Calculate Organ Doses Research Articles

Organ doses evaluation for chest computed tomography procedures with TL dosimeters: Comparison with Monte Carlo simulations.

PurposeTo evaluate organ doses in routine and low‐dose chest computed tomography (CT) protocols using an experimental methodology. To compare experimental results with results obtained by the National Cancer Institute dosimetry system for CT (NCICT) organ dose calculator. To address the differences on organ dose measurements using tube current modulation (TCM) and fixed tube current protocols.MethodsAn experimental approach to evaluate organ doses in pediatric and adult anthropomorphic phantoms using thermoluminescent dosimeters (TLDs) was employed in this study. Several analyses were performed in order to establish the best way to achieve the main results in this investigation. The protocols used in this study were selected after an analysis of patient data collected from the Institute of Radiology of the School of Medicine of the University of São Paulo (InRad). The image quality was evaluated by a radiologist from this institution. Six chest adult protocols and four chest pediatric protocols were evaluated. Lung doses were evaluated for the adult phantom and lung and thyroid doses were evaluated for the pediatric phantom. The irradiations were performed using both a GE and a Philips CT scanner. Finally, organ doses measured with dosimeters were compared with Monte Carlo simulations performed with NCICT.ResultsAfter analyzing the data collected from all CT examinations performed during a period of 3 yr, the authors identified that adult and pediatric chest CT are among the most applied protocol in patients in that clinical institution, demonstrating the relevance on evaluating organ doses due to these examinations. With regards to the scan parameters adopted, the authors identified that using 80 kV instead of 120 kV for a pediatric chest routine CT, with TCM in both situations, can lead up to a 28.7% decrease on the absorbed dose. Moreover, in comparison to the standard adult protocol, which is performed with fixed mAs, TCM, and ultra low‐dose protocols resulted in dose reductions of up to 35.0% and 90.0%, respectively. Finally, the percent differences found between experimental and Monte Carlo simulated organ doses were within a 20% interval.ConclusionsThe results obtained in this study measured the impact on the absorbed dose in routine chest CT by changing several scan parameters while the image quality could be potentially preserved.

57. Comparison of organ dose results from different software in CT exams

Purpose During last years the number of CT exams increased causing an increment of collective dose. Our purpose was to estimate organ doses for the main CT scans performed in our hospital to provide data useful for cancer risk estimation. We calculated organ dose using different commercial software and evaluated the influence of exposure parameters. Methods Using the RDIM system Nexo[DOSE]® (Bracco, Italy) we collected exposure information for the main CT protocols: scanner, CTDIvol, voltage, collimation, pitch. The scan region was deduced from the CT images of a patients’ sample under the specific procedure. Using the RadLex Playbook, CT protocols are clustered in macro-areas with the same scan region and phases number. So, starting from 595 protocols, we have obtained only 12 stylized protocols to simulate. For these protocols, we calculated organ dose using CT-Expo, NCICT, NCICTX and Virtual Dose. Each software uses its own phantom family. CT-Expo uses the first generation of computational mathematical phantoms. NCICT, NCICTX and Virtual Dose use a hybrid-voxel phantom, more realistic and, for the last two software, adaptable to the patient habitus. Since the scan length is the primary origin of variability in the dose calculation, for each protocol the organs completely inside the scan region have been considered separately from the partially irradiated and from distributed ones. Results Only using CT-Expo organ doses present dependence from collimation, pitch and scanner model. Discrepancies using different software are within 30% for organs inside the scan region, while they can be more significant, till 150–200%, for the other organs. Conclusions To manage the organ dose information, a data interpretation is needed, which could explain the discrepancies between results from different software. Since the result is strongly related to the algorithm and to the phantom used, the organ dose result for CT exam is to relate to the software.

