Phantom Surface Research Articles

Focused Shear Wave Beam Propagation in Tissue-Mimicking Phantoms.

Ultrasound transient elastography (TE) technologies for liver stiffness measurement (LSM) utilize vibration of small, flat pistons, which generate shear waves that lack directivity. The most common cause for LSM failure in practice is insufficient shear wave signal at the needed depths. We propose to increase shear wave amplitude by focusing the waves into a directional beam. Here, we demonstrate the generation and propagation of focused shear wave beams (fSWBs) in gelatin. Directional fSWBs are generated by vibration at 200-400 Hz of a concave piston embedded near the surface of gelatin phantoms and measured with high-frame-rate ultrasound imaging. Five phantoms with a range of stiffnesses are employed. Shear wave speeds assessed by fSWBs are compared with those by radiation-force-based methods (2D SWE). fSWB amplitudes are compared to predictions using an analytical model. fSWB-derived shear wave speeds are in good agreement with 2D SWE. The amplitudes of fSWBs are localized to the LSM region and are significantly greater than unfocused shear waves. Overall agreement with theory is observed, with some discrepancies in the theoretical source condition. Focusing shear waves can increase the signal in the LSM region for TE. Challenges for translation include coupling piston vibration with the patient skin and increased attenuation in vivo compared to the phantoms employed here. Fibrosis is the most predictive measure of patient outcome in non-alcoholic fatty liver disease. Increased shear wave amplitude in the LSM region can reduce fibrosis assessment failure rates by TE, thus reducing the need for invasive methods like biopsy.

An iterative algorithm to estimate the energy spectrum of an electron beam from PDD curves

Electron beam central-axis percentage depth dose (PDD) curves in water phantom are routinely employed to evaluate the electron beam energy at the phantom surface, in particular the mean and most probable energies from the values of R 50 (half-value range) and Rp (practical range). However, these two quantities are not enough to evaluate important details of the energy distribution, such as the FWHM (Full Width Half Maximum) and the possible presence of a low-energy tail. This paper presents a numerical method that allows estimating the shape of the energy spectrum from a PDD curve. The algorithm uses a database consisting of a set of depth dose curves for monochromatic beams computed by FLUKA in the range 0.1-7.0 MeV by steps of 0.1 MeV and, using an adaptive iterative Monte Carlo process, reconstructs the incident energy spectrum by minimizing the distance between the measured PDD and the computed one. Applications of a MATLAB code based on this algorithm to simulated and real measurements of electron beams done at APAM lab (ENEA Frascati) are presented. This approach represents a strong simplification with respect to energy analysis based on the use of a magnetic spectrometer.

Investigation of Effect of Air Gap between Surface and Bolus on Dose Distribution for 6 MV Photon Beam

In radiotherapy, tissue equivalent boluses are frequently used in the treatment of superficially located tumors. The air gap between the patient's skin and the bolus may cause dosimetric uncertainties. This study aims to dosimetrically investigate the effect of the air gap between the surface and the bolus on dose distribution. Computed tomography (CT) images of the phantom were obtained and transferred to the treatment planning system (TPS). In the TPS, a bolus was placed on the phantom surface and then air gaps were created between the bolus and the surface. The effect of the air gaps between the surface and the 5 mm thick bolus on the dose distribution was analyzed with the point doses obtained from the TPS. For the 6 MV X-ray, it was observed that the air gap negatively affected the surface doses calculated by TPS. Accordingly, an inverse correlation was found between air gap and surface dose. It is recommended that bolus use, especially in curved anatomical regions, should be applied before CT scanning as much as possible. When using bolus material in radiotherapy, it is recommended to be careful not to leave an air gap between the surface and the bolus.

Realization of the absorbed dose to water for 70 kV electronic brachytherapy sources for surface applications

Objective. The purpose of this work is to establish a primary standard for the absorbed dose to water for surface applications with 70 kV electronic brachytherapy sources and thereby to investigate several reference conditions with respect to applicability in metrology institutes, calibration labs and clinics. Approach. A primary standard for the absorbed dose to water for LDR-Seeds (ipFAC) was utilized. For this, the method of evaluation was modified to account for the different geometries in interstitial and surface brachytherapy and for the different energy distributions of the radiation fields, respectively. The correction factors required to determine the absorbed dose to water were evaluated using Monte Carlo (MC) simulations. MC-calculations were also used to estimate the uncertainties of this method. Main results. It could be shown that determining the absorbed dose to water in 1 cm depth below the surface of a water phantom D w (1 cm) is feasible with the ipFAC. Thereby the method to determine D w (1 cm) when the source is placed at 50 cm distance and the beam is collimated turns out to be more robust to variations in the directional emittance of the source than placing the source applicator assembly directly on the phantom. Significance. The first method features significantly lower uncertainties, 1.4% compared to 3.7% (both for k = 2), for the second one. However, a calibration based on a transfer chamber calibrated with the second method is more practical and easier to implement in clinical routine.

