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Patient radiation doses in paediatric interventional cardiology and optimization actions
Journal Pre-proof Patient radiation doses in paediatric interventional cardiology and optimization actions Carlos Ubeda, Eliseo Vano, Nemorino Riquelme, Daniel Aguirre, Hector Vasquez, Cristian Chavez, Dandaro Dalmazzo PII:
S0969-806X(19)30764-9
DOI:
https://doi.org/10.1016/j.radphyschem.2019.108539
Reference:
RPC 108539
To appear in:
Radiation Physics and Chemistry
Received Date: 6 July 2019 Revised Date:
29 August 2019
Accepted Date: 21 October 2019
Please cite this article as: Ubeda, C., Vano, E., Riquelme, N., Aguirre, D., Vasquez, H., Chavez, C., Dalmazzo, D., Patient radiation doses in paediatric interventional cardiology and optimization actions, Radiation Physics and Chemistry (2019), doi: https://doi.org/10.1016/j.radphyschem.2019.108539. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.
Patient radiation doses in paediatric interventional cardiology and optimization actions
Carlos Ubeda, PhD. Medical Technology Department, Health Sciences Faculty, Universidad de Tarapaca, Arica, Chile, [email protected]. Tel. +56.58.2205703 and fax +56.58.205705. Eliseo Vano, PhD. Radiology Department, Faculty of Medicine, Complutense University and IdIS, San Carlos Hospital, 28040 Madrid, Spain. Nemorino Riquelme, MSc. Hemodynamic Department, Cardiovascular Service, Luis Calvo Mackenna Hospital, Santiago, Chile. Daniel Aguirre, MD. Hemodynamic Department, Cardiovascular Service, Luis Calvo Mackenna Hospital, Santiago, Chile. Hector Vasquez, MSc. Office of continuing education-FACSAL, Health Sciences Faculty, Universidad de Tarapaca, Arica, Chile. Cristian Chavez, PhD. Health Sciences Faculty, Universidad San Sebastian, Santiago, Chile. Dandaro Dalmazzo, MSc. Faculty of Health and Odontology, Universidad Diego Portales, Santiago, Chile.
Short running title: Patient radiation dose in paediatrics (interventional)
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Abstract (195 words) This work presents patient radiation dose data for paediatric interventional cardiology procedures in a large paediatric hospital in Chile. This will contribute to setting national diagnostic reference levels (DRLs) for Chile in the near future. The dosimetric data collection period was from January 2018 to December 2018. The local DRLs were calculated as the 3rd quartile of patient dose data distributions for kerma area-product (Pka) values. The sample of collected clinical procedures (261) was divided into diagnostic and therapeutic procedures and grouped into five weight bands. The Pka differences found between diagnostic and therapeutic procedures were not statistically significant when comparing the same weight bands, as a result of which we propose a single DRL value for both types of procedure. The local DRLs were 4.9 Gy·cm2 (<5 kg), 6.6 Gy·cm2 (5-<15 kg), 13.7 Gy·cm2 (15-<30 kg), 30.7 Gy·cm2 (30-<50 kg) and 29.7 Gy·cm2 (50-<80 kg), respectively. The conclusion from comparing our results with other existing DRL values is that there is ample scope to continue optimising by reducing patient dose values. Equipment performance, settings used and examination protocols should be reviewed as corrective actions and adapted to patient weight.
Keywords: interventional cardiology, paediatrics, diagnostic reference levels, radiation doses.
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Main text: 2605 (without references and tables) 4009 total 1. Introduction Patients paediatric can receive high radiation levels during interventional cardiology procedures (ICPs) (Bacher et al., 2005; Ubeda et al., 2012, 2015). In comparison with adults, interventional radiological examinations in children carry a higher average risk for the development of cancer per unit of radiation dose (Khong et al., 2013, Preston et al., 2007). The higher radiation risk in children is explained by their longer life expectancy (Linet et al., 2009), which allows more time for any harmful effects of radiation to manifest, and by the fact that developing organs and tissues are more sensitive to the effects of radiation (ICRP, 2007).
Diagnostic reference levels (DRLs) are an essential tool in the management of patient dose and hence in optimizing of radiation protection taking into account the clinical benefits for patients. The International Commission on Radiological Protection (ICRP) has recommended the use of DRLs for interventional procedures and in paediatric imaging, describing them as useful for good practice and as an aid in optimization (ICRP, 2017). Median patient dose values deriving from the procedures performed in a particular room can be compared with local or national DRLs to identify whether the median values obtained for that room are higher or lower than existing DRLs, and thereby to decide whether any corrective actions might be necessary. This comparison of local practice data with the existing DRLs values is the first step in optimizing protection and can be used for patient dose audit (ICRP, 2017).
In the past, patient age has been used to define groups of children for the purpose of establishing paediatric DRLs (Dragusin et al., 2008; Tsapaki et al., 2008; Chida et al., 2010; Vano et al., 2011; Ubeda et al., 2012, 2015; Verghese et al., 2012; Jones et al., 2016). However, Kleinman et al. (2010) have demonstrated that individual patient size does not correlate well with patient age, suggesting that it is preferable to use groupings based on paediatric patient body size. For their part,
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Järvinen et al. (2015) argue that weight is a more reliable factor to link with DRL than age. The ICRP recommends the use of weight bands for establishing paediatric DRL values (ICRP, 2017) and this approach has also been adopted in the European Guidelines on DRLs (EC, 2016).
Paediatric patient dose values and DRLs remain scarce in the global scientific literature, particularly in Latin America and the Caribbean. However, Chile has been systematically working in collaboration with the International Atomic Energy Agency (IAEA) to foster a radiation protection culture and to improve radiation dose management in paediatric ICPs.