53. IGRT Cone Beam CT: Patient specific organ dose evaluation

Purpose Daily images from CBCT could deliver significant dose to the patient, which should be considered and evaluated. It is essential to associate the absorbed dose delivered by the imaging procedures to the treatment of each patient. Aim of this work is to calculate organ doses for patients undergoing Cone Beam CT (CBCT) when treated with radiotherapy. Methods The system in use was an Elekta CBCT (XVI) and the protocols analysed were four: head, pelvis, chest and chest 4D with different parameters. The formula for organ dose calculation was obtained from Rampado et al. [1] where dose to organs were evaluated by means of Monte Carlo simulation in phantom; the effect of patient size were also accounted for. Dose to organs involved in CBCT scans is: D T = D W , 1 Ph · ( D T / D W , 1 Ph ) tab · a · e - bx where D W , 1 Ph is the measured dose in a phantom for the specific protocol, x is the effective diameter of the patient, ( D T / D W , 1 Ph ) tab , a and b are tabulated data from the article cited above. Patients were analyzed from March to June 2017. For each case were registered: the effective diameter from simulation CT, CBCT protocol, number of CBCT scans. Results Two hundred patients were considered. For head protocol, the mean CBCT doses were about 20 ± 10 mGy for all organs. Instead, doses of about 400 ± 150 mGy were evaluated for pelvis protocol. CBCT Doses for Chest 4D protocol were lower than other chest ones (about 50 ± 25 mGy vs 400 ± 150 mGy). This difference was due to number of CBCT scans/treatment fractions. Conclusions Doses from CBCT procedures should be accounted for; based on organ doses calculation, a program of dose optimization could be performed.

35 Calculation of organ doses for CT examination

Introduction Ionising radiation needs to be precisely evaluated since CT scan is the main radiological examination today. Biological effects caused by radiation are estimated with computational methods as it’s not possible to measure the real doses delivered directly to a specific organ. The DOSITRACE software is a Dose Archiving and Communication System (DACS) based on a new calculation method which allows a more reliable estimation of organ doses. The aim of this study was to compare our results with the results given by the VIRTUALDOSE [1] software using the Monte-Carlo method. Methods CTDIvol, current and rotation time for each acquisition were used to calculate organ doses (ICPR). Four CT protocols (abdomen-pelvis, chest-abdomen-pelvis, chest and thorax) were used with three different CT scans. Thirty patients were selected for each protocol. In total, CT scan exams were analysed and our results were compared with the ones obtained with the VIRTUALDOSE software. Results There was only a 20% difference in the estimation of organ doses between the VIRTUALDOSE and DOSITRACE software’s results which is not statistically significant. Conclusions We demonstrated that DOSITRACE is a reliable software in order to calculate organ doses.

Investigation the potential of Boron neutron capture therapy (BNCT) to treat the lung cancer

Introduction: Boron neutron capture therapy (BNCT) is recommended to treat the glioblastoma tumor. It is well known that neuron beams are more effective treatment than photon beams to treat hypoxia tumors due to interaction of neutron with nucleus and production of heavy particles such as 7Li and alpha particle. In this study to evaluate the suitability of BNCT for treating of lung cancer, the dose distributions of neutron beam were calculated in lung tumor volume and in peripheral organs at risk (OARs). Materials and Methods: Dose distribution in Boron neutron capture therapy to treat lung cancer was calculated by MCNPX (2.6.0) code. A 3×3×3 cm3 tumor was located in left lung of ORNL phantom and was irradiated with a rectangular field of neutron positioned at surface source distance (SSD) of 10 cm. recommended spectrum of MIT (Massachusetts Institute of Technology) was used. Tumor was loaded with different concentrations of Boron 0, 10, 30 and 60 ppm. Dose delivered to OARs such as heart, spinal cord, right lung … were calculated. Results: The results show that neutron flux significantly decreased followed to penetrate in lung tissue. Neutron flux decreased in all energy bins of irradiated MIT spectrum; maximum fall- off occurred in the range of epithermal energy. Dose distribution was not depended to SSD. The absorbed dose in tumor was 2.16×10-14, 2.6×10-14, 3.44×10-14 and 4.72×10-14 Gy(per one irradiated neutron from source) for boron concentration of 0, 10, 30 and 60 ppm, respectively. From the OARs, the heart tissue absorbed the maximum dose of 1.66×10-15 Gy (per one irradiated neutron from source). Conclusion: Our simulated model was successful to calculated organ doses in BNCT. As the boron concentration in lung tumor increases, absorbed dose increased while dose uniformity trended downward. Our results show that the MIT neutron source is suitable to treat deep lung tumors while OVRs’ dose maintains within the threshold dose.