The performance of a new type accelerator uRT-linac 506c evaluated by a quality assurance automation system.

The purpose of this study was to evaluate the performance of our quality assurance (QA) automation system and to evaluate the machine performance of a new type linear accelerator uRT-linac 506c within 6months using this system. This QA automation system consists of a hollow cylindrical phantom with 18 steel balls in the phantom surface and an analysis software to process electronic portal imaging device (EPID) measurement image data and report the results. The performance of the QA automation system was evaluated by the tests of repeatability, archivable precision, detectability of introduced errors, and the impact of set-up errors on QA results. The performance of this linac was evaluated by 31 items using this QA system over 6months. This QA system was able to automatically deliver QA plan, EPID image acquisition, and automatic analysis. All images acquiring and analysis took approximately 4.6min per energy. The preset error of 0.1mm in multi-leaf collimator (MLC) leaf were detected as 0.12±0.01mm for Bank A and 0.10±0.01mm in Bank B. The 2mm setup error was detected as -1.95±0.01mm, -2.02±0.01mm, 2.01±0.01mm for X, Y, Z directions, respectively. And data from the tests of repeatability and detectability of introduced errors showed the standard deviation were all within 0.1mm and 0.1°. and data of the machine performance were all within the tolerance specified by AAPM TG-142. The QA automation system has high precision and good performance, and it can improve the QA efficiency. The performance of the new accelerator has also performed very well during the testing period.

Evaluation of Elasticity, Dose Reduction, and Image Quality on Sr-Pb Shield for Thoracic CT Examination

The performance of chest CT always involved the scanning of breast since it was positioned within the scan range. It makes this organ always receives an amount of radiation that potentially harms the biological system. Many attempts have been performed to reduce the radiation doses objected to breast, including the utilization of radio-protective shield. This study aims to develop the radio-protector shield silicon rubber (SR) - Lead (Pb) based for the breast. The shield was developed with a thickness of 0.6 mm and SR:Pb ratios of 100:0, 98:2, 96:4, 94:6, and 92:8. After that, the shield was placed over an anthropomorphic phantom. The shield’s reliability was tested in terms of elasticity, radiation dose, and image quality. The elasticity level of a material was indicated by Young's modulus yielded. Our results showed that the Young's modulus decreased as the percentage of Pb increased. Breast surface dose was measured using a Radcal ion chamber on the surface of the breast phantom. The measured dose was reduced as Pb increased, the dose using shielding at the highest percentage of 92:8 wt% is 8.71 mGy. The measured SNR without using shielding is 18.38, while the measured SNR using shielding 100:0, 98:2, 96:4, 94:6 and 92:8 was 18.47; 17.45; 16.65; 15.49, and 14.23, respectively. SR-Pb shielding has a Young’s modulus less than 0.035 GPa and can cover the chest of phantom well. SR-Pb shield was able to reduce the breast dose by 26% while the image quality in all variations of the SR:Pb ratio was above the rose criterion value with an insignificant decrease.

How efficient are metal-polymer and dual-metals-polymer non-lead radiation shields?

