IMRT/VMAT HEAD AND NECK

Question 1

What is SIB?

Answer 1

Simultaneous integrated boost- Delivering different dose per day to different target regions in the same number of overall fractions

Question 2

Example of SIB H AND N?

Answer 2

70 in 35- primary tumour
63 in 35 - ?
56 in 35-?

Question 3

Why is VMAT preferred over IMRT?

Answer 3

• 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

Question 4

Beam arrangement?

Answer 4

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

Question 5

EUD = equivalent uniform dose

Answer 5

• The dose if given uniformly to a ROI that will give the same biological
response as the planned heterogeneous dose distribution for the ROI

Question 6

Effect of High density artefacts caused by fillings?

Answer 6

• Dose calculation accuracy negatively impacted

* Need to be contoured and density overrides applied

Question 7

ICRU 83 level 2 dose reporting?

Answer 7

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

Question 8

Brainstem?

Answer 8

Max 54 Gy- Permanent cranial neuropathy or necrosis

Question 9

Optic Chiasm/nerve?

Answer 9

Max 55 Gy-Optic neuropathy, vision loss

Question 10

Mandible?

Answer 10

Max 70 Gy??- Osteoradionecrosis

Question 11

Parotid?

Answer 11

Single parotid mean of 20Gy
Both parotids mean of 25Gy

Long term salivary function less than 25%

Question 12

Spinal Cord?

Answer 12

Max dose 45Gy

Myelopathy/+ Paralysis

Question 13

Cochlea?

Answer 13

Mean dose less than 45Gy

Sensory neural hearing loss

Question 14

TMJ?

Answer 14

Max dose less than 60Gy

Trismus osteoradionecrosis

Question 15

Pharynx and Larynx

Answer 15

PH: Mean dose less than 50Gy- Dysphagia and aspiration
LA:Mean dose less than 50Gy- Vocal dysfunction, dysphagia, aspiration

Question 16

Why is the isocentre in the centre of PTV 56?

Answer 16

As this is the largest volume we are prescribing dose to

Question 17

Why would we contour the pharyngeal constrictors and lips?

Answer 17

To dose dumping resulting in side effects