Adult Phantom Research Articles

Monte Carlo simulations of the whole-body counter at Spiez Laboratory Switzerland: Impact of phantom size and biokinetic model

Whole-body counters (WBC) are used to detect potential intake of radioisotopes in the human body. To achieve a precise measurement of an incorporated activity, a WBC needs to be properly characterized and calibrated. However, due to technical limitations, not every geometry can be calibrated using adequate physical phantoms. To extend the use of a standard calibration to other geometries, we performed GEANT4 Monte Carlo (MC) simulations characterizing the WBC at the Spiez Laboratory, Switzerland. The aim of our project was threefold: (1) to validate our MC model against an experimental model, (2) to study the impact of a person's size on the detection efficiency of the WBC and (3) to study the impact of intake scenarios on the estimation of whole-body activity. First, we simulated the calibration of the WBC with the IGOR phantoms. Then, we computed the detection efficiency of the WBC for homogenous whole-body contamination using ICRP adult voxel phantoms scaled to sizes. We computed the bias of the activity that would be measured by the WBC relative to the activity contained in the body in case of inhalation, modeled by the ICRP biokinetic models. Our computed detection efficiency obtained with the IGOR phantoms agreed within 5% with the calibration measurements. We found that WBC efficiency depends on the weight over height ratio (w/h). We proposed a criterion for the calibration curve selection adequate for any person, and we validated this criterion using ICRP pediatric phantoms. We estimated that the precision of a whole-body activity measurement in the case of a homogeneous activity distribution is at the level of 20%. Finally, for a non-homogenous contamination of the body by inhalation, we showed that the WBC measurements can overestimate intake up to 40–80% depending on the absorption type of the substance into the blood, and the size of the scanned person. In conclusion, our study confirms the need of using phantoms with different sizes to calibrate a WBC and shows that in case of a highly non-homogenous distribution of the radioisotope in the body, the WBC may significantly overestimate the whole-body activity. To limit this bias, we recommend scanning the entire body with the detectors instead of setting them at fixed positions or increasing the distance between the detectors and the phantom.

A dynamic blood flow model to compute absorbed dose to circulating blood and lymphocytes in liver external beam radiotherapy

We have developed a novel 4D dynamic liver blood flow model, capable of accurate dose estimation to circulating blood cells during liver-directed external beam radiotherapy, accounting for blood recirculation and radiation delivery time structure. Adult male and adult female liver computational phantoms with detailed vascular trees were developed to include the hepatic arterial, hepatic portal venous, and hepatic venous trees. A discrete time Markov Chain approach was applied to determine the spatiotemporal distribution of 105 blood particles (BP) in the human body based on reference values for cardiac output and organ blood volumes. For BPs entering the liver, an explicit Monte Carlo simulation was implemented to track their propagation along ∼2000 distinct vascular pathways through the liver. The model tracks accumulated absorbed dose from time-dependent radiation fields with a 0.1 s time resolution. The computational model was then evaluated for 3 male and 3 female patients receiving photon (VMAT and IMRT) and proton (passive SOBP and active PBS) treatments. The dosimetric impact of treatment modality, delivery time, and fractionation on circulating blood cells was investigated and quantified using the mean dose (), V >0Gy, V >0.125Gy, and D 2%. Average reductions in V >0Gy, V >0.125Gy and D 2% of 45%, 6%, 53%, 19% respectively, were observed for proton treatments as compared to photon treatments. Our simulation also showed that V >0Gy, V >0.125Gy, and D 2% were highly sensitive to the beam-on time. Both V >0Gy and V >0.125Gy increased with beam-on time, whereas D 2% decreased with increasing beam-on time, demonstrating the tradeoff between low dose to a large fraction of blood cells and high dose to a small fraction of blood cells. Consequently, proton treatments are not necessarily advantageous in terms of dose to the blood simply based on integral dose considerations. Instead, both integral dose and beam-on time can substantially impact relevant dosimetric indices.

A reconstruction approach for proton computed tomography by modeling the integral depth dose of the scanning proton pencil beam.