Lead shields are often used to attenuate ionising radiations. However, to make lighter, recyclable and more efficient shields compared to lead, combinations of new metallic compounds together with polymer, for example, flexible polyvinyl chloride (PVC) have been developed recently. In this study, the capabilities of non-lead radiation shields made of one or two metallic compounds and polymer were evaluated. Monte Carlo (MC)-based BEAMnrc code was used to build a functional model based on a Philips X-ray machine in the range of radiographic energies. The MC model was then verified by IPEM Report 78 as a standardised global reference. The MC model was then used to evaluate the efficiency of non-lead-based garments made of metallic compound and polymer (MCP) including BaSO4 -PVC, Bi2 O3 -PVC, Sn-PVC and W-PVC, as well as dual-metallic compounds and polymer (DMCP) including Bi2 O3 -BaSO4 -PVC, Bi2 O3 -Sn-PVC, W-Sn-PVC and W-BaSO4 -PVC. The absorbed doses were determined at the surface of a water phantom and compared directly with the doses obtained for 0.5 mm pure lead (Pb). Bi2 O3 -BaSO4 -PVC and W-BaSO4 -PVC were found to be efficient shields for most of the energies. In addition to the above radiation shields, Bi2 O3 -Sn-PVC was also found to be effective for the spectrum of 60 keV. Bi2 O3 -BaSO4 -PVC as a non-lead dual metals-PVC shield was shown to be more efficient than pure lead in diagnostic X-ray range. Combination of two metals-PVC, a low atomic number (Z) metal together with a high atomic number metal, and also single-metal-PVC shields were shown to be efficient enough to apply as radiation protection shields instead of lead-based garments.

Analysis of surface roughness in optical coherence elastography using a novel phantom

Compression optical coherence elastography (OCE) has shown promise in detecting diseases, such as breast cancer, based on changes in the elasticity of tissue. While the mechanical models used in OCE assume a flat surface, tissue typically exhibits surface topography that can lead to inaccurate estimation of elasticity in OCE images (elastograms). The coupling of surface topography and heterogeneous mechanical properties in tissue make it challenging to study the relative impact of surface roughness on image formation. To address this, we developed mechanically homogeneous phantoms that accurately replicate the surface topography of human breast tissue. Surface topography of breast tissue specimens was captured in three-dimensional (3-D) optical coherence tomography (OCT) scans. Molds replicating the surface roughness of tissue were generated using 3-D modelling and 3-D printing. The phantoms were then fabricated in the molds using polydimethylsiloxane. OCT was used to validate the accuracy of the phantom surface topography and the phantoms were then used to determine the impact of surface roughness in compression OCE elastograms. Surface roughness phantoms were shown to accurately reflect the surface topography of six breast tissue specimens with a correlation of 0.96 ± 0.03. When imaged with a variant of compression OCE called quantitative micro-elastography, surface roughness resulted in a slight decrease in elasticity accuracy with a mean percentage error of 8.2 % for a flat phantom compared to 11.7 % for the roughness phantom, and a larger decrease in elasticity precision, or sensitivity, with a mean relative standard deviation of 9.4 % for the flat phantom compared to 21.2 %, for the roughness phantom. Our results show that contrast in elastograms moderately correlated with the phantom surface profile (r = 0.59, p < 0.001) and that surface roughness introduces spatially-varying elasticity that should be considered in the analysis of elastograms in compression OCE.

Investigation of Surface Dose Accuracy of Two Dose Calculation Algorithms Using Thermoluminescent Dosimeters

Accurate estimation of the surface dose in radiotherapy is very important in reducing skin reactions. This study aims to evaluate the accuracy of two different treatment planning algorithms in calculating the surface dose in a specially designed phantom using thermoluminescent dosimetry (TLD). In this study, a special phantom was designed for surface dose measurement. The phantom surface consisted of an adhesive bolus for the adhesion of TLDs. 121 TLDs were placed 1 cm apart on the bolus surface. In TPS, irradiation plans were created at different fields and source-surface distances (SSD). Dose calculations were made with Anisotropic Algorithm algorithms (AAA) and Pencil Beam Convolution (PBC) algorithms for all plans. The mean dose was measured for each point. For each of the 4x4, 6x6, 8x8, 10x10, and 12x12 cm2 domains, the TLDs within the domain were approximately 1 cm inward from the edge. To measure the effect of SSD on surface dose, the isocenter point was located at depths of 0 cm, 2.5 cm and 5.0 cm, respectively. The surface dose at each depth was measured with TLDs. The doses calculated by the AAA and PBC algorithms were compared with the doses measured by TLDs. The AAA algorithm overestimates the surface dose by 4% compared to the TLD measurement for the 4x4 field. The surface dose calculation of the PBC algorithm was found to be high when compared to TLD measurements for all SSDs and fields. There was a significant difference between the PBC algorithm dose calculation and TLD measurements in all fields and SSDs (p&amp;lt;0.001). It was observed that the AAA algorithm performed better in calculating the surface dose than the PBC algorithm. AAA and PBC algorithm users are advised to be more careful about surface dose calculation.

