Ubeda, C.1; Miranda, P.2; Vano, E.3 & Nader, A.4
The correspondence should be addressed to Carlos Ubeda de la Cerda. Email: email@example.com
Received in May 07, 2019. Accepted in July 27, 2019.
UBEDA, C.; MIRANDA, P.; VANO, E. & NADER, A. Results and future perspectives of radiological protection in pediatric interventional cardiology for Chile. J. health med. sci., 5(3):175-181, 2019.
ABSTRACT: This work aims to show the main results achieved in Chile during the years following the Bonn Conference on paediatric interventional cardiology (IC) procedures and discuss further actions to improve radiation safety in this medical practice. All the X-ray systems used in paediatric IC procedures in Chile have been characterized in terms of dose and image quality. Besides diagnostic reference levels by age ranges and weights have been established. Furthermore, it has been measured the scatter dose levels at the cardiologist position, for 10 common types of paediatric IC procedures and categorized for four age groups using phantoms to simulate patients. To maintain and improve radiation safety in paediatric IC, it is expected to revise and update the legislation governing the use of ionizing radiation, including the improvement of the Quality Assurance programs and training in Radiation Protection.
KEY WORDS: interventional cardiology, quality assurance programs, ionizing radiation, radiation protection.
MATERIAL AND METHOD
All the X-ray systems (three with image intensifiers and three with flat detectors) used in paediatric IC procedures in Chile have been characterized in terms of dose and image quality, using the protocols agreed during the DIMOND and SENTINEL European program and adapted in our case to paediatric procedures. The third quartile values for the ESAK quantity were used as investigation levels (ILs), for different polymethyl methacrylate (PMMA) phantom thicknesses for setting the interventional cardiology systems (Ubeda et al., 2015a).
Likewise, using the appropriate experimental arrangement has been measured the scatter dose levels. The detectors measuring scatter radiation were positioned at the usual cardiologist distance during working conditions to estimate doses to: the eyes position (Ubeda et al., 2016) and the lower limbs position (Ubeda et al., 2017a).
The collection of a large sample of patient dose data allowed to calculate national DRLs (the used data were collected from January 2011 to September 2013). For each patient, the procedure identification, age, gender, weight, height, dose-area product (DAP) and cumulative dose (at the patient entrance reference point), total number of cine images and fluoroscopy time were registered. Data were extracted from the patient dose reports available in the different X-rays systems (Ubeda et al., 2012; 2015b).
Finally, patient organ doses and effective doses were also calculated using the PCXMC 2.0 Rotation software. This software is based on the Monte Carlo method and has been developed by STUK (Radiation and Nuclear Safety Authority in Finland) (Ubeda et al., 2017b).
Tables I and II show for all the evaluated X-ray systems, values of ESAK per minute and ESAK per frame in all fluoroscopy modes and cine mode, respectively.
Table I. Entrance surface air kerma per minute (mGy/min) for the different X-ray systems in all fluoroscopy modes (low (LF), medium (MF) and high dose (HF)) to entrance surface of different thicknesses of phantom (PMMA).
Table II. Entrance surface air kerma per frame (µGy/fr) for different thicknesses of phantom (PMMA) in cine mode for the different X-ray systems.
Table III shows staff scattered dose values at cardiologist’s eye position (personal dose equivalent, Hp(0.07)) for all X-ray systems and estimated for the ten procedures simulated from 4 to 16 cm of PMMA. Each value refers to a single procedure.
Table III. Entrance surface air kerma (ESAK) values estimated for the ten procedures (A to J) simulated with 4, 8, 12 and 16 cm of polymethyl methacrylate (PMMA) for all evaluated X-ray systems (ID no.).
Table IV shows staff scattered dose values at cardiologist’s lower extremities position (personal dose equivalent, Hp (0.07)) for all x-ray systems, estimated for the ten procedures simulated from 4 to 16 cm of PMMA. Each value refers to a single procedure.
