|Year : 2007 | Volume
| Issue : 4 | Page : 122
Radiation Safety in Nuclear Imaging and Radionuclide Therapy
Radiological Physics & Advisory Division, Bhabha Atomic Research Centre, CT&CRS Building, Anushaktinagar, Mumbai - 400094, India
Bhabha Atomic Research Centre, CT&CRS Building, Anushaktinagar, Mumbai-400 094
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Tandon P. Radiation Safety in Nuclear Imaging and Radionuclide Therapy. Indian J Nucl Med 2007;22:122
| Introduction|| |
In Nuclear Medicine, the major advances in the past decade have taken place due to the development of new radiopharmaceuticals both in diagnostic and therapy fields. The therapy is no longer confined to radioiodine 131 I for the treatment of thyrotoxicosis and cancer of thyroid. Also, large quantities of radioactivity for even carrying out diagnostic procedures using 99m Tc compounds are in use for e.g. in perfusion imaging. Thus, practices in nuclear medicine department have to be carefully planned and properly performed. While handling any unsealed radionuclides, it is essential to always be conversant of all radiation health safety practices. As the major concern while handling unsealed sources is the risk of irradiation and contamination to medical and paramedical staff, laboratory personnel, patients and also the general public. In this article, apart from the radiation safety, the salient features of newly developed products such as 99m Tc, cyclotron products, radionuclide therapy, products for radiosynovectomy, products for radioimmunotherapy (RIT) and radiopeptidetherapy (RPT), product for loco regional delivery for radionuclidetherapy (RNT) and the products for endovascular radionuclide therapy (EVRT) etc have been given in brief.
| 1 99mTc-Products|| |
The recent generation of 99m Tc products comprises compounds for:
- imaging blood flow to myocardium and brain
- imaging lesion such as infection/inflammation
- tumour and thrombus formation.
Due to the favourable characteristics of 99m Tc from radiation dosimetry angle and to enhance the quality of imagse/information from a study, individual patient dose ranging 555 MBq to 1.11 GBq are frequently used. It is a common practice at user end, for reasons of economy, to use maximum amounts of 99m Tc activity per kit vial, typically ranging 3.7 to 11.1 GBq. Although, the half life is only 6 hr, the total amount of activity thus handled per lot, that too mostly everyday, is very high. Appropriate care and radiation safety procedures should be ensured at all stages of formulation, handling, injection and imaging. Actual retention of activity in the organ of interest could be just a fraction of injected dose, with much of the injected activity is being excreted through urine over a few hours. Thus, it is not only the concern for exposure to occupational workers and surrounding personnel, but also possess potential contamination problems.
| 2 PET Products|| |
a) PET Products in Neurology
18 FDG was originally proposed for estimating regional cerebral blood flow and shown as a good activity during variety of mental functions, since glucose is the source of energy for brain. Similarly, 15 O and 11 C labeled receptor radiopharmaceuticals are used for investigation in patients for neurological disorder.
b) FDG in Cardiology
This isotope is a good tool for myocardial viability studies.
c) FDG in Oncology
The role FDG in tumor metabolism, as a better grading/staging indicator of tumor prognosis.
The Medical Cyclotron facility coupled with the radiochemistry laboratory handling large amounts of radioactivity during synthesis presents radioactive contamination problems. In addition to the prompt gamma, the primary and secondary neutrons generated during the production give rise to induced radioactivity in the cyclotron components and vault room walls and this problem is much more serious to handle.
| 3 Radionuclide Therapy (RNT)|| |
Radionuclides offer a means for selective irradiation of unwanted cells, e.g. cancer cells. The ability to target the abnormal tissues with maximum doses of radiation and at the same time sparing the normal cells is however, a daunting task. In other words attaining the degree of specificity required would dictate the practicability of RNT. The choice of therapeutics radionuclide depends on the basis of the half-life, the type and energy of the particulate emissions. There is a choice depending on the volume to be irradiated, alpha emitters, auger/conversion electron emitters, hard beta emitters and soft beta emitters. Apart from these factors, ease of production logistics would also be an important criterion for wide spread utility. From Indian context, apart from the well known 131 I and P 32 , other therapeutic radionuclides of high relevance and practicability are 153 Sm, 166 Ho, 90 Y, 186 Re and 186+188 Re.
