Adult Phantom Research Articles

Radiation Dose Comparison according to Different Organ Characteristics at Same Scan Parameters Using CareDose 4D: An Adult and Pediatric Phantom Evaluation

Radiation Dose Comparison according to Different Organ Characteristics at Same Scan Parameters Using CareDose 4D: An Adult and Pediatric Phantom Evaluation

DOES THE USE OF CONTEMPORARY CT SCANNERS ALTER THE RADIATION DOSE DEBATE IN THE IMAGING WORK UP FOR PULMONARY EMBOLISM?

The aim of this study was to compare patient doses from ventilation perfusion single photon emission computed tomography (V/Q SPECT) and computed tomography pulmonary angiography (CTPA) performed on contemporary scanners. Effective dose (ED) for V/Q SPECT was calculated using organ doses per unit administered activity of the radiopharmaceuticals. Organ doses in CT were measured using nanoDot aluminium oxide optically stimulated dosemeters placed within a female adult anthropomorphic phantom. To simulate a larger patient, the phantom was wrapped in three layers of Superflab sheets. The V/Q SPECT resulted in ED of 2.82 mSv and a breast dose of 1.12 mGy. The CTPA dose was 1.82±0.42 and 3.43±0.91 mSv, whilst dose to the breast tissue was 2.86±0.86 and 5.95±0.44 mGy for small- and medium-sized patients, respectively.

Dosimetric dependence of ocular structures on eye size and shape for external radiation fields of electrons, photons, and neutrons

The dosimetric dependence of ocular structures on eye size and shape was investigated within the standard ICRP Publication 116 irradiation geometries. A realistic transport geometry was constructed by inserting a scalable and deformable stylised eye model developed in our previous study within the head of the ICRP Publication 110 adult male reference computational phantom. Beam irradiations of external electrons, photons, and neutrons on this phantom were simulated using the Monte Carlo radiation transport code PHITS in the geometries of AP, RLAT, PA and ROT. Absorbed doses in ocular structures such as ciliary body, retina, and optic nerves were computed as well as that in lens. A clear dosimetric dependence of ocular structures on eye size and shape was observed for external electrons while only a small dependence was seen for external photons and neutrons. Difference of the tendency was attributed to their depth-dose distributions where spread dose distributions were created by photons and neutrons while more concentrated distributions were created by external electrons.

Effective dose conversion coefficient for gamma ray exposure from an overhead plume

The external radiation exposure from an overhead plume containing gamma emitting radionuclides can contribute substantial dose to the ground receptor during normal operations as well as accidental release conditions of nuclear facilities. In order to estimate the effective dose conversion coefficients (DCCs) directly, a finite plume Monte Carlo model along with the reference phantom at the ground receptor location needs to be implemented. In the present study, a comprehensive simulation of radiation transport from the Gaussian plume source to the ICRP reference adult voxel phantoms (receptor) is carried out using the FLUKA Monte Carlo code. The organ absorbed doses as well as the effective DCCs of the adult reference phantom are computed for different meteorological parameters and downwind distances. To illustrate the application of this model, an overhead Gaussian plume containing two different gamma emitting radionuclides, 135Xe and 41Ar are considered. From these simulations, the ratio of the effective dose rate to the kerma rate are estimated as 0.6 Sv Gy−1 and 0.65 Sv Gy−1 for the exposure from 135Xe and 41Ar, respectively. This ratio is constant irrespective of the meteorological conditions and cloud models. Further results show that the effective DCCs as a function of the downwind distance vary by an order of magnitude for an unstable weather category; however, the variations are very small in the case of a stable category. This study demonstrates an accurate method for calculating the effective dose to the ground receptor from an external plume which can be further applied for any radionuclide under any meteorological condition.

