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Journal of Applied Clinical Medical... Nov 2013Lack of underlying material can lead to dose reduction in kilovoltage radiotherapy treatments because of backscatter reduction. Conversely, the use of lead shielding can... (Review)
Review
Lack of underlying material can lead to dose reduction in kilovoltage radiotherapy treatments because of backscatter reduction. Conversely, the use of lead shielding can lead to large dose enhancement close to the lead interface. GAFCHROMIC film has been shown to be of use in verification of local backscatter factors compared to reference data in codes of practice, but careful handling and multiple readings are required to reduce systematic uncertainties to between 3% and 4%. Monte Carlo modeling of the specific treatment unit should be performed in cases which are found to differ from reference values before alternative values are adopted clinically, but these cases are expected to be few. GAFCHROMIC film may also be used to estimate backscatter reduction more readily than customized ionization chambers, for a range of beam qualities, applicator sizes and depth, with and without lead shielding. Differences were found between different studies, and it is not clear to what extent these are due to variation in equipment and/or technique. However, a layer of wax around lead shielding of 1 mm thickness should be sufficient to eliminate lead enhancement effects for all kilovoltage energies from 40 kV to 300 kV.
Topics: Computer Simulation; Humans; Monte Carlo Method; Radiometry; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Scattering, Radiation
PubMed: 24257277
DOI: 10.1120/jacmp.v14i6.4358 -
Medical Physics Nov 2023Radiation dosimetry is essential for radiation therapy (RT) to ensure that radiation dose is accurately delivered to the tumor. Despite its wide use in clinical...
BACKGROUND
Radiation dosimetry is essential for radiation therapy (RT) to ensure that radiation dose is accurately delivered to the tumor. Despite its wide use in clinical intervention, the delivered radiation dose can only be planned and verified via simulation. This makes precision radiotherapy challenging while in-line verification of the delivered dose is still absent in the clinic. X-ray-induced acoustic computed tomography (XACT) has recently been proposed as an imaging tool for in vivo dosimetry.
PURPOSE
Most of the XACT studies focus on localizing the radiation beam. However, it has not been studied for its potential for quantitative dosimetry. The aim of this study was to investigate the feasibility of using XACT for quantitative in vivo dose reconstruction during radiotherapy.
METHODS
Varian Eclipse system was used to generate simulated uniform and wedged 3D radiation field with a size of 4 cm 4 cm. In order to use XACT for quantitative dosimetry measurements, we have deconvoluted the effects of both the x-ray pulse shape and the finite frequency response of the ultrasound detector. We developed a model-based image reconstruction algorithm to quantify radiation dose in vivo using XACT imaging, and universal back-projection (UBP) reconstruction is used as comparison. The reconstructed dose was calibrated before comparing it to the percent depth dose (PDD) profile. Structural similarity index matrix (SSIM) and root mean squared error (RMSE) are used for numeric evaluation. Experimental signals were acquired from 4 cm 4 cm radiation field created by Linear Accelerator (LINAC) at depths of 6, 8, and 10 cm beneath the water surface. The acquired signals were processed before reconstruction to achieve accurate results.
RESULTS
Applying model-based reconstruction algorithm with non-negative constraints successfully reconstructed accurate radiation dose in 3D simulation study. The reconstructed dose matches well with the PDD profile after calibration in experiments. The SSIMs between the model-based reconstructions and initial doses are over 85%, and the RMSEs of model-based reconstructions are eight times lower than the UBP reconstructions. We have also shown that XACT images can be displayed as pseudo-color maps of acoustic intensity, which correspond to different radiation doses in the clinic.
CONCLUSION
Our results show that the XACT imaging by model-based reconstruction algorithm is considerably more accurate than the dose reconstructed by UBP algorithm. With proper calibration, XACT is potentially applicable to the clinic for quantitative in vivo dosimetry across a wide range of radiation modalities. In addition, XACT's capability of real-time, volumetric dose imaging seems well-suited for the emerging field of ultrahigh dose rate "FLASH" radiotherapy.
