bluuebunny/crossref_metadata_2025 huggingface dataset:
Highly Efficient Photodegradation of Organic Pollutants Assisted by Sonoluminescence
Authors: Volkova Anna V. , Nemeth Silke , Skorb Ekaterina V. , Andreeva Daria V.
Published: September 2014

The mechanism of the photodegradation of azo dyes via ultrasonication is studied using a combination of the high‐performance liquid chromatography and UV–vis spectroscopy with detailed analysis of the kinetics. Based on the kinetics studies of the sonodegradation, it was proposed that the degradation of azo dyes was a multistage process that involved: (1) the direct attack of azo bonds and phenyl rings of dyes by the sonochemically formed reactive oxygen species; (2) the activation of semiconductor particles by the light emitted during cavitation and the triggering of the photocatalytic pathways of dye degradation and (3) increase of the adsorption capacity of the semiconductor particles due to the sonomechanically induced interparticle collisions. The detailed kinetics study can help in following an effective process up‐scaling. It was demonstrated that extremely short pulses of light flashes in a cavitated mixture activated the surface of photocatalysts and significantly enhanced dye degradation processes.
Hyperhemolysis syndrome in a patient without a hemoglobinopathy, unresponsive to treatment with eculizumab
Authors: Gupta Shruti , Fenves Andrew , Nance Sandra Taddie , Sykes David B. , Dzik Walter “Sunny”
Published: September 2014

Background

Hyperhemolysis is a serious transfusion reaction, most often described in patients with hemoglobinopathies. Hyperhemolysis is characterized by the destruction of host red blood cells (RBCs), in addition to donorRBCs, via an unknown mechanism.

Study Design and Methods

We present the case of a 58‐year‐old woman with treated human immunodeficiency virus and a normal hemoglobin (Hb) electrophoresis who developed hyperhemolysis in the setting of a delayed hemolytic transfusion reaction (DHTR).

Results

The patient wasABOgroupBand had a previously identified anti‐Fyballoantibody. After transfusion ofFyb–RBCs, she developed aDHTRand was found to have anti‐E, anti‐Cw, anti‐s, and an additional antibody to an unrecognized high‐frequencyRBCalloantigen. Subsequent transfusion ofABO‐compatibleRBCsthat were negative forFyb,E,Cw, and s antigens resulted in immediate intravascular hemolysis. In the absence of bleeding, her hematocrit (Hct) decreased to 10.2%. An extensive serologic evaluation failed to identify the specificity of the high‐frequency antibody. Severe hemolytic reactions also occurred despite pretransfusion conditioning with eculizumab. TheHctand clinical symptoms slowly improved after the cessation of transfusions and treatment with erythropoietin and steroids. This case demonstrates several noteworthy features including hyperhemolysis in a patient without aHbdisorder, the development of an antibody to an unknownRBCantigen, and the failure of eculizumab to prevent intravascular hemolysis after transfusion.

Conclusion

Hyperhemolysis is not restricted to patients with hemoglobinopathies. Whether eculizumab offers any benefit in the hyperhemolysis syndrome or in the prevention of intravascular hemolysis due toRBCalloantibodies remains uncertain.
Poster — Thur Eve — 17: In‐phantom and Fluence‐based Measurements for Quality Assurance of Volumetric‐driven Adaptation of Arc Therapy
Authors: Schaly B , Hoover D , Mitchell S , Wong E
Published: September 2014

During volumetric modulated arc therapy (VMAT) of head and neck cancer, some patients lose weight which may result in anatomical deviations from the initial plan. If these deviations are substantial a new treatment plan can be designed for the remainder of treatment (i.e., adaptive planning). Since the adaptive treatment process is resource intensive, one possible approach to streamlining the quality assurance (QA) process is to use the electronic portal imaging device (EPID) to measure the integrated fluence for the adapted plans instead of the currently‐used ArcCHECK device (Sun Nuclear). Although ArcCHECK is recognized as the clinical standard for patient‐specific VMAT plan QA, it has limited length (20 cm) for most head and neck field apertures and has coarser detector spacing than the EPID (10 mm vs. 0.39 mm). In this work we compared measurement of the integrated fluence using the EPID with corresponding measurements from the ArcCHECK device. In the past year nine patients required an adapted plan. Each of the plans (the original and adapted) is composed of two arcs. Routine clinical QA was performed using the ArcCHECK device, and the same plans were delivered to the EPID (individual arcs) in integrated mode. The dose difference between the initial plan and adapted plan was compared for ArcCHECK and EPID. In most cases, it was found that the EPID is more sensitive in detecting plan differences. Therefore, we conclude that EPID provides a viable alternative for QA of the adapted head and neck plans and should be further explored.
Poster — Thur Eve — 21: Off‐axis dose perturbation effects in water in a 5 × 5 cm2 18 MV photon beam for the PTW microLion and Exradin A1SL ionization chambers
Authors: O'Grady K , Davis S D , Papaconstadopoulos P , Seuntjens J
Published: September 2014

