Managing radiation exposure in complex cardiac imaging

The case submitted by IM Seyoung describes effective management of absorbed dose in patients and operators during the transcathether closure of an atrial septal defect in adults after a change in the cinefluoroscopy rate.

Case objective
The team tried to prove that absorbed dose of patients and operators was effectively managed by decreasing the cinefluoroscopy rate from 15 frames/sec to 7.5 frames/sec in transcatheter closure of atrial septal defect. 

IM Seyoung

 

Samsung Medical Center

 

Korea

IM Seyoung

 

Samsung Medical Center

 

Korea

The case submitted by IM Seyoung describes effective management of absorbed dose in patients and operators during the transcathether closure of an atrial septal defect in adults after a change in the cinefluoroscopy rate.

Case objective
The team tried to prove that absorbed dose of patients and operators was effectively managed by decreasing the cinefluoroscopy rate from 15 frames/sec to 7.5 frames/sec in transcatheter closure of atrial septal defect. 
When the cinefluoroscopy frame rate was reduced from 15 frames/sec to 7.5 frames/sec during a transcatheter closure of ASD in adult patients, the absorbed dose to patients and operators was effectively managed.”

––  IM Seyoung - Radiological Technologist

Samsung Medical Center, Seoul, South-Korea

Clinical and patient background

This was a retrospective study that utilized a review of existing medical records. A total of 80 patients were enrolled in this study. The patients with an ASD who underwent a transcatheter closure in the Samsung Medical Center from August 2012 to February 2015 were selected. Patients less than 18 years old who required additional diagnostic catheterization due to pulmonary hypertension, as well as coronary syndrome patients, were excluded from this study.

The transcatheter device closure for an ASD was performed by an experienced cardiologic interventionist, who had previously conducted more than 200 cases. 

The cardiac catheterization was performed using an Allura Xper FD 10/10 (Phillips Medical System, Best, Netherlands). This study used a system of catheterization of a structural heart anomaly at 7.5 frames/sec and 15 frames/sec for fluoroscopy and cinefluoroscopy, respectively. 

The use of a transcatheter closure of an ASD of 15 frames/sec for cine-fluoroscopy was changed to 7.5 frames/sec in August 2013. Therefore, the patients were divided into two study groups of 40 patients each, in which either 15 frames/rate was used (until July 2013) or 7.5 frames/rate was used (since August 2013).

Patient demographic data, hemodynamic data, ASD characteristics and procedure outcomes were reviewed. Patient catheterization sheets were reviewed for exposure to fluoroscopy and cinefluoroscopy radiation doses at the end of procedures.


Dose management methods and techniques that were used

The operator absorbed dose during the procedures was measured using a normal adult sized Alderson Radiation Therapy (ART) phantom. The adult chest phantom was put on the bed to precisely simulate treatments. The phantom height was 170 cm, with a table height of 93 cm. In addition, a source to image receptor distance of 92 cm and a 25 inch detector were used.

A total of 5 radio-photo-luminescent dosimeter glasses (PLD, AGC THCHNO GLASS CO., LTD) were attached to both eyes, both thyroid glands and to the left side of the chest . Chest phantom lead protectors (0.5 mmPb Greenlite, INFAB CO., LTD, USA), thyroid protectors (0.5 mmPb Greenlite, INFAB CO., LTD, USA) and glasses (0.07 mmPb TORAY, HOSINA CO., LTD, Japan) were also used.

The operator absorbed dose were performed under the following 10 different conditions: 2, 4, 6, 8 and 10 seconds, each at rates of both 7.5 frames/sec and 15 frames/sec. The tests were repeated 12 times. The dosimeter glasses were analyzed using a radio photo luminescent glass dosimeter reader (FGD-1000, Asahi Technol Glass Co., Japan) after pre-heating for 30 minutes at 70°C. The dosimeter glasses were annealed for 1 hour at 400°C and analysis was conducted before the test for zeroing.

Continuous data were expressed by the mean and standard deviation. Chi square, Fisher’s exact test, paired t-test and Student’s t-test were used between groups. The ANOVA and Scheffe methods were used for multiple comparisons. SPSS (Windows version 2.0) was used for analysis, and p < 0.05 was defined as statistically significant. This study was approved by the institutional review board and informed consent was waived.


Results

Patients’ cumulative dose area product at 7.5 frames/sec was effectively managed when compared to the other group. The operator absorbed dose increased significantly over the entire duration for all sites except for the chest at 15 frames/sec but only for both eyes at 7.5 frames/sec. The absorbed dose for all sites except the chest was effectively managed at 7.5 frames/sec.

Comparison of the characteristics and radiation exposure to patients between groups

A comparison of the two groups (7.5 frames/sec vs. 15 frames/sec) showed no significant differences in age, body weight, height and BSA. The male sex was more predominant in the 7.5 frames/sec patient group than the 15 frames/sec patient group (42.5% vs 20.0%, p = 0.03).

The ASD closure procedure showed no differences between groups with regard to the shunt ratio (Qp/Qs), closure guided by intra-cardiac echocardiography, device size and use of balloon assist technique. There was no significant difference in the cinefluoroscopy and fluoroscopy time. The cumulative cinefluoroscopy dose-area product(DAP) in patients of 7.5 frames/sec was effectively managed when compared to the other study group. The cumulative fluoroscopy DAP were not different between the two groups. However, the total DAP (fluoroscopy DAP + cinefluoroscopy DAP) were different between the two groups (p < 0.001).


Cinefluoroscopy absorbed dose of operator

For every exposure duration, the highest absorbed dose was observed in the left eye. All measurements were taken using radio-photo-luminescent dosimeter glasses on the ART phantom. No significant difference was found in the exposure duration of 7.5 frames/sec for 2 seconds. The amounts of operator absorbed dose with increased duration exposure for all five sites except the chest, even with appropriate protection at 15 frames/sec. There were significant absorbed dose increases for both eyes only at a duration increase of 7.5 frames/sec.

The absorbed dose measurements for the five phantom sites resulted in effective dose management at 7.5 frames/sec. There were no significant differences at every site for the 2 second duration rate as well as for the chest at every absorbed dose.

We extrapolated left eye operator absorbed dose amounts for the ASD device closure and compared the two groups. The cinefluoroscopy times in the two groups were 6.9 seconds for 7.5 frames/sec and 10.7 seconds for 15 frames/sec. Therefore, we calculated absorbed dose of 7.561 μGy for 7.5 frames/sec and 8.814 μGy for 15 frames/sec. 

Conclusions

When the cinefluoroscopy frame rate was reduced from 15 frames/sec to 7.5 frames/sec during a transcatheter closure of ASD in adult patients, the absorbed dose to patients and operators was effectively managed. With a longer exposure duration, the absorbed dose to the left eye of the operator increased when using cinefluoroscopy. Therefore, the study results indicate that a cinefluoroscopy rate of 7.5 frames/sec was more beneficial than 15 frames/sec.

 

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