Phantom Surface Research Articles

Percentage depth dose (PDD) and Beam profile measurements using CT based MAGAT gel dosimetry system and Monte Carlo calculation


 
 
 Abstract
 The aim of this project is to develop and to evaluate the CT based MAGAT (methacrylic acid, gelatine and tetrakis phosphonium chloride) polymer gel dosimetry for measuring 3D dose distributions in radiation treatment. The MAGAT gel was prepared based on the formulation proposed in the literature. The percentage depth dose (PDD) and beam profile of 8 x 8 cm2 field size photon beam from a 6 MV linear accelerator were measured. Monte Carlo simulation was carried out to calculate PDD and beam profiles in the simulated MAGAT gel phantom to verify the data measured using MAGAT gel dosimetry for the 8 x 8 cm2 field size. The PDD and beam profile calculated using simulated MAGAT gel phantom agreed very well with that measured using MAGAT gel dosimetry. However, there were some differences between the simulated PDD with that measured at the surface region due to the electron contamination at the surface of the simulated phantom. In conclusion, the results showed that the CT based MAGAT gel dosimetry system is promising method to measure three- dimensional dose distribution based on PDD and Beam profile measurement.
 Keywords: MAGAT gel, CT, Monte Carlo simulation
 
 

Development of Monte Carlo based real-time treatment planning system with fast calculation algorithm for boron neutron capture therapy

PurposeWe simulated the effect of patient displacement on organ doses in boron neutron capture therapy (BNCT). In addition, we developed a faster calculation algorithm (NCT high-speed) to simulate irradiation more efficiently. MethodsWe simulated dose evaluation for the standard irradiation position (reference position) using a head phantom. Cases were assumed where the patient body is shifted in lateral directions compared to the reference position, as well as in the direction away from the irradiation aperture.For three groups of neutron (thermal, epithermal, and fast), flux distribution using NCT high-speed with a voxelized homogeneous phantom was calculated. The three groups of neutron fluxes were calculated for the same conditions with Monte Carlo code. These calculated results were compared. ResultsIn the evaluations of body movements, there were no significant differences even with shifting up to 9mm in the lateral directions. However, the dose decreased by about 10% with shifts of 9mm in a direction away from the irradiation aperture.When comparing both calculations in the phantom surface up to 3cm, the maximum differences between the fluxes calculated by NCT high-speed with those calculated by Monte Carlo code for thermal neutrons and epithermal neutrons were 10% and 18%, respectively. The time required for NCT high-speed code was about 1/10th compared to Monte Carlo calculation. ConclusionsIn the evaluation, the longitudinal displacement has a considerable effect on the organ doses.We also achieved faster calculation of depth distribution of thermal neutron flux using NCT high-speed calculation code.

Measurement and simulation of secondary neutrons from uniform scanning proton beams in proton radiotherapy

It has long been known that exposure from secondary neutrons in proton radiotherapy can lead to increased risk of secondary cancers later in a patient's life. The assessment of secondary neutrons is, therefore, important to the overall quality of the treatment. In this study, we investigated the neutron dose equivalent outside of the primary proton treatment field as a function of distance to the isocenter and angle relative to the central axis. CR-39 plastic nuclear track detectors (PNTD) were exposed to uniform scanning proton beams at the ProCure Proton Therapy Center, Oklahoma City, OK. The contribution of neutron dose equivalent was investigated for two different experimental configurations, namely hollow-phantom, and cylindrical-phantom. Numerical simulations were performed using the Monte Carlo code FLUKA for similar experimental conditions. Three proton beams of range 5 cm, 18 cm, and 32 cm with 4 cm modulation width, 38 cm snout to phantom surface distance and a 5 cm diameter aperture were used for the study. The measured ratio of neutron dose equivalent to the primary proton dose (H/D) fell off with distance and ranged from 2.1 mSv/Gy to 50.1 mSv/Gy. The contribution of internal neutrons to the overall neutron dose equivalent were found to be up to 64% near the treatment field.

