Out-of-field doses and neutron dose equivalents for electron beams from modern Varian and Elekta linear accelerators.
Abstract Out-of-field doses from radiotherapy can cause harmful side effects or eventually lead to secondary cancers. Scattered doses outside the applicator field, neutron source strength values, and neutron dose equivalents have not been broadly investigated for high-energy electron beams. To better understand the extent of these exposures, we measured out-of-field dose characteristics of electron applicators for high-energy electron beams on two Varian 21iXs, a Varian TrueBeam, and an Elekta Versa HD operating at various energy levels. Out-of-field dose profiles and percent depth-dose curves were measured in a W...
Source: Journal of Applied Clinical Medical Physics - July 28, 2016 Category: Physics Authors: Cardenas CE, Nitsch PL, Kudchadker RJ, Howell RM, Kry SF Tags: J Appl Clin Med Phys Source Type: research

Electrocardiogram-gated coronary CT angiography dose estimates using ImPACT.
Abstract The primary study objective was to assess radiation doses using a modified form of the Imaging Performance Assessment of Computed Tomography (CT) scanner (ImPACT) patient dosimetry for cardiac applications on an Aquilion ONE ViSION Edition scanner, including the Ca score, target computed tomography angiography (CTA), prospective CTA, continuous CTA/cardiac function analysis (CFA), and CTA/CFA modulation. Accordingly, we clarified the CT dose index (CTDI) to determine the relationship between heart rate (HR) and X-ray exposure. As a secondary objective, we compared radiation doses using modified ImPACT, a ...
Source: Journal of Applied Clinical Medical Physics - July 28, 2016 Category: Physics Authors: Kobayashi M, Asada Y, Matsubara K, Suzuki S, Koshida K, Matsunaga Y, Haba T, Kawaguchi A, Toyama H, Kato R Tags: J Appl Clin Med Phys Source Type: research

Imaging acquisition display performance: an evaluation and discussion of performance metrics and procedures.
Abstract When The Joint Commission updated its Requirements for Diagnostic Imaging Services for hospitals and ambulatory care facilities on July 1, 2015, among the new requirements was an annual performance evaluation for acquisition workstation displays. The purpose of this work was to evaluate a large cohort of acquisition displays used in a clinical environment and compare the results with existing performance standards provided by the American College of Radiology (ACR) and the American Association of Physicists in Medicine (AAPM). Measurements of the minimum luminance, maximum luminance, and luminance uniform...
Source: Journal of Applied Clinical Medical Physics - July 28, 2016 Category: Physics Authors: Silosky MS, Marsh RM, Scherzinger AL Tags: J Appl Clin Med Phys Source Type: research

Validation of total skin electron irradiation (TSEI) technique dosimetry data by Monte Carlo simulation.
Abstract Total skin electron irradiation (TSEI) is a complex technique which requires many nonstandard measurements and dosimetric procedures. The purpose of this work was to validate measured dosimetry data by Monte Carlo (MC) simulations using EGSnrc-based codes (BEAMnrc and DOSXYZnrc). Our MC simulations consisted of two major steps. In the first step, the incident electron beam parameters (energy spectrum, FWHM, mean angular spread) were adjusted to match the measured data (PDD and profile) at SSD = 100 cm for an open field. In the second step, these parameters were used to calculate dose distributions at the ...
Source: Journal of Applied Clinical Medical Physics - July 28, 2016 Category: Physics Authors: Nevelsky A, Borzov E, Daniel S, Bar-Deroma R Tags: J Appl Clin Med Phys Source Type: research

A cross-sectional study of the radiation dose and image quality of X-ray equipment used in IVR.
This study was conducted in 2014 at 13 medical facilities using 18 IVR X-ray systems. We evaluated image quality and simultaneously measured the radiation dose. Entrance surface doses for fluoroscopy (duration, 1 min) and cineradiography (duration, 10 s) are measured using a 20-cm-thick acrylic plate and skin dose monitor. The image quality (such as spatial resolution and low-contrast detectability) of both fluoroscopy and cineradiography was evaluated using a QC phantom. For fluoroscopy, the average entrance surface dose using the 20-cm-thick acrylic plate was 13.9 (range 2.1-28.2) mGy/min. For cineradiography, the averag...
Source: Journal of Applied Clinical Medical Physics - July 28, 2016 Category: Physics Authors: Inaba Y, Chida K, Kobayashi R, Zuguchi M Tags: J Appl Clin Med Phys Source Type: research

