A Scalp Dose Cutoff That Prevents Permanent Alopecia in Scalp-Avoidance Whole-Brain Volumetric-Modulated Arc Radiotherapy for Pediatric Patients with Medulloblastomas

Abstract

<h3>Purpose/Objective(s)</h3> Permanent alopecia significantly impacts the quality-of-life. We perform scalp-avoidance volumetric-modulated whole brain radiotherapy (SA-WBRT) as a component of craniospinal irradiation (CSI). However, the scalp cutoff dose that prevents permanent alopecia remains unknown. Here, we estimate the optimal cutoff dose for patients undergoing the St. Jude Medulloblastoma-96 protocol. <h3>Materials/Methods</h3> Eight pediatric patients (median age 8 years 0 months, range 4 years 8 months to 12 years 10 months) with medulloblastoma treated from May 2011 to August 2018 were enrolled. All patients underwent CSI and boost radiotherapy followed by four cycles of dose-intensive chemotherapy. Four patients were treated with conventional WBRT and the others with SA-WBRT. We defined permanent alopecia as hair loss persisting for 1 year after radiotherapy completion, graded by two reviewers for each patient using the SALT score; grades 3 and 4 alopecia were considered severe. We divided the scalp into top, back, left, and right areas and calculated the equivalent doses in 2-Gy fractions (assuming α/β = 2) to 50% of these areas (EQD50%); we compared these values to the alopecia grades. We drew receiver operating characteristic curves to determine the predictive performances of the EQD50% <i>in terms of</i> severe permanent alopecia and derived EQD50% cutoffs for the four scalp areas. <h3>Results</h3> The median follow-up period was 71 months (range 50.8-109.0 months) from start of radiotherapy. No patient experienced disease progression in the 5 years after radiotherapy, and no severe side effect was observed in patients undergoing SA-WBRT. Such patients tended to have less severe permanent alopecia than those who underwent conventional WBRT (4 vs. 10 regions, P = 0.07). The scalp EQD50% of SA-WBRT was significantly lower than that of conventional WBRT (16.6 ± 3.6 vs. 20.2 ± 5.5 Gy, P = 0.038). The optimal EQD50% cutoff for severe permanent alopecia was 21.2 Gy (area under the curve 83%; 83% sensitivity; 78% specificity). The severe alopecia area was markedly reduced when 21.2 Gy served as the cutoff (27.2 vs. 80.0%, P = 0.008). <h3>Conclusion</h3> SA-WBRT significantly reduced the scalp EQD50% and prevented severe permanent alopecia compared to conventional WBRT. The optimal cutoff dose was 21.2 Gy.