Topics: X-Rays; In Vivo Dosimetry; Tomography, X-Ray Computed; Radiometry; Phantoms, Imaging; Acoustics; Radiotherapy Dosage
PubMed: 37203253
DOI: 10.1002/mp.16476 -
Journal of Applied Clinical Medical... Nov 2018To assess the efficiency of combined use of ArcCheck detector (AC) and portal dosimetry (PDIP) for delivery quality assurance of head and neck and prostate...
PURPOSE
To assess the efficiency of combined use of ArcCheck detector (AC) and portal dosimetry (PDIP) for delivery quality assurance of head and neck and prostate volumetric-modulated arc therapy.
MATERIALS AND METHODS
Measurement processes were studied with the Gamma index method according to three analysis protocols. The detection sensitivity to technical errors of each individual or combined measurement processes was studied by inserting collimator, dose and MLC opening error into five head and neck and five prostate initial treatment plans. A total of 220 plans were created and 660 analyses were conducted by comparing measurements to error free planned dose matrix.
RESULTS
For head and neck localization, collimator errors could be detected from 2° for AC and 3° for PDIP. Dose and MLC errors could be detected from 2% and 0.5 mm for AC and PDIP. Depending on the analysis protocol, the detection sensitivity of total simulated errors ranged from 54% to 88% for AC vs 40% to 74% for PDIP and 58% to 92% for the combined process. For the prostate localization, collimator errors could be detected from 4° for AC while they could not be detected by PDIP. Dose and MLC errors could be detected from 3% and 0.5 mm for AC and PDIP. The detection sensitivity of total simulated errors ranged from 30% to 56% for AC vs 16% to 38% for PDIP and 30% to 58% for combined process.
CONCLUSION
The combined use of the two measurement processes did not statistically improve the detectability of technical errors compared to use of single process.
Topics: Head and Neck Neoplasms; Humans; Male; Prognosis; Prostatic Neoplasms; Quality Assurance, Health Care; Radiometry; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Radiotherapy, Intensity-Modulated
PubMed: 30338922
DOI: 10.1002/acm2.12460 -
The British Journal of Radiology Oct 2019To measure leakage ambient dose equivalent H*(10) from stray secondary neutron and photon radiation around proton therapy (PT) facility and evaluate adequacy of...
OBJECTIVES
To measure leakage ambient dose equivalent H*(10) from stray secondary neutron and photon radiation around proton therapy (PT) facility and evaluate adequacy of shielding design.
METHODS AND MATERIALS
H*(10) measurement were carried out at 149 locations around cyclotron vault (CV), beam transport system (BTS) and first treatment room (GTR3) of a multiroom PT facility using WENDI-II and SmartIon survey meter. Measurement were performed under extreme case scenarios wherein maximum secondary neutrons and photons were produced around CV, BTS and GTR3 by stopping 230MeV proton of 300nA on beam degrader, end of BTS and isocenter of GTR3. Weekly time average dose rate (TADR) were calculated from H*(10) value measured at selective hot spots by irradiating actual treatment plans of mix clinical sites.
RESULTS
The maximum total H*(10) were within 2 µSv/hr around CV, 5 µSv/hr around outer wall of BTS which increases up to 62 µSv/hr at the end of inside BTS corridor. Maximum H*(10) of 20.8 µSv/hr in treatment control console (P125), 23.4 µSv/hr behind the common wall between GTR3 and GTR2 (P132) and 25.7 µSv/hr above isocenter (P99) were observed around GTR3. Reduction of beam current from 6 to 3 nA and 1 nA at nozzle exit lead to decrease in total H*(10) at P125 from 20.8 to 11.35 and 4.62 µSv/hr. In comparison to extreme case scenario, H*(10) value at P125, P132 and P99 from clinically relevant irradiation parameters were reduce by a factor ranging from 8.6 for high range cube to 46.4 for brain clinical plan. The maximum weekly TADR per fraction was highest for large volume, sacral chordoma patient at 8.5 µSv/hr compare to 0.3 µSv/hr for brain patient. The calculated weekly TADR for 30 mix clinical cases and 15 fractions of 1 L cube resulted total weekly TADR of 83-84 µSv/hr at P125, P132 and P99. The maximum annual dose level at these hot spots were estimated at 4.37 mSv/Yr.