Dosimetric characterization of foam padding with posterior fields in palliative radiation therapy

Patients undergoing external beam radiation therapy for the palliative treatment of painful bony metastases may have difficulty maintaining a still position on a rigid uncovered couch top, both during CT simulation as well as during patient setup, image guidance, and treatment on the linear accelerator. For these patients, a thin foam pad or mattress is sometimes used to mitigate patient discomfort. It was desired to quantify the effect of the padding in cases in which the patient is to be treated supine with posterior beams when the majority of the beam weighting traverses both the couch and the pad. Ion chamber measurements in-phantom were acquired with 6 MV, 10 MV, and 15 MV photon beams. At depths of maximum dose, the pad resulted in a difference of signal collected ≤1%. At the phantom surface, the pad resulted in an increase in signal ranging from 1% to 6.5% for the measured beams. CT data of the pad, both with and without applied pressure, indicated that the pad had average HU values close to air.

Performance of a Nonlinear Magnetic Handheld Probe for Intraoperative Sentinel Lymph Node Detection: A Phantom Study

ObjectiveThis study investigates the performance of the DiffMag handheld probe (nonlinear magnetometry), to be used for sentinel lymph node detection. Furthermore, the performance of DiffMag is compared with a gamma probe and a first-order magnetometer (Sentimag®, linear magnetometry).MethodsThe performance of all three probes was evaluated based on longitudinal distance, transverse distance, and resolving power for two tracer volumes. A phantom was developed to investigate the performance of the probes for a clinically relevant situation in the floor of the mouth (FOM).ResultsConsidering the longitudinal distance, both DiffMag handheld and Sentimag® probe had comparable performance, while the gamma probe was able to detect at least a factor of 10 deeper. Transverse distances of 13, 11, and 51 mm were measured for the small tracer volume by the DiffMag handheld, Sentimag®, and the gamma probe, respectively. For the large tracer volume this was 21, 18, and 55 mm, respectively. The full width at half maximum, at 7 mm probe height from the phantom surface, was 14, 12, and 18 mm for the small tracer volume and 15, 18, and 25 mm for the large tracer volume with the DiffMag handheld, Sentimag®, and gamma probe, respectively.ConclusionsWith a high resolving power but limited longitudinal distance, the DiffMag handheld probe seems suitable for detecting SLNs which are in close proximity to the primary tumor. In this study, comparable results were shown using linear magnetometry. The gamma probe reached 10 times deeper, but has a lower resolving power compared with the DiffMag handheld probe.

Influence of dosimeter depth on estimating patient's eye lens dose in head computed tomography: A measurement and Monte Carlo simulation study

The distance between the posterior cornea and anterior surface of the lens is approximately 3 mm, and it is unclear whether the dose measured near the ocular surface of the phantom accurately reflects the lens dose without any specific correction factors. This study aimed to investigate the influence of the depth for the estimation of the eye lens doses of the patient during head computed tomography (CT) examination using measurement and Monte Carlo simulation. During the measurement, the absorbed dose on the surface and at a depth of 3 mm from the surface of the cylinder phantom, corresponding to the positions of the right and left eyes, was obtained using optically stimulated luminescence dosimeters at tube voltages of 80 and 120 kV. In the Monte Carlo simulations, an anthropomorphic phantom and custom-made cylinder phantoms, which were made of polymethyl methacrylate (PMMA) and polyurethane, respectively, were used, and absorbed doses were obtained on the surface and at a depth of 3 mm from the surface of the phantoms. In the measurement, the absorbed dose at the 3-mm depth from the surface of the phantom was significantly higher than that on the surface of the phantom for both tube voltages (p < 0.01). In the simulation, the absorbed doses at a depth of 3 mm from the surface of the phantom model were significantly higher than those on the surface of the phantom model regardless of the material and structure of the phantom (p < 0.01). The ratio of the absorbed dose on the surface to that at a depth of 3 mm ranged from 0.93 to 0.95 regardless of the material and structure of the phantom. These results highlight the importance of lens dosimetry considering the depth of the lens.

PETRA: A pencil beam trimming algorithm for analytical proton therapy dose calculations with the dynamic collimation system.

