For a head‑and‑neck cancer recurrence 8 years after an initial curative radiotherapy course of approximately 66–70 Gy, what re‑irradiation dose is recommended and what are the carotid artery dose constraints as an organ‑at‑risk?

Reirradiation Dosing and Carotid Artery Constraints After 8 Years

For head and neck cancer recurrence 8 years after initial radiotherapy of 66-70 Gy, deliver at least 60 Gy (and up to 66-70 Gy if feasible) to the recurrent tumor while keeping the cumulative carotid artery dose below 120 Gy to prevent life-threatening carotid blowout syndrome. 1, 2

Target Dose for Reirradiation

The reirradiation dose depends critically on whether the recurrence overlaps with the previously treated volume:

• If the recurrence is in a previously untreated area: Deliver at least 74 Gy using conventional fractionation (2 Gy per fraction), treating with the same intent as a radiation-naïve tumor 1

• If the recurrence overlaps with the prior radiation field: No optimal dose is established by guidelines, requiring professional judgment based on cumulative dose constraints 1. However, clinical practice data shows:

  • Median reirradiation doses of 60 Gy are commonly used with IMRT techniques 3
  • Doses ranging from 50-72 Gy in conventional fractionation have been reported, with higher doses (≥60 Gy) associated with better local control 4, 5
  • Postoperative reirradiation shows superior 5-year locoregional control (46%) compared to definitive reirradiation (20%) 5

• The 8-year interval is favorable: This long time interval between treatments is a key factor for limiting toxicity, as tissue recovery varies by organ and is difficult to quantify 1. However, complete tissue recovery should never be assumed 1

Critical Carotid Artery Dose Constraints

The cumulative maximum dose to the carotid artery must not exceed 120 Gy to prevent carotid blowout syndrome:

• A cumulative dose threshold of 119-120 Gy has been identified as the critical cutoff, with ROC analysis showing excellent discrimination (AUC = 0.92, sensitivity 1.00, specificity 0.89) 2

• Carotid blowout syndrome is a severe, life-threatening complication reported in 4.1% of reirradiated patients 4

• The American Heart Association emphasizes particular caution when reirradiating the carotid artery due to these severe complications 1

Practical Dosimetric Planning Algorithm

Follow this stepwise approach:

1. Reconstruct the previous dose distribution accurately from the initial 66-70 Gy treatment—this is mandatory before proceeding 1

2. Calculate cumulative doses to all organs at risk, particularly:

   • Carotid arteries: Keep cumulative maximum dose <120 Gy 2
   • Spinal cord: Limit cumulative dose to 50 Gy with conventional fractionation 1
   • Mandible: Keep cumulative near-maximum dose <119 Gy to reduce osteoradionecrosis risk (AUC = 0.74) 2

3. Determine if high-dose reirradiation is feasible:

   • If organ-at-risk constraints can be met: Treat with curative intent using 60-70 Gy 1, 6
   • If constraints cannot be met: Consider low-dose palliative reirradiation only if negligible toxicity risk 1

4. Use IMRT or advanced techniques to spare organs at risk—IMRT shows borderline improved locoregional control (49% vs 36%) without increased late complications compared to conventional techniques 5

Expected Toxicity Profile

Severe late toxicity (grade ≥3) occurs in approximately 29-30% of patients:

• The most common severe complications are radionecrosis, dysphagia requiring feeding tube, and trismus 4

• Grade ≥4 late toxicity occurs in approximately 28% at 5 years 5

• Median lifetime cumulative radiation doses of 116 Gy have been safely delivered using IMRT 3

• One case series reported successful second reirradiation with cumulative doses exceeding 180 Gy using stereotactic techniques in highly selected patients 7

Common Pitfalls to Avoid

• Never proceed without accurate reconstruction of the previous dose distribution—this is the foundation of safe reirradiation planning 1

• Do not assume complete tissue recovery despite the 8-year interval, as recovery varies unpredictably by organ 1

• Avoid exceeding 120 Gy cumulative dose to carotid arteries under any circumstances given the life-threatening nature of carotid blowout 2

• Do not use low-dose palliative reirradiation unless it can be performed with negligible toxicity risk—if curative-intent dosing is feasible, it should be pursued 1