ANSI/HPS N13.56-2012 (R2019): Sampling and Monitoring Releases of Airborne Radioactivity in the Workplace No abstract available

Characterization of Extrafocal Dose Influence on the Out-of-Field Dose Distribution by Monte Carlo Simulations and Dose Measurements Out-of-field scattered and transmitted extrafocal radiation may induce secondary cancer in long-term survivors of external radiotherapy. Pediatric patients have higher life expectancy and tend to receive higher secondary radiation damage due to geometric and biological factors. The goal of this study is to characterize the location and the magnitude of extrafocal dose regions in the case of three-dimensional conformal radiotherapy and volumetric arc therapy, to apply this information to clinical treatment cases, and to provide mitigation strategies. Extrafocal dose has been investigated in a Varian TrueBeam linac equipped with a high-definition 120 multileaf collimator using different physical and virtual phantoms, dose calculation (including Monte Carlo techniques), and dose measurement methods. All Monte Carlo calculations showed excellent agreement with measurements. Treatment planning system calculations failed to provide reliable results out of the treatment field. Both Monte Carlo calculations and dose measurements showed regions with higher dose (extrafocal dose areas) when compared to the background. These areas start to be noticeable beyond 11 cm from the isocenter in the direction perpendicular to the multileaf collimator leaves’ travel direction. Out-of-field extrafocal doses up to 160% of the mean dose transmitted through the closed multileaf collimator were registered. Two overlapping components were observed in the extrafocal distribution: the first is an almost elliptical blurred dose distribution, and the second is a well-defined rectangular dose distribution. Extra precautions should be taken into consideration when treating pediatric patients with a high-definition 120 multileaf collimator to avoid directing the extrafocal radiation into a radiosensitive organ during external beam therapy.

Radionuclide Concentrations in Different Water Sources From Nigeria Gamma spectrometric analysis was done on all the different sources of water samples in the rural communities of Egbeda Local Government Area of Oyo State in Nigeria. Water samples were collected from 6 boreholes, 11 streams, 5 taps, and 41 hand-dug wells. The water samples were analyzed using a high-purity germanium detector at the National Institute of Radiation Protection and Research, Ibadan, Nigeria. Radionuclides found in the water samples include 40K, 232Th, and 238U. The average amount of 40K found in the borehole, stream, tap, and well water is 3.22, 2.23, 2.11, and 1.77 Bq L−1, respectively. The average amount of 232Th found in the borehole, stream, tap, and well water is 0.57, 0.46, 0.47, and 0.55 Bq L−1, respectively. The average amount of 238U found in the borehole, stream, tap, and well water is 0.54, 0.27, 0.29, and 0.61 Bq L−1, respectively. The annual effective doses calculated from radionuclides in the water are 0.11, 0.09, 0.09, and 0.11 mSv for borehole, stream, tap, and well, respectively.

Activation of Collimators Irradiated With Clinical Proton Beams and Development of a Semiempirical Model for Activity Calculation Patient-specific collimators used in proton therapy are activated after use. The aim of this work is to assess the residual activity in brass collimators considering clinical beams, so far studied only for monoenergetic beams, and to develop a model to calculate the activity. Eight brass collimators irradiated with different clinical and monoenergetic beams were included in the study. The collimators were analyzed with gamma spectrometry in the framework of three independent studies carried out at the two French proton therapy sites. Using FLUKA (a fully integrated particle physics Monte Carlo simulation package), simulations were performed to determine radionuclides and activities for all the collimators. The semiempirical model was built using data calculated with FLUKA for a range of clinical beams (different maximum proton energies, modulations, and doses). It was found that there was global coherence in experimental results from different studies. The relevant radionuclides at 1 mo postirradiation were 57Co, 58Co, and 65Zn, and additionally, 54Mn, 56Co, and 60Co for high-energy beams. For nondegraded monoenergetic beams, differences between FLUKA and spectrometry were within those reported in reference benchmark studies (±30%). Due to the use of perfect monochromatic sources in the FLUKA model, FLUKA results systematically underestimated experimental activities for clinical beams, especially for 65Zn, depending on the beam energy spread (modulation, degradation, beam line characteristics). To account for the energy spread, correction factors were derived for the semiempirical model. The model is applicable to the most relevant radionuclides and total amounts. Secondary neutrons have a negligible contribution to the activity during treatment with respect to proton activation.

Assessing the Committed Effective Dose From 226Ra in Thermal Spring Water From San Diego De Alcala, Chihuahua, Mexico The oral administration of mineral-rich spring water is known as hydropinic treatment and is used to treat certain ailments. Health benefits are attributed to thermal spring water containing radioactive elements such as radium; this has popularized use of such radioactive water in various parts of the world, causing those who ingest it to increase their internal radiation dose. The goal of this study was to assess the activity concentrations of 226Ra present in the thermal spring waters of San Diego de Alcala, in the state of Chihuahua, Mexico, and to estimate the health risk posed to patients by the effective dose received from ingesting this water during hydropinic treatments. Water samples were taken from different areas of the San Diego de Alcala thermal springs, and pH, temperature, electrical conductivity, and total dissolved solids were measured. The 226Ra activity concentrations were measured with a liquid scintillation counter. The activity concentrations of 226Ra in sampled water varied from 125 to 452 mBq L−1 with an average of 276 ± 40 mBq L−1. The committed effective dose from each of the 226Ra activity concentrations found in samples ranged from 9.80 × 10−5 to 4.0 × 10−3 mSv for hydropinic treatments being carried out in San Diego de Alcala thermal spring spas. Different treatments had different intake rates (200, 600, 1,000, and 1,500 mL d−1) and occurred over periods of 2 or 3 wk. According to the guidelines of the US Environmental Protection Agency, the maximum permissible amount of radium in drinking water is 185 mBq L−1; the 226Ra content in most of the collected samples exceeded this limit. The committed effective doses varied with 226Ra concentration and intake rate; none exceeded the World Health Organization’s reference dose for drinking water of 0.1 mSv y−1, which is the maximum amount to which the population should be exposed.