The Dynamic Collimation System (DCS) has been shown to produce superior treatment plans to uncollimated pencil beam scanning (PBS) proton therapy using an in-house treatment planning system (TPS) designed for research. Clinical implementation of the DCS requires the development and benchmarking of a rigorous dose calculation algorithm that accounts for pencil beam trimming, performs monitor unit calculations to produce deliverable plans at all beam energies, and is ideally implemented with a commercially available TPS. To present an analytical Pencil bEam TRimming Algorithm (PETRA) for the DCS, with and without its range shifter, implemented in the Astroid TPS (.decimal, Sanford, Florida, USA). PETRA was derived by generalizing an existing pencil beam dose calculation model to account for the DCS-specific effects of lateral penumbra blurring due to the nickel trimmers in two different planes, integral depth dose variation due to the trimming process, and the presence and absence of the range shifter. Tuning parameters were introduced to enable agreement between PETRA and a measurement-validated Dynamic Collimation Monte Carlo (DCMC) model of the Miami Cancer Institute's IBA Proteus Plus system equipped with the DCS. Trimmer position, spot position, beam energy, and the presence or absence of a range shifter were all used as variables for the characterization of the model. The model was calibrated for pencil beam monitor unit calculations using procedures specified by International Atomic Energy Agency Technical Report Series 398 (IAEA TRS-398). The integral depth dose curves (IDDs) for energies between 70 MeV and 160 MeV among all simulated trimmer combinations, with and without the ranger shifter, agreed between PETRA and DCMC at the 1%/1mm 1-D gamma criteria for 99.99% of points. For lateral dose profiles, the median 2-D gamma pass rate for all profiles at 1.5%/1.5mm was 99.99% at the water phantom surface, plateau, and Bragg peak depths without the range shifter and at the surface and Bragg peak depths with the range shifter. The minimum 1.5%/1.5mm gamma pass rates for the 2-D profiles at the water phantom surface without and with the range shifter were 98.02% and 97.91%, respectively, and, at the Bragg peak, the minimum pass rates were 97.80% and 97.5%, respectively. The PETRA model for DCS dose calculations was successfully defined and benchmarked for use in a commercially available TPS.

Effect of varying X-ray tube voltage and additional filtration on image quality and patient dose in digital radiography system

This study investigated the effect of varying x-ray tube voltage and additional filtration thicknesses on radiation dose and image quality in digital radiography system. The polymethylmethacrylate (PMMA) phantoms of different thicknesses simulating both the adult chest and abdomen and the pediatric patient's chest examinations were used. X-ray tube voltage range of 70–125 kVp was used for adult patient chest radiography, 70–100 kVp for adult patient abdominal radiography, and 50–70 kVp for pediatric 1-year-old chest examination. 0.1–0.3 mm Cu and 1.0 mm Al filters were used as additional filters. Patient doses were measured with an ionization chamber, considering the irradiation parameters recommended for radiographic examinations performed in radiology clinics in the EUR 16260 protocol. The Entrance Skin Dose (ESD) was calculated from the air kerma value measured at the entrance surface of the PMMA phantoms. Effective dose values were calculated by employing PCXMC 2.0 program. For image quality evaluations, CDRAD, LCD-4, Beam stop and Huttner test object used together with PMMA phantoms and Alderson RS-330 Lung/Chest phantom were used. Figure of Merit (FOM), which allows quantitative assessment in terms of image quality and patient dose, has been calculated. Based on the calculated FOM values were evaluated at the tube voltages and additional filter thicknesses recommended in the EUR 16260 protocol. Entrance Skin Dose and Inverse Image Quality Figure (IQFinv) value obtained from contrast detail analysis decreased with increasing filter thickness and tube voltage. Decrease in ESD and IQFinv with increasing tube voltage without additional filter was 56% and 21% for adult chest radiography, 69% and 39% for adult abdominal radiography and 34% and 6% for 1-year-old pediatric chest radiography. When calculated FOM values are examined, it can be recommended to use a 0.1 mm Cu filter at 90 kVp and a 0.1 mm Cu + 1.0 mm Al filter at 125 kVp for adult chest radiography. For adult abdominal radiography, 0.2 mm Cu filter at 70 and 80 kVp and 0.1 mm Cu filter at 90 and 100 kVp were found to be appropriate. It was determined that the appropriate additional filter at 70 kVp for 1-year-old chest radiography was 1.0 mm Al+0.1 mm Cu.

