Patient-specific radiological protection precautions following Cs collagen embedded Cs-131 implantation in the brain

Abstract

Objective: Cesium-131 brachytherapy is an adjunct for brain tumor treatment, offering potential clinical and radiation protection advantages over other isotopes including iodine-125. We present evidence-based radiation safety recommendations from an initial experience with Cs-131 brachytherapy in the resection cavities of recurrent, previously irradiated brain metastases.

Methods: Twenty-two recurrent brain metastases in 18 patients were resected and treated with permanent Cs-131 brachytherapy implantation using commercially procured seed-impregnated collagen tiles (GammaTile, GT Medical Technologies). Exposure to intraoperative staff was monitored with NVLAP-accredited ring dosimeters. For patient release considerations, NCRP guidelines were used to develop an algorithm for modeling lifetime exposure to family and ancillary staff caring for patients based on measured dose rates.

Results: A median of 16 Cs-131 seeds were implanted (range 6-46) with median cumulative strength of 58.72U (20.64-150.42). Resulting dose rates were 1.19 mSv/h (0.28-3.3) on contact, 0.08 mSv/h (0.01-0.35) at 30 cm, and 0.01 mSv/h (0.001-0.03) at 100 cm from the patient. Modeled total caregiver exposure was 0.91 mSv (0.16-3.26), and occupational exposure was 0.06 mSv (0.02-0.23) accounting for patient self-shielding via skull and soft tissue attenuation. Real-time dose rate measurements were grouped into brackets to provide close contact precautions for caregivers ranging from 1-3 weeks for adults and longer for pregnant women and children, including cases with multiple implantations.

Conclusions: Radiological protection precautions were developed based on patient-specific emissions and accounted for multiple implantations of Cs-131, to maintain exposure to staff and the public in accordance with relevant regulatory dose constraints.

Keywords: brachytherapy; brain metastases; radiation safety.