Materials and Methods
This study was approved by the Institutional Review Board.
Patient cohort
The study enrolled a total of 198 paediatric patients (up to 16 years of age) with CHD who underwent either diagnostic or therapeutic IC procedures. Congenital heart defects included atrial and ventricular septal defect, tetralogy of Fallot, patent ductus arteriosus, pulmonary artery stenosis and coarctation of the aorta. Patients were categorized into three body weight (BW) groups according to institutional acquisition protocols: group A (BW < 6 kg), group B (6 kg < BW < 20 kg) and group C (BW > 20 kg).
Imaging protocol
All the procedures performed with a biplane angiography system equipped with a flat panel detector and employing an automatic exposure control technique. Images were acquired in two angiographic projections: anterorposterior (AP) and lateral (LAT). Cine-angiography frame rates were ranged between 7.5 frames per second to 30 frames per second depending on the heart rate. Anti-scatter grid was only used in patients weighing more than 20 kg.
Radiation exposure
For the establishment of DRLs, air kerma-area product (PKA), air kerma at reference point (Ka,r), fluoroscopy time (FT) and number of cine frames were retrieved from the hospital’s Picture Archiving and Communication System (PACS), as suggested by Radiation Protection 185 [3]. LDRLs were calculated as the 75th percentile (3rd quartile) of PKA, Ka,r, FT and number of cine frames.
Results
Patient cohort
From the 198 participants, 109 paediatric patients were subjected to diagnostic IC procedures, whilst 89 paediatric patients underwent therapeutic IC procedures. Among them, 93 patients (47%) were females. Patients’ demographic data are presented in Table 1.
Table 1. Demographic data of patients subjected to diagnostic and therapeutic IC procedures.
Type of IC proceure
|
BW Group
|
n |
F/M |
Age (years) |
Weight (kg) |
Height (cm) |
Diagnostic
|
group A |
26 |
13/13 |
0.2±0.2 |
4.2±1.2 |
55.8±6.1 |
group B |
63 |
26/37 |
2.7±1.5 |
12.6±3.7 |
91.8±14.7 |
group C |
20 |
8/12 |
8.5±2.9 |
30.6±10.6 |
136.2±17.0 |
Therapeutic
|
group A |
20 |
7/13 |
0.2±0.2 |
4.3±0.9 |
68.7±35.1 |
group B |
20 |
13/6 |
2.50±1.8 |
12.8±4.4 |
89.0±15.9 |
group C |
49 |
26/23 |
9.4±3.3 |
38.6±14.9 |
143.4±18.6 |
BW: body weight
n: number of patients
F/M: Female/Male
Values represent mean ± standard deviation
Radiation exposure
The estimated LDRLs for diagnostic and therapeutic paediatric IC procedures are summarized in Table 2.
Table 2. 75th percentiles for PKA, Ka,r, FT and number of cine frames for diagnostic and therapeutic paediatric IC procedures per body weight group.
Type of IC proceure |
BW Group
|
PKA (Gy*cm2) |
Ka,r (mGy) |
FT
(min)
|
Number of cine frames |
Diagnostic |
group A |
2.0 |
70.4 |
9.0 |
1925.0 |
group B |
5.1 |
95.5 |
9.2 |
1688.2 |
group C |
6.0 |
64.9 |
7.5 |
895.0 |
Therapeutic |
group A |
1.8 |
47.8 |
5.4 |
1067.5 |
group B |
3.3 |
75.8 |
7.8 |
1234.0 |
group C |
12.0 |
122.6 |
7.6 |
619.0 |
BW: body weight
PKA: air kerma-area product
Ka,r: air kerma at reference point
FT: fluoroscopy time
In terms of PKA, LDRLs were found equal to 2.0 (group A), 5.1 (group B) and 6.0 (group C) Gy*cm2 for diagnostic and 1.8 (group A), 3.3 (group B) and 12.0 (group C) Gy*cm2 for therapeutic IC procedures. Results indicate that doses may vary substantially depending on the procedural scope. PKA tends to increase with increasing BW group in both diagnostic and therapeutic IC procedures, while it seems that a smaller number of cine frames is required for heavier (older) children. The highest value for maximum skin entrance dose (384 mGy) was observed in a 6-year-old boy with tetralogy of Fallot who was subjected to pulmonary artery angioplasty. Estimated LDRLs based on PKA fall well within the range of previously reported corresponding values [4,5], which however exhibit a wide variation.