Chile is a medium-size country with 17,574,003 million inhabitants, where paediatric interventional cardiology is carried out in a few hospitals (INE, 2019). Calvo Mackenna Hospital performs around 35% of all cardiac paediatric procedures in the country and Roberto del Río Hospital accounts for around 25% of these procedures. The other Chilean paediatric hospitals are expected to participate in a national programme in the coming years. Chile has yet to establish national DRLs, but local levels have been obtained at Calvo Mackenna Hospital.
This paper represents an additional contribution to setting national DRLs for paediatric interventional cardiology in Chile and suggesting optimization actions derived from a comparison with existing local DRLs and other published results in the scientific literature. The paper also proposes the setting of DRLs by weight band rather than by age band for a second large hospital in Chile (Roberto del Rio Hospital). This has been addressed in previous publications for the largest hospital in Chile (Calvo Mackenna Hospital) (Ubeda et al., 2012, 2015).
2. Materials and Methods The study was conducted at the Haemodynamics department of Roberto del Río Hospital, Chile. The recruitment period was from January 2018 to December 2018. The study design was
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retrospective. This centre has been continuously involved in three technical cooperation projects since 2008 (RLA 9057, RLA 9067 and RLA 9075) (Sanchez et al., 2016) with the support of the IAEA.
A biplane angiography x-ray system (Allura Xper FD20/20 biplane; Philips Healthcare, Best, the Netherlands), installed in 2012 was used in the survey. This angiography system was equipped with flat panel detectors, with a generator of 100 kW at 125 kV. Three fluoroscopy modes were available: low, medium and high dose. Each mode was configured in pulsed mode at 12 or 15 pulses/s. Cine mode was typically used at 30 frames/s. The system had eight fields of view (15, 19, 22, 27, 31, 37, 42 and 48 cm in diagonal). The exam protocols could be pre-programmed with X-per Settings. The system allows acquisitions in three-dimensional rotational angiography (3D-RA), but it is not used. Distance from isocentre to floor was 107 cm and focus-to-isocentre distance was 76 cm.
The system was equipped with an internal flat ionization chamber to measure kerma area-product (Pka) or dose-area product values (ICRU, 2005) and cumulative air kerma at the patient entrance reference point (Ka,r) (IEC, 2010), equivalent to incident air kerma without backscatter (ICRU 2005) at the patient entrance reference point. The patient entrance reference point is a point intended to represent the position of the patient’s skin at the entrance site of the x-ray beam during an intervention procedure. For fluoroscopic systems with an isocentre, the patient entrance reference point is located 15 cm from the isocentre toward the focal spot for C-arm interventional x-ray equipment (IEC, 2010). This position is appropriate for adult patients but requires some correction for paediatrics, as patient skin is (usually) placed no further than 15 cm from isocentre (Vano et al., 2008). The total Pka and Ka,r for each procedure were corrected by a calibration and mean attenuation factor of 0.85, derived from the table and mattress attenuation measured for the x-ray beam qualities used in this system for paediatric procedures (Ubeda et al., 2015).
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The methodology to collect patient dose data and to calculate local DRLs was the same as used in previous papers (Ubeda et al., 2012, 2015, 2018) and aligned with the latest ICRP recommendations (ICRP, 2017). The sample of collected clinical procedures was divided into diagnostic and therapeutic procedures and initially grouped into the five weight bands recommended by the European Guidelines: <5 kg, 5-<15 kg, 15 -< 30 kg, 30-< 50 kg and 50-< 80 kg (EC, 2016). For this initial evaluation and considering the sample size, we did not analyse our data for the different therapeutic procedures or level of complexity for the weight groups. Rather, all therapeutic procedures were analysed together. A separate analysis could be performed in the future when sample size allows and cardiologists have made progress in analysing the complexity of procedures. The following data were extracted manually by the operators from patient dose reports produced by the Philips x-ray system at the end of each selected ICP: procedure identification, patient age, gender, weight, height, Pka, Ka,r, number of cine series and fluoroscopy time.
To assist in optimizing procedures, three full characterizations (in terms of dose and image quality of the angiography system during 2013, 2015 and 2018) were carried out using protocols agreed upon during the DIMOND and SENTINEL European program (Faulkner et al., 2008, Vano et al., 2008), and adapted to paediatric procedures. For the final characterization, a RaySafe Xi dosimeter with a solid-state detector (RaySafe, 2019) in contact with polymethyl methacrylate (PMMA) slabs was used to measure incident air kerma (ICRU, 2005). The detector was placed inside the radiation field, but not in the automatic exposure control area. A backscatter factor of 1.3 was used (ICRU, 2005) to calculate entrance surface air kerma (ESAK), thereby facilitating a comparison of the results with other published measurements. Some of the results of the final characterization are shown in table 4.
The Mann–Whitney test (95% confidence level) was used to compare median Pka values for the two procedure groups (diagnostic and therapeutic). This non-parametric comparison procedure tests
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hypotheses and is used to find differences between two independent samples that are not necessarily normally distributed. Values of p<0.05 were considered statistically significant. SPSS 20.0 software was used (IBM, 2019).
3. Results Table 1 shows the anthropometric characteristics of the subjects.
Table 2 summarises mean, median and 3rd quartile values for kerma area-product (Pka), cumulative air kerma at patient entrance reference point (Ka,r), and fluoroscopy time (FT) for all procedures and frequencies.
Figures 1 and 2 show a summary of Pka values (proposed as local DRLs) separated by type of procedure (diagnostic and therapeutic) and for all procedures grouped by weight band.
