Radiation safety audit of a high volume Nuclear Medicine Department.

INTRODUCTION: Professional radiation exposure cannot be avoided in nuclear medicine practices. It can only be minimized up to some extent by implementing good work practices. AIM AND
OBJECTIVES: The aim of our study was to audit the professional radiation exposure and exposure rate of radiation worker working in and around Department of nuclear medicine and molecular imaging, Tata Memorial Hospital.
MATERIALS AND METHODS: We calculated the total number of nuclear medicine and positron emission tomography/computed tomography (PET/CT) procedures performed in our department and the radiation exposure to the radiation professionals from year 2009 to 2012.
RESULTS: We performed an average of 6478 PET/CT scans and 3856 nuclear medicine scans/year from January 2009 to December 2012. The average annual whole body radiation exposure to nuclear medicine physician, technologist and nursing staff are 1.74 mSv, 2.93 mSv and 4.03 mSv respectively.
CONCLUSION: Efficient management and deployment of personnel is of utmost importance to optimize radiation exposure in a high volume nuclear medicine setup in order to work without anxiety of high radiation exposure.

INTRODUCTION

The radiation safety of radiation worker, general public and environment always remains a matter of concern particularly in a high volume Nuclear Medicine Department. Professional radiation exposure and exposure to the patient and the general public cannot be avoided in nuclear medicine practice, where open sources of radiation are handled and radioisotope is administered in the form of radiopharmaceutical resulting in the patient himself becoming a moving source of radiation. As health care professionals, it becomes our duty to attend to patients’ needs, though they might themselves be sources of radiation. Thus, it becomes imperative to strike a balance between health care ethics and radiation safety. In order to achieve the ‘As low as reasonably achievable (ALARA)’ principle in our practice and minimize radiation exposure, effective communication explaining the test procedure prior to administration of radioisotope, implementation of good work practice and basic concepts of radiation safety in a judicious manner keeping time, distance and shielding in the mind are a must.[1]

Positron emission tomography/computed tomography (PET/CT) is gaining immense popularity in the oncology fraternity as a diagnostic tool for staging, restaging and follow-up of various oncology indications. It has become an integral part of patient management in oncology and is gradually replacing the conventional modalities like CT and magnetic resonance imaging.[2] PET radiopharmaceuticals are positron-emitting isotopes, which decay by emitting two annihilation photons of 511 keV in opposite directions. These high-energy photons result in an extra amount of radiation exposure to the radiation worker working in nuclear medicine.[3] Since protective clothing like lead apron, lead gloves, etc., are not effective in minimizing the radiation dose to the professionals, radiation exposure from positron-emitting radio-isotopes has become a matter of concern amongst professionals working in PET/CT department.

In the last few years, the demand for PET/CT procedures by treating oncologists has increased globally and in our hospital as well, which has put lots of pressure on PET/CT department to perform more cases every day. Our department has been performing an average of 30 PET/CT and 25 nuclear medicine procedures every day on one PET/CT scanner and one single photon emission computed tomography/CT (SPECT/CT) scanner. Work of this magnitude is considered as high volume radiation work for a Nuclear Medicine Department. Amongst several efforts to minimize the radiation exposure and achieve ALARA, one is the distribution of radioactive work among nuclear physicians, nursing staffs and technologists and rotation of staffs for radioactive and nonradioactive duties. Although personal radiation exposure never crossed the prescribed limit of 20 mSv/year for an individual in our department, we decided to audit the professional radiation exposure and other radiation safety data of last 4 years available with us to minimize the radiation safety concern among professionals further and to look for any scope for further improvement.