A PTW microLion liquid ionization chamber and an Exradin A1SL air‐filled ionization chamber have been modeled using the egs_chamber user code of the EGSnrc system to determine their perturbation effects in water in a 5 × 5 cm2 18 MV photon beam. A model of the Varian CL21EX linear accelerator was constructed using the BEAMnrc Monte Carlo code, and was validated by comparing measured PDDs and profiles from the microLion and A1SL chambers to calculated results that included chamber models. Measured PDDs for a 5 × 5 cm2 field for the microLion chamber agreed with calculations to within 1.5% beyond a depth of 0.5 cm, and the A1SL PDDs agreed within 1.0% beyond 1.0 cm. Measured and calculated profiles at 10 cm depth agreed within 1.0% for both chambers inside the field, and within 4.0% near the field edge. Local percent differences increased up to 15% at 4 cm outside the field. The ratio of dose to water in the absence of the chamber relative to dose in the chamber's active volume as a function of off‐axis distance was calculated using the egs_chamber correlated sampling technique. The dose ratio was nearly constant inside the field and consistent with the stopping power ratios of water to detector material, but varied up to 3.3% near the field edge and 5.2% at 4 cm outside the field. Once these perturbation effects are fully characterized for more field sizes and detectors, they could be applied to clinical water tank measurements for improved dosimetric accuracy.
Poster — Thur Eve — 22: A water calorimeter for low‐energy particle beams
Authors: Renaud J , Rossomme S , Sarfehnia A , Vynckier S , Seuntjens J
Published: September 2014

In this work, the feasibility of absolute dose to water measurements in low‐energy electron beams using a water calorimeter specifically developed for shallow measurements is established. The calorimeter design consists of a cylindrical glass vessel encased in a block of expanded polystyrene. The vessel has a front window thickness of 1.1 mm, a 4 cm radius, and is 2.5 cm in depth. The vessel‐block assembly sits inside a thermally‐insulated box and is air‐cooled to an operating temperature of 4 °C. Radiation‐induced thermal gradients were simulated in a geometric model of the calorimeter using a finite element analysis software package. 52 absorbed dose to water measurements were performed in a 6 and 8 MeV electron beam (zmax of 1.32 and 1.76 cm, respectively) for 60 seconds at a repetition rate of 400 MU/min and an SSD of 120 cm. Within the vessel, the depth of measurement was set to 1.08 cm relative to the inner front window. The average measured dose to water was 59.6 ± 0.2 cGy/100 MU (6 MeV), and 63.7 ± 0.3 cGy/100 MU (8 MeV). The associated heat transfer corrections were determined to be 1.026 ± 0.003 and 1.017 ± 0.004 for the 6 and 8 MeV beams, respectively. The most significant source of uncertainty in this study was the repeatability (type A, 0.42%). It is expected that performing fewer consecutive measurements under higher dose rate conditions will improve the stability of the thermal background, thereby improving the repeatability and reducing the overall standard uncertainty.
Poster — Thur Eve — 23: Dose and Position Quality Assurance using the RADPOS System for 4D Radiotherapy with CyberKnife
Authors: Marants R , Vandervoort E , Cygler J E
Published: September 2014

Introduction:

RADPOS 4D dosimetry system consists of a microMOSFET dosimeter combined with an electromagnetic positioning sensor, which allows for performing real‐time dose and position measurements simultaneously. In this report the use of RADPOS as an independent quality assurance (QA) tool during CyberKnife 4D radiotherapy treatment is described. In addition to RADPOS, GAFCHROMIC® films were used for simultaneous dose measurement.

Methods:

RADPOS and films were calibrated in a Solid Water® phantom at 1.5 cm depth, SAD= 80 cm, using 60 mm cone. CT based treatment plan was created for a Solid Water® breast phantom containing metal fiducials and RADPOS probe. Dose calculations were performed using iPlan pencil beam algorithm. Before the treatment delivery, GAFCHROMIC® film was inserted inside the breast phantom, next to the RADPOS probe. Then the phantom was positioned on the chest platform of the QUASAR, to which Synchrony LED optical markers were also attached. Position logging began for RADPOS and the Synchrony tracking system, the QUASAR motion was initiated and the treatment was delivered.

Results:

RADPOS position measurements very closely matched the LED marker positions recorded by the Synchrony camera tracking system. The RADPOS measured dose was 2.5% higher than the average film measured dose, which is within the experimental uncertainties. Treatment plan calculated dose was 4.1 and 1.6% lower than measured by RADPOS and film, respectively. This is most likely due to the inferior nature of the dose calculation algorithm.

Conclusions:

Our study demonstrates that RADPOS system is a useful tool for independent QA of CyberKnife treatments.
Poster — Thur Eve — 24: Commissioning and preliminary measurements using an Attix‐style free air ionization chamber for air kerma measurements on the BioMedical Imaging and Therapy beamlines at the Canadian Light Source
Authors: Anderson D , McEwen M , Shen H , Siegbahn EA , Fallone BG , Warkentin B
Published: September 2014

Synchrotron facilities, including the Canadian Light Source (CLS), provide opportunities for the development of novel imaging and therapy applications. A vital step progressing these applications toward clinical trials is the availability of accurate dosimetry. In this study, a refurbished Attix‐style (cylindrical) free air chamber (FAC) is tested and used for preliminary air kerma measurements on the two BioMedical Imaging and Therapy (BMIT) beamlines at the CLS. The FAC consists of a telescoping chamber that relies on a difference measurement of collected charge in expanded and collapsed configurations. At the National Research Council's X‐ray facility, a Victoreen Model 480 FAC was benchmarked against two primary standard FACs. The results indicated an absolute accuracy at the 0.5% level for energies between 60 and 150 kVp. A series of measurements were conducted on the small, non‐uniform X‐ray beams of the 05B1‐1 (∼8 – 100 keV) and 05ID‐2 (∼20 – 200 keV) beamlines for a variety of energies, filtrations and beam sizes. For the 05B1‐1 beam with 1.1 mm of Cu filtration, recombination corrections of less than 5 % could only be achieved for field sizes no greater than 0.5 mm × 0.6 mm (corresponding to an air kerma rate of ∼ 57 Gy/min). Ionic recombination thus presents a significant challenge to obtaining accurate air kerma rate measurements using this FAC in these high intensity beams. Future work includes measurements using a smaller aperture to sample a smaller and thus more uniform beam area, as well as experimental and Monte Carlo‐based investigation of correction factors.
Poster — Thur Eve — 27: Flattening Filter Free VMAT Quality Assurance: Dose Rate Considerations for Detector Response
Authors: Viel Francis , Duzenli Cheryl , Camborde Marie‐Laure , Strgar Vincent , Horwood Ron , Atwal Parmveer , Gete Ermias , Karan Tania
Published: September 2014