Table 3 shows median Pka values by age band reported in this paper compared with those reported in similar surveys.
To assist with optimization strategies and to suggest improvements in the hospital’s imaging protocols, we have compared the results of the quality controls with the x-ray system at the other major paediatric hospital in Chile (Calvo Mackenna Hospital).
Table 4 shows entrance surface air kerma (ESAK) values for the evaluated acquisition modes reported in this study compared with the biplane angiography x-ray system belonging to Calvo Mackenna Hospital. Both were characterized in the year 2018.
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Discussion Table 1 shows median height, weight and body mass index (BMI) values for the five weight bands reported in our survey for paediatric patient dosimetry. Dose monitoring was performed for 261 paediatric ICPs. Median patient height and weight values increased as expected from the lightest to the heaviest group. The minimum number of 30 patients per group recommended for a DRL study in ICRP 135 (ICRP, 2017) was satisfied in all cases except for the 30-<50 kg weight band (25 patients).
Table 2 summarizes three descriptive statistics for Pka, Ka,r, and FT for weight bands and their frequencies. ICPs performed for the 30-<50 kg weight band showed the highest median values for Pka (14.2 Gy·cm2) and FT (12.9 min); this corresponds to the classification of “early adolescence” in the European Guidelines on DRLs for Paediatric Imaging (EC, 2016). The lowest median value for Pka (1.9 Gy·cm2) was for the “neonate” classification corresponding to the <5 kg weight band. Our Ka,r values across all weight bands were far below the threshold proposed by the ICRP for deterministic effects on the skin (2 Gy for transient erythema) (ICRP, 2000).
DRLs based on Pka quantities (3rd quartile as recommended by the ICRP) are useful as a guide to good practice and an optimization aid. Pulses and frames per second (rate), image recording technique and exposure programme options used should be included as complementary information to the DRLs to help in the optimisation strategies (ICRP, 2017). For optimization actions, the investigation should include a review of equipment performance, settings used and examination protocols (Martin, 2011). In table and figure 1, the 3rd quartile values are proposed as a local DRLs obtained in paediatric ICPs by weight bands. According to the p values shown in figure 2, the Pka differences found between diagnostic and therapeutic procedures were not statistically significant when comparing the same weight band. Similar results were obtained in a previous work in another paediatric hospital in Chile, where Pka values were grouped by age band (Ubeda et al., 2015). Our
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results confirm the proposal made by McFadden et al. (2013) and by Jones et al. (2016) to the effect that a single reference level should be used as a benchmark and applied to both diagnostic and therapeutic procedures. Figure 2 shows the proposed local DRLs for different weight bands for all paediatric ICPs. The 3rd quartile Pka values were 4.9 Gy·cm2 (<5 kg), 6.6 Gy·cm2 (5-<15 kg), 13.7 Gy·cm2 (15-<30 kg), 30.7 Gy·cm2 (30-<50 kg) and 29.7 Gy·cm2 (50-<80 kg), respectively. It is surprising that the 3rd quartile values (assumed as local DRLs) for the 50-80 kg band were similar to the 30-50 kg band. This will be analysed in the future when analysing the various therapeutic procedures and their complexity. Some procedures may be easier for larger children requiring lower radiation doses (median fluoroscopy time values are lower in the highest weight band).
There should be a periodic validation of the dosimetric values shown by the x-ray system and transferred to the patient dose reports (Malusek et al., 2014). The built-in Pka meter may require the application of a correction factor, especially for high kVs and high Cu filtration. In our case, the validation was performed using a RaySafe Xi dosimeter with a duly calibrated solid-state detector (RaySafe, 2019).
According to ICRP 135, DRL values based on patient age will be of value primarily to facilitate comparison with older data (ICRP, 2017). Thus, table 3 shows median Pka values for different age categories. The values of this survey tended to be lower than those reported by Verghese et al. (2011), similar to those reported by Kottou et al. (2018) and higher than those reported by Martinez et al. (2007) except for the 10-<16 age band, but higher than those reported for Calvo Mackenna Hospital (Ubeda et al., 2012) for all age bands. It should be noted that Calvo Mackenna Hospital has been involved in several IAEA programmes to optimize radiation dose management in paediatric ICPs since 2009. An optimization programme has been applied for 8 to 10 years at this hospital, which has enabled it to maintain lower dose levels than those usually published elsewhere. This difference can also be explained by the settings of both x-ray systems shown in the
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characterization results (see table 4), where the dose rates for fluoroscopy modes and dose per cine frame were lower for different thicknesses. The exam protocols for the x-ray system at Calvo Mackenna Hospital have been refined, while this process remains necessary at Roberto del Río Hospital, which has considerable scope for optimization. Equipment performance, settings used and examination protocols should be reviewed as corrective actions and adapted to patient weight (Martin, 2011). Unlike in European countries (which comply with Directive 2013/59 (EC, 2014)), Chile has not yet incorporated into its radiological protection legislation (SD, 1984, 1985) the implementation of quality assurance programmes, including the obligation to establish DRLs, or the characterization and commissioning of x-ray fluoroscopy systems used in paediatric ICPs.
Conclusions The Pka differences found between diagnostic and therapeutic procedures in paediatric interventional cardiology were not statistically significant when comparing the same weight bands, for which reason we initially propose a single DRL value for both procedures. The local DRLs values presented in this paper were 4.9 Gy·cm2 (<5 kg), 6.6 Gy·cm2 (5-<15 kg), 13.7 Gy·cm2 (15<30 kg), 30.7 Gy·cm2 (30-<50 kg) and 29.7 Gy·cm2 (50-<80 kg), respectively. Roberto del Río Hospital has considerable scope for optimizing procedures. Equipment performance, settings used and examination protocols should be reviewed as corrective actions and adapted to patient weight.
