Phantom Material Research Articles

Low-cost 3D print–based phantom fabrication to facilitate interstitial prostate brachytherapy training program

PurposeThe purpose of this study was to manufacture a realistic and inexpensive prostate phantom to support training programs for ultrasound-based interstitial prostate brachytherapy. Methods and MaterialsFive phantom material combinations were tested and evaluated for material characteristics; Ecoflex 00–30 silicone, emulsion silicone with 20% or 50% mineral oil, and regular or supersoft polyvinyl chloride (PVC). A prostate phantom which includes an anatomic simulated prostate, urethra, seminal vesicles, rectum, and normal surrounding tissue was created with 3D-printed molds using 20% emulsion silicone and regular and supersoft PVC materials based on speed of sound testing. Needle artifact retention was evaluated at weekly intervals. ResultsSpeed of sound testing demonstrated PVC to have the closest ultrasound characteristics of the materials tested to that of soft tissue. Several molds were created with 3D-printed PLA directly or cast on 3D-printed PLA with high heat resistant silicone. The prostate phantom fabrication workflow was developed, including a method to produce dummy seeds for low-dose-rate brachytherapy practice. A complete phantom may be fabricated in 1.5–2 h, and the material cost for each phantom was approximated at $23.98. ConclusionsA low-cost and reusable phantom was developed based on 3D-printed molds for casting. The proposed educational prostate phantom is an ideal cost-effective platform to develop and build confidence in fundamental brachytherapy procedural skills in addition to actual patient caseloads.

Synthetic polymer hydrogels as potential tissue phantoms in radiation therapy and dosimetry

The efficacy of synthetic polymers as hydrogel phantoms for radiation therapy and dosimetry has been investigated for photon and charged particle (electron, proton and alpha particle) interactions. Tissue equivalence has been studied in terms of photon mass energy-absorption coefficients, KERMA (kinetic energy released per unit mass), equivalent atomic number and energy absorption build-up factors, relative to human tissues (skin, soft tissue, cortical bone and skeletal muscle), in the energy range 0.015–15 MeV. For charged particle interactions, ratio of effective atomic number is examined for tissue-equivalence in the energy region of 10 keV–1 GeV. Well established theoretical formulations are used for computation of photon mass-energy absorption effective atomic number, electron density and KERMA. Five-parameter geometric progression (G-P) fitting approximation is used to compute the values of energy absorption build-up factors. Effective atomic number for charged particle interaction is determined using logarithmic interpolation method. Using the analytical methodology, it has been revealed that all the selected synthetic polymers have good tissue-equivalence relative to all tissue except cortical bone. In particular, polyglycolic acid (PGA) and poly-lactic-co-glycolic acid (PLGA) prove to be best substitute material for photon interactions. On the other hand, % difference between effective atomic number for charged particle relative to human tissues is found least for polyethylene glycol (PEG) demonstrating adequate tissue-equivalence. Therefore, the present study is expected to be useful to choose most appropriate phantom material for radiation therapy.

3-D H-Scan Ultrasound Imaging and Use of a Convolutional Neural Network for Scatterer Size Estimation

H-Scan ultrasound (US) is a new imaging technology that estimates the relative size of acoustic scattering objects and structures. The purpose of this study was to introduce a three-dimensional (3-D) H-scan US imaging approach for scatterer size estimation in volume space. Using a programmable research scanner (Vantage 256, Verasonics Inc, Kirkland, WA, USA) equipped with a custom volumetric imaging transducer (4 DL7, Vermon, Tours, France), raw radiofrequency (RF) data was collected for offline processing to generate H-scan US volumes. A deep convolutional neural network (CNN) was modified and used to achieve voxel mapping from the input H-scan US image to underlying scatterer size. Preliminary studies were conducted using homogeneous gelatin-based tissue-mimicking phantom materials embedded with acoustic scatterers of varying size (15 to 250 μm) and concentrations (0.1 to 1%). Two additional phantoms were embedded with 63 or 125 µm-sized microspheres and used to test CNN estimation accuracy. In vitro results indicate that 3-D H-scan US imaging can visualize the spatial distribution of acoustic scatterers of varying size at different concentrations (R2 > 0.85, p < 0.03). The result of scatterer size estimation reveals that a CNN can achieve an average mapping accuracy of 93.3%. Overall, our preliminary in vitro findings reveal that 3-D H-scan US imaging allows the visualization of tissue scatterer patterns and incorporation of a CNN can be used to help estimate size of the acoustic scattering objects.