Development of Prototype Iranian male pelvic phantom for internal dosimetry

Introduction: Existing phantoms have been constructed based on Caucasian, non-Caucasian and race-specific datasets. According to previous studies made efforts to present Korean- specific phantoms and Chinese female phantom based on CVH dataset due to compare the resulting internal dosimetry with the Caucasian based data showed possible racial difference in human anatomy between Caucasian and non- Caucasian populations. These phantoms have been used for internal radionuclide dosimetry and other nuclear-medicine applications. Specific absorbed fractions (SAF) are tools for internal dose estimation of radionuclide intake. The differences were due to the racial and anatomical differences in organ mass and inter-organ distance. Many studies have been tried to provide an accurate and reliable data for internal radiation dose calculations. Therefor we construct an Iranian computational phantom to evaluate radiation dose organs within male pelvic region based on Iranian datasets. Internal dosimetry on organ is getting more important from the viewpoint of radiation protection of organ at risk. Materials and Methods: The first version of computational Iranian male pelvis phantom(PIPM) is provided by 5 MRI datasets of Iranian male for precise organ dose calculation, at first organs within pelvic region are segmented by enhancing their margins in each slice, determination of organs volume then, prototype Iranian male pelvis phantom was developed by modifying the equation of internal organs of the ORNL adult phantom finally, this phantom was imported to general purpose Monte Carlo code to simulate photon transport from internal radiation source. Results: The results showed that the individual comparable phantom can be calculated with acceptable accuracy using geometric registration. Comparison of dose calculation for Iranian male pelvic, MIRD and RADAR phantoms showed that differences of self-SAF were affected by organ volume differences. The average of the percent SAF deviation was calculated in testes organ -7.73%, -5.53% for PIMP phantom into MIRD and RADAR phantoms respectively. The largest deviation was observed in urinary bladder organ follow as 37.3%, 52.3% into MIRD and RADAR phantoms and it is shown -23.5% variations in self-SAF prostate organ into MIRD phantom. This phantom could be used for absorbed dose calculation of Iranian male pelvic region with acceptable accuracy in nuclear medicine. Conclusion: A prototype computational Iranian adult male pelvis phantom was represented from 5 Iranian adult males; the results showed that comparable phantom can be calculated internal absorbed dose with significant differences. Accurate voxel phantom is needed for dosimetric simulation in nuclear medicine for malignant tumors in male pelvic region. However, most of the existing voxel phantoms are constructed on the basis of Caucasian or non-Chinese population. It might be provided first Iranian male reference volume organ dataset for future researches.

Dosimetric assessment of the exposure of radiotherapy patients due to cone-beam CT procedures.

Cone-beam computed tomography (CBCT) is widely used for pre-treatment verification and patient setup in image-guided radiation therapy (IGRT). CBCT imaging is employed daily and several times per patient, resulting in potentially high cumulative imaging doses to healthy tissues that surround exposed target organs. Computed tomography dose index (CTDI) is the parameter used by CBCT equipment as indication of the radiation output to patients. This study aimed to increase the knowledge on the relation between CBCT organ doses and weighted CTDI (CTDIW) for a thorax scanning protocol. A CBCT system was modelled using the Monte Carlo (MC) radiation transport program MCNPX2.7.0. Simulation results were validated against half-value layer (HVL), axial beam profile, patient skin dose (PSD) and CTDI measurements. For organ dose calculations, a male voxel phantom ("Golem") was implemented with the CBCT scanner computational model. After a successful MC model validation with measurements, a systematic comparison was performed between organ doses (and their distribution) and CTDI dosimetry concepts [CTDIW and cumulative dose quantities f100(150) and [Formula: see text]]. The results obtained show that CBCT organ doses vary between 1.2 ± 0.1mGy and 3.3 ± 0.2mGy for organs located within the primary beam. It was also verified that CTDIW allows prediction of absorbed doses to tissues at distances of about 5cm from the isocentre of the CBCT system, whereas f100(150) allows prediction of organ doses at distances of about 10cm from the isocentre, independently from its location. This study demonstrates that these dosimetric concepts are suitable methods that easily allow a good approximation of the additional CBCT imaging doses during a typical lung cancer IGRT treatment.

