bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐D‐304A‐05: Optimal Material Selection of Primary Modulator for Scatter Correction Based On the K‐Edge Discontinuity
Authors: Gao H , Watkins R , Zhu L , Fahrig R
Published: April 2010

Purpose: To select an optimal material for the primary modulator in order to minimize its effect of beam hardening (BH). A measurement‐based scatter correction method that uses a checkerboard pattern of attenuating material (primary modulator) placed between the X‐ray source and the object has been developed and verified. In the practical implementation, BH is a limiting factor because the signal modulation depends on the object in the field of view (FOV). Methods: The transmission factor for different modulator materials (Be, Al, Cu, Ag, W, Ho, Er and Tm) was calculated for object thicknesses ranging from 0 to 30 cm equivalent water by using a simulated spectrum of our tabletop cone‐beam CT system at 120 kVp. We then generated scatter‐free projection images of a 30‐cm diameter water cylinder, with and without the modulator in place, and reconstructed CT slices after demodulation. Visibility of rings was compared for no noise, and with 2% added Gaussian noise. We also measured the transmission factors of 25 μm of Cu, W and Er for different combinations of Al (0–8 mm) and Cu (0–0.3 mm) filtration. Results: For a transmission factor of ∼0.9, simulations show that Er provides the least amount of variability as a function of added filtration (max variation<1.8%). The ring artifacts in simulated reconstructions were significantly reduced when using the Er, particularly in the presence of noise. Measured variability of transmission factors were 2.5%, 1.0% and 8.6% for 25 μm of Cu, Er and W, respectively. Conclusions: An optimization of modulator material to minimize BH artifact was proposed and validated. The variation of the transmission factor as a function of X‐ray energy reaches a local minimum when the K‐edge of the modulator material is near the mean energy of the spectrum. Design and evaluation of an Erbium modulator is underway.
MO‐D‐304A‐07: Investigation of a Diamond X‐Ray Target for Use with Megavoltage Cone‐Beam CT
Authors: Sawkey D , Lu M , Wu V , Faddegon B , Morin O , Cheung J , Aubin M , Gangadharan B , Bani‐Hashemi A
Published: April 2010

Purpose. Compare images and spectra using a dual energy diamond x‐ray target for megavoltage cone‐beam CT (MVCBCT) with those of carbon and tungsten targets. Materials and Methods. A Siemens Oncor linac with megavoltage cone‐beam CT was modified to use either a tungsten, carbon, or diamond target for imaging. The carbon target was used with an accelerating potential of 4.2 MV. The diamond target had a higher density than the carbon, thus reducing electron leakage and allowing the linac waveguide to operate at the same accelerating potential as the treatment beam, namely 6 MV. For this study, the diamond target was operated at both 4.2 and 6 MV. With both diamond and carbon targets, the flattening filter was out of the beam path. Images were acquired both of phantoms, to determine contrast‐to‐noise ratio (CNR), and patients. Results. CNR measured with the phantom were nearly the same with the diamond target and the carbon target when both were operated at 4.2 MV. At 6 MV, CNR with the diamond target was degraded, especially for tissue. The highest quality images of head and neck patients were with the diamond target at 4.2 MV. As compared to the carbon target, there were fewer scattering artifacts, and tissue resolution was better. At 6 MV, there were even fewer artifacts but the contrast was reduced. Conclusions. The diamond target is a viable alternative to the carbon target for the IBL. It can be used at either the same energy as the treatment beam, which simplifies commissioning and QA, or at reduced energy for enhanced contrast.

Support from Siemens OCS.
MO‐D‐304A‐08: Characterizing the Scatter Radiation of a Micro‐CT Scanner Using Monte Carlo
Authors: Manser P , Volken W , Zulliger M , Laib A , Rueegsegger P , Fix MK
Published: April 2010