A generalized system of tissue-mimicking materials for computed tomography and magnetic resonance imaging

The advent of technologies such as magnetic resonance imaging (MRI)-guided radiation therapy has led to the need for phantom materials that are capable of producing tissue-like contrast on both MRI and computed tomography (CT) imaging modalities. The purpose of this work is to develop a system of easily made and formed materials with adjustable T1 and T2 relaxation times, and x-ray attenuation properties, for mimicking soft tissue and bone with both MRI and CT imaging modalities. The effects on T1/T2 relaxation times and CT numbers were quantified for a range of gadolinium contrast (0–25 μmol g-1), agarose (0%–8% w/w), glass microspheres (0%–10% w/w) and CaCO3 (0%–50% w/w) concentrations in a carrageenan-based gel. 105 gel samples were prepared with the additives, carrageenan and water. Samples were imaged in a 3D-printed holding structure to find the attainable range of T1/T2 relaxation time and CT number combinations. T1 and T2 relaxation time maps were generated using voxel-wise inversion-recovery and spin-echo techniques, respectively. A multivariate linear regression model was generated to allow the materials system to be generalized to semi-arbitrary T1/T2 relaxation times and CT numbers. Nine diverse tissue types were mimicked for fit model validation. The achievable T1/T2 relaxation times and CT numbers for the additive concentrations tested in this study spanned from 82 to 2180 ms, 12 to 475 ms, and −117 to +914 Hounsfield units (HU), respectively. The mean absolute error between the fit model predicted and measured T1/T2 relaxation times and CT numbers for the nine tested tissue types was 113 ± 64 ms, 16 ± 26 ms and 11 ± 14 HU, respectively. In conclusion, we have created a system of materials capable of producing tissue-like contrast for 3.0 T MRI and CT imaging modalities.

A Comparative Study of Skin Phantoms for Microwave Applications.

In the here-reported study, we investigated the dielectric properties of three different skin-mimicking materials used in the reported controlled experiments for development and testing of microwave-range medical devices. Each of the phantom materials under consideration is tested in two forms: a thicker, larger block and a 2-mm sheet. The measured properties are compared to a reference of human skin tissue measurements from literature. Depending on the frequency range of the medical device in development, some phantoms are more suitable to represent human skin than others. We observe that all phantoms still show lower dielectric properties than the human skin reference, but are suitable representations of skin at microwave applications if used as 2-mm thin layers.

Characterization of Rhizophora SPP. particleboards with SOY protein isolate modified with NaOH/IA-PAE adhesive for use as phantom material at photon energies of 16.59–25.26 keV