Effects of needle inner surface topography on friction and biopsy length

The effects of inner surface topography on friction force and the coefficient of friction between an inner surface of needle and tissue phantom during needle insertion and on biopsy length are examined using polished, and unpolished needles. In this paper, the inner surfaces of the needles are altered by magnetic abrasive finishing (MAF), and the needle inner surfaces were smoothed from 0.43 to 0.02µm Sa (referred to as the smoothly polished needle) or 0.26µm Sa (referred to as the roughly polished needle). With polyvinyl chloride (PVC) as a tissue-mimicking phantom material, the smoothly polished needle results in the smallest inner friction force (0.0024N/mm), the smallest coefficient of friction (0.35), and the longest biopsy length (34.3mm). The roughly polished needle produces the largest inner friction force (0.0041N/mm), the largest coefficient of friction (0.56), and the shortest biopsy length (30.5mm). Although the inner surface roughness of the roughly polished needle is lower than that of the unpolished needle, the inner friction force and coefficient of friction are larger than those of the unpolished needle. This may be caused by the ridges and grooves in the circumferential direction of the roughly polished needle made with MAF. Based on the surface topography data, the ratchet mechanism is utilized to calculate the coefficient of friction. The results suggest a higher coefficient of friction in the roughly polished needle. The biopsy tests also show the shortest biopsy sample is extracted using the roughly polished needles, which exhibit the greatest inner friction force.

Abstract 12670: Variability in Radiation Dose and Image Quality: A Comparison Across Fluoroscopy-system Vendors and Generations of Equipment

Introduction: Increased recognition of the potentially harmful effects of ionizing radiation has spurred technological advances to reduce exposure during fluoroscopy. However there is currently little understanding of the dose-image quality (IQ) relationship between fluoroscopy vendors and across generations of equipment used for imaging during pediatric catheterization. Methods: We evaluated latest generation fluoroscopy systems from Phillips, Siemens, GE and Toshiba, and an older generation Phillips system (2004 release). Fluoroscopy and cineangiography were performed on a tissue simulation anthropomorphic phantom using a standardized imaging approach. Phantom surface exposures were used for Monte Carlo simulations to calculate radiation effective dose, accounting for differences in beam parameters. We also imaged a fluoroscopy IQ phantom to assess contrast-detail and line-per-inch visualization. IQ images were scored by 3 blinded reviewers with scores averaged to produce a composite rating (scale 0-18). To assess the impact of imaging approach we then simulated a neonatal cardiac catheterization incorporating “typical” imaging protocols provided by institutions using the various systems. Results: Effective doses and IQ scores are summarized in the table. Effective doses varied by >400% with the older generation system consistently delivering markedly higher doses. The associated figure summarizes dose and IQ for a simulated neonatal cardiac catheterization which accounts for measured doses as well as the reported institutional imaging parameters summarized in the figure legend. Conclusion: These data demonstrate substantial technological improvements in fluoroscopy equipment and may be useful to justify institutional “upgrades”. Comparing latest generation systems across vendors and institutions, we found variability in the dose-IQ relationship that reflects both equipment and imaging approach.

Microwave Sensing of Acoustically Induced Local Harmonic Motion: Experimental and Simulation Studies on Breast Tumor Detection

Sensing acoustically induced local harmonic motion using a microwave transceiver system may provide useful information for detecting nonpalpable tumors in dense breast tissue. For this purpose, we propose the harmonic motion microwave Doppler imaging method, in which the first harmonic of the phase modulated signal due to local harmonic motion is sensed. This signal is related to the dielectric, elastic, and acoustic properties of the vibrating region. The purpose of this paper is twofold: 1) to demonstrate the concept of this method with experiments using phantom materials mimicking the elastic and electrical properties of the breast tissue and 2) to investigate the effect of fibroglandular region size and vibration frequency on the received signal, using numerical simulations. A breast phantom with a tumor phantom inclusion (5-mm diameter and 7-mm height) inside fibroglandular region is constructed for the experimental study. The response due to a focused ultrasound probe is linearly scanned at 30-mm depth from the phantom surface, and the Doppler signal level is tracked using a spectrum analyzer. It is shown that the tumor phantom is resolvable inside the surrounding fibroglandular region with about a 3–5-dB decrease in the signal level. The simulations, using the finite-difference time-domain method, show that the received signal level depends on the relative size of the fibroglandular region with respect to the vibrating region size. Further experimental and numerical studies are needed to investigate the feasibility of this method and to optimize the imaging system design.