Introduction:

Radiation detector responses can be affected by dose rate. Due to higher dose per pulse and wider range of mu rates in FFF beams, detector responses should be characterized prior to implementation of QA protocols for FFF beams. During VMAT delivery, the MU rate may also vary dramatically within a treatment fraction. This study looks at the dose per pulse variation throughout a 3D volume for typical VMAT plans and the response characteristics for a variety of detectors, and makes recommendations on the design of QA protocols for FFF VMAT QA.

Materials and Methods:

Linac log file data and a simplified dose calculation algorithm are used to calculate dose per pulse for a variety of clinical VMAT plans, on a voxel by voxel basis, as a function of time in a cylindrical phantom. Diode and ion chamber array responses are characterized over the relevant range of dose per pulse and dose rate.

Results:

Dose per pulse ranges from <0.1 mGy/pulse to 1.5 mGy/pulse in a typical VMAT treatment delivery using the 10XFFF beam. Diode detector arrays demonstrate increased sensitivity to dose (+./− 3%) with increasing dose per pulse over this range. Ion chamber arrays demonstrate decreased sensitivity to dose (+/− 1%) with increasing dose rate over this range.

Conclusions:

QA protocols should be designed taking into consideration inherent changes in detector sensitivity with dose rate. Neglecting to account for changes in detector response with dose per pulse can lead to skewed QA results.
Poster — Thur Eve — 28: Enabling trajectory‐based radiotherapy on a TrueBeam accelerator with the Eclipse treatment planning system
Authors: Mullins J , Asiev K , DeBlois F , Morcos M , Seuntjens J , Syme A
Published: September 2014

The TrueBeam linear accelerator platform has a developer's mode which permits the user dynamic control over many of the machine's mechanical and radiation systems. Using this research tool, synchronous couch and gantry motion can be programmed to simulate isocentric treatment with a shortened SAD, with benefits such as smaller projected MLC leaf widths and an increased dose rate. In this work, water tank measurements were used to commission a virtual linear accelerator with an 85 cm SAD in Eclipse, from which several arc‐based radiotherapy treatments were generated, including an inverse optimized VMAT delivery. For each plan, the pertinent treatment delivery information was extracted from control points specified in the Eclipse‐exported DICOM files using the pydicom package in Python, allowing construction of an XML control file. The dimensions of the jaws and MLC positions, defined for an 85 cm SAD in Eclipse, were scaled for delivery on a conventional SAD linear accelerator, and translational couch motion was added as a function of gantry angle to simulate delivery at 85 cm SAD. Ionization chamber and Gafchromic film measurements were used to compare the radiation delivery to dose calculations in Eclipse. With the exception of the VMAT delivery, ionization chamber measurements agreed within 3.3% of the Eclipse calculations. For the VMAT delivery, the ionization chamber was located in an inhomogeneous region, but gamma evaluation of the Gafchromic film plane resulted in a 94.5% passing rate using criteria of 3 mm/3%. The results indicate that Eclipse calculation infrastructure can be used.
Sci—Thur AM: YIS ‐ 02: Radiogenomic Modeling of Normal Tissue Toxicities in Prostate Cancer Patients Receiving Hypofractionated Radiotherapy
Authors: Coates J , Jeyaseelan K , Ybarra N , David M , Faria S , Souhami L , Cury F , Duclos M , El Naqa I
Published: September 2014

Inter‐patient radiation sensitivity variability has recently been shown to have a genetic component. This genetic component may play a key role in explaining the fluctuating rates of radiation‐induced toxicities (RITs). Single nucleotide polymorphisms (SNPs) have thus far yielded inconsistent results in delineating RITs while copy number variations (CNVs) have not yet been investigated for such purposes. We explore a radiogenomic modeling approach to investigate the association of CNVs and SNPs, along with clinical and dosimetric variables, in radiation induced rectal bleeding (RB) and erectile dysfunction (ED) in prostate cancer patients treated with curative hypofractionated irradiation. A cohort of 62 prostate cancer patients who underwent hypofractionated radiotherapy (66 Gy in 22 fractions) between 2002 to 2010 were retrospectively genotyped for CNV and SNP rs5489 in the xrcc1 DNA repair gene. Late toxicity rates for RB grade 2 & 3 and grade 3 alone were 29.0% and 12.9%, respectively. ED toxicity was found to be 62.9%. Radiogenomic model performance was evaluated using receiver operating characteristic area under the curve (AUC) and resampling by cross‐validation. Binary variables were evaluated using Chi‐squared contingency table analysis and multivariate models by Spearman's rank correlation coefficient (rs). Ten patients were found to have three copies of xrcc1 CNV (RB: χ2=14.6, p<0.001 and ED: χ2=4.88, p=0.0272) and twelve had heterozygous rs25489 SNP (RB: χ2=0.278, p=0.599 and ED: χ2=0.112, p=0.732). Radiogenomic modeling yielded significant, cross‐validated NTCP models for RB (AUC=0.665) and ED (AUC=0.754). These results indicate that CNVs may be potential predictive biomarkers of both late ED and RB.
Poster — Thur Eve — 30: 4D VMAT dose calculation methodology to investigate the interplay effect: experimental validation using TrueBeam Developer Mode and Gafchromic film
Authors: Teke T , Huang V , Milette MP , Thomas SD
Published: September 2014