To present a proton computed tomography (pCT) reconstruction approach that models the integral depth dose (IDD) of the clinical scanning proton beam into beamlets. Using a multilayer ionization chamber (MLIC) as the imager, the proposed pCT system and the reconstruction approach can minimize extra ambient neutron dose and simplify the beamline design by eliminating an additional collimator to confine the proton beam. Monte Carlo simulation was applied to digitally simulate the IDDs of the exiting proton beams detected by the MLIC. A forward model was developed to model each IDD into a weighted sum of percentage depth doses of the constituent beamlets separated laterally by 1mm. The water equivalent path lengths (WEPLs) of the beamlets were determined by iteratively minimizing the squared L2-norm between the forward projected and simulated IDDs. The final WEPL values were reconstructed to pCT images, that is, proton stopping power ratio (SPR) maps, through simultaneous algebraic reconstruction technique with total variation regularization. The reconstruction process was tested with a digital cylindrical water-based phantom and an ICRP adult reference computational phantom. The mean of SPR within regions of interest (ROIs) and the WEPL along a 4mm-wide beam ( ) were compared with the reference values. The spatial resolution was analyzed at the edge of a cortical insert of the cylindrical phantom. The percentage deviations from reference SPR were within±1% in all selected ROIs. The mean absolute error of the reconstructed SPR was 0.33%, 0.19%, and 0.27% for the cylindrical phantom, the adult phantom at the head and lung region, respectively. The corresponding percentage deviations from reference were 0.48±0.64%, 0.28±0.48%, and 0.22±0.49%. The full width at half maximum of the line spread function (LSF) derived from the radial edge spread function (ESF) of a cortical insert was 0.13cm. The frequency at 10% of the modulation transfer function (MTF) was 6.38cm-1 . The mean signal-to-noise ratio (SNR) of all the inserts was 2.45. The mean imaging dose was 0.29 and 0.25cGy at the head and lung region of the adult phantom, respectively. A new pCT reconstruction approach was developed by modeling the IDDs of the uncollimated scanning proton beams in the pencil beam geometry. SPR accuracy within±1%, spatial resolution of better than 2mm at 10% MTF, and imaging dose at the magnitude of mGy were achieved. Potential side effects caused by neutron dose were eliminated by removing the extra beam collimator.

Organ dose from Varian XI and Varian OBI systems are clinically comparable for pelvic CBCT imaging.

Pelvic cone-beam computed tomography (CBCT) occurs daily in many radiotherapy clinics as a part of image-guided verification before treatment. These images are acquired by the use of ionizing radiation. The dose received by CBCT imaging is often not quantified in a patient's radiation therapy prescription. The purpose of this work was to quantify the dose from a TrueBeam XI pelvic CBCT imaging system. The dose to organs from this imaging protocol was then compared with published dose data for OBI v1.4 pelvic CBCT imaging. A model of the Varian XI imager was constructed using GATE Monte Carlo scripting language. The model was calibrated by correlation with experimental measurements. An IBA 3D water tank was used to perform relative dose measurements in water. An adult anthropomorphic Alderson phantom with embedded thermolumeniscent dosimeters was used to evaluate dose from prostate CBCT imaging. Following the calibration, the GATE model was used to simulate the dose from the XI pelvic CBCT protocol to the ICRP computational anthropomorphic phantom. The Monte Carlo model constructed in GATE was validated for use in dose estimates for the XI pelvic imaging protocol. The D50 and D10 values tabulated the pelvic CBCT protocol show that doses to organs in the pelvic region are comparable for both systems. For a clinician who intends to evaluate the dose to organs as a result of CBCT imaging of the pelvis from the TrueBeam XI system, for the purposes of treatment planning, the doses reported for OBI v1.4 given in AAPM TG-180 provide a valid estimate.