MATERIALS AND METHODS

Thermo luminescent dosimeter

Thermoluminescence is the property of certain materials to emit light when they are stimulated by heat. Materials such as lithium fluoride, lithium borate, calcium fluoride, and calcium sulfate (CaSO4) have been used to make thermoluminescence dosimeters (TLDs). CaSO4 crystal doped with dysprosium TLD is used to monitor professional radiation exposure. The principle features of this dosimeter are its high sensitivity to low-energy radiation and its relatively low fading which permits measurements down to <2.6 × 10-8 C kg (0.1 mR).[4]

Radiation safety policy in our hospital

In India, the Atomic Energy Regulatory Board (AERB) is the regulating authority which provides frameworks and guidelines regarding radiation installation and regulates the same. As per the AERB guidelines, Radiation Safety Committee (RSC) is constituted in our hospital. RSC conducts quarterly radiation safety meeting to audit the implementation of radiation safety guidelines in the hospital and quality assurance status of equipments.[5] RSC gives specific instructions to of Radiation Safety Officer (RSO) in-charge, Hospital, to implement radiation safety instruction if required. RSO in-charge of the hospital is responsible to implement the radiation safety guidelines through departmental RSO. Hospital RSC allows deployment of only qualified staff or regular staff who have undergone prior training in basic concepts of radiation safety and routine work in a radiation department. Specific precautions and great care is taken during the handling the radiation to avoid any kind of mishaps at workplace. A pool of nursing and support staff for radiology and nuclear medicine is maintained. Staff members posted in that pool are trained to work in Nuclear Medicine Department and other aspects of radiation safety and are then alternately rotated in the Nuclear Medicine and Radiology Departments on a monthly basis.

Personal monitoring in the department

Thermo luminescent dosimeter is used for personal monitoring in our hospital. All staff members in our department are provided two sets of personalized TLDs, that is, one for chest and one for the wrist to monitor whole body as well as extremity radiation exposure as per the AERB guidelines. One TLD is kept as control TLD in a designated non-radioactive area in our department.[5] Radiation workers strictly wear TLDs only during working hours after which the TLDs are kept in a nonradioactive area designated in our department. The TLDs are procured from Bhabha Atomic Research Centre (BARC). These TLDs are replaced every 3 months with the used TLDs sent to BARC for measurement of cumulative radiation exposure during the 3 month period. The TLD readings are communicated to us by post. The records of the TLD reading of every radiation worker in our department are maintained in our personal monitoring register as advised by AERB. Yearly radiation dose received by an individual radiation worker are calculated by adding all four quarterly doses and lifetime accumulated dose is also updated for each individual radiation worker regularly.

Lay out of the department

In our department, SPECT/CT and PET/CT facilities are separate units comprising of independent radio pharmacy and post-injection waiting areas. The patient flow has been designed to prevent inter-mingling of patients from both modalities. Layout of the department is approved by AERB as independent SPECT/CT and PET/CT unit.

Workflow in the department

A standard workflow is established and followed in our department [Figure 1]. We have a dedicated appointment counter for the patient who is referred for a nuclear scan in our department. Personnel handling the appointments are instructed by qualified staff of our department. They are very well aware about the tests and requirements of the tests. At the time of appointment, specific instructions regarding the test are provided to the patient. Instructions are provided orally as well as in the form of printed instructions detailing the test procedure and patient preparation specific to the test along with an appointment date and time. List of appointed patients with required tests for the day is also provided at the nursing stations and placed at the console table every day in the morning. On the date of appointment when patient reports at the nursing station, nursing-in-charge verifies the patient and test prescribed with the available list with her and refers the patient to the resident doctors for taking relevant clinical history and to verify the adequacy of the test. Once the test is confirmed and the patient is prepared, the relevant instructions are given to the patient for scan and post-scan precautions like delay in breast-feeding and to avoid proximity with others, especially children. Scanning is then performed as per the guidelines following which the patient is sent home.