Pediatric cone beam CT on Varian Halcyon and TrueBeam radiotherapy systems: radiation dose and positioning accuracy evaluations

Medical exposure to ionizing irradiation has become a recognised carcinogenic risk. Balancing the concomitant imaging dose and positioning accuracy is critical in image-guided-radiotherapy (IGRT) especially for children, whose higher biological susceptibility and longer expected life make them more vulnerable to develop secondary cancer. This work aims to evaluate and benchmark the imaging dose and positioning accuracy of a new MV cone-beam-CT (CBCT)-guided IGRT system, Varian Halcyon, against conventional kV CBCT. Weighted-CT-dose-index (CTDIw) were measured for Varian TrueBeam kV CBCT, and computed for Halcyon MV CBCT using Eclipse system as validated before. Simulating the IGRT workflow, the positioning accuracy of correcting a known shift was tested on various regions of 1-year, 5-year and adult anthropomorphic phantoms, respectively. Inter-scanner and inter-protocol comparisons of dose and accuracy were performed. kV CTDIw for ‘Head’, ‘Thorax’, ‘Pelvis’ and ‘Image Gently’ (in CTDIΦ16cm/CTDIΦ32cm phantoms, respectively) protocols were measured as 4.5 mGy, 5.4 mGy, 19.3 mGy, and 1.1 mGy/0.5 mGy, respectively. Using ‘High Quality’ mode, MV CTDIw in the CTDIΦ16cm and CTDI Φ32cm phantoms were computed as 84.5 mGy and 63.8 mGy (imaging length = 28 cm), 68.8 mGy and 55.5 mGy (imaging length = 16 cm), respectively, which were about twice of ‘Low Dose’ mode. The maximum positioning deviation observed on Halcyon was 0.51 mm (‘Low Dose’ adult thorax), which was lower than that of standard (0.58 mm, ‘Pelvis’ adult pelvis) and ‘Image Gently’ kV CBCT (1.57 mm, adult pelvis). Accuracy of ‘Image Gently’ kV CBCT head & neck and thoracic imaging were clinically acceptable for adults (maximum deviation = 0.54 mm, adult thorax). Complying with Image Gently campaign, dose-efficient protocols should be used for pediatric IGRT, achieving comparable positioning accuracy on the new Halcyon MV CBCT system relative to the conventional kV CBCT.

Evaluation of organ doses following prostate treatment with permanent brachytherapy seeds: a Geant4 Monte Carlo simulation study

This study aimed to evaluate the absorbed doses received by the organs at risk (OARs) following prostate treatment with permanent Iodine-125 (125I) brachytherapy seeds. In order to simulate an enlarged abnormal prostate due to malignancy, the MIRD5 adult male anthropomorphic phantom (readily available in the Geant4 Monte Carlo package) was modified by increasing the prostate volume to 35 cm3. The permanent seeds were constructed with an outer cylindrical dimension of 4.5 mm (length) × 0.8 mm (diameter). The effects of various activity per seed (0.5, 0.6 and 0.8 mCi), number of seeds (62, 78, 94 and 110 seeds) and radionuclides, i.e. Palladium-103 (103Pd), 125I and Cesium-131 (131Cs), towards the absorbed dose to the OARs (i.e. rectum, urinary bladder and both testicles) were investigated. In this study, prostate dose of up to 237 Gy was simulated, which resulted in 11 Gy dose to rectum, 7 Gy to urinary bladder and 4 Gy to each testicle. The doses were considered as reasonable, given the low dose rate nature of the treatment, allowing tissue repair for the OARs. Optimal seeds arrangement was found to consist of 78 or fewer seeds, as it resulted in the lowest dose to the OARs. For similar prostate dose, 103Pd resulted in the lowest dose to the OARs, followed by 125I and 131Cs. Permanent seed brachytherapy allows high dose to be delivered to the prostate, while ensuring minimal dose to the OARs.

Evaluation of organ doses following high dose rate (HDR) brachytherapy of breast cancer: a Geant4 Monte Carlo simulation study

