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ORIGINAL ARTICLE
Year : 2018  |  Volume : 33  |  Issue : 3  |  Page : 209-213  

Radiation exposure to the personnel performing robotic arm-assisted positron emission tomography/computed tomography-guided biopsies


Department of Nuclear Medicine and Positron Emission Tomography/Computed Tomography, Postgraduate Institute of Medical Education and Research,Chandigarh, India

Date of Web Publication11-Jun-2018

Correspondence Address:
Rajender Kumar
Department of Nuclear Medicine and Positron Emission Tomography/Computed Tomography, Postgraduate Institute of Medical Education and Research, Chandigarh - 160 012
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijnm.IJNM_31_18

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   Abstract 


Purpose: The aim of the study was to estimate the radiation burden to personnel performing robotic arm-assisted positron emission tomography/computed tomography (PET/CT)-guided metabolic biopsies and to staff assisting the procedure in a PET/CT facility. Materials and Methods: We estimated the whole-body exposures to physicians and staff based on the dose rate measurement with an ionization chamber-based calibrated survey monitor and pocket dosimeters during the robotic arm-assisted 2-[F-18]-fluoro-2-deoxy-D-glucose PET/CT-guided biopsies from September 2016 to February 2017. In addition, we also noted the time to biopsy after injection and total biopsy time during which the staff was exposed to the radiation. Results: In this prospective study, PET/CT-guided biopsy was performed in 50 patients (males – 36, females – 14) with a mean age of 54 ± 15 years (range17–78 years). Of the 50 biopsy procedures, 18 were lung biopsies, 10 were bone biopsies, and 22 biopsies were from abdomen/pelvic lesions. The mean time taken for the procedure was 26 ± 11 min. The mean time elapsed between injection and procedure was 182 ± 85 min and mean injected activity of 138.38 ± 74 MBq. The mean whole-body exposure per procedure to an interventionist and an assistant was 1.88 ± 0.82 μSv and 1.04 ± 0.75 μSv, respectively. The mean exposure rates at 0-m and 1-m distance from the patient were 30.77 ± 14.61 μSv/h and 2.59 ± 1.49 μSv/h, respectively. Conclusion: We conclude that the interventionist received the highest mean effective dose as compared to the helping staffs. The occupational radiation exposure was found to be within the limits as specified by the regulatory authorities (International Commission on Radiological Protection-103), and PET/CT-guided biopsies were safe from radiation protection point of view.

Keywords: Gun monitor, personnel exposure measurement, pocket dosimeter, robotic arm assisted positron emission tomography/computed tomography-guided biopsies


How to cite this article:
Lakhanpal T, Mittal BR, Kumar R, Watts A, Rana N, Singh H. Radiation exposure to the personnel performing robotic arm-assisted positron emission tomography/computed tomography-guided biopsies. Indian J Nucl Med 2018;33:209-13

How to cite this URL:
Lakhanpal T, Mittal BR, Kumar R, Watts A, Rana N, Singh H. Radiation exposure to the personnel performing robotic arm-assisted positron emission tomography/computed tomography-guided biopsies. Indian J Nucl Med [serial online] 2018 [cited 2019 Dec 12];33:209-13. Available from: http://www.ijnm.in/text.asp?2018/33/3/209/234127




   Introduction Top


Currently, 2-{F-18}-fluoro -2-deoxy-D -glucose positron emission tomography/computed tomography (18 F-FDG PET/CT) is the most widely used molecular imaging technique for diagnosis and management of cancer patients in comparison to other conventional imaging techniques.[1] However, imaging alone is not helpful to differentiate cancerous tissue from noncancerous one, lest it specifies the tumor type. Hence, biopsy remains the most definitive diagnostic procedure for most tumors. Biopsy of the lesions needs to be carefully planned and performed after correlating with the findings from ultrasonography, contrast-enhanced CT, magnetic resonance imaging, or other radiologic findings.[2] Because of the high energy of the annihilation radiation, shielding requirements are an important consideration in the design of PET/CT hybrid imaging facility. Various aspects of PET shielding designs have been addressed in a number of publications, yet while doing PET/CT-guided biopsy, these shielding requirements can be fulfilled to an extent.[3] In such a situation, the definite concern is about the radiation dose one has to bear owing to interventional procedures. Although the radiation doses cannot be completely omitted, the exposure can be monitored to minimize the radiation levels to be within the permissible limits.[4] Based on the recent advances in technology, PET/CT-guided biopsies have gained more importance than conventional image-guided biopsies in the last few years.[5] However, the fear of radiation exposure due to PET radiotracer looms in the mind of interventionist and is of great concern. The aim of this study was to assess the radiation exposure rate and whole-body radiation doses received by the interventionist and assisting physician while performing the robotic arm-assisted FDG PET/CT-guided biopsies at a tertiary health care center and to compare the occupational radiation burdens with the limits prescribed by the International Commission on Radiological Protection (ICRP Publication No. 103).[4]


   Materials and Methods Top


This prospective study was conducted from September 2016 to February 2017 at the PET/CT center with the facility of robotic arm-assisted PET/CT-guided biopsies. The study comprising PET/CT-guided procedures was approved by the Institute Ethics Committee. A total of 50 patients in whom CT-guided biopsy was inconclusive and who were referred for PET/CT-guided biopsy for various clinical reasons were included in the study. The patients who refused to give consent and those with deranged coagulation profile (platelet counts, prothrombin time, international normalized ratio, and partial thromboplastin time) were excluded.

