bluuebunny/crossref_metadata_2025 huggingface dataset:
Sci‐Thur PM Therapy‐10: Is there an optimal starting gantry angle for equiangular‐spaced beam arrangements in IMRT?
Authors: Potrebko P , McCurdy B
Published: July 2006

Equiangular‐spaced beam arrangements are the standard for intensity‐modulated radiotherapy (IMRT). However, since the choice of starting gantry angle is arbitrary, the question arises of whether there exist optimal starting gantry angles which will produce clinically significant improvements. To investigate the effect of beam orientation, the starting gantry angles in a 5‐beam equiangular‐spaced arrangement were incremented by 5°. Fifteen IMRT plans were generated per patient using 6 MV photon beams with static MLC delivery for 5 prostate, 5 lung, and 5 head‐and‐neck cancer patients. The plans were compared based on Planning Target Volume (PTV) and Organ‐at‐Risk (OAR) dose‐volume histograms, PTV mean dose, OAR maximum dose, total number of segments, and total number of monitor units. A fundamental geometric PTV conformity analysis was also conducted for each increment in gantry angle. To achieve this, divergent ray tracing was performed from the beam source coordinates through the PTV Beam's‐Eye‐View to produce a 3D cone beam matrix. The geometric conformity index (ratio of beam overlap volume to PTV volume) was then calculated. Clinically insignificant variations in PTV mean dose were found for all treatment sites as the starting gantry angles were incremented. This observation was further supported by the small variation in geometric conformity index with gantry increment. The variations in rectal V 75 Gy, spinal cord DVH, and parotid V 30 Gy were clinically significant for the prostate, lung, and head‐and‐neck patients, respectively. It is evident that the choice of starting gantry angle in IMRT equiangular‐spaced beam arrangements must be chosen with care.
Sci‐Thur PM Therapy‐12: Use of patient‐specific planning target volumes in conformal radiotherapy of lung cancer: simple estimates of potential dosimetric benefit in tumor motion management
Authors: Burnett SSC , Hoisak JDP , Sixel KE , Cheung PCF
Published: July 2006

Purpose: To estimate the volume of lung receiving at least 20 Gy (V20) for three tumor‐motion management strategies: population‐based uniform 15 mm margin, free‐breathing individualized margins, and reduced margins for gating with a 0.33 duty cycle.

Methods: We have used a simple formula to combine set‐up error with target motion and to individualize planning target volumes (PTV) for four non‐small cell lung cancer patients. Previous measurements of set‐up error and fluoroscopy data synchronized to a spirometer were used as inputs for our calculations. Tumor motion was characterized in terms of the standard deviation of superior‐inferior (sup‐inf) displacements in each fluoroscopy image. Single‐phase treatment plans were generated such that at least 97% of the PTV was enclosed by the 60 Gy isodose, spinal cord dose was kept below 45 Gy, and V20 was minimized.

Results: The table shows the PTV margins in the sup‐inf direction and the corresponding V20 values, as read from the dose‐volume histograms.

Conclusion: Reductions in lung V20 and spinal cord dose are possible by use of patient‐specific margins. For more mobile tumors, gating may provide additional gains. Since tumor motion is predominantly in the superior‐inferior direction, uniform margins are not optimal.
Po‐Thur Eve General‐05: Novel Intermediate Energy Photon Treatment of Small Lesions: A Monte Carlo Simulation and Treatment Planning Study
Authors: Presutti J , O'Malley L , Sharpe M , Keller B , Beachey D , Pignol J
Published: July 2006

Stereotactic radiosurgery affords great conformality for small tumour volumes. Our study proposes that the radiological penumbra for an intermediate energy photon beam (IEP, 0.2 – 1 MeV) is greatly reduced compared to a megavoltage beam. From Monte Carlo simulation, an 800kV beam of field size less than 2×2 cm2 was generated from electrons impinging upon a 0.5mm tungsten target. This beam generated a radiological penumbral width (80%–20%) of less than 300μm for small field sizes at depth=5cm in water. A virtual IEP treatment unit (PDD's and profiles generated from Monte Carlo) was created in a Pinnacle treatment planning system (v6.2). An 11 beam non‐coplanar arrangement was used to cover a target volume situated in the middle of a phantom head and at 1mm from a critical structure. Dose volume histograms generated for both the 800kV and a standard 6MV beam showed that the volume of critical structure receiving 10% of the prescription dose was 27% versus 41%. The maximum dose received by the target was 110% (800kV) and 127% (6MV). The 800kV and 6MV beams were dosed to 92% and 78% isodose lines respectively for comparable target coverage. The reduction of radiological penumbra is linked to reduced photon scattering (using small field sizes) and the reduced secondary electron range (using IEP). An 800 kV beam shows superiority over a standard 6MV beam resulting in greater homogeneity and conformality to the target and better sparing of a critical structure in close contact with the target.
Po‐Thur Eve General‐06: Experimental Validation of the Eclipse AAA Algorithm
Authors: Murray B , Newcomb C , Breitman K , Connors S , Dunscombe P , Field G , MacKenzie M , Rathee S , Robinson D , Warkentin H , Fallone B
Published: July 2006