The interplay effect between the tumor motion and the radiation beam modulation during a VMAT treatment delivery alters the delivered dose distribution from the planned one. This work present and validate a method to accurately calculate the dose distribution in 4D taking into account the tumor motion, the field modulation and the treatment starting phase. A QUASAR™ respiratory motion phantom was 4D scanned with motion amplitude of 3 cm and with a 3 second period. A static scan was also acquired with the lung insert and the tumor contained in it centered. A VMAT plan with a 6XFFF beam was created on the averaged CT and delivered on a Varian TrueBeam and the trajectory log file was saved. From the trajectory log file 10 VMAT plans (one for each breathing phase) and a developer mode XML file were created. For the 10 VMAT plans, the tumor motion was modeled by moving the isocentre on the static scan, the plans were re‐calculated and summed in the treatment planning system. In the developer mode, the tumor motion was simulated by moving the couch dynamically during the treatment. Gafchromic films were placed in the QUASAR phantom static and irradiated using the developer mode. Different treatment starting phase were investigated (no phase shift, maximum inhalation and maximum exhalation). Calculated and measured isodose lines and profiles are in very good agreement. For each starting phase, the dose distribution exhibit significant differences but are accurately calculated with the methodology presented in this work.
Poster — Thur Eve — 31: Dosimetric Effect of Respiratory Motion on RapidArc Lung SBRT Treatment Delivered by TrueBeam Linear Accelerator
Authors: Jiang Runqing , Zhan Lixin , Osei Ernest
Published: September 2014

Volumetric modulated arc therapy (VMAT) allows fast delivery of stereotactic radiotherapy. However, the discrepancies between the calculated and delivered dose distributions due to respiratory motion and dynamic multileaf collimators (MLCs) interplay are not avoidable. The purpose of this study is to investigate RapidArc lung SBRT treatment delivered by the flattening filter‐free (FFF) beam and flattened beam with Varian TrueBeam machine. CIRS Dynamic Thorax Phantom with in‐house made lung tumor insertion was CT scanned both in free breathing and 4DCT. 4DCT was used to determine the internal target volume. The free breathing CT scan was used for treatment planning. A 5 mm margin was given to ITV to generate a planning target volume. Varian Eclipse treatment planning was used to generate RapidArc plans based on the 6 MV flattened beam and 6MV FFF beam. The prescription dose was 48 Gy in 4 fractions. At least 95% of PTV was covered by the prescribed dose. The RapidArc plans with 6 MV flattened beam and 6MV FFF beam were delivered with Varian TrueBeam machine. The dosimetric measurements were performed with Gafchromic XR‐RV3 film, which was placed in the lung tumor insertion. The interplay between the dynamic MLC‐based delivery of VMAT and the respiratory motion of the tumor degraded target coverage and created undesired hot or cold dose spots inside the lung tumor. Lung SBRT RapidArc treatments delivered by the FFF beam of TrueBeam linear accelerator is superior to the flattened beam. Further investigation will be performed by Monte Carlo simulation.
Poster — Thur Eve — 36: Implementation of constant dose rate and gantry speed arc therapy(CDR‐CAS‐IMAT) for thoracic esophageal carcinoma on Varian 23EX
Authors: Zhang Ruohui , Fan Xiaomei , Bai Wenwen , Han Chun
Published: September 2014

Objective:

The purpose of this study is to propose an alternative planning approach for VMAT using constant dose rate and gantry speed arc therapy(CDR‐CAS‐IMAT) implementation on conventional Linac Varian 23EX and used IMRT as a benchmark to evaluate the performance.

Methods and materials:

Eighteen patients with thoracic esophageal carcinoma who were previously treated with IMRT on Varian 23EX were retrospectively planned for CDR‐CAS‐IMAT plans. Dose prescription was set to 60 Gy to PTVs in 30 fractions. The planning objectives for PTVs and OAR were corresponding with the IMRT plans. Dose to the PTVs and OAR were compared to IMRT with respect to plan quality, MU, treatment time and delivery accuracy.

Results:

CDR‐CAS‐IMAT plans led to equivalent or superior plan quality as compared to IMRT, PTV's CI relative increased 16.2%, while small deviations were observed on minimum dose for PTV. Volumes in the cord receiving 40Gy were increased from 3.6% with IMRT to 7.0%. Treatment times were reduced significantly with CDR‐CAS‐IMAT(mean 85.7s vs. 232.1s, p < .05), however, MU increased by a factor of 1.3 and lung V10/5/3.5/aver were relative increase 6.7%,12%,17.9%,4.2%, respectively. And increased the E‐P low dose area volume decreased the hight dose area. There were no significant difference in Delta4 measurements results between both planning techniques.