This study aimed to evaluate the absorbed doses received by the organs at risk (OARs) following Iridium-192 (192Ir) high dose rate (HDR) brachytherapy of the left breast. The MIRD5 adult female anthropomorphic phantom, readily available in the Geant4 Monte Carlo package was used. However, the left breast was modified from 195 to 145 cm3, to represent a breast following lumpectomy. Left breast was chosen due to its higher cancer occurrence than the right breast. The HDR sources were constructed with an outer cylindrical dimension of 4.5 mm (length) × 0.9 mm (diameter). Various influencing parameters were studied, i.e. catheter arrangement (single versus dual plane), source inter-dwell distances (5 versus 10 mm), and different radionuclides, i.e. Cobalt-60 (60Co) and 192Ir, by delivering a total treatment dose of 32 Gy to the left breast. Absorbed doses to the OARs (e.g. left lung, heart, right breast, spleen, etc.) were then evaluated. A maximum left lung dose of 1.5 Gy was recorded, while doses to the other OARs were all below 1 Gy. The treatment using dual plane catheter arrangement contributed to a slightly higher dose to the OARs, despite equal dose to the breast. There was no dose difference between different inter-dwell distances used in this study. 60Co resulted in a slightly higher left lung dose than that of 192Ir, while the results were the opposite for the other OARs. HDR brachytherapy allows high dose to be delivered to the breast within a short period of time, with minimal absorbed doses to the OARs.

Tolerance levels of mass density for CT number calibration in photon radiation therapy.

Computed tomography (CT) data are required to calculate the dose distribution in a patient’s body. Generally, there are two CT number calibration methods for commercial radiotherapy treatment planning system (RTPS), namely CT number‐relative electron density calibration (CT‐RED calibration) and CT number‐mass density calibration (CT‐MD calibration). In a previous study, the tolerance levels of CT‐RED calibration were established for each tissue type. The tolerance levels were established when the relative dose error to local dose reached 2%. However, the tolerance levels of CT‐MD calibration are not established yet. We established the tolerance levels of CT‐MD calibration based on the tolerance levels of CT‐RED calibration. In order to convert mass density (MD) to relative electron density (RED), the conversion factors were determined with adult reference computational phantom data available in the International Commission on Radiological Protection publication 110 (ICRP‐110). In order to validate the practicability of the conversion factor, the relative dose error and the dose linearity were validated with multiple RTPSes and dose calculation algorithms for two groups, namely, CT‐RED calibration and CT‐MD calibration. The tolerance levels of CT‐MD calibration were determined from the tolerance levels of CT‐RED calibration with conversion factors. The converted RED from MD was compared with actual RED calculated from ICRP‐110. The conversion error was within ±0.01 for most standard organs. It was assumed that the conversion error was sufficiently small. The relative dose error difference for two groups was less than 0.3% for each tissue type. Therefore, the tolerance levels for CT‐MD calibration were determined from the tolerance levels of CT‐RED calibration with the conversion factors. The MD tolerance levels for lung, adipose/muscle, and cartilage/spongy‐bone corresponded to ±0.044, ±0.022, and ±0.045 g/cm3, respectively. The tolerance levels were useful in terms of approving the CT‐MD calibration table for clinical use.

Monte carlo study of organ doses and related risk for cancer in Tanzania from scattered photons in cervical radiation treatment involving Co-60 source

PurposeThe present work aimed to evaluate organ doses and related risk for cancer from external beam radiation treatment (EBRT) and high-dose-rate (HDR) brachytherapy (BT) involving Co-60 source for patients with cervical carcinoma in Tanzania based on Monte Carlo methods and to evaluate the secondary cancer risks in their lifetime. MethodsEBRT and HDR-BR were modelled by using the MCNPX Monte Carlo (MC) code. The MC simulations were performed by using validated models and isocentric irradiation of an adult female computational phantom. The organ doses and cancer risks estimates were obtained. ResultsThe highest absorbed doses of 6.98 × 10−2 and 5.74 × 10−2 Sv/Gy were recorded in the bladder for BT and EBRT. The higher risk was found for colon at 1.06 × 10−3 in the HDR-BT and 9.75 × 10−5 in the EBRT per 100,000 population at exposure age of 35 years than in the other organs. The risk magnitude decreased with increasing age at exposure. In general, the secondary cancer risks in all sites considered from EBRT and HDR-BR for cervical cancer patient were lower than the baseline risks. ConclusionsThe chances of developing secondary cancer take years following radiation therapy are extremely low, but the results of present study can support to establish a future database on secondary cancer risks involving radiation therapy in patients with cervical cancer by using HDR-BR and EBRT with Co-60 source in Tanzania and other developing countries.