ORGAN DOSE ESTIMATION ACCOUNTING FOR UNCERTAINTY FOR PEDIATRIC AND YOUNG ADULT CT SCANS IN THE UNITED KINGDOM.

Since our previous publication of organ dose for the pediatric CT cohort in the UK, there have been questions about the magnitude of uncertainty in our dose estimates. We therefore quantified shared and unshared uncertainties in empirical CT parameters extracted from 1073 CT films (1978-2008) from 36 hospitals in the study and propagated these uncertainties into organ doses using Monte Carlo random sampling and NCICT organ dose calculator. The average of 500 median brain and marrow doses for the full cohort was 35 (95% confidence interval: 30-40) mGy and 6 (5-7) mGy, respectively. We estimated that shared uncertainty contributed ~99% of coefficient of variation of median brain doses in brain scans compared to unshared uncertainty (1% contribution). We found that the previous brain doses were slightly underestimated for <1990 and overestimated for >1990 compared to the results in the current study due to the revised CTDI models based on CT films.

Influence of the SPECT calibration source position on the absorbed dose calculation for 131I-NaI therapy using GATE simulations

Many research groups have studied nuclear medicine image quantification to improve its accuracy in dose estimation. This work aims to evaluate the influence of the source calibration position for absorbed dose calculation for a 131I-NaI therapy using Monte Carlo (MC) simulations. The calibration approach consisted of a cylindrical phantom filled with water. A cylindrical 131I source with 361.1 ± 3.6 kBq ml−1 was positioned at the center of the phantom and its outer part. Images were acquired with 150 00 counts per projection image acquired with SPECT detector (high counts density—HCD) and 3000 counts per projection (low counts density—LCD). MC simulations, performed with GATE code, were validated by comparing the S values of a water sphere uniformly filled with 131I, as from the sphere model of OLINDA/EXM 1.1. Calibration factors deviation between central and peripheral calibrations is more significant for HCD (18.3%) than for LCD images (3.7%). The 3D dose distribution map obtained from GATE resulted in a dose factor equal to 1.5 × 10−3 mGy/(MBq.s). For both HCD and LCD images, the commonly used approach, which employs the central source calibration to obtain the dose from a peripheral source, resulted in dose overestimation. Results suggest that organ dose calculation can be improved considering the organ position in the field of view. Finally, patients’ radiation protection in dosimetry studies could be improved considering the calibration source position, due to the superior accuracy in dose calculation.

Organ at risk dose measurements following radiotherapy treatment for breast cancer patients

Radiotherapy technologies are one of the most common treatments for cancer, they have been successfully used to damage cancer cells, with as little harm as possible to nearby healthy cells, however Secondary cancer risk following radiotherapy is an increasingly important topic in clinical oncology with impact on treatment decision making and on patient management. The objective of this study is to measure the skin radiation dose received by the treated breast as well as the dose to the lungs in cancer patients undergoing breast radiotherapy and estimate the probability for radiation-induced cancer, i.e. secondary cancer and the probability of lung cancer. Usage of RANDO phantoms and GafChromic dosimetry films to do dose measurements during breast radiotherapy. Measured dose and calculated organ dose from patients were compared. The calculated doses were done using the effective dose formula. Measured point doses of both lungs were compared to those calculated by TPS (treatment planning system). Relative Risk (RR) and Probability of Causation (PC) of lungs- probability of cancer- were calculated from patient’s mean doses to the organs (right lung and left lung) using the model described in BEIR V report. RR mean values were 1.278 and 1.032 for ipsilateral and contralateral lungs respectively. In addition, PC mean values were 20.93 % and 3.099% for ipsilateral and contralateral lungs respectively. Breast cancer patients are susceptible to an increased risk of secondary cancer of ipsilateral lungs more than in the contralateral ones.