CONCLUSION
We have carried out an extensive measurement of H*(10) under different conditions. The shielding thickness of our PT facility is adequate to limit the dose to occupational worker and general public within the permissible stipulated limit. The data reported here can bridge the knowledge gap in ambient dose around PT facility and can also be used as a reference for any new and existing proton facility for intercomparison and validation.
ADVANCES IN KNOWLEDGE
First extensive investigation of neutron and photon H*(10) around PT facility and can bridge the knowledge gap on ambient dose.
Topics: Cyclotrons; Health Facility Environment; Neutrons; Photons; Proton Therapy; Radiation Monitoring; Radiation Protection; Radiometry; Scattering, Radiation
PubMed: 31287739
DOI: 10.1259/bjr.20190382 -
Magnetic Resonance in Medicine Nov 2005This article describes an EPR spectrometer specifically designed and constructed for EPR spectroscopy in humans. The spectrometer is based on a permanent magnet,... (Clinical Trial)
Clinical Trial
This article describes an EPR spectrometer specifically designed and constructed for EPR spectroscopy in humans. The spectrometer is based on a permanent magnet, suitable for measurements at 1200 MHz. The magnet has a full 50 cm gap between the poles, which facilitates accurate and comfortable placement of the subject for the EPR measurement at any location on the human body. The bridge includes features to facilitate clinical operations, including an indicator for phasing of the reference arm and a 2 level RF amplifier. Resonators with holders for each type and site of measurement have been developed that comfortably position the resonator and the patient and prevent artifacts due to motion. The initial applications for which the spectrometer has been designed are for oximetry using loops on the surface, oximetry using implanted resonators for measuring deep sites, and measurements in the teeth for determination of exposures to clinically significant doses of ionizing radiation.
Topics: Electron Spin Resonance Spectroscopy; Equipment Design; Equipment Failure Analysis; Humans; Oximetry; Radiation Dosage; Radiometry
PubMed: 16193470
DOI: 10.1002/mrm.20689 -
The British Journal of Radiology Jun 2015This article presents an overview of the recent developments and requirements in radiotherapy dosimetry, with particular emphasis on the development of optical fibre... (Review)
Review
This article presents an overview of the recent developments and requirements in radiotherapy dosimetry, with particular emphasis on the development of optical fibre dosemeters for radiotherapy applications, focusing particularly on in vivo applications. Optical fibres offer considerable advantages over conventional techniques for radiotherapy dosimetry, owing to their small size, immunity to electromagnetic interferences, and suitability for remote monitoring and multiplexing. The small dimensions of optical fibre-based dosemeters, together with being lightweight and flexible, mean that they are minimally invasive and thus particularly suited to in vivo dosimetry. This means that the sensor can be placed directly inside a patient, for example, for brachytherapy treatments, the optical fibres could be placed in the tumour itself or into nearby critical tissues requiring monitoring, via the same applicators or needles used for the treatment delivery thereby providing real-time dosimetric information. The article outlines the principal sensor design systems along with some of the main strengths and weaknesses associated with the development of these techniques. The successful demonstration of these sensors in a range of different clinical environments is also presented.
Topics: Humans; Optical Fibers; Radiometry; Radiotherapy
PubMed: 25761212
DOI: 10.1259/bjr.20140702 -
Journal of Applied Clinical Medical... Feb 2011Electronic portal imaging device (EPID) plays an important role in radiation therapy portal imaging, geometric and dosimetric verification. Consistent image quality and...