Noise reduction performance of a deep learning-based reconstruction in brain computed tomography images acquired with organ-based tube current modulation.

We aimed to evaluate the image quality of brain computed tomography (CT) images reconstructed using deep learning-based reconstruction (DLR) in organ-based tube current modulation (OB-TCM) acquisition. An anthropomorphic head phantom and a cylindrical low-contrast phantom were scanned at the standard dose level for adult brain CT in axial volume acquisition without OB-TCM. Moreover, image acquisition with OB-TCM was performed. The radiation dose on the eye lens was measured using a scintillation fibre-optic dosimeter placed on the anthropomorphic phantom's eye surface. The task transfer function (TTF), contrast-to-noise ratio (CNR), and low-contrast object specific CNR obtained from low-contrast phantom images reconstructed with filtered back projection (FBP), hybrid iterative reconstruction (HIR), and two types of DLR (DLRCTA and DLRLCD) were compared. In result, OB-TCM achieved a 32.5% dose reduction in the eye lens. Although HIR, DLRCTA, and DLRLCD showed lower TTF than FBP, the difference in TTF at the highest contributing spatial frequency corresponding to the contrast rod diameter was < 10%. Despite the OB-TCM acquisition, DLRCTA and DLRLCD achieved significantly lower noise and a higher CNR than FBP without OB-TCM (p < 0.05). However, low-contrast object specific CNR was equivalent among all reconstruction methods for the objective diameter of 5mm and slightly improved in DLRLCD for the objective diameter of 7mm. DLR with OB-TCM acquisition enabled dose reduction for the eye lens and high CNR image appearance, whereas the low contrast detectability evaluated by low-contrast object specific CNR did not always improve.

Development of a new coordinate calibration phantom for a light-section-based optical surface monitoring system.

A calibration phantom made of Derlin requires manual translational and rotational adjustments when calibrating a light-section-based optical surface monitoring system (VOXELAN) with a phantom material that insufficiently reflects the red-slit laser of the system. This study aimed to develop a new calibration phantom using different materials and to propose a procedure that minimizes setup errors. The new phantom, primarily made of PET100, which exhibits good reflectivity without scattering or attenuating the red-slit laser at the phantom surface, was shaped in a manner similar to that of previous designs. The detection accuracy and stability were evaluated using six different regions of interest (ROIs) and compared with previous phantom designs. The coordinate coincidence between the machine and VOXELAN was compared for both phantom designs. The detection accuracy and stability of the new phantom in the reference ROI setting were found to be better than those of previous phantoms. In the lateral, longitudinal, and vertical directions, the coordinate coincidences in translational directions for the previous phantom were obtained at 1.07 ± 0.66, 1.46 ± 0.47, and 0.26 ± 0.83mm, whereas those for the new phantom were obtained at 0.28 ± 0.21, 0.18 ± 0.30, and -0.30 ± 0.29mm, respectively. The rotational errors of the two phantoms were identical. The new phantom exhibited improved detection stability because of its good reflectivity. Additionally, the new placement procedure was linked to the six-degrees-of-freedom couch. A combination of the new phantom and its new placement procedure is suitable for coordinate calibration of VOXELAN.

Dose rate assessment of spot-scanning very high energy electrons radiotherapy driven by laser plasma acceleration

Laser plasma accelerators (LPA) can produce very high-energy electrons (VHEE) with ultra-short bunch duration, which may facilitate the application of ultra-high dose rate radiotherapy (FLASH-RT) to treat deep-seated tumors. The study aims to evaluate the dose rate delivery by spot-scanning VHEE beams produced by LPA and to discuss the feasibility and beam specifications for FLASH-RT implementation. Various dose rate metrics, including averaged dose rate (ADR), dose-averaged dose rate (DADR), and dose-threshold dose rate (DTDR), are examined in the context of spot-scanning. Theoretical analysis and Monte Carlo simulations are employed to quantify the dose rate distribution for a water phantom and explore the impact of beam parameters. All the beam parameters are based on experimental results. With a lower pulse repetition rate of 5 Hz, ADR can only reach a dose rate in the order of 10−1Gy/s, while attaining the FLASH-RT dose rate of 40Gy/s necessitates the utilization of high-power lasers with a kilohertz working repetition rate. In contrast to ADR, DADR and DTDR remain independent of the scanning path and can reach the ultra-high dose rate surpassing 1014Gy/s at the phantom surface. Meanwhile, the ultrashort electron bunch can be stretched during scattering within the water, resulting in a dependence of DADR and DTDR on the penetration depth. Both the charge per shot and angular spread are important parameters in dose rate calculations. This investigation offers insights into practical beam parameters for preclinical applications and supplies guidance for designing the LPAs suitable for future spot-scanning VHEE FLASH-RT.