3D image acquisition in scoliosis correction surgery: Radiation exposure of a paediatric patient cohort

3D spine imaging has become a popular technique in orthopaedic surgery to assist with the placement of screws and rods for the treatment of scoliosis. It is most often used in combination with navigation software to reduce the risk of surgical-induced patient paralysis. One way to acquire this type of imaging is to use an X-ray c-arm that rotates around the patient, mimicking a cone beam CT acquisition. Although this technique has been successfully implemented in many centres, there is a deficit of information in the literature with regard to the consequent patient radiation exposure, in particular, where an eccentric or non-circular orbit is utilised. This information is particularly important for paediatric patients, as they are the most likely candidates for this type of surgery. Our study estimates the radiation dose to paediatric patients who have undergone scoliosis correction surgery, using the proprietary non-circular orbit employed by a Ziehm Vision RFD 3D C-arm. We estimate and compare patient organ doses using this eccentric orbit with one where a simple circular orbit is assumed. We further compare our calculated organ doses with those imparted by traditional 2D fluoroscopic techniques, and calculate the risk of future radiation induced cancer for this patient cohort. The doses presented here will be useful to other centres in establishing diagnostic reference levels for this increasingly common technique.

OA138] Organ dose estimate in CT exams: Inter-comparison of four commercial software and characterization of the main CT procedures used in asst Niguarda (Milan, Italy)

Purpose To compare organs dose evaluation from different commercial software and to characterize the main CT procedures of our hospital to provide data for radiation risk estimation. Methods We collected the information regarding the exposure for the main CT procedures used in our hospital through the RDIM system Nexo[DOSE]® (Bracco, Italy). We analysed the main CT protocols and clustered them in macro-groups, considering scan region and phases number. For each group, we defined a stylized protocol, which summarizes the most common exam features and mean dosimetric parameters, so that it can represent the whole macro-cluster. In the stylized protocol, some CT parameters were set equally to the most frequent values (axial/spiral mode, voltage, collimation, pitch, slice thickness), while the remaining were defined as the median values (mAs, CTDIvol, DLP, scan length). The scan region for each phase was deduced from the CT images of a patients’ sample under the specific procedure. Then, we calculated organ dose using four commercial software: CT-Expo, NCICT, NCICTX and Virtual Dose. Each software uses its own phantom family. CT-Expo uses the first generation of computational mathematical phantoms. NCICT, NCICTX and Virtual Dose use a hybrid-voxel phantom, more realistic and, for the last two software, adaptable to the patient habitus. Results Starting from about 35000 CT exams and 595 protocols, we obtained 13 macro-groups. In comparison with the mean value, the average range of dose values from different software is 25% for organs inside the scan region and 80% for organs partially irradiated. CT-Expo is the only software that shows dependence from collimation, pitch, slice thickness and scanner model. For the others software, the only parameters affecting organ dose calculation are voltage and CTDIvol. In this study, the discrepancies obtained changing voltage are within 15% for all software. On the other hand, the scan length is the primary source of variability in the dose calculation. Conclusions Organ dose estimate is the first step to calculate effective dose and to evaluate radiation risk: a deep and critical interpretation of the results is necessary since the values range can cause a large variation in final estimate.

Estimating the uncertainty of calculated out-of-field organ dose from a commercial treatment planning system.

Therapeutic radiation to cancer patients is accompanied by unintended radiation to organs outside the treatment field. It is known that the model‐based dose algorithm has limitation in calculating the out‐of‐field doses. This study evaluated the out‐of‐field dose calculated by the Varian Eclipse treatment planning system (v.11 with AAA algorithm) in realistic treatment plans with the goal of estimating the uncertainties of calculated organ doses. Photon beam phase‐space files for TrueBeam linear accelerator were provided by Varian. These were used as incident sources in EGSnrc Monte Carlo simulations of radiation transport through the downstream jaws and MLC. Dynamic movements of the MLC leaves were fully modeled based on treatment plans using IMRT or VMAT techniques. The Monte Carlo calculated out‐of‐field doses were then compared with those calculated by Eclipse. The dose comparisons were performed for different beam energies and treatment sites, including head‐and‐neck, lung, and pelvis. For 6 MV (FF/FFF), 10 MV (FF/FFF), and 15 MV (FF) beams, Eclipse underestimated out‐of‐field local doses by 30%–50% compared with Monte Carlo calculations when the local dose was <1% of prescribed dose. The accuracy of out‐of‐field dose calculations using Eclipse is improved when collimator jaws were set at the smallest possible aperture for MLC openings. The Eclipse system consistently underestimates out‐of‐field dose by a factor of 2 for all beam energies studied at the local dose level of less than 1% of prescribed dose. These findings are useful in providing information on the uncertainties of out‐of‐field organ doses calculated by Eclipse treatment planning system.