Physical dosimetric reconstruction of a case of large area back skin injury due to overexposure in an interventional procedure

To estimate the physical dose of skin and key organs in a case of overexposure during a cardiac interventional procedure. MethodsThe female patient aged 50 suffered from overexposure during cardiac interventional therapy in a hospital, Xinxiang city, Henan province, China in January 2020. The mesh-type phantom for the patient was constructed based on the adult mesh-type reference computational phantoms (MRCPs) released by the International Commission on Radiological Protection Publication 145 (ICRP145) and phantom deformation technology. Models of exposure scenario were constructed and simulated with particle and heavy ion transport code system (PHITS) according to exposure conditions. ResultsThe maximum absorbed dose of key organs/tissues under irradiation in posteroanterior (PA) and 30° left anterior oblique directions(LOA) was 632.4 and 305.6 ​mGy, respectively. The left lung, heart, and left mammary gland received a larger dose under both irradiation conditions. The ratio of the absorbed dose with and without shielding was calculated, and the relative difference in most organs was <1% between two directions. The iso-dose curve of the back skin revealed the distribution of the absorbed dose (0.1 −5.2 ​Gy). The dose estimate of key tissues/organs was higher than the conventional level, especially the local skin, up to 5.2 ​Gy. ConclusionsThe interventional procedure in this case resulted in a higher dose. Monte Carlo codes combined with the MRCPs can be employed to estimate physical dose to individuals in concrete irradiation scenarios.

Estimation of electron-specific absorbed fractions with the InterDosi code using ICRP adult female voxel-based phantom

The International Commission on Radiological Protection (ICRP) through its publications recommends the estimation of Specific Absorbed Fractions (SAFs) using voxelized phantoms in order to assess the doses internally absorbed by organs exposed to ionizing radiation. In the present work, we report a large set of SAFs calculated using the ICRP Adult Female (ICRP-AF) phantom. The new Geant4-based code called InterDosi version 1.0 was used to simulate monoenergetic electrons of 20 different energies, ranging from 0.005 to 10 MeV, emitted uniformly from 18 different source organs. In order to estimate SAFs in 169 target organs/regions, 360 Monte Carlo multithreaded simulations were run on 32 CPUs of the HPC-MARWAN-CNRST computing grid. The calculated SAFs were compared to the recent results obtained using GATE 8.1 code and published by the OpenDose collaboration. It is shown that the obtained results are in well-agreement with the reference values, with absolute discrepancies less than 0.6% for a self-absorption condition and less than 5% in almost all energies for a cross-absorption condition. We concluded that InterDosi code might be used for dosimetry of internal electron emitters.

Development of a quasi-humanoid phantom to perform dosimetric and radiobiological measurements for out-of-field doses from external beam radiation therapy.

Our understanding of low dose, out‐of‐field radiation and their radiobiological effects are limited, in part due to the rapid technological advances in external beam radiotherapy, especially for non‐coplanar and dynamic techniques. Reliable comparisons of out‐of‐field doses produced by advanced radiotherapy techniques are difficult due to the limitations of commercially available phantoms. There is a clear need for a functional phantom to accurately measure the dosimetric and radiobiological characteristics of out‐of‐field doses, which would in turn allow clinicians and medical physicists to optimize treatment parameters. We designed, manufactured, and tested the performance of a quasi‐humanoid (Q‐H) adult phantom. To test the physics parameters, we used computed tomography (CT) scans of assembled Q‐H phantom. Static open field and dynamic techniques were measured both in‐ and out‐of‐field with ionization chambers and radiochromic films for two configurations (full solid and with water‐filled containers). In the areas simulating soft tissues, lung, and bones, median Hounsfield units and densities were, respectively: 129.8, ‐738.7, 920.8 HU and 1.110, 0.215, 1.669 g/cm3. Comparison of the measured to treatment planning systems (TPS) in‐field dose values for the sample volumetric arc therapy (VMAT) (6 MV flattening filter‐free (FFF)) plan, 96.4% of analyzed points passed the gamma evaluation criteria (L2%/2 mm, threshold (TH) 10%) and less than 1.50% for point dose verification. In the two phantom configurations: full poly(methyl) methacrylate (PMMA) and with water container, the off‐axis median doses for open field, relative to the central axis of the beam (CAX) were similar, respectively: 0.900% versus 0.907% (15 cm distance to CAX); 0.096% versus 0.120% (35 cm); 0.018% versus 0.018% (52 cm); 0.009% versus 0.008% (74 cm). For VMAT 6 MV FFF, doses relative the CAX were, respectively: 0.667% (15 cm), 0.062% (35 cm), 0.019% (52 cm), 0.016% (74 cm). The Q‐H phantom meets the International Commission on Radiation Units and Measurements (ICRU) and American Association of Physicists in Medicine (AAPM) recommended phantom criteria, providing medical physicists with a reliable, comprehensive system to perform dose calculation and measurements and to assess the impact on radiobiological response and on the risk of secondary tumor induction.