Electronic portal imaging device (EPID) plays an important role in radiation therapy portal imaging, geometric and dosimetric verification. Consistent image quality and stable radiation response is necessary for proper utilization that requires routine quality assurance (QA). A commercial 'EPID QC' phantom weighing 3.8 kg with a dimension of 25 × 25 × 4.8 cm³ is used for EPID QA. This device has five essential tools to measure the geometric accuracy, signal-to-noise ratio (SNR), dose linearity, and the low- and the high-contrast resolutions. It is aligned with beam divergence to measure the imaging and geometric parameters in both X and Y directions, and can be used as a baseline check for routine QA. The low-contrast tool consists of a series of holes with various diameters and depths in an aluminum slab, very similar to the Las Vegas phantom. The high-resolution contrast tool provides the modulation transfer function (MTF) in both the x- and y-dimensions to measure the focal spot of linear accelerator that is important for imaging and small field dosimetry. The device is tested in different institutions with various amorphous silicon imagers including Elekta, Siemens and Varian units. Images of the QA phantom were acquired at 95.2 cm source-skin-distance (SSD) in the range 1-15MU for a 26 × 26 cm² field and phantom surface is set normal to the beam direction when gantry is at 0° and 90°. The epidSoft is a software program provided with the EPID QA phantom for analysis of the data. The preliminary results using the phantom on the tested EPID showed very good low-contrast resolution and high resolution, and an MTF (0.5) in the range of 0.3-0.4 lp/mm. All imagers also exhibit satisfactory geometric accuracy, dose linearity and SNR, and are independent of MU and spatial orientations. The epidSoft maintains an image analysis record and provides a graph of the temporal variations in imaging parameters. In conclusion, this device is simple to use and provides testing on basic and advanced imaging parameters for daily QA on any imager used in clinical practices.
Topics: Algorithms; Copper; Equipment Design; Humans; Materials Testing; Models, Statistical; Particle Accelerators; Phantoms, Imaging; Quality Control; Radiation Monitoring; Radiometry; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Reproducibility of Results; Silicon
PubMed: 21587179
DOI: 10.1120/jacmp.v12i2.3350 -
Igaku Butsuri : Nihon Igaku Butsuri... 2016Flattening filter-free (FFF) beams generated by linear accelerators have been widely adopted in many hospitals recently for radiation therapy. FFF technology can provide... (Review)
Review
Flattening filter-free (FFF) beams generated by linear accelerators have been widely adopted in many hospitals recently for radiation therapy. FFF technology can provide higher dose rates so that shortening of the treatment time and less intra-fraction motion error are expected.In Japan, the current way of determining absorbed dose to water for FFF beams is to follow the Standard Dosimetry 12 protocol which was developed for flattened beams. Since it has been reported that the flattened beams and FFF beams have different beam properties, it is necessary to evaluate the usefulness of Standard Dosimetry 12 protocol for FFF beam dosimetry.This report reviews physical and dosimetric properties of FFF beams especially in terms of the effect on absorbed dose to water dosimetry using an ionization chamber. From the review, it became evident that the absorbed dose to water is underestimated by volume averaging effect of the ionization chamber. On the other hand, the absorbed dose to water is overestimated by using the beam-quality specifier TPR to predict the restricted mass collision stopping power ratio for FFF beams. Therefore, an alternative method was proposed for absorbed dose to water dosimetry of FFF beams based on Standard Dosimetry 12.
