RESUMO
This study reports clinical performance in the sparing of infrahyoid swallowing organs at risk (SWOARs) in oropharynx cancer intensity-modulated radiation therapy (IMRT) plans. Rates of meeting dose-volume planning goals are reported and compared with geometry-based estimates of what is achievable. This study also develops 3 measures of target-SWOAR geometry and tests their usefulness in providing geometry-based dose-volume planning goals. A total of 50 oropharynx cancer IMRT plans were reviewed. Success rates in meeting institutional dose-volume goals were determined for the glottic larynx (G), postcricoid pharynx (P), and esophagus (E). The following 3 measures of target-SWOAR geometry were investigated as methods of identifying geometry-based planning goals: presence of gross disease in neck levels 3 to 4, target-SWOAR overlap, and a 3-dimensional (3D) measure of target-SWOAR geometry. Locally advanced disease was predominant in this patient population with target volumes overlapping SWOARs in 68% to 98% of cases. Clinical rates of success in meeting dose-volume goals varied by SWOAR (16% to 82%) but compared well with estimated potentially achievable rates in most cases (14% average difference between clinical and potential). Cases grouped by the presence of levels 3 to 4 neck nodes or target-SWOAR overlap did not have significantly different SWOAR doses. Cases grouped using a 3D measure of target-SWOAR geometry differed significantly, providing useful geometry-based planning goals (e.g., mean Glottis dose <45Gy was achieved 19%, 44%, or 81% of the time in each of 3 groups). This study describes the technical challenge of sparing SWOARs and investigates several potential methods for grouping cases to assist with treatment plan evaluation. Quantifying the 3-D relationship between the targets and SWOARs is a promising way of approaching this complex problem. Data presented in this paper may be useful to evaluate treatment plans using objective geometry-based goals.