Durability of the parotid-sparing effect of intensity-modulated radiotherapy (IMRT) in early stage nasopharyngeal carcinoma: A 15-year follow-up of a randomized prospective study of IMRT versus two-dimensional radiotherapy.

Background: The durability of improved xerostomia with intensity-modulated radiotherapy (IMRT) in patients with early stage nasopharyngeal carcinoma (NPC) is uncertain. We conducted a long-term prospective assessment of participants treated with IMRT or two-dimensional radiotherapy (2DRT) in a prior randomized study.

Methods: Parent study participants (IMRT, n = 28; 2DRT, n = 28) who were free of second malignancy or recurrence were eligible. Long-term radiotherapy-related toxicities were graded according to the Radiation Therapy Oncology Group (RTOG) criteria. Long-term patient-reported outcomes were assessed by the six-item xerostomia (XQ) and two European Organisation for Research and Treatment of Cancer (EORTC) questionnaires (QLQ-C30, QLQ-H&N35). Overall survival (OS), locoregional relapse-free survival (LRFS), distant relapse-free survival (DRFS), and the rate of symptomatic late complications (SLCs) were estimated for the entire cohort (n = 56).

Results: Totally, 21 (IMRT, n = 10; 2DRT, n = 11) patients gave consent and were assessed for an overall median follow-up of 15.5 years. There was significantly less RTOG ≥grade 2 xerostomia with IMRT versus 2DRT (20% vs. 90%; p = 0.001), but no significant difference in XQ scores. Patients in the IMRT arm reported lower mean scores for the "dry mouth" domain of EORTC QLQ-H&N35 (p = 0.02) and showed trends toward better 15-year OS (81.5% vs. 53.8%, p = 0.06), LRFS (70.6% vs. 53.8%, p = 0.38), and DRFS (81.5% vs. 53.8%, p = 0.07). SLCs were more frequent in the 2DRT arm.

Conclusions: The parotid-sparing effect of IMRT in NPC treatment is durable, with significantly less physician- and patient-scored xerostomia at 15 years. IMRT results in better long-term survival and fewer SLCs.