Figure 1

Workflow followed in the department

Radiation handling

All the medical and nonmedical staffs working in our department are adequately trained in radiation safety. Majority of our radiation workers have RSO training and certification by the competent authority. RSO and other trained personnel provide adequate training and orientation to the nursing staff, medical students, technologist trainees, and other support staff regarding radiation safety, safe handling of radioisotope and handling of the radioactive patient before assigning them to routine work. Utmost care and precautions are taken during handling of radioisotope and injected patients to avoid any mishaps, which could lead to unnecessary radiation exposure to the patient, radiation worker and the general public. To maximize our work and to follow the principle of ALARA we have distributed the radiation work among the professionals working in the department. Nuclear medicine physicians handle the injection of radioisotopes and any interaction with the injected patients if required. Technologists are responsible for formulation of radiopharmaceuticals, quality control of nuclear medicine equipments and radiopharmaceuticals, dispensing of radiopharmaceuticals and acquiring the scans. Nursing staffs are responsible for intravenous access, postimaging removal of intravenous catheter and any other minor assistance to the patient required during the uptake time. During the study period, about 12 nuclear medicine physicians, seven nuclear medicine technologists and eight nursing staff were posted in our department to perform the routine radioactive work. Out of eight nursing staff, four were posted at a given time in nuclear medicine and radiology rotations as mentioned above. Technologists are rotated on image acquisition and radiopharmacy duty alternately for 2 weeks. Technologists and staff nurses are also rotated in PET and SPECT on a monthly basis. Nuclear medicine physicians are likewise rotated in PET and SPECT on a monthly basis. Since most of the radiation exposure to the nuclear medicine physician is from radiopharmaceutical injections, this duty is equally shared by the physicians every day.

Radiation survey, radioactive waste management and disposal

Radiation survey and radioactive waste management and disposal are of utmost importance and are an integral part of radiation safety to maintain the quality of work as well as comply with the regulatory requirement.[5] Periodic radiation survey is a part of the routine work in the department and is performed by a qualified person under the supervision of RSO every week as well as whenever there is suspicion of contamination. The radiation survey locations in our department are outside the L-bench, outside the fume hood, 1 m from active dust bin, near injection table, 1 m from patient in patient waiting area, at the entry of waste storage room, one meter from the patient table in the machine room, at the console and at the nursing stations. Contamination monitors are installed in PET and SPECT console room to monitor hand contamination of personnel every time they handle any radioisotope in the radio-pharmacy. All the radiation workers strictly use gloves during handling radioisotope. We have adequately shielded work area, L-bench and lead container, dispensing units, syringe carrier and syringe shield, etc., to give proper protection at workplace. Lead lined dust bins are used to discard radioactive syringes, needles, vials and other articles separately to maintain proper segregation of radioactive waste. The radiation wastes generated in our department are separated as liquid and solid waste. We segregate liquid waste and solid (sharp and nonsharp) radioactive waste separately for individual radioisotopes right at the beginning. Radiation waste is allowed to decay in the radioactive waste storage room for 10 half-lives or more as required and discarded under the supervision of RSO when the exposure rate is below the prescribed limit of 3.7 MBq/day and 185 MBq/m3. We monitor and record the exposure rate of waste before disposal. Discarded waste is then treated like any hospital waste as per our hospital waste management policies.

Radiation safety audits

We performed a retrospective audit of radiation exposure received by the radiation workers in our department during the last 4 years. We recorded the total number of PET/CT and nuclear medicine procedures that were performed in the department every year along with the total number of radiation workers in the department in each calendar year and the nature of work of individual workers. We used our radioactivity logbook to calculate the total radioactivity used in the department. Radiation survey register, radiation accident register, radio pharmacy register were also audited for knowing the radiation safety survey status, and the total amount of radioisotope handled and used in the department.

Calculations

The average annual whole body radiation dose received by nuclear medicine physicians, technologists, and nurses were calculated following formula.

Nuclear medicine physician

EA, AVG, P = (∑ EQ, P)/(TQ, R, P) × 4

EA, AVG, P = Average whole body annual exposure for physician

EQ, P = Quarterly whole body radiation exposure for physician

TQ, R, P = Total number of quarterly reading for physician.

Technologists

EA, AVG, T = (∑ EQ, T)/(TQ, R, T) × 4

EA, AVG, T = Average whole body annual exposure for technologists

EQ, T = Quarterly whole body radiation exposure for technologists

TQ, R, T = Total number of quarterly reading for technologists.