Predicting deliverability of volumetric-modulated arc therapy (VMAT) plans using aperture complexity analysis.
Abstract The purpose of this study was to evaluate the ability of an aperture complexity metric for volumetric-modulated arc therapy (VMAT) plans to predict plan delivery accuracy. We developed a complexity analysis tool as a plug-in script to Varian's Eclipse treatment planning system. This script reports the modulation of plans, arcs, and individual control points for VMAT plans using a previously developed complexity metric. The calculated complexities are compared to that of 649 VMAT plans previously treated at our institution from 2013 to mid-2015. We used the VMAT quality assurance (QA) results from the 649 ...
Source: Journal of Applied Clinical Medical Physics - July 28, 2016 Category: Physics Authors: Younge KC, Roberts D, Janes LA, Anderson C, Moran JM, Matuszak MM Tags: J Appl Clin Med Phys Source Type: research

Characterization and evaluation of 2.5 MV electronic portal imaging for accurate localization of intra- and extracranial stereotactic radiosurgery.
Abstract 2.5 MV electronic portal imaging, available on Varian TrueBeam machines, was characterized using various phantoms in this study. Its low-contrast detectability, spatial resolution, and contrast-to-noise ratio (CNR) were compared with those of conventional 6 MV and kV planar imaging. Scatter effect in large patient body was simulated by adding solid water slabs along the beam path. The 2.5 MV imaging mode was also evaluated using clinically acquired images from 24 patients for the sites of brain, head and neck, lung, and abdomen. With respect to 6 MV, the 2.5 MV achieved higher contrast and preserved sharp...
Source: Journal of Applied Clinical Medical Physics - July 28, 2016 Category: Physics Authors: Song KH, Snyder KC, Kim J, Li H, Ning W, Rusnac R, Jackson P, Gordon J, Siddiqui SM, Chetty IJ Tags: J Appl Clin Med Phys Source Type: research

A novel phantom and procedure providing submillimeter accuracy in daily QA tests of accelerators used for stereotactic radiosurgery.
Abstract Stereotactic radiosurgery (SRS) places great demands on spatial accuracy. Steel BBs used as markers in quality assurance (QA) phantoms are clearly visible in MV and planar kV images, but artifacts compromise cone-beam CT (CBCT) isocenter localization. The purpose of this work was to develop a QA phantom for measuring with sub-mm accuracy isocenter congruence of planar kV, MV, and CBCT imaging systems and to design a practical QA procedure that includes daily Winston-Lutz (WL) tests and does not require computer aid. The salient feature of the phantom (Universal Alignment Ball (UAB)) is a novel marker for ...
Source: Journal of Applied Clinical Medical Physics - July 28, 2016 Category: Physics Authors: Brezovich IA, Popple RA, Duan J, Shen S, Wu X, Benhabib S, Huang M, Cardan RA Tags: J Appl Clin Med Phys Source Type: research

Re: Estimating and reducing dose received by cardiac devices for patients undergoing radiotherapy.
PMID: 27455507 [PubMed - in process] (Source: Journal of Applied Clinical Medical Physics)
Source: Journal of Applied Clinical Medical Physics - July 28, 2016 Category: Physics Authors: Mihailidis DN Tags: J Appl Clin Med Phys Source Type: research

Response to Re: Estimating and reducing dose received by cardiac devices for patients undergoing radiotherapy.
Abstract In reply to Dimitris N. Mihailidis regarding our manuscript entitled "Estimating and reducing dose received by cardiac devices for patients undergoing radiotherapy". PMID: 27455508 [PubMed - in process] (Source: Journal of Applied Clinical Medical Physics)
Source: Journal of Applied Clinical Medical Physics - July 28, 2016 Category: Physics Authors: Archambault L, Varfalvy N, Bourgouin A Tags: J Appl Clin Med Phys Source Type: research

