Visualization of Low-Level Gamma Radiation Sources Using a Low-Cost, High-Sensitivity, Omnidirectional Compton Camera
January 30th, 2020
We present experimental protocols for visualizing various low-level gamma radiation sources in the ambient environment using a low-cost, high-sensitivity, omnidirectional, gamma-ray imaging Compton camera.
This simple method allows the rapid visualization of low-level gamma radiation sources with ambient surface and, or air dose rates over a few microsieverts per hour or less. The detector is omnidirectional, highly sensitive, inexpensive and portable, and can be used for low-level gamma radiation sources within RI facilities, and out of the ward around Fukushima. The method can serve as a next-generation technology for environmental radiation monitoring, replacing the conventional stationary dose rate monitors, currently in use in RI facilities on hospitals.
Demonstrating the procedure will be Nina Kuwata and Katsuki Kubayashi, students from my laboratory. For monitoring of a sealed radiation source within a radioisotope facility, set the Compton camera beside the wall-mounted dose rate monitor, and measure the height of the detectors from the ground. The wall-mounted dose rate monitor consists of a parallel plate ionization chamber, and can constantly monitor the air dose rate of the position at one minute intervals.
Power on the Compton camera with the online computer and initiate the simultaneous measurement with the Compton camera and the dose rate monitor. Place a Cesium-137 sealed source at the A position, 3.6 meters away from the detectors. After 30 minutes, move the sealed source to position B, 6.7 meters away from the detectors.
After another 30 minutes, move the sealed source to position C, 6.7 meters away from the detectors. After another 30 minutes, move the sealed source to position D, one meter from the detectors. After 30 more minutes, move the sealed source outside the room for 30 minutes, and stop all of the measurements.
For environmental monitoring within a PET facility, early in the morning before patients arrive, set the Compton camera in front of the reception desk in the PET facility, and measure the height of the detectors from the ground. Place the online computer in the staff room and power on the camera and computer. When all of the materials are in place, start the measurements.
Stop monitoring after all of the patients have left for the day. For radioisotope measurement outside, place the Compton camera near the building of interest, at which the existence of some radiological Cesium hotspots with service dose rates of one microsieverts per hour, or less, are suspected. Set the height of the detectors to 1.5 meters from the ground, and power on the camera and computer.
Then, acquire Compton camera measurements for 30 minutes. Here, the time variation of the trigger rate measured by the Compton camera in a radioisotope facility, after applying a time lag selection of two head counters less than one microsecond, is shown. The trigger rate changed every 30 minutes, depending on the position of the sealed source, as confirmed from the data measured by the stationary dose rate monitor.
Five periods were set to represent the five positions of the sealed source. As illustrated in these omnidirectional images, for periods one to four of monitoring, the position of the Cesium-137 sealed source can be successfully identified from the gamma ray images shown in red. The overall time variations of the trigger rates measured in a PET facility during the daytime reveals a remarkable enhancement in the trigger rate with various patterns, which could be attributed to the movement of patients injected with Fluorine-18 Fluorodeoxyglucose around the reception desk.
For example, focusing on the period from 6, 200 to 7, 000 seconds, a series of enhancements with two plateaus become apparent. In these images of the facility, the directions of the gamma ray peaks in both images correspond to the directions of the sofa and the restroom behind the wall. Considering the trigger rates of both monitoring periods, it is likely that a patient entered the restroom for two minutes, and afterwards, sat on the sofa for a few minutes before the PET scan.
In the outdoor measurement in Fukushima field, the protocol reveals that the gamma ray images concerning ground-level distribution of low-level radioactive Cesium contamination can be acquired. Our decontamination procedure can be used in areas with low-level radioactive Cesium contamination, released by the Fukushima Daiichi nuclear power plant accident, and we improved the present PET system.
Overview
This article presents experimental protocols for visualizing low-level gamma radiation sources using a cost-effective, high-sensitivity Compton camera. The method is suitable for environmental monitoring in various settings, including radioisotope facilities and areas affected by radiation.
Key Study Components
Area of Science
- Radiation detection
- Environmental monitoring
- Gamma-ray imaging
Background
- Low-level gamma radiation sources pose monitoring challenges.
- Conventional stationary dose rate monitors are limited in flexibility.
- Advancements in imaging technology can enhance radiation monitoring.
- The Compton camera offers a portable and sensitive alternative.
Purpose of Study
- To develop a method for rapid visualization of gamma radiation sources.
