Estimation of the eye lens doses in a catheterization laboratory from available image parameters
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Background and objective: New data on eye lens dosimetry supports the theory that the threshold of radiation-induced cataracts could be substantially lower than previously believed with some investigators arguing that cataracts could be classified as a stochastic rather than a deterministic effect. Based on these new data, the International Commission on Radiological Protection (ICRP) has reduced the occupational eye lens dose limit from 150 mSv to 20 mSv averaged over a defined period of 5 years, with no single year exceeding 50 mSv. The new reduction in the annual dose limit will have considerable implications particularly in high exposure environments such as interventional cardiology and radiology. It is therefore imperative that strategies for effective dose reduction, radiation protection, eye dose monitoring, and dosimetry be implemented in countries that have already adopted the new eye dose limit. The main aim of this study was to develop methods that can be applied to estimate eye dose equivalent from the available imaging parameters and whole-body equivalent measured over the lead apron at the chest level. The study also aimed to establish a method to estimate eye lens dose based on the workload of interventionalists. Material and methods: The study included four interventional cardiologists. A total of 127 procedures were performed in a period of three months. The procedures were categorised into diagnostic (CA) and therapeutic (CA+PCI) procedures. During these procedures, two different active dosimeters were used to measure scatter dose (one attached on the canthus of the protective eyewear to measure eye lens dose (ELD) and the other at the chest level to measure whole-body dose) to the cardiologists. The dose area product (DAP), air kerma (Ka,r), fluoroscopic time, total cine images were recorded after every procedure. The efficacy of the protective eyewear used at Universitas Hospital was evaluated in a separate study. Results: Average eye dose per CA and CA+PCI procedures were 195.1±112 and 391.8±202.9 µSv, respectively. The average dose per procedure obtained by combining all the monitored procedures was 250.9±168.3 µSv. The minimum workload necessary to exceed the annual eye lens dose limit calculated using an equation established in this study was 80 procedures. The dose reduction factor of the protective eyewear was ~2. Applying this factor increased the minimum procedures necessary for a doctor to exceed the limit to 160 procedures per year. Excellent correlation was found between ELD and DAP (R2 = 0.78). Excellent correlation was also found between ELD and Ka,r (R2 = 0.72). A poor but significant correlation was found between ELD and chest dose (R2 = 0.45). Three methods based on the ratios of ELD to DAP, Ka,r and chest dose were established. The calculation error using the methods based on DAP and Ka,r was ±20%. The respective calculation error was ±37% using the method based on chest dose. Conclusion: The accumulated eye dose of interventional cardiologists working at the Universitas Hospital can easily surpass the newly set annual eye lens dose limit after performing relatively low numbers of interventional procedures. The high average dose per procedure reported in this study highlights immediate need for implementation of radiation optimization strategies to mitigate the risk of radiation-induced cataracts. This is the first study in South Africa to establish methods that can be used to estimate eye lens doses at any time. More research is needed in the South African context to further investigate eye lens dose in interventional suits. This will allow for comparison of results obtained at different institutions and improvement in accuracy of estimation methods.