Some musings on our labor's meaning and the legacy of our departing friends; on who, why, and how we should publish obituaries.
PMID: 27455509 [PubMed - in process] (Source: Journal of Applied Clinical Medical Physics)
Source: Journal of Applied Clinical Medical Physics - July 28, 2016 Category: Physics Authors: Mills MD Tags: J Appl Clin Med Phys Source Type: research

Dosimetric assessment of brass mesh bolus for postmastectomy photon radiotherapy
Brass mesh bolus has been shown to be an acceptable substitute for tissue-equivalent bolus to increase superficial dose for chest wall tangent photon radiotherapy. This work investigated the increase in surface dose, the change in the dose at depth, and the safety implications of higher energy photon beams when using brass mesh bolus for postmastectomy chest wall radiotherapy. A photon tangent plan was delivered to a thorax phantom, and the superficial dose ranged from 40% –72% of prescription dose with no bolus. The surface dose increased to 75%–110% of prescription dose with brass mesh bolus and 85%–109...
Source: Journal of Applied Clinical Medical Physics - July 26, 2016 Category: Physics Source Type: research

Anatomy-based definition of point A utilizing three-dimensional volumetric imaging approach for high-dose-rate (HDR) intracavitary brachytherapy dose prescription when treating cervical cancer using limited resources
This study was designed to determine whether volumetric imaging could identify consistent alternative prescription methods to Manchester/point A when prescribing radiation dose in the treatment of cervical cancer using HDR intracavitary brachy ­therapy (ICBT). One hundred and twenty-five treatment plans of 25 patients treated for carcinoma of the cervix were reviewed retrospectively. Each patient received 5 fractions of HDR ICBT following initial cisplatin-based pelvic chemoradiation, and radiation dose was originally prescribed to point A (ICRU-38). The gross tumor volume (GTV) and high-risk clinical target volume (HR...
Source: Journal of Applied Clinical Medical Physics - July 16, 2016 Category: Physics Source Type: research

Some musings on our labor ’s meaning and the legacy of our departing friends; on who, why, and how we should publish obituaries
- (Source: Journal of Applied Clinical Medical Physics)
Source: Journal of Applied Clinical Medical Physics - July 13, 2016 Category: Physics Source Type: research

Some musings on our labor’s meaning and the legacy of our departing friends; on who, why, and how we should publish obituaries
- (Source: Journal of Applied Clinical Medical Physics)
Source: Journal of Applied Clinical Medical Physics - July 13, 2016 Category: Physics Source Type: research