Table IV. Scatter dose (Hp (0.07)) values estimated for the ten procedures (A to J) simulated with 4, 8, 12 and 16 cm of polymethyl methacrylate (PMMA) for all evaluated X-ray systems (ID no.).
Fig. 1. 3rd quartile values for dose-area product grouped by procedure type (diagnostic and therapeutic) and age range (Ubeda et al., 2015b).
Table V presents the mean, median, standard deviation, and third quartiles for the DAP/body weight ratio for diagnostic and therapeutic procedures.
Table V. Mean, standard deviation (SD), median and 3rd quartile (Q75) values for the DAP/body weight ratio for diagnostic and therapeutic procedures (Ubeda et al., 2015b).
Figures 2 summarize effective dose values (median) for diagnostic and therapeutic procedures, grouped by age range and weight band.
Fig. 2. Median values for effective dose grouped by procedure type (diagnostic and therapeutic) and seven weight bands (Ubeda et al., 2017b).
According to Tables I and II, the ratio between the maximum and the minimum value of dose rates for the different evaluated systems was 555 times (considering the different imaging modes and the different simulates patient thicknesses, from 4 to 16 cm of PMMA). For low fluoroscopy mode, ESAK rates ranged from 0.11 to 33.1 mGy min-1. For medium fluoroscopy mode values ranged from 0.18 to 53.8 mGy min-1 and for high fluoroscopy mode from 0.34 to 61.0 mGy min-1. For cine mode, the ratio between the maximum and the minimum value of ESAK per frame for the different systems was 41 times and their values ranged from 1.9 to 78.2 mGy fr-1. On the other hand, the ILs obtained during the survey for the different PMMA thicknesses and fluoroscopy modes (low, medium and high dose) were as follows: 0.62, 1.59 and 3.43 mGy min-1, respectively, for 4 cm PMMA; 1.41, 3.08 and 6.01 mGy min-1, respectively, for 8 cm PMMA; 2.82, 5.96 and 11.93 mGy min-1, respectively, for 12 cm PMMA and 6.72, 14.27 and 18.10 mGy min-1, respectively, for 16 cm PMMA (Ubeda et al., 2015a).
Table III shows scattered dose values at cardiologist’s eye lens position. These reported values allow an estimation of staff dose received in paediatric cardiac laboratories if a ceiling-suspended screen is not used. The cardiologist’s eye lens for the ten kind of simulated procedures ranged from 0.20 to 116 μSv per procedure (factor of 580). If we assume a typical workload of twenty procedures per month, exclusively examining patients aged between 0 to <1 yrs could mean a scattered dose from 4 to 152 μSv per month. In the case of patients aged between 10 to <15 yrs, the monthly range may be from 340 to 2320 μSv. The use of personal protective shielding should also be used in paediatric IC procedures (Ubeda et al., 2016).
Table IV shows scattered dose values at cardiologist’s lower extremities position. These reported values allow an estimation of staff dose received in paediatric cardiac laboratories if a ceiling-suspended screen is not used. The cardiologist lower extremities for the ten kind of simulated procedures ranged from 1 to 375 μSv (factor of 375). If a typical workload of 20 procedures per month is assumed, exclusively examining patients aged between below 15 y of age could mean a scattered dose from 580 to 7500 μSv per month (Ubeda et al., 2017a). Therefore, the maximum annual dose that may reach the cardiologist’s lower extremities would be ~90 mSv, which represents 18 % of the limit for extremities established by the International Commission on Radiological Protection (ICRP, 2007).
The 3rd quartile values obtained for DAP by diagnostic and therapeutic procedures and age ranges were 1.17 and 1.11 Gy cm2 for <1 yr; 1.74 and 1.90 Gy cm2 for 1 to <5 yrs; 2.83 and 3.22 Gy cm2 for 5 to <10 yrs; and 7.34 and 8.68 Gy cm2 for 10 to <16 yrs, respectively (Fig. 1). According to Table V, the 3rd quartile value obtained for the DAP/body weight ratio for the full sample of procedures was roughly 0.17 (Gy cm2/kg) for diagnostic and therapeutic procedures (Ubeda et al., 2015b).