Computation Speeds and Memory Requirements of Mesh-Type ICRP Reference Computational Phantoms in Geant4, MCNP6, and PHITS.

Recently, Task Group 103 of the International Commission on Radiological Protection completed the development of new adult male and female mesh-type reference computational phantoms, which are planned for use in future International Commission on Radiological Protection dose coefficient calculations. In the present study, the performance of major Monte Carlo particle transport codes, i.e., Geant4, MCNP6, and PHITS, were investigated for the mesh-type reference computational phantoms by performing transport simulations of photons, electrons, neutrons, and helium ions for some external and internal exposures, and simultaneously measuring the memory usage, initialization time, and computation speed of the adult male mesh-type reference computational phantom in the codes. The measured results were then compared with the values measured with the current adult male voxel-type reference computational phantom in International Commission on Radiological Protection Publication 110 as well as five voxel phantoms produced from the adult male mesh-type reference computational phantom with different voxel resolutions, i.e., 0.1 × 0.1 × 0.1 mm, 0.6 × 0.6 × 0.6 mm, 1 × 1 × 1 mm, 2 × 2 × 2 mm, and 4 × 4 × 4 mm. From the results, it was found that in all of the codes, the memory usage of the mesh-type reference computational phantom is greater than that of the voxel-type reference computational phantom and the lowest resolution voxelized phantom, but it is sufficiently lower than the maximum memory, 64 GB, that can be installed in a personal computer. The required initialization time of the mesh-type reference computational phantom and of the voxel-type reference computational phantom and voxelized phantoms in resolutions lower than 0.6 × 0.6 × 0.6 mm was less than a few minutes in all of the codes. As for the computation speed among the codes, MCNP6 showed the worst performance for the mesh-type reference computational phantom, which was slower than that for the voxel-type reference computational phantom by up to ~50 times and slower than that for all of the voxelized phantoms by up to ~40 times. By contrast, PHITS showed the best performance for the mesh-type reference computational phantom, which was faster than that for the voxel-type reference computational phantom by up to ~3 times and faster than that for all of the voxelized phantoms by up to ~20 times. This high performance of PHITS is indeed encouraging considering that it is used nowadays by the International Commission on Radiological Protection for most dose coefficient calculations.

Evaluation of Doses Absorbed to a Bone Marrow Stem Cell Layer from Short-lived Radionuclides in the Blood Vessels and from Long-lived Radionuclides in the Cortical Bone

The International Commission on Radiological Protection (ICRP) internal dose assessment model, currently adopted in Japanese regulation, assumes uniform distribution of radionuclides in bone marrow blood (ICRP Publication 60). Recent studies have revealed a localization of hematopoietic stem cells (HSCs) and immune cells in the perivascular region of the bone marrow sinusoids, suggesting a need to consider nonuniform distributions of the blood source and HSCs. To evaluate energy transfer to HSCs, a simplified model of cervical vertebrae with bone tissues and blood vessels was built using data from the adult Japanese male phantom. Doses absorbed by HSCs from blood and hard bone sources were calculated using a Monte Carlo simulation, and absorbed fractions (AFs) and specific absorbed fractions (SAFs) from electrons were compared with those in the ICRP 1990 model. In the cervical vascular model, electron SAFs from sinusoidal blood in the red bone marrow (RBM) to the target perivascular region were 1.2 to 6.9 times higher than the SAF in the ICRP 1990 model, suggesting an underestimation of the RBM dose. Electrons from the cortical bone source to the perisinusoidal target exhibited energy transfer. The ICRP 1990 model underestimates electron SAFs from radionuclides in sinusoidal blood and cortical bones. A more elaborate model is needed to examine doses for the RBM and effects on hematopoietic and immune functions.

