MEYER project: Towards a national protocol for in vivo measurement of 131I in the thyroid of exposed populations in emergencies.

The "MEYER" project (Protocolo Nacional para la MEdida de Yodo en tiroides en Emergencias Radiológicas), initiated by Spain's National R&D Platform for Radiological Protection (PEPRI), aims to enhance national capabilities for the rapid screening of the exposed population to iodine-131 (131I) during nuclear or radiological emergencies. Its primary objective is to address challenges in quantifying internal thyroid contamination in large-scale emergencies, where internal dosimetry services may became overwhelmed. The project is structured into three phases. In phase 1, age-dependent thyroid phantoms representing children (aged 1, 5, and 10 years old) and adults were developed. Each phantom incorporated a vial with a radioactive solution of 133Ba and 137Cs to simulate 131I contamination. A calibration protocol for both spectrometric and non-spectrometric devices was established, followed by an intercalibration campaign involving seven entities and the calibration of their own devices. Phase 2 focused on validating these protocols through the organization of an intercomparison campaign at selected centres, including hospitals, dosimetry services and military units. Finally, phase 3 involves the project's conclusion and the dissemination of results. This study presents the findings from the intercalibration campaign (Phase 1). Preliminary results indicate that counting efficiency values for most calibrated devices decreases with the age-dependent phantom type, with variations reaching up to 60%. Gamma cameras showed high detection sensitivity, making them suitable for large-scale screening in emergencies. On the other hand, surface contamination monitors and radiometers present lower sensitive compared to gamma cameras. These findings highlight the importance of leveraging existing equipment to enhance emergency management strategies.