Although radioiodine therapy has been extensively used in the treatment of differentiated thyroid cancer (DTC) for more than 60 years, doubts still persist as to its being a safe procedure with outpatients when applying I-131 activities greater than 1.1 GBq (30 mCi). Under these circumstances, patient internment is very rarely indicated on a purely medical basis, and then only so when considering radiologic protection. Apart from being a measure for protecting household members and the environment from presumed radioactive exposure or contamination, this usually implies an increase in the costs of therapy, with little or no consideration for the patient's interests or needs. Moreover, the availability of dedicated hospital units for this kind of therapy has not been critically evaluated by public health-care systems. Thus, hospital confinement of patients based exclusively on administered activity or initial radiation rates, and without due analysis of the social and human factors involved, is a reported mandatory attitude,1 open to extensive discussion and in need of reexamination.2–5
Moreover, scientific data lending support to a more flexible therapeutic approach are more often based either on theoretical assumptions or clinical studies with scarce casuistic and scant demonstration of the radiologic impact from outpatient radioiodine therapy, thereby giving rise to questions on involved radiologic security.
On considering the aforementioned points, this work tends to buttress a previous study6 of measuring the radiologic exposure of family members and the environment during outpatient radioiodine therapy for DTC, when applying activities of less than 7.4 GBq (200 mCi). The scientific evidence presented herein allows for a more thorough discussion and clearer judgment on whether the confinement of radioactive patients constitutes an essential safety measure for radioiodine therapy in the 21st century, while simultaneously furnishing elements for improving the quality of patient medical assistance.
A total of 100 patients, 89 women and 11 men, were treated with ablative radioiodine therapy for DTC at the School of Medicine of the University of São Paulo. The patients' average age (±standard deviation [SD]) was 49 (±13) years, ranging from 19 to 70 years. All I-131 activities, from 3.9 GBq (106 mCi) to 7.8 GBq (211 mCi), were administered according to the patient's therapeutic requirements (Fig. 1).
Treatment was undertaken on an outpatient basis, considering as much the acceptable living conditions and interest of the patient, as well as their willingness to comply with medical and radiation safety guidelines. Signed formal consent was obtained from all the patients and their caregivers. The experimental design of the study was previously approved by the local institutional ethics committee (Protocol number: 0164/07), as well as by the National Nuclear Energy Commission (document number: 1386/08-CGMI/CNEN).
Inclusion criteria also included a negative β-human chorionic gonadotropin measurement, patient aged between 18 and 70 years, male or female, anatomopathologic confirmation of DTC, previous total or near-total thyroidectomy with an interval of at least 1 month, medical indication of radioiodine therapy based on whole-body scan with radioiodine, thyroglobulin dosage, and the absence of additional pathology, such as renal dysfunction, capable of compromising outpatient therapy, and finally the informed consent form signed by the patient. The acceptable living condition for performing outpatient therapy included the absence of either children or pregnant women within the patient's household during therapeutic proceedings, the existence of an adequate sewage and water supply system in the patient's residence itself, the possibility of sleeping alone in a separate room for a minimum period of 3 days, the patient's ability to take care of herself or himself, and to understand and follow the written instructions. The actual interviewing was undertaken by a nuclear medicine physician and a radiation safety officer, to determine whether the patient could be released for outpatient treatment.
Doses of an antiacid production drug were administered to patients for at least 3 days, an antiemetic drug also being indicated when the occasion arose following therapy, to control excessive secretion of gastric acid, nausea, and vomiting. The patients were released for breakfast 2 hours after activity administration (orally by means of capsules). All administrations, undertaken at the Nuclear Medicine Department, were supervised by a nuclear medicine physician and a radiation safety officer. Subsequently, the patients were released to return home by private means (taxi or private vehicle). A list, in simple and easily comprehensible wording, of radiation safety measures and medical instructions was given to all. This list also included a description of the appropriate response to diverse circumstances, such as nausea, vomiting, etc, as well as indications of salutary hygiene habits and contacts in an emergency. The patients were instructed to avoid unnecessary, prolonged, and close contact with anybody else during the first 5 days after radioiodine administration. With an aim to reduce radiation exposure involving the general public, the patients were requested to avoid leaving home for at least 3 days after activity administration, except under an emergency. One copy of these written instructions was kept in the patient's file. These instructions were amply discussed with the patient and family members at the Nuclear Medicine Department, before radioiodine administration. Any therapeutic side effects in the patients over the 5 days after activity administration were analyzed through a form given to all the patients, to be filled in daily recording any clinical symptoms.