Acknowledgments The current work has been carried out under the framework of the International Atomic Energy Agency regional project RLA/9/075, “Strengthening National Infrastructure for End-Users to Comply with Regulations and Radiological Protection Requirements”.
Funding This research was partially supported by the Direction of Research at the Tarapaca University,
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through senior research project No. 7713-18.
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Figures captions Figure 1. 3rd quartile Pka values (Q3) for kerma area-product for diagnostic and therapeutic procedures. The data are for the <5 kg, 5-<15 kg, 15-<30 kg, 30-<50 kg and 50-<80 kg weight bands. . Boxes represent the interquartile range; the vertical bars extend to the highest and lowest values, excluding ‘‘outliers’’ (°) and ‘‘extreme values’’ (*).
Figure 2. 3rd quartile Pka values (Q3) for kerma area-product for all procedures. The data are for the <5 kg, 5<15 kg, 15-<30 kg, 30-<50 kg and 50-<80 kg weight bands. Boxes represent the interquartile range; the vertical bars extend to the highest and lowest values, excluding ‘‘outliers’’ (°) and ‘‘extreme values’’ (*).
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Table 1. Sample size (n), median (range) values of age, height, weight and body mass index (BMI) by weight band. Weight n band (kg)
Age (years)
Height (cm)
Weight (kg)
BMI (kg/m2)
<5 5-<15 15-<30 30-<50 50-<80
0.1 (0.0-7.7) 0.9 (0.3-4.7) 6.3 (3.0-15.4) 12.2 (1.3-15.0) 13.9 (9.8-16.2)
50.0 (30.0-63.0) 70.0 (54.0-103.0) 114.5 (92.0-150.0) 147.0 (126.0-176.0) 161.0 (136.0-181.0)
3.3 (1.8-4.9) 8.1 (5.1-14.9) 20.0 (15.0-27.0) 39.2 (31.0-49.0) 61.5 (50.0-79.1)
13.8 (9.2-30.0) 15.6 (12.3-23.8) 15.4 (11.9-21.5) 18.7 (12.5-23.2) 24.00 (16.9-29.7)
61 77 64 25 33
Table 2. Sample size (n), median and 3rd quartile values for kerma area product (Pka), cumulative air kerma at patient entrance reference point (Ka,r) (corrected with a mean attenuation factor of 0.85 for the table and mattress for the frontal X-ray beam) and fluoroscopy time (FT) by weight band. Weight Pka (Gy·cm2) Ka,r (mGy) FT (min) band n Median – 3rd Median – 3rd Median – 3rd (kg) <5 61 1.9 – 4.9 50.1 – 119.0 10.6 – 22.6 5-<15 77 2.7 – 6.6 38.6 – 98.9 9.9 – 20.1 15-<30 64 6.9 – 13.7 69.0 – 135.5 12.0 – 18.4 30-<50 25 14.2 – 30.7 97.4 – 259.4 12.9 – 17.0 50-<80 34 12.6 – 29.7 105.6 – 222.1 12.7 – 20.0
Table 3. Comparison of median Pka values for paediatric cardiology reported in this and other papers (values adapted by the authors of this paper) for all procedures (diagnostic and therapeutic). Kottou Ubeda Martinez Verghese Age This paper et al. et al. et al. et al. band (2019) (2018) (2011) (2012) (2007) (years) (Gy·cm2) 2 2 2 2 (Gy·cm ) (Gy·cm ) (Gy·cm ) (Gy·cm ) <1 1.9 4.6 0.9 2 2.1 1 -<5 2.9 8.3 1.5 3 4.7 5 -<10 4.5 11.5 2.1 7 6.3 10-<16 15.4 24.7 5.0 14 13.6
Table 4. ESAK per second (s) and frame, number of pulses per second (NP) for low (FL), medium (FM) and high (FH) fluoroscopy dose and cine (CI) acquisition modes and all polymethylmethacrylate (PMMA) thicknesses used in the survey. Siemens Axiom Artis BC Philips Allura Xper FD20/20 system system (Calvo Mackenna Hospital) (Roberto del Río Hospital) PMMA (cm) Acquisition FOV NP ESAK ESAK NP ESAK ESAK mode (cm) (s-1) (µGy/s) (µGy/fr) (s-1) (µGy/s) (µGy/fr) 4 FL 22 10 2.1 0.2 12 10.5 0.9 4 FM 22 10 3.3 0.3 15 22.0 1.5 4 FH 22 10 6.0 0.6 15 58.2 3.9 4 CI 22 30 76.6 2.6 30 75.5 2.5 8 FL 22 10 4.8 0.5 12 21.9 1.8 8 FM 22 10 7.6 0.8 15 45.1 3.0 8 FH 22 10 17.6 1.8 15 94.5 6.3 8 CI 22 30 245.0 8.2 30 383.4 12.8 12 FL 22 10 10.6 1.1 12 47.0 3.9 12 FM 22 10 18.2 1.8 15 98.1 6.5 12 FH 22 10 39.3 3.9 15 191.7 12.8 12 CI 22 30 278.0 9.3 30 884.3 29.5 16 FL 22 10 26.4 2.6 12 170.0 14.2 16 FM 22 10 46.6 4.7 15 349.8 23.3 16 FH 22 10 105.9 10.6 15 504.1 33.6 16 CI 22 30 1024.0 34.1 30 3354.8 111.8
The study was carried out as part of International Atomic Energy Agency The diagnostic reference levels by weight bands were from 4.9 to 29.7 Gy·cm2 These values are the second data of diagnostic reference levels for Chile These values are the third data of diagnostic reference levels for Latin America
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S0969-806X(19)30764-9
DOI:
https://doi.org/10.1016/j.radphyschem.2019.108539
Reference:
RPC 108539
To appear in:
Radiation Physics and Chemistry
Received Date: 6 July 2019 Revised Date:
29 August 2019
Accepted Date: 21 October 2019
Please cite this article as: Ubeda, C., Vano, E., Riquelme, N., Aguirre, D., Vasquez, H., Chavez, C., Dalmazzo, D., Patient radiation doses in paediatric interventional cardiology and optimization actions, Radiation Physics and Chemistry (2019), doi: https://doi.org/10.1016/j.radphyschem.2019.108539. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.
