eContour

This is a 54 y/o man with locally advanced nasopharyngeal carcinoma, stage IVA, T4N1M0 who presented with R cervical adenopathy and right CN IX, X, XI, XII palsies with MRI showing disease in the right fossa of Rosenmuller and right skull base including the parapharyngeal space and jugular foramen.

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Rx:

  • Gross disease in nasopharynx and right neck treated to 69.96 cGy in 33 fractions with VMAT based planning and daily IGRT.
  • High-risk area around the primary tumor and high-risk nodal basins received 59.4 cGy (bilateral RP, II, III and Va).
  • Low-risk elective nodal basins received 54.12 cGy (R Ib, bilateral IV and Vb).
  • Pre-Induction Chemo CT simulation can be helpful, especially since induction chemotherapy is now a category 1 recommendation for all T3N1+ or N2+ cases and for now, a modified pre-chemo volume is still treated to the full dose. 

Chemotherapy:

  • This patient underwent induction chemotherapy with 3 cycles of cisplatin + gemcitabine prior to chemoradiation with concurrent cisplatin.

Sim/Planning:

  • Simulation scan was completed with patient in supine position with thermoplastic head/ shoulder mask and IV contrast.

 

Case contributed by UCSD.

Per Lee Radiother Oncol 2018 for CTV delineation in nasopharyngeal carcinoma.

The intermediate risk CTV for a T4 tumor should include:

  • A margin of at least 1cm around the GTV + entire nasopharynx
  • Posterior 5mm of nasal cavity, maxillary sinus, bilateral pterygoid fossa, bilateral parapharyngeal space, and ipsilateral cavernous sinus 
  • Foramen Ovale, Rotundum, Lacerum and Petrous tip of temporal bone on involved side.
  • Entire sphenoid sinus.
  • 1/3 of clivus (all if invaded).

This patient had right CN IX, X, XI, XII palsies on exam, so these nerves were traced and included in the high dose CTV.

  • GTV was delineated on both MRI and PET, and these volumes were combined and adjusted based on CT simulation scan.
  • High Risk Tumor volume - Rx with 69.96 cGy is GTV +3-5 mm
  • Several atlases are available to assist with cranial nerve tracing including Ho PRO 2014 and Bakst IJROBP 2019.

Low risk - Rx with 54 cGy volume includes bilateral IB-V, with IB often omitted in the N0 neck. 

For cases of advanced nasopharyngeal carcinoma with cranial nerve deficits on exam, close attention should be paid to nerve tracing of the involved cranial nerves.

To ensure adequate tracing of these pathways back to at least the skull base, it is useful to remember where each cranial nerve leaves the skull:

  • CNI: Cribiform plate
  • CNII: Optic Canal
  • CNIII: Superior Orbital Fissure
  • CNIV: Superior Orbital Fissure
  • CNV1: Superior Orbital Fissure
  • CNV2: Foramen Rotundum
  • CVV3: Foramen Ovale
  • CVVI: Superior Orbital Fissure
  • CNVII: Sylomastoid Foramen
  • CNVIII: Internal acoustic meatus
  • CNIX: Jugular Foramen
  • CNX: Jugular Foramen
  • CNXI: Jugular Foramen
  • CNXII: Hypoglossal canal

CT Bone Windows are beneficial in visualizing the foramina, specifically Fromen Rotundum, Froamen Lacerum and Foramen Ovale.