Feasibility of safe outpatient treatment in pediatric patients following intraventricular radioimmunotherapy with 131I-omburtamab for leptomeningeal disease

Abstract

Background: Radiolabeled antibody ¹³¹I-omburtamab was administered intraventricularly in patients with leptomeningeal disease under an institutionally approved study (#NCT03275402). Radiation safety precautions were tailored for individual patients, enabling outpatient treatment based on in-depth, evidence-based recommendations for such precautions. The imperative advancement of streamlined therapeutic administration procedures, eliminating the necessity for inpatient isolation and resource-intensive measures, holds pivotal significance. This development bears broader implications for analogous therapies within the pediatric patient demographic.

Methods: Intraventricular radioimmunotherapy (RIT) with 925-1850 MBq (25-50 mCi) of ¹³¹I-omburtamab was administered via the Ommaya reservoir, in designated rooms within the pediatric ambulatory care center. Dosimeters were provided to staff involved in patient care to evaluate exposure during injection and post-administration. Post-administration exposure rate readings from the patient on contact, at 0.3 m, and at 1 m were taken within the first 30 minutes, and the room was surveyed after patient discharge. Duration of radiation exposure was calculated using standard U.S. Nuclear Regulatory Commission (US NRC) regulatory guidance recommendations combined with mean exposure rates and whole-body clearance estimates. Exposure rate measurements and clearance data provided patient-specific precautions for four cohorts by age: < 3 y/o, 3-10 y/o, 10-18 y/o, and 18+.

Results: Post-administration exposure rates for patients ranged from 0.16-0.46 μSv/hr/MBq at 1 ft and 0.03-0.08 μSv/hr/MBq at 1 m. Radiation exposure duration ranged from 1-10 days after release for the four evaluated cohorts. Based on the highest measured exposure rates and slowest whole-body clearance, the longest precautions were approximately 78% lower than the regulatory guidance recommendations. Radiation exposure to staff associated with ¹³¹I-omburtamab per administration was substantially below the annual regulatory threshold for individual exposure monitoring.

Conclusion: ¹³¹I-omburtamab can be administered on an outpatient basis, using appropriate patient-based radiation safety precautions that employ patient-specific exposure rate and biological clearance parameters. This trial is registered with the National Library of Medicine's ClinicalTrials.gov. The registration number is NCT03275402, and it was registered on 7 September 2017. The web link is included here. https://clinicaltrials.gov/study/NCT03275402.

Keywords: Brain metastases; radiation safety; radiopharmaceutical.

Figure 1

Distribution of normalized exposure rates in μSv/hr/MBq