bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sci‐Thur AM: YIS – 01: New technologies for astatine‐211 targeted alpha therapy research
Authors: Crawford Jason , Yang Hua , Schaffer Paul , Ruth Thomas 
Published: August 2016

Purpose:The short‐range, densely ionizing α‐particles emitted by 211At (t1/2=7.2h) are well suited for the treatment of diffuse microscopic disease, using cancer targeting biomolecules. 211At availability is limited by the rarity of α‐cyclotrons required for standard production. Image‐based dosimetry is also limited for 211At, which emits low intensity X‐rays. Our goal was to leverage state‐of‐the‐art infrastructure at TRIUMF to produce and evaluate two related isotopes, 211Rn (t1/2=14.6h, 73% decay to 211At) as a generator for 211At, and 209At (t1/2=5.4h, X‐ray/gamma‐ray emitter) as a novel 211At surrogate for preclinical imaging studies.Methods:Produced by spallation of uranium with 480 MeV protons, mass separated ion beams of short‐lived francium isotopes were implanted into NaCl targets where 211Rn or 209At were produced by radioactive decay, in situ. 211Rn was transferred to dodecane from which 211At was efficiently extracted and evaluated for clinical applicability. High energy SPECT/CT was evaluated for measuring 209At activity distributions in mice and phantoms.Results:Our small scale 211Rn/211At generator system provided high purity 211At samples. The methods are immediately scalable to the level of radioactivity required for in vivo experiments with 211At. 209At‐based high energy SPECT imaging was determined suitable for pursuing image‐based dosimetry in mouse tumour models. In the future, we will utilize quantitative 209At‐SPECT for image‐based dose calculations.Conclusion:These early studies provided a foundation for future endeavours with 211At‐based α‐therapy. Canada is now significantly closer to clinical targeted α‐therapy of cancer.
Sci‐Thur AM: YIS – 02: Imaging dose distributions through the detection of radiation‐induced acoustic waves
Authors: Hickling Susannah , Lei Hao , Hobson Maritza , Leger Pierre , Wang Xueding , El Naqa Issam 
Published: August 2016

Purpose:X‐ray acoustic computed tomography (XACT) is an emerging technique that images the dose deposited within an object following linac irradiation by detecting acoustic waves induced via the photoacoustic effect. This work shows that XACT images can be formed in soft‐tissue equivalent material and that dosimetric information can be extracted from such images.Methods:Acoustic waves induced in a water tank following irradiation by a 10 MV flattening filter free photon beam were detected with an immersion ultrasound transducer at 60 angles surrounding the radiation field. A back‐projection algorithm was used to reconstruct an XACT image from the detected transducer signals. Profiles extracted from XACT images were compared to profiles measured with ion chambers as per the current clinical protocol.Results:XACT images were successfully formed of simple 4 cm × 4 cm and 6 cm × 3 cm fields, as well as of more complicated multi‐leaf collimator defined fields. For the 6 cm × 3 cm field, 74% and 87% of the XACT profile points in the 6 cm and 3 cm dimensions, respectively, passed a 7% / 4 mm gamma test when compared to ion chamber measurements. In a complicated puzzle piece shaped field, 86% of the pixels in an extracted profile passed a 7% / 4 mm gamma test.Conclusions:XACT is capable of imaging the dose distribution delivered by a variety of field sizes and shapes in water, and is a viable technique for both water tank and in vivo dosimetry.
Sci‐Thur AM: YIS – 04: Stopping power‐to‐Cherenkov power ratios and beam quality specification for clinical Cherenkov emission dosimetry of electrons: beam‐specific effects and experimental validation
Authors: Zlateva Yana , Seuntjens Jan , El Naqa Issam 
Published: August 2016