Adult caregivers involved in aiding patients during therapy were identified (n = 90) and supplied with a chest thermoluminescent dosimeter (TLD) to measure the dose of whole-body radiation received over the 5 days while being exposed to the patient after radioiodine administration. The process of measuring doses started immediately after activity administration at the Nuclear Medicine Department. Radiation potential within the respective living quarters (patient's bedroom, caregiver's bedroom, bathroom, kitchen, and living room) was measured by using the same measurement methodology as described above. The schematic design used in this study is identical to that used in a previous study by our group.6
The CaSO4:Dy TLD was used in this study for measuring both doses of whole-body radiation and the potential radiation dose within patients' homes. This type of dosimeter renders a satisfactory linear response for measuring radiation doses ranging from 10 μGy to 10 Gy, besides presenting a uniform energy response. A dose of 0.1 mSv was assumed to be a minimum recordable dose by the laboratory of dosimetry (PRORAD, Radiation Protection Advisors Ltd, Porto Alegre, Rio Grande do Sul, Brazil). For the potential exposure, radiation doses received by caregivers and all those measured throughout the residential living quarters were treated as effective dose. This consideration is acceptable for radiation protection purposes.
Patients' exposure rates were measured anteriorly at 1 meter away, precisely at the moment of activity administration and on the third day of therapy. These measurements facilitated our estimating the decrease in the field of radiation near the patients, and, according to the rates, in formulating recommendations on more flexible radiation protection measures.
As radioiodine excretion occurs by various means, viz, perspiration, saliva, breath, feces, and urine, the contamination of surrounding surfaces and objects inside the home is highly possible. Prior analysis permitted identification of those areas and objects (eg, floors, door knobs, chairs, fruit plates, couches, faucets, etc) extremely prone to contamination. These were surveyed by using a Geiger-Müller pancake probe. Detector signals in counts per minute (CPM) were converted to Bq/cm2 by means of a representative function (kCPM = 0.247 × (Bq/cm2) − 0.227) obtained by I-131 standard sources and detector response.
All solid waste generated by the patients during therapy was identified and checked with a Geiger-Müller detector, so as to avoid the release of contaminated waste into the environment or urban waste system. In this case, the detector signal in CPM was converted into “activity dispersed into a volume” by using a representative function (CPM = 287 × (μCi/L) − 123) obtained by measuring I-131 standard sources dispersed into a known volume of water coupled with detector response. The maximum activity level of I-131 for release was based on the local regulatory agency document (National Nuclear Energy Commission),7 as well as International Atomic Energy Agency (IAEA) recommendations.8 To reduce, as far as possible, the storage of contaminated solid waste, patients were requested to use appropriate toilet paper and subsequently flush all through the sanitary sewer, as well as diminish to the minimum the generation of waste during therapy.
On considering our previous experience,6 home visits, only by radiation safety officers, took place on the first and third day after activity administration, the patient being contacted by phone on the second day by the nuclear medicine physician, and thereafter only whenever necessary. During the first home visit, TLDs were placed at representative points in each room inside the patient's residence, any necessary clinical care also being extended at the time. Clinical conditions of the patients were checked at the second home visit, and confirmed by a nuclear medicine physician by phone, to thus ensure adequate compliance with research project requirements, as the patients were already under the researchers' full responsibility. Patient radiation emission, surface contamination inside the residence itself, and contaminated waste were monitored with a radiation detector on this second visit.