In this work, Rhizophora spp. particleboard phantoms were made using SPI-based adhesives, modified with sodium hydroxide and itaconic acid polyamidoamine-epichlorohydrin (0, 5, 10, and 15 wt%). An X-ray computed tomography (CT) imaging system was used to ascertain the CT numbers and density distribution profiles of the particleboards. The SPI-based/NaOH/IA-PAE/Rhizophora spp. particleboard phantoms with 15 wt% IA-PAE addition level had the highest solid content, flexural strength, flexural modulus, and internal bonding strength of 36.06 ± 1.08%, 18.61 ± 0.38 Nmm−2, 7605.76 ± 0.89 Nmm−2, and 0.463 ± 0.053 Nmm−2, respectively. The moisture content, mass density, water absorption, and dimensional stability were 6.93 ± 0.27%, 0.962 ± 0.037 gcm−3, 22.36 ± 2.47%, and 10.90 ± 0.86%, respectively. The results revealed that the mass attenuation coefficients and effective atomic number values within the 16.59–25.26 keV photon energy region, were close to the calculated XCOM values in water, with a p-value of 0.077. Moreover, the CT images showed that the dissimilarities in the discrepancy of the profile density decreased as the IA-PAE concentrations increased. Therefore, these results support the appropriateness of the SPI-based/NaOH/IA-PAE/Rhizophora spp. particleboard with 15 wt% IA-PAE adhesive as a suitable tissue-equivalent phantom material for medical health applications.

Rhizophora spp. Particleboards incorporating defatted soy flour bonded with NaOH/IA-PAE: Towards a water equivalent phantom material

Defatted soy flour (DSF)-based Rhizophora spp. particleboard phantoms with varying content of itaconic acid polyamidoamine-epichlorohydrin (IA-PAE) and sodium hydroxide were prepared, and characterized using Fourier transform infrared spectroscopy, 1H-nuclear magnetic resonance, differential scanning calorimetry, thermogravimetric analysis, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction spectroscopy. The results indicated that the mass attenuation coefficients, Zeff values with a percentage difference of approximately 0.13% to water, and p-value estimation of 0.057 were in good agreement to the calculated XCOM values in water. These findings revealed that 15 wt% increment in IA-PAE content had the quality of having properties that are appropriate for use as a water-equivalent phantom material for quality control and dosimetry work.

Four-dimensional (4D) phase velocity optical coherence elastography in heterogeneous materials and biological tissue.

The variations of mechanical properties in soft tissues are biomarkers used for clinical diagnosis and disease monitoring. Optical coherence elastography (OCE) has been extensively developed to investigate mechanical properties of various biological tissues. These methods are generally based on time-domain data and measure the time-of-flight of the localized shear wave propagations to estimate the group velocity. However, there is considerable information that can be obtained from examining the mechanical properties such as wave propagation velocities at different frequencies. Here we propose a method to evaluate phase velocity, wave velocity at various frequencies, in four-dimensional space (x, y, z, f), called 4D-OCE phase velocity. The method enables local estimates of the phase velocity of propagating mechanical waves in a medium. We acquired and analyzed data with this method from a homogeneous reference phantom, a heterogeneous phantom material with four different excitation cases, and ex vivo porcine kidney tissue. The 3D-OCE group velocity was also estimated to compare with 4D-OCE phase velocity. Moreover, we performed numerical simulation of wave propagations to illustrate the boundary behavior of the propagating waves. The proposed 4D-OCE phase velocity is capable of providing further information in OCE to better understand the spatial variation of mechanical properties of various biological tissues with respect to frequency.

Physical and mechanical properties of soy-lignin bonded Rhizophora spp. particleboard as a tissue-equivalent phantom material

Experimental binderless and adhesive-bonded particleboards were made from three different sample sizes, 0 to 103 µm, 104 to 210 µm, and 211 to 500 µm from Rhizophora spp. wood trunk at 1.0 g cm-3. The objective was to evaluate the physical and mechanical properties of the particleboards. The binderless and soy-lignin bonded particleboards were fabricated and studied based on the density, internal bonding, modulus of rupture, water absorption, and thickness swelling. Microstructure study using scanning electron microscopy (SEM) and elemental analysis by carbon hydrogen nitrogen (CHN) analyser were also performed. Particleboards with adhesives improved the internal bond strength. Smaller particle sizes also were shown to be able to improve the thickness swelling outcomes, with lower hygroscopic properties. The SEM images showed that smaller particle size allowed better bonding with adhesives and provided superior strength in the fabrication of tissue equivalent phantom material. The CHN ratio demonstrated by soy flour and lignin revealed no major difference when compared with the Rhizophora spp. samples, showing basic chemical composition of natural adhesives, which was crucial in the fabrication of tissue-mimicking phantom. The study revealed the potential of soy flour and lignin as adhesives for the fabrication of Rhizophora spp. particleboard as a tissue equivalent phantom material.