Impact of Contralateral Breast Shielding on the Risk of Developing Radiation-induced Cancer from Full-field Digital Mammography Screening

ObjectiveThe objective of this study was to investigate the impact of contralateral breast shielding on the risk of developing radiation-induced cancer from four-view full-field digital mammography (FFDM) screening. MethodsA poly methyl methacrylate-polyethylene breast phantom and adult ATOM dosimetry phantom were used to measure organ dose on four FFDM machines using craniocaudal and mediolateral oblique projections for each breast. A lead rubber shield of 0.25 mm equivalent lead thickness was used to protect the contralateral breast. Organs dose, effective dose, and effective risk were calculated. For effective risk estimations, the impact of the shield was considered for the routine screening views. ResultsThe contralateral breast dose was reduced by more than 95%. For each FFDM machine, contralateral breast dose reduction in μGy were 35.20 reduced to 1.93, 41.40 reduced to 0.01, 22.85 reduced to 1.24, and 22.76 reduced to 1.66. Effective risk reduction was significant (P < .05). For all FFDM machines, a small reduction was identified in sternum bone marrow dose due to the use of contralateral breast shield. ConclusionsThe results of the study demonstrate the value of a contralateral breast shield. More research is required to determine whether such a shield has clinical utility.

The impact of head miscentering on the eye lens dose in CT scanning: Phantoms study

The aim of this study was to evaluate the eye lens dose due to miscentering, either above or under the isocenter, and to assess the possibility of eye lens dose reduction by using miscentering phenomenon. We used two types of phantoms (head CTDI and adult anthropomorphic phantoms) and two types of detectors (pencil ionization chamber and radiophotoluminescence detectors). Measurements using the head CTDI phantom and pencil ionization chamber were performed at the upper peripheral hole of the CTDI phantom, whereas measurements using RPL detectors were performed on the surface of the eyes of the anthropomorphic phantom. Each measurement was performed with position phantoms at the isocenter and also at the positions ±2, ±4, and ±6 cm under and above the isocenter. The impact of miscentering on noise was also observed. Our results show that the dose to the eye decreases with increasing position of the phantoms from the isocenter, and increases with decreasing position of the phantoms from the isocenter. Miscentering above the isocenter can potentially reduce the dose to the eye lens, which is a sensitive organ to ionizing radiation.

Quantifying dose-creep for Skull and chest radiography using dose area product and entrance surface dose: Phantom study

Digital radiography allows for image manipulation, giving radiographers the ability to adjust the grey level of the image using latitude-algorithm. In doing such, patients receiving unnecessary radiation-dose often goes undetected. The aim of present study has been to quantify dose-creep using dose area product (DAP) and entrance surface dose (ESD) for skull and chest exams using phantoms. Furthermore, to investigate possible correlation between DAP and ESD. Adult anthropomorphic phantoms were used to produce a series of anterior-posterior (AP) and lateral (LAT) skull and chest images varying the mAs to yield optimal and overexposed images for each projection. Thermoluminescent dosimeter (TLD) was placed at the surface of the centered phantom to measure the ESD. DAP values were gathered and correlated with ESD values using Spearman's correlation coefficient test while Wilcoxon-test was used to calculate the statistical difference. Dose-creep was calculated as the percentage difference between optimum and over exposure results. The highest estimated dose-creep of (51%) was demonstrated for chest AP projection as calculated from DAP values. Using Spearman's correlation, a significant strong positive correlation was revealed for DAP and ESD optimum (r = 0.916, p = 0.0006) and overexposure (r = 0.8992, p = 0.0009), respectively. Dose-creep can be considerably high raising the need for thorough investigations and society awareness.

S VALUES FOR NEUROIMAGING PROCEDURES ON KOREAN PEDIATRIC AND ADULT HEAD COMPUTATIONAL PHANTOMS.

Over the past decades, the application of single-photon emission computed tomography and positron emission tomography in neuroimaging has markedly increased. In the current study, we used a series of Korean computational head phantoms with detailed cranial structures for 6-, 9-, 12-, 15-y-old children and adult and a Monte Carlo transport code, MCNPX, to calculate age-dependent specific absorbed fraction (SAF) for mono-energetic electrons ranging from 0.01 to 4 MeV and S values for seven radionuclides widely used in nuclear medicine neuroimaging for the combination of ten source and target regions. Compared to the adult phantom, the 6-y phantom showed up to 1.7-fold greater SAF (cerebellum < cerebellum) and up to 1.4-fold greater S values (vitreous body < lens) for 123I. The electron SAF data, combined with our previous photon SAF data, will facilitate absorbed dose calculations for various cranial structures in patients undergoing neuroimaging procedures.