Shot Noise Explains the Petkau 22Na+ Result for Rupture of a Model Phospholipid Membrane The action of free radicals is believed responsible for much or most biological injury resulting from exposure to ionizing radiation. These molecules in solution possess short lifetimes on the order of nanoseconds to microseconds. As a result, the dose—which measures the energy dissipated in tissue due to radiolysis—should not be considered a reliable indicator of the free radical concentration, nor of the chemical effects that follow from it. Rather, the chemical state of affected tissue is properly represented only by the dissipated power, which describes the distribution of energy with time. The present report demonstrates the validity of this assertion using data contained in a report describing a benchtop experiment published in 1972. The experiment used the visible rupture of a model phospholipid membrane as a means to quantify the degree of chemical insult caused by ionizing radiation. The experiment found that beta doses in the range from 1–10 rad were equivalent to x-ray rupture doses of 3,500 rad. This report demonstrates that the experimental results are convincingly explained by reference to the properly calculated time-averaged dissipated power due to beta decay. The theoretical explanation is derived by analogy to a well-understood result from electronic systems known as shot noise. If the result described in this report is demonstrated to extrapolate from the benchtop to living systems, then it is likely that exposure to beta radiation via internal incorporation is far more hazardous than commonly believed. The finding could be revolutionary in the field of health physics.

On the Assessment of Human Exposure to Electromagnetic Fields Transmitted by 5G NR Base Stations The fifth-generation new radio cellular network will be rolled out within the next few years. Several assessment methods of human exposure to electromagnetic fields transmitted by fifth-generation new radio base stations are discussed. Currently no method exists that allows extrapolation to the maximum theoretical exposure. Thus two new extrapolation methods are proposed. A 95th percentile exposure can be derived from the maximum theoretical exposure by an agreed-upon reduction factor if a more realistic exposure assessment is required.

Preliminary Dose Assessment for Emergency Response Exercise Using Unsealed Radioactive Contamination A preliminary dose assessment for an emergency response exercise using unsealed radioactive sources was performed based on conservative calculation methods. The assessment was broken into four parts: activation, distribution, exercise participation, and post-exercise monitoring. The computer code MicroShield was used to determine external exposure from the source during and after distribution. Internal exposure via inhalation and ingestion was estimated by assuming fractional intakes of activity and converting to dose using annual limits on intake and dose coefficients. It was determined from the dose assessment that a radionuclide-dependent range of 37 MBq to 1.5 GBq can be used to achieve detectable dose rates during the exercise without exceeding assumed administrative dose limits. Of the identified radionuclides, 99mTc results in the lowest dose and is recommended from a radiological safety standpoint. However, the choice of which radionuclide and what activity to use for an exercise should be made based on budget and the logistics of the actual exercise.

Successful Migration from Radioactive Irradiators to X-ray Irradiators in One of the Largest Medical Centers in the US This paper summarizes about 9 years of effort by Mount Sinai to successfully migrate completely from radioactive irradiators to x-ray irradiators without compromising patient care or research studies. All the effort by Mount Sinai to permanently remove the risk of malicious use of radioactive materials as Radiological Dispersal Device or dirty bomb is reviewed. Due to the unique characteristics of the cesium chloride (137CsCl) used in irradiators, it is especially susceptible to be used as a dirty bombs. Mount Sinai originally had four of such irradiators. To reduce and eventually remove the risk of malicious use of radioactive materials, Mount Sinai in New York City has taken several steps. One of such measures was to harden the radioactive irradiators to make the radioactive materials harder to be stolen for malicious purposes. By increasing the delay time, the local law enforcement agency (LLEA) will have more time to stop the intruder. Another measure taken was to implement enhanced security in facilities having radioactive materials. We collaborated with the National Nuclear Security Administration and used state-of-the-art security equipment such as Biometric Access Control and 24/7 video monitoring. In addition, a remote monitoring system with alarms was installed and connected to LLEA for constant monitoring and possible intervention, if necessary, in a timely manner. The other measure taken was to limit the number of people who have access to such radioactive materials. We adopted a single person operator method and reduced the number of people having access from 145 people to only a few people. The adoption of such measures has reduced the risk significantly; however, the best way to remove the permanent risk of these radioactive materials that may be used for a dirty bomb is to use alternative technology to replace these high-activity radioactive sources. In 2013, Mount Sinai purchased its first x-ray irradiator to investigate the feasibility of using x-ray irradiators instead of cesium irradiators for research purposes for cells and small mice. The results from comparison studies were promising, which led to the decision of permanent migration of all cesium irradiators to x-ray irradiators. As of January 2018, Mount Sinai successfully disposed all its 137Cs irradiators. At this time, Mount Sinai, as one of the largest health care institutions in NY with about 50,000 employees, has migrated completely to alternative technology and removed the risk of malicious use of radioactive materials permanently.

Health Physics Society Prospectus No abstract available