TISSUE EQUIVALENT MATERIALS FROM SPC-SPI/NAOH/IA-PAE BONDED MANGROVE WOOD CHARACTERIZED FOR RADIATION THERAPY DOSIMETRY

This research focuses on dosimetric measurements in bio-based tissue equivalent phantom materials, designed using soy protein concentrate (SPC), soy protein isolate (SPI), Rhizophora spp. wood, sodium hydroxide, and itaconic acid polyamidoamine-epichlorohydrin resin with an ionization chamber and GafchromicTH EBT3 film dosimeters. The measurements were performed under exposure to 6 MV and 10 MV photon, and 6 MeV and 15 MeV electron beams. The particleboard samples were exposed to a dose of 100 cGy and 10 x 10 cm2 field size at a source-to-surface distance of 100 cm. The dosimeters were irradiated at measurement depths of 1.5, 2.5 and 3.0 cm, respectively, inside the phantom slabs. The particleboards presented superior physical and mechanical properties. The dose measurements revealed excellent agreement with that of water and solid water phantoms. In addition, comparison between the measured dosimetric properties is well within 2%, 2%, 10% and 5.5% for 6 MV, 6 MeV, 10 MV and 15 MeV energies of the maximum dose for the field size tested. This study had successfully shown that SPC-SPI/NaOH/IA-PAE bonded Rhizophora spp. particleboards are promising tissue equivalent phantom materials with merit for medical applications.

Cardiac Tissue-Mimicking Ballistic Gel Phantom for Ultrasound Imaging in Clinical and Research Applications

Ballistic gel was investigated as a tissue-mimicking material in an anthropomorphic cardiac phantom for ultrasound imaging. The gel was tested for its acoustic properties and its compatibility with conventional plastics molding techniques. Speed of sound and attenuation were evaluated in the range 2–12 MHz. The speed of sound was 1537 ± 39 m/s, close to typical values for cardiac tissue (∼1576 m/s). The attenuation coefficient was 1.07 dB/cm·MHz, within the range of values previously reported for cardiac tissue (0.81–1.81 dB/cm·MHz). A cardiac model based on human anatomy was developed using established image segmentation processes and conventional plastic molding techniques. Key anatomic features were observed, captured and identified in the model using an intracardiac ultrasound imaging system. These favorable results along with the material's durability and processes that allow for repetitive production of detailed whole-heart models at low cost are promising. There are numerous applications for geometrically complex phantoms in research, training, device development and clinical use.

Tuning Viscoelasticity with Minor Changes in Speed of Sound in an Ultrasound Phantom Material

The acoustic properties of ultrasound phantom materials have always been important, but with new applications interrogating tissue mechanical properties, viscoelasticity has also become an interesting feature to consider. Along with Young's modulus, the viscous component of tissue is affected by certain diseases and can therefore be used as a biomarker. Furthermore, viscoelasticity varies between tissue types and individuals, and therefore it would be useful with a phantom material that reflects this physiological range. Here we describe a gel for ultrasound imaging with a range of mechanical properties given by mixing different ratios of two oil-based gels, clear ballistic and styrene–ethylene/butylene–styrene (SEBS). The gels were mixed in five different proportions, ranging from 0–100% of either gel. For each of the gel compositions, we measured time of flight to determine speed of sound, narrowband ultrasound transmission for attenuation, stress–relaxation for viscoelasticity, mass and volume. Analysis of the stress–relaxation data using the generalized Maxwell model suggests that the material can be described by five parameters, E0, E1, E2, η1 and η2, and that each of these parameters decreases as more SEBS is incorporated into the mixed material. Instantaneous Young's modulus (the sum of E0, E1 and E2 in our model) ranges between 49 and 117 kPa for the different ratios, similar to values reported for cancerous tissue. Despite the large span of obtainable mechanical properties, speed of sound is relatively constant regardless of composition, with mean value estimates (± 95 % CI) between 1438 ± 9 and 1455 ± 3 m/s for pure and mixed gels. This was attributed to a variation in density and Poisson's ratio, following from the relation linking them to speed of sound and elasticity. Furthermore, both speed of sound and attenuation were within a suitable range for ultrasound phantoms. Combining this ballistic gel with SEBS copolymer in oil allows for control of mechanical properties, both elastic and viscous as evaluated by the material model. Furthermore, it does so without compromising ease of use, longevity and safety of the pre-made gel.

