Aim: To evaluate the patterns of loco-regional recurrences in head and neck cancer patients\nMethods: Twenty-six out of 112 patients treated with primary or postoperative 3D CRT or IMRT for their primary\nand recurrent disease between 2007 and 2013 were included. The CT images of recurrent disease were rigidly\nregistered with the primary CT images for each patient. To assess overlaps and overlap localization, the recurrence\nvolume overlapping with the primary target volume was identified. For relapses occurring in the regional lymph\nnodes, the epicenter distance in recurrences and primary volumes and dose in recurrences were also identified. The\nrecurrences were defined as in-field, marginal or out-of-field.\nResults: The majority of the failures occurred within 1 year after completed primary treatment. The dose differences\nin recurrence volume were not statistically significant when patients were treated with IMRT or 3D CRT. Recurrence\nin 15/26 of the included patients occurred in the regional lymph nodes located fully or partly inside the primary\ntarget volume or the elective lymph node region. The majority of recurrences were recognized as in-field,\nindependent of the primary treatment.\nConclusion: Recurrence in the majority of the patients occurred in the regional lymph nodes located in high dose\narea. The cause of recurrence may be due to inadequate total dose in the primary treatment and/or lack of optimal\nprimary diagnosis leading to inadequate primary target delineation
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