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Target volume definition

GTV:

Gross tumor volume:

Use all information available from clinical examination and imaging

(physician drawing target volume must have examined the patient!)

CTV:

GTV + potential routes of subclinical spread

GTV - CTV margins: fixed margins generally don

’

t work

• Soft tissues: generous margins (1-1.5 cm)

• Bone, cartilage, air cavities: tighter margins

• Known routes of spread:

Nasopharynx: cavernous sinus

• Neck nodes: 0.5 cm; if extranodal growth ≥ 1.0 cm

PTV:

CTV - PTV margins:

• 5 mm is generally adequate

• Can be reduced to 2-3 mm with customized positioning and immobilization devices and

DPI/CBCT-based correction protocols. To 1-2 mm with robust fixation and CBCT online.