Positron emission tomography/computed tomography acquisition protocol

All the patients were asked to remain fasting for at least 4 h before whole-body PET/CT scan. The whole-body PET/CT acquisition was done using a dedicated PET/CT scanner (Discovery 710 or Discovery STE 16; GE Healthcare, Milwaukee, USA), 60 min after intravenous administration of 222–370 MBq of 18 F-FDG. Attenuation correction of PET images was done using helical CT with the slice thickness of 1.25 mm. Reconstruction of PET images was done using ordered subset expectation maximization algorithm, with two iterations and 28 subsets, and Gaussian postfiltering (full width at half maximum, 6 mm). After reviewing the whole-body PET/CT scan, the site and trajectory of biopsy were planned on the basis of FDG avidity and location of the lesion. The interventional procedure was planned 3–4 h postradiotracer injection. Patients were immobilized in a fixed position using vacuum-assisted patient motion arrester bed during the biopsy procedure. A limited one bed position PET/CT scan of the desired region was acquired in the Robio protocol.

Positron emission tomography/computed tomography-guided biopsy

The DICOM PET/CT images were transferred to the automated robotic arm planning console (ROBIO-EX, Perfint Healthcare Pvt. Ltd, Chennai, India) docked alongside the patient bed. The path of the biopsy was determined by the physician on the basis of hypermetabolic lesion of interest on ARA planning console after loading the fused PET/CT images. The robotic arm was positioned according to the planned path, and biopsy needle was inserted to the target lesion. After confirming the position of the needle with low-dose CT (40 mA) fused with PET, the tissue samples were retrieved from the target lesion under surgical asepsis.

Dose rate measurements

An ionization chamber-based calibrated RAM ION Digi-Log (Rotem Industries Ltd, Israel) portable survey monitor [Figure 1]a was used for the measurement of exposure rates. The measurement range of the instrument was 1 μSv/h to 500 mSv/h (0.1 mR/h to 50 R/h) with an accuracy of ± 10% of reading within measuring range and gamma dependence better than ± 20% at 20 keV to 1.3 MeV. The exposure rates were measured at the 0-m [Figure 2]a and 1-m distance [Figure 2]b from the patient.
Figure 1: Photograph showing instruments used for dose rate measurement with RAM ION Digi-Log (Rotem Industries Ltd, Israel) Portable Survey Monitor (a) and dose measurement with RADOS RAD60 (LAURUS Systems, Inc. USA) Personal Pocket Dosimeters (b)

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Figure 2: Photograph showing dose rate measurement with RAM ION Digi-Log (Rotem Industries Ltd, Israel) Portable Survey Monitor (white arrows) at 0-m (a) and 1-m (b) distance from the patient table during robotic arm-assisted positron emission tomography/computed tomography-guided biopsy

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Dose measurements

The personal pocket dosimeter (PD) [Figure 1]b RADOS RAD60 (LAURUS Systems, Inc., USA) with energy compensated Si-diode detector and an inbuilt alarm was used for dose measurements during the PET/CT-guided biopsies procedure [Figure 3]a. The measurement range of the instrument was 1 μSv–9.99 Sv or 0.1 mrem–999 rem and the dose rate was 5 μSv/h–3Sv/h or 5 mrem/h–300 rem/h. The instrument had dose rate linearity better than ±15%, up to 3 Sv/h (300 rem/h). The dosimeters were worn by the interventionist [Figure 3]b and assisting physician during the entire biopsy procedure. At the end of biopsy procedure, the radiation doses to both the physicians were recorded.
Figure 3: Photograph showing interventionist performing robotic arm-assisted positron emission tomography/computed tomography-guided biopsy procedure (a) with needle insertion to the lesion. The dose measurement with RADOS RAD60 (LAURUS Systems, Inc. USA) Personal Pocket Dosimeter (white arrow) to interventionist during positron emission tomography/computed tomography-guided biopsy procedure (b)

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The time to biopsy after intravenous injection of F-18 FDG was recorded. In addition, we also recorded the time consumed for PET/CT-guided biopsy during which the staff was exposed to the radiation. In our center, we are routinely doing two biopsy procedures per day with five working days in a week and a total 42 working weeks in a year. The whole-body occupational exposure to the interventionist and assisting physician was calculated on the basis of following formula:

Whole-body occupational exposure (μSv/year) = mean radiation doses per procedure (μSv) ×2 procedures per day × 5 working days in a week × 42 working weeks in a year.


