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 Table of Contents 
ORIGINAL ARTICLE
Year : 2014  |  Volume : 37  |  Issue : 2  |  Page : 101-105  

Eye lens dose estimation during interventional radiology and its impact on the existing radiation protection and safety program: In the context with new International Commission on Radiological Protection guidelines


Department of Medical Physics, Tata Memorial Hospital, Mumbai, Maharashtra, India

Date of Web Publication18-Dec-2014

Correspondence Address:
Suresh Chaudhari
Department of Medical Physics, Tata Memorial Hospital, Mumbai, Maharashtra 400 012
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-0464.147291

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  Abstract 

Interventional radiology procedures are used for diagnosing certain medical conditions. The radiologists and medical professionals are exposed to ionizing radiation from X-rays of the equipments and also from scattered radiation during these procedures. The radiation exposure to the eye is more important to be assessed while performing such procedures. ICRP has revised the annual dose limit to the lens of the eye from 150 mSv to 20 mSv. In view of this revision, a study was carried out to evaluate the dose to the lens of the eye during interventional radiology. The paper gives the details of calibration of TLDs using a head phantom, predict annual equivalent dose and also highlight the dependence of dose on the position of TLD on the head. It is observed the predicted annual equivalent doses to the lens of eye are in the range of 25 mGy to 37 mGy. The selection of dosimeter placement may also result in an uncertainty of -14% to 20%.

Keywords: Eye lens dose, interventional radiology, tissue reactions


How to cite this article:
Chaudhari S. Eye lens dose estimation during interventional radiology and its impact on the existing radiation protection and safety program: In the context with new International Commission on Radiological Protection guidelines . Radiat Prot Environ 2014;37:101-5

How to cite this URL:
Chaudhari S. Eye lens dose estimation during interventional radiology and its impact on the existing radiation protection and safety program: In the context with new International Commission on Radiological Protection guidelines . Radiat Prot Environ [serial online] 2014 [cited 2022 Jan 19];37:101-5. Available from: https://www.rpe.org.in/text.asp?2014/37/2/101/147291


  Introduction Top


The International Commission on Radiological Protection (ICRP) has reviewed recent epidemiological evidence suggesting that there are some tissue reaction effects, particularly those with very late manifestation, where threshold doses are or might be lower than previously considered. The commission has issued a statement after its meeting on April 21, 2011. [1] Subsequently, the commission has brought out an ICRP publication 118 (2012) on "ICRP statement on tissue reactions and early and late effects of radiation in normal tissues and organs - Threshold doses for tissue reactions in a radiation protection context."

For the lens of the eye, the threshold in absorbed dose is now considered to be 0.5 Gy. For occupational exposure in planned exposure situations the commission now recommends an equivalent dose limit for the lens of the eye of 20 mSv in a year, averaged over the defined periods of 5 years, with no single year exceeding 50 mSv. The previous recommendation given in ICRP publication 103 was 150 mSv/year. This has led to scientific debates in various forums and national and regional bodies responsible for radiation protection and radiation regulations find it necessary to assess its impact in the existing program on radiation protection and safety.

The medical staff working in interventional radiology is exposed to
scattered
radiation
from
the
patient, may
receive
relatively
high
absorbed
dose to
 the eye. [2] The eye lens doses are not measured in India, and occupational dose limits set by the Atomic Energy Regulatory Board are not yet affected. It is necessary to measure the eye lens doses in interventional radiology and the impact of lowering occupational doses on work practice.

In this context, a dosimetry study was undertaken and designed to investigate the eye lens doses received by interventional radiology personnel and its impact on the existing radiation protection and safety program.


  Materials and methods Top


Interventional radiology at institute

Interventional radiology is nonsurgical radiology procedure to treat and diagnose various medical conditions. An X-ray unit equipped with digital flat panel detectors, and monitors are used to visualize the position of the catheter and the anatomy of the patient. The interventions radiologist, technician, and other work at a close distance from X-ray unit and patient which acts as a primary source of scatter radiation. A typical interventional radiology procedure is shown in [Figure 1]. For a given procedure two interventional radiologists, two technologists, and two nursing staffs are involved. Procedures were performed on Innova 4100 (GE Healthcare, USA) with maximum kV: 125, maximum mA: 1000, filtration: 0.3 mm Cu and Ax ARTIS ZEE (Siemens Healthcare, USA) with maximum kV: 150, maximum mA: 800, filtration: 2 mm Al. Both machines are capable to perform fluoroscopy, digital radiography, and digital subtraction angiography (DSA).
Figure 1: Interventional radiology procedure