The Medical Physics departments of the Tom Baker Cancer Center (TBCC) and the Cross Cancer Institute (CCI) independently performed preliminary evaluation of the new Analytical Anisotropic Algorithm (AAA) implemented in Varian's Eclispe (v. 6.0) treatment planning system (TPS). The TPS was pre‐commissioned with “Golden Beam Data” from the vendor. We measured central and off‐axis profiles in several beam configurations including: open square, rectangular and asymmetric (half‐blocked) beams; wedged square and half‐blocked beams; square fields at three SSDs; open and wedged oblique beams; irregular field defined by MLC and cerrobend blocks. All measurements were performed on Varian 2100EX linear accelerators. Measurements were made to assess the dose in heterogeneous media at both the CCI (CIRS Thorax IMRT phantom) and at the TBCC (TLDs in a Rando phantom). Profiles were evaluated in the buildup, penumbra, inner and outer beam regions as per AAPM Task Group 53.

Measured and calculated profiles agreement was very good in all regions except for the inner beam region at the CCI, attributed a difference in interpolation schemes at the two institutions and the large volume ion chamber used for measurements. The AAA penumbra was also found to be steeper than measured penumbra since AAA was pre‐commissioned using diode measurements. Total scatter factors for most measurements differed by less than 2% from the calculated ones except for the hard wedges where differences up to 4% were found. Anthropomorphic phantoms measurements differed from AAA by as much as 5.6%.

Funding provided by Varian.
Po‐Thur Eve General‐09: Dynamic evaluation for the treatment outcome incorporating prostate organ motion
Authors: Jiang R , Barnett R , Chow J , Grigorov G , Chen J
Published: July 2006

This paper is to calculate the cumulative dose considering internal organ motion and patient repositioning of prostate patient using the one fractional treatment plan method for a specific phantom and patients. In the multi‐fractional radiation treatment, it is desirable to consider the internal organ motion from fraction to fraction. The PTV positional variations can be measured and expressed as the fractional equivalent uniform dose (FEUD) deviation by randomly picking up the FEUD using Monte Carlo method in every fraction. The average EUD deviations for PTV with hundreds of simulations are 3.3% for phantom and 1.8% for 5 prostate patients. The changes of rectal volume and position are also simulated by shifting the geometric center of the rectum and changing the rectal radius to model the rectal deformation using Pinnacle3 planning system and FEUD for rectum are estimated. The prostate margin, together with the inter‐fraction variations in rectal position and shape, affects the delivered dose to the rectum. The effect of the dose fluctuations is larger for the normal tissues than the target, and the change of rectal position would cause more complication compared to the rectal volume change. The method provides a simple way to estimate the tumor control probability and normal tissue complication probability dynamically with considering internal organ motion and repositioning errors throughout the whole treatment course. It is possible to test a treatment plan against a range of possible patterns of organ motion with this dynamic evaluation for the treatment outcome.
Po‐Thur Eve General‐10: Dose gradient analyses in the prostate organ motion: treatment plan evaluation independent of DVH
Authors: Jiang R , Barnett R , Chow J , Grigorov G , Chen J
Published: July 2006

The aim of this study is to investigate internal organ motion using the profiles of the PTV dose gradients independent of DVH. In this study, the four‐beam box (4BB) and 5‐beam IMRT of three prostate patients were analyzed. Patients with small (17.3 cm3), medium (51.6 cm3) and large (87.1 cm3) prostate volumes were selected from Grand River Regional Cancer Center (GRRCC). A Pinnacle3 planning system was used to determine the PTV dose profiles crossing the isocenter in the L‐R, A‐P and S‐I directions. The convolution of the “static” dose and the Gaussian distribution were used to describe the discrepancy between the prescribed and delivered dose affected by patient repositioning and internal organ motion. The “shoulder” shape of the PTV profile determines the dose delivered to the tumor and critical organs when internal organ motion was considered. A “line equivalent uniform dose” (LEUD) was used to evaluate the shoulder dose deviation. The profile shapes influence the organ at risk (OAR) dose distribution more significantly for 4BB in comparison with IMRT especially in the posterior direction. The LEUD deviation in the range from 7.7% to 2.8% for S‐I and A‐P directions, respectively, was observed for the standard deviation of 1. The analysis of the PTV profile shape is a powerful tool for further improvement of IMRT treatment plan optimization. The results can be included as a parameter in the objective function used in the IMRT optimization.
Po‐Thur Eve General‐12: ProLoc: An image‐guided localization software for target positioning
Authors: Osei E , Fan C , Jeevasagayam G , Alexander A , Seguin M , Darko J
Published: July 2006

An image‐guided localization system has been developed for daily localization of the prostate using electronic portal images, digitally reconstructed radiographs (DRR) and implanted radio‐opaque fiducial markers or anatomic landmarks. This paper describes the computer program (ProLoc) and its potentials with particular application to the daily localization of the prostate during radiation therapy treatment. Three radio‐opaque markers are implanted in the prostate before radiotherapy treatment. Reference positions of the markers are established from orthogonal DRR images and the center of mass determined. Before treatment each day, orthogonal images are acquired using the electronic portal image devices (EPID). Projected marker positions and the center of mass are determined and align to the reference position of the center of mass. Couch position adjustment is then performed to reposition the patient to the reference position. This software has the potential to determine prostate movement over the course of routine radiotherapy using implanted markers or anatomic landmarks. It also has the potential to determine marker migration in the prostate and gives an indication of weather the prostate is increasing or decreasing in size. Localization of the prostate within the patient and proper alignment with the radiation beam are critical components of radiotherapy. Daily target of the prostate has been shown to be technically feasible. This system provides the ability to significantly reduce treatment margins for cancers confined to the prostate. ProLoc may be used to measure the marker shifts and positions on the daily portal films with an accuracy of less than 1.5mm.
Po‐Thur Eve General‐19: Energy dispersive x‐ray diffraction system: Analysis of noise at low momentum transfer arguments
Authors: LeClair R , Wang Y , Zhao P
Published: July 2006