   Results Top


A total of 50 patients (36 males and 14 females) with a mean age of 54 ± 15 years (17–78 years) underwent PET/CT-guided biopsies from September 2016 to February 2017. Of these 50 patients, the sites of biopsies were lung and mediastinum (n = 18), bone (n = 10), and abdominal and pelvic (n = 22) lesions. The mean time elapsed between the radiotracer administration and biopsy sampling was 182 ± 85 min, the mean injected activity was 138.38 ± 74 MBq, and the mean time taken for biopsy procedures was 26 ± 11 min per procedure. The details of time elapsed, time for biopsy, and injected activities are listed in [Table 1].
Table 1: Values of injected dose of radiotracer, time elapse and time taken for biopsy

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The mean exposure rates measured per procedure at surface (0 m) and 1-m distance from the patient were 30.77 μSv/h and 2.59 μSv/h, respectively. The exposure rates for different biopsy procedure are listed in [Table 2]. The mean radiation doses received by the interventionist and assistant physician per procedure were 1.88 μSv and1.04 μSv. The details of mean dose received by the interventionist and assistant physician during various F-18 FDG PET/CT-guided biopsy procedure are also listed in [Table 2].
Table 2: Exposure and exposure rate measurements for lung, bone, and abdominal and pelvic biopsies

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The calculated whole-body occupational exposure to the interventionist and assisting physician was 790 (1.88 μSv ×2 × 5 × 42) μSv/year or 0.79 mSv/year and 437 μSv/year (1.04 μSv × 2 × 5 × 42) or 0.437 mSv/year. The details of the whole-body occupational exposure are listed in [Table 3].
Table 3: Exposure limits of the personnel performing and personnel assisting biopsy

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   Discussion Top


Radiation protection is a major concern while dealing with any type of radiation. To minimize the exposure, radiation protection principles, i.e., time, distance, and shielding, are assigned by the regulatory bodies. F-18 FDG PET/CT is routinely used in clinical oncology for diagnosis and response evaluation. Apart from these, it can help in detection of the hypermetabolic region within the tumor and guide the biopsy from the optimal site.[6]

However, during these interventional studies, it is difficult to minimize the exposure by increasing distance as it requires the physician performing biopsies to be in close contact with the patient. The source of radiation during the biopsy procedures is the patient itself; therefore, shielding the source is not feasible. Furthermore, wearing the lead apron is not feasible to the clinician carrying out intervention due to its heavy load as the greater thickness of the apron is required to stop the 511 keV photons. The only parameter that can be taken care of is time. To minimize the time, it is necessary to properly plan the procedure. The critical groups exposed to radiation during the biopsy procedure are interventionist, helping physician and other staff involved in the procedure. Hence, it is subservient to monitor the radiation dose received by these groups and to check the whether the annual dose is within the prescribed limits.

There are many studies which measured the radiation dose received by the staff during the FDG PET/CT.[7],[8],[9],[10],[11],[12],[13],[14] In the literature, different personnel monitoring devices to measure the effective dose during PET/CT scan have been reported. The finger dose measurements were done using thermoluminescent dosimeter (TLD),[7] PD, and ring dosimeter,[9] while whole-body and extremity exposures were measured using TLD badges and electronic personnel dosimeters.[11]

PET-CT-guided robotic arm-assisted system is a robotic device which helps in fast and accurate placement of needle to the target lesion for diagnosis and treatment planning. It helps in accurately targeting the deep-seated lesions requiring multiple angulations in a single pass and in reducing the time spend in vicinity of the patient and hence radiation exposure. In addition, the radiation exposure to the patient and interventionist is also lesser because the needle placement is not done under the fluoroscopy. In the present study, we measured the radiation exposure dose and exposure rate per procedure to the personnel performing robotic arm-assisted PET/CT-guided biopsy and annual radiation exposures were calculated. A recent study evaluated the effective whole-body dose rate of each staff during the PET/CT procedure with the help of dose rate meter and recorded the dose received per working day, time spend in contact with patient, and daily injected activity. In addition, they measured the instantaneous dose rates at 0.1, 0.5, 1.0, and 2.0 m from the mid-thorax from the patient.[13] However, there is no literature regarding the radiation exposure to the staff during robotic arm-assisted PET/CT-guided biopsies.

In our study, the mean radiation exposure rate at the surface and over 1 m was 30.77 ± 14.61 and 2.59 ± 1.49, which is far less than the values measured by Pant and Senthamizhchelvan.[14] The reason behind this is that PET-guided biopsies were done after 3–4 h of radiotracer injection and lesser radiotracer was injected to the patients. We noticed that the exposure rate was reduced at 1 m compared to surface exposure rate by a factor of 10.7. Hence, the personnel assisting can reduce the radiation exposure considerably by maintaining the distance.