3 (a) 131 I-MIBG
This is used for the treatment of patients suffering from pheocromocytoma, neuroblastoma and medullary carcinoma of thyroid. For therapeutic formulations, radioactive concentration is usually in the range of 185-555 MBq/ml and specific activity > 1.11 GBq/gm of MIBG. It is quite common in patients suffering from primary malignancies of especially breast, prostate and lung, to develop secondaries and bone is the frequent target focal site. The prominent symptom caused by bone metastasis is intractable pain, which can seriously affect patients' quality of life. In such cases bone seeking radiopharmaceuticals play a significant role in the treatment. The radionuclide of choice in such case are 32 P, 90 Sr, 153 Sm, 117m Sn and 186 Re. Owing to the renal route of excretion, patient preparation and precautions for safe discharge of radioactivity need to be taken as with the radiopharmaceutical.
3 (b) Products for Radiation Synovectomy
The chronic disease of crippling pain in bone joints due to inflammation in synovial joints, like rheumatoid arthritis has been well tackled with locally instilled particulate formulation containing a beta emitter radionuclide. The procedure called (radio) synoviorthesis or radiation synovectomy offers an alternative to surgery. This has triggered the need for therapeutic radionuclides ranging from soft to hard beta energy, typically 0.3 MeV of 169 Er for small joints like finger joints to 2.27 MeV of 90 Y for large joints.
3 (c) Product of Radioimmunotherapy (RIT) and Radiopeptidetherapy (RPT)
Radioimmunotherapy (RIT) using radiolabelled monoclonal antibodies to tumour associated antigen (TAAg) and Radiopeptidetherapy (RPT) using radiolabelled peptides specific for receptors on lesions targeted are the other major recent developments. The first product which got approval was 131 I labelled B1 anti C20 monoclonal antibody for lymphoma.
3 (d) Products for Loco-Regional Delivery for RNT
For the Pankaj Tandon et al sake of completion of discussions, a mention of products for treatment of hepatic cancers, by intra hepatic arterial injection of special formulations, such as 131 I - Lipiodol could be made. The product is delivered to the tumour taking advantage of higher blood flow to hepatic tumour from the hepatic artery. Recently, 188/186 Re-Sulphide-Lipiodol and 166 Ho-Chitosan have been reported for similar therapy.
3 (e) Products for Endovascular Radionuclide Therapy (EVRT)
An important emerging area in interventional cardiology is the endovascular radiation treatment of arterial walls following balloon angioplasty (PTCA) to minimise the incidence of re-stenosis by prevention of neo-intimal proliferation. Stent based techniques ( 32 P coated stent) and catheter based techniques ( 192 Ir source, 32 P/ 89 Sr coated source attached to the catheter) are being explored. An attractive alternative to the above approaches is offered by the use of liquid formulations (preferably renal excretory compounds) of suitable radiotherapeutic radionuclide such as 188 Re (T = 16.9 hrs, Eβ = 2.12 MeV) filled in low pressure balloons for insertion post balloon angioplasty for a pre-calculated time, of the order of minutes. Other radionuclides of choice are 166 Ho and 90 Y. Appropriate gadgets and techniques need to be evolved for filing and using angioplasty balloons for EVRT practices in safe manner.
| 4 Other Products and Techniques|| |
188 Re-DMSA is currently being investigated for possible treatment of medullary carcinoma of thyroid. Radioisotope Guided Surgery (RIGS) a new, promising, radiotracer approach for surgical oncology. It aids in minimal, essential excision of tissues of lesion alone in patients of some types of cancer. This technique is based on the highly specific localisation of tumour avid tracer in the lesion requiring to be resected. For example 99m Tc-sestamibi or 99m Tc-tetrofosmin, one can precisely locate lesions in the case of breast cancer. During surgery, a finely collimated hand-held radiation detector probe can be used to identify the exact region of radioactivity, in turn, of tumour lesion. As the non-lesion tissues will not accumulate the tracer, it would be possible for the surgeon to minimally remove the culprit tissues and spare most of the other surrounding normal tissues. Although, this technique is still in evolving stage and not yet often practiced.
