Public exposure from I-131 hospitalized isolated patients in NIMRA Jamshoro Pakistan

Purpose/ Background: To treat the cancerous tissues the unsealed radioisotopes are being in clinical practice since 7 decades. From these unsealed sources, I-131 is the choice of treatment for the treating thyroid cancers. Orally administered I-131 patients are to be kept isolated in hospital for some period until captured activity in the body reaches to national and international limits for the avoidance of unacceptably high radiation exposures to patients' family members and the general public to keep ALARA (as low as reasonably achievable) principal in mind. The main rationale of this study was to calculate the exposure/dose of the general public. Material and Methods: This work presents the exposure rate and dose to the general public in the corridor and the non-radioactive patients admitted in adjacent room from I-131 administered isolated patients treated at NIMRA (Nuclear Institute of Medicine and Radiotherapy) Jamshoro Pakistan. In this study exposure from 23 thyroid cancer patients treated with different activities of I-131 (50 to 200 mCi) from January 2011 to December 2012 were included. Results: The average exposure rate in the corridor was about 5.17 μSv/hr (2.14 μSv/hr to 8.15 μSv/hr) and the cumulative dose to nonradioactive patients residing in an adjacent room was 0.647 mSv (0.192 mSv to 1.664 mSv). Conclusion: This study concludes that the exposure rate to the general public especially the admitted non-radioactive patient in the adjacent room is almost within the limits of 1 mSv as specified in national and international standards.


Introduction
Radioiodine (I-131) is primarily β-emitting radionuclide with 610 keV energy followed by a 364 keV photon. 1-5 β ray emitted from radioiodine contributes the major radiation dose to the thyroid tissue and the gamma ray photon may give rise the potential radiation hazard to others. 1,2 After first usage of I-131 by Saul Hertz and Arthur Roberts in January 1941 6 , it becomes an admired treatment option for patients with thyroid cancer. Obliviously the Patients administered I-131 therapeutic dosages are sources of undesir-able high radiation exposure to close family members and the general public.
Usually the patients are to be hospitalized until the exposure rate from the patient's body surface at one meter falls to acceptable levels of 1 mSv 7-9 according to national and international standard 9-11 and ALARA principal. 12 The main aim of this study was to record and calculate the exposure rate/dose to general public especially patients admitted in an adjacent room at Nuclear Institute of Medicine and Radiotherapy (NIMRA) Jamshoro Pakistan.

Methods and Materials
Exposure rate measurement is a key factor in radioiodine administered patients. The aim of the measurement of exposure rate is to maintain the radiation exposure/dose of the general public as low as reasonably achievable. 12,13 If the administered activity to the patient is more than 30 mCi, hospitalization of patient is necessarily in a special isolation room is required until the achievement of captured activity to less than 30 mCi or the drop off of exposure rate to less than 50 Sv/hour. 12,14 Twenty three radioiodine administered patients at NIMRA Jamshoro Pakistan with ages ranged from 17 to 68 years and administered I-131 activities ranged from 50 mCi to 200 mCi were included in this study. Patients' data such as age, sex, administered activity, date and time of administration were recorded. [15][16][17] Initial exposure measurement for each of patient was recorded at the time of administration of activity with twice daily exposure rate measurement in corridor and adjacent room to isolation room were noted with calibrated LAMSE RM1001-RD survey meter (Figure 1). The procedure was briefed to the each patient and oral & written instructions regarding isolation of patient were given to patient in order to keep the dose to family members and general public minimum. 9,10,16,[18][19][20]26 The instructions were i) keeping the patient alone during hospital stay in a special isolated room; ii) allowing caregivers/family members to present meals and water to the patient for very short periods; iii) ensuring plenty of liquids intake; iv) chewing lemon/orange candies for minimizing salivary glands' dose; v) strongly advising lactating mothers to stop breast feeding to their babies immediately to prevent radioiodine ingestion through breast milk to the babies; vi) recommending pregnancy avoidance for a period of 4 -6 months after I-131 administration; vii) instructing the patients for maintaining safe distance between themselves and their family members & general public, ensuring separate arrangements of sleeping, avoiding public transport travel and avoiding visit of public places such as shopping centers, restaurants, theatres & public events; viii) for reduction of dose to caregivers/close family members, patients and their caregivers instructed for complying the same instructions at home after discharge from hospital for one to two weeks as maintained in isolation room.   Memon SA et al. 26 reported that this clearance of magnitude of (65 -68) %. This indicated that the isolation period of isolated patients in ward is short so the public dose may be minor.

Results
The data of exposure rates in corridor and dose to patients admitted in adjacent room is presented in Table 1. The recorded average exposure rates from isolated patients in corridor is ranged from 2.14 µSv/hr to 8.15 µSv/hr (average of 5.17 µSv/hr) and the cumulative doses to nonradioactive patients admitted adjacent room as indicated in Table 1 is ranges from 0.192 mSv to 1.664 mSv with an average of 0.647 mSv. 91% (n = 21) of patients in adjacent room received less dose than allowable limit of 1 mSv 9-11 as shown in Figure 3. Only 2 (9%) patients contribute some higher doses to non-radioactive patients admitted in adjacent room due to longer stay in isolation room than other patients.
The results of this study pointed out that the exposure to family members of patients and the general public can be minimized with i) sufficient radiation safety precautions and measurements. ii) abiding the instructions by I-131 administered patients.

Discussion
Along with family members/caregivers, the general public/non-radioactive patient admitted in adjacent room are also at risk from I-131 administered patients isolated in ward but through proper radiation protection measurements it can be effectively managed. 27 The exposure rate/dose of the general public from patients administered with I-131 during stay at hospital needs some considerations. The comparison of current study is not possible due to non-availability of data on this study topic.
Although many studies 14,17,26,[28][29][30][31][32][33][34] have been conducted on the dose to caregivers/family members of the patients as summarized in Table 2 but no data was found for exposure rate/dose to the general public from the I-131 therapeutic patients. As Table 2 showed that the doses to caregivers/family members of the patients are within acceptable limits, which pointed out that the dose to the general public, will also be in the allowable limits and the patients treated with radioiodine do not contribute a significant radiation dose to the public. 35 reported that the most of activity cleared from patient in first 24 hours which confirmed that the public dose will not be significant due to short isolation period of patients in ward.
Due to deficiency in research on the current topic, the comparison is impossible but the studies 2, 15, 21-26 vigorously supported the result of the current study.

Conclusion
The current study indicates that the exposure rate in corridor is within acceptable limits and most of data for dose to non-radioactive patients in adjacent room is also within tolerable limits. As there is no previous data available due to lack of research on the current topic so authors suggest that more studies may be conducted on subject to compare the dose to the general public and for the authentication of current study.