An energy dispersive x‐ray diffraction system has been built to measure the diffraction signals of breast tissue. The diffraction signals are a function of the momentum transfer argument, x=(E/hc)sin(θ/2), where E = photon energy and θ = scatter angle. The current system has noise problems for signals measured at x < 1.3 nm−1 where it is anticipated that most of the contrast exist for diagnosing normal breast tissue versus cancerous tissue. For a 5 mm thick 5 mm diameter water sample, the scatter signals at low x obtained at 9° with a 3 mm diameter 50 kV beam are about 70% higher than what are to be expected. Values at higher x values are however in good agreement with those in the literature. In this work we measured the scattered field from the pinhole since it could contribute to the large signals at low x values. The scattered count rates were measured at angles of 2 to 15 degrees in the usual way. For smaller angles including zero we used a 1.5 mm by 1.5 mm beam stopper centered at the bottom of the pinhole. A 100 μm diameter W aperture was placed above the detector and the field was sampled at various locations in the shadow of the beam stopper. The results suggest that the scatter from the pinhole could increase the diffraction signals at low x by 6%. Based on these findings we intend to revisit our measurement of the incident spectrum and the multiple scatter.
Po‐Thur Eve General‐20: A Novel Non‐Invasive 3D Ultrasound Imaging Phenotype of Carotid Atherosclerosis
Authors: Egger M , Chiu B , Spence JD , Fenster A , Parraga G
Published: July 2006

Atherosclerosis — a chronic, inflammatory disease involving the development of atherosclerotic lesions in the major vessels of the vasculature is the major underlying cause of cardiovascular disease. To better understand how and where carotid atherosclerosis changes occur when plaques progress and regress, we are validating a new phenotype of carotid atherosclerosis — the measurement of carotid vessel wall volume (VWV). This measurement can be applied to understand local plaque volume changes in human subjects. Five research subjects with carotid plaque area ⩾ 0.5 cm2 were studied. 3D US images were acquired for the left and right carotids of each subject. VWV measurements were carried out using 3D Quantify Software and repeated five times by a single observer, with a minimum of two days between each measurement repetition. The observer stepped transversely through the image volume in 1mm increments, manually tracing vessel and lumen boundaries. VWV was calculated by subtracting the total lumen volume from the total vessel volume. A correspondence map was established between reconstructed vessel and lumen surfaces; the distance between each pair of correspondence points was estimated to be plaque thickness. These atherosclerosis plaque thickness maps generated from vessel wall volume segmentations allow us to visualize plaque thickness distribution and plaque topology along the length of the carotid vessel. In longitudinal studies evaluating plaque progression or regression, this technique should allow for the generation of topology difference maps between time points. These difference maps can provide new information regarding local plaque changes at specific points along the carotid vessel.
Po‐Thur Eve General‐21: A 2‐Dimensional Ultrasound Breast Biopsy System: a device for early detection of breast cancer
Authors: Bluvol N , Downey D , Fenster A
Published: July 2006

Image‐guided needle biopsies are currently used to provide a definitive diagnosis of breast cancer; however, difficulties in tumour targeting exist as the ultrasound scan plane and biopsy needle must remain coplanar throughout the procedure to display the actual needle tip position. The additional time associated with aligning and maintaining this coplanar relationship results in increased patient discomfort. These problems are particularly significant when sampling smaller early stage tumours (e.g. ductal carcinoma in situ). Biopsy procedural efficiency is further hindered since needle pathway interpretation is often difficult, especially for needle insertions at large depths that usually require multiple reinsertions. We have developed a system that would increase the speed and accuracy of current breast biopsy procedures using readily available 2‐dimensional ultrasound technology. This system is composed of a passive articulated mechanical arm that attaches to a 2‐dimensional ultrasound transducer. The arm is connected to a computer through custom electronics and software, which were developed as an interface for tracking the positioning of the mechanical components in real‐time. The arm couples to the biopsy needle and provides visual guidance for the physician performing the procedure in the form of a real‐time projected needle pathway overlay on an ultrasound image of the breast. Testing has shown a needle‐tip to target normal distance of 0.52 mm. We believe that with this improved ultrasound biopsy guidance we will be able to reduce the ‘false negative’ rate of biopsies, especially in the hands of less experienced physicians, during early stage cancer and hence with smaller tumours.
Po‐Thur Eve General‐22: 111In‐Tropolone‐Labeled Mesenchymal Stem Cells: In Vivo Radiotracer Kinetics
Authors: Jin Y , Kong H , Wells G , Sykes J , Prato F
Published: July 2006