Conclusion:

CDR‐CAS‐IMAT plans can be implemented smoothly and quickly into a busy cancer center, which improved PTV CI and reduces treatment time but increased the MU and low dose irradiated area. An evaluation of weight loss must be performed during treatment for CDR‐CAS‐IMAT patients.
Sci—Thur AM: YIS ‐ 04: Gold Nanoparticle Enhanced Arc Radiotherapy: A Monte Carlo Feasibility Study
Authors: Koger B , Kirkby C
Published: September 2014

Introduction:

The use of gold nanoparticles (GNPs) in radiotherapy has shown promise for therapeutic enhancement. In this study, we explore the feasibility of enhancing radiotherapy with GNPs in an arc‐therapy context. We use Monte Carlo simulations to quantify the macroscopic dose‐enhancement ratio (DER) and tumour to normal tissue ratio (TNTR) as functions of photon energy over various tumour and body geometries.

Methods:

GNP‐enhanced arc radiotherapy (GEART) was simulated using the PENELOPE Monte Carlo code and penEasy main program. We simulated 360° arc‐therapy with monoenergetic photon energies 50 – 1000 keV and several clinical spectra used to treat a spherical tumour containing uniformly distributed GNPs in a cylindrical tissue phantom. Various geometries were used to simulate different tumour sizes and depths. Voxel dose was used to calculate DERs and TNTRs. Inhomogeneity effects were examined through skull dose in brain tumour treatment simulations.

Results:

Below 100 keV, DERs greater than 2.0 were observed. Compared to 6 MV, tumour dose at low energies was more conformai, with lower normal tissue dose and higher TNTRs. Both the DER and TNTR increased with increasing cylinder radius and decreasing tumour radius. The inclusion of bone showed excellent tumour conformality at low energies, though with an increase in skull dose (40% of tumour dose with 100 keV compared to 25% with 6 MV).

Conclusions:

Even in the presence of inhomogeneities, our results show promise for the treatment of deep‐seated tumours with low‐energy GEART, with greater tumour dose conformality and lower normal tissue dose than 6 MV.
Poster — Thur Eve — 38: Feasibility of a Table‐Top Total Body Irradiation Technique using Robotic Couch Motion
Authors: Chin Erika , Otto Karl , Hoppe Richard , Hsu Annie , Loo Billy , Million Lynn , Xing Lei , Fahimian Benjamin
Published: September 2014

Purpose:

To develop and test the feasibility of a table‐top implementation for total body irradiation (TBI) via robotic couch motion and coordinated monitor unit modulation on a standard C‐arm linac geometry.

Methods:

To allow for collision free delivery and to maximize the effective field size, the couch was rotated to 270° IEC and dropped to 150 cm from the vertical radiation source. The robotic delivery was programmed using the TrueBeam STx Developer Mode using custom XML scripting. To assess the dosimetry of a sliding 30×20 cm2 field, irradiation on a solid water phantom of varying thickness was analyzed using EDR2 radiographic film and OSLDs. Beam modulation was achieved by dividing the couch path into multiple segments of varying dose rates and couch speeds in order to deliver 120 cGy to the midline.

Results:

The programmed irradiation in conjunction with coordinated couch motion was successfully delivered on a TrueBeam linac. When no beam modulation was employed, the dose difference between two different phantom sections was 17.0%. With simple beam modulation via changing dose rates and couch speeds, the desired prescription dose can be achieved at the centre of each phantom section within 1.9%. However, dose deviation at the junction was 9.2% due to the nonphysical change in the phantom thickness.

Conclusions:

The feasibility of robotic table‐top TBI on a C‐arm linac geometry was experimentally demonstrated. To achieve a more uniform dose distribution, inverse‐planning allowing for a combination of dose rate modulation, jaw tracking and MLC motion is under investigation.
Poster — Thur Eve — 40: Automated Quality Assurance for Remote‐Afterloading High Dose Rate Brachytherapy
Authors: Kim Anthony , Ravi Ananth
Published: September 2014

High dose rate (HDR) remote afterloading brachytherapy involves sending a small, high‐activity radioactive source attached to a cable to different positions within a hollow applicator implanted in the patient. It is critical that the source position within the applicator and the dwell time of the source are accurate. Daily quality assurance (QA) tests of the positional and dwell time accuracy are essential to ensure that the accuracy of the remote afterloader is not compromised prior to patient treatment. Our centre has developed an automated, video‐based QA system for HDR brachytherapy that is dramatically superior to existing diode or film QA solutions in terms of cost, objectivity, positional accuracy, with additional functionalities such as being able to determine source dwell time and transit time of the source. In our system, a video is taken of the brachytherapy source as it is sent out through a position check ruler, with the source visible through a clear window. Using a proprietary image analysis algorithm, the source position is determined with respect to time as it moves to different positions along the check ruler. The total material cost of the video‐based system was under $20, consisting of a commercial webcam and adjustable stand. The accuracy of the position measurement is ±0.2 mm, and the time resolution is 30 msec. Additionally, our system is capable of robustly verifying the source transit time and velocity (a test required by the AAPM and CPQR recommendations), which is currently difficult to perform accurately.
Poster — Thur Eve — 42: Radiochromic film calibration for low‐energy seed brachytherapy dose measurement
Authors: Morrison H , Menon G , Sloboda R
Published: September 2014

