Estimates of Radiation Doses and Cancer Risk from Food Intake in Korea.

The aim of this study was to estimate internal radiation doses and lifetime cancer risk from food ingestion. Radiation doses from food intake were calculated using the Korea National Health and Nutrition Examination Survey and the measured radioactivity of (134)Cs, (137)Cs, and (131)I from the Ministry of Food and Drug Safety in Korea. Total number of measured data was 8,496 (3,643 for agricultural products, 644 for livestock products, 43 for milk products, 3,193 for marine products, and 973 for processed food). Cancer risk was calculated by multiplying the estimated committed effective dose and the detriment adjusted nominal risk coefficients recommended by the International Commission on Radiation Protection. The lifetime committed effective doses from the daily diet are ranged 2.957-3.710 mSv. Excess lifetime cancer risks are 14.4-18.1, 0.4-0.5, and 1.8-2.3 per 100,000 for all solid cancers combined, thyroid cancer, and leukemia, respectively.

EVALUATION OF DOSE IN SLEEP BY MATTRESS CONTAINING MONAZITE.

Some companies in Korea have sold beds which contain a processed product containing monazite powder. Consumers may receive external exposure by radiation emitted by progeny radionuclides in uranium and thorium, and internal exposure through the breathing of radon progeny radionuclides produced in the decay chain. Thus, in this study, age specific dose conversion factors (mSv y-1 Bq-1) by external exposure and dose conversion factors by internal exposure (mSv y-1 per Bq m-3) were derived. Besides, a dose assessment program were developed to calculate dose by taking into account real conditions. And the age specific dose was evaluated using the radioactive concentration measured by the NSSC. As a results, external exposure was assessed to get effective doses in the range of 0.00086 to 0.0015 mSv y-1 by external exposure and a committed effective doses in the range of 1.3 to 12.26 mSv y-1 by internal exposure for all age groups.

An engagement factor for caregiver radiation dose assessment with radioiodine treatment.

This study aims to suggest ways to better manage thyroid cancer patients treated with high- and low-activity radioiodine ((131)I) by assessing external radiation doses to family members and caregivers and the level of radiation in the surrounding environment. The radiation doses to caregivers of 33 inpatients (who were quarantined in the hospital for 2-3 d after treatment) and 31 outpatients who received radioiodine treatment after thyroidectomy were measured using passive thermoluminescence dosemeters. In this study, 33 inpatients were administered high-activity (100-200 mCi) (131)I, and 31 outpatients were administered low-activity (30 mCi) (131)I. The average doses to caregivers were measured at 0.61 mSv for outpatients and 0.16 mSv for inpatients. The total integrated dose of the recovery (recuperation) rooms where the patients stayed after release from hospital was measured to be 0.83 mSv for outpatients and 0.23 mSv for inpatients. To reflect the degree of engagement between the caregiver and the patient, considering the duration and distance between two during exposure, the authors used the engagement factor introduced by Jeong et al. (Estimation of external radiation dose to caregivers of patients treated with radioiodine after thyroidectomy. Health Phys 2014; 106: :466-474.). This study presents a new engagement factor (K-value) of 0.82 obtained from the radiation doses to caregivers of both in- and out-patients treated with high- and low-activity radioiodine, and based on this new value, this study presented a new predicted dose for caregivers. A patient treated with high-activity radioiodine can be released after 24 h of isolation, whereas outpatients treated with low-activity radioiodine should be isolated for at least 12 h.

Estimation of external radiation dose to caregivers of patients treated with radioiodine after thyroidectomy.

