Local Failure Rate in Oropharyngeal Carcinoma Patients Treated with Intensity-modulated Radiotherapy Without High-dose Clinical Target Volume.

Purpose: Our purpose was to evaluate whether omitting high-dose clinical target volume radiation (CTV-HD) around the gross tumor volume (GTV) in patients with oropharyngeal squamous cell carcinoma (OSCC) treated with intensity-modulated radiotherapy (IMRT) was associated with increased local failure.

Methods And Materials: Patients diagnosed with stage I to stage IV OSCC between December 2004 and April 2017 were retrospectively reviewed. All patients were treated with radical radiotherapy using IMRT, with or without neoadjuvant or concurrent chemotherapy. In accordance with institution guidelines, CTV-HD was not used. Local failure was defined as disease persistence or reappearance at the primary tumor site. When primary failure was documented, the computed tomography/positron emission tomography (CT/PET) scan that showed primary failure was fused with the original treatment scan. Each recurrent tumor was contoured to evaluate the pattern of recurrence. Recurrences were categorized as in-field, marginal, or out-of-field if >95%, 20%-95%, or <20% of the recurrent tumor volume, respectively, was encompassed by the 95% high-dose prescription isodose line of the original treatment plan. We then determined whether omitting CTV-HD was associated with increased locoregional failure.

Results: A total of 272 patients with OSCC were assessed. The median follow-up from initial treatment was 43 months (range: 3-194 months). Seven patients were lost to follow-up. The overall five-year survival rate was 87%. The three- and five-year disease-free survival rates were 86% and 83%, respectively. Forty-one patients had 53 treatment failures (16 were local, eight were regional, and 29 were distant; some patients had treatment failures in multiple locations). Fourteen (87.5%) of the local recurrences were in-field, one (6.25%) was marginal, and one (6.25%) was out-of-field.

Conclusion: Our analysis of patients with oropharyngeal cancer suggests that local failure is mostly in-field and potentially due to radioresistance, rather than a marginal miss of the tumor. It suggests that omitting CTV-HD is feasible and safe.