PCXMC cone beam computed tomography dosimetry investigations.

With cone beam computed tomography (CBCT) in image guided radiation therapy being amongst the most widely used imaging modalities, there has been an increasing interest in quantifying the concomitant dose and risk. Whilst there have been several studies on this topic, there remains a lack of standardisation and knowledge on dose variations and the impact of patient size. Recently, PCXMC (a Monte Carlo simulator) has been used to assess both the concomitant dose and dosimetric impact of patient size variations for CBCT. The scopes of these studies, however, have included only a limited range of imaging manufacturers, protocols, and patient sizes. An approach using PCXMC and MATLAB was developed to enable a generalised method for rapidly quantifying and formulating the concomitant dose as a function of patient size across numerous CBCT vendors and protocols. The method was investigated using the Varian on board imaging 1.6 default pelvis and pelvis spotlight protocols, for 94 adult and paediatric phantoms over 6 age groups with extensive height and mass variations. It was found that dose varies significantly with patient size, as much as doubling and halving the average for patients of lower and higher mass, respectively. These variations, however, can be formulated and accounted for using the method developed, across a wide range of patient sizes for all CBCT vendors and protocols. This will enable the development of a comprehensive catalogue to account for concomitant doses in almost any clinically relevant scenario.

Optimization of pediatric FDG-PET/CT examinations based on physical indicators using the SiPM-PET/CT system.

This study aimed to investigate the appropriate Silicon photomultiplier -PET/CT acquisition and image reconstruction conditions for each age group. The original phantom was developed to reflect the thickness and width of the torso in each age group (neonates, 1-year-olds, 5-year-olds, 10-year-olds, 15-year-olds, and adults). The ratio of hot spheres to background radioactivity was 4:1, and the radioactivity concentration was adjusted according to the Japanese consensus guidelines for appropriate implementation of pediatric nuclear medicine examinations. We evaluated the root mean square error (RMSE) as an assessment/function of the standardized uptake value of each hot sphere, the background variability (N10 mm), the % contrast of the hot sphere (QH, 10 mm/N10 mm), and the noise equivalent counts to determine the optimal reconstruction parameters and the appropriate acquisition time. The minimum RMSE was obtained by setting the half-width of the Gaussian filter to 0-2 mm for iteration 1 or 2 and to 2-4 mm for iteration 3 or more. The acquisition times that satisfied the image quality equivalent to 120 s acquisitions in the adult phantoms were 30 s in the neonatal and 1-year-old phantoms, 60 s in the 5- and 10-year-old phantoms, and 75 s in the 15-year-old phantoms. This study demonstrated that good PET images could be obtained with short acquisition times when the examination is performed under appropriate reconstruction conditions.

IDACstar2.0: A MCNP application to perform realistic dose estimations from internal or external contamination with radiopharmaceuticals

The IDACstar (Internal Dose Assessment by Computer) software is a Monte Carlo based standalone MCNP input generator software developed to perform complex radiation dose calculations using both the paediatric and adult ICRP reference phantoms. An extension of the IDACstar software was applied to two different exposure scenarios. One of the scenarios was a hypothetical case of a contaminated diaper from urine of a 1-year old patient undergoing a diagnostic kidney examination with 99mTc-labelled mercaptoacetyl triglycerine (MAG3), which resulted in an effective dose estimate of 0.088 mSv to the child. The second case was a clinical case of 18F-FDG extravasation in an adult patient and applied to all 10 age-specific phantoms with weight-modified administrations of the radiopharmaceutical. The effective dose was estimated for the 15-, 10-, 5- and 1- year old as 5.1 mSv, 4.9 mSv, 4.7 mSv, and 4.7 mSv, respectively. The updated version of the IDACstar software provides the possibility of performing realistic dose estimations to paediatric patients from internal or external contamination with radiopharmaceuticals.