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The types and number of procedures performed at institute are summarized in [Table 1]. As can be seen from [Table 1], most of the procedures are time-consuming and uses DSA mode.
Table 1: Types and number of procedures performed at institute


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Selection of personal dose equivalent Hp(d)

The personal dose equivalent, Hp(d), is an operational quantity for individual monitoring. It is defined as the dose equivalent in soft tissue at an appropriate depth, d (mm), below a specified point on the human body. There is currently limited dosimetry available for the measurement of the eye dose and consensus on the application of correction factors for currently measured quantities such as Hp(10) and Hp(0.07). The ICRP and the ICRU have recommended Hp(3) for measuring equivalent eye lens doses as the lens is between 2 and 4 mm behind the front of the eye. [3],[4] However, in pure photon radiation fields, like interventional radiology, Hp(0.07) dosimeters can be used to monitor the lens dose when appropriately positioned near eye.

Phantom

A simulating anthropomorphic phantom was designed and developed in-house. The body of the phantom was constructed with Styrofoam (Texsa India Ltd., India) of density 0.1 g/cm 3 . The height of the phantom was 170 cm which corresponds to the average height of radiologists working in the department. A thermoplastic mold (Orfit Industries) of density 1.13 g/cm 3 was prepared to simulate head and face. The eye lens was simulated with 3 mm thick and 2 cm diameter wax of density 0.88-1 g/cm 3 . Additional 5 mm layer of wax was added for backscatter.

Radiation dosimeter and position of the dosimeter

The ideal detector for low energy radiation in diagnostic radiology is LiF: Mg, Cu, P (thermoluminescent dosimeter [TLD]-100H) chips due to their higher thermoluminescent (TL) sensitivity. However, due to nonavailability of this dosimeter, LiF: Mg, Ti which is less sensitive compared to LiF: Mg, Cu, P was used.

40 mg of LiF: Mg, Ti powder was packed in a plastic pouch of dimension 0.5 cm × 0.5 cm.

The
TLDs
were
annealed
at 400°C for 1 h followed by 100°C for 2 h. TLD measurements were read with a commercial TLD-reader system (Rexon UL-320, USA).

The position of the TLD is a concern while measuring eye lens dose. [3] Since direct personnel eye dose measurement is not possible, relationship between eye lens dose in phantom and dosimeters around eye was estimated. 27 TLDs from the same batch were used for this study.

To measure actual lens dose, two dosimeters were placed directly behind the simulated lens. Since the depth of measurement was 3 mm, it is estimated in terms of Hp(3). In addition, the correlation of lens dose with respect to dosimeters placed at different locations was also investigated. For this, the dosimeters were placed at the level of glabella, lateral canthus of right eye, lateral canthus of left eye, supraorbital ridge of right eye, supraorbital ridge of left eye, infraorbital ridge of right eye, infraorbital ridge of left eye and neck [Figure 2]. These dosimeters estimated the dose in terms of Hp(0.07). One TLD was used for measuring the background.

Figure 2: Position of thermoluminescent dosimeters on phantom

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Measurement conditions

The phantom measurements were performed in real time when actual patient procedure was being carried out.

For achieving accuracy in dose estimation, phantom was placed near the radiologist performing the interventional procedures. The tube-phantom distance was maintained same as the tube-radiologist distance (~1.5 m).

Where it was not possible to place the phantom near radiologist, the phantom was placed opposite to radiologist at same distance.

A cumulative reading of half the monthly workload was obtained. For the procedures, average kV and mA was 75 ± 9 kV, 413 ± 208 mA, respectively. The study was performed without protective lead goggles.

Calibration

The max Tube potential of the machines used in this study was 150 kV with average 100 kV being used for the patients. To reduce uncertainty in the calibration, the dosimeters were calibrated at same potential and filtration. TLDs were calibrated at energy of 100 kV with inherent filtration of 5 mm Aluminum (Imagin, Panacea Medical Systems, India). The calibration of the machine was performed with Solid State R/F detector (Unfors RaySafe AB, Sweden) traceable to the primary standard.