MCNP SIMULATIONS WITH A PERSONALISED VOXEL PHANTOM TO VERIFY 131I CONTENT IN THYROID ESTIMATED BASED ON MEASUREMENTS WITH AN NaI(Tl) SPECTROMETER.

One of the authors (O.K.) stayed in the area located ~110 km south from the Fukushima Daiichi Nuclear Power Plant during the arrival of radioactive plumes released into the environment due to the accident in March 2011 in Japan. A previous study determined his 131I thyroid content using an NaI(Tl) spectrometer. The one remaining issue was to investigate the measurement error due to inevitable differences in the configuration (e.g. the thyroid shape and volume) between the physical phantom employed for calibration of the spectrometer and the real subject. In the present study, Monte Carlo simulations for the thyroid measurements were performed using the Monte Carlo N-Particle (MNCP) code to investigate discrepancies in peak efficiencies of the spectrometer between the personalised voxel phantom created from O.K.'s magnetic resonance images and the several typical/reference phantoms that exist. As a result, the peak efficiencies for the Oak Ridge Institute of Nuclear Studies (ORINS) phantom were found to be comparable to those for the reference voxel phantoms reproducing realistic human anatomy (the Adult Male phantom and the Japanese Male phantom). The peak efficiency for the personalised phantom, on the other hand, was fairly close to that of the other physical phantom (the Transfer phantom) actually used for the calibration of the spectrometer, suggesting that the 131I thyroid content determined for him in the previous study was sufficiently accurate. The discrepancies of peak efficiencies at the primal photon energy of 131I (365 keV) among the different phantoms were improved by extending the distance between the neck and the spectrometer; however, the appropriate measurement geometry in an actual situation will depend on the primary purpose of the measurements and should be determined accordingly.

Use of bismuth shield for protection of superficial radiosensitive organs in patients undergoing computed tomography: a literature review and meta-analysis.

The study aimed to assess the effect of bismuth (Bi) shielding on dose reduction and image quality in computed tomography (CT) through a literature review. A search was conducted in the following databases: Web of Science, PubMed, Google Scholar, and Scopus. Studies that reported estimated dose reduction with bismuth shielding during imaging of the eye, thyroid, and breast were included, and a meta-regression analysis was used to examine the influence of the CT scanner type on the dose reduction. The studies included a total of 237 patients and 34 pediatric and adult anthropomorphic phantoms for whom the radiation dose was reported. Bismuth shielding was recommended in 88.89% of the studies based on the maintenance of appropriate image quality under shielding. Noise associated with Bi shielding was 7.5%, 263%, and 23.5% for the eye, thyroid, and breast, respectively. The fixed-effects pooled estimate of dose reduction was 34% (95% CI: 13-55; p < 0.001) for the eye, 37% (95% CI 14-61; p < 0.001) for the thyroid, and 36% (95% CI 36-55; p < 0.001) for the breast. The image quality, usage of foams, CT scanner type, beam energies, and backscatter radiation were important factors that directly affected the efficacy of Bi shielding to reduce the radiation dose at the superficial radiosensitive organs.

Internal radiation dose assessment of radiopharmaceuticals prepared with cyclotron-produced 99m Tc.

