Dosimetric impact of target definitions on normal structures in head and neck cancer.

Background and purpose: Previous work by our group suggests smaller target volumes may result in equivalent locoregional control for head and neck cancer. We evaluated whether smaller target volumes may also result in improved normal tissue sparing.

Methods and materials: Ten patients with Stage III-IV head and neck cancer were contoured and planned according to target definitions in RTOG 0522 in a two dose level plan (RTOG), as well as a three dose level plan, using smaller target volumes and an intermediate dose prescription (3Dose). Plans were compared for coverage of targets and sparing of normal tissues

Results: The high dose target, elective nodal target, and total volume targeted were significantly smaller in 3Dose plans (p < 0.001). There was no difference in volume receiving 100% of each prescription level in RTOG or 3Dose plans. Mean dose to contralateral parotid, mandible, larynx, and inferior pharyngeal constrictor, and maximum dose to brainstem were significantly lower in 3Dose plans. There was no significant difference in maximum dose to spinal cord or volume of tissue not otherwise specified receiving 70 Gy.

Conclusions: Smaller target volumes with the addition of an intermediate dose volume results in improved sparing of most normal tissues.