Direct in vitro labeling of cells with ‐tropolone followed by in vivo SPECT imaging gives no information about the fate of the cells but simply tells where the has gone. It is necessary to study the kinetics of label after transplantation and determine the connection between and the presence of viable cells. Two sets (n=5) of mesenchymal stem cells (MSC) were labeled with ‐tropolone and then killed by using an ultrasound probe to rupture the cell membrane or by freezing the cells at −80°C for 60min. The resulting cell debris and supernatant were used to label two new sets of MSC. The labeling efficiency was measured and compared to a control labeled with ‐tropolone. 1.5×107 MSC labeled with 1.32MBq were killed using the ultrasound probe and then injected into the myocardium of a canine (without infarction). Whole body and SPECT images were acquired over 13 hrs post‐injection. The animal was then sacrificed and the amount of remaining in tissue samples from the heart was measured. (0.2±0.5)% and (0.3±0.5)% labeling efficiencies were found for cells labeled with ultrasound‐killed and frozen‐killed cells, while the labeling efficiency of the control cells was found to be (53.0±2.0)% for a 30min cell culture. After 13hrs, <4% of injected remained in the myocardium. Analysis of the SPECT images indicated a biological half‐life of 2.3 hours. It was concluded that leaked from dead MSC does not label other viable MSC and will be rapidly cleared from the myocardium.
Po‐Thur Eve General‐25: Development of a Tissue Sample Analysis System Using Diffraction Enhanced Imaging and Small and Wide Angle Scattering
Authors: Bewer B , Chapman D , Cunningham I
Published: July 2006

Current methods of x‐ray imaging, whether it is a dental x‐ray or an image of a broken bone, use absorption properties of the body for contrast in the image. This reliance on absorption to obtain an image creates problems when the soft tissues of the body are the subjects of interest. The difficulty in obtaining suitable contrast image is particularly challenging when the difference in absorption properties of two adjacent tissues are small.

This challenge of obtaining a high contrast soft tissue image requires revisiting the processes of radiation interaction. The common x‐ray interactions within the diagnostic energy range are: 1) the photoelectric effect; 2) Compton scattering; and 3) Coherent scattering. For absorption x‐ray techniques the first process, the photoelectric effect, is responsible for the contrast in the image. The remaining processes of x‐ray interaction, scattering, degrade the absorption image and efforts are made to remove scattering from absorption images in the form of anti‐scatter grids and are somewhat effective. In recent years however techniques have emerged that are not degraded by scattering or even use scatter as a method of analysis and imaging.

The first technique is diffraction enhanced imaging and uses x‐ray crystal diffraction as a method of removing scatter. The choice of the crystal diffraction plane will determine the level of scatter rejection. The second method is small and wide angle x‐ray scattering, (SAXS, WAXS). In this technique the unique scatter patterns from various tissues are used to form an image.
Po‐Thur Eve General‐26: Tracking intraprostatic volumes for determining non‐linear warping algorithm variability
Authors: Venugopal Niranjan , McCurdy Boyd , Hnatov Alex , Dubey Arbind
Published: July 2006

Magnetic resonance spectroscopy imaging (MRSI) is becoming routinely used for diagnosis and treatment planning of prostate cancer. MRSI provides physicians and physicists with information related to metabolic activity of tissues within the prostate. During the MRSI data acquisition, an endorectal radio frequency coil is utilized to boost signal strength in the localized volume, and brings about a ∼10 fold increase in the signal to noise ratio. A challenge exist is using the MRSI data collected using the endorectal coil technique. The endorectal coil, while crucially important to data acquisition, is filled with approximately with ∼100cc's of air. This pushes the prostate superiorly/anteriorly, deforming the prostate and consequently the spectroscopic imaging data in a non‐linear manner. In this application, the coil‐deformed MRS images are warped back to a non‐deformed state, using a single data set. A non‐linear warping algorithm is presented to achieve this. For this case study, physicians were able to contour both the total prostate volume, and intraprostatic nodules. While choosing anatomical tie points along the external prostate surface (needed for the non‐linear warping algorithm), analysis of the nodules revealed the algorithm accuracy ranges from 63–93%. While the algorithm accuracy itself, when reproducing the total prostate volume, achieved an accuracy of 97%.
Po‐Thur Eve General‐27: Analytical model for electron arc beam output determination using an Elekta SL‐25 linear accelerator
Authors: Duchesne C , Mondat M , Wierzbicki W
Published: July 2006

The clinical implementation of electron arc therapy requires a large amount of measured dosimetric data. All necessary measurements were done on an Elekta SL‐25 with a 10 MeV electron beam. Beam output and PDD measurements were performed in five different cylindrical acrylic phantoms using TLDs. The phantom radius (di) ranged between 5.1 and 15.2 cm, the total arc angles (α) varied between 60° and 160° and the number of monitor units (MU) per degree between 0.5 and 7. Based on this data bank, an analytical model was developed for monitor unit (MU) calculation. This model estimates arc beam output at the depth of maximum dose (dmax) as a function of di and α for a given field width at isocentre (w). Curve fitting of the complete set of beam output data was done with an asymptotic relationship between the dose rate at dmax and the inverse square of di. The dependence of the beam output on α was introduced by assuming an explicit function of α for each parameter of the model. Results show that the calculated beam output data is a good approximation for all measured data for all phantoms and arc angles: 89% of the calculated values are within ± 3% of the measured ones and all calculated points are within a ± 5% error range. The MU calculation then becomes straightforward, without the need of measuring each clinical case.
Po‐Thur Eve General‐30: Determination of the optical properties of tissue‐simulating phantoms by interstitial frequency domain measurements
Authors: Xu H , Patterson M
Published: July 2006