Validation of organ dose calculations with PyMCGPU-IR in realistic interventional set-ups.

Interventional radiology procedures are associated with high skin dose exposure. The 2013/59/EURATOM Directive establishes that the equipment used for interventional radiology must have a device or a feature informing the practitioner of relevant parameters for assessing patient dose at the end of the procedure. This work presents and validates PyMCGPU-IR, a patient dose monitoring tool for interventional cardiology and radiology procedures based on MC-GPU. MC-GPU is a freely available Monte Carlo (MC) code of photon transport in a voxelized geometry which uses the computational power of commodity Graphics Processing Unit cards (GPU) to accelerate calculations. PyMCGPU-IR was validated against two different experimental set-ups. The first one consisted of skin dose measurements for different beam angulations on an adult Rando Alderson anthropomorphic phantom. The second consisted of organ dose measurements in three clinical procedures using the Rando Alderson phantom. The results obtained for the skin dose measurements show differences below 6%. For the clinical procedures the differences are within 20% for most cases. PyMCGPU-IR offers both, high performance and accuracy for dose assessment when compared with skin and organ dose measurements. It also allows the calculation of dose values at specific positions and organs, the dose distribution and the location of the maximum doses per organ. In addition, PyMCGPU-IR overcomes the time limitations of CPU-based MC codes.

Effect of I-131 Radioisotope Activities on Organ Dose Used in Nuclear Medicine

There are many ways to be exposed to radiation in life. Medical applications, in particular, are the most important form of severe exposure. In medical applications, Computed Tomography (CT) scans are in the first place, while nuclear medicine is in the second place. Of course, the dose absorbed by the exposed tissue and therefore the organs is directly proportional to the risks to health. In nuclear medicine, due to the radioisotopes placed in the body for therapeutic purposes, some doses are not given only to the organ and/or tissues where the tumor is placed, but also to other surrounding organ and tissues. In this study, the change in the doses received by the thyroid gland, thymus, and lymph nodes according to the activities of the iodine radioisotope I-131 placed in the thyroid gland of adult phantoms (both male and female) were investigated with the Monte Carlo-based code.

Dose reduction potential in diagnostic single energy CT through patient-specific prefilters and a wider range of tube voltages.

Various studies have demonstrated that additional prefilters and/or reduced tube voltages have the potential to significantly increase the contrast-to-noise ratios at unit dose (CNRDs) and thereby to significantly reduce patient dose in clinical CT. An exhaustive analysis, accounting for a wide range of filter thicknesses and a wide range of tube voltages extending beyond the 70 to 150kV range of today's CT systems, including their specific choice depending on the patient size, is, however, missing. Therefore, this work analyzes the dose reduction potential for patient-specific selectable prefilters combined with a wider range of tube voltages. We do so for soft tissue and iodine contrast in single energy CT. The findings may be helpful to guide further developments of x-ray tubes and automatic filter changers. CT acquisitions were simulated for different patient sizes (semianthropomorphic phantoms for child, adult, and obese patients), tube voltages (35-150kV), prefilter materials (tin and copper), and prefilter thicknesses (up to 5mm). For each acquisition soft tissue and iodine CNRDs were determined. Dose was calculated using Monte Carlo simulations of a computed tomography dose index (CTDI) phantom. CNRD values of acquisitions with different parameters were used to evaluate dosereduction. Dose reduction through patient-specific prefilters depends on patient size and available tube current among others. With an available tube current time product of 1000mAs dose reductions of 17% for the child, 32% for the adult and 29% for the obese phantom were achieved for soft tissue contrast. For iodine contrast dose reductions were 57%, 49%, and 39% for child, adult, and obese phantoms, respectively. Here, a tube voltage range extended to lower kV isimportant. Substantial dose reduction can be achieved by utilizing patient-specific prefilters. Tube voltages lower than 70kV are beneficial for dose reduction with iodine contrast, especially for small patients. The optimal implementation of patient-specific prefilters benefits from higher tube power. Tin prefilters should be available in 0.1mm steps or lower, copper prefilter in 0.3mm steps or lower. At least 10 different prefilter thicknesses should be used to cover the dose optima of all investigated patient sizes and contrast mechanisms. In many cases it would be advantageous to adapt the prefilter thickness rather than the tube current to the patient size, that is, to always use the maximum available tube current and to control the exposure by adjusting the thickness of the prefilter.