Patient radiation doses in paediatric interventional cardiology and optimization actions
Carlos Ubeda, PhD. Medical Technology Department, Health Sciences Faculty, Universidad de Tarapaca, Arica, Chile, [email protected]. Tel. +56.58.2205703 and fax +56.58.205705. Eliseo Vano, PhD. Radiology Department, Faculty of Medicine, Complutense University and IdIS, San Carlos Hospital, 28040 Madrid, Spain. Nemorino Riquelme, MSc. Hemodynamic Department, Cardiovascular Service, Luis Calvo Mackenna Hospital, Santiago, Chile. Daniel Aguirre, MD. Hemodynamic Department, Cardiovascular Service, Luis Calvo Mackenna Hospital, Santiago, Chile. Hector Vasquez, MSc. Office of continuing education-FACSAL, Health Sciences Faculty, Universidad de Tarapaca, Arica, Chile. Cristian Chavez, PhD. Health Sciences Faculty, Universidad San Sebastian, Santiago, Chile. Dandaro Dalmazzo, MSc. Faculty of Health and Odontology, Universidad Diego Portales, Santiago, Chile.
Short running title: Patient radiation dose in paediatrics (interventional)
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Abstract (195 words) This work presents patient radiation dose data for paediatric interventional cardiology procedures in a large paediatric hospital in Chile. This will contribute to setting national diagnostic reference levels (DRLs) for Chile in the near future. The dosimetric data collection period was from January 2018 to December 2018. The local DRLs were calculated as the 3rd quartile of patient dose data distributions for kerma area-product (Pka) values. The sample of collected clinical procedures (261) was divided into diagnostic and therapeutic procedures and grouped into five weight bands. The Pka differences found between diagnostic and therapeutic procedures were not statistically significant when comparing the same weight bands, as a result of which we propose a single DRL value for both types of procedure. The local DRLs were 4.9 Gy·cm2 (<5 kg), 6.6 Gy·cm2 (5-<15 kg), 13.7 Gy·cm2 (15-<30 kg), 30.7 Gy·cm2 (30-<50 kg) and 29.7 Gy·cm2 (50-<80 kg), respectively. The conclusion from comparing our results with other existing DRL values is that there is ample scope to continue optimising by reducing patient dose values. Equipment performance, settings used and examination protocols should be reviewed as corrective actions and adapted to patient weight.
Keywords: interventional cardiology, paediatrics, diagnostic reference levels, radiation doses.
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Main text: 2605 (without references and tables) 4009 total 1. Introduction Patients paediatric can receive high radiation levels during interventional cardiology procedures (ICPs) (Bacher et al., 2005; Ubeda et al., 2012, 2015). In comparison with adults, interventional radiological examinations in children carry a higher average risk for the development of cancer per unit of radiation dose (Khong et al., 2013, Preston et al., 2007). The higher radiation risk in children is explained by their longer life expectancy (Linet et al., 2009), which allows more time for any harmful effects of radiation to manifest, and by the fact that developing organs and tissues are more sensitive to the effects of radiation (ICRP, 2007).
Diagnostic reference levels (DRLs) are an essential tool in the management of patient dose and hence in optimizing of radiation protection taking into account the clinical benefits for patients. The International Commission on Radiological Protection (ICRP) has recommended the use of DRLs for interventional procedures and in paediatric imaging, describing them as useful for good practice and as an aid in optimization (ICRP, 2017). Median patient dose values deriving from the procedures performed in a particular room can be compared with local or national DRLs to identify whether the median values obtained for that room are higher or lower than existing DRLs, and thereby to decide whether any corrective actions might be necessary. This comparison of local practice data with the existing DRLs values is the first step in optimizing protection and can be used for patient dose audit (ICRP, 2017).
In the past, patient age has been used to define groups of children for the purpose of establishing paediatric DRLs (Dragusin et al., 2008; Tsapaki et al., 2008; Chida et al., 2010; Vano et al., 2011; Ubeda et al., 2012, 2015; Verghese et al., 2012; Jones et al., 2016). However, Kleinman et al. (2010) have demonstrated that individual patient size does not correlate well with patient age, suggesting that it is preferable to use groupings based on paediatric patient body size. For their part,
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Järvinen et al. (2015) argue that weight is a more reliable factor to link with DRL than age. The ICRP recommends the use of weight bands for establishing paediatric DRL values (ICRP, 2017) and this approach has also been adopted in the European Guidelines on DRLs (EC, 2016).
Paediatric patient dose values and DRLs remain scarce in the global scientific literature, particularly in Latin America and the Caribbean. However, Chile has been systematically working in collaboration with the International Atomic Energy Agency (IAEA) to foster a radiation protection culture and to improve radiation dose management in paediatric ICPs.
