Patterns of failure after reirradiation with intensity-modulated radiation therapy and the competing risk of out-of-field recurrences.

<bold>Purpose: </bold>To describe patterns of failure (POF) after reirradiation (reRT) with intensity modulated radiation therapy (IMRT) for recurrent/second primary squamous cell carcinoma of the head and neck.<bold>Methods: </bold>From 08/2004-02/2013, 75 consecutive patients received reRT with IMRT. Gross tumor was generally treated with a 5mm planning target volume (PTV) margin. For postoperative cases, a 5mm PTV was added to the clinical target volume which included the postoperative bed. Elective neck coverage was not standard. POF were characterized by correlating the recurrent tumor location on CT-imaging with the reRT IMRT plan.<bold>Results: </bold>Patients received definitive reRT (55%) or postoperative reRT (45%) to a median 60Gy (range, 59.4-70Gy). Most patients (88%) received concurrent chemotherapy including induction (16%). The median overall survival was 1.8years. Isolated local-regional recurrence (LRR) was the most common failure-type (2-year cumulative incidence [CI] 22.5% [95% C.I. 13.6-32.7%]), but concurrent LRR and distant-failure occurred frequently (2-year CI LRR+distant-failure 19.6% [95% C.I. 11.3-29.5%]); isolated distant-failure was rare (2-year CI 5.7% [95% C.I. 1.8-12.8%]). The 2-year in-field control was 65% (95% C.I. 52-81%) reflecting encouraging control within the irradiated target. Patients with gross disease were more likely to recur in-field (p=0.02), whereas postoperative patients were more likely to recur out-of-field/marginally than in-field (p=0.02).<bold>Conclusions: </bold>POF after reRT differ when treating gross disease or postoperatively and should be considered when delineating reRT targets. Aggressive local therapy resulted in favorable in-field control, yet there remains a high competing risk of regional and distant micrometastatic disease. Better systemic agents are needed to control clinically occult local-regional and distant disease. [ABSTRACT FROM AUTHOR]