for cystic tumours
- Peritumoral cysts as a separate entity
- Caution in treating cystic tumours
- Neurofibromatosis type 2: the clinical problem
- Malignant transformation risk in NF2
- Reported radiosurgery outcomes in NF2
- Difficulty of salvage surgery after failed radiation
- Less aggressive salvage resection
- Re-irradiation and choice of salvage
Other lateral skull base tumours
- Cerebellopontine angle meningioma: features
- Radiosurgical technique for meningioma
- Surgical and radiosurgical results in CPA meningioma
- Facial nerve schwannoma: the surgical dilemma
- Radiosurgery outcomes in facial nerve schwannoma
- Indication for radiosurgery in facial schwannoma
- Radiosurgery for paraganglioma: technique
- Frame considerations for cervical extension
- Outcomes of radiosurgery for jugular paraganglioma
Summary and references
- Dose summary across lateral skull base tumours
- Key dose constraints to remember
- Take-home points
- Remaining uncertainties
- Conclusions from the chapter
- References
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- Haynes-Glasscock-Shambaugh Surgery of the Ear, Seventh Edition
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