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Head and Neck Surgery
Principles of Radiation Therapy
Types of Radiation
Units of Radiation Energy
Radiation Sources
Radiation Delivery
Conventional Radiation
Intensity Modulated Radiation Therapy
Brachytherapy
Indications for Postoperative Radiotherapy
Timing of Radiation Therapy
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Head and Neck Surgery
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• Photon: most common form
• Electron: superficial penetration ideal for skin
• Neutron: high-energy particle and highly toxic
• Selectively used for salivary gland malignancies
• Proton: low-energy particle with a sharp falloff of dose beyond the target (Bragg peak)
• Increasingly used for skull base where dose to critical adjacent structures must be minimized
• Carbon ion: high-energy particle with a sharp Bragg peak
• Gray (Gy): 1 Gy equals 1 J of energy deposited per kilogram material
• Radiation-absorbed dose (rad): 100 rad = 1 Gy
• Doses range from 30 to 70 Gy
• Cobalt (Co-60), iridium (Ir-192), and cesium (Cs-137)
• Linear accelerator
• X-rays and electron energy of 4-25 MeV
• Accelerated electrons strike tungsten to produce x-rays
• Conventional radiation
• Intensity modulated radiation therapy (IMRT)
• Brachytherapy
• Stereotactic body radiation therapy (SBRT)
• Manual blocks are cut to shape the beam.
• Multileaf collimators are introduced to shape the radiation field.
• Inverse planning
• Ideal radiation dose distribution is based on imaging
• Computer algorithm is applied to achieve the ideal distribution
• Precise control
• Multiple small “beamlets” converge on targets
• Multiple beamlet conformations contour the dose
• Minimization of the dose to critical structures
• Salivary glands
• Pharyngeal constrictors
• Temporal lobe
• Optic nerve
• Cochlea
• Spinal cord
• Radioisotopes applied to tumor bed
• Permanent implants (beads) or interstitial catheters
• Rapid dose falloff of radiation
• Lip cancer
• Nasopharyngeal recurrence
• Base of tongue recurrence
• Advanced-stage disease: pT3, pT4
• Multiple positive nodes
• Without extracapsular extension (radiation alone)
• With extracapsular extension (concurrent chemoradiation)
• Positive surgical margins
• Reresection preferable if possible
• Concurrent chemoradiation if reresection is not possible
• Perineural invasion
• Adjuvant: 4-6 weeks after surgery
