bluuebunny/crossref_metadata_2025_split huggingface dataset:
Using lesion washout volume fraction as a biomarker to improve suspicious breast lesion characterization
Authors: Huang Jie , Schafer Sarah M. , Aben Gerald R. , Hoisington Lori A. 
Published: February 2017

The purpose of this study was to evaluate using lesion washout (WO) volume fraction as a biomarker to improve the characterization of suspicious breast lesions. Study lesions consisted of a total of 60 malignant tumors (BI‐RADS 6) and 62 suspicious lesions (BI‐RADS 4 or 5). The biopsies of these suspicious lesions resulted in a total of 30 malignant tumors and 32 benign lesions, respectively, yielding a 48.4% positive predictive value (PPV) of the biopsies. The mean and standard deviation of the lesion WO volume fraction of these 60 BI‐RADS 6 malignant tumors were first computed to establish a 99% sensitivity threshold value for malignant tumors, and then the biomarker was used to characterize the suspicious lesions. Using the biomarker would characterize all the malignant tumors as malignant, 12 out of the 32 benign lesions as benign, potentially resulting in a 24% improvement rate in the PPV of the biopsies (from 48.4% to 60%) and consequently a 22.5% reduction rate in the false‐positive rate of benign biopsies (from 51.6% to 40%). The lesion WO volume fraction biomarker could improve the computer‐based assessment of breast MRI by increasing the PPV of breast biopsies and reducing the number of unnecessary biopsies without compromising sensitivity.PACS number: 87.61.Tg, 87.19.Xj
Use of diverging apertures to minimize the edge scatter in passive scattering proton therapy
Authors: Zhao Tianyu , Cai Bin , Sun Baozhou , Grantham Kevin , Mutic Sasa , Klein Eric 
Published: February 2017

The purpose of this study was to evaluate the use of diverging‐cut aperture to minimize collimator contamination in proton therapy. Two sets of apertures with nondivergent and divergent edge were fabricated to produce a field at the radiation isocenter of a single‐room proton therapy unit. Transverse profiles were acquired in a scanning water tank with both aperture sets. Up to 9.5% extra dose was observed from aperture scattering near the field edges with the nondivergent aperture set at 2 cm above the water surface and remained 3.0% at depth of 10 cm. For the divergent set, the contamination was reduced to less than 3.5% and 1.3%, respectively. Our study demonstrated that scattering from apertures contaminated the dose distribution near the field edge at shallow depth. A diverging‐cut aperture was capable of reducing the contamination and is recommended for use in passive scattering proton therapy, especially when critical organs are lateral and proximal to the target at shallow depth.PACS numbers: 87.55.ne, 87.56.nk
Noncoplanar verification: a feasibility study using Philips' Pinnacle3 treatment planning system
Authors: Yohannes Indra , Prasetio Heru , Bert Christoph 
Published: February 2017

Noncoplanar fields are normally used to improve the dose conformity of the target while sparing organs at risk. One of the methods to verify the dose distribution from the noncoplanar fields is by comparing their planar dose distributions from the treatment planning system (TPS) and the measured ones; for example, using film or electronic portal imaging devices (EPID). The planar dose distributions of the measurement tools, that are normally perpendicular to the central axis of the beam, can be calculated by creating special structures to mimic them in the TPS. With TPS commercially available today, however, it is not easy to create these special structures, especially in the noncoplanar configuration. For this work, we have written in‐house scripts in the Pinnacle3 TPS that can create the structures and define them as virtual planes. These virtual planes can be generated for any arbitrary gantry and couch angles, as well as source to planar distance, so that the planar dose maps at these planes can be computed. Two independent quality assurance (QA) tools were used to validate the planar dose distributions computed using the scripts for three open fields and one IMRT field at several different couch angles. The absolute planar dose patterns measured by the QA tools for all fields at all couch angles were found to be in good agreement, more than 95% (gamma criteria 3% delta dose and 3 mm distance to agreement), with the calculated ones by TPS. The results of this feasibility study can be valuable either for pretreatment dose verification or for in vivo dosimetry that directly implements the planar dose distributions from the TPS, particularly for the noncoplanar fields.PACS numbers: 87.55.de, 87.55.Qr, 87.56.Fc
Inter‐ and intrafractional dose uncertainty in hypofractionated Gamma Knife radiosurgery
Authors: Kim Taeho , Sheehan Jason , Schlesinger David 
Published: February 2017

