Intensity-modulated radiotherapy as the boost or salvage treatment of nasopharyngeal carcinoma: the appropriate parameters in the inverse planning and the effect of patient's anatomic factors on the planning results.

The current study demonstrates that the large increase in normal tissue penalty often degrades target dose uniformity without a concomitant large improvement in normal tissue dose, especially in anatomically unfavorable patients. The excessively large normal tissue penalties do not improve treatment plans for patients having unfavorable geometry.