Nurses

EA, AVG, N = (∑ EQ, N)/(TQ, R, N) × 4

EA, AVG, N = Average whole body annual exposure for nurses

EQ, N = Quarterly whole body radiation exposure for nurses

TQ, R, N = Total number of quarterly reading for nurses.

Since the same staff was rotated in PET/CT and SPECT/CT, the separation of exposure by PET radioisotope and SPECT radioisotope was not possible. The ratio of SPECT to PET studies in our department was 1:1.68 and hence we have calculated the average whole body radiation dose based on this ratio by the following formula:

EPr, P = (ET, P/ TNM, Pr)

EPr, P = Total whole body radiation exposure to the physician performing one nuclear medicine scan and 1.68 PET scan

ET, P = Total radiation exposure to physicians in 4 years

TNM, Pr = Total nuclear medicine procedure performed in 4 years.

EPr, T = (ETot, T /TNM, Pr)

EPr, T = Total whole body radiation exposure to the technologists performing one nuclear medicine procedure and 1.68 PET/CT procedure

ETot, T = Total radiation exposure to the technologists in 4 years

TNM, Pr = Total nuclear medicine procedure performed in 4 years.

EPr, N = (ETot, N/ TNM, Pr)

EPr, N = Total whole body radiation exposure to the nurses performing one nuclear medicine scan procedure and 1.68 PET/CT procedure

ETot, N = Total radiation exposure to the nurses in 4 years

TNM, Pr = Total nuclear medicine procedure performed in 4 years.

On the basis of a similar reasoning as mentioned above, we have also calculated the radiation dose received by professionals during handling 1 GBq of fluoride (F-18) based radiopharmaceuticals and 1.12 GBq 99mTc and other radioisotopes used in nuclear medicine by the following formula:

EAct, P = (ETot, P/ RIT, PET)

EAct, P = Total whole body radiation exposure to the physician by using 1 GBq PET radiopharmaceuticals and 1.12 GBq 99mTc and other radioisotope used in nuclear medicine.

ETot, P = Total radiation exposure to physicians in 4 years

RIT, PET = Total amount of PET radiopharmaceuticals used 4 years.

EAct, T = (ETot, T /RIT, PET)

EAct, T = Total whole body radiation exposure to the technologists by using 1 GBq PET Radiopharmaceuticals and 1.12 GBq 99mTc and other radioisotope used in nuclear medicine.

ETot, T = Total radiation exposure to the technologists in 4 years

RIT, PET = Total amount of PET radiopharmaceuticals used 4 years.

EAct, N = (ETot, N /RIT, PET)

EAct, N = Total whole body radiation exposure to the nurses using 1 GBq PET Radiopharmaceuticals and 1.12 GBq 99mTc and other radioisotope used in nuclear medicine.

ETot, N = Total radiation exposure to the nurses in 4 years

RIT, PET = Total amount of PET radiopharmaceuticals used 4 years.

RESULTS

Record books were maintained properly and all relevant records were available with the RSO in the department. Radiation survey report during the study duration of 4 years (2009-2012) does not show any significant fluctuations in the radiation exposure rates observed at different locations in the department. Ten individual radiation survey records were picked randomly for each year and averaged location wise as shown in graph and table for the entire period of 4 years [Figures 2 and 3] [Tables 1 and 2]. A few instances of minor radiation spillage had occurred in the department, and the necessary steps were taken to decontaminate the place and professionals involved under the supervision of RSO. These incidences were recorded, reported and communicated to relevant higher authorities. There was one instance in which contamination of one radiation professional occurred and subsequent TLD readings showed a high level of exposure. In this particular instance the TLD was contaminated by radioactivity during spillage, which was documented in the radiation safety report made at that time. As this TLD reading was not the actual radiation exposure received by the professional and hence has not been considered as actual radiation exposure and is thereby excluded in our study.

