ASYMMETRIC ARC TECHNIQUE FOR POSTERIOR PHARYNGEAL WALL AND RETROPHARYNGEAL SPACE TUMORS

Purpose: Tumors of the posterior pharyngeal wall and nasopharyngeal ca ncer with retropharyngeal extension can partly encircle the cervical v ertebrae. Treating the patient within spinal cord tolerance can cause a geographic miss, A simple technique has been developed to avoid this problem. Methods and Materials: The standard fields for posterior pha ryngeal wall and nasopharyngeal tumors are used up to 36-40 Gy, A plan ning computed tomography (CT) scan is taken during the second or third week of treatment with the patient fitted in a new shell ensuring tha t the cord is straight and parallel to the treatment couch, The asymme tric are technique consists of two posterior arcs with closure of one jaw beyond the central axis. Each are delivers the total dose to each ipsilateral side, while the median region of the U-shaped volume is tr eated by the summation of both arcs. Results: We have treated 10 patie nts using asymmetric arcs in the last 3 years, This technique proved t o be a versatile way of treating targets wrapped around the spine. The technique allows better individualization for target volume irregular ities than the partial rotation with a central bar.