The feasibility of atlas-based automatic segmentation of MRI for H & N radiotherapy planning
Atlas-based autosegmentation is an established tool for segmenting structures for CT-planned head and neck radiotherapy. MRI is being increasingly integrated into the planning process. The aim of this study is to assess the feasibility of MRI-based, atlas-based autosegmentation for organs at risk (OAR) and lymph node levels, and to compare the segmentation accuracy with CT-based autosegmentation. Fourteen patients with locally advanced head and neck cancer in a prospective imaging study underwent a T1-weighted MRI and a PET-CT (with dedicated contrast-enhanced CT) in an immobilization mask. Organs at risk (orbits, parotids...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Response to Re: Estimating and reducing dose received by cardiac devices for patients undergoing radiotherapy
In reply to Dimitris N. Mihailidis regarding our manuscript entitled "Estimating and reducing dose received by cardiac devices for patients undergoing radiotherapy" (Source: Journal of Applied Clinical Medical Physics)
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Re: Estimating and reducing dose received by cardiac devices for patients undergoing radiotherapy
- (Source: Journal of Applied Clinical Medical Physics)
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Out-of-field doses and neutron dose equivalents for electron beams from modern Varian and Elekta linear accelerators
Out-of-field doses from radiotherapy can cause harmful side effects or eventually lead to secondary cancers. Scattered doses outside the applicator field, neutron source strength values, and neutron dose equivalents have not been broadly investigated for high-energy electron beams. To better understand the extent of these exposures, we measured out-of-field dose characteristics of electron applicators for high-energy electron beams on two Varian 21iXs, a Varian TrueBeam, and an Elekta Versa HD operating at various energy levels. Out-of-field dose profiles and percent depth-dose curves were measured in a Wellhofer water pha...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Monte Carlo calculations and experimental measurements of the TG-43U1-recommended dosimetric parameters of 125I (Model IR-Seed2) brachytherapy source
A new design of 125I (Model IR-Seed2) brachytherapy source has been manufactured recently at the Applied Radiation Research School, Nuclear Science and Technology Research Institute in Iran. The source consists of six resin beads (0.5 mm diameter) that are sealed in a cylindrical titanium capsule of 0.7 mm internal and 0.8 mm external diameters. This work aims to evaluate the dosimetric parameters of the newly designed 125I source using experimental measurements and Monte Carlo (MC) simulations. Dosimetric characteristics (dose rate constant, radial dose function, and 2D and 1D anisotropy functions) of the IR-Seed2 were de...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Validation of total skin electron irradiation (TSEI) technique dosimetry data by Monte Carlo simulation
Total skin electron irradiation (TSEI) is a complex technique which requires many nonstandard measurements and dosimetric procedures. The purpose of this work was to validate measured dosimetry data by Monte Carlo (MC) simulations using EGSnrc-based codes (BEAMnrc and DOSXYZnrc). Our MC simulations consisted of two major steps. In the first step, the incident electron beam parameters (energy spectrum, FWHM, mean angular spread) were adjusted to match the measured data (PDD and profile) at SSD = 100 cm for an open field. In the second step, these parameters were used to calculate dose distributions at the treatment distance...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Fricke gel dosimeter with improved sensitivity for low-dose-level measurements
Fricke solution has a wide range of applications as radiation detector and dosimetry. It is particularly appreciated in terms of relevant comparative advantages, like tissue-equivalence when prepared in aqueous media like gel matrix, continuous mapping capability, independence of dose rate and incident direction, as well as linear dose response. This work presents the development and characterization of an improved Fricke gel system, based on modified chemical compositions, making possible its application in clinical radiology due to its improved sensitivity. Properties of standard Fricke gel dosimeter for high-dose levels...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

A cross-sectional study of the radiation dose and image quality of X-ray equipment used in IVR
This study was conducted in 2014 at 13 medical facilities using 18 IVR X-ray systems. We evaluated image quality and simultaneously measured the radiation dose. Entrance surface doses for fluoroscopy (duration, 1 min) and cineradiography (duration, 10 s) are measured using a 20-cm-thick acrylic plate and skin dose monitor. The image quality (such as spatial resolution and low-contrast detectability) of both fluoroscopy and cineradiography was evaluated using a QC phantom. For fluoroscopy, the average entrance surface dose using the 20-cm-thick acrylic plate was 13.9 (range 2.1–28.2) mGy/min. For cineradiography, the ...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