Comparison of Bolus Materials to Highly Absorbent Polypropylene and Rayon Cloth

This study assesses the utility of a highly absorbent polypropylene and rayon cloth (HAPRC) as a bolus material in radiation therapy. A comparison of various bolus materials used clinically at our center to the test bolus material, water-saturated HAPRC, was conducted. The reproducibility of the physical density was assessed by computerized tomography (CT) scanning the water-saturated HAPRC on a uniform density block phantom on multiple occasions, allowing the cloth to dry fully between subsequent CT scans. The cloth was found to have a consistent physical density between 0.8 and 1.0 g/cm3. To evaluate the dosimetric impact of the various bolus materials, metal oxide semiconductor field effect transistor dosimetry measurements were performed for a 6 MV treatment beam on the anterior surface of an anthropomorphic thorax phantom. The ability of the bolus material to conform to an irregular surface was assessed by CT scanning the various bolus materials overlaying the nose of an anthropomorphic head phantom and another irregularly shaped test object. The HAPRC conforms well to irregular contours and is relatively inexpensive compared to Superflab and thermoplastic sheets. Before implementing the material into the clinical setting, an appropriate process for laundering the material should be determined, for hygienic reasons.

ESTIMATION OF NEUTRON SCATTER CORRECTION FOR CALIBRATION OF PERSONNEL DOSIMETER AND DOSERATEMETER AGAINST 241Am-Be SOURCE-MONTE CARLO SIMULATION AND MEASUREMENTS.

Neutron scatter contributions as a function of distance along the transverse axis of 241Am-Be source were estimated by three different methods such as shadow cone, semi-empirical and Monte Carlo. The Monte Carlo-based FLUKA code was used to simulate the existing room used for the calibration of CR-39 detector as well as LB6411 doseratemeter for selected distances from 241Am-Be source. The modified 241Am-Be spectra at different irradiation geometries such as at different source detector distances, behind the shadow cone, at the surface of the water phantom were also evaluated using Monte Carlo calculations. Neutron scatter contributions, estimated using three different methods compare reasonably well. It is proposed to use the scattering correction factors estimated through Monte Carlo simulation and other methods for the calibration of CR-39 detector and doseratemeter at 0.75 and 1 m distance from the source.

Influence of standard RF coil materials on surface and buildup dose from a 6 MV photon beam in magnetic field.

Magnetic resonance guided teletherapy systems aspire to image the patient concurrently with the radiation delivery. Thus, the radiofrequency (RF) coils used for magnetic resonance imaging, placed on or close to patient skin and in close proximity to the treatment volume, would be irradiated leading to modifications of radiation dose to the skin and in the buildup region. The purpose of this work is to measure and assess these dose modifications due to standard off-the-shelf RF coil materials. A typical surface coil was approximated as layered sheets of polycarbonate, copper tape, and Teflon to emulate the base, conductor, and cover, respectively. A separate investigation used additional coil materials, such as copper pipe, plastic coil housing, a typical coil padding material, and a thin copper conductor. The materials were placed in the path of a 6 MV photon beam at various distances from polystyrene phantoms in which the surface and buildup doses were measured. The experiments were performed on a clinical Varian linac with no magnetic field and with a 0.21 T electromagnet producing a magnetic field parallel to the beam central axis. The authors repeated similar experiments in the presence of a 0.22 T magnetic field oriented perpendicular to the beam central axis using an earlier linac-MR prototype, with a biplanar permanent magnet. The radiation detectors used for the measurements were two different parallel plate ion chambers and GAFChromic films. A typical open beam surface dose of 20% (relative to open beam Dmax) was increased to 63% by the coil padding material and to >74% by all other materials when placed in direct contact with the phantom, irrespective of magnetic field presence or orientation. Without a magnetic field, the surface dose decreased as the test materials were moved away from the phantom surface toward the radiation source, reaching between 30% and 40% at 10 cm gap between the phantom and the test materials. In the presence of the transverse magnetic field, the surface dose reduction was more rapid reaching a dose level of 30%-40% with only 3-4 cm gap. In the presence of the parallel magnetic field, as expected, the surface dose did not decrease considerably as the gap between the phantom surface and test materials was increased; the surface dose remained >60% at 10 cm gap for all tested materials except for the thin copper conductor. As expected, placing coil materials in direct contact with the phantom surface increases the surface dose considerably. The surface dose is reduced by creating a gap between the coil materials and phantom surface. This dose reduction happens more rapidly in the presence of a transverse magnetic field. However, the surface dose stays relatively large irrespective of the gap in the presence of a parallel magnetic field. Thus, the standard, off-the-shelf RF coils should be used with caution in integrated linac-MR systems, especially those using a parallel magnetic field orientation in which case the RF coils will probably need to be reconfigured to create open ports for the radiation beam.