Comparative Analysis of Neutron, Proton, Alpha and Beta Radiation Shielding Parameters of PES and PVDC

In medical applications, where polymers and plastics are used as tissue equivalent and phantom materials, the determination of accurate values of radiation shielding parameters becomes very important. In this context, the present work is aimed at determining the values of radiation shielding parameters of two polymers, viz. polyethersulphone (PES) and polyvinylidenechloride (PVDC) and then doing a comparative analysis of their shielding abilities in order to find a better material for shielding. The neutron shielding parameter was determined and was also compared with some common neutron shielding materials such as Boric Acid, Boron Carbide and Graphite. Furthermore, the shielding against charged particles i.e. neutron, proton and alpha particle was also studied with the help of the parameters, ‘mass stopping power’ and ‘projected range’. It was speculated that PES is superior to PVDC for shielding against neutrons, protons, alpha and beta radiation due to higher content of low atomic number elements per monomer unit. So, PES can be used potentially for radiation shielding in medical field.

Multicenter evaluation of MRI-based radiomic features: A phantom study.

This work describes the development of a novel radiomics phantom designed for magnetic resonance imaging (MRI) that can be used in a multicenter setting. The purpose of this study is to assess the stability and reproducibility of MRI-based radiomic features using this phantom across different MRI scanners. A set of phantoms were three-dimensional (3D) printed using MRI visible materials. One set of phantoms were imaged on seven MRI scanners and one was imaged on one MRI scanner. Radiomics analysis of the phantoms, which included first-order features, shape and texture features was performed. Intraclass correlation coefficient (ICC) was used to assess the stability of radiomic features across eight scanners and the reproducibility of two printed models on one scanner. Coefficient of variation (COV) was used to assess the reproducibility of radiomics measurements in the phantom on a single scanner. The phantom models provide sufficient signal-to-noise and contrast in all the tumor models permitting robust automatic segmentation. During a 12-month period of monitoring, the phantom material was stable with T1 and T2 of 150.7±6.7ms and 56.1±3.9ms, respectively. Of all the radiomic features computed, 34 of 69 had COV<10%. Features from first-order statistics were the most robust in stability across the eight scanners with eight of 12 (67%) having high stability. About 29 of 50 (58%) texture features had high stability and no shape features had high stability features across the eight scanners. A novel MRI radiomics phantom has been developed to assess the reproducibility and stability of MRI-based radiomic features across multiple institutions. The variation in radiomic feature stability demonstrates the need for caution when interpreting these features for clinical studies.

Measurement of radiation attenuation parameters of modified defatted soy flour-soy protein isolate-based mangrove wood particleboards to be used for CT phantom production.