We also noticed that the exposure rate in bone biopsies was lesser than others biopsy procedures, likely due to lesser administered activity and more time elapsed after the injection for the procedure. However, keeping the time elapse to be the constant, increase in the administered activity increases the exposure rate.

The personnel exposures during PET/CT scan had been measured by many authors. Damir et al.[7] measured the whole-body and finger dose at two time points. During the first 6 months, they measured the values without shielding precautions (without a shielding for sterile syringe and without lead container for shielding syringe) and during the next 6 months with shielding precautions (with shielding for sterile syringe and with lead container for shielding syringe). The average annual whole-body radiation dose for technologist before shielding was 7.82 mSv and after shielding was 5.76 mSv. Donmoon et al.[9] measured the whole-body dose received by radiopharmacist, technologist, and nurses by electronic dosimeter and finger doses by ring dosimeter during 4 months in 70 PET/CT studies. The whole-body and finger radiation doses were 1.07 + 0.09 μSv and 265.65 + 107.55 μSv to the radiopharmacist and 1.77 + 0.46 μSv and 4.84 + 1.08 μSv to the technologist, respectively. Pant and Senthamizhchelvan [14] estimated the radiation exposure to the physicians and technologist working in their PET/CT facility based on the dose rate measurements with calibrated survey meter and PD. The mean dose measured at chest level for PET/CT procedure was 3–25 μSv and 0.62 μSv for the physician and technologist, respectively.

In the present study, we also noted that the radiation exposure to the interventionist performing the procedure was higher than the assisting physician in all the procedures because of more time spent and less distance from the patient. Ryan et al.[15] measured the median effective dose to the primary operator, technologist, and nurse anesthetist during PET/CT-guided intervention over a period of 6 months in 12 patients with the help of optically stimulated dosimeters. Radiation exposure was then correlated with procedure time and CT-guided fluoroscopy/ultrasound. The measured median effective dose to the primary operator was 0.02 mSv and was significantly less than the prescribed limits.[4] In our study, we also observed the mean personal exposure per procedure for interventionist and assisting physician were 1.88 ± 0.82 μSv and 1.04 ± 0.75 μSv, respectively, which were significantly below the prescribed limits (ICRP-103).

According to AAPM task group 108,[16],[17] total absorbed dose can be estimated knowing the administered activity, number of patients scanned per week, uptake time, and decay correction factor. The radiation exposure to the clinician performing the biopsy can be estimated using the observed values of mean radiation dose. The estimated exposure in our study was 769 μSv/year or 0.769 mSv/year for lung biopsies, 630 μSv/year or 0.63 mSv/year for bone biopsies, and 840 μSv/year or 0.84 mSv/year abdominal and pelvis lesion. The mean estimated exposure was 790 μSv/year or 0.79 mSv/year.

On comparison of our results of personal exposure, with the ICRP occupational radiation dose limits of 20 mSv/year for whole body, we found that the occupational exposure to the interventionist and assisting physician was very minimal and much below specified limits. Our results have also revealed that by reducing the dose of FDG and time for the procedure the personal exposure can be further reduced and our interventionist can continue to work with their maximum capacity of ~ 420 PET/CT-guided biopsies in a whole year.


   Conclusion Top


The robotic arm-assisted PET/CT-guided biopsies were found to be a safe interventional procedure from radiation exposure point of view, and the radiation exposure to the interventionist and assisting physician was within the safe limits as specified by the regulatory authorities (ICRP-103; under section 5.10). In addition, good work practice and lesser tracer dose can further reduce the exposure and procedure can be done without fear of radiation.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

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Guillet B, Quentin P, Waultier S, Bourrelly M, Pisano P, Mundler O, et al. Technologist radiation exposure in routine clinical practice with 18F-FDG PET. J Nucl Med Technol 2005;33:175-9.  Back to cited text no. 11
    
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Benatar NA, Cronin BF, O'Doherty MJ. Radiation dose rates from patients undergoing PET: Implications for technologists and waiting areas. Eur J Nucl Med 2000;27:583-9.  Back to cited text no. 13
    
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Pant GS, Senthamizhchelvan S. Radiation exposure to staff in a PET/CT facility. Indian J Nucl Med 2006;21:100-3.  Back to cited text no. 14
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Ryan ER, Thornton R, Sofocleous CT, Erinjeri JP, Hsu M, Quinn B, et al. PET/CT-guided interventions: Personnel radiation dose. Cardiovasc Intervent Radiol 2013;36:1063-7.  Back to cited text no. 15
    
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    Figures

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

  [Table 1], [Table 2], [Table 3]



 

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