IMRT/VMAT HEAD AND NECK Flashcards
What is SIB?
Simultaneous integrated boost- Delivering different dose per day to different target regions in the same number of overall fractions
Example of SIB H AND N?
70 in 35- primary tumour
63 in 35 - ?
56 in 35-?
Why is VMAT preferred over IMRT?
- Faster
- Less QA
- Can alter gantry speed and dose rate
- Similar target coverage and OAR sparing
Disadvantages:
Increased integral dose = Increased risk of secondary malignancy
Beam arrangement?
9 Fields, equally spaced not opposing.
Cannot be opposing as this limits optimiser
Technique
• ( G180, G140, G100, G60, G20, G340, G300, G260, G220)
• Coll = 0 for all beams except G180, G100 and G260:
• G180: Coll rotated to 270 so MLC can shield spinal cord
• G100 and G260: Coll rotated to miss shoulders
EUD = equivalent uniform dose
• The dose if given uniformly to a ROI that will give the same biological
response as the planned heterogeneous dose distribution for the ROI
Effect of High density artefacts caused by fillings?
- Dose calculation accuracy negatively impacted
* Need to be contoured and density overrides applied
ICRU 83 level 2 dose reporting?
Level 2 dose reporting
• D50% (D Median) should be 100% of prescribed dose
• Prescriptive value D95%
• Dmean
• Near Minimum D98% (>95% of prescribed dose)
• Near Maximum: D2% (<107 % of prescribed dose)
• Prescribe to a volume not RP
Brainstem?
Max 54 Gy- Permanent cranial neuropathy or necrosis
Optic Chiasm/nerve?
Max 55 Gy-Optic neuropathy, vision loss
Mandible?
Max 70 Gy??- Osteoradionecrosis
Parotid?
Single parotid mean of 20Gy
Both parotids mean of 25Gy
Long term salivary function less than 25%
Spinal Cord?
Max dose 45Gy
Myelopathy/+ Paralysis
Cochlea?
Mean dose less than 45Gy
Sensory neural hearing loss
TMJ?
Max dose less than 60Gy
Trismus osteoradionecrosis
Pharynx and Larynx
PH: Mean dose less than 50Gy- Dysphagia and aspiration
LA:Mean dose less than 50Gy- Vocal dysfunction, dysphagia, aspiration