A comparative study based on image quality and clinical task performance for CT reconstruction algorithms in radiotherapy
In this study we designed and implemented a new comparative analysis method associating image quality, radiation dose, and patient size with radiotherapy task performance, with the purpose of guiding the clinical radiotherapy usage of CT reconstruction algorithms. The iDose4 iterative reconstruction algorithm was selected as the target for comparison, wherein filtered back-projection (FBP) reconstruction was regarded as the baseline. Both phantom and patient images were analyzed. A layer-adjustable anthropomorphic pelvis phantom capable of mimicking 38–58 cm lateral diameter-sized patients was imaged and reconstructe...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Biplane interventional pediatric system with cone-beam CT: dose and image quality characterization for the default protocols
The aim of this study was to assess image quality and radiation dose of a biplane angiographic system with cone-beam CT (CBCT) capability tuned for pediatric cardiac procedures. The results of this study can be used to explore dose reduction techniques. For pulsed fluoroscopy and cine modes, polymethyl methacrylate phantoms of various thicknesses and a Leeds TOR 18-FG test object were employed. Various fields of view (FOV) were selected. For CBCT, the study employed head and body dose phantoms, Catphan 504, and an anthropomorphic cardiology phantom. The study also compared two 3D rotational angiography protocols. The entra...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Electrocardiogram-gated coronary CT angiography dose estimates using ImPACT
The primary study objective was to assess radiation doses using a modified form of the Imaging Performance Assessment of Computed Tomography (CT) scanner (ImPACT) patient dosimetry for cardiac applications on an Aquilion ONE ViSION Edition scanner, including the Ca score, target computed tomography angiography (CTA), prospective CTA, continuous CTA/cardiac function analysis (CFA), and CTA/CFA modulation. Accordingly, we clarified the CT dose index (CTDI) to determine the relationship between heart rate (HR) and X-ray exposure. As a secondary objective, we compared radiation doses using modified ImPACT, a whole-body dosimet...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Imaging acquisition display performance: an evaluation and discussion of performance metrics and procedures
When The Joint Commission updated its Requirements for Diagnostic Imaging Services for hospitals and ambulatory care facilities on July 1, 2015, among the new requirements was an annual performance evaluation for acquisition workstation displays. The purpose of this work was to evaluate a large cohort of acquisition displays used in a clinical environment and compare the results with existing performance standards provided by the American College of Radiology (ACR) and the American Association of Physicists in Medicine (AAPM). Measurements of the minimum luminance, maximum luminance, and luminance uniformity, were performe...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Automated Calculation of Water-equivalent Diameter (DW) Based on AAPM Task Group 220
In this study, DW was calculated for standard CTDI phantoms and patient images. Two types of phantom were used, one representing the head with a diameter of 16 cm and the other representing the body with a diameter of 32 cm. Images of 63 patients were also taken, 32 who had undergone a CT head examination and 31 who had undergone a CT thorax examination. There are three main parts to our algorithm for automated DW calculation. The first part is to read 3D images and convert the CT data into Hounsfield units (HU). The second part is to find the contour of the phantoms or patients automatically. And the third part is to auto...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

An energy minimization method for the correction of cupping artifacts in cone-beam CT
The purpose of this study was to reduce cupping artifacts and improve quantitative accuracy of the images in cone-beam CT (CBCT). An energy minimization method (EMM) is proposed to reduce cupping artifacts in reconstructed image of the CBCT. The cupping artifacts are iteratively optimized by using efficient matrix computations, which are verified to be numerically stable by matrix analysis. Moreover, the energy in our formulation is convex in each of its variables, which brings the robustness of the proposed energy minimization algorithm. The cupping artifacts are estimated as a result of minimizing this energy. The result...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