- To demonstrate the effectiveness of the Compton camera in various environments.
- To provide protocols for monitoring in radioisotope facilities and outdoor settings.
Methods Used
- Set up the Compton camera alongside traditional dose rate monitors.
- Conduct measurements at various distances from a sealed Cesium-137 source.
- Monitor environmental radiation in a PET facility before patient arrival.
- Acquire data on gamma ray emissions and analyze trigger rates.
Main Results
- Successful identification of Cesium-137 sources through gamma ray imaging.
- Trigger rates varied significantly based on source position and patient movement.
- Demonstrated capability to monitor low-level radioactive contamination outdoors.
- Enhanced understanding of radiation distribution in monitored areas.
Conclusions
- The Compton camera is a viable tool for environmental radiation monitoring.
- It can replace conventional methods in various settings.
- Further development may improve monitoring of low-level radioactive contamination.
Frequently Asked Questions
Executive Industry Relevance
Visualizing low-level gamma radiation sources supports target validation in radiopharmaceutical development by enabling precise tracking of tracer distribution and environmental contamination. The Compton camera’s high sensitivity and portability enhance mechanistic de-risking in preclinical studies involving radiolabeled compounds. This capability improves predictive confidence in biodistribution studies and radiation safety monitoring across discovery and translational workflows.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of radiotracer biodistribution and pathway clarification in preclinical models.
- Operational Value: Provides omnidirectional imaging to clarify functional target engagement and reduce mechanistic ambiguity.
- Predictive Value: Supports portfolio triage by visualizing low-level gamma emissions from radiolabeled compounds in vivo or in situ.
Screening & Assay Development
- Scientific Value: Prepares validated biological systems for downstream screening by mapping background radiation interference.
- Operational Value: Ensures assay standardization through reproducible, quantitative gamma-ray imaging across multiple measurement points.
- Scalability: Facilitates platform reuse in diverse settings, from radioisotope facilities to field environments, enabling reliable compound evaluation.
Translational & Preclinical Research
- Translational Continuity: Connects discovery-phase imaging to preclinical validation by monitoring radiotracer movement in real time.
- Risk-Adjusted Advancement: Visualizes radioactivity movement, such as patient-mediated 18F-FDG distribution, to inform safety and dosing decisions.
- Mechanistic De-risking: Focuses on predictive de-risking by confirming environmental containment and reducing off-target radiation exposure risks.
Pipeline & Workflow Integration
The method integrates into the discovery continuum from early target validation through lead identification to preclinical studies, particularly for radiopharmaceutical programs requiring radiation distribution mapping.
- Discovery Biology: Supports hypothesis testing by visualizing gamma emissions from sealed sources or radiotracers to clarify spatial distribution.
- Screening: Delivers assay readiness via reproducible trigger rate measurements and omnidirectional imaging for comparative condition analysis.
- Analytics: Generates quantitative trigger rate data and gamma-ray images that enable teams to compare source positions and movement patterns over time.
- Translational Research: Links to preclinical continuity by tracking patient-injected radiotracer movement in nuclear medicine facilities, aligning with biomarker alignment goals.
- Enterprise Reuse: Positions the Compton camera as a reusable capability across facilities, reducing reliance on stationary monitors and enabling adaptive environmental surveillance.
Operational & Enterprise Impact
- Scientific Value: Predictive confidence in radiotracer behavior, target validation through spatial gamma mapping, reduction of mechanistic ambiguity in biodistribution.
- Operational Value: Standardization via repeatable measurement protocols, reproducibility across indoor and outdoor settings, scalability from lab to field applications.
- Strategic Value: Better go/no-go decisions in radiopharmaceutical development, capital efficiency by replacing fixed monitors, reduced late-stage biological risk from undetected radiation spread.
- Portfolio Impact: Risk-adjusted prioritization of compounds based on visualized radiation distribution and contamination potential.
Implementation Considerations
- Requires expertise in radiation detection, gamma-ray imaging, and Compton camera operation.
- Needs instrumentation including the Compton camera, online computer for data acquisition, and calibration sources like 137Cs for validation.
- Demands cross-team standardization between radiochemistry, imaging, and safety teams for consistent environmental monitoring protocols.
- Involves adaptation considerations when deploying across model systems, from benchtop sealed sources to dynamic patient environments and outdoor contamination zones.
- Includes practical limitations such as sensitivity to very low dose rates (<1 µSv/h) and the need for time-lag selection in trigger rate analysis to reduce noise, as supported by source material.