Chile is a medium-size country with 17,574,003 million inhabitants, where paediatric interventional cardiology is carried out in a few hospitals (INE, 2019). Calvo Mackenna Hospital performs around 35% of all cardiac paediatric procedures in the country and Roberto del Río Hospital accounts for around 25% of these procedures. The other Chilean paediatric hospitals are expected to participate in a national programme in the coming years. Chile has yet to establish national DRLs, but local levels have been obtained at Calvo Mackenna Hospital.
This paper represents an additional contribution to setting national DRLs for paediatric interventional cardiology in Chile and suggesting optimization actions derived from a comparison with existing local DRLs and other published results in the scientific literature. The paper also proposes the setting of DRLs by weight band rather than by age band for a second large hospital in Chile (Roberto del Rio Hospital). This has been addressed in previous publications for the largest hospital in Chile (Calvo Mackenna Hospital) (Ubeda et al., 2012, 2015).
2. Materials and Methods The study was conducted at the Haemodynamics department of Roberto del Río Hospital, Chile. The recruitment period was from January 2018 to December 2018. The study design was
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retrospective. This centre has been continuously involved in three technical cooperation projects since 2008 (RLA 9057, RLA 9067 and RLA 9075) (Sanchez et al., 2016) with the support of the IAEA.
A biplane angiography x-ray system (Allura Xper FD20/20 biplane; Philips Healthcare, Best, the Netherlands), installed in 2012 was used in the survey. This angiography system was equipped with flat panel detectors, with a generator of 100 kW at 125 kV. Three fluoroscopy modes were available: low, medium and high dose. Each mode was configured in pulsed mode at 12 or 15 pulses/s. Cine mode was typically used at 30 frames/s. The system had eight fields of view (15, 19, 22, 27, 31, 37, 42 and 48 cm in diagonal). The exam protocols could be pre-programmed with X-per Settings. The system allows acquisitions in three-dimensional rotational angiography (3D-RA), but it is not used. Distance from isocentre to floor was 107 cm and focus-to-isocentre distance was 76 cm.
The system was equipped with an internal flat ionization chamber to measure kerma area-product (Pka) or dose-area product values (ICRU, 2005) and cumulative air kerma at the patient entrance reference point (Ka,r) (IEC, 2010), equivalent to incident air kerma without backscatter (ICRU 2005) at the patient entrance reference point. The patient entrance reference point is a point intended to represent the position of the patient’s skin at the entrance site of the x-ray beam during an intervention procedure. For fluoroscopic systems with an isocentre, the patient entrance reference point is located 15 cm from the isocentre toward the focal spot for C-arm interventional x-ray equipment (IEC, 2010). This position is appropriate for adult patients but requires some correction for paediatrics, as patient skin is (usually) placed no further than 15 cm from isocentre (Vano et al., 2008). The total Pka and Ka,r for each procedure were corrected by a calibration and mean attenuation factor of 0.85, derived from the table and mattress attenuation measured for the x-ray beam qualities used in this system for paediatric procedures (Ubeda et al., 2015).
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The methodology to collect patient dose data and to calculate local DRLs was the same as used in previous papers (Ubeda et al., 2012, 2015, 2018) and aligned with the latest ICRP recommendations (ICRP, 2017). The sample of collected clinical procedures was divided into diagnostic and therapeutic procedures and initially grouped into the five weight bands recommended by the European Guidelines: <5 kg, 5-<15 kg, 15 -< 30 kg, 30-< 50 kg and 50-< 80 kg (EC, 2016). For this initial evaluation and considering the sample size, we did not analyse our data for the different therapeutic procedures or level of complexity for the weight groups. Rather, all therapeutic procedures were analysed together. A separate analysis could be performed in the future when sample size allows and cardiologists have made progress in analysing the complexity of procedures. The following data were extracted manually by the operators from patient dose reports produced by the Philips x-ray system at the end of each selected ICP: procedure identification, patient age, gender, weight, height, Pka, Ka,r, number of cine series and fluoroscopy time.
To assist in optimizing procedures, three full characterizations (in terms of dose and image quality of the angiography system during 2013, 2015 and 2018) were carried out using protocols agreed upon during the DIMOND and SENTINEL European program (Faulkner et al., 2008, Vano et al., 2008), and adapted to paediatric procedures. For the final characterization, a RaySafe Xi dosimeter with a solid-state detector (RaySafe, 2019) in contact with polymethyl methacrylate (PMMA) slabs was used to measure incident air kerma (ICRU, 2005). The detector was placed inside the radiation field, but not in the automatic exposure control area. A backscatter factor of 1.3 was used (ICRU, 2005) to calculate entrance surface air kerma (ESAK), thereby facilitating a comparison of the results with other published measurements. Some of the results of the final characterization are shown in table 4.
The Mann–Whitney test (95% confidence level) was used to compare median Pka values for the two procedure groups (diagnostic and therapeutic). This non-parametric comparison procedure tests
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hypotheses and is used to find differences between two independent samples that are not necessarily normally distributed. Values of p<0.05 were considered statistically significant. SPSS 20.0 software was used (IBM, 2019).
3. Results Table 1 shows the anthropometric characteristics of the subjects.
Table 2 summarises mean, median and 3rd quartile values for kerma area-product (Pka), cumulative air kerma at patient entrance reference point (Ka,r), and fluoroscopy time (FT) for all procedures and frequencies.
Figures 1 and 2 show a summary of Pka values (proposed as local DRLs) separated by type of procedure (diagnostic and therapeutic) and for all procedures grouped by weight band.
Table 3 shows median Pka values by age band reported in this paper compared with those reported in similar surveys.