Figure 2

The radiation survey reading at various places in the positron emission tomography/computed tomography unit in the department from year 2009 to 2012

Figure 3

The radiation survey reading at various places in the single photon emission computed tomography (CT)/CT unit in the department from year 2009 to 2012

Table 1

Radiation survey of PET/CT facility (from year 2009 to 12)

Table 2

Radiation survey of SPECT/CT facility (from year 2009 to 12)

An average of 2500 GBq of radioisotope was used per year in PET imaging and 2600 GBq of radioisotope/year in SPECT imaging over the period of 4 years. 2489.84 GBq maximum and 2146.74 GBq minimum amount of radioisotope was used for PET imaging in year 2012 and 2009 respectively. A maximum of 2854.25 GBq and minimum of 2349.54 GBq radioisotope was used for SPECT imaging in year 2012 and 2009 respectively. The details of radioactivity used over the period of four are shown in table and also graph [Figure 4]. We performed an average of 6478 PET/CT scans and 3856 nuclear medicine scans/year from January 2009 to December 2012. The highest number of PET/CT scans (6952) were performed in the year 2012 and the lowest (5863) were performed in the year 2009. Likewise the highest number of nuclear medicine scans (4124) were performed in 2012 and the lowest number (3524) were performed in the year 2009. Details of the number of PET/CT and nuclear medicine procedures performed over the period of 4 years are shown in Figure 5. Average annual whole body radiation exposure to nuclear medicine physicians, technologists and nursing staff was found to be 1.74 mSv, 2.93 mSv and 4.03 mSv respectively. Highest individual average whole body radiation exposure to the nuclear medicine physician was 2.12 mSv recorded in 2012, to the technologist was 3.28 mSv recorded in 2009 and to the staff nurse was 4.67 mSv recorded in year 2009. Likewise, lowest individual average whole body radiation exposure to the nuclear medicine physician was 1.73 mSv in 2011 to the technologist was 2.41 mSv in 2011 and staff nurse was 3.03 mSv in year 2012. The details of average annual whole body radiation exposure to the radiation worker are shown in Figure 6. Annual whole body total radiation exposure to the different professional groups shown as percentage radiation exposure over a period of 4 years is depicted in Figure 7. Total whole body radiation exposure to the nuclear medicine physicians, technologists, and staff nurses were found to be 3.7 6μSv, 4.67 μSv and 4.29 μSv respectively for every 1.68 PET scan and one nuclear medicine scans. Similarly, total whole body radiation exposure to the nuclear medicine physicians, technologists and staff nurses were 6.32 μSv, 7.79 μSv and 7.16 μSv respectively for every 1 GBq F-18 isotopes and 1.12 GBq Tc-99m and other nuclear medicine isotopes.

Figure 4

(a) Percentage of positron emission tomography (PET) and single photon emission computed tomography (SPECT) radiopharmaceuticals used in 4 years. (b) PET and SPECT radiopharmaceuticals used from years 2009 to 2012

Figure 5

(a) Percentage of positron emission tomography/computeed tomography (PET/CT) and nuclear medicine procedure performed in 4 years. (b) PET/CT and nuclear medicine procedure performed from year 2009 to 2012

Figure 6

Average annual whole body radiation exposure received by nuclear medicine physician, technologist and nurse from year 2009 to 2012

Figure 7

Percentage of whole body radiation exposure received by nuclear medicine physicians, technologists and nurses in 4 years. (a) Total annual whole body radiation exposure received by all nuclear medicine physicians together, technologists together and nurses together from year 2009 to 2012