Technetium-99m (99m Tc) is the radioisotope most widely used in diagnostic nuclear medicine. It is readily available from 99 Mo/99m Tc generators as the β- decay product of the 99 Mo (T&frac12; =66h) parent nuclide. This latter is obtained as a fission product in nuclear reactors by neutron-induced reactions on highly enriched uranium. Alternative production routes, such as direct reactions using proton beams on specific target materials [100 Mo(p,2n)99m Tc], have the potential to be both reliable and relatively cost-effective. However, results showed that the 99m Tc extracted from proton-bombarded 100 Mo-enriched targets contains small quantities of several Tc radioisotopes (93m Tc, 93 Tc, 94 Tc, 94m Tc, 95 Tc, 95m Tc, 96 Tc, and 97m Tc). The aim of this work was to estimate the dose increase (DI) due to the contribution of Tc radioisotopes generated as impurities, after the intravenous injection of four radiopharmaceuticals prepared with cyclotron-produced 99m Tc (CP-99m Tc) using 99.05% 100 Mo-enriched metallic targets. Four 99m Tc radiopharmaceuticals (pertechnetate, sestamibi (MIBI), hexamethylpropylene-amine oxime (HMPAO) and disodium etidronate (HEDP)) were considered in this study. The biokinetic models reported by the International Commission on Radiological Protection (ICRP) for each radiopharmaceutical were used to define the main source organs and to calculate the number of disintegrations per MBq that occurred in each source organ (Nsource ) for each Tc radioisotope present in the CP-99m Tc solution. Then, target organ equivalent doses and effective dose were calculated for each Tc radioisotope with the OLINDA/EXM software versions 1.1 and 2.0, using the calculated Nsource values and the adult male phantom as program inputs. Total effective dose produced by all Tc isotopes impurities present in the CP-99m Tc solution was calculated using the fraction of total activity corresponding to each radioisotope and compared with the effective dose delivered by the generator-produced 99m Tc. In all cases, the total effective DI of CP-99m Tc radiopharmaceuticals calculated with either versions of the OLINDA software was less than 10% from 6 up to 12h after EOB. 94m Tc and 93m Tc are the Tc radioisotopes with the highest concentration in the CP-99m Tc solution at EOB. However, their contribution to DI 6h after EOB is minimal, due to their short half-lives. The radioisotopes with the largest contribution to the effective DI are 96 Tc, followed by 95 Tc and 94 Tc. This is due to the types of their emissions and relatively long half-lives, although their concentration in the CP-99m Tc solution is five times lower than that of 94m Tc and 93m Tc at the EOB. The increase in the radiation dose caused by other Tc radioisotopes contained in CP-99m Tc produced as described here is quite low. Even though the concentrations of the 94 Tc and 95 Tc radioisotopes in the CP-99m Tc solution exceed the limits established by the European Pharmacopoeia, CP-99m Tc radiopharmaceuticals could be used in routine nuclear medicine diagnostic studies if administered from 6 to 12h after the EOB, thus maintaining the effective DI within the 10% limit.

Study for pediatric protocol optimization in chest CT scans

Radiological exams are increasingly used in clinic for diagnostic analysis of different types of pathologies. These tests are associated with a dose that is received by the patient. In addition, the risks in exposure to ionizing radiation are different according to the group which the individual belongs. According to age, the group of children is more radiosensitive than adults. In this work we have obtained values of the air-weighted kerma index for chest scans studies in a Genereal Electric Computed Tomography (CT) scanner model Discovery with 64-channels. Using an adult protocol, two scans have been performed, one using a cylinder standard PMMA phantom while the second one has used an oblong chest phantom designed for a two year old pediatric patient. Furthermore, other protocols have been selected by varying the X-ray tube current but maintaining the same voltage, in order to obtain a reduction in the dose received by the pediatric patient but maintaining the image quality. The use of the adult protocol in the child phantom has generated a value in the air-weighted kerma index 89.47% greater than that received using the adult phantom. As small patients receive higher doses, the use of specific protocols for children is important for the dose reduction in CT tests. Due to the different characteristics of CT scanners and in order to optimize these protocols with regard to dose and diagnostic image quality, there is a need to have pediatric phantoms in health centers

Assessment of exposure after injection of 99mTc-labeled intact monoclonal antibodies and their fragments into humans.

Human pharmacokinetics and internal radiation dosimetry of normal organs after injection with the 99mTc-labeled monoclonal antibody (intact and fragments) are simulated by the WinAct program and IDAC (Internal Dose Assessment by Computer) software. The WinAct program is used to calculate the cumulative activity in organs and tissues. The calculated cumulative activity is inputted to the IDAC software, an internal dosimetry program for nuclear medicine based on the International Commission on Radiological Protection (ICRP) adult reference voxel phantom, and the absorbed doses by the organs and tissues are estimated. The obtained absorbed doses for the 99mTc-labeled monoclonal antibody (intact and fragments) are compared with the published figures by ICRP-128. The WinAct program method to calculate the cumulative activity is more accurate, as the fraction distribution, Fs, is described and calculated for organs, not only for intake, as in the ICRP model, but also for elimination.