Dosimetry is Key to Good Epidemiology: Workers at Mallinckrodt Chemical Works had Seven Different Source Exposures.

Mallinckrodt Chemical Works was the earliest uranium processing facility in the Manhattan Project, beginning in 1942. Even then, concern existed about possible health effects resulting from exposure to radiation and pitchblende dust. This concern was well founded as the facility processed Belgian Congo pitchblende ore that was up to 60% pure uranium with high U content and up to 100 mg of radium per ton. Workers were exposed to external gamma radiation plus internal radiation from inhalation and ingestion of pitchblende dust (uranium, radium, and silica). Multiple sources of exposure were available for organ dose reconstruction to a degree unique for an epidemiologic study. Personal film badge measures available from 1945 captured external exposures. Additional external exposure included 15,518 occupational medical x-rays and 210 radiation exposure records from other facilities outside of Mallinckrodt employment. Organ dose calculations considered organ-specific coefficients that account for photon energy and job-specific orientation of workers to the radiation source during processing. Intakes of uranium and radium were based on 39,451 uranium urine bioassays and 2,341 breath radon measurements, and International Commission on Radiological Protection (ICRP) Publication 68 biokinetic models were used to estimate organ-specific radiation absorbed dose. Estimates of exposure to airborne radon and its short-lived progeny were based on radon measurements in work areas where radium-containing materials were handled or stored, together with estimated exposure times in these areas based on job titles. Dose estimates for radon and its short-lived progeny were based on models and methods recently recommended in ICRP Publication 137. This comprehensive dosimetric approach follows methods outlined by the National Council on Radiation Protection Scientific Committee 6-9 for the Million Worker Study. Annual doses were calculated for six organs: lung, brain, heart, kidney, colon and red bone marrow. Evaluation and adjustment for individual cumulative measures of pitchblende dust inhalation were made for lung and kidney diseases.

Assessment of PCXMC for patients with different body size in chest and abdominal x ray examinations: a Monte Carlo simulation study

A PC Program for x ray Monte Carlo (PCXMC) has been used to calculate organ doses in patient dosimetry and for the exposure assessment in epidemiological studies of radiogenic health related risks. This study compared the dosimetry from using the built-in stylized phantoms in the PCXMC to that of a newer hybrid phantom library with improved anatomical realism. We simulated chest and abdominal x ray projections for 146 unique body size computational phantoms, 77 males and 69 females, with different combinations of height (125–180 cm) and weight (20–140 kg) using the built-in stylized phantoms in the PCXMC version 2.0.1.4 and the hybrid phantom library using the Monte Carlo N-particle eXtended transport code 2.7 (MCNPX). Unfortunately, it was not possible to incorporate the hybrid phantom library into the PCXMC. We compared 14 organ doses, including dose to the active bone marrow, to evaluate differences between the built-in stylized phantoms in the PCXMC and the hybrid phantoms (Cristy and Eckerman 1987 Technical Report ORNL/TM-8381/V1, Oak Ridge National Laboratory, Eckerman and Ryman 1993 Technical Report 12 Oak Ridge, TN, Geyer et al 2014 Phys. Med. Biol. 59 5225–42). On average, organ doses calculated using the built-in stylized phantoms in the PCXMC were greater when compared to the hybrid phantoms. This is most prominent in AP abdominal exams by an average factor of 2.4-, 2.8-, and 2.8-fold for the 10-year-old, 15-year-old, and adult phantoms, respectively. For chest exams, organ doses are greater by an average factor of 1.1-, 1.4-, and 1.2-fold for the 10-year-old, 15-year-old, and adult phantoms, respectively. The PCXMX, due to its ease of use, is often selected to support dosimetry in epidemiological studies; however, it uses simplified models of the human anatomy that fail to account for variations in body morphometry for increasing weight. For epidemiological studies that use PCXMC dosimetry, associations between radiation-related disease risks and organ doses may be underestimated, and to a greater degree in pediatric, especially obese pediatric, compared to adult patients.