For the first time, Rhizophora spp. (Rh. spp.) particleboard phantoms were developed using defatted soy flour (DSF) and soy protein isolate (SPI) modified by sodium hydroxide and itaconic acid polyamidoamine-epichlorohydrin (IA-PAE) adhesive. The microstructural characterization and X-ray diffraction patterns of the material revealed that the modified DSF and SPI adhesives became more compact and homogeneous when NaOH/IA-PAE was added, which prevented damage by moisture. It was confirmed that the composite is crystalline with (101), (002), and (004) orientations. Phantoms made of this material were scanned with X-ray computed tomography (CT) typically used for abdominal examinations with varying energies corresponding to 80, 120, and 135kVp, to determine CT numbers, electron densities, and density distribution profiles. The radiation attenuation parameters were found to be not significantly different from those of water (XCOM) with p values [Formula: see text] 0.05 for DSF and SPI. The DSF- and SPI-based particleboard phantoms showed CT numbers close to those of water at the three X-ray CT energies. In addition, electron density and density distribution profiles of DSF-SPI-Rh. spp. particleboard phantoms with 15 wt% IA-PAE content were even closer to those of water and other commercial phantom materials at the three X-ray CT energies. It is concluded that DSF-SPI with NaOH/IA-PAE added can be used as a potential adhesive in Rh. spp. particleboard phantoms for radiation dosimetry.

Analysis of multiple shear wave modes in a nonlinear soft solid: Experiments and finite element simulations with a tilted acoustic radiation force

Tissue nonlinearity is conventionally measured in shear wave elastography by studying the change in wave speed caused by the tissue deformation, generally known as the acoustoelastic effect. However, these measurements have mainly focused on the excitation and detection of one specific shear mode, while it is theoretically known that the analysis of multiple wave modes offers more information about tissue material properties that can potentially be used to refine disease diagnosis. This work demonstrated proof of concept using experiments and finite element simulations in a uniaxially stretched phantom by tilting the acoustic radiation force excitation axis with respect to the material's symmetry axis. Using this unique set-up, we were able to visualize two propagating shear wave modes across the stretch direction for stretches larger than 140%. Complementary simulations were performed using material parameters determined from mechanical testing, which enabled us to convert the observed shear wave behavior into a correct representative constitutive law for the phantom material, i.e. the Isihara model. This demonstrates the potential of measuring shear wave propagation in combination with shear wave modeling in complex materials as a non-invasive alternative for mechanical testing.

Radiological, dosimetric and mechanical properties of a deformable breast phantom for radiation therapy and surgical applications

The displacement of tumor bed walls during oncoplastic breast surgery (OBS) decreases the accuracy of using surgical clips as the sole surrogate for tumor bed location. This highlights the need for better communication of OBS techniques to radiation oncologists. To facilitate OBS practice and investigate clip placement reliability, a realistic silicone-based breast phantom was constructed with components emulating a breast parenchyma, epidermis, areola, nipple, chest wall, and a tumor. OBS was performed on the phantom and surgical clips were placed to mark the tumor bed. The phantom was imaged with CT, MRI, and ultrasound (US). The parenchyma’s signal-to-noise ratio (SNR) and clips to parenchyma’s contrast-to-noise ratio (CNR) were measured. The phantom’s CT Hounsfield Unit (HU), relative electron density (RED), and mass density were determined. 6 and 10 MV photon beam attenuation measurements were performed in phantom material. The Young’s Modulus and ultimate tensile strength (UTS) of the phantom parenchyma and epidermis were measured. Results showed that the breast phantom components were visible on all imaging modalities with adequate SNR and CNR. The phantom’s HU is 130 ± 10. The RED is 0.983. Its mass density is 1.01 ± 0.01 g cm−3. Photon attenuation measurements in phantom material were within 1% of those in water. The Young’s Moduli were 13.4 ± 4.2 kPa (mechanical) and 30.2 ± 4.1 kPa (US elastography) for the phantom parenchyma. The UTS’ were 0.05 ± 0.01 MPa (parenchyma) and 0.23 ± 0.12 MPa (epidermis). We conclude that the phantom’s imaging characteristics resemble a fibroglandular breast’s and allow clear visualization of high-density markers used in radiation therapy. The phantom material is suitable for dose measurements in MV photon beams. Mechanical results confirmed the phantom’s similarity to breast tissue. The phantom enables investigation of surgical clip displacements pre- and post-OBS, and is useful for radiation therapy quality assurance applications.