The optical properties of tissue‐simulating phantoms were estimated by measuring the phase and amplitude of the fluence at two detectors due to an isotropic source. Absorption and reduced scattering coefficients could be recovered within 10% and slightly over 10% respectively, either using the data from two detectors 3mm apart or those from two detectors 5mm apart with light collected by one detector attenuated by a neutral density filter, over a wide range of optical properties, μa=0.008 to 0.17mm−1 and μs′=0.3 to 1.8mm−1. In addition, the effects of source anisotropy and inaccurate fiber position on the recovered optical properties were studied by Monte Carlo simulations.
Po‐Thur Eve General‐31: Dosimetric Impact of Planning a Boost within a Boost in Permanent Seed Implants
Authors: Beaulieu L , Aubin S , Varfalvy N , Lessard E , Pouliot J , Vigneault E , Martin AG
Published: July 2006

Purpose: To investigate the dosimetric impact on the target volume, boost volume (BV) and urethra of performing limited volume boosts in seed implants.

Method and Materials: 35 localized prostate cancer patients with detailed biopsy results were treated with permanent seed implants Personalized plans in which BV corresponding to regions of positive biopsy were generated intra‐operatively based on a simulated annealing inverse planning algorithm. The dose objectives are 144 Gy to the prostate with a 3–4 mm margin, 2/3 (1/3) of the prostate covered by 150% (200%) of the prescription dose (PD), urethra V150 less than 10% and D5 should below 220 Gy. Finally, 100% of BV should receive 150% PD (or 216 Gy).

Results: Comparing plans without and with BV show no significant change in the number of seeds, needles, prostate V100 and V200. Prostate V150 (D90) show significant differences increasing from 65% (187Gy) to 70% (191Gy). By forcing the coverage of the BV, the 150% isodose lines (which extend outside the prostate) shift inside of the prostate. Small increase in prostate V150 leads to significant increases of the BV V150 from 79% to 94%. BV do not translate to higher urethra doses. Thus multiple seed reconfigurations inside the prostate are achievable to cover BV.

Conclusion: Specific areas within the prostate can be boost to receive 150% of the PD with no impact on the urethra. The plans lead essentially to a rearrangement of the seed positions. Potential radiobiological advantages could be obtained at no cost (procedure or time).
Po‐Thur Eve General‐33: Feasibility of a Multileaf Collimator and Method for Multi‐slice Tomotherapy
Authors: Cadman P , Mackie T , Reckwerdt P
Published: July 2006

Purpose: Current methods for delivery of serial or helical tomotherapy are based on a collimator design which can, at most, irradiate two slices simultaneously as the source rotates around the patient. We investigate the feasibility of a novel multileaf collimator design and method for multi‐slice tomotherapy.

Method and Materials: The MLC incorporates a compact pivoting leaf design. Intensity modulation is achieved through binary actuation of adjacent leaves. Multiple leaf banks are employed for multi‐slice tomotherapy delivery. Each fan beam will have a different divergence in the axial direction. Two multi‐slice delivery methods are evaluated where (a) pitch is determined by a given collimated slice which does not irradiate beyond the adjacent slice (regular pitch) or (b) pitch is determined by different collimated slices irradiating the same region in the patient (multi‐slice pitch). Junctioning effects were studied for a cylindrical phantom irradiated with open (unmodulated) fan beams.

Results: A prototype MLC leaf has been tested which can switch between open and closed positions in a few tens of milliseconds. Regular pitch delivery produced the greatest inhomogeneity between regions irradiated by different collimated slices. The proposed multi‐slice pitch delivery method avoids regular pitch junctioning effects by irradiating all areas with all collimated slices.

Conclusions: These results indicate that multi‐slice tomotherapy is feasible with the benefits of shorter treatment times and it may allow for the use of Co‐60 as a tomotherapy radiation source.

Conflict of Interest: Research was supported in part through a licensing agreement with TomoTherapy Inc.
Po‐Thur Eve General‐36: On the Use of 100% Isodose Volume for Treatment Time Verification of HDR Prostate Implants
Authors: Arsenault C
Published: July 2006

An important quality assurance check for high‐dose‐rate (HDR) brachytherapy is the pre‐treatment verification of the total treatment time. Simple hand calculations based on the prostate volume have been used in the past to perform this verification. However, the accuracy of these checks is approximately 8 to 10%. The approach proposed here recommends using a power‐law function and the volume of the 100% isodose (Viso100) to quickly calculate the total treatment time. Our results show that this calculated treatment time is within 3% of the actual treatment time in 98% of our implants. This is significantly better than similar approaches using the prostate volume. The improved correlation between Viso100 and the total treatment time is explained by the use of dwell positions close to the edge, or even outside, of the prostate. The use of these dwell positions, which is required to ensure coverage of the target volume, significantly increase the total treatment volume and consequently Viso100. However, this increase in total treatment volume does not correspond to an increase in the planned target volume.
Po‐Thur Eve General‐38: The Virtual Radiotherapy Department
Authors: Murray B , Chwyl B , Campbell K , Connors S , Dundas G , Eberle S , Fawcett S , Field C , Richardson S , Sandahl D , Schouten M , Yakimovich C
Published: July 2006