DEVELOPMENT OF A SET OF MESH-BASED AND AGE-DEPENDENT CHINESE PHANTOMS AND APPLICATION FOR CT DOSE CALCULATIONS

Phantoms for organ dose calculations are essential in radiation protection dosimetry. This article describes the development of a set of mesh-based and age-dependent phantoms for Chinese populations using reference data recommended by the Chinese government and by the International Atomic Energy Agency (IAEA). Existing mesh-based RPI adult male (RPI-AM) and RPI adult female (RPI-AF) phantoms were deformed to form new phantoms according to anatomical data for the height and weight of Chinese individuals of 5 years old male, 5 years old female, 10 years old male, 10 years old female,15 years old male, 15 years old female, adult male and adult female-named USTC-5 M, USTC-5F, USTC-10M, USTC-10F, USTC-15M, USTC-15F, USTC-AM and USTC-AF, respectively. Following procedures to ensure the accuracy, more than 120 organs/tissues in each model were adjusted to match the Chinese reference parameters and the mass errors were within 0.5%. To demonstrate the usefulness, these new set of phantoms were combined with a fully validated model of the GE LightSpeed Pro 16 multi-detector computed tomography (MDCT) scanner and the GPU-based ARCHER Monte Carlo code to compute organ doses from CT examinations. Organ doses for adult models were then compared with the data of RPI-AM and RPI-AF under the same conditions. The absorbed doses and the effective doses of RPI phantoms are found to be lower than these of the USTC adult phantoms whose body sizes are smaller. Comparisons for the doses among different ages and genders were also made. It was found that teenagers receive more radiation doses than adults do. Such Chinese-specific phantoms are clearly better suited in organ dose studies for the Chinese individuals than phantoms designed for western populations. As already demonstrated, data derived from age-specific Chinese phantoms can help CT operators and designers to optimize image quality and doses.

Comparison of the effectiveness of polymer gel dosimeters (Magic and Pagatug) for organ dose calculation in brachytherapy, nuclear medicine and teletherapy

Purpose: To investigate and compare two polymer gel dosimeters, Magic and Pagatug, as organ dosimeters for 3D measurement of dose distribution in brachytherapy, nuclear medicine and teletherapy. Methods: Magic and Pagatug polymer gels were compared with soft tissue based on irradiation with low energy photons during therapeutic applications. Comparison was simulated using Monte-Carlobased MCNPX code. ORNL phantom–Female was used to model some vital organs (kidneys, ovaries and uterus). The right kidney was proposed to be the source of irradiation and the two organs were exposed to this irradiation. Results : The effective atomic numbers of soft tissue, Magic and Pagatug were 6.86134, 7.07 and 7.2884, respectively. The results showed that Magic and Pagatug, were comparable to soft tissue with regard to application in nuclear medicine and teletherapy. Differences between gel dosimeters and soft tissue were defined as the dose responses. This difference was < 8.1, < 4 and < 76.8 % for teletherapy, nuclear medicine and brachytherapy, respectively. Conclusion: Due to slight differences between the effective atomic numbers of these polymer gel dosimeters and soft tissue, the polymer gels are not suitable for brachytherapy since the photoelectric interaction is dominant for low energy photons, and the interaction relates to Z4. The results demonstrate that the gel dosimeters are best suited for nuclear medicine. Keywords : Magic, Pagatug, Brachytherapy, Nuclear medicine, Teletherapy, Organ dosimetry, Soft tissue

ESTIMATION OF FEMALE RADIATION DOSES AND BREAST CANCER RISK FROM CHEST CT EXAMINATIONS.