Beam monitor calibration in scanned light-ion beams.

To propose a formalism for the reference dosimetry of scanned light-ion beams consistent with IAEA TRS-398 and Alfonso et al. [Med. Phys. 35, 5179-5186 (2008)]. To identify machine-specific reference (msr) fields and plan-class specific reference (pcsr) fields consistent with the definitions given by Alfonso et al. To review the literature of beam monitor calibration in scanned beams using three different methods in terms of this common formalism. Four types of msr fields are identified as those that are meant to calibrate the beam monitor for scanned beams with particular energies. Two types of pcsr fields are identified as those that are meant to apply one or more tuning factors to the entire delivery chain. The formalism establishes the energy-dependent relation between the number of particles incident on the phantom surface and the beam monitor reading and distinguishes three routes to determine the beam monitor calibration function: (i) the use of a calibrated reference ionization chamber in a single-layer scanned beam, (ii) the use of a cross-calibrated large-area parallel plate ionization chamber in a single-energy beamlet, and (iii) the use of a calibrated reference ionization chamber in a box field to adjust a calibration curve obtained by a Faraday cup or an ionization chamber. Examples of all three methods and comparisons between them from the literature are analysed. The formalism can form the basis of future dosimetry recommendations for scanned particle beams and the analysis of the literature data in terms of this formalism can form the basis of data compilations for the application of the dosimetry procedures.

Response of TLD badges and cards for measurement of the operational quantity Hp(10) to a137Cs source

The operational quantity, H p (10), for strongly penetrating radiation was measured by a dosimeter placed on a phantom surface for individual external dose monitoring. Measurement of H p (10) was carried out with a 137 Cs source using CaSO4 :Dy Teflon-based TLD badges and cards placed on the surface of a PMMA as well as water phantom at a depth of 10 mm. The ratio of response of the TLD discs to TLD badges and that of the TLD cards under similar conditions were identical for different experimental conditions. This experiment quantified the impact of the cassette on the dose measurement. Minor changes in the PMMA phantom thickness beyond 15 cm showed an insignificant impact on the dosimeter response.

Influence of Pulse Repetition Frequency on 3-D Power Doppler Quantification

Three-dimensional power Doppler quantification has limited application because of its high dependency on attenuation. The purpose of the study described here was to assess if different degrees of attenuation, depending on pulse repetition frequency (PRF) adjustment, alter 3-D power Doppler quantification in a region of 100% moving blood when using vascularization index, flow index and vascularization flow index (VFI). A cubic-shaped gelatin phantom with a 1.8-mm-internal-diameter silicon tube was used. The tube, placed at 45° to the phantom's surface, was filled with blood-mimicking fluid with as constant maximum velocity of 30 cm/s. Two different attenuation blocks (low and high attenuation) were alternatively placed between the phantom and the transvaginal transducer. One single observer acquired 10 data sets for each PRF level from 0.3 to 7.5 kHz, using the high- and low-attenuation blocks, for a total of 200 3-D power Doppler data sets. We assessed VFI from 1.5-mm-diameter spherical samples, virtually placed inside the tube, always at the same position. No difference was noted between high- and low-attenuation VFI values when using a PRF of 0.3 kHz. As PRF increased, it was observed that VFI quantification progressively differed between low and high attenuation. Also, a slope on VFI values for both high- and low-attenuation models could be observed when increasing PRF, particularly above 4.0 kHz. We concluded that PRF adjustment is very relevant when using VFI to quantify 3-D power Doppler signal.