Topics: Radiometry; Radiotherapy Dosage; Water
PubMed: 28428458
DOI: 10.11323/jjmp.36.2_79 -
Physics in Medicine and Biology Aug 2018Because of the concerns associated with radiation exposure at a young age, there is an increased interest in pediatric absorbed dose estimates for imaging agents. Almost... (Comparative Study)
Comparative Study
Because of the concerns associated with radiation exposure at a young age, there is an increased interest in pediatric absorbed dose estimates for imaging agents. Almost all reported pediatric absorbed dose estimates, however, have been determined using adult pharmacokinetic data with radionuclide S values that take into account the anatomical differences between adults and children based upon the older Cristy-Eckerman (C-E) stylized phantoms. In this work, we use pediatric model-derived pharmacokinetics to compare absorbed dose and effective dose estimates for F-FDG in pediatric patients using S values generated from two different geometries of computational phantoms. Time-integrated activity coefficients of F-FDG in brain, lungs, heart wall, kidneys and liver, retrospectively, calculated from 35 pediatric patients at the Boston's Children Hospital were used. The absorbed dose calculation was performed in accordance with the Medical Internal Radiation Dose method using S values generated from the University of Florida/National Cancer Institute (UF/NCI) hybrid phantoms, as well as those from C-E stylized computational phantoms. The effective dose was computed using tissue-weighting factors from ICRP Publication 60 and ICRP Publication 103 for the C-E and UF/NCI, respectively. Substantial differences in the absorbed dose estimates between UF/NCI hybrid pediatric phantoms and the C-E stylized phantoms were found for the lungs, ovaries, red bone marrow and urinary bladder wall. Large discrepancies in the calculated dose values were observed in the bone marrow; ranging between -26% to +199%. The effective doses computed by the UF/NCI hybrid phantom S values were slightly different than those seen using the C-E stylized phantoms with percent differences of -0.7%, 2.9% and 2.5% for a newborn, 1 year old and 5 year old, respectively. Differences in anatomical modeling features among computational phantoms used to perform Monte Carlo-based photon and electron transport simulations for F, and very likely for other radionuclides, impact internal organ dosimetry computations for pediatric nuclear medicine studies.
Topics: Child; Child, Preschool; Female; Fluorodeoxyglucose F18; Humans; Infant; Infant, Newborn; Male; Monte Carlo Method; Neoplasms; Organs at Risk; Phantoms, Imaging; Photons; Radiation Dosage; Radiation Exposure; Radiometry; Retrospective Studies
PubMed: 30022768
DOI: 10.1088/1361-6560/aad47a -
Radiation Oncology (London, England) Jun 2013The lack of sensitive biocompatible particle track detectors has so far limited parallel detection of physical energy deposition and biological response. Fluorescent...
BACKGROUND
The lack of sensitive biocompatible particle track detectors has so far limited parallel detection of physical energy deposition and biological response. Fluorescent nuclear track detectors (FNTDs) based on Al₂O₃:C,Mg single crystals combined with confocal laser scanning microscopy (CLSM) provide 3D information on ion tracks with a resolution limited by light diffraction. Here we report the development of next generation cell-fluorescent ion track hybrid detectors (Cell-Fit-HD).
METHODS
The biocompatibility of FNTDs was tested using six different cell lines, i.e. human non-small cell lung carcinoma (A549), glioblastoma (U87), androgen independent prostate cancer (PC3), epidermoid cancer (A431) and murine (VmDk) glioma SMA-560. To evaluate cell adherence, viability and conformal coverage of the crystals different seeding densities and alternative coating with extracellular matrix (fibronectin) was tested. Carbon irradiation was performed in Bragg peak (initial 270.55 MeV u⁻¹). A series of cell compartment specific fluorescence stains including nuclear (HOECHST), membrane (Glut-1), cytoplasm (Calcein AM, CM-DiI) were tested on Cell-Fit-HDs and a single CLSM was employed to co-detect the physical (crystal) as well as the biological (cell layer) information.
RESULTS
The FNTD provides a biocompatible surface. Among the cells tested, A549 cells formed the most uniform, viable, tightly packed epithelial like monolayer. The ion track information was not compromised in Cell-Fit-HD as compared to the FNTD alone. Neither cell coating and culturing, nor additional staining procedures affected the properties of the FNTD surface to detect ion tracks. Standard immunofluorescence and live staining procedures could be employed to co-register cell biology and ion track information.
CONCLUSIONS
The Cell-Fit-Hybrid Detector system is a promising platform for a multitude of studies linking biological response to energy deposition at high level of optical microscopy resolution.
Topics: Aluminum Oxide; Animals; Biocompatible Materials; Carbon; Cell Line, Tumor; Crystallization; Fluorescent Antibody Technique; Heavy Ion Radiotherapy; Humans; Magnesium; Materials Testing; Mice; Microscopy, Confocal; Proton Therapy; Radiometry
PubMed: 23758749
DOI: 10.1186/1748-717X-8-141