Radionuclide 131 I Administration
In an approved nuclear medicine department, a qualified Nuclear Medicine Physician, Nuclear Medicine Technologist and a Radiation Safety Officer (RSO) are the prerequisites for any radionuclide therapy unit. As we all are well aware that of all the therapeutic procedures dealing with the use of radionuclides, 131 I is the most widely used unsealed source of radionuclide for treatment of thyroid cancer and hyperthyroidism and carries with it most of the problems associated with therapy applications. Radioiodine solutions being highly volatile, requires special handling. While handling large therapeutic quantities of 131 I, in addition to the external radiation hazard, the risk of internal contamination is also magnified and thus stringent precautions should be taken to avoid this internal hazard as 37 KBq (1 Ci) of 131 I results in a radiation dose of about 1.3 cGy (1.3 rad) to the thyroid, based on a 30% thyroid uptake and thyroid mass of 20 gms. Nuclear Medicine Physician and other radiation worker involved in administration of the activity should wear disposable rubber gloves and protective clothing. Because of the hazards associated with liquid form of 131 I as described, the vial containing 131 I should be handled inside a well-ventilated fume-hood. Prior to administration, the patient requiring therapy should be properly identified and the therapeutic activity should be ascertained by measuring in a calibrated isotope calibrator. The three cardinal/radiation protection principles of time, distance and shielding should be effectively implemented to keep the personnel exposure as low as reasonably achievable. The vial containing the 131 I solution should be placed in a lead pig, decapped inside the fume hood and diluted with water so that in case the patient accidentally coughs or spills 131 I while drinking, the droplets will not be too concentrated. The patient should be instructed about the precautions to be taken while drinking the radioactivity. The patient should never be allowed to handle the vial containing 131 I. After patient has taken the 131 I, water should once again be added to the vial to ensure that all the 131 I is administered. This to certain extent decontaminates the vial and straw. Following this, the patient should also be given water in a disposable paper cup to wash down the oral activity into the stomach. To restrict spread of contamination, one should place absorbent papers on the edge of the fume hood and on the floor with a PVC sheet beneath, prior to starting of the treatment procedure. During treatment of neural crest tumors with 131 I-MIBG, the patency of the I.V line should be ascertained prior to injecting the radio-pharmaceutical into the dextrose saline bag. If the treatment has to be given inside the patients isolation room, as done in case of non-ambulatory patients, care must be taken in transporting the radionuclide to the room to prevent spillage and exposure to the personnel involved. After completion of treatment procedure, all personnel involved should be monitored for contamination. The Radiation Safety Officer (RSO) should maintain a record of exposure-rate readings over the stomach and/or at 1m from the patient, after treatment.
Radiation Safety Precaution during Pre and Post-therapy
In high dose therapy i.e. Cancer of thyroid treatment, 131 I is administered orally to the patient. In order to enhance absorption of 131 I from the stomach, the patient should be on an empty stomach at least 1 to 2 hours before and after therapy. This not only minimizes the radiation dose to the stomach but also reduces the volume of the vomitus if the patient develops nausea during or after the administration. The patient should be asked to remove any denture appliances such as removable bridges and dentures before drinking the 131 I solution. Otherwise, any 131 I that may adhere to these denture appliances, on removal by the patient, can result in transfer of contamination to surfaces and personnel's.