Effect of transverse magnetic field on dose distributions of yttrium 90 skin patch source

The total dose absorbed on the tumor cell from the skin patch sources used in clinical superficial brachytherapy should be limited within the target tumor volume in order to minimize the potential side effects. Average range of the beta particles within tissue may exceed the thickness of a superficial skin tumor beyond the target tumor volume, causing side effects by damaging the deeper located healthy tissue and the bone underneath the tumor. It is desired to minimize the possible side effects by selecting a short-range radionuclide. Administering the treatment under an external magnetic field is another option for reducing side effects. To achieve this, in this study, the percentage deep dose (PDD) and transverse dose profile (TDP) distributions of the skin patch source labeled with Yttrium 90 (90Y) using the GEANT4-based GAMOS Monte Carlo code were examined before and after applying magnetic field, and it was evaluated whether it was possible to limit the dose within a certain volume or not.&#x0D; Simulation results showed that, along with the application of a transverse magnetic field, the dose values increased by 7.2% and 3.1% respectively at 0.25 mm and 1.0 mm depths whereas it decreased by 9.4%, 25.0%, 41.8% and 57.6%, at 2.0 mm, 3.0 mm, 4.0 mm and 5.0 mm depths respectively on the central axis from the surface of the tissue phantom with respect to the 0 T values of the field. In case of a superficial skin tumor with a thickness of 3.0 mm from the skin surface, the amount of dose accumulated in the tumor volume for 0 T value of the transverse magnetic field was 89% of the total dose, while it increased to 98% at the intensity of 1.5 T, and the dose received by the healthy tissue under the tumor decreased by 10.1%.

Eye lens dose for medical staff assisting patients during computed tomography: comparison of several types of radioprotective glasses

Medical staff sometimes assists patients in the examination room during computed tomography (CT) scans for several purposes. This study aimed to investigate the dose reduction effects of four radioprotective glasses with different lead equivalents and lens shapes. A medical staff phantom was positioned assuming body movement restraint of the patient during chest CT, and Hp(3) at the eye surfaces of the medical staff phantom and inside the lens of the four types of radioprotective glasses were measured by changing the distance of the staff phantom from the gantry, eye height, and width of the nose pad. The Hp(3) at the right eye surface with glasses of 0.50–0.75 mmPb and 0.07 mmPb was approximately 83.5% and 58.0%, respectively, lower than that without radioprotective glasses. The dose reduction rates at left eye surface increased with over-glass type glasses by 14%–28% by increasing the distance from the CT gantry to the staff phantom from 25 to 65 cm. The dose reduction rates at the left eye surface decreased with over-glass type glasses by 26%–31% by increasing the height of the eye lens for the medical staff phantom from 130 to 170 cm. The Hp(3) on the left eye surface decreased by 46.9% with the widest nose pad width compared to the narrowest nose pad width for the glasses with adjustable nose pad width. The radioprotective glasses for staff assisting patients during CT examinations should have a high lead equivalent and no gap around the nose and under the front lens.

Accuracy of the catalyst surface guidance system for patient monitoring during cranial SRS treatments.

The use of surface guided imaging in cranial stereotactic radiotherapy provides a non-ionising form of patient position verification that gives information on when patient position errors may require corrections to be applied. This work assessed the accuracy of Catalyst+ HD system for treatment geometries commonly used in cranial SRS. Average Catalyst reported error as a function of couch rotation agreed with measured kV and MV walkout within 0.5mm for the lateral and longitudinal directions. Change in Catalyst reported error with isocentre depth relative to the monitoring region of interest (ROI) from the surface was assessed and showed variation above 0.5mm, but within 1mm for isocentre depths ranging from 3 to 15cm from the phantom surface. Gantry occlusion of Catalyst cameras caused a shift in reported position error that was also dependent on isocentre depth relative to the monitoring ROI. SRS MapCHECK patients specific QA results showed improvement in gamma passing rates for a workflow where Catalyst reported errors above 0.5mm were corrected.