The purpose of this study was to investigate the accuracy of radiochromic film calibration procedures used in external beam radiotherapy when applied to I‐125 brachytherapy sources delivering higher doses, and to determine any necessary modifications to achieve similar accuracy in absolute dose measurements. GafChromic EBT3 film was used to measure radiation doses upwards of 35 Gy from 6 MV, 75 kVp and (∼28 keV) I‐125 photon sources. A custom phantom was used for the I‐125 irradiations to obtain a larger film area with nearly constant dose to reduce the effects of film heterogeneities on the optical density (OD) measurements. RGB transmission images were obtained with an Epson 10000XL flatbed scanner, and calibration curves relating OD and dose using a rational function were determined for each colour channel and at each energy using a non‐linear least square minimization method. Differences found between the 6 MV calibration curve and those for the lower energy sources are large enough that 6 MV beams should not be used to calibrate film for low‐energy sources. However, differences between the 75 kVp and I‐125 calibration curves were quite small; indicating that 75 kVp is a good choice. Compared with I‐125 irradiation, this gives the advantages of lower type B uncertainties and markedly reduced irradiation time. To obtain high accuracy calibration for the dose range up to 35 Gy, two‐segment piece‐wise fitting was required. This yielded absolute dose measurement accuracy above 1 Gy of ∼2% for 75 kVp and ∼5% for I‐125 seed exposures.
Poster — Thur Eve — 44: Linearization of Compartmental Models for More Robust Estimates of Regional Hemodynamic, Metabolic and Functional Parameters using DCE‐CT/PET Imaging
Authors: Blais AR , Dekaban M , Lee T‐Y
Published: September 2014

Quantitative analysis of dynamic positron emission tomography (PET) data usually involves minimizing a cost function with nonlinear regression, wherein the choice of starting parameter values and the presence of local minima affect the bias and variability of the estimated kinetic parameters. These nonlinear methods can also require lengthy computation time, making them unsuitable for use in clinical settings. Kinetic modeling of PET aims to estimate the rate parameter k3, which is the binding affinity of the tracer to a biological process of interest and is highly susceptible to noise inherent in PET image acquisition. We have developed linearized kinetic models for kinetic analysis of dynamic contrast enhanced computed tomography (DCE‐CT)/PET imaging, including a 2‐compartment model for DCE‐CT and a 3‐compartment model for PET. Use of kinetic parameters estimated from DCE‐CT can stabilize the kinetic analysis of dynamic PET data, allowing for more robust estimation of k3. Furthermore, these linearized models are solved with a non‐negative least squares algorithm and together they provide other advantages including: 1) only one possible solution and they do not require a choice of starting parameter values, 2) parameter estimates are comparable in accuracy to those from nonlinear models, 3) significantly reduced computational time. Our simulated data show that when blood volume and permeability are estimated with DCE‐CT, the bias of k3 estimation with our linearized model is 1.97 ± 38.5% for 1,000 runs with a signal‐to‐noise ratio of 10. In summary, we have developed a computationally efficient technique for accurate estimation of k3 from noisy dynamic PET data.
Poster — Thur Eve — 45: Comparison of different Monte Carlo methods of scoring linear energy transfer in modulated proton therapy beams
Authors: Granville DA , Sawakuchi GO
Published: September 2014

In this work, we demonstrate inconsistencies in commonly used Monte Carlo methods of scoring linear energy transfer (LET) in proton therapy beams. In particle therapy beams, the LET is an important parameter because the relative biological effectiveness (RBE) depends on it. LET is often determined using Monte Carlo techniques. We used a realistic Monte Carlo model of a proton therapy nozzle to score proton LET in spread‐out Bragg peak (SOBP) depth‐dose distributions. We used three different scoring and calculation techniques to determine average LET at varying depths within a 140 MeV beam with a 4 cm SOBP and a 250 MeV beam with a 10 cm SOBP. These techniques included fluence‐weighted (Φ‐LET) and dose‐weighted average (D‐LET) LET calculations from: 1) scored energy spectra converted to LET spectra through a lookup table, 2) directly scored LET spectra and 3) accumulated LET scored ‘on‐the‐fly’ during simulations. All protons (primary and secondary) were included in the scoring. Φ‐LET was found to be less sensitive to changes in scoring technique than D‐LET. In addition, the spectral scoring methods were sensitive to low‐energy (high‐LET) cutoff values in the averaging. Using cutoff parameters chosen carefully for consistency between techniques, we found variations in Φ‐LET values of up to 1.6% and variations in D‐LET values of up to 11.2% for the same irradiation conditions, depending on the method used to score LET. Variations were largest near the end of the SOBP, where the LET and energy spectra are broader.
Sci—Thur AM: YIS ‐ 05: 10X‐FFF VMAT for Lung SABR: an Investigation of Peripheral Dose
Authors: Mader J , Mestrovic A
Published: September 2014

Flattening Filter Free (FFF) beams exhibit high dose rates, reduced head scatter, leaf transmission and leakage radiation. For VMAT lung SABR, treatment time can be significantly reduced using high dose rate FFF beams while maintaining plan quality and accuracy. Another possible advantage offered by FFF beams for VMAT lung SABR is the reduction in peripheral dose. The focus of this study was to investigate and quantify the reduction of peripheral dose offered by FFF beams for VMAT lung SABR.

The peripheral doses delivered by VMAT Lung SABR treatments using FFF and flattened beams were investigated for the Varian Truebeam linac. This study was conducted in three stages, (1): ion chamber measurement of peripheral dose for various plans, (2): validation of AAA, Acuros XB and Monte Carlo for peripheral dose using measured data, and (3): using the validated Monte Carlo model to evaluate peripheral doses for 6 VMAT lung SABR treatments. Three energies, 6X, 10X, and 10X‐FFF were used for all stages.