Purpose:To advance towards clinical Cherenkov emission (CE)‐based dosimetry by investigating beam‐specific effects on Monte Carlo‐calculated electron‐beam stopping power‐to‐CE power ratios (SCRs), addressing electron beam quality specification in terms of CE, and validating simulations with measurements.Methods:The EGSnrc user code SPRRZnrc, used to calculate Spencer‐Attix stopping‐power ratios, was modified to instead calculate SCRs. SCRs were calculated for 6‐ to 22‐MeV clinical electron beams from Varian TrueBeam, Clinac 21EX, and Clinac 2100C/D accelerators. Experiments were performed with a 20‐MeV electron beam from a Varian TrueBeam accelerator, using a diffraction grating spectrometer with optical fiber input and a cooled back‐illuminated CCD. A fluorophore was dissolved in the water to remove CE signal anisotropy.Results:It was found that angular spread of the incident beam has little effect on the SCR (≤ 0.3% at dmax), while both the electron spectrum and photon contamination increase the SCR at shallow depths and decrease it at large depths. A universal data fit of R50 in terms of C50 (50% CE depth) revealed a strong linear dependence (R2 > 0.9999). The SCR was fit with a Burns‐type equation (R2 = 0.9974, NRMSD = 0.5%). Below‐threshold incident radiation was found to have minimal effect on beam quality specification (< 0.1%). Experiments and simulations were in good agreement.Conclusions:Our findings confirm the feasibility of the proposed CE dosimetry method, contingent on computation of SCRs from additional accelerators and on further experimental validation. This work constitutes an important step towards clinical high‐resolution out‐of‐beam CE dosimetry.
Sci‐Thur PM ‐ Colourful Interactions: Highlights 06: Patient‐specific calibration of cone‐beam computed tomographic (CBCT) image sets for on‐line dose tracking and plan assessment
Authors: MacFarlane Michael , Wong Daniel , Johnson Carol , Bzdusek Karl , Battista Jerry , Chen Jeff 
Published: August 2016

Purpose:To develop a radiotherapy dose tracking and plan evaluation technique using cone‐beam computed tomography (CBCT) images.Methods:We developed a patient‐specific method of calibrating CBCT image sets for dose calculation. The planning CT was first registered with the CBCT using deformable image registration (DIR). A scatter plot was generated between the CT numbers of the planning CT and CBCT for each slice. The CBCT calibration curve was obtained by least‐square fitting of the data, and applied to each CBCT slice. The calibrated CBCT was then merged with original planning CT to extend the small field of view of CBCT. Finally, the treatment plan was copied to the merged CT for dose tracking and plan evaluation. The proposed patient‐specific calibration method was also compared to two methods proposed in literature. To evaluate the accuracy of each technique, 15 head‐and‐neck patients requiring plan adaptation were arbitrarily selected from our institution. The original plan was calculated on each method's data set, including a second planning CT acquired within 48 hours of the CBCT (serving as gold standard). Clinically relevant dose metrics and 3D gamma analysis of dose distributions were compared between the different techniques.Results:Compared to the gold standard of using planning CTs, the patient‐specific CBCT calibration method was shown to provide promising results with gamma pass rates above 95% and average dose metric agreement within 2.5%.Conclusions:The patient‐specific CBCT calibration method could potentially be used for on‐line dose tracking and plan evaluation, without requiring a re‐planning CT session.
Sci‐Thur PM – Colourful Interactions: Highlights 07: Canadian Computed Tomography Survey: National Diagnostic Reference Levels
Authors: Wardlaw Graeme M , Martel Narine 
Published: August 2016

Purpose:The Canadian Computed (CT) Tomography Survey sought to collect CT technology and dose index data (CTDI and DLP) at the national level in order to establish national diagnostic reference levels (DRLs) for seven common CT examinations of standard‐sized adults and pediatric patients.Methods:A single survey booklet (consisting of four sections) was mailed to and completed for each participating CT scanner. Survey sections collected data on (i) General facility and scanner information, (ii) routine protocols (as available), (iii) individual patient data (as applied) and (iv) manual CTDI measurements.Results:Dose index (CTDIvol and DLP) and associated patient data from 24 280 individual patient exam sequences was analyzed for seven common CT examinations performed in Canada: Adult Head, Chest, Abdomen/Pelvis, and Chest/Abdomen/Pelvis, and Pediatric Head, Chest, and Abdomen. Pediatric examination data was sub‐divided into three age ranges: 0–3, 3–7 and 7–13 years.DRLs (75th percentile of dose index distributions) were found for all thirteen groups. Further analysis also permitted segmentation of examination data into 8 sub‐groups, whose dose index data was displayed along with group histograms – showing relative contribution of axial vs. helical, contrast use (C+ vs. C‐), and application of fixed current vs. dose reduction (DR) – 75th percentiles of DR sub‐groups were, in almost all cases, lower than whole group (examination) DRLs.Conclusions:The analysis and summaries presented in the pending survey report can serve to aid local CT imaging optimization efforts within Canada and also contribute further to international efforts in radiation protection of patients.
Sci‐Thur PM – Brachytherapy 03: Identifying the impact of seroma visualization on permanent breast seed implant brachytherapy
Authors: Morton Daniel , Batchelar Deidre , Hilts Michelle , Tetreault‐Laflamme Audrey , Mou Benjamin , Lucas Sarah , Crook Juanita 
Published: August 2016