A Geiger-Müller Model 190 detector (SN 2316; Victoreen Co., Elimpex-Medizintechnik, Moedling, Austria) with either a β-γ probe (Model 491–40, SN 3806, Victoreen Co.), or a pancake probe (Model 489–110D, SN 1392, Victoreen Co.), were used to measure exposure rates and surface contamination, respectively. The detector was calibrated by the Institute of Energy and Nuclear Research and National Nuclear Energy Commission, Department of Radiation Metrology.
Of the 100 patients studied, only 10 (10%) failed to return the clinical evaluation forms while undergoing radioiodine therapy. The incidence of nausea and vomiting, as well as antiemetic drug administration, are shown in Table 1. Nausea occurred mainly during the first 3 days after activity administration, with only 2 patients (2%) presenting periods of vomiting, adequately controlled by drug.
All patient exposure rates, measured at the time of radioiodine administration and on the third day after therapy, are given in Figure 2. The initial exposure rate of 1 patient was not measured, as the Geiger-Müller detector was not available at the moment of therapy administration, the same occurring with another patient during the second home visit by the radiation safety officer.
Assuming that, apart from the patients themselves, all those who were critically exposed to radioactive patients had adequately followed radioprotection guidelines, radiation doses measured with TLDs should represent factual individual exposure. Eighty-seven individuals received doses of less than 1.0 mSv, the maximum registered whole-body dose in all the 90 monitored cases reaching 1.6 mSv. Total radiation-dose incidence, as registered in this study, appears in Figure 3.
The free access of patients everywhere within their homes can lead to the widespread existence of potential points of radiation contamination, potentially harmful to anyone else inside. TLDs were strategically placed in each room and the measured doses plotted (Fig. 4). The mean values for the radiation doses measured in all the 414 monitored living areas were as follows: patient's bedroom, 0.70 (±0.42) mSv; living room, 0.22 (±0.21) mSv; bathroom, 0.21 (±0.17) mSv; kitchen, 0.15 (±0.12) mSv; and caregiver's bedroom, 0.11 (±0.12) mSv. The maximum registered dose, 3.0 mSv observed in a single living room, was not computed for mean dose calculation, when considering the great difference between this and others registered in the same type of living space. This dose was most probably registered through TLD overexposure in unusual circumstances.
Surface contamination measured on the third day post activity administration ranged from undetectable values (background radiation) to 899.30 Bq/cm2, thus distributed: bathroom, 11.43 (±32.70) Bq/cm2; patient's bedroom, 5.49 (±41.72) Bq/cm2; kitchen, 2.06 (±3.09) Bq/cm2; and living room, 1.74 (±3.52) Bq/cm2; with an overall average of 5.58 (±28.19) Bq/cm2 for all the 1659 measured surfaces. SD was high as a result of the wide dispersion of data. All contamination levels encountered throughout the entire residence appear in Figure 5. It can be noted that patients' bedrooms and bathrooms registered the highest levels of surface contamination. The worst points were a pillowcase, and several bathroom faucets. With the exception of toilet rims, all contaminated areas were less than 100 cm2.
A total of 176 wastebaskets were monitored with Geiger-Müller detectors, to evaluate the amount of radioiodine activity discharged into the environment by contaminated solid wastes. On an average, each patient produced no more than 1.0 liters of contaminated solid waste over the first 3 days post activity administration, with a mean radioiodine concentration estimated at 363.91 kBq (9.84 μCi) per liter. This is approximately 3 times less than the exemption level indicated by the IAEA and the local regulatory agency, ie, 1.0 MBq (27.03 μCi).7,8 Furthermore, when considering the worst scenario (point-source) and air kerma-rate constant for I-131 (5.95 × 10−5 mSv/(MBq.h) at 1 meter),9 the doses estimated for a source of 363.91 kBq at 1.0 meters and 0.25 meters were 0.022 μSv/h and 0.35 μSv/h, respectively.