Measured data indicates that 10X‐FFF delivers the lowest peripheral dose of the three energies studied. AAA and Acuros XB dose calculation algorithms were identified as inadequate, and Monte Carlo was validated for accurate peripheral dose prediction. The Monte Carlo‐calculated VMAT lung SABR plans show a significant reduction in peripheral dose for 10X‐FFF plans compared to the standard 6X plans, while no significant reduction was showed when compared to 10X. This reduction combined with shorter treatment time makes 10X‐FFF beams the optimal choice for superior VMAT lung SABR treatments.
Sci—Thur AM: YIS ‐ 10: Use of the Microsoft Kinect for applications of patient surface data to radiotherapy
Authors: Guillet Dominique , Syme Alasdair , DeBlois François
Published: September 2014

Current techniques to acquire patient surface data are often very expensive and lack flexibility. In this study, the use of the Microsoft Kinect to reliably acquire 3D scans of patient surface is investigated. A design is presented to make the system easily applicable to the clinic. Potential applications of the device to radiotherapy are also presented.

Scan reproducibility was tested by repeatedly scanning an anthropomorphic phantom. Scan accuracy was tested by comparing Kinect scans to the surface extracted from a CT dataset of a Rando® anthropomorphic phantom, which was considered as the true reference surface. Average signed distances of 0.12 ± 2.34 mm and 0.13 ± 2.04 mm were obtained between the compared surfaces for reproducibility and accuracy respectively. This is conclusive, since it indicates that the variations observed come largely from noise distributed around an average distance close to 0 mm. Moreover, the range of the noise is small enough for the system to reliably capture a patient's surface. A system was also designed using two Kinects used together to acquire 3D surfaces in a quick and stable way that is applicable to the clinic. Finally, applications of the device to radiotherapy are demonstrated. Its use to detect local positioning errors is presented, where small local variations difficult to see with the naked eye are clearly visible. The system was also used to predict collisions using gantry and patient scans and thus ensure the safety of unconventional trajectories.
Sci—Thur AM: YIS ‐ 11: Estimation of Bladder‐Wall Cumulative Dose in Multi‐Fraction Image‐Based Gynaecological Brachytherapy Using Deformable Point Set Registration
Authors: Zakariaee R , Brown C J , Hamarneh G , Parsons C A , Spadinger I
Published: September 2014

Dosimetric parameters based on dose‐volume histograms (DVH) of contoured structures are routinely used to evaluate dose delivered to target structures and organs at risk. However, the DVH provides no information on the spatial distribution of the dose in situations of repeated fractions with changes in organ shape or size. The aim of this research was to develop methods to more accurately determine geometrically localized, cumulative dose to the bladder wall in intracavitary brachytherapy for cervical cancer. The CT scans and treatment plans of 20 cervical cancer patients were used. Each patient was treated with five high‐dose‐rate (HDR) brachytherapy fractions of 600cGy prescribed dose. The bladder inner and outer surfaces were delineated using MIM Maestro software (MIM Software Inc.) and were imported into MATLAB (MathWorks) as 3‐dimensional point clouds constituting the “bladder wall”. A point‐set registration toolbox for MATLAB, Coherent Point Drift (CPD), was used to non‐rigidly transform the bladder‐wall points from four of the fractions to the coordinate system of the remaining (reference) fraction, which was chosen to be the emptiest bladder for each patient. The doses were accumulated on the reference fraction and new cumulative dosimetric parameters were calculated. The LENT‐SOMA toxicity scores of these patients were studied against the cumulative dose parameters. Based on this study, there was no significant correlation between the toxicity scores and the determined cumulative dose parameters.
Sci—Thur PM: Imaging — 02: Repeated landmark use for patient‐to‐image registration reduces fiducial registration error in patient‐to‐image mapping in image guided neurosurgery
Authors: Gerard I.J. , Hall J.A. , Mok K. , Collins D.L.
Published: September 2014

The patient‐to‐image mapping for an image guided neurosurgical procedure is traditionally determined through the identification of 9 anatomical landmark pairs on both diagnostic preoperative magnetic resonance images and the patient in the operating room. In this study we investigate the effect of using an increased number of point pairs on the mean fiducial registration error of the landmark registration. This was first evaluated in the lab on a custom built precision milled linear testing apparatus. It was used in conjunction with an optical tracking system and a tracked surgical pointer. A volume of 700 points was registered and showed a plateau of the mean fiducial registration error when a large number of points were used. This was then extended to the operating room where 5 sets of the 9 anatomical landmarks were used for registration and compared to the registration only done with 1 set. A significant improvement (one tailed t‐test) was seen in five of the six cases showing an improvement in patient‐to‐image registration with no significant addition to operation duration.
Sci—Thur PM: Imaging — 03: A novel Čerenkov detector based on air‐spaced light guiding taper for megavoltage x‐ray imaging
Authors: Teymurazyan A , Rowlands J A , Pang G
Published: September 2014

Electronic Portal Imaging Devices (EPIDs) have been used in radiation therapy and are still needed on linear accelerators (Linacs) equipped with kilovoltage cone beam CT (kV‐CBCT) or MRI systems. Recently a new concept of a high quantum efficiency (QE) Čerenkov Portal Imaging Device (CPID) for MV x‐ray imaging in radiation therapy was introduced. It relies on Čerenkov effect for x‐ray detection. The proposed design consisted of a matrix of optical fibres aligned with the incident x‐rays and coupled to an active matrix flat panel imager (AMFPI) for image readout. A weakness of such design is that too few Čerenkov light photons reach the AMFPI for each incident x‐ray and an AMFPI with an avalanche gain is required. In this work we propose to replace the optical fibers in the CPID with light guides without a cladding layer that are suspended in air. The air between the light guides takes on the role of the cladding layer found in a regular optical fiber. Since air has a significantly lower refractive index, a much superior light collection efficiency is achieved. Our Monte Carlo studies have shown that the modified new CPID has a QE more than an order of magnitude greater than that of current clinical systems and yet a spatial resolution similar to that of current flat‐panel based EPIDs. Furthermore it has been demonstrated that the new CPID does not require an avalanche gain in the AMFPI and is quantum noise limited at dose levels corresponding to a single Linac pulse.
Sci—Thur PM: Imaging — 05: Calibration of a SPECT/CT camera for quantitative SPECT with 99mTc
Authors: Gaudin Émilie , Montégiani Jean‐François , Beauregard Jean‐Mathieu , Després Philippe
Published: September 2014

