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

Abstract

Objectives: To 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 methods: 56 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 10mm (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.

Results: Median interval time from end of treatment to LRF was 186days. 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).

Conclusions: The 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.

Keywords: CTV; Head and neck cancer; IMRT; Loco-regional failure; Persistence; Radiation; Radical; Radiotherapy; Recurrence; Volumetric.