DISCUSSION

There is no lower limit for radiation exposure that can be considered safe for humans. Radiation exposure may bring deterministic or stochastic effects depending upon the level and type of exposure.[567] Deterministic effects are mainly due to acute radiation exposure of high magnitude and appear above a certain threshold level. Cataract is a type of deterministic effect of radiation, which occurs both by chronic as well as acute exposure. The stochastic effect is probabilistic in nature without any threshold and any amount of radiation exposure can cause a stochastic effect. The probability of stochastic effect increases by increasing amount of radiation exposure.[567] So radiation exposure should either be avoided or controlled to keep it at a minimum. The regulation of radiation exposure at work place is extremely important to control the radiation burden. There are international and national agencies that regulate the radiation installation. International commission of radiological protection (ICRP) passes international advisory from time to time and proposes the exposure dose limit for radiation professionals, general public and environment to protect them from ionizing radiation.[7] Each country has its own regulatory body to formulate radiation safety guidelines and implement it nationally. AERB is the regulatory body in India. AERB has passed the radiation safety guidelines and proposed the dose limit for radiation worker, general public and the environment.[5] ALARA is a novel concept adopted by regulatory agencies to avoid unnecessary radiation exposure to the professional, general public and the environment.[567] To achieve ALARA the Nuclear Medicine Department should be properly designed and approved by the competent authority, radioactive sources should by properly shielded and all the equipment in the department should be calibrated by certified agencies.[89] Guidelines prescribe the approval of Nuclear Medicine Departments by the regulatory agency for proper layouts, shielding and calibration of equipment and radiation safety instruments. The annual whole body radiation dose limit prescribed by ICRP and AERB is 20 mSv/year.[567] for radiation workers. Researchers have performed many studies in the past and numerous data are available in the literature regarding radiation exposure in diagnostic nuclear medicine and PET/CT imaging. Several studies have shown an increase in radiation exposure among professionals in a Nuclear Medicine Department since the introduction of PET scanning.[31011121314] Robinson, et al.[10] in 2003 found the total radiation dose received by technologists was 31 μSv/by using 1280 MBq F-18 daily. Chiesa et al.[11] calculated the radiation dose received by the technologist during various studies. They found that technologists received 1.17 μSv/myocardial perfusion study which was maximum in conventional nuclear medicine but technologists received 5.7 μSv/PET procedure which is around 5 times that of radiation received in conventional nuclear medicine. Peet et al.[13] have also found 4.8 μSv/PET procedure radiation exposure to the staff. Pant and Senthamizhchelvan[15] estimated the radiation exposure received by a radiation worker working in PET/CT facility. They found that nuclear medicine physicians were getting a dose of 3.24 μSv/procedure and 8.76 nSv/MBq which was comparitively more than the corresponding figures for technologists which were 0.62 μSv/procedure and 1.66 nSv/MBq. Jha et al.[16] estimated radiation dose received by radiation worker in the process of flurodeoxyglucose injection alone and demonstrated that the person who is injecting the dose received 1.3 times more whole body radiation exposure than the person dispensing. In this study they calculated the per procedure and per MBq radiation dose received by various professionals involved in the injection process as 2.2 uSv for nuclear physician, 1.8 uSv for nurses and 1.3 uSv for technologist. Our study is a retrospective audit of radiation safety data available in our department. The staff were posted on rotation in PET and SPECT so the segregation of received dose because of PET and SPECT studies was not possible. We found in our study that the radiation dose received by nuclear medicine physician, technologist and staff nurse were 3.76 μSv, 4.67 μSv and 4.29 μSv respectively for every 1.68 PET scan and one nuclear medicine scan. Our data shows that the radiation exposure to individual staff in our department was significantly lesser than any of the above-mentioned studies[101112131415] and we feel that this could be due to the sharing of radioactive work among nurses, nuclear physicians and technologists. So the professional radiation exposure is reasonably low and quite satisfactory considering the high volume workload in our department. Our results also show that the nurses are getting more annual whole body radiation exposure than nuclear medicine physicians and technologists. However, since the nurses cumulatively work for a maximum period of 6 months in the Nuclear Medicine Department, the individual whole body radiation exposure is half of the shown annual dose, which is less than that received by technologists and physicians.

CONCLUSION

Efficient management and deployment of personnel is of utmost importance to optimize radiation exposure in a high volume nuclear medicine setup in order to work without anxiety of high radiation exposure.