Purpose:Uncertainties in target identification can reduce treatment accuracy in permanent breast seed implant (PBSI) brachytherapy. This study evaluates the relationship between seroma visualization and seed placement accuracy.Methods:Spatially co‐registered CT and 3D ultrasound (US) images were acquired for 10 patients receiving PBSI. Seromas were retrospectively contoured independently by 3 radiation oncologists on both CT and US and respective consensus volumes were defined, CTVCT and CTVUS. The seroma clarity and inter‐user conformity index (CI), as well as inter‐modality CI, volume, and positional differences were evaluated. Correlations with seed placement accuracy were then assessed. CTVs were expanded by 1.25cm to create PTVCT and PTVUS and evaluate the conformity with PTVClinical (CTVClinical+1.25cm) used in treatment planning. The change in PTV coincidence by expanding PTVClinical by 0.25cm was determined.Results:CTVUS were a mean 68 ± 12% smaller than CTVCT and generally had improved clarity and inter‐user conformity. No correlations between seed displacement and CTVUS‐CTVCT positional difference or CI were observed. Greater seed displacements were associated with larger CTVUS‐CTVCT volume differences (r=−0.65) and inter‐user CT CI (r=−0.74). A median (range) 88% (71–99%) of PTVCT and 83% (69–100%) of PTVUS were contained within PTVClinical. Expanding treatment margins to 1.5cm increased coincidence to 98% (86–100%) and 94% (82–100%), respectively.Conclusions:Differences in seroma visualization impacts seed displacement in PBSI. Reducing dependence on CT by incorporating 3DUS into target identification, or expanding CT‐based treatment margins to 1.5cm may reduce or mitigate uncertainties related to seroma visualization.
Sci‐Thur PM – Brachytherapy 06: 3D Printed Surface Applicators for High Dose Rate Brachytherapy
Authors: Clarke Scott , Yewondwossen Mammo , Robar James 
Published: August 2016

Purpose:The purpose of this work is to develop a new applicator for administering high dose rate (HDR) brachytherapy using 3D printing technology. Primary advantages of using a 3D printed applicator will be to offer a more streamlined approach for therapists and patients while achieving better conformity, reproducibility, and patient specific applicators.Methods:A phantom study was conducted to measure the effectiveness of a 3D printed surface applicator by analyzing tumours on three locations of the body: the foot, nose, and scalp. The applicator was designed using Eclipse and further modified using Blender to create the catheter tunnels before being printed on a Lulzbot Taz 5 3D printer. A radiation plan was made using Oncentra Brachytherapy for a control treatment option using Freiburg Flaps and one with the novel method of a 3D printed applicator. A comparative analysis was made using D90, D100, V100, V150, and V200Results:The 3D printed applicator showed comparable dose coverage with significant improvements on highly irregular surfaces when analyzed against a plan made using Freiburg Flaps. Although both plans exhibited complete tumour coverage, the 3D applicator showed improvements in D90 and V150 and the 3D applicator had a dose homogeneity index (DHI) of 0.99 compared to a DHI of 0.97 for the control. Therapist prep time also dropped significantly due to the lack of need for a thermoplastic mesh.Conclusions:3D printed applicators for treatment of superficial sites proved to offer more patient convenience, less prep time, better conformity and tighter margins.
Poster ‐ 17: Characterization and correction of radiation induced background in scanning water tanks
Authors: Ali Elsayed 
Published: August 2016

