Analysis of loco-regional failures in head and neck cancer after radical radiation therapy

• In IMRT era, accurate target volume definition is paramount in head and neck cancer.
• Loco-regional failure remains a significant cause of mortality and morbidity.
• The vast majority of recurrences occurred in the gross tumor volume area.
• Volumetric target delineation could be safe and useful in reducing toxicity.
• Dose escalation may result in an improvement in local control.

SummaryObjectivesTo investigate the anatomical distribution of loco-regional treatment failures (LRF) in patients with head and neck squamous cell carcinoma (HNSCC) in relation to clinical target volume (CTV) delineation.Materials and methods56 patients with LRF were retrospectively identified. Patients were previously treated with radical intensity modulated radiotherapy (IMRT) +/− chemotherapy. Target volumes include gross tumour volume (GTV), its volumetric expansion of 10 mm (GTV-HD), CTV high dose (CTV-HD) delineated by anatomic expansion from GTV and CTV low dose (CTV-LD) defined to receive a prophylactic dose. LRF were evaluated by PET-CT or CT scan.We analysed the association between sites of LRF and target volumes and dosimetry, using image co-registration. Based on percentage of volume that received 95% of prescribed dose, LRF were classified as in-field, marginal or out-field.ResultsMedian interval time from end of treatment to LRF was 186 days. 65 (95.6%) LRF were classified as in-field. Considering primary target volumes, 40 (58.8%) LRF occurred inside GTV, 13 (19.1%) in GTV-HD and 7 (10.3%) in CTV-HD. The overall 1-year and 2-year post-failure survival (PFS) was 45.8% and 24.2%, respectively. Post radiation LRF managed with salvage surgery had a significantly higher median PFS when compared with palliative treatments (p = 0.003).ConclusionsThe majority of LRF occurred within GTV/GTV-HD, suggesting it is safe to reduce the CTV to a volumetric expansion. Given the low incidence of geographical misses, future studies should be directed towards dose escalation of high-risk volumes. Potential reduction of RT-related toxicity with volumetric expansion could facilitate salvage surgery.