Radiation Protection and Environment

ORIGINAL ARTICLE
Year
: 2021  |  Volume : 44  |  Issue : 3  |  Page : 141--145

Initial experience on the use of real-time displayed radiation dose monitoring system in computed tomography fluoroscopy


Driss Raissi, Thomas M Seay, Jie Zhang 
 Department of Radiology, University of Kentucky College of Medicine, Lexington, KY, USA

Correspondence Address:
Driss Raissi
800 Rose Street, Lexington, KY, USA
USA

Abstract

This study presents our initial experience on the effective approach to apply real-time radiation dose monitoring during computed tomography (CT)-guided interventional procedures and the potential effects on overall radiation dose. A phantom study using multiple detectors at different body levels was conducted to determine badge positioning and possible effects on scatter radiation doses at three angles; parallel, perpendicular, and 45° relative to the CT gantry. A retrospective study was also conducted to compare scatter radiation and patient radiation doses during live CT fluoroscopy-guided procedures. Highest dose rates were observed when detector faced the scatter source in the perpendicular position to the gantry. There is no significant difference between wearing the detector at the shoulder or at the waist level. The use of real-time dose monitoring system provides immediate feedback during CT fluoroscopy procedures allowing for timely behavior modification.



How to cite this article:
Raissi D, Seay TM, Zhang J. Initial experience on the use of real-time displayed radiation dose monitoring system in computed tomography fluoroscopy.Radiat Prot Environ 2021;44:141-145


How to cite this URL:
Raissi D, Seay TM, Zhang J. Initial experience on the use of real-time displayed radiation dose monitoring system in computed tomography fluoroscopy. Radiat Prot Environ [serial online] 2021 [cited 2022 May 18 ];44:141-145
Available from: https://www.rpe.org.in/text.asp?2021/44/3/141/334781


Full Text



 Introduction



Interventional radiology, with its use of computed tomography (CT) fluoroscopy and fluoroscopy-guided procedures, is an area where operating physicians may encounter relatively high radiation exposure, with an average estimated effective dose of 2–4 mSv/year.[1] Awareness of radiation dose during procedures can be critical in protecting patients and the medical staff. It is known that effective dose to patient and operator varies by procedure type and duration, but Buls et al. estimated a median effective dose of 19.7 mSv for the patient during various CT fluoroscopy procedures through direct thermoluminescent dosimetry.[2] An active dosimetry system that gives real-time feedback regarding the ongoing operator radiation exposure would theoretically allow medical staff to modify their behavior to minimize intra-procedural radiation dose to themselves and patients. The use of such a system during fluoroscopy-guided procedures and digital subtraction acquisition potentially helps optimize medical staff radiation protection by allowing a change in working habits, thus, reducing radiation dose to patients and operators.[3],[4],[5]

The use of a real-time system poses a major challenge in CT-fluoroscopy due to operator's position relative to the patient and/or the gantry (the scatter source) and physician position changes during procedures since the level of radiation exposure is dependent on the ever changing angulation between the radiation source, the operator, and dosimeter.[6],[7]

We present our initial experience with real-time dosimeter fitted to register the dose-rate values while displaying real-time dose-rate and accumulated occupational doses on a screen inside the CT fluoroscopy suite. The goal is to evaluate the use of a real-time personal dose monitoring device during CT fluoroscopy procedures, the impact of the constantly changing detector positions during the procedure on the measured personal dose, and if associated with any changes of patient radiation dose.

 Materials and Methods



A RaySafe i2 (Fluke Corporation, Glenwood, IL, USA) solid-state real-time dosimeter system was used. This system includes six wireless badge dosimeters that detect radiation exposure and transfer data to be displayed in real time on its screen component [Figure 1].{Figure 1}

Scanning was performed using Siemens Definition AS 40 slice (Siemens Healthcare, Erlangen, Germany) with the following parameters, slice thickness of 3 mm, 120 kV, 200–400 mAs, 0.5 s rotation time, using manufacturer provided adult body protocols.

Phantom study

The phantom study was developed to determine whether badge detector positioning affects scatter radiation detected. An anthropomorphic chest phantom was positioned beside the CT gantry where the operating physician typically stands during a procedure to serve as the operator phantom. Six badge detectors were attached to upper, middle, and lower positions of the operator phantom at the mid anterior clavicular line bilaterally [Figure 2]. A CT polymethyl methacrylate body phantom was scanned with the same CT protocol and exposure time to serve as the scatter source (i.e. the patient) for all the tests.{Figure 2}

The operator chest-phantom was exposed at three different angles, parallel, perpendicular, and 45° relative to the CT bore.

”In vivo” study

The purpose of this study was to determine badge detector positioning and its impact on the level of radiation exposure during real-time CT fluoroscopy procedures. Badge detectors were positioned at the level of the shoulder and abdomen in two interventional radiologists who were monitored [Figure 3]. Both physicians have more than 10 years' experience using CT-fluoroscopy. Badge detector positioning was obtained from a total of 48 CT fluoroscopy-guided procedures, of which physician L performed 16 procedures and physician S performed 32 procedures.{Figure 3}

Patient radiation dose monitoring

Patient radiation dose (dose length product [DLP]) within 1 month was retrospectively reviewed before and after the use of RaySafe i2 solid-state real-time dosimetry system. DLPs were retrieved from 32 patients, of which 17 procedures were performed before and 15 procedures after the use of real-time dose monitoring system RaySafe i2. The CT fluoroscopy-guided procedures included renal, liver, lung, and lymph node biopsies; abdominal mass biopsies; paravertebral and disc biopsies [Figure 4].{Figure 4}

Statistics analysis

All statistical analyses were completed in SAS 9.4 (SAS Institute Inc., Cary, NC, USA). For continuous variables, we used t-tests to check for data differences between before and after use of real-time dosimetry monitoring. P ≤ 0.05 was selected to signify statistical significance.