The purpose of this study is to evaluate inter‐ and intrafractional dose variations resulting from head position deviations for patients treated with the Extend relocatable frame system utilized in hypofractionated Gamma Knife radiosurgery (GKRS). While previous reports characterized the residual setup and intrafraction uncertainties of the system, the dosimetric consequences have not been investigated. A digital gauge was used to measure the head position of 16 consecutive Extend patients (62 fractions) at the time of simulation, before each fraction, and immediately following each fraction. Vector interfraction (difference between simulation and prefraction positions) and intrafraction (difference between postfraction and prefraction positions) shifts in patient position were calculated. Planned dose distributions were shifted by the offset to determine the time‐of‐treatment dose. Variations in mean and maximum target and organ at risk (OAR) doses as a function of positional shift were evaluated. The mean vector interfraction shift was 0.64 mm (Standard Deviation (SD): 0.25 mm, maximum: 1.17 mm). The mean intrafraction shift was 0.39 mm (SD: 0.25 mm, maximum: 1.44 mm). The mean variation in mean target dose was 0.66% (SD: 1.15%, maximum: 5.77%) for interfraction shifts and 0.26% (SD: 0.34%, maximum: 1.85%) for intrafraction shifts. The mean variation in maximum dose to OARs was 7.15% (SD: 5.73%, maximum: 30.59%) for interfraction shifts and 4.07% (SD: 4.22%, maximum: 17.04%) for intrafraction shifts. Linear fitting of the mean variation in maximum dose to OARs as a function of position yielded dose deviations of 10.58%/mm for interfractional shifts and 7.69%/mm for intrafractional shifts. Positional uncertainties when performing hypofractionated Gamma Knife radiosurgery with the Extend system are small and comparable to frame‐based uncertainties (). However, the steep dose gradient characteristics of GKRS mean that the dosimetric consequences of positional uncertainties should be considered as part of treatment planning. These dose uncertainties should be evaluated in the context of tumor response and OAR tolerance for hypofractionated treatment scenarios where any increase in dose may be tempered by the increased protection hypofractionation provides to normal tissue.PACS number(s): 87.52.‐g
A novel method for radiotherapy patient identification using surface imaging
Authors: Wiant David B. , Verchick Quinton , Gates Percy , Vanderstraeten Caroline L. , Maurer Jacqueline M. , Hayes T. Lane , Liu Han , Sintay Benjamin J. 
Published: February 2017

Performing a procedure on the wrong patient or site is one of the greatest errors that can occur in medicine. The addition of automation has been shown to reduce errors in many processes. In this work we explore the use of an automated patient identification process using optical surface imaging for radiotherapy treatments. Surface imaging uses visible light to align the patient to a reference surface in the treatment room. It is possible to evaluate the similarity between a daily set‐up surface image and the reference image using distance to agreement between the points on the two surfaces. The higher the percentage overlapping points within a defined distance, the more similar the surfaces. This similarity metric was used to intercompare 16 left‐sided breast patients. The reference surface for each patient was compared to 10 daily treatment surfaces for the same patient, and 10 surfaces from each of the other 15 patients (for a total of 160 comparisons per patient), looking at the percent of points overlapping. For each patient, the minimum same‐patient similarity score was higher than the maximum different‐patient score. For the group as a whole a threshold was able to classify correct and incorrect patients with high levels of accuracy. A 10‐fold cross‐validation using linear discriminant analysis gave cross‐validation loss of 0.0074. An automated process using surface imaging is a feasible option to provide nonharmful daily patient identification verification using currently available technology.PACS number(s): 87.53.Jw, 87.55.N‐, 87.55.Qr, 87.57.N‐, 87.63.L‐
Benchmarking of five commercial deformable image registration algorithms for head and neck patients
Authors: Pukala Jason , Johnson Perry B. , Shah Amish P. , Langen Katja M. , Bova Frank J. , Staton Robert J. , Mañon Rafael R. , Kelly Patrick , Meeks Sanford L. 
Published: February 2017

Benchmarking is a process in which standardized tests are used to assess system performance. The data produced in the process are important for comparative purposes, particularly when considering the implementation and quality assurance of DIR algorithms. In this work, five commercial DIR algorithms (MIM, Velocity, RayStation, Pinnacle, and Eclipse) were benchmarked using a set of 10 virtual phantoms. The phantoms were previously developed based on CT data collected from real head and neck patients. Each phantom includes a start of treatment CT dataset, an end of treatment CT dataset, and the ground‐truth deformation vector field (DVF) which links them together. These virtual phantoms were imported into the commercial systems and registered through a deformable process. The resulting DVFs were compared to the ground‐truth DVF to determine the target registration error (TRE) at every voxel within the image set. Real treatment plans were also recalculated on each end of treatment CT dataset and the dose transferred according to both the ground‐truth and test DVFs. Dosimetric changes were assessed, and TRE was correlated with changes in the DVH of individual structures. In the first part of the study, results show mean TRE on the order of 0.5 mm to 3 mm for all phantoms and ROIs. In certain instances, however, misregistrations were encountered which produced mean and max errors up to 6.8 mm and 22 mm, respectively. In the second part of the study, dosimetric error was found to be strongly correlated with TRE in the brainstem, but weakly correlated with TRE in the spinal cord. Several interesting cases were assessed which highlight the interplay between the direction and magnitude of TRE and the dose distribution, including the slope of dosimetric gradients and the distance to critical structures. This information can be used to help clinicians better implement and test their algorithms, and also understand the strengths and weaknesses of a dose adaptive approach.PACS number(s): 87.57.nj, 87.55.dk, 87.55.Qr
Ocular brachytherapy dosimetry for and in the presence of gold nanoparticles: a Monte Carlo study
Authors: Asadi Somayeh , Vaez‐zadeh Mehdi , Vahidian Mohammad , Marghchouei Mahdieh , Masoudi S. Farhad 
Published: February 2017