With the number of clinical cases increasing each year, there is pressure on all clinical staff to do more clinical service. At the same time there is a demand to train more students in all of the radiotherapy disciplines. Regulatory agencies are also demanding more continuing education and upgrading for existing staff. We have recently introduced a new clinical treatment planning system, which requires a significant amount of training for all staff members. To meet these increased demands for training all levels of learners we have developed a “Virtual Radiotherapy Department”. The Virtual Radiotherapy Department will provide on line teaching of basic physics and treatment planning for radiation therapy students, radiation oncology residents, and physics graduate students and residents. By using on‐line interactive tools it is possible to teach all the different students at different levels by making basic information available to all students, but linking to more advanced information for those that require it.

On‐line videos have been created describing several clinical techniques using various equipment. These videos will be used to provide students instruction as well as for continuing education for existing staff or new staff. These tools will be used to provide training to all users as we introduce our new treatment planning system, showing them exactly how to complete various tasks. These videos are customized to our treatment processes; therefore, they show users exactly what is required in the most efficient manner.

Funding Provided by Alberta Health and Wellness and Varian.
Sci‐Fri AM General‐03: Variation in the relative volumes and ionization response of four cylindrical ion chambers using micro‐computed tomography
Authors: McNiven A , Umoh J , Holdsworth D , Kron T , Battista J
Published: July 2006

High accuracy in absolute dose measurements is required in radiation therapy and dosimetric protocols require the use of air ionization chambers. These protocols involve chamber specific calibration factors, which depend fundamentally upon the chamber volume. In this work, we investigate the ability of micro‐computed tomography (micro‐CT) to determine differences in the chamber volume of four nominally identical Exradin A1SL cylindrical ion chambers. A GE Locus micro‐CT imaging system (General Electric Healthcare, London, Ontario) was used to acquire 20 micron resolution images of the four ion chambers. The ionization response of each chamber in a 10×10cm2 10 MV x‐ray reference field was also measured, and the readings were corrected for polarity and ion recombination effects. GE MicroView software (Version 2.1.1) and its semi‐automatic pixel volume measurement option was used to determine the sensitive air volume of the ion chambers. Both the ionization response of the chambers and the volumes were normalized to the chamber with the largest values. The relative differences in response and volume for each chamber agreed within 1%. Micro‐CT is a promising tool for the accurate determination of chamber volume, and potentially for the independent determination of chamber calibration factors.
Sci‐Fri AM General‐06: The Moving Slanted‐Edge Method: A Novel Technique to Measure the Temporal Response of a Fluoroscopic System
Authors: Friedman SN , Cunningham IA
Published: July 2006

Fluoroscopic procedures are generally acknowledged to lead to large patient doses. It is important to have a method of measuring detector performance. Applications of cascaded‐systems theory to measure detector performance of fluoroscopic systems have produced unexpectedly high results due to the reduction in measured noise caused by temporal averaging between frames as a result of system lag. Methods have been proposed to remove this affect of lag, which require the system temporal resolution through the system temporal modulation transfer function (MTF). No method currently exists to easily and accurately measure the system temporal MTF of a fluoroscopic system. We have developed a novel technique, the “moving slanted‐edge method”, to make measurements of system temporal MTF from the image data of a fluoroscopic system.

We translate a tungsten sheet across the detector with constant velocity, vo, and calculate a spatiotemporal coordinate for each pixel based on distance and time from passage of the edge. The resulting data is used to calculate a vo‐dependent MTF. The system (spatial) MTF and vo‐dependent MTF are mapped onto the temporal axis using the edge velocity. The system temporal MTF is calculated by dividing the vo‐dependent MTF by the (spatial) MTF.

This method was validated on a bench‐top fluoroscopic system consisting of a three‐year old Dunlee image intensifier coupled to a CCD camera. The system temporal MTF was calculated using the moving slanted‐edge method (vo=45 cm/s) and the optical decay curve of the image intensifier. Excellent agreement was found between the two methods.
Sci‐Fri PM Imaging‐04: Physical Characterization of a High‐resolution 16‐bit CCD Detector for Mammography
Authors: Elbakri IA , Tesic MM , Xiong Q
Published: July 2006

We are evaluating the performance of a charge‐coupled device (CCD) detector for digital mammography. The detector is an array of four 1 × 5 cm CCD's coupled (without demagnification) through a fiber optic plate to a 180‐micron layer of Cesium Iodide. The detector has time‐delay integration electronics that enables it to be used in slot‐scanning full field digital mammography. With 27‐micron pixel pith, its resolution approaches that of film‐screen mammography (FSM). The detector also acquires 16‐bit data, which provides more contrast levels and facilitates imaging the edges of the breast. We measure the modulation transfer function, noise power spectrum and detective quantum efficiency in the scan and frame (detector stationary) modes. Our results show that the detector is capable of resolving information near its Nyquist frequency and has a DQE(0) approaching 50% in the scan mode. The DQE is higher than that of FSM cassettes and is comparable to other digital mammography detectors.
Sci‐Fri PM Imaging‐05: Prediction of multiple scatter distributions using an iterative Monte Carlo technique for X‐ray Scatter Mammography
Authors: Van Uytven E , Pistorius S , Gordon R
Published: July 2006