A routine quality assurance test for CT automatic exposure control systems
The study purpose was to develop and validate a quality assurance test for CT automatic exposure control (AEC) systems based on a set of nested polymethylmethacrylate CTDI phantoms. The test phantom was created by offsetting the 16 cm head phantom within the 32 cm body annulus, thus creating a three part phantom. This was scanned at all acceptance, routine, and some nonroutine quality assurance visits over a period of 45 months, resulting in 115 separate AEC tests on scanners from four manufacturers. For each scan the longitudinal mA modulation pattern was generated and measurements of image noise were made in two annular ...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Measurement of image rotation angle in CT for radiotherapy treatment planning
In this study, a method of quantitative testing of image rotation in CT is presented, based on the automated analysis of an image of a phantom half-filled with water. A plug-in was written for ImageJ software for automated detection of a water surface in an image and measurement of its angle relative to a horizontal line. A water phantom can be used for the evaluation of image rotation for axial mode. In helical mode the movement of the table would cause movement of the water. The difference between image rotation for axial and helical scans can be evaluated by measuring and comparing the angles of the tabletop surface for...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Characterization and evaluation of 2.5 MV electronic portal imaging for accurate localization of intra- and extracranial stereotactic radiosurgery
2.5 MV electronic portal imaging, available on Varian TrueBeam machines, was characterized using various phantoms in this study. Its low-contrast detectability, spatial resolution, and contrast-to-noise ratio (CNR) were compared with those of conventional 6 MV and kV planar imaging. Scatter effect in large patient body was simulated by adding solid water slabs along the beam path. The 2.5 MV imaging mode was also evaluated using clinically acquired images from 24 patients for the sites of brain, head and neck, lung, and abdomen. With respect to 6 MV, the 2.5 MV achieved higher contrast and preserved sharpness on bony struc...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Performance evaluation of the RITG148+ set of TomoTherapy quality assurance tools using RTQA2 radiochromic film
Version 6.3 of the RITG148+ software package offers eight automated analysis routines for quality assurance of the TomoTherapy platform. A performance evaluation of each routine was performed in order to compare RITG148+ results with traditionally accepted analysis techniques and verify that simulated changes in machine parameters are correctly identified by the software. Reference films were exposed according to AAPM TG-148 methodology for each routine and the RITG148+ results were compared with either alternative software analysis techniques or manual analysis techniques in order to assess baseline agreement. Changes in ...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

A novel phantom and procedure providing submillimeter accuracy in daily QA tests of accelerators used for stereotactic radiosurgery*
Stereotactic radiosurgery (SRS) places great demands on spatial accuracy. Steel BBs used as markers in quality assurance (QA) phantoms are clearly visible in MV and planar kV images, but artifacts compromise cone-beam CT (CBCT) isocenter localization. The purpose of this work was to develop a QA phantom for measuring with sub-mm accuracy isocenter congruence of planar kV, MV, and CBCT imaging systems and to design a practical QA procedure that includes daily Winston-Lutz (WL) tests and does not require computer aid. The salient feature of the phantom (Universal Alignment Ball (UAB)) is a novel marker for precisely localizi...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Low-dose 2.5 MV cone-beam computed tomography with thick CsI flat-panel imager
This study evaluates the feasibility of low-dose megavoltage cone-beam imaging with the 2.5MV beam and a thick cesium iodide detector, which is a high-efficiency imager. Basic imaging properties such as spatial resolution and modulation transfer function were assessed for the 2.5 MV prototype imaging system. For image quality and imaging dose, a series of megavoltage cone-beam scans were acquired for the head, thorax, and pelvis of an anthropomorphic phantom and were compared to kilovoltage cone-beam and 6X megavoltage cone-beam images. To demonstrate the advantage of MV imaging, a phantom with metallic inserts was scanned...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Validation of the Calypso Surface Beacon Transponder
Calypso L-shaped Surface Beacon transponder has recently become available for clinical applications. We herein conduct studies to validate the Surface Beacon transponder in terms of stability, reproducibility, orientation sensitivity, cycle rate dependence, and respiratory waveform tracking accuracy. The Surface Beacon was placed on a Quasar respiratory phantom and positioned at the isocenter with its two arms aligned with the lasers. Breathing waveforms were simulated, and the motion of the transponder was tracked. Stability and drift analysis: sinusoidal waveforms (200 cycles) were produced, and the amplitudes of phases ...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