Purpose:To characterize and correct for radiation‐induced background (RIB) observed in the signals from a class of scanning water tanks.Methods:A method was developed to isolate the RIB through detector measurements in the background‐free linac console area. Variation of the RIB against a large number of parameters was characterized, and its impact on basic clinical data for photon and electron beams was quantified. Different methods to minimize and/or correct for the RIB were proposed and evaluated.Results:The RIB is due to the presence of the electrometer and connection box in a low background radiation field (by design). The absolute RIB current with a biased detector is up to 2 pA, independent of the detector size, which is 0.6% and 1.5% of the central axis reference signal for a standard and a mini scanning chamber, respectively. The RIB monotonically increases with field size, is three times smaller for detectors that do not require a bias (e.g., diodes), is up to 80% larger for positive (versus negative) polarity, decreases with increasing photon energy, exhibits a single curve versus dose rate at the electrometer location, and is negligible for electron beams. Data after the proposed field‐size correction method agree with point measurements from an independent system to within a few tenth of a percent for output factor, head scatter, depth dose at depth, and out‐of‐field profile dose. Manufacturer recommendations for electrometer placement are insufficient and sometimes incorrect.Conclusions:RIB in scanning water tanks can have a non‐negligible effect on dosimetric data.
Poster ‐ 38: On the physical and dosimetric properties of 3D printed electron bolus fabricated using polylactic acid
Authors: Sasaki David , Jensen Martin , Rickey Daniel W , Dubey Arbind , Harris Chad , McCurdy Boyd 
Published: August 2016

Purpose:3D printing technology could simplify and improve electron bolus fabrication. The purpose of this study was to characterize the density, dimensional accuracy, uniformity, and attenuation of PLA boluses fabricated with a low‐cost 3D printer.Methods:Several solid square slabs were printed with specific requested dimensions and 100% infill using different fill patterns. These pieces were imaged using an x‐ray flat panel imager in order to check for uniformity of the prints.Percentage depth doses (PDDs) were measured downstream of the slabs in solid water using a parallel plate chamber and compared to measurements in water in order to characterize attenuation.The dimensions of the PLA slabs were measured using digital calipers. The slabs were also weighed to find their density.Results:The fill pattern used to create boluses can affect the attenuation of the bolus. Fill patterns should be chosen carefully and quality assurance should be done for each printed piece.PLA causes the electron PDD to shift towards shallower depths, compared to water, by 1.7 mm for each centimeter of PLA.Agreement with design dimensions was within 1 mm in the plane of the printer bed, and within 1/3 of a millimeter (roughly the thickness of a single layer), perpendicular to the printer bed. Average density was in the range 1.20 – 1.22.Conclusions:3D printing shows great promise for use in fabricating electron bolus. This work indicates that printed PLA can be a suitable material provided the increased attenuation is properly accounted for.
Poster ‐ 44: Development and implementation of a comprehensive end‐to‐end testing methodology for linac‐based frameless SRS QA using a modified commercial stereotactic anthropomorphic phantom
Authors: Liu Derek , Mutanga Theodore 
Published: August 2016

Purpose:An end‐to‐end testing methodology was designed to evaluate the overall SRS treatment fidelity, incorporating all steps in the linac‐based frameless radiosurgery treatment delivery process. The study details our commissioning experience of the Steev (CIRS, Norfolk, VA) stereotactic anthropomorphic head phantom including modification, test design, and baseline measurements.Methods:Repeated MR and CT scans were performed with interchanging inserts. MR‐CT fusion accuracy was evaluated and the insert spatial coincidence was verified on CT. Five non‐coplanar arcs delivered a prescription dose to a 15 mm spherical CTV with 2 mm PTV margin.Following setup, CBCT‐based shifts were applied as per protocol. Sequential measurements were performed by interchanging inserts without disturbing the setup. Spatial and dosimetric accuracy was assessed by a combination of CBCT hidden target, radiochromic film, and ion chamber measurements. To facilitate film registration, the film insert was modified in‐house by etching marks.Results:MR fusion error and insert spatial coincidences were within 0.3 mm. Both CBCT and film measurements showed spatial displacements of 1.0 mm in similar directions. Both coronal and sagittal films reported 2.3 % higher target dose relative to the treatment plan. The corrected ion chamber measurement was similarly greater by 1.0 %. The 3 %/2 mm gamma pass rate was 99% for both filmsConclusions:A comprehensive end‐to‐end testing methodology was implemented for our SRS QA program. The Steev phantom enabled realistic evaluation of the entire treatment process. Overall spatial and dosimetric accuracy of the delivery were 1 mm and 3 % respectively.
Poster ‐ 45: The effect of plan modulation on VMAT liver SBRT treatments: A motion interplay study
Authors: Hubley Emily , Hunter William , Sinha Richie , Pierce Greg 
Published: August 2016