The radiation safety procedures to be followed in case the patients in a non-ambulatory or bed-ridden are much more stringent and elaborate. The patient is catheterized at least 24-48 hours prior to therapy so that any complication resulting due to the catheter will be observed during this period and also allowing time for the patient to get adjusted to the catheter. If the catheter is introduced just before therapy, then any complications due to it following therapy will result in significant radiation exposure to the physician and nursing staff attending to the patient inside the isolation room. In addition, the patient is put on a liquid diet two days before therapy to reduce the bowel activities during the period of isolation, which otherwise can be a source of contamination and exposure. If female patients of thyroid carcinoma in the reproductive age group are undergoing therapy, the details of menstrual history should be obtained to rule out pregnancy. Pregnancy is a contraindication for radioiodine therapy. Patients of thyroid carcinoma and neural crest tumor are generally hospitalized in an approved isolation room/ward after therapy till the activity level reduces to the limit prescribed by the competent authority. There are two main reasons for isolating the patient. Firstly, the patient is a source of significant radiation exposure to the occupational staff, family members and visitors. Secondly, there is a major risk of contamination from urine, saliva and perspiration especially in the first 24-48 hours. Also, there are added complications like patient feeling nauseated and vomiting, which are best dealt with under supervision, during the period of isolation. If a patient is receiving radioiodine therapy for the first time, the term "isolation" should be carefully explained to the patient and their accompanying relatives. The patient should be reassured that both nuclear medicine physician and nursing staff will be communicating as and when required. The patient may not have a feeling that during the isolation period h/she has been considered as neglected because their family members, relatives and friends have also been restricted to meet him/her. Ideally, the patient should be informed about what is expected of him/her during the isolation period. Patient co-operation is very much essential if radioactive contamination and external radiation exposure to the medical, paramedical, nursing staff and visitors are to be minimized.
Radiation Protection for the Nursing Staff
Staff indulged in nursing care of the patient should be familiar with all radiation safety procedures which are involved during treatment procedures. They should be provided with personnel monitoring badges. Pregnant nurses should not be allowed to work in a therapy ward. Nursing care to the patient should always be given across a shoe barrier such as medication, food etc. so as to spend minimum time in direct contact with the patient. During the period of isolation, in the first 48 hours after therapy the sampling of blood and urine for pathological examination should be strictly avoided, to prevent contamination of the laboratory. In case it is required, it has to be done/taken in consultation with RSO only. In case of any medical and/or radiation related emergency, the nursing staff should have list of names and addresses with telephone numbers of the Nuclear Medicine Physician and RSO, so as to contact them immediately, if required.
Radiation Protection for the Visitors
The visitors must follow instructions of the nursing staff as per the RSO or Nuclear Medicine Physician i.e. the duration of visit and restrictions on distance from the patient. It should also be communicated to the visitor about not entering the isolation room and abstain from physical contact with the patient. Children and pregnant women should be prohibited to visit the patient.
Patient Monitoring and Discharge Criteria of Patient from Isolation Ward
In general, the measurement of exposure-rate over the surface of the neck, metastatic site, stomach, thigh and at 1 meter distance from the patient should be carried out using an ionization chamber type of radiation survey meter to enable one to know whether there is a desired concentration of 131 I in tissues or not. The record of these measurement details only will determine the date and conditions of discharge.
The limit at which the patient can be discharged varies from country to country. As per the International Atomic Energy Agency (IAEA) Basic Safety Standards (BSS), an activity of 1.1 GBq (30 mCi) of 131 I is specified as the discharge limit. In India, the patient is discharged only when the whole body 131 I activity is less than or equal to 555 MBq (15 mCi), a limit stipulated by Atomic Energy Regulatory Board (AERB). For an adult patient, 1.1 GBq (30 mCi) of 131 I retained in the body corresponds to an exposure-rate of about 50-60 Sv/h (5-6 mR/h) at a distance of one metre. The patient is discharged with some basic instructions/guidelines on keeping safe distances from pregnant women and small children at home. The objective of retaining the patient in the hospital is to minimize the radiation risk to the general public and family members/relatives.
