Treatment planning and delivery of intensity-modulated radiation therapy for primary nasopharynx cancer

Purpose: To implement intensity-modulated radiation therapy (IMRT) for prim ary nasopharynx cancer and to compare this technique with conventional trea tment methods. Methods and Materials: Between May 1998 and June 2000, 23 patients with pri mary nasopharynx cancer were treated with IMRT delivered with dynamic multi leaf collimation, Treatments were designed using an inverse planning algori thm, which accepts dose and dose-volume constraints for targets and normal structures. The IMRT plan was compared with a traditional plan consisting o f phased lateral fields and a three-dimensional (3D) plan consisting of a c ombination of lateral fields and a 3D conformal plan. Results: Mean planning target volume (PTV) dose increased from 67.9 Gy with the traditional plan, to 74.6 Gy and 77.3 Gy with the 3D and IMRT plans, r espectively, PTV coverage improved in the parapharyngeal region, the skull base, and the medial aspects of the nodal volumes using IMRT and doses to a ll normal structures decreased compared to the other treatment approaches, Average maximum cord dose decreased from 49 Gy with the traditional plan, t o 44 Gy with the 3D plan and 34.5 Gy with IMRT. With the IMRT plan, the vol ume of mandible and temporal lobes receiving more than 60 Gy decreased by 1 0-15% compared to the traditional and 3D plans. The mean parotid gland dose decreased with IMRT, although it was not low enough to preserve salivary f unction. Conclusion: Lower normal tissue doses and improved target coverage, primari ly in the retropharynx, skull base, and nodal regions, were achieved using IMRT. IMRT could potentially improve locoregional control and toxicity at c urrent dose levels or facilitate dose escalation to further enhance locoreg ional control. (C) 2001 Elsevier Science Inc.