Quantitative Fluorescence Sensing Through Highly Autofluorescent, Scattering, and Absorbing Media Using Mobile Microscopy.

Compact and cost-effective systems for in vivo fluorescence and near-infrared imaging in combination with activatable reporters embedded inside the skin to sample interstitial fluid or blood can enable a variety of biomedical applications. However, the strong autofluorescence of human skin creates an obstacle for fluorescence-based sensing. Here we introduce a method for quantitative fluorescence sensing through highly autofluorescent, scattering, and absorbing media. For this, we created a compact and cost-effective fluorescence microscope weighing <40 g and used it to measure various concentrations of a fluorescent dye embedded inside a tissue phantom, which was designed to mimic the optical characteristics of human skin. We used an elliptical Gaussian beam excitation to digitally separate tissue autofluorescence from target fluorescence, although they severely overlap in both space and optical spectrum. Using ∼10-fold less excitation intensity than the safety limit for skin radiation exposure, we successfully quantified the density of the embedded fluorophores by imaging the skin phantom surface and achieved a detection limit of ∼5 × 10(5) and ∼2.5 × 10(7) fluorophores within ∼0.01 μL sample volume that is positioned 0.5 and 2 mm below the phantom surface, corresponding to a concentration of 105.9 pg/mL and 5.3 ng/mL, respectively. We also confirmed that this approach can track the spatial misalignments of the mobile microscope with respect to the embedded target fluorescent volume. This wearable microscopy platform might be useful for designing implantable biochemical sensors with the capability of spatial multiplexing to continuously monitor a panel of biomarkers and chronic conditions even at patients' home.

Ultrasound in Biomedical Engineering: Ultrasound Microbubble Contrast Agents Promote Transdermal Permeation of Drugs

This report discusses a new development in the use of ultrasound microbubble contrast agents on transdermal drug delivery. The medium surrounding the microbubbles at the optimum concentration from liquid to gel can be modified and it can still achieve the same enhancement for transdermal drug permeation as liquid medium. It was also found that under the same ultrasound power density, microbubbles of larger particle sizes can extend the penetration depths of dye at the phantom surface.

Translucent poly(vinyl alcohol) cryogel dosimeters for simultaneous dose buildup and monitoring during chest wall radiation therapy.

Chest wall radiation therapy treatment delivery was monitored using a 5 mm thick radiochromic poly(vinyl alcohol) cryogel that also provided buildup material. The cryogels were used to detect positioning errors and measure the impact of shifts for a chest wall treatment that was delivered to a RANDO phantom. The phantom was shifted by ±2,±3, and ±5 mm from the planned position in the anterior/posterior (A/P) direction; these shifts represent setup errors and the uncertainty associated with lung filling during breath‐hold. The two‐dimensional absolute dose distributions measured in the cryogel at the planned position were compared with the distributions at all shifts from this position using gamma analysis (3%/3 mm, 10% threshold). For shifts of ±2,±3, and ±5 mm the passing rates ranged from 94.3% to 95.6%, 74.0% to 78.8%, and 17.5% to 22.5%, respectively. These results are consistent with the same gamma analysis performed on dose planes calculated in the middle of the cryogel and on the phantom surface using our treatment planning system, which ranged from 94.3% to 95.0%, 76.8% to 77.9%, and 23.5% to 24.3%, respectively. The Pinnacle dose planes were then scaled empirically and compared to the cryogel measurements. Using the same gamma metric, the pass rates ranged from 97.0% to 98.4%. The results of this study suggest that cryogels may be used as both a buildup material and to evaluate errors in chest wall treatment positioning during deep‐inspiration breath‐hold delivery. The cryogels are sensitive to A/P chest wall shifts of less than 3 mm, which potentially allows for the detection of clinically relevant errors.PACS number(s): 87.55.km, 87.57.uq

