Diagnostic reference levels for fluoroscopically guided procedures in a South African tertiary hospital

An audit of patient radiation doses in interventional radiology at a South African hospital

Background

Interventional radiology (IR) is becoming more relevant in patient care and is associated with increased patient radiation exposure and radiation-induced adverse effects. Diagnostic reference levels (DRLs) are crucial for radiation control. There is a paucity of published DRLs for IR in South Africa and sub-Saharan Africa.

Objectives

This study aimed to determine local DRLs for fluoroscopically-guided IR procedures and compare the achieved DRLs with published local and international DRLs.

Method

Retrospective, descriptive, single-centre study. Kerma air product (KAP), reference point air kerma (K_a,r) and fluoroscopy time (FT) were collected for patients (12 years and older) who underwent IR procedures at a university hospital from 01 January 2019 to 31 December 2019. The 75th percentile of the distribution of each dose parameter (KAP, K_a,r and FT) per procedure was calculated and taken as the local diagnostic reference levels (LDRL). The established LDRLs were compared to published DRLs.

Results

A total of 564 cases were evaluated. The 13 most frequent procedures (with 15 or more cases) represented 86.1% (487/564). Percutaneous transhepatic biliary drainage was the most common procedure (n = 146, 25.9%). Diagnostic cerebral angiogram DRLs exceeded the published DRL data ranges for all parameters (DRL 209.3), and interventional cerebral angiogram exceeded published ranges (DRL 275). Uterine artery embolisation (UAE) exceeded these ranges for KAP and K_a,r. (KAP-954.9 Gy/cm², K_a,r-2640.8 mGy).

Conclusion

The LDRLs for diagnostic cerebral angiogram, interventional cerebral angiogram and UAE exceeded published international DRL ranges. These procedures require radiation optimisation as recommended by the International Commission on Radiological Protection (ICRP).

Contribution

In addition to informing radiation protection practices at the level of the institution, the established LDRLs contribute towards Regional and National DRLs.

TYPICAL VALUES OF DOSIMETRIC DATA FOR CARDIAC FLUOROSCOPY-GUIDED PROCEDURES IN A SOUTH AFRICAN TEACHING HOSPITAL

Currently there are limited diagnostic reference level (DRL) data for South African (SA) public sector cardiac fluoroscopy-guided procedures (FGPs). A 4-y retrospective study of dosimetric data on 6265 patients determined typical values (50th percentile) of dosimetric data for the seven most frequent cardiac FGPs at a SA teaching hospital. Kerma-area-product (KAP), reference point air Kerma (Ka,r) and fluoroscopy time (FT) were, respectively, calculated for coronary angiography (CA) (n = 1935; 61Gy.cm2, 624 mGy, 5 min); CA with left ventriculography (n = 1687; 85Gy.cm2, 840 mGy, 3.9 min), valve screening (n = 129; 6Gy.cm2, 164 mGy, 2.3 min), percutaneous coronary intervention (n = 1922; 145Gy.cm2, 1569 mGy, 11.9 min), pacemaker implantation (n = 432; 9Gy.cm2, 100 mGy, 6.5 min), pericardial tap (n = 115; 1.9Gy.cm2, 18 mGy, 1.5 min) and transcatheter aortic valve implantation (n = 45; 65Gy.cm2, 658 mGy, 14.1 min). This work presents the largest SA public sector cardiac FGP dosimetric data to date and provides a key resource for future work in this domain.

Effect of equalization filters on measurements with kerma-area product meter in a cardiovascular angiography system

Purpose

This study aimed to evaluate the effect of equalization filters (EFs) on the kerma‐area product (KAPQKM) and incident air‐kerma (Ka,i,QKM) using a kerma‐area product (KAP) meter. In addition, potential underestimations of the Ka,i,QKM values by EFs were identified.

Materials and methods

A portable flat‐panel detector (FPD) was placed to measure the X‐ray beam area (A) and EFs dimension at patient entrance reference point (PERP). Afterward, a 6‐cm³ external ionization chamber was placed to measure incident air‐kerma (Ka,i,Qext) at PERP instead of the portable FPD. KAP reading and Ka,i,Qext were simultaneously measured at several X‐ray beam qualities with and without EFs. The X‐ray beam quality correction factor by KAP meter (kQ,Q0KM) was calculated by A, Ka,i,Qext and KAP reading to acquire the KAPQKM and Ka,i,QKM. Upon completion of the measurements, KAPQKM, Ka,i,QKM, and Ka,i,Qext were plotted as functions of tube potential, spectral filter, and EFs dimension. Moreover, Ka,i,QKM/Ka,i,Qext values were calculated to evaluate the Ka,i,QKM underestimation.

Results

The kQ,Q0KM values increased with an increase in the X‐ray tube potential and spectral filter, and the maximum kQ,Q0KM was 1.18. KAPQKM and Ka,i,QKM decreased as functions of EFs dimension, whereas Ka,i,Qext was almost constant. Ka,i,QKM/Ka,i,Qext decreased with an increase in EFs dimension but increased with an increase in tube potential and spectral filter, and the range was 0.55–1.01.

Conclusions

Ka,i,QKM value was up to approximately two times lower than the Ka,i,Qext values by EFs. When using the Ka,i,QKM value, the potential Ka,i,QKM underestimation with EFs should be considered.

An audit of published South African diagnostic reference level data

Diagnostic reference levels (DRLs) are accepted as a dose optimisation tool for patients undergoing x-ray imaging and are required by South African (SA) legislation for 26 fluoroscopically guided procedures (FGPs). The aim of this paper is to collate all published SA data on DRLs in preparation for a project to establish national DRLs. Systematic searches were conducted of various applicable databases. All research that proposed DRLs for any imaging procedure in South Africa was included. Twenty-one works met inclusion criteria, the earliest from 2001. Two-thirds of all work reported on FGPs and five studies documented computed tomography DRLs. Three publications focussed exclusively on paediatric imaging DRLs. No studies on mammography or dental radiography were found. For clinical procedures with more than one proposed DRL, the range of proposed DRL varied by up to a factor of five. The highest proposed DRL is 373.1 Gy cm²for endovascular aneurysm/aortic repair procedures. Data were collected in six public hospitals and two private hospital groups. Thirty-six authors contributed to the manuscripts, but only six studies had an inter-disciplinary authorship. This is the first paper to provide a comprehensive review of SA DRL data and thereby advances international radiation protection initiatives. The data suggests there is room for more interdisciplinary work and that there must be rigorous standardization of reported parameters and data collection. This audit also highlights the need for standardized terminology, particularly for FGPs.