While quantitation is the norm in PET, it is not widely available yet in SPECT. This work's aim was to calibrate a commercially available SPECT/CT system to perform quantitative SPECT. Counting sensitivity, dead‐time (DT) constant and partial volume effect (PVE) of the system were assessed.

A dual‐head Siemens SymbiaT6 SPECT/CT camera equipped with low energy high‐resolution collimators was studied. 99mTc was the radioisotope of interest because of its wide usage in nuclear medicine. First, point source acquisitions were performed (activity: 30–990MBq). Further acquisitions were then performed with a uniform Jaszczak phantom filled with water at high activity (25–5000MBq). PVE was studied using 6 hot spheres (diameters: 9.9–31.2 mm) filled with 99mTc (2.8MBq/cc) in the Jaszczak phantom, which was: (1) empty, (2) water‐filled and (3) water‐filled with low activity (0.1MBq/cc). The data was reconstructed with the Siemens's Flash3D iterative algorithm with 4 subsets and 8 iterations, attenuation‐correction (AC) and scatter‐correction (SC). DT modelling was based on the total spectrum counting rate. Sensitivity was assessed using AC‐SC reconstructed SPECT data.

Sensitivity and DT for the sources were 99.51±1.46cps/MBq and 0.60±0.04µs. For the phantom, sensitivity and DT were 109.9±2.3cps/MBq and 0.62±0.13µs. The recovery‐coefficient varied from 5% for the 9.9mm, to 80% for the 31.2mm spheres.

With our calibration methods, both sensitivity and DT constant of the SPECT camera had little dependence on the object geometry and attenuation. For small objects of known size, recovery‐coefficient can be applied to correct PVE. Clinical quantitative SPECT appears to be possible and has many potential applications.
Sci—Thur PM: Imaging — 06: Canada's National Computed Tomography (CT) Survey
Authors: Wardlaw GM , Blackler W , Asselin J‐F , Martel N
Published: September 2014

The value of computed tomography (CT) in medical imaging is reflected in its' increased use and availability since the early 1990's; however, given CT's relatively larger exposures (vs. planar x‐ray) greater care must be taken to ensure that CT procedures are optimised in terms of providing the smallest dose possible while maintaining sufficient diagnostic image quality. The development of CT Diagnostic Reference Levels (DRLs) supports this process. DRLs have been suggested/supported by international/national bodies since the early 1990's and widely adopted elsewhere, but not on a national basis in Canada. Essentially, CT DRLs provide guidance on what is considered good practice for common CT exams, but require a representative sample of CT examination data to make any recommendations. Canada's National CT Survey project, in collaboration with provincial/territorial authorities, has collected a large national sample of CT practice data for 7 common examinations (with associated clinical indications) of both adult and pediatric patients. Following completion of data entry into a common database, a survey summary report and recommendations will be made on CT DRLs from this data. It is hoped that these can then be used by local regions to promote CT practice optimisation and support any dose reduction initiatives.
Sci—Thur PM: Imaging — 07: Assessment of iterative reconstruction algorithms in four commercial MDCT scanners: a phantom study
Authors: Omotayo Azeez , Elbakri Idris
Published: September 2014

We performed an objective phantom‐based image quality evaluation of five commercial iterative reconstruction methods available on four different multi‐detector CT (MDCT) scanners at different dose levels as well as the conventional filtered back‐projection (FBP) reconstruction. Using the Catphan500 phantom, we evaluated the CT uniformity, CT number accuracy, noise, modulation transfer function (MTF) and noise‐power spectrum (NPS). The reconstruction algorithms were evaluated over a CTDIvol range of 0.75 – 18.7 mGy on four major MDCT scanners: GE DiscoveryHD750 (ASIR™ and VEO™); Siemens Somatom Definition AS+ (SAFIRE™); Toshiba Aquilion64 (AIDR3D™); and Philips Ingenuity iCT256 (iDose4™). Images were reconstructed using FBP and the respective iterative reconstructions on all scanners. CT number accuracy and CT uniformity were not affected by the choice of reconstruction method on all scanners. In the dose range of 1.3 – 1.5 mGy, noise reduction compared to FBP using iterative reconstruction was 11% – 51% on GE; 10% – 52% on Siemens; 49% – 62% on Toshiba; and 13% – 44% on Philips scanners. Most algorithms did not affect the MTF, except for VEO™ which produced an increase in the limiting resolution of up to 30%. NPS peak shifted towards lower frequencies NPS amplitude decreased with all iterative algorithms. Compared to FBP, iterative algorithms reduce image noise and increase CNR at the same dose. Noise propagation is Poisson distributed with FBP and ASIR™, while VEO alters the noise dependence with dose. The iterative algorithms available on different scanners achieved different levels of noise reduction and spatial resolution improvements.