This study, besides providing a large amount of experimental dosimetric data from outpatient radioiodine therapy for DTC, when applying radioiodine activities up to 7.4 GBq (200 mCi), also reinforced a previous work6 undertaken by our group with 20 treated patients and a reduced data base, aimed at estimating the radiologic impact on both the environment and the most exposed persons during ambulatory procedures.
As the patient's own family members and close friends lent support either during therapy or by living in the same residence, they were the most exposed persons to radiation, mainly through external exposure, with only a slight contribution from internal exposure through the ingestion or inhalation of contaminated substances with radioiodine. With the aim of reducing these doses of radiation, certain radioprotective precautions should be adhered to by all those involved, with more or less flexibility according to the degree of exposure in each individual case.
In the present study, a total of 90 of the most exposed individuals were monitored by using a chest-TLD each, this beginning immediately following activity administration at the Nuclear Medicine Department, and continuing over 5 days. All the monitored individuals were requested to use TLDs throughout the time spent inside the patients' residences, ceasing to do so only when sleeping and taking a bath. The mean value (±SD) for all the registered whole-body doses was 0.27 (±0.28) mSv (Fig. 3), with 87 monitored individuals having received an accumulated whole-body dose of less than 1.0 mSv, the maximum registered reaching 1.6 mSv throughout the period of measurement. Despite the dispersion of doses, all registered whole-body doses were, on an average, extremely small when compared with the radiation level considered acceptable in a similar situation (medical exposure, 5.0 mSv per procedure).10–14 Similar results were reported in other studies on hyperthyroidism or thyroid cancer outpatient treatment, with all reported mean values attaining less than 1.0 mSv.15–19 Although caregiver thyroid glands were not surveyed with a radiation detector in this study, radiation exposure from contamination or radioiodine intake seems to have been much lower than external exposure. This was also shown by other researchers,19,20–22 and thoroughly discussed in a previous study by our group.6
Although the actual measurement extended over 5 days after radioiodine administration, this time-span was enough to ensure compliance with 95% of the total dose from patients. In a previous published study, it was shown that by the end of this period almost all radioiodine activity administered to patients had already been excreted.23
Caregivers could be a limiting factor to accuracy in whole-body radiation measurement, because on failing to use the TLD as instructed, registered doses could be either under- or overestimated. However, due to the similarity in results, it is believed that radiation safety instructions were followed as closely as possible by all concerned.
The potentiality of radiation doses measured inside all the 414 living areas of patients' residences (patient's bedroom, caregiver's bedroom, bathroom, kitchen, and living room) appears in Figure 4. The mean doses registered for all the monitored areas were 0.31 (±0.34) mSv. There was a similarity with the results reported by Grigsby et al,18 although in this case, measurement lasted for 10 days after radioiodine therapy in a group of 30 treated patients, when using identical methodology.
The mean value for all the 1659 measured surfaces was 5.58 Bq/cm2, with patients' bedrooms and bathrooms presenting the highest levels of contamination (Fig. 5). This is probably due to patients spending more time in the former on the first and second days after radioiodine administration, whereas due to taking care of personal hygiene in the latter. In spite of this, wipe-tests and decontamination procedures revealed that most surface contamination was removable by using simple cleaning methods.
Despite the necessity of continuing decontamination procedures, such as washing bathrooms, it was possible to release all contaminated areas and objects from control, based on their attaining acceptable levels, as stipulated by IAEA and International Commission on Radiological Protection, this involving potentiality of radiation doses in the worst scenario (eg, ingestion of contaminated objects), 10 μSv/annum of radioactive sources with exemption from control, 300 μSv/annum of released radioactive sources for non restrictive use, and 1.0 mSv/annum of released radioactive sources for restrictive use.8,24–26 Even considering the worst hypothetical scenario (ingestion of contaminated objects of 100 cm2, with a mean radioiodine activity of 5.58 Bq/cm2), and using a conversion factor from activity to radiation dose (μSv/Bq),27 the estimated radiation dose was only around 0.23 mSv. It was noteworthy that 99.58% of all the encountered contaminated areas were released for nonrestrictive use, on considering a maximum potentiality of 300 μSv received from the hypothetical ingestion of contaminated objects, and all activity having been converted to internal doses.