A 15 cm × 15 cm × 30 cm phantom was used for calibration. The field size was restricted to 15 cm × 15 cm and target to detector distance was 60 cm. The air kerma rate at phantom surface was measured with Solid State R/F detector. The optimum setting of kV and mA was found for the dose in the range of 1-25 mGy. The TLDs were calibrated in the same phantom. A sensitivity calibration graph for dose versus TL count was obtained.

The estimated organ dose was derived by following formula.



Extrapolation to annual doses

Since the phantom measurements were performed for the half the monthly workload, the annual dose was estimated by extrapolating the measured doses to yield annual dose.

The workload in terms of mA.min was calculated for the procedures performed, and the measured dose was extrapolated to annual occupational doses by following formula.




  Results and discussion Top


Calibration

The sensitivity calibration graph for dose versus TL count was found to be linear over the measurement range of 1-25 mGy [Figure 3]. The sensitivity of TL samples was found to be within ± 3%.
Figure 3: Calibration graph of dose versus total leukocyte count

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Extrapolated annual doses

The doses measured were extrapolated to annual doses and found to be within the new limits recommended by ICRP. [Table 2] lists the annual doses measured at different positions.
Table 2: Measured and extrapolated annual doses


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The doses at different points around the eye may be used to correlate with the lens doses and dosimeters at these points can be used for routine personnel dosimetry. [Table 3] lists the correction factors for the dosimeters to estimate the lens doses.
Table 3: Correction factor with respect to eye lens dose


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The study tried to measure the eye lens doses in actual radiology procedure using a convenient, simple phantom geometry. It also tried to locate the dosimeter position around the eye which may be used to estimate eye lens dose. However, the phantom constructed does not fully simulate the human geometry due to lack of enough backscatter material. Only eyeball constructed with wax with additional 5 mm wax acted as backscatter. The influence of backscatter arising beyond the 2.5 cm depth at reference point of measurement (d = 3 mm) was considered negligible.

The phantom was always placed in an upright position, although the radiologist may be working in inclined head position. Though the phantom could simulate the distance of radiologist from the X-ray tube, the uncertainty associated with variable head position of radiologist may influence the actual dose received by radiologist. The actual lens dose incurred by the radiologist may be estimated by placing the dosimeters directly on the radiologist.

Considering average dose reduction factor of five due to protective lead goggles, the annual doses with lead goggles for the right and left eye lens were estimated as 6 mGy, 5.06 mGy respectively. [5]


  Conclusions Top


Interventional radiology incurs much dose during the procedures to radiologist and technologists. The periodic updates of ICRP must be known and followed. Experimental evidence will give us a close estimation of personnel doses and confidence to ensure radiological safety of the occupational workers during these procedures. Since direct estimation of lens dose is not possible, it can be estimated by placing the dosimeters around the appropriate position related to the eye lens. However, this study demonstrates that the selection of dosimeter placement is crucial and may result in uncertainty of −14% to +20% of the actual lens dose.

The phantom study revealed the eye lens doses received are beyond the recent ICRP limit of per year. Hence, adequate protection measures should be used to limit the occupational doses as recommended by ICRP.

The protective lead goggles demonstrate the reduction of dose by 80%. The interventional radiology personnel should be encouraged to use protective equipment to reduce the individual doses.

 
  References Top

1.
International Commission on Radiological Protection (ICRP), Statement on tissue reactions, ICRP-4825-3093-1464, 21 April, 2011.  Back to cited text no. 1
    
2.
Kim KP, Miller DL, Balter S, Kleinerman RA, Linet MS, Kwon D, et al. Occupational radiation doses to operators performing cardiac catheterization procedures. Health Phys 2008;94:211-27.  Back to cited text no. 2
    
3.
Martin CJ. Personal dosimetry for interventional operators: When and how should monitoring be done? Br J Radiol 2011;84:639-48.  Back to cited text no. 3
[PUBMED]    
4.
Behrens R, Dietze G. Monitoring the eye lens: Which dose quantity is adequate? Phys Med Biol 2010;55:4047-62.  Back to cited text no. 4
    
5.
McVey S, Sandison A, Sutton DG. An assessment of lead eyewear in interventional radiology. J Radiol Prot 2013;33:647-59.  Back to cited text no. 5
    


    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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