 Results



The phantom study demonstrated that detected scatter radiation depended on chest-phantom positioning in relation to the CT bore. The scattered dose rates varied from 1.56 to 6.76 mSv/h for parallel phantom position, 6.63 to 11.12 mSv/h for 45° position, 7.05 to 11.11 mSv/h for perpendicular position. The dose rate variations are partially due to the distance between detectors and scatter source and incident angle of the scatter radiation on the badge. The highest dose rates were observed when detector faced the scatter source in the perpendicular position to the gantry.

The in vivo study showed no significant difference between wearing the detector at the shoulder or at the waist level [Figure 5] and [Figure 6]. The mean dose rates at shoulder versus waist were, respectively, 0.16 ± 0.15 mSv/h and 0.17 ± 0.15 mSv/h for physician L (P = 0.851), and 0.57 ± 1.54 mSv/h and 0.89 ± 1.90 mSv/h for physician S (P = 0.462). There were occasions when the shoulder detector picked up scatter and the waist detector did not. This may be due to the positioning of the operator at the time of exposure. [Figure 5] and [Figure 6] show dose rates and accumulated dose for physician L and physician S, respectively, during 1-month monitoring.

In the patient radiation dose monitoring study, DLPs were retrieved from 32 patients (17 procedures before and 15 procedures with real-time dose monitoring), and no difference in patient dose was observed with mean total DLP of 538 mGy * cm ± 251.09 mGy * cm before dose monitoring study and total DLP of 563.26 ± 184.60 mGy * cm with real-time dose monitoring (P = 0.753) [Figure 7].{Figure 5}{Figure 6}{Figure 7}

 Discussion



Dose monitoring is a necessary part of an effective radiation dose management program. Up to date, dose badges are still the most common mean of measuring scatter radiation exposure in healthcare workers.[1] The use of a real-time dose monitor providing immediate feedback on ongoing radiation exposure may help reduce both personnel and patient radiation dose. CT fluoroscopy-guided procedures are highly dynamic with constant operator mobility from and to the source of the radiation, i.e. gantry. Not only is there a constant change in distance but also in the operator's body positioning/angulation relative to the CT gantry. The operator's constant movement does affect the recorded scatter radiation dose since the detector's position relative to the radiation source is constantly changing.[7] Real-time solid-state detector radiation monitoring offers feedback to the operator allowing for immediate behavior modification, and this could possibly decrease excessive scatter radiation exposure.

Of note, our study shows that the most accurate scatter radiation measurement was obtained with the phantom in perpendicular position relative to the CT gantry. Awareness of this fact may help the operator modify his or her behavior to obtain accurate measurement of the ongoing exposure and better implement the tools available for radiation safety such as shielding, further distancing him or herself or decreasing patient dose even further. Furthermore, it is noteworthy that the measured doses in the parallel position may be falsely lower and give the operator the wrong impression regarding his or her ongoing radiation exposure. Most interventionalists operate the CT-fluoroscopy unit in a parallel to 45° angle to the CT gantry, so perhaps a detector that can be fully operational in that angular range would the most adequate.

Shoulder and waist detector measurements did not show any significant difference in measured scatter radiation. This could be due to our small sample or also related to the fact that scatter beam angle is relatively similar by being placed on the patient phantom's trunk which is a relatively flat surface. Orientation of the detector, hence the operator, to the bore of the CT gantry may be the most important factor affecting operator's measured exposure, hence, accuracy of measured scatter dose is angle dependent.

Badge detector positioning determines exposure rate measurements and accumulated dose. The variation in dose measurement between shoulder and waist detector positioning is likely due to variability of physician body position relative to the CT gantry during CT fluoroscopy procedures rather than to the waist versus shoulder detector location. Hence, accumulated dose between the two detectors was not significantly different in the operator phantom study (therefore, only one badge may be needed).

No significant difference in the patient's exposure dose was observed. This finding may be due to very succinct radiation protection measures undertaken by both operators, rendering the real-time scatter dose feedback of minimal value to experienced operators with baseline optimal radiation protection practice, a fact that is supported by the literature.[8]

However, our small sample size, different patient body habitus, and case complexity or lack of, may have surreptitiously affected our results and limit the applications of our findings. Data were only collected from two operating physicians with >10 years of experience, so this may not be reflective of the true exposure doses for the entire population of interventional radiologists. Finally, the exposure doses to the operator are specific to the procedures common to our institution, and this does not encompass the entirety of interventional procedures. A larger and more homogenous study should be pursued to evaluate whether patient's exposure dose would be affected by the use of real-time solid-state dose monitoring during CT fluoroscopy-guided procedures.

 Conclusions



Real-time solid-state detector use can give immediate feedback during CT fluoroscopy procedures and allow timely behavior modification. It is important to note the effect of operator's orientation relative to the CT gantry on measured scatter radiation dose, as measured dose strongly depends on operator's orientation relative to the CT gantry with perpendicular position offering the most accurate dose measurement. There was no significant difference in patient dose exposure, and this is a good surrogate that there was no significant increased operator or medical personnel exposure either. Furthermore, detector placement at the waist versus shoulder does not appear to have a significant impact on measured radiation doses.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

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