A Prospective 10-year Observational Study of Reduction of Radiotherapy Clinical Target Volume and Dose in Early-stage Nasopharyngeal Carcinoma

Abstract

Objective: Current guideline recommends a uniform method of delineation of subclinical disease within the clinical target volume (CTVp) for all stages of nasopharyngeal carcinoma (NPC). We performed a prospective observational study to investigate the outcomes with a reduced CTVp and radiation dose for early-stage NPC. Methods: Patients with newly diagnosed biopsy-proven WHO II-III AJCC/UICC 6th edition T1-2N0-1 were enrolled. All patients were treated with intensity-modulated radiotherapy (IMRT) alone. We categorized CTVp into CTVp1 (high risk) and CTVp2 (low risk). CTVp1 comprised of gross tumor (on MRI or CT) plus 5-mm margin (3-mm posteriorly) and prescribed to 60 Gy/30 fractions (fr). CTVp2 was generated from CTVp1 plus 5-mm margin (3-mm posteriorly), excluding the maxillary and cavernous sinuses, and were prescribed to 54 Gy/30 fr. The prescribed dose to GTVp and GTVn were 68 Gy/30 fr and 60-66 Gy/30 fr, respectively. Primary end-point was local recurrence-free survival (LRFS). This study was registered in ClinicalTrials.gov, number XXXX. Results: From May 2001 to August 2006, 103 patients were recruited and completed IMRT. With a median follow-up of 15.2 years (range = 2.1-18.1 years), only one patient had local failure. 10-year LRFS, regional recurrence-free survival (RRFS), distant metastasis-free survival (DMFS) and overall survival (OS) were 90.3%, 88.3%, 90.3% and 91.2%, respectively. Among late IMRT-related adverse events, we recorded two patients with G1 cranial nerve injury, three patients with G3 hearing loss, and three patients with G3 subcutaneous fibrosis. No patients had temporal lobe necrosis, brainstem injury or trismus. Conclusion: Decreased CTV margins and radiation doses can achieve long-term tumor control with mild late toxicities for early-stage NPC patients.