A small-scale realistic inter-laboratory accident dosimetry comparison using the TL/OSL from mobile phone components

An inter-laboratory comparison of a small-scale field experiment was conducted in the framework of the Korea retrospective dosimetry network (KREDOS) to verify the reliability and compatibility of thermoluminescence and optically stimulated luminescence techniques for accident dosimetry. Three institutes participated in this comparison, including the Korea Atomic Energy Research Institute, the Korea Institute of Nuclear Safety and the University of Salzburg. Two adult CIRS torso phantoms were used as virtual subjects exposed to a high-activity Ir-192 source, developing both homogeneous and inhomogeneous exposures in a shielded enclosure. The target materials for dose estimation were mobile phone components, such as resistors, display glasses, and chip cards. LiF:Mg,Cu, Si thermoluminescent (TL) detectors were used as reference dosimeters. The mobile phones were attached to the chest, hip, and thighs of the anthropomorphic phantoms. The measured doses ranged from 100 mGy to 2 Gy, depending on the position of the mobile phone on the phantom. The proficiency of the dose assessment was tested at three laboratories. Using the applied protocols, the local dose distribution on the display glasses was unclear, but the distribution around the body was confirmed.

A Review of Doses for Dental Imaging in 2010-2020 and Development of a Web Dose Calculator.

Dental imaging is one of the most common types of diagnostic radiological procedures in modern medicine. We introduce a comprehensive table of organ doses received by patients in dental imaging procedures extracted from literature and a new web application to visualize the summarized dose information. We analyzed articles, published after 2010, from PubMed on organ and effective doses delivered by dental imaging procedures, including intraoral radiography, panoramic radiography, and cone-beam computed tomography (CBCT), and summarized doses by dosimetry method, machine model, patient age, and technical parameters. Mean effective doses delivered by intraoral, 1.32 (0.60–2.56) μSv, and panoramic, 17.93 (3.47–75.00) μSv, procedures were found to be about1% and 15% of that delivered by CBCT, 121.09 (17.10–392.20) μSv, respectively. In CBCT imaging, child phantoms received about 29% more effective dose than the adult phantoms received. The effective dose of a large field of view (FOV) (>150 cm2) was about 1.6 times greater than that of a small FOV (<50 cm2). The maximum CBCT effective dose with a large FOV for children, 392.2 μSv, was about 13% of theeffective dose that a person receives on average every year from natural radiation, 3110 μSv. Monte Carlo simulations of representative cases of the three dental imaging procedures were then conducted to estimate and visualize the dose distribution within the head. The user-friendly interactive web application (available at http://dentaldose.org) receives user input, such as the number of intraoral radiographs taken, and displays total organ and effective doses, dose distribution maps, and a comparison with other medical and natural sources of radiation. The web dose calculator provides a practical resource for patients interested in understanding the radiation doses delivered by dental imaging procedures.