The aim of the present Monte Carlo study is to evaluate the variation of energy deposition in healthy tissues in the human eye which is irradiated by brachytherapy sources in comparison with the resultant dose increase in the gold nanoparticle (GNP)‐loaded choroidal melanoma. The effects of these nanoparticles on normal tissues are compared between and as two ophthalmic brachytherapy sources. Dose distribution in the tumor and healthy tissues has been taken into account for both brachytherapy sources. Also, in certain points of the eye, the ratio of the absorbed dose by the normal tissue in the presence of GNPs to the absorbed dose by the same point in the absence of GNPs has been calculated. In addition, differences of the absorbed dose in the tumor observed in the comparison of simple water phantom and actual simulated human eye in presence of GNPs are also a matter of interest that have been considered in the present work. The difference between the eye globe and the water phantom is more obvious for than that of the when the ophthalmic dosimetry is done in the presence of GNPs. Whenever these nanoparticles are utilized in enhancing the absorbed dose by the tumor, the use of brachytherapy source will greatly amplify the amount of dose enhancement factor (DEF) in the tumor site without inflicting much damage to healthy organs, when compared to the source. For instance, in the concentration of 30 mg GNPs, the difference amongst the calculated DEF for between these phantoms is 5.3%, while it is 2.45% for . Furthermore, in Monte Carlo studies of eye brachytherapy, more precise definition of the eye phantom instead of a water phantom will become increasingly important when we use as opposed to .PACS number(s): 87.53.Jw, 87.85.Rs, 87.10.Rt
Experimental validation of a kV source model and dose computation method for CBCT imaging in an anthropomorphic phantom
Authors: Poirier Yannick , Tambasco Mauro 
Published: February 2017

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 () 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 model to compute absorbed dose in homogeneous and anthropomorphic phantoms using our previously validated in‐house kV dose computation software (kVDoseCalc). We compared these computed absorbed doses to doses derived from ionization chamber measurements acquired at several points in a homogeneous cylindrical phantom and from thermoluminescent detectors (TLDs) placed in the anthropomorphic phantom. In the homogeneous cylindrical phantom, computed values of absorbed dose relative to the center of the phantom agreed with measured values within of local dose, except in regions of high‐dose gradient where the distance to agreement (DTA) was 2 mm. The computed absorbed dose in the anthropomorphic phantom generally agreed with TLD measurements, with an average percent dose difference ranging from to , depending on the characterized CBCT imaging protocol. The low‐dose thorax and the standard dose scans showed the best and worst agreement, respectively. Our results also broadly agree with published values, which are approximately twice as high as the nominal would suggest. The results demonstrate that our previously developed method for modeling and characterizing a kV X‐ray source could be used to accurately assess patient‐specific absorbed dose from kV CBCT procedures within reasonable accuracy, and serve as further evidence that existing assessments underestimate absorbed dose delivered to patients.PACS number(s): 87.57.Q‐, 87.57.uq, 87.10.Rt
The step‐and‐shoot IMRT overshooting phenomenon: a novel method to mitigate patient overdosage
Authors: Zhen Heming , Ouyang Luo , Bao Qinan , Qin Nan , Stojadinovic Strahinja , Pompos Arnold 
Published: February 2017

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 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 MU overshoot of the first segment of every beam. The 3D patient dose was recalculated from the counter records and compared to the planned dose, showing that the overshoot resulted in on average 2.05% of PTV error, and 2.49%, 2.61% and 2.45% of error for rectum, bladder, and bowel, respectively. The initial plans were then modified by inserting a specially designed MLC segment to the start of every beam. The modified plans were also delivered five times. The dose from the modified delivery was calculated using counter recorded CP MU. The corresponding parameters were all within 0.31% from the original plan. IMRT QA results also show a 2.2% improvement in ion chamber point‐dose agreement. The results demonstrate that the proposed plan modification method effectively eliminates the overdosage from the overshooting phenomenon.PACS number(s): 87.55.Qr, 87.55.km
Clinical implications of the overshoot effect for treatment plan delivery and patient‐specific quality assurance for step‐and‐shoot IMRT
Authors: Baines John A. , Zawlodzka Sylwia J. , Parfitt Matthew L. , Hickey Brigid E. , Pullar Andrew P. 
Published: February 2017

