Results of a Multi-institutional Randomized Phase 3 Trial of Parotid-Sparing Whole Brain Radiotherapy

PURPOSE/OBJECTIVE(S)

Observational studies have reported that xerostomia is common after conventional whole brain radiotherapy (WBRT) and associated with parotid dose. In this multi-institutional, single-blind randomized controlled trial, we hypothesized that patient-reported xerostomia is reduced in patients randomized to parotid-sparing vs. standard WBRT fields.

MATERIALS/METHODS

Between 2018 and 2021, patients receiving conventional WBRT (30-35 Gy in 10-15 fractions) for any diagnosis were enrolled at 3 academic institutions. Patients were randomized between standard WBRT fields covering the C1 vertebra with no prospective parotid delineation (control) vs. parotid-sparing fields without C1 coverage (experimental). Patients completed the University of Michigan Xerostomia Questionnaire (Scored 0-100, higher is worse) at baseline, EndRT, 2 weeks, 1 month, 3 months, and 6 months. Patients were excluded from toxicity analyses if baseline xerostomia score was >50 or if they did not complete any post-baseline questionnaires. The primary endpoint was proportion of patients with ≥15 point absolute increase in xerostomia score from baseline to 1 month; 108 patients were needed for an 80% power to detect a 22% absolute difference (1-sided significance of 0.05). The secondary endpoint was the rate of marginal failures.

RESULTS

The study closed early after 56 patients were randomized. Median survival was 4.6 months. 46 patients (23 in each arm) were eligible for analysis. Mean parotid dose was 17 vs. 10 Gy in the standard vs. parotid-sparing arms, respectively. The table below shows mean xerostomia score and proportion of patients with ≥15 increase in xerostomia score at each time point. There was no difference in the proportion of patients experiencing ≥15 increase in xerostomia score at 1 month, though there was a trend toward lower xerostomia score at 1 month in patients randomized to parotid-sparing fields (p = 0.07, Table). Xerostomia rates were also significantly improved in the parotid-sparing arm at EndRT (p = 0.03), but no longer-term difference was observed with greater attrition at 3 and 6 months. On linear regression, there was a trend toward association between mean parotid dose and xerostomia score at 1 month (p = 0.06). There were no reported marginal failures in either arm.

CONCLUSION

Parotid-sparing without coverage of the C1 vertebra appears safe and may meaningfully reduce acute xerostomia in patients with limited life expectancy who are candidates for conventional WBRT, although the study was underpowered to detect a significant difference at 1 month.