A comparison of effective dose and risk for different collimation options used in AP shoulder radiography

IntroductionRadiography forms the cornerstone of the evaluation of shoulder disorders. While the benefits of radiography exceed the risks, there continues to be a compelling case for reduction of radiation exposure from diagnostic radiography. The aim of this project was to evaluate the radiation dose and risk for a variety of collimation settings used during anteroposterior (AP) shoulder radiography. MethodsThis was a phantom based study where an ATOM adult dosimetry phantom was loaded with 272 thermoluminescent dosimeters (TLDs). Following loading, the phantom was setup for an AP shoulder X-ray projection with standard 25 × 30 cm rectangular collimation. The phantom was exposed three times and then the TLDs were removed and read. The experiment was repeated using a diamond shaped collimation and rectangular collimation with a minimum field of view to portray only relevant anatomy. Using the TLD dose measurements the effective doses and radiation risks were determined and compared. ResultsAs expected, organs neighbouring the shoulder experienced the highest absorbed doses (greater than 0.01 mGy); these organs included breast, lung and thyroid gland. The effective doses for standard rectangular, small rectangular and diamond collimation were 0.011, 0.008 and 0.016 mSv, respectively. When compared to standard collimation, a small field of view reduced effective dose by 27.3% and when moving to a diamond shape there was a 45.5% increase. The differences are likely driven by differences in the coverage of the radiosensitive lung and breast tissue. ConclusionBy utilising a variety of different collimation settings, effective dose can be reduced. Reducing the radiation dose is both financially beneficial and results in a lower stochastic risk for patients. Image quality must also be considered when choosing different collimation settings. It stands to reason that by reducing the field size, dose will be reduced, and our study has served to quantify the effects in a practical situation. Implications for practiceThe utilisation of smaller/tight collimation is recommended as it offers the lowest dose when compared with other types of collimations. Although well-known this study serves to remind practitioners of the practical importance of collimation and is associated effect on effective dose and risk.

A customizable anthropomorphic phantom for dosimetric verification of 3D-printed lung, tissue, and bone density materials.

To design and manufacture a customized thoracic phantom slab utilizing the 3D printing process, also known as additive manufacturing, consisting of different tissue density materials. Here, we demonstrate the 3D-printed phantom's clinical feasibility for imaging and dosimetric verification of volumetric modulated arc radiotherapy (VMAT) plans for lung and spine stereotactic ablative body radiotherapy (SABR) through end-to-end dosimetric verification. A customizable anthropomorphic phantom slab was designed using the CT dataset of a commercial phantom (adult female ATOM dosimetry phantom, CIRS Inc.). Material extrusion 3D printing was utilized to manufacture the phantom slab consisting of acrylonitrile butadiene styrene material for the lung and the associated lesion, polylactic acid (PLA) material for soft tissue and spinal cord, and both PLA and iron-reinforced PLA materials for bone. CT images were acquired for both the commercial phantom and 3D-printed phantom for HU comparison. VMAT plans were generated for spine and lung SABR scenarios and were delivered as per departmental SABR protocols using a Varian TrueBeam STx linear accelerator. End-to-end dosimetry was implemented with radiochromic films, analyzed with gamma criteria of 5% dose difference, and a distance-to-agreement of 1mm, at a 10% low-dose threshold by comparing with calculated dose using the Acuros algorithm of the Eclipse treatment planning system (v15.6). 3D-printed phantom inserts were observed to produce HU ranging from -750 to 2100. The 3D-printed phantom slab was observed to achieve a similar range of HU from the commercial phantom including a mean HU of -760 for lung tissue, a mean HU of 50 for soft tissue, and a mean HU of 220 and 630 for low- and high-density bone, respectively. Film dosimetry results show 2D-gamma passing rates for lung SABR (internal and superior) and spine SABR (inferior and superior) over 98% and 90%, respectively. The end-to-end testing of VMAT plans for spine and lung SABR suggests the clinical feasibility of the 3D-printed phantom, consisting of different tissue density materials that emulate lung, soft tissue, and bone in kV imaging and megavoltage photon dosimetry. Further investigation of the proposed 3D printing techniques for manufacturability and reproducibility will enable the development of clinical 3D-printed phantoms in radiotherapy.

