Latest NPC Contouring Guidelines
For nasopharyngeal carcinoma target delineation, MRI-CT image fusion is mandatory, with gross tumor volume carefully delineated following international consensus guidelines that emphasize MRI superiority for skull base extension, perineural disease, and intracranial involvement. 1
Core Imaging Requirements
MRI-CT Fusion Protocol
- MRI fusion with CT simulation is mandatory for all NPC target delineation, particularly to assess skull base tumor extension, cranial nerve involvement, and intracranial disease 1
- MRI demonstrates superior detection of:
- CT remains superior for detecting neck nodal disease and cortical bone invasion 1
Multidisciplinary Review
- Radiation oncologists should review CT/MRI with a head and neck radiologist when uncertainty exists regarding disease extent or response to induction chemotherapy 1
Target Volume Definitions
Gross Tumor Volume (GTV)
- GTV must be carefully delineated following international consensus guidelines with exploitation of MRI-CT fusion capabilities 1
- Target includes primary tumor, pathological nodes, and adjacent regions at risk for microscopic spread 1
- Both sides of the neck (levels II-V and retropharyngeal nodes) should be included due to high incidence of occult nodal involvement 1
Clinical Target Volume (CTV)
- International consensus guidelines provide specific guidance on CTV delineation 1
- Dose prioritization and acceptance criteria for IMRT planning must follow established international guidelines 1
Special Contouring Scenarios
Post-Induction Chemotherapy
- Pre-induction scan must be fused with post-induction CT simulation to illustrate initial disease extent 1
- GTV should generally follow pre-induction tumor extent, especially within bony anatomy (strong recommendation) 1
- This approach is critical at the skull base due to:
Alternative approach: Reduced GTV based on post-chemotherapy MRI volumes may be feasible if pre-induction tumor areas receive at least intermediate dose (64 Gy), which improves quality of life without compromising local control 1
Node-Negative Disease
- Upper neck versus whole-neck prophylactic radiotherapy shows similar lower neck control rates 1
- Reduced nodal volume approach is feasible in node-negative NPC to reduce toxicity burden 1
Dose Prescriptions
Standard Dosing
- 70 Gy in 33-35 fractions (2.0-2.12 Gy per fraction) delivered over 7 weeks (5 fractions/week) for macroscopic disease 1
- 50-60 Gy for potential at-risk sites 1
Dose Modifications
- Additional 2-4 Gy boost in 1-2 fractions may be considered for MRI-detected residual tumor at end of IMRT 1
- Slightly lower total dose (66-68 Gy) may be considered for very responsive small primaries 1
- Larger fraction sizes should be avoided, especially with concurrent chemotherapy, due to substantial late toxicity concerns 1
- Extreme caution when increasing total dose above 70 Gy due to high risk of osteoradionecrosis, carotid pseudoaneurysm, and neurological toxicities 1
Technical Delivery
IMRT Technique
- Either sequential boost or simultaneous integrated boost (SIB) technique acceptable 1
- SIB is the technique of choice due to convenience and resource-saving while maintaining single treatment phase 1
- Sequential boost allows adaptation to anatomic changes during treatment 1
Image Guidance
- Daily image guidance should be implemented to minimize interfractional setup variation 1
- Enables customized PTV margins and monitoring of geometric/dosimetric changes 1
Critical Pitfalls to Avoid
- Never contour without MRI-CT fusion - this is mandatory, not optional 1
- Do not reduce GTV at skull base after induction chemotherapy unless intermediate dose (≥64 Gy) covers pre-induction extent 1
- Avoid using CT alone for target delineation as it misses critical disease extent at skull base and perineural involvement 1
- Do not use larger fraction sizes (>2.12 Gy) with concurrent chemotherapy due to unproven efficacy and substantial late toxicity 1