Glandular dose in digital mammography: Monte carlo method using voxel phantoms

Introduction In breast, the glandular tissues are of high sensitivity to radiation and for this reason the mean dose to the glandular tissues is the most suitable dosimetric quantity. According to the IAEA protocols the Mean Glandular Dose (MGD) is derived from measurements of the incident Air Kerma at the surface of phantom and of the HVL, using tabulated conversion coefficients. Disadvantage of the method is the fact that for calculations use a very simple model of the breast. Purpose The purpose of this study is to assess the mean glandular dose in breast using Monte Carlo code and voxel phantoms in standing posture. Materials and methods Fifty different phantoms (breast’s thickness from 2 to 8 cm for both CC and MLO modes and for glandular fractions in the range of 1.0–100%) and EGSnrc Monte Carlo code was used to calculate the interaction of photons with matter and estimate the MGD to the breast. The calculations were made for the x-ray spectra from a Mo target (tube voltage range 26–32 kV) filtered by Rh. Results For breast phantoms of 2.0–8.0 cm thick and 0.1–100% glandular fraction CC view acquisitions can result in a MGD of 0.452–2.572 mGy. In MLO view acquisitions MGD values ranged between 0.486 and 2.089 mGy. MGD is decreased with increasing glandularities and with increasing breast thickness in general. Conclusion The voxel phantoms is a powerful tool for the study of breast dosimetry. When there is some knowledge of the distribution of glandular tissue within the breast, the results of this study can be used to provide for individual cases.

Electron beam output of an ELEKTA Sli-Plus linear accelerator for irregular shaped fields and for extended SSD

Introduction A dosimetric study of the electron beam output of the ELEKTA Sli-Plus linear accelerator is being presented: (a) when customized electron cutouts are used in order to shape the field, (b) when the treatment is performed in extended Source-Skin Distance. Purpose We have investigated how the machine output varies when electron cutouts of different shapes and sizes are inserted into the beam with the aim to establish a method to predict the beam output in similar circumstances. In order to determine the effective SSDs and the position of the effective point source, the Inverse Square Law (ISL) method has been used for all electron energies and applicators in order to correct the output at extended SSDs applying the ISL correctly. Materials and methods An extended set of output measurements has been performed using electron beams blocked by customized electron cutouts. Measurements have also been carried out in a water phantom at the depth of maximum dose as a function of the air gap g between the far end of the applicator and the phantom surface. Measurements have been compared to calculations with the Oncentra Masterplan treatment planning system. Results & conclusion Our results indicate that the electron beam output does not vary significantly with the insertion of an electron cutout into the beam and therefore, the monitor units determined for a given electron applicator can be used for the blocked beam as well. Monitor Units can also be safely determined by using the SSD eff in order to account for the change in output and depth-dose distribution. Disclosure The authors declare that they have no conflict of interest or any relationship that may bias their presentation.

Investigation of depth dose distribution from electron beam at shallow depth by means of Gafchromic EBT3 polymer films and ionization chamber

Introduction Radiochromic film Gafchromic EBT3 can be used in the geometry when it is parallel to the beam axis allowing obtain absorbed dose depth distribution in a phantom during “single shot” of an accelerator. This method is useful for characterization of the electron beams of intraoperative accelerators because for this modality one needs a precise knowledge of the dose depth distribution starting from the phantom surface. Purpose The purpose of this work is to compare experimentally and in simulation depth dose curves obtained using Gafchromic EBT3 film and ionization chamber. Materials and methods The experimental comparison of the depth dose curves was carried out using 6 and 9 MeV electron beams of Elekta Synergy accelerator and 6 MeV electron beam of intraoperative therapy betatron. The dose distributions were measured by ionization chambers and by Gafchromic EBT3 films in different phantoms. The Monte-Carlo simulation of the process was carried out using PCLab software developed at Tomsk Polytechnic University that allows simulation of the beam interaction with the matter. Results Experimental results show that percentage depth dose measured by the film at the shallow depths is less than the one measured by ionization chamber. Simulation results show the same difference. The simulation also shows that depth dose distribution “measured” by the film is close to the one in the pure water. Conclusion Results show that depth dose distribution from electron beam in water measured by radiochromic film is more precise at shallow depths than the one measured by ionization chamber.