To assist with optimization strategies and to suggest improvements in the hospital’s imaging protocols, we have compared the results of the quality controls with the x-ray system at the other major paediatric hospital in Chile (Calvo Mackenna Hospital).
Table 4 shows entrance surface air kerma (ESAK) values for the evaluated acquisition modes reported in this study compared with the biplane angiography x-ray system belonging to Calvo Mackenna Hospital. Both were characterized in the year 2018.
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Discussion Table 1 shows median height, weight and body mass index (BMI) values for the five weight bands reported in our survey for paediatric patient dosimetry. Dose monitoring was performed for 261 paediatric ICPs. Median patient height and weight values increased as expected from the lightest to the heaviest group. The minimum number of 30 patients per group recommended for a DRL study in ICRP 135 (ICRP, 2017) was satisfied in all cases except for the 30-<50 kg weight band (25 patients).
Table 2 summarizes three descriptive statistics for Pka, Ka,r, and FT for weight bands and their frequencies. ICPs performed for the 30-<50 kg weight band showed the highest median values for Pka (14.2 Gy·cm2) and FT (12.9 min); this corresponds to the classification of “early adolescence” in the European Guidelines on DRLs for Paediatric Imaging (EC, 2016). The lowest median value for Pka (1.9 Gy·cm2) was for the “neonate” classification corresponding to the <5 kg weight band. Our Ka,r values across all weight bands were far below the threshold proposed by the ICRP for deterministic effects on the skin (2 Gy for transient erythema) (ICRP, 2000).
DRLs based on Pka quantities (3rd quartile as recommended by the ICRP) are useful as a guide to good practice and an optimization aid. Pulses and frames per second (rate), image recording technique and exposure programme options used should be included as complementary information to the DRLs to help in the optimisation strategies (ICRP, 2017). For optimization actions, the investigation should include a review of equipment performance, settings used and examination protocols (Martin, 2011). In table and figure 1, the 3rd quartile values are proposed as a local DRLs obtained in paediatric ICPs by weight bands. According to the p values shown in figure 2, the Pka differences found between diagnostic and therapeutic procedures were not statistically significant when comparing the same weight band. Similar results were obtained in a previous work in another paediatric hospital in Chile, where Pka values were grouped by age band (Ubeda et al., 2015). Our
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results confirm the proposal made by McFadden et al. (2013) and by Jones et al. (2016) to the effect that a single reference level should be used as a benchmark and applied to both diagnostic and therapeutic procedures. Figure 2 shows the proposed local DRLs for different weight bands for all paediatric ICPs. The 3rd quartile Pka values were 4.9 Gy·cm2 (<5 kg), 6.6 Gy·cm2 (5-<15 kg), 13.7 Gy·cm2 (15-<30 kg), 30.7 Gy·cm2 (30-<50 kg) and 29.7 Gy·cm2 (50-<80 kg), respectively. It is surprising that the 3rd quartile values (assumed as local DRLs) for the 50-80 kg band were similar to the 30-50 kg band. This will be analysed in the future when analysing the various therapeutic procedures and their complexity. Some procedures may be easier for larger children requiring lower radiation doses (median fluoroscopy time values are lower in the highest weight band).
There should be a periodic validation of the dosimetric values shown by the x-ray system and transferred to the patient dose reports (Malusek et al., 2014). The built-in Pka meter may require the application of a correction factor, especially for high kVs and high Cu filtration. In our case, the validation was performed using a RaySafe Xi dosimeter with a duly calibrated solid-state detector (RaySafe, 2019).
According to ICRP 135, DRL values based on patient age will be of value primarily to facilitate comparison with older data (ICRP, 2017). Thus, table 3 shows median Pka values for different age categories. The values of this survey tended to be lower than those reported by Verghese et al. (2011), similar to those reported by Kottou et al. (2018) and higher than those reported by Martinez et al. (2007) except for the 10-<16 age band, but higher than those reported for Calvo Mackenna Hospital (Ubeda et al., 2012) for all age bands. It should be noted that Calvo Mackenna Hospital has been involved in several IAEA programmes to optimize radiation dose management in paediatric ICPs since 2009. An optimization programme has been applied for 8 to 10 years at this hospital, which has enabled it to maintain lower dose levels than those usually published elsewhere. This difference can also be explained by the settings of both x-ray systems shown in the
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characterization results (see table 4), where the dose rates for fluoroscopy modes and dose per cine frame were lower for different thicknesses. The exam protocols for the x-ray system at Calvo Mackenna Hospital have been refined, while this process remains necessary at Roberto del Río Hospital, which has considerable scope for optimization. Equipment performance, settings used and examination protocols should be reviewed as corrective actions and adapted to patient weight (Martin, 2011). Unlike in European countries (which comply with Directive 2013/59 (EC, 2014)), Chile has not yet incorporated into its radiological protection legislation (SD, 1984, 1985) the implementation of quality assurance programmes, including the obligation to establish DRLs, or the characterization and commissioning of x-ray fluoroscopy systems used in paediatric ICPs.
Conclusions The Pka differences found between diagnostic and therapeutic procedures in paediatric interventional cardiology were not statistically significant when comparing the same weight bands, for which reason we initially propose a single DRL value for both procedures. The local DRLs values presented in this paper were 4.9 Gy·cm2 (<5 kg), 6.6 Gy·cm2 (5-<15 kg), 13.7 Gy·cm2 (15<30 kg), 30.7 Gy·cm2 (30-<50 kg) and 29.7 Gy·cm2 (50-<80 kg), respectively. Roberto del Río Hospital has considerable scope for optimizing procedures. Equipment performance, settings used and examination protocols should be reviewed as corrective actions and adapted to patient weight.
