Abstract
This research project is focused on investigation and simulation of radiation detector failures. This technical device are used in Nuclear Medicine where the problem associated with detection canceled to major damage to staff and patients.
Investigation focused on the determination of failure cause for detectors and other equipment like monitors and so on and assessment of post-detection actions
Simulation focused on the determination of a mathematical equation of detector failure prediction and assessment of suitability of the detectors (optional)
The first phase will result in the list of major failure causes referred to detectors and the associated equipment. The method are based in statistical data analysis and simulation using electron tools, the exact list of calculated parameters and software will be determined during the simulation phase of the project. Suitability assessment is optional due to the need in survey and will be carried out only if agreed with practicing professionals.
Introduction
In 1895Wilhelm Röntgen discovered X rays. A lot has changed and now different types of particles, different physical and chemical methods are used for imaging and for radiation determination. (Grupen 2012).
Nuclear Medicine is a fast growing field (Candela 2015; Ranger 1999), but radiation exposure remains dangerous, so the accurate detection is essential
Today the basic radiation detector systems look like the one presented on figure 1.
Figure 1 Basic radiation detector system
Describing radiation detectors Seco (2014) listed three general modes of operation. The most common ones used in dosimetry to detect and evaluate radiation are pulse mode enabling work up to very high event rates and current mode, the third one is mean square voltage mode.
Background
Failures when operating radiation detector can happen as for any other technical device, but in this case they could cost members of stuff and patients even their lives.
The failures can be in detector itself or in transferring elements: monitors, cables and so on. Several types of detectors used in Nuclear Medicine are listed below together with the most common specific problems (Seco 2014):
End-window Geiger Muller detector (GMD)
These well-known and probably the most commonly used detector is a very vulnerable to damage by contact stiff parts, with any angular thing. For example, technicians can accidently damage it with tools. In such case, the detectors can implode leading to the whole replacement, as it is impossible to repair it. Solvents affect the performance of the detector as the conductive coating (DAG) is sensitive to them and can be even removed. It is impossible to prevent contact with chemicals. Thus, it is a common problem, which it is hard to identify on initiatory state, so it is uneasy to prevent further damage.
Scintillation detectors
Thin-window alpha and beta scintillation detectors
Thin window pron to damage, which generally results in leakages. Light transgresses and, as a result, background count rates rises or whistling noises became visible affecting the results and professional decisions. Still it is not fatal, as the professional can replace the foil. This replacement is relatively easy to perform. Photo-multiplier tubes sensitivity towards magnetic interference is familiar to all experts; it can become a major problem in the facilities lacking space or with insufficiently considered organization. Even magnetic behavior of cables should be taken into account.
Sodium iodide scintillation detectors
In these detectors water contamination is intolerable, because it effectively increases the energy critical points and reduces the sensitivity ending light leakage or the formation of yellow patches. The main cause of the contamination is damaged integrity. In the worst case, damage leads to shattering of the crystal and following obvious loss in sensitivity. As for the other scintillation detectors, magnetic fields should be avoided.
Sealed thin-window proportional counters
These detectors do not implode, however gradually lose their sensitivity if punctured. This damage despite different nature still leads to total replacement like in the GMD cases, but even more expensive, so it definitely can become a problem for public departments. The increased service costs should be budgeted as damages can show any moment. The progressive sensitivity-cutting is also dangerous, because it can pass unnoticed or be misinterpreted.
Ion chambers
Contamination with water is intolerable. The dry atmosphere inside is indispensable. The desiccant should not be exhausted otherwise it is very likely to observe the increased background baseline (either positive or negative tendency), and the increased fluctuation level. This problem could be eliminated via drying according to the manufacturer’s instructions. Typical several hours in a warm and dry atmosphere are enough to bring it back to work.
The cables, monitors and other surfaces can also be damaged or contaminated showing as a detector failure, as such damages directly or indirectly affect the detector.
Design
The objective of this research project is investigation of radiation detector failures. This would be an analytic research with a potential for future practical part.
Investigation
Determination of causes (radiation detector technical check, cable and other things technical check, timing and detection methods, costs if applicable)
Simulation
Determination of a mathematical equation of detector failure prediction (propose and test an equation)
Methods
The actual data and sample detectors will be used for investigation. The factors will be range using mathematical analytical techniques. Numerical data are to be analyzed using corresponding statistics practices.
The assessment of post detection procedures will include timing, efficiency and guarantees. In the best case it should include data analysis and survey, which is optional.
The simulation will be done using either MS Excel or Mathcad applications, depending on the number of factors chosen for simulation and the nature of mathematical dependence. As a result, of the investigations and the simulations the most important factors and the equation to predict potential falters to be listed.
The equation should be tested using. Usually, the deviations for the equation should not be more than 5%, preferred more than 1%. The reliability should be calculated using any appropriate means, if it is lower than 80%, than a new simulation to be done. If it is not possible to suggest the equation with reliability exceeding 95%, the simulation should be considered completed, though unreliable for further calculations.
If the research will be included in any other project in part or in whole, that the simulations should be completed with positive result.
The assessment of detector suitability, which is marked as optional, supposes the assessment of expediency to use such detectors in different health facilities taking into account failure likelihood and repair/service/calibration and any other applicable costs. In the best case, it should include the survey among the practicing professional. Still it could be self-assessment or an alternative survey conducted among fellow students willing to evaluate the given technical and financial data. It is highly probable that for students’ survey an additional research summarizing advantages and disadvantages for each of the investigated detectors will be needed, as students should be aware of medical aspects. I fit is too complex or people are unwilling to cooperate that the additional evaluation should be performed using the results of the technical/financial assessment survey.
The further research proposal will be written after the investigation and simulation parts are completed no matter how the survey goes, it is highly possible that the potential lays in more detailed investigation of technical causes or broadening the number of detectors and get into contact with different health organization to find the way to test the equation on practice. The last point is essential to prove the theoretical excavation and will need at least 10, but better 25 detectors of each type and 6 month for observation. The check protocol developed together with the further research proposal is to be completed every week.
Referances
Candela-Juan, C, Niatsetski, Y, Ouhib, Z, Ballester, F, Vijande, J and Perez-Calatayud, J, 2015, Commissioning and periodic tests of the Esteya® electronic brachytherapy system. Journal of Contemporary Brachytherapy, vol. 7, no. 2, pp. 189-195.
Grupen, C & Buvat, I, 2012, Handbook of Particle Detection and Imaging, Springer.
Peterson TE & Furenlid, LR, 2011, SPECT detectors: the Anger Camera and beyond. Physics in medicine and biology, vol. 56, no. 17, pp. R145-R182.
Ranger, NT, 1999, The AAPM/RSNA Physics Tutorial for Residents, RadioGraphics , vol. 19, no. 2, pp. 481-502
Seco, J, Clasie, B and M, Partridge, 2014, Review on the characteristics of radiation detectors for dosimetry and imaging Phys. Med. Biol., vol. 59, pp. R303–R347