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 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 , and for 5 MU/segment, 10 MU/segment, and 20 MU/segment, respectively. At 300 MU/min, each of these values is approximately halved. Interfractional variation of these effects (10 fractions), as well as dosimetric variations for intermediate segments, are reduced at the lower dose rate. QA point‐dose measurements for a sample of head and neck SSIMRT beams were on average 2.9% (600 MU/min) and 1.7% (300 MU/min) higher than Pinnacle3 planned doses. In comparison for prostate beams , measured point doses were 0.8% (600 MU/min) and 0.4% (300 MU/min) higher. The reduction in planned‐measured point‐dose discrepancies at 300 MU/min can be attributed in part to the inclusion of the first segment (overshoot) in the admixture of segments that deliver measured dose. Pinnacle3 plans for 10/9 head and neck/prostate treatments were adjusted by to include the effects of overshoot and undershoot at 600 MU/min. Comparing original and adjusted plans for each site indicated that the original plan was preferred in 70% and 89% of head and neck and prostate cases, respectively. The disparity between planned and delivered treatment that this suggests can potentially be mitigated by treating SSIMRT at a dose rate below 600 MU/min.PACS number(s): 87.55.Qr, 87.56.bd, 87.56.N‐
A routine quality assurance test for CT automatic exposure control systems
Authors: Iball Gareth R. , Moore Alexis C. , Crawford Elizabeth J. 
Published: February 2017

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 regions of interest. The scanner displayed CTDIvol and DLP were also recorded. The impact of a range of AEC configurations on dose and image quality were assessed at acceptance testing. For systems that were tested more than once, the percentage of CTDIvol values exceeding 5%, 10%, and 15% deviation from baseline was 23.4%, 12.6%, and 8.1% respectively. Similarly, for the image noise data, deviations greater than 2%, 5%, and 10% from baseline were 26.5%, 5.9%, and 2%, respectively. The majority of CTDIvol and noise deviations greater than 15% and 5%, respectively, could be explained by incorrect phantom setup or protocol selection. Barring these results, CTDIvol deviations of greater than 15% from baseline were found in 0.9% of tests and noise deviations greater than 5% from baseline were found in 1% of tests. The phantom was shown to be sensitive to changes in AEC setup, including the use of 3D, longitudinal or rotational tube current modulation. This test methodology allows for continuing performance assessment of CT AEC systems, and we recommend that this test should become part of routine CT quality assurance programs. Tolerances of for CTDIvol and for image noise relative to baseline values should be used.PACS number(s): 87.57.Q‐
Characteristics of quantitative perfusion parameters on dynamic contrast‐enhanced MRI in mammographically occult breast cancer
Authors: Ryu Jung Kyu , Rhee Sun Jung , Song Jeong Yoon , Cho Soo Hyun , Jahng Geon‐Ho 
Published: February 2017

The purpose of this study was to compare the characteristics of quantitative perfusion parameters obtained from dynamic contrast‐enhanced (DCE) magnetic resonance imaging (MRI) in patients with mammographically occult (MO) breast cancers and those with mammographically visible (MV) breast cancers. Quantitative parameters (AUC, , and ) from 13 MO breast cancers and 16 MV breast cancers were mapped after the DCE‐MRI data were acquired. Various prognostic factors, including axillary nodal status, estrogen receptor (ER), progesterone receptor (PR), Ki‐67, p53, E‐cadherin, and human epidermal growth factor receptor 2 (HER2) were obtained in each group. Fisher's exact test was used to compare any differences of the various prognostic factors between the two groups. The Mann‐Whitney U test was applied to compare the quantitative parameters between these two groups. Finally, Spearman's correlation was used to investigate the relationships between perfusion indices and four factors — age, tumor size, Ki‐67, and p53 — for each group. Although age, tumor size, and the prognostic factors were not statistically different between the two groups, the mean values of the quantitative parameters, except in the MV group, were higher than those in the MO group without statistical significance . The value was significantly different between the two groups , but the other parameters were not. In the MO group, with size, with p53, and and with Ki‐67 had significant correlations (). However, in the MV group, only showed significant correlation with age. The value was only the perfusion parameter of statistical significance between MO and MV breast cancers.PACS number(s): 87.19.U‐, 87.61.‐c