Due to the remarkable increase in thyroid cancer cases, the number of patients treated with radioiodine (I) shows a sharply increasing trend in recent years. Accordingly, radiation exposure of other people, particularly caregivers or comforters, after release of patients from hospitals is getting more attention than ever. In the present study, empirical equations are proposed for estimation of doses to caregivers. Only patients administered with therapeutic amounts of ¹³¹I after thyroidectomy were considered. External radiation doses to 70 caregivers or family members were measured using thermoluminescence dosimeters (TLDs). The mean, external, effective dose to caregivers, during a nursing period of 5-9 d after patient quarantine for 3-4 d in the hospital, was 0.12 ± 0.10 mSv. This is only 2.5% of the dose limit recommended by the International Commission on Radiological Protection for caregivers. By analyzing those individual doses to the caregivers, values of a factor affecting caregiver doses, K, are obtained for use in estimation of caregivers' doses. The factor reflects the degree of engagement of the caregiver to the patient, and hence it is named the "engagement factor." The mean value of the engagement factor in this study was 1.3 ± 0.88. With the help of the engagement factor, the total external dose to a caregiver can be estimated as 1.1 × Q0 × e⁻°·°5(Tr) mSv, where Q0 is the administered activity of ¹³¹I (GBq) and T(r) is the patient's release time (h) after admistration of radioiodine. Based on the dose estimation model developed in this study, by comparing the cost of extended quarantine against that incurred by release of the patient, including the burden of radiation exposure of caregivers or family members, the reasonableness of current quarantine periods was revisited. It was found that the dichotomous policy (i.e., hospitalizing patients administered ¹³¹I over 1.1 GBq for a period of 3-4 d compared with treating other patients administered below 1.1 GBq as outpatients) is unjustifiable; this is particularly true for those treated with a few GBq. Based upon the dose estimation model presented herein, tables suggesting an appropriate quarantine period depending upon the activity of the administered ¹³¹I are provided for use as reference in deciding when to release patients treated with therapy levels of ¹³¹I after thyroidectomy.

Groundshine dose-rate conversion factors of soil contaminated to different depths.

For assessment of external doses from the ground contaminated with radionuclides, the dose-rate conversion factors (DCFs) prescribed in FGR (Federal Guidance Report) 12 have been used. Recently, significant changes were made by International Commission on Radiological Protection in dosimetric models and parameters, which include use of Reference Phantoms and revised tissue-weighting factors, as well as the updated decay data of radionuclides. The DCFs for effective and equivalent doses due to groundshine from contaminated soil were re-calculated by taking the changes into account. In this study, the DCFs for effective and equivalent doses were calculated for depths of 1, 5 and 15 cm and for infinite deposition. Doses to the Reference Phantoms were calculated by Monte Carlo simulations with the MCNPX 2.7.0 radiation transport code for 26 mono-energy photons between 0.01 and 10 MeV. Transport calculations were performed for the source volume within the converging of distances and depths practically contributing to the dose rates, which were determined by a simple model. With the resulting doses, empirical response functions were constructed as a function of photon energy. The DCFs for the radionuclides considered important were evaluated by combining the photon emission data of the radionuclide and the response functions. Finally, the contributions of accompanied beta particles to the skin equivalent doses and the effective doses were calculated separately and added to the DCFs. For radionuclides considered in this study, the new DCFs for the different depths agreed within 10 % with the data in FGR12.

Measurements and prediction of the ambient dose rate from patient receiving radioiodine administration after thyroid ablation.

Empirical equations were proposed for the prediction of the ambient dose equivalent rates from patients administered with radioiodine for the treatment of thyroid cancers. Ambient dose equivalent rates were measured for 59 patients who received high-dose (131)I treatment after thyroid ablation at different times after the administration. An ion chamber was used to measure the dose equivalent rates at 1 m away from the body and on contact to the thyroid of the patients. The resulting equations for estimating dose equivalent rates at 1 m from the body and on contact to the thyroid are, respectively, dot H(1)(body)=0.236e(-0.0501t) (mSv h(-1) GBq(-1)) and dot H(c)(thy)=2.676e(-0.0443t) (mSv h(-1) GBq(-1)). The effective half-times in total body appeared to be 13.86 h.