Absorbed dose rate coefficients for 134Cs and 137Cs with steady-state distribution in the human body: S-coefficients revisited

In the event of an accidental release of radioactive elements from a nuclear power plant, it has been shown that the radionuclides contributing the most to long-term exposure are 134Cs and 137Cs. In the case of nuclear power plant fallout, with subsequent intake of radionuclides through the food chain, the internal absorbed dose to target tissues from protracted intake of radionuclides needs to be estimated. Internal contamination from food consumption is not caused by a single intake event; hence, the committed equivalent dose, calculated by a dose coefficient or dose per content function, cannot be easily used to calculate the cumulative absorbed dose to relevant target tissues in the body. In this study, we calculated updated absorbed dose rate coefficients for 134Cs and 137Cs based on data from the International Commission on Radiological Protection (ICRP) on specific absorbed fractions. The absorbed dose rate coefficients are provided for male and female adult reference phantoms, respectively, assuming a steady-state distribution of Cs that we calculated from the ICRP biokinetic model for Cs. With these coefficients, the absorbed dose to the listed target tissues, separately and to the total body, are related to the number of nuclear transitions (time-integrated activity) in each listed source region. Our new absorbed dose rate coefficients are given for the complete set of target tissues and have not been presented before. They are also provided for aggregated categories of organs to facilitate epidemiological studies.

Comparison of Indian BOMAB and ICRP voxel phantom for calibration of shadow shield whole body counter

In-vivo whole body monitors are calibrated with various types of phantoms like Bottle Mannikin absorption phantom (BOMAB), IGOR phantom, Masonite cut sheet phantom, realistic numerical phantoms (NORMAN, ICRP voxel phantom). These phantoms contain either point sources, rod sources, uniform source or radionuclides distributed in soft tissues etc. In this study the efficiency values of Shadow Shield wholebody counter (SSC) for 137Cs and 60Co obtained theoretically using ICRP adult voxel male reference phantom (ICRP-AM) having sources distributed in soft tissues and muscles ICRP-AM(S) are compared with the measured efficiencies of Indian BOMAB phantom having mid axial source distribution (BOM-I(A)). The results show that the efficiency value of BOM-I(A) for 137Cs and 60Co is 30% and 20% lower respectively compared to that of ICRP-AM(S). This is due to the variation in size, composition and source distribution between the two phantoms. Study using Indian Voxel phantom shows that the increase in the size of ICRP-AM contributed to an increase of 14% for 137Cs. In case of 60Co the size did not have any influence. Uniform distribution has 9% and 17% higher efficiency than axial distribution for 137Cs and 60Co respectively as shown by the simulation study using uniformly filled Indian BOMAB phantom (BOM-I(U)). The actual tissue composition and source distribution in soft tissue as shown by Indian voxel has efficiencies 12-14% higher compared to BOM-I(U). The systemic error due to the axial source distribution is recognized and quantified to be 22-25% lower compared to that of a realistic phantom with radionuclides in soft tissue and muscle. This study has resulted in an efficiency of the system using Indian realistic Voxel phantom. The efficiencies are 0.65 CPS/kBq for 137Cs and 0.49 CPS/kBq for 60Co.

Dose quantities for measurement and comparison of doses to individual patients in computed tomography (CT)

The dose quantities displayed routinely on CT scanners, the volume averaged CT dose index (CTDIvol) and dose length product, provide measures of doses calculated for standard phantoms. The American Association of Medical Physics has published conversion factors for the adjustment of CTDIvol to take account of variations in patient size, the results being termed size-specific dose estimate (SSDE). However, CTDIvol and SSDE, while useful in comparing and optimising doses from a set procedure, do not provide risk-related information that takes account of the organs and tissues irradiated and associated cancer risks. A derivative of effective dose that takes account of differences in body and organ sizes and masses, referred to here as size-specific effective dose (SED), can provide such information. Data on organ doses from NCICT software that is based on Monte Carlo simulations of CT scans for 193 adult phantoms have been used to compute values of SED for CT examinations of the trunk and results compared with corresponding values of SSDE. Relationships within ±8% were observed between SED and SSDE for scans extending over similar regions for phantoms with a wide range of sizes. Coefficients have been derived from fits of the data to estimate SED values from SSDEs for different regions of the body for scans of standard lengths based on patient height. A method developed to take account of differences in scan length gave SED results within ±5% of values calculated using the NCI phantom library. This approach could potentially be used to estimate SED from SSDE values, allowing their display at the time a CT scan is performed.