The analysis of dose in organs and effective doses, has been performed on a larger sample (data were collected over seven years from January 2008 to December 2015). A sample of 1506 procedures were divided into four age and seven weight groups. Organ doses (median values) for diagnostic and therapeutic procedures were: active bone marrow 0.90 and 0.64 mGy; heart 1.99 and 1.46 mGy; lungs 3.56 and 2.59 mGy; thyroid 1.27 and 0.83; and breast (in the case of females) 1.78 and 1.36 mGy. The ranges for effective doses (median values) and weight bands were 1.2-3.9 mSv for diagnostic procedures and 1.0 – 2.5 mSv for therapeutic procedures (Fig. 2) (Ubeda et al., 2017b).
This survey for Chile allowed to obtain a preliminary set of typical ESAK values in X-ray systems (fluoroscopy and cine acquisitions) used in paediatric IC procedures and third quartile (proposed as ILs). Medical physicists and service engineers can consider these values for guidance in setting cardiac equipment and paediatric protocols and suggesting further potential optimisation actions when appropriate. Furthermore, these values, together with image quality, could also serve as criteria to consider replacement of old X-ray systems.
For the ten common procedures selected, scattered dose at cardiologist eye lens ranged from 0.20 to 116 μSv per procedure. Large differences between the X-ray systems were found in our study. Furthermore, the maximum annual occupational doses for the cardiologist’s lower extremities was estimated in 90 mSv (if protection curtains are not used). To maintain and improve radiation safety in paediatric IC it is expected to revise and update the national legislation on the use of ionizing radiation, promoting the use of the Quality Assurance programmes and training in Radiation Protection.
The DRL values obtained for Chile could be used by other hospitals in the Latin America region to compare their current values and consider whether optimization actions are needed.
The values obtained for organ and effective dose were similar for diagnostic and therapeutic procedures, diagnostic procedures showing slightly higher values than therapeutic procedures. The resulting set of dose values will permit comparisons with other imaging procedures (comparing the same age bands) for justification purposes.
The current work has been carried out under the frame of the International Atomic Energy Agency regional project, RLA/9/075-output 4 “Strengthening National Infrastructure for End-Users to Comply with Regulations and Radiological Protection Requirements”. C. Ubeda acknowledges the support of the Direction of Research at the Tarapacá University, through senior research project No. 7713-18.
UBEDA, C.; MIRANDA, P.; VANO, E. & NADER, A. Resultados y perspectivas futuras de protección radiológica en cardiología intervencionista pediátrica para Chile. J. health med. sci., 5(3):175-181, 2019.
RESUMEN: El objetivo de este trabajo fue mostrar los resultados principales conseguidos en Chile durante los años siguientes a la Conferencia de Bonn sobre Cardiología Intervencionista (CI) pediátrica y discutir futuras acciones para mejorar la seguridad radiológica en la práctica médica. Todos los sistemas de rayos x utilizados en procedimientos de CI pediátricos en Chile son caracterizados por su calidad de imagen y dosis. Se establecieron niveles de referencia diagnósticos por rango de edad y peso; además, se midieron los niveles de dosis dispersa en la posición del cardiólogo para 10 tipos comunes de procedimientos de CI pediátricos y se categorizaron por grupos de edad usando fantomas como simulador de pacientes. Para mantener y mejorar la seguridad radiológica en la CI pediátrica, se espera una revisión y actualización de la legislación que maneja el uso de radiación ionizante, incluyendo la mejora de programas de Control de Calidad y preparación en Protección Radiológica.
PALABRAS CLAVE: cardiología intervencionista, programas de control de calidad, radiación ionizante, protección radiológica.
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Carlos Ubeda de la Cerda
Clinical Sciences Department
Health Sciences Faculty
Universidad de Tarapacá