Purpose:To investigate whether increasing the degree of MLC leaf modulation in VMAT liver SBRT treatment plans increases the dose differences due to the interplay effect.Methods:Two VMAT plans, delivering 54Gy in three fractions, with differing degrees of MLC aperture modulation were created for each of 10 patients. To simulate respiratory motion, an in‐house program was used to shift the positions of each active MLC leaf at every 0.6° of gantry rotation, according to the amplitude of a respiratory trace. To isolate the interplay effect from dose blurring, motion was simulated using four different starting points in the respiratory cycle. The same starting point was used for each of the three fractions, representing a worst case scenario. The four resultant dose distributions from each plan were subtracted from each other, and dose differences in the GTV were quantified using the standard deviation of the differential DVH.Results:Dose differences up to 1Gy were found in the GTV of the dose subtractions, indicating the presence of interplay effects. A Wilcoxon Signed Rank test indicates a significant (p<0.05) increase in the standard deviations of the low‐modulation plans to those with a higher degree of modulation. No planning constraints were exceeded with the introduction of respiratory motion.Conclusions:VMAT liver SBRT plans with a high degree of modulation exhibit an increased susceptibility to interplay effects. The dose differences due to interplay are not large enough to markedly decrease the plan quality.
Poster ‐ 51: A tumor motion‐compensating system with tracking and prediction – a proof‐of‐concept study
Authors: Guo Kaiming , Teo Peng (Troy) , Kawalec Philip , Pistorius Stephen 
Published: August 2016

Purpose:This work reports on the development of a mechanical slider system for the counter‐steering of tumor motion in adaptive Radiation Therapy (RT). The tumor motion was tracked using a weighted optical flow algorithm and its position is being predicted with a neural network (NN).Methods:The components of the proposed mechanical counter‐steering system includes: (1) an actuator which provides the tumor motion, (2) the motion detection using an optical flow algorithm, (3) motion prediction using a neural network, (4) a control module and (5) a mechanical slider to counter‐steer the anticipated motion of the tumor phantom. An asymmetrical cosine function and five patient traces (P1–P5) were used to evaluate the tracking of a 3D printed lung tumor. In the proposed mechanical counter‐steering system, both actuator (Zaber NA14D60) and slider (Zaber A‐BLQ0070‐E01) were programed to move independently with LabVIEW and their positions were recorded by 2 potentiometers (ETI LCP12S‐25). The accuracy of this counter‐steering system is given by the difference between the two potentiometers.Results:The inherent accuracy of the system, measured using the cosine function, is −0.15 ± 0.06 mm. While the errors when tracking and prediction were included, is (0.04 ± 0.71) mm.Conclusion:A prototype tumor motion counter‐steering system with tracking and prediction was implemented. The inherent errors are small in comparison to the tracking and prediction errors, which in turn are small in comparison to the magnitude of tumor motion. The results show that this system is suited for evaluating RT tracking and prediction.
Poster ‐ 52: Smoothing constraints in Modulated Photon Radiotherapy (XMRT) fluence map optimization
Authors: McGeachy Philip , Villarreal‐Barajas Jose Eduardo , Zinchenko Yuriy , Khan Rao 
Published: August 2016

Purpose:Modulated Photon Radiotherapy (XMRT), which simultaneously optimizes photon beamlet energy (6 and 18 MV) and fluence, has recently shown dosimetric improvement in comparison to conventional IMRT. That said, the degree of smoothness of resulting fluence maps (FMs) has yet to be investigated and could impact the deliverability of XMRT. This study looks at investigating FM smoothness and imposing smoothing constraint in the fluence map optimization.Methods:Smoothing constraints were modeled in the XMRT algorithm with the sum of positive gradient (SPG) technique. XMRT solutions, with and without SPG constraints, were generated for a clinical prostate scan using standard dosimetric prescriptions, constraints, and a seven coplanar beam arrangement. The smoothness, with and without SPG constraints, was assessed by looking at the absolute and relative maximum SPG scores for each fluence map. Dose volume histograms were utilized when evaluating impact on the dose distribution.Results:Imposing SPG constraints reduced the absolute and relative maximum SPG values by factors of up to 5 and 2, respectively, when compared with their non‐SPG constrained counterparts. This leads to a more seamless conversion of FMS to their respective MLC sequences. This improved smoothness resulted in an increase to organ at risk (OAR) dose, however the increase is not clinically significant.Conclusions:For a clinical prostate case, there was a noticeable improvement in the smoothness of the XMRT FMs when SPG constraints were applied with a minor increase in dose to OARs. This increase in OAR dose is not clinically meaningful.