NASOPHARYNX-TARGET VOLUME DELINEATION

General Principles of Planning and Target Delineation

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  • Physical exam + imaging required for accurate delineation of primary tumor.
  • Endoscopic evaluation must assess anterior nasal space, nasopharynx, oropharynx; document extent and infiltration.
  • MRI (contrast-enhanced) recommended unless contraindicated; fuse MRI with planning CT; MRI ideally acquired in treatment position.
  • Marrow infiltration best seen on T1-weighted non-contrast sequence. MRI critical for skull base + perineural disease.
  • PET/CT: Use as guide only—may underestimate or overestimate disease extent, especially at skull base.
  • PET/CT extremely helpful for identifying small lymph-node metastases.
  • Simulation: supine, neutral head, 5-point thermoplastic mask with skull coverage; CT 2–3 mm slices with IV contrast from vertex to 2 cm below sternoclavicular joints.
  • Beam-split technique → thick slices acceptable if using low anterior neck AP/PA (only in N0 patients).
  • EBER should be obtained from biopsies; EBV DNA can be obtained in CLIA/approved labs.
  • Target volumes include GTV + CTV (primary CTV70 and subclinical CTV54–59.4).
  • Figures 1.1–1.6 (not included here) demonstrate example cases.
  • Sequential SIB/boost dosing: subclinical 50–54 Gy + sequential boost of 16–20 Gy → total dose ~70 Gy.

Suggested Target Volumes — Gross Disease Region

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VolumeDefinition & Description
GTVnp
  • Primary: All gross disease by exam + imaging.
  • Imaging must evaluate skull base invasion + perineural spread.
  • Neck: All ≥1 cm nodes in short axis, necrotic nodes; PET-avid nodes; contour any doubtful node.
CTV70np
  • Primary: CTV = GTVnp + 3–5 mm.
  • IF complete certainty → CTV70 = GTVnp (no margin).
  • 0 mm margin acceptable if tumor adjacent to critical OARs (brainstem, spinal cord).
  • If near ipsilateral optic nerve → informed discussion re: sacrificing ipsilateral optic apparatus; aim to protect contralateral optic + chiasm.
  • Neck: CTVn70 = GTVn + 3–5 mm.
  • Nodes ~1 cm → lower doses 63–66 Gy may be considered.
PTV70np
  • PTV70 = CTV70 + 3–5 mm.
  • If critical OAR compromise → PTV margin may be reduced.
  • Neck PTV: PTVn70 = CTVn70 + 3 mm.
  • If radiation oncologist certain → GTVnp = CTVnp (without margin), and GTVn = CTVn (without margin).
  • 5 mm margin can be added to CTV70 to create PTV70.

Suggested Target Volumes — High-Risk Subclinical Region

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VolumeDescription
CTV56–59.4
  • Primary: CTV56–59.4 = GTVnp + 10 mm (when possible) + whole nasopharynx.
  • Include soft palate, posterior nasal cavity ≥5 mm behind choana.
  • Include posterior maxillary sinus, pterygopalatine fossa (V2), posterior ethmoid sinus (select cases).
  • Include cavernous sinus → Meckel’s cave if T3–T4 or involved side-only.
  • Include pterygoid fossae/parapharyngeal space; sphenoid sinus: inferior half if T1–T2; full sinus if T3–T4.
  • Review bone window to ensure skull base foramina coverage.
  • Neck: bilateral retropharyngeal nodes + all levels IB–V.
  • Level IB may be omitted in N0 and selected N+ if no suspicious IB nodes.
  • May omit contralateral low neck for N0 disease.
PTV56–59.4
  • PTV = CTV56–59.4 + 3–5 mm.
  • If near brainstem, chiasm, spinal cord → PTV margin can be 0 mm.
  • Neck: PTV54.12–56 = CTV54.12–56 + 3 mm.