Compton and Rayleigh x‐ray scatter have been shown by several authors to be a source of information for electron density imaging. However, as these techniques rely on single scatter information only, the presence of second order and higher scatter typically requires collimation of the detector, reducing the usefulness of many scatter technique for in‐vivo imaging. Compton scatter radiography (CRSR) is a single scatter imaging technique that uses a scanning pencil beam and a mammographic geometry to extract 3D atomic structure information of the breast from a single projection. CRSR uses an uncollimated scatter geometry, and the detector system records both single and multiple scatter signal, the latter component being as large as 40% of the total scatter signal at some locations. The error tolerances of CSR (∼1%) require accurate prediction of second‐order and higher scattered photons. Under a mammographic setting, this work describes an iterative method of multiple scatter prediction using Monte Carlo simulation and CRSR imaging. Simulations were performed with a mammographic phantom to test the validity of this approach. A 5×5×5 cm3 phantom was constructed containing a small calcification 3 cm deep and 1 cm from each beam‐parallel phantom edge. The multiple scatter component accounts for 26.2% of the total scatter, and CSR image reconstruction shows significant errors and a failure to localize the calcification. After multiple scatter prediction, 0.82% of the multiple scatter remains unaccounted for, and the calcification was successfully localized with a 1×1×2.5 mm3 resolution.
Sci‐Fri PM Imaging‐06: Registered Digital Stereotactic Mammography and 3D‐Ultrasound for Breast Biopsy Guidance
Authors: Irwin MR , Gardi L , Downey D , Fenster A
Published: July 2006

Large core needle biopsy is a common procedure used to obtain histological samples when a suspicious lesion is detected in diagnostic breast images. The procedure is typically performed using image guidance, with ultrasound (US) and stereotactic mammography (SM) being the most common modalities used. Each of these imaging methods, however, has limitations that impact their clinical utility. For example, some breast structures are not visible in ultrasound. Mammography provides better visualization of features such as microcalcifications, but does not support real‐time imaging. A prototype device combining the advantages of digital SM and 3D‐US with computer‐aided needle guidance was developed at our centre. The objective of this work was to determine the position of biopsy targets with an error of less than 0.5 mm. A methodology was first developed to calibrate the SM system. Then, by imaging a set of the same physical points identifiable in both SM and 3DUS images, the two modalities were registered. In both cases, the target registration error (TRE) was calculated to quantify the error in determining the position of points imaged within the breast. For locating points in the SM images alone, the TRE was found to be 0.35 mm. The TRE found in registering the two modalities was 0.37 mm. The TRE value is clinically relevant as it indicates the position error associated with selecting an arbitrary image point for biopsy. When compared to the typical breast biopsy needle diameter of 2.1 mm, the calculated TRE from the two imaging modalities was sufficiently small.
Sci‐Fri PM Imaging‐12: Multimodal Contrast Agent for Combined CT and MR Imaging
Authors: Zheng J , Dunne M , Allen C , Jaffray D
Published: July 2006

Interest in the area of multimodality imaging has also been prompted by the realization that such techniques offer much more sophisticated characterization of the morphology and physiology of tissues and organs, and that confidence gained in the accurate correspondence or registration of different modalities greatly enhances their value. This study is aimed to provide a contrast agent based approach to combine information obtained in CT and MR. Specifically, a liposome‐based dual modality contrast agent co‐encapsulating iohexol, an iodine‐based CT contrast agent, and gadoteridol, a gadolinium‐based MR contrast agent, was developed and characterized. Previously, our group characterized the in vitro physico‐chemical properties of this liposome‐based contrast agent. In this study, CT and MR‐based assessments of the in vivo stability of the liposome‐based contrast agent was conducted in a rabbit model. Visual contrast enhancement and measurable signal increases produced by the presence of the contrast agent carrying liposomes was induced in various organ systems (i.e. heart and blood vessels, liver, spleen, kidney and intestines) in both imaging systems over a 7‐day period. The blood circulation half‐life of the present liposome formulation in rabbits was found to be 45.4 ± 2.5 hours. The simultaneous signal enhancement seen in both CT and MR, and the long circulation life of this liposome‐based contrast agent makes it attractive for use in applications such as longitudinal blood pool imaging, feature‐based CT and MR image registration, and imaging‐based tracking of liposomal therapeutics.
Sci‐Sat AM (1) General‐01: In vitro measurement of cell kill by IMRT fields
Authors: Moiseenko V , Duzenli C , Durand R
Published: July 2006