Water equivalence of a solid phantom material for radiation dosimetry applications.

Radiological water equivalence of solid phantoms used for radiotherapy is often desired, but is non-trivial to achieve across the range of therapeutic energies. This study evaluated the water equivalence of a new solid phantom material in beam qualities relevant to radiotherapy applications. In-phantom measured depth distributions were compared to that in water to assess the relative attenuation and scatter characteristics of the material. The phantom material was found to be dosimetrically equivalent to water within (1.0 ± 1.0)% for megavoltage photon beam qualities, (1.5 ± 1.3)% for megavoltage electron beam qualities, (1.5 ± 1.5)% for medium-energy kilovoltage X-rays and (3.0 ± 1.5)% for low-energy kilovoltage X-rays.

Dosimetric characteristics of the INTRABEAM ® system with spherical applicators in the presence of air gaps and tissue heterogeneities.

The main aim of this study was to investigate the dosimetric characteristics of the INTRABEAM ® system in the presence of air gaps between the surface of applicators (APs) and tumor bed. Additionally, the effect of tissue heterogeneities was another focus. Investigating the dosimetric characteristics of the INTRABEAM® system is essential to deliver the required dose to the tumor bed correctly and reduce the delivered dose to the ribs and lung. Choosing the correct AP size and fitting it to the lumpectomy cavity is essential to remove the effect of air gaps and avoid inaccurate dose delivery. Consequently, the Geant4 toolkit was used to simulate the INTRABEAM ® system with spherical APs of various sizes. The wall effect of the ion chamber (IC) PTW 34013 used in the present study was checked. The simulations were validated in comparison with measurements, and then used to calculate any inaccuracies in dose delivery in the presence of 4- and 10-mm air gaps between the surface of the APs and the tumor bed. Also, the doses received due to tissue heterogeneities were characterized. It turned out that measurements and simulations were approximately in agreement (± 2%) for all sizes of APs. The perturbation factor introduced by the IC due to differences in graphite-coated polyethylene and air as compared to the phantom material was approximately equal to one for all AP. The greatest relative dose delivery difference was observed for an AP with a diameter of 1.5cm, i.e., 44% and 70% in the presence of 4- and 10-mm air gaps, respectively. In contrast, the lowest relative dose delivery difference was observed for an AP with a diameter of 5cm, i.e., 24% and 42% in the presence of 4- and 10-mm air gaps, respectively. Increasing APs size showed a decrease in relative dose delivery difference due to the presence of air gaps. In addition, the undesired dose received by the ribs turned out to be higher when a treatment site closer to the ribs was assumed. The undesired dose received by the ribs increased as the AP size increased. The lung dose turned out to be decreased due to the shielding effect of the ribs, small lung density, and long separation distance from the AP surface.

Photon mass attenuation coefficients, effective atomic numbers, CT numbers and density profiles of cured DSF-SPC-based Rhizophora spp. particleboard phantoms coupled with NaOH/IA-PAE at different concentrations

Rhizophora spp. (R. spp.) particleboard phantoms based on defatted soy flour and soy protein concentrate were fabricated using itaconic acid polyamidoamine-epichlorohydrin (IA-PAE) at different concentrations with the incorporation of NaOH. The results showed that the mass attenuation coefficients and effective atomic numbers of the particleboard phantoms at 16.59–25.26 keV photon energies were in good agreement within 0.88% and 0.01% of the XCOM values in water with p-values of 0.072 and 0.075. In addition, DSF-SPC-R. spp. phantom with 15 wt% IA-PAE content shows the nearest CT numbers, electron density, and density profiles to water substitutes at three CT energies. These results indicate the suitability of cured DSF-SPC-R. spp. particleboards as phantom materials for the selected X-ray energies.