Radioactive waste from patients' residences after diagnosis or therapeutic procedures with radiopharmaceuticals is relatively common, the level of contamination varying from patient to patient, according to how far radioprotection instructions have been abided by. A larger amount is more likely in outpatient than inpatient treatment, as most activity is excreted by patients during the first 3 days post therapy. It is imperative to identify the level of this contamination, and define the risk involved to the general public and the environment as a whole.
Throughout these proceedings, all the patients produced contaminated solid wastes with radioiodine, and the estimated volume produced by each reached less than 1.0 liter in the first 3 days after activity administration. Furthermore, the mean radioiodine concentration was estimated at 363.91 kBq (9.84 μCi) per liter, in other words, about 3 times less than the exemption level indicated by the IAEA and the local regulatory agency, of 1.0 MBq (27.03 μCi).7,8 In general, radioactive waste from patients' bathrooms and kitchens was produced through the impossibility of their complying with all radioprotection instructions, or through occasional neglect, such as not disposing of toilet paper through sanitary sewers. Despite the waste ingestion hypothesis, obviously totally conservative, the dose rate from this amount of activity, 0.022 μSv/h at 1.0 meter from the source, is 12 times less than that from background radiation (0.27 μSv/h; 2.4 mSv/annum; 8.760 hours/annum).28 In addition, the dispersion of this waste by mixing with normal urban waste, and the length of time required for any contamination or exposure, reduces any presumed impact on the human environment. Thus, as shown by other studies and from the data presented here, it would seem there is no radiologic impact from releasing this radioactive waste for urban waste-management.29–34 Furthermore, as already well-described by other authors,35 if specific radioprotection instructions are given to patients, such as diminishing the ingestion of food that produces necessary residues, viz, fruit with peel and cores, fried chicken, etc, and not using paper plates, disposable cups, or flatware, the production of radioactive waste may be, if not avoided, at least reduced.
Radiation doses to caregivers accompanying patients on the journey back home after radioiodine activity administration, either by public transport or their own car, have been intensively studied,19,20,36,37 whereby a dose rate of about 0.10 mSv/h has been reported. For journeys taking a few hours, the dose transmitted to a passenger close to the patient is below the acceptable level (less than 1.0 mSv for the general public and less than 5.0 mSv for caregivers), even within a distance of less than 1.0 meter from the source. A reduction in dose can occur by avoiding unnecessary time spent inside a vehicle and maximizing the distance between the patient and the caregiver. Regarding public transport, the best alternative is to avoid the local rush hour. Nevertheless, and if possible, patients should preferably return home by their own car, rather than by public transport or a taxi.
Generally, the basis for choosing to intern patients who have received over 1.1 GBq (30 mCi) of radioiodine activity is linked to the risk of public and environmental exposure following their release from the hospital.3,4 Although internment is certainly a means of reducing this risk, several questions need to be answered before overall implementation, such as, (1) the extent of radiation exposure received by patient's family members (if this exists); (2) the level of surface contamination inside the patient's residence; (3) the amount of radioactive waste produced by individual patients, and the radiologic impact on the environment when this waste is released for urban waste-management; (4) the additional cost generated by hospital confinement; and (5) the possibility of this giving rise to other problems, ie, limiting patient care, especially in the case of under-developed countries with a dearth of available rooms for this specific treatment.