Breast organ doses, effective doses and lifetime attributable risk (LAR) of breast cancer from chest CT scans are presented for 200 female patients surveyed from 10 hospitals in the West Bank and Gaza Strip, Palestine. Patient data were collected and organized in a database from May to November 2016. Data include age (15-80 years), weight, height, and calculated body mass index. Exposure data were also recorded for every examination. Exposure data includes milliampere-second (mAs), X-ray tube kilovoltage (kVp), computed tomography dose index, dose length product, manufacturer, name and type of operated CT scanner. Organ and effective doses were evaluated using a web-based commercially available Monte Carlo software: VirtualDose™CT, a product of Virtual Phantoms, Inc. The software utilizes male and female tissue equivalent phantoms of all ages and sizes including pregnant patients. The corresponding phantom was selected for every patient according to patient's tomographic parameters. Calculated organ doses were used to estimate the LAR of breast cancer according to BEIR VII Phase 2 report. It was found that radiation doses resulting from the same exam vary widely between different hospitals, depending on the parameters used and the type of scanner. For all patients, the breast organ dose ranged from 6.5 to 28 mGy per examination, with an average breast organ dose of 15 mGy. The effective dose from chest CT scan per examination ranged from 3 to 14.7 mSv with an average of 7 mSv. For younger females (15-29 years), the LAR of breast cancer risk was estimated to be around 0.05%. For older female patients (60-79 years), the risk was ~0.001%. It was found that LAR decreases remarkably with patient's age. Values obtained in this study vary between hospitals, they are generally low and consistent with other studies reported worldwide.

Radiotherapy for non-malignant shoulder syndrome: Is there a risk for radiation-induced carcinogenesis?

PurposeTo estimate the organ-specific probability for carcinogenesis following radiotherapy for non-malignant shoulder syndrome. MethodsPhoton-beam radiation therapy to 6 Gy for shoulder syndrome was simulated with a Monte Carlo code. An androgynous computational phantom representing a typical adult was used to calculate the radiation dose to out-of-field organs having a predilection for carcinogenesis. The organ-specific lifetime attributable risk (LAR) for out-of-field cancer induction was estimated by the organ dose calculations and the proper risk factors introduced by the BEIR-VII report. The average dose (Dav) and organ equivalent dose (OED) of lung, which was partially included within the treatment volume, was found from 3d-conformal radiotherapy plans. The Dav and OED were used to estimate the lung cancer risk with a linear and mechanistic models, respectively. All risk assessments were made for 50- and 60-year-old male and female patients. ResultsMonte Carlo simulations resulted in an out-of-field organ dose range of 0.7–48.4 mGy. The LARs for out-of-field cancer induction were (1.4 × 10−4)% to (2.8 × 10−2)%. These probabilities were at least 403 times lower than the respective lifetime intrinsic risk (LIR) values. The Dav and OED of lung was up to 164.9 and 142.3 mGy, respectively. The LAR for developing lung malignancies varied from 0.11 to 0.18% by the model used and the patient’s age and gender. The lung cancer risks were 36–64 times smaller than the LIRs. ConclusionsThe estimated probabilities for developing malignancies due to radiotherapy for non-malignant shoulder syndrome are minor relative to the natural cancer occurrence rates.

THE MAYAK WORKER DOSIMETRY SYSTEM (MWDS-2013) FOR INTERNALLY DEPOSITED PLUTONIUM: AN OVERVIEW.

The Mayak Worker Dosimetry System (MWDS-2013) is a system for interpreting measurement data from Mayak workers from both internal and external sources. This paper is concerned with the calculation of annual organ doses for Mayak workers exposed to plutonium aerosols, where the measurement data consists mainly of activity of plutonium in urine samples. The system utilises the latest biokinetic and dosimetric models, and unlike its predecessors, takes explicit account of uncertainties in both the measurement data and model parameters. The aim of this paper is to describe the complete MWDS-2013 system (including model parameter values and their uncertainties) and the methodology used (including all the relevant equations) and the assumptions made. Where necessary, Supplementary papers which justify specific assumptions are cited.