Acknowledgments The current work has been carried out under the framework of the International Atomic Energy Agency regional project RLA/9/075, “Strengthening National Infrastructure for End-Users to Comply with Regulations and Radiological Protection Requirements”.
Funding This research was partially supported by the Direction of Research at the Tarapaca University,
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through senior research project No. 7713-18.
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Figures captions Figure 1. 3rd quartile Pka values (Q3) for kerma area-product for diagnostic and therapeutic procedures. The data are for the <5 kg, 5-<15 kg, 15-<30 kg, 30-<50 kg and 50-<80 kg weight bands. . Boxes represent the interquartile range; the vertical bars extend to the highest and lowest values, excluding ‘‘outliers’’ (°) and ‘‘extreme values’’ (*).
Figure 2. 3rd quartile Pka values (Q3) for kerma area-product for all procedures. The data are for the <5 kg, 5<15 kg, 15-<30 kg, 30-<50 kg and 50-<80 kg weight bands. Boxes represent the interquartile range; the vertical bars extend to the highest and lowest values, excluding ‘‘outliers’’ (°) and ‘‘extreme values’’ (*).
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Table 1. Sample size (n), median (range) values of age, height, weight and body mass index (BMI) by weight band. Weight n band (kg)
Age (years)
Height (cm)
Weight (kg)
BMI (kg/m2)
<5 5-<15 15-<30 30-<50 50-<80
0.1 (0.0-7.7) 0.9 (0.3-4.7) 6.3 (3.0-15.4) 12.2 (1.3-15.0) 13.9 (9.8-16.2)
50.0 (30.0-63.0) 70.0 (54.0-103.0) 114.5 (92.0-150.0) 147.0 (126.0-176.0) 161.0 (136.0-181.0)
3.3 (1.8-4.9) 8.1 (5.1-14.9) 20.0 (15.0-27.0) 39.2 (31.0-49.0) 61.5 (50.0-79.1)
13.8 (9.2-30.0) 15.6 (12.3-23.8) 15.4 (11.9-21.5) 18.7 (12.5-23.2) 24.00 (16.9-29.7)
61 77 64 25 33
Table 2. Sample size (n), median and 3rd quartile values for kerma area product (Pka), cumulative air kerma at patient entrance reference point (Ka,r) (corrected with a mean attenuation factor of 0.85 for the table and mattress for the frontal X-ray beam) and fluoroscopy time (FT) by weight band. Weight Pka (Gy·cm2) Ka,r (mGy) FT (min) band n Median – 3rd Median – 3rd Median – 3rd (kg) <5 61 1.9 – 4.9 50.1 – 119.0 10.6 – 22.6 5-<15 77 2.7 – 6.6 38.6 – 98.9 9.9 – 20.1 15-<30 64 6.9 – 13.7 69.0 – 135.5 12.0 – 18.4 30-<50 25 14.2 – 30.7 97.4 – 259.4 12.9 – 17.0 50-<80 34 12.6 – 29.7 105.6 – 222.1 12.7 – 20.0
Table 3. Comparison of median Pka values for paediatric cardiology reported in this and other papers (values adapted by the authors of this paper) for all procedures (diagnostic and therapeutic). Kottou Ubeda Martinez Verghese Age This paper et al. et al. et al. et al. band (2019) (2018) (2011) (2012) (2007) (years) (Gy·cm2) 2 2 2 2 (Gy·cm ) (Gy·cm ) (Gy·cm ) (Gy·cm ) <1 1.9 4.6 0.9 2 2.1 1 -<5 2.9 8.3 1.5 3 4.7 5 -<10 4.5 11.5 2.1 7 6.3 10-<16 15.4 24.7 5.0 14 13.6
Table 4. ESAK per second (s) and frame, number of pulses per second (NP) for low (FL), medium (FM) and high (FH) fluoroscopy dose and cine (CI) acquisition modes and all polymethylmethacrylate (PMMA) thicknesses used in the survey. Siemens Axiom Artis BC Philips Allura Xper FD20/20 system system (Calvo Mackenna Hospital) (Roberto del Río Hospital) PMMA (cm) Acquisition FOV NP ESAK ESAK NP ESAK ESAK mode (cm) (s-1) (µGy/s) (µGy/fr) (s-1) (µGy/s) (µGy/fr) 4 FL 22 10 2.1 0.2 12 10.5 0.9 4 FM 22 10 3.3 0.3 15 22.0 1.5 4 FH 22 10 6.0 0.6 15 58.2 3.9 4 CI 22 30 76.6 2.6 30 75.5 2.5 8 FL 22 10 4.8 0.5 12 21.9 1.8 8 FM 22 10 7.6 0.8 15 45.1 3.0 8 FH 22 10 17.6 1.8 15 94.5 6.3 8 CI 22 30 245.0 8.2 30 383.4 12.8 12 FL 22 10 10.6 1.1 12 47.0 3.9 12 FM 22 10 18.2 1.8 15 98.1 6.5 12 FH 22 10 39.3 3.9 15 191.7 12.8 12 CI 22 30 278.0 9.3 30 884.3 29.5 16 FL 22 10 26.4 2.6 12 170.0 14.2 16 FM 22 10 46.6 4.7 15 349.8 23.3 16 FH 22 10 105.9 10.6 15 504.1 33.6 16 CI 22 30 1024.0 34.1 30 3354.8 111.8
The study was carried out as part of International Atomic Energy Agency The diagnostic reference levels by weight bands were from 4.9 to 29.7 Gy·cm2 These values are the second data of diagnostic reference levels for Chile These values are the third data of diagnostic reference levels for Latin America
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