The step-and-shoot IMRT overshooting phenomenon: a novel method to mitigate patient overdosage
The goal of this work is to evaluate the dosimetric impact of an overshooting phenomenon in step-and-shoot IMRT delivery, and to demonstrate a novel method to mitigate the issue. Five pelvis IMRT patients treated on Varian 2100C EX linacs with larger than +4.5% phantom ion chamber point-dose difference relative to planned dose were investigated. For each patient plan, 5 fractions were delivered. DynaLog files were recorded and centi-MU pulses from dose integrator board for every control point (CP) were counted using a commercial pulse counter. The counter recorded CP MU agrees with DynaLog records, both showing an ~ 0.6MU ...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Evaluation of a combined respiratory-gating system comprising the TrueBeam linear accelerator and a new real-time tumor-tracking radiotherapy system: a preliminary study
A combined system comprising the TrueBeam linear accelerator and a new real-time, tumor-tracking radiotherapy system, SyncTraX, was installed in our institution. The goals of this study were to assess the capability of SyncTraX in measuring the position of a fiducial marker using color fluoroscopic images, and to evaluate the dosimetric and geometric accuracy of respiratory-gated radiotherapy using this combined system for the simple geometry. For the fundamental evaluation of respiratory-gated radiotherapy using SyncTraX, the following were performed:1) determination of dosimetric and positional characteristics of sinusoi...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Development of a Monte Carlo model for treatment planning dose verification of the Leksell Gamma Knife Perfexion radiosurgery system
Detailed Monte Carlo (MC) modeling of the Leksell Gamma Knife (GK) Perfexion (PFX) collimator system is the only accurate ab initio approach appearing in the literature. As a different approach, in this work, we present a MC model based on film measurement. By adjusting the model parameters and fine-tuning the derived fluence map for each individual source to match the manufacturer’s ring output factors, we created a reasonable virtual source model for MC simulations to verify treatment planning dose for the GK PFX radiosurgery system. The MC simulation model was commissioned by simple single shots. Dose profiles and...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Physically constrained voxel-based penalty adaptation for ultra-fast IMRT planning
Conventional treatment planning in intensity-modulated radiation therapy (IMRT) is a trial-and-error process that usually involves tedious tweaking of optimization parameters. Here, we present an algorithm that automates part of this process, in particular the adaptation of voxel-based penalties within normal tissue. Thereby, the proposed algorithm explicitly considers a priori known physical limitations of photon irradiation. The efficacy of the developed algorithm is assessed during treatment planning studies comprising 16 prostate and 5 head and neck cases. We study the eradication of hot spots in the normal tissue, eff...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Experimental validation of a kV source model and dose computation method for CBCT imaging in an anthropomorphic phantom
We present an experimental validation of a kilovoltage (kV) X-ray source characterization model in an anthropomorphic phantom to estimate patient-specific absorbed dose from kV cone-beam computed tomography (CBCT) imaging procedures and compare these doses to nominal weighted CT-dose index (CTDIw) dose estimates. We simulated the default Varian on-board imager 1.4 (OBI) default CBCT imaging protocols (i.e., standard-dose head, low-dose thorax, pelvis, and pelvis spotlight) using our previously developed and easy to implement X-ray point-source model and source characterization approach. We used this characterized source mo...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

The feasibility of atlas-based automatic segmentation of MRI for H&N radiotherapy planning
Atlas-based autosegmentation is an established tool for segmenting structures for CT-planned head and neck radiotherapy. MRI is being increasingly integrated into the planning process. The aim of this study is to assess the feasibility of MRI-based, atlas-based autosegmentation for organs at risk (OAR) and lymph node levels, and to compare the segmentation accuracy with CT-based autosegmentation. Fourteen patients with locally advanced head and neck cancer in a prospective imaging study underwent a T1-weighted MRI and a PET-CT (with dedicated contrast-enhanced CT) in an immobilization mask. Organs at risk (orbits, parotids...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