Comparative patient organ dose levels for maxillofacial examinations performed with different radiological facilities

Introduction Maxillofacial radiologic examinations often result in irradiation of the thyroid gland, parotid glands and lens due to primary exposure or scatter radiation. Organ exposure depends on imaging modalities and protocols. Purpose The purpose of this investigation was to evaluate radiation doses to the above-mentioned organs for CT, cone beam CT (CBCT) and panoramic radiographs (orthopantomography, OPT). Materials and methods The absorbed dose was measured on the surface of a head phantom with thermoluminescence dosimeters. The phantom was imaged with CT, CBCT and OPT using standardized protocols employed in clinical routine. The areas examined included the paranasal sinuses, the entire head and the mandible depending on the protocol used. Dose measurements were performed individually for each modality and each protocol. Results Doses to the thyroid gland when located outside the area of interest were lowest for all modalities (range: 0.01–1.22 mGy; measurement uncertainty: 10% at k = 2). Depending on the examination protocol, doses to the eye lens (due to primary beam or scattered radiation) showed wide variability (range: 0.02–26.22 mGy). The parotid glands were the only organs systematically placed in the primary beam for all modalities and protocols. Values ranged from 1.40–29.11 mGy with the highest values for CT examinations. For OPT, doses to the parotid glands were strongly inhomogeneous due to its operating mode. Conclusion CT was the most irradiating modality. The mean doses to the parotid glands were similar for CBCT and OPT, while doses to organs in the scattered field were systematically higher for CBCT than OPT. Disclosure The authors declare that they have no relevant material or financial interests that relate to the research described in this study.

A tracking system to calculate patient skin dose in real-time during neurointerventional procedures using a biplane x-ray imaging system.

Neurovascular interventional procedures using biplane fluoroscopic imaging systems can lead to increased risk of radiation-induced skin injuries. The authors developed a biplane dose tracking system (Biplane-DTS) to calculate the cumulative skin dose distribution from the frontal and lateral x-ray tubes and display it in real-time as a color-coded map on a 3D graphic of the patient for immediate feedback to the physician. The agreement of the calculated values with the dose measured on phantoms was evaluated. The Biplane-DTS consists of multiple components including 3D graphic models of the imaging system and patient, an interactive graphical user interface, a data acquisition module to collect geometry and exposure parameters, the computer graphics processing unit, and functions for determining which parts of the patient graphic skin surface are within the beam and for calculating dose. The dose is calculated to individual points on the patient graphic using premeasured calibration files of entrance skin dose per mAs including backscatter; corrections are applied for field area, distance from the focal spot and patient table and pad attenuation when appropriate. The agreement of the calculated patient skin dose and its spatial distribution with measured values was evaluated in 2D and 3D for simulated procedure conditions using a PMMA block phantom and an SK-150 head phantom, respectively. Dose values calculated by the Biplane-DTS were compared to the measurements made on the phantom surface with radiochromic film and a calibrated ionization chamber, which was also used to calibrate the DTS. The agreement with measurements was specifically evaluated with variation in kVp, gantry angle, and field size. The dose tracking system that was developed is able to acquire data from the two x-ray gantries on a biplane imaging system and calculate the skin dose for each exposure pulse to those vertices of a patient graphic that are determined to be in the beam. The calculations are done in real-time with a typical graphic update time of 30 ms and an average vertex separation of 3 mm. With appropriate corrections applied, the Biplane-DTS was able to determine the entrance dose within 6% and the spatial distribution of the dose within 4% compared to the measurements with the ionization chamber and film for the SK150 head phantom. The cumulative dose for overlapping fields from both gantries showed similar agreement. The Biplane-DTS can provide a good estimate of the peak skin dose and cumulative skin dose distribution during biplane neurointerventional procedures. Real-time display of this information should help the physician manage patient dose to reduce the risk of radiation-induced skin injuries.