Optimisation of Radiation Dose to Non-Target Tissues
To minimize the radiation dose delivered to the stomach following oral administration of a therapeutic dosage of radioiodine, it is important that such administration is carried out with the patient on an empty stomach. As indicated earlier, it not only enhances absorption of 131 I, but also considerably reduces the dose to the stomach. Salivary gland concentrates radioiodine and sialedinitis is one of the acute complications resulting from therapy. Patients' during the first two days of therapy should be asked to chew a lemon or any agent that increases salivation. Excessive salivation results in accelerated clearance of 131 I from salivary tissue, thus minimizing the radiation dose to the tissue. Radioiodine is primarily excreted through urine and therefore the kidneys, bladder and gonads are likely to get a considerable radiation dose. The patient should be asked to drink plenty of fluids and void as frequently as possible. Frequent hydration and voiding will definitely minimize the radiation dose delivered to the kidneys, bladder and more importantly the gonads. Lactating breast concentrates 131 I and therefore nursing mothers should strictly avoid breast-feeding the child for a time period (at least 4 weeks) suggested by the Nuclear Medicine Physician. During the first 2 days after therapy, the mother should be encouraged to suck out the milk using a breast pump. It is the responsibility of the physician to advocate measures to be taken by such patients so that the exposure to the breast tissue is kept as low as reasonably achievable.
Handling Emergency Situations
In general, any emergency/accidents situation arises in the nuclear medicine department has to be handled in a very careful manner and for handling such situations, an emergency preparedness program should be available in the institute. The emergencies that one may foresee during 131 I treatment of thyroid carcinoma are spillage, misadministration and death of the patient.
Death of a patient after treatment is also a radiation emergency. However, meticulous pre-planning for this eventuality is important. The regulations governing the disposal of cadavers containing radioactivity varies from country to country. In our country, guidelines provided by AERB on safe disposal of cadavers are applicable. No special precautions are normally necessary for cremation, burial or post-mortem/embalming, if the corpse contains 131 I activity less than limit prescribed by the Competent Authority and given in Table 1 However, if the dead body contains activity higher than this, then depending upon whether cremation, burial, autopsy or an embalming procedure is to be carried out, the precautions and restrictions undertaken will vary. During cremation, prior authorisation and specific safety precautions to be followed, must be obtained from RSO. In case of burial, relatives should be prevented from coming in contact with the cadaver and people must be at a distance from the coffin. The designated RSO shall recommend methods on dose reduction to the personnel involved in washing, preparing and transporting the body to the burial ground. The cadaver should be handled with disposable gloves and kept on plastic sheets to control spread of contamination. If an autopsy is being performed, the RSO should supervise the proceedings. It is important that the autopsy physician know that he is dealing with a cadaver containing radioactivity and therefore body fluids should be treated as contaminated and perhaps 131 I concentrating tissues be removed during the autopsy to avoid unnecessary radiation exposure. During post-mortem or embalming all contamination control measures should be adopted under the guidance and supervision of the RSO.
In general, the Nuclear Medicine department should have the decontamination kit to deal with the contamination resulting from spillages. All efforts should be made to restrict spread of contamination. Misadministration is considered to have occurred if any of the following has taken place which may also lead to an emergency situation; resulting from spillages. All efforts should be made to restrict spread of contamination. Misadministration is considered to have occurred if any of the following has taken place which may also lead to an emergency situation; identity of the radionuclide, the patient, the route of administration and performance of the isotope calibrator.
| Conclusion|| |
It can be seen that the future of nuclear medicine will be dominated mostly by the therapeutic products and Cyclotron produced radionuclides only. Consequently, there is a need for greater awareness of radiation safety design, practices and monitoring in nuclear medicine departments. In the interest of bringing benefits to needy patients, all the safety related measures would warrant utmost attention for implementation and sustenance. By making and implementing the proper radiation safety program the radiation exposure to the patient, nuclear medicine physician, nurses, staff and public can be kept as low as reasonably achievable.[Table 1]
| References|| |
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