On flattening filter-free portal dosimetry
The objective of the present study is to research the feasibility of said verifications (with the older versions of the software and EPID). By placing the EPID at a greater distance, the images can be acquired without saturation, yielding a linearity similar to the flattened mode. For the image prediction, a method was optimized based on the clinically used algorithm (analytical anisotropic algorithm (AAA)) over a homogeneous phantom. The depth inside the phantom and its electronic density were tailored. An application was developed to allow the conversion of a dose plane (in DICOM format) to Varian’s custom format f...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Predicting deliverability of volumetric-modulated arc therapy (VMAT) plans using aperture complexity analysis
The purpose of this study was to evaluate the ability of an aperture complexity metric for volumetric-modulated arc therapy (VMAT) plans to predict plan delivery accuracy. We developed a complexity analysis tool as a plug-in script to Varian’s Eclipse treatment planning system. This script reports the modulation of plans, arcs, and individual control points for VMAT plans using a previously developed complexity metric. The calculated complexities are compared to that of 649 VMAT plans previously treated at our institution from 2013 to mid-2015. We used the VMAT quality assurance (QA) results from the 649 treated plan...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Clinical implications of the overshoot effect for treatment plan delivery and patient-specific quality assurance for step-and-shoot IMRT
In this work, overshoot and undershoot effects associated with step-and-shoot IMRT (SSIMRT) delivery on a Varian Clinac 21iX are investigated, and their impact on patient-specific QA point dose measurements and treatment plan delivery are evaluated. Pinnacle3 SSIMRT plans consisting of 5, 10, and 15 identical 5 × 5 cm2 MLC defined segments and MU/segment values of 5 MU, 10 MU, and 20 MU were utilized and delivered at 600/300 MU/min. Independent of the number of segments the overshoot and undershoot at 600 MU/min were approximately ± 10%, ± 5%, and ± 2.5% for 5 MU/segment, 10 MU/segment, and 20 MU...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Dosimetric accuracy of the cone-beam CT-based treatment planning of the Vero system: a phantom study
In this study, the CBCT images of the Vero system from a complex inhomogeneity phantom can be applied for the TPS dose calculation if the system is calibrated using tissue-equivalent materials scanned at high tube voltage (i.e., 120 kV). (Source: Journal of Applied Clinical Medical Physics)
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Two-year experience with the commercial Gamma Knife Check software
The Gamma Knife Check software is an FDA approved second check system for dose calculations in Gamma Knife radiosurgery. The purpose of this study was to evaluate the accuracy and the stability of the commercial software package as a tool for independent dose verification. The Gamma Knife Check software version 8.4 was commissioned for a Leksell Gamma Knife Perfexion and a 4C unit at the University of Pittsburgh Medical Center in May 2012. Independent dose verifications were performed using this software for 319 radiosurgery cases on the Perfexion and 283 radiosurgery cases on the 4C units. The cases on each machine were d...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Treatment accuracy without rotational setup corrections in intracranial SRT
The aim of this study was to evaluate the impact of actual rotational setup errors on dose distributions in intracranial stereotactic radiotherapy (SRT) with different alternatives for treatment position selection. A total of 38 SRT fractions from 18patients were retrospectively evaluated with rotational setup errors obtained from actual treatments. The planning computed tomography (CT) images were rotated according to online cone-beam CT (CBCT) images and the dose distribution was recalculated to the rotated CT images using three different patient positionings derived from: 1) an automatic 6D match neglecting rotation cor...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

A novel arc geometry setting for pelvic radiotherapy with extensive nodal involvement
The aim of this study was to find optimal planning approach for large planning targets with complicated geometry requiring wide field openings. The study presents a novel approach for arc geometry design for pelvic targets with extensive nodal involvement. A total of 15 patients with anorectal carcinoma or vulvar cancer were selected retrospectively. For each patient, one seven-field IMRT plan and three VMAT plans were calculated: one with two 360° arcs with no limitations for the field size (VMATw); one with two asymmetrically field-size-restricted 360° arcs (VMATr); and the proposed novel approach which consisted...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research

Effective method of measuring the radioactivity of [131I]-capsule prior to radioiodine therapy with significant reduction of the radiation exposure to the medical staff
We describe an alternative method, allowing a considerable reduction of the radiation exposure. Two [131I]-capsules (A01 = 2818.5; A02 = 7355.0 MBq) were measured multiple times in their own delivery lead containers — that is to say, [131I]-capsules remain inside the containers during the measurements (shielded measurement) using a dose calibrator and a well-type and a thyroid uptake probe. The results of the shielded measurements were correlated linearly with the [131I]-capsules radioactivity to create calibration curves for the used devices. Additional radioactivity measurements of 50 [131I]-capsules of different r...
Source: Journal of Applied Clinical Medical Physics - July 8, 2016 Category: Physics Source Type: research