In partial response to the above queries, and considering the assayed radiometric data presented here, it was found that human exposure was negligible and radiologic impact on the human environment nonmeasurable following outpatient radioiodine therapy, when applying activities of less than 7.4 GBq (200 mCi), and using the methodology described earlier in the text, therefore contrary to the premise of interning radioactive patients based solely on administered radioiodine activity. On the contrary, the experimental data here presented will pave the way for a more lucid discussion and judgment on whether the confinement of radioactive patients is necessary to provide a safe nuclear medicine procedure.
A reduction in public or private health-care spending for radioiodine therapy procedures is a further important question requiring close attention. For example in Brazil, the financial cost of an ablative procedure, applying either 3.7 GBq or 5.55 GBq, is around $800.00 and $2500.00 in a public and private health-care system, respectively, involving 2 days of hospital internment in either case. If the patient is released for home treatment, the cost of therapy may be reduced by 60% to 86%, respectively. This reduction cannot be ignored, as the incidental savings could be applied to other public health-care requirements.
Even so, there is ample scientific evidence indicating that low dose radiation does not produce significant damage to exposed cells,38 and that health risks from annual doses below 100 mSv are either too slight to be observed or nonexistent.39–45 Moreover, realization that the most exposed caregivers will receive this level of dose once a year or during his or her entire life span, obviates the need for worrying about exposure from outpatient radioiodine therapy. Nevertheless, it is extremely important to emphasize the fundamental need for maintaining control over any kind of radiation exposure.
One way to maintain radiation exposure at controlled levels is to provide patients and their families with an optimized protocol of radiation protection and medical action to be followed during therapy, like those presented at NCRP 155.5 These protocols should inform the approach necessary for protecting both the patient's household members, including children, caregivers, friends, etc, and the public as a whole. Another important aspect is that patients should be released from hospital internment on medical counsel in consultation with the facility radiation safety officer. The decision to intern or not should take into account the adequacy of the patient's physical and mental conditions to comply with radiation and medical instructions, as well as individual living conditions.
All radioprotection and medical instructions should be written in simple and easily comprehensible wording, and should be given to the patient and family members in oral and written form, a copy being kept on record in the facility, and in the patient's medical file for such a time as indicated by local authorities. These written instructions should be signed by the patient, the patient's physician, and the radiation-safety officer.
Any radioiodine activity should be administered to DTC patients by a physician, supervised and accompanied by the facility radiation safety officer, especially when administered under an ambulatory regimen. This logistic procedure is important to reduce global radiation exposure to others.
We believe that the data presented here will be useful when contemplating rigid adherence to patient hospital confinement procedures as a means of providing safe iodine-131 therapy. Furthermore, both the methodology of releasing patients, and the radiation protection and medical guidelines described in this work, ICRP 94,3 SS-63,4 and NCRP 155,5 could be of use for professionals wishing to treat thyroid cancer patients with radioiodine under an outpatient basis, although the guidelines themselves should be optimized according to local lifestyle habits, patient's requirements, and additional scientific data.
The experimental data presented here will raise queries regarding the hospital confinement of radioactive patients, based only on radioiodine activity administration. Nevertheless, our preliminary results certainly stimulate further discussion and judgment on the matter, thus indicating that the most appropriate decision to hospitalize or release a patient should be defined individually. Furthermore, the treatment of DTC by applying radioiodine activities of up to 7.4 GBq (200 mCi), on an outpatient basis, is a safe procedure when accompanied by qualified professionals and with adequate medical and radiation protection guidelines. This alternative therapy should be carefully discussed and disseminated to other professionals and government authorities, when considering the high potentiality for health-care cost reduction and improvement in the quality of life of both the patients and their families.
The authors thank all those involved in this research, including patients and their families, nuclear medicine physicians, and nurses and their assistants, as well as nuclear medicine secretaries. They also thank CNEN—Brazilian National Nuclear Energy Commission for permitting development of this original study (document number: 1386/08-CGMI/CNEN), and FAPESP—Fundação de Amparo à Pesquisa do Estado de São Paulo (research contract No. 08/54179-3) for sponsoring this work.
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