A great benefit of recent advances in non-invasive examination using modalities like echocardiography, cardiac CT and MRI is that the number of indications for diagnostic cardiac angiography has decreased in comparison with the past. Nevertheless, reliable and detailed measurement of blood flow, vascular resistance and blood pressure still depends on invasive angiography.
According to ICRP publication 135, there are no current national DRL values for pediatric interventional radiology or interventional cardiology. Several countries have tried to establish local pediatric DRL values for interventional procedures[12]. There are however no studies that attempt any form of qualitative synthesis (Fig. 1). Therefore, our study may be the first instance in the literature of large-scale, national DRL research applied to pediatric interventional cardiology.
The present nationwide survey found that the radiation dose used in pediatric diagnostic and therapeutic cardiac catheterization was much higher than reported in previous literature[7–10]. As compared with previous reports, radiation dose was remarkably high: from 2 to 4 times greater in those aged 1 to 5 years and 1.2 to 4.5 times greater in those aged 6 to 15 years (Fig. 3, 4). There are several possible reasons for such obvious differences. First, Ubeda’s et al., who investigated DRL in Chile and Costa Rica and determined 75th percentile values for diagnostic and interventional cardiac catheterization, based their findings on results from just a single center in both countries. In this study, all equipment for Chile, Costa Rica, and Spain was from the same manufacturer. In contrast, our DRL data originate from equipment from various manufacturers. Therefore, the acquisition parameters, SID, frame and pulse rates, and added filtration used by the device differ. We have not performed detailed analyses, but this is one possible cause for the higher DRL in Japan. The present study included 43 facilities from an entire nation in which there might be a wide range of dose settings within each hospital.
Second, in addition to variation in dose settings, results might be influenced by other factors including a wide variety of angiography units from many vendors, the size of the field being irradiated, soft line elimination filters, bed height, and source image distance. In other words, while 75th percentile values were 2–3 times higher than in the articles referred to above, our result might fundamentally reflect a national reference level.
Third, Japan is in a unique situation regarding control of radiation exposure, as there are very few medical physicists in the entire country. Radiological technologists thus need to play the role of medical physicists in managing the radiation dose.
Comparing diagnostic and therapeutic interventions, Ubeda’s results were similar. In this study there were no significant differences for Ka,r between the diagnostic and therapeutic procedures.
However, the Ka,r (189 mGy) of treatment procedures was 1.3 times the Ka,r (142.1 mGy) of diagnostic procedures, and Ka,r tended to be higher than the diagnosis.
In addition, it is necessary to consider diagnosis and treatment separately when formulating DRL because significant differences are found for FT and CI.
A further observation is that many facilities use the same fluoroscopy rates (7.5 pulses/sec) and exposure rates (30 frames/sec) for both diagnostic and therapeutic cardiac catheterizations. Previous reports describe fluoroscopy rates and exposure rates of 10–15 pulses/sec and 10–30 frames/sec[15], almost the same as in the present survey.
Among various methods used for exposure dose reduction, decreasing fluoroscopy rates and exposure rates is thought to be one of the most effective techniques during cardiac catheterization[16, 17]. It is necessary to use fluoroscopy rates and exposure rates in a manner that is appropriate to the patient’s specific diagnosis and individual status.
In addition to delays in establishing DRLs for cardiac angiography, national guidelines regarding clinical examinations used for decision making in diagnosis of and drug therapy for pediatric patients with congenital heart disease and cardiovascular disorders have only recently been published[18]. Compared to other countries, acquisition of diagnostic guidelines and national DRLs may be somewhat late; we therefore hope that establishing DRLs for cardiac catheterization will quickly lead to national dose regulation.
Our study has some limitations. First, national DRLs are usually determined by the accumulation of data from many cases. For each age group in the diagnostic cardiac catheterization group, the number of cases was large 26 to 137 and we therefore consider the values to be reliable. However, the number of cases for therapeutic cardiac catheterization (excluding ages 1–5), for which DRL data are available, is small, and may therefore be less reliable. We intend to examine more cases in the future. More detailed data may also be derived where missing values are present using multiple imputation of values. Second, we did not evaluate individual cases or diseases. Further evaluation will therefore be necessary to take into account differences between diagnostic and interventional radiology (IVR) procedures. Third, kV, mA, pulse duration and frame duration values were not collected, nor were details of any additional filtering. Also, pediatric exposure doses by age were evaluated. However, pediatric DRLs recommend the use of weight categories, rather than age bands[19]. DRLs presented as a function of patient weight rather than weight categories. Therefore, it is necessary to further analyze using weight categories. Fourth, fluoroscopy rate and exposure rate are programmable techniques, and may therefore vary across the different protocols programmed into fluoroscopic units. Therefore, fluoroscopy and exposure rates were not collected. However, the device manufacturer, inch size, number of fluoroscopic pulses, and number of imaging frames were specified for each case. Fifth, there are numerous patient factors that influence the derivation of DRLs in interventional procedures, unlike in general radiography. These patient factors may include variable patient anatomy (e.g., body habitus, vascular tree variations, blood vessel diameters), lesion variability, and factors related to operator and equipment. These factors may all play a role in DRLs. Finally, we did not evaluate the images acquired at cardiac catheterization for vascular enhancement and subjective image quality.