Patterns Of Failure After Definitive Reirradiation For Patients With Head And Neck Cancer

In the setting of curative intent head and neck (HN) reirradiation (reRT), the goal is to adequately cover disease with as small a volume as appropriate to minimize normal tissue toxicity. However, it can be a challenge to gauge the extent microscopic disease beyond the gross tumor that needs to be included in the reRT volume to maximize local disease control. Here, we determined the patterns of failure (POF) after definitive reRT with IMRT and proton. From 1999 to 2015, 148 patients with previously irradiated inoperable HN cancer received definitive reRT (median dose 66Gy). Those who had locoregional recurrence (LRR) and intact imaging data were analyzed. Using deformable imaging registration, diagnostic images at time of recurrence were coregistered with reRT treatment planning images. Site of recurrence was delineated and evaluated by 4 radiation oncologists and a radiologist with HN expertise. The POFs were classified into 5 types based on spatial and dosimetric criteria: A (central high dose), B (peripheral high dose), C (central elective dose), D (peripheral elective dose), and E (extraneous dose). For patients who had multiple sites of recurrences, each site was classified independently. The kappa statistic was used to assess the inter-observer agreement on failure classification. 44 patients developed LRR. Of these, 27 patients representing 33 sites of failures had restorable imaging data for analysis. Median time to failure was 21 weeks (range: 4 – 220 weeks). Of the 33 failure sites, 16 were mucosal and 17 were nodal. POFs were: 14 (42%) Type A, 5 (15%) Type B, 1 (3%) Type C, and 13 (39%) Type E. Therefore, 27 (82%) of failures were either within or outside the high dose (HD) field, with 6 (18%) marginal failures. Among recurrences outside the HD volume (Type E), 5 were mucosal and 8 nodal. Of the mucosal relapses, 3 were non-contiguous mucosal sites, whereas for contiguous mucosal recurrences the median distance from the HD region was 3cm (range: 2.7 – 3.2 cm). Of nodal relapses, 6 were from mucosal reRT, 2 were contralateral neck, and 4 were ipsilateral neck of which 3 were ≥1 nodal levels away from the reRT nodal level. Out of 33 failures, there were only 4 discrepancies in inter-observer classifications. All 4 were in cases whereby >95% of recurrence were within the HD region and there was small extension of disease outside the region on several CT slices. The overall agreement kappa was 0.92. Overall, this method of POF classification appeared reproducible between observers, with excellent agreement between radiation oncologists and radiologist. In patients who recurred after reRT, the majority was either within the central HD region, or completely outside the HD region suggesting poor disease biology rather than inadequate treatment volumes.Abstract 2873; Table 1POFObservers12345Mucosal Type A Type B Type E8 3 59 2 59 2 58 3 510 1 5Nodal Type A Type B Type C Type E6 2 1 85 3 1 84 4 1 85 3 1 85 3 1 8 Open table in a new tab