Results of the in vitro measurements of cell kill from IMRT fields compared to acute dose delivery are presented. Survival was assayed for three cell lines: Chinese hamster V79 fibroblasts, human cervical carcinoma SiHa and colon adenocarcinoma WiDr. An actual head and neck seven field IMRT plan produced for Varian iX, 120 Millennium MLC linear accelerator was used. The calculated IMRT dose to the point of irradiation in the acrylic phantom was 2.1Gy, verified by measurements with an IC10 ionization chamber. The dose varied within 2% through dimensions of the specimen. Two scenarios were explored: 1. regular IMRT delivery, irradiation time of approximately 5min, and 2. IMRT delivery which required MLC re‐initialization after three fields were delivered, irradiation time of 10min. For comparison the same dose of 2.1Gy was delivered by parallel‐opposed pair (POP) in 75s. Persistent increase in cell survival following irradiation with IMRT fields was observed for all cell lines. This increase varied from small for V79 cells: 0.833±0.018 (95% confidence limits) from POP compared to 0.860±0.040 for IMRT with MLC re‐initialization, to very pronounced for the radiosensitive SiHa cell line: 0.390±0.046 for POP irradiation compared to 0.591±0.080 from IMRT requiring MLC re‐initialization. For WiDr cell line survival was 0.744±0.038 for POP, and 0.809±0.023 for regular IMRT. We observed a persistent, although not always statistically significant increase in cell survival from IMRT fields. While this study does not account for features present in vivo, it provides useful insight into biological consequences of IMRT as assayed by cell survival.
Sci‐Sat AM (1) General‐04: Quantitative impact of 3D inter fractional patient setup errors on TCP/NTCP
Authors: Jans H , Syme A , Rathee S , Fallone B
Published: July 2006

Patient setup errors in external beam radiation therapy are a cause for differences between planned dose distribution and the one delivered to the patient. A changed dose distribution results in a changed tissue response, expressed as tumor control probability (TCP) and normal tissue complication probability (NTCP). A method was developed to calculate the changes of TCP and NTCP resulting from measured patient setup errors.

Patient position was measured with a 2D‐3D registration method using orthogonal EPID images of the patient in treatment position. Setup errors were expressed as 6 degrees of freedom (rigid body translations and rotations); non‐rigid transformations and internal organ motion was not considered. The measured setup errors were used to change beam angles and couch position in a copy of the original treatment plan, such that an equivalent beams‐eye‐view of the patient was achieved for each treatment beam. The dose distribution for this modified treatment plan was then calculated. This procedure was repeated in additional copies of the original treatment plan for each fraction in which patient position had been measured. Once the treatment was completed, dose distributions for all measured fractions were added and the dose‐volume‐histograms (DVHs) were calculated for each region of interest. The DVHs in turn served as a basis for the calculation of TCP and NTCP. This method was applied to two prostate patients, whose position was measured during six fractions of their treatment. The setup errors did not change the TCP, but NTCP of the rectum increased by 9.0% and 2.2% respectively.
Sci‐Sat AM (1) General‐06: Theoretical estimation of dose volume constraints and their impact on DVH selection
Authors: Schinkel C , Stavrev P , Stavreva N , Fallone B
Published: July 2006

Dose‐volume constraints are essential for treatment planning optimization using physical objective functions. A theoretical approach to the problem of choosing dose‐volume constraints based on the reverse normal tissue complication probability (NTCP) mapping into dose‐volume space is developed. Dose‐volume histograms (DVHs) are randomly simulated and those resulting in clinically acceptable levels of complication, e.g. NTCP of 5±0.5%, are selected and averaged producing a mean DVH which is proven to result in the same level of NTCP. The points from the averaged DVH are proposed to serve as dose‐volume constraints for treatment planning optimization using physical objective functions. The population based Critical Volume and the Lyman NTCP models with parameter sets taken from literature were used for the NTCP estimation. Constraint points for 16 organs are calculated. These dose‐volume constraints are not unique and depend on the range in which the maximum dose to the organ at risk, Dmax, is allowed to vary. It is theoretically proven that the radiation treatment optimization based on physical objective functions can sufficiently well restrict the dose to the organs at risk resulting in sufficiently low NTCP values through the employment of several appropriate dose‐volume constraints. At the same time, the pure physical approach to optimization is self‐restrictive due to the pre‐assignment of acceptable NTCP levels thus excluding possible better solutions to the problem.
Sci‐Sat AM (1) General‐09: Dose dependence of MOSFET sensitivity for clinical photon energy spectra between 30kV and 60Co
Authors: Lavallee M , Beaulieu L , Gingras L
Published: July 2006

Since MOSFETs medical applications in radiotherapy and radiology are gaining popularity, evaluating them under radiation of different energies is of major interest. This study is a characterization of MOSFET sensitivity with regards to total integrated dose. Their sensitivity is expressed by the calibration factor (CFw) and allows the user to associate the reading displayed by the device (mV) to a dose value (cGy). The CFw of seven p‐type, duals bias MOSFETs were measured at several points in time. The radiation sources used were a unit (〈E〉γ: 1.25 MeV), an HDR unit (〈E〉γ: 0.38 MeV) and an orthovoltage unit providing two x‐rays energies respectively of 30 kV (〈E〉γ: 14.8 keV) and 150 kV (〈E〉γ: 70.1 keV). The CFw value diminishes with increasing threshold voltage, especially for low energy radiation. It was stable for irradiations. Decreases of 6%, 5% and 15% were observed respectively for radiation energies of , 150 kV and 30 kV. This behavior is explained by an alteration of the effective field applied on the MOSFET (bias), caused by the accumulation of holes at the interface. It is strongly dependent on the nature of the radiation (LET) and particularly affects low x‐ray energies. Those results are of major interest since, following the company recommendations, the device should be calibrated every 7 000 mV; this recommendation could lead to significantly underestimated doses. A calibration of the device before every use, and multiple measurements to get a mean dose value should compensate for the observed phenomenon.