Purpose: Micro‐CT scanners are used to create high‐resolution images and to measure physical properties (e.g. bone mineral density) of the objects observed. Modern micro‐CT scanners make use of cone beam geometry making the image information suffering from scatter radiation. This work aims to characterize the scatter radiation in the detector plane of a micro‐ct scanner using Monte Carlo methods. Method and Materials: EGSnrc was used to simulate the particle transport through the main components of the XtremeCT (Scanco Medical AG, Switzerland) and through different phantoms. Based on phase space information in the detector plane, the primary and the scatter radiation were analyzed. By implementing a dedicated LATCH method, the scatter radiation was subdivided into several components providing a detailed characterization of the scatter radiation. In order to study the dependence of these scatter components on the object to be scanned, Monte Carlo simulations were performed for different phantoms which vary in size or composition. Results: For typical object sizes the scattered radiation contribution is in the order of 10% of the total radiation in the detector plane. Most of these scattered particles result from interactions in the object. As expected, the relative scatter contribution increases with increasing density and size of the object. On the other hand, the Monte Carlo simulations show that scatter radiation, particularly the component which is due to scattering within the object, contains information about the structure of the object and this information increases with increasing density. Conclusion: In this work, the scatter radiation of a micro‐CT scanner was analyzed using Monte Carlo simulations. It is shown that the scattered radiation is dominated by scattering within the object. The results of this work provide a basis for future scatter correction methods in micro‐CT applications. Conflict of Interest: This work was supported by Scanco Medical AG.
MO‐D‐213A‐03: Practical Aspects of PET Accreditation
Authors: Esser Peter D
Published: April 2010

PET scanner accreditation is based on reviews of images acquired from the ACR PET phantom. The phantom is relatively easy to fill and set up for a PET study and can be used to measure tomographic uniformity, spatial resolution, and the detectability of “hot” lesions. The variety of resolution and “hot” components enables the reviewers to see relatively subtle differences in system performance.

The accreditation phantom images are submitted to a review panel of qualified medical physicists for scoring. The Nuclear Medicine Accreditation Committee has defined acceptable standards for uniformity, spatial resolution and lesion detection.

Uniformity and noise are evaluated qualitatively by inspection of reconstructed tomographic sections. Optimal density ranges should be comparable to those used for clinical images. Spatial resolution is judged by identifying the smallest “cold” rods in the phantom and lesion detectability is determined from the “hot” cylinders. The same protocol is also used for the “cold” cylinders that demonstrate the effectiveness of the attenuation and scatter corrections.

Learning Objectives:

1. Be aware of the ACR PET accreditation process and PET Physicist Qualifications.

2. Understand the ACR PET Phantom and testing required for ACR accreditation.

3. Understand how phantom images are reviewed by the ACR.

4. Be able to activate the ACR Phantom.

5. Understand phantom image acquisition and processing.

6. Understand PET phantom image contrast, resolution, and uniformity.
MO‐EE‐A1‐02: Dose Escalation by Target‐Tracking Treatments Planned by 4D Direct Aperture Optimization: A Proof of Principle
Authors: McQuaid D , Webb S
Published: April 2010

Purpose: To evaluate a novel 4D direct aperture optimization system capable of planning a 4D‐tracking delivery while ensuring compliance with the delivery constraints. The planning system was tested by deriving the change in tumor‐control probability (TCP) by dose escalation with a fixed mean lung dose (MLD) in a digital phantom dataset. Method and Materials: The treatment fields were divided into phases matched to phases of a 4D‐patient model. Compliance with delivery constraints was ensured by restricting equipment configurations within phases and changes between phases to deliverable settings. The optimization cost was evaluated by comparing the dose distribution summed over the breathing cycle with a prescription. The potential clinical benefit of the system was evaluated with a dose escalation study on a 4D digital phantom. The acceptable MLD was derived from a reference static plan with 64Gy prescribed to the target with motion‐encompassing margins. The TCP was optimized for the fixed MLD, where the TCP was evaluated at 12 months using the method of Martel et al. (1999). Results: With a fixed MLD (13Gy) the 4D‐tracking treatment achieved a mean target dose of 79.6Gy as compared to 63.8Gy for a static plan and 73.9Gy for a plan optimized on the 4D patient but with no motion of the delivery equipment (denoted 4D‐static plan). The resultant TCP increased from 49.6% for the reference plan to 75.4% for the 4D‐tracking plan compared to 45.6% for the static plan and 66.5% for the 4D‐static plan. Conclusion: A treatment‐planning system capable of optimizing target‐tracking treatments complying with delivery constraints has been developed and tested. The tracking deliveries produced have been evaluated by the allowed dose escalation for a simple example case, where a substantial improvement in TCP was observed. This finding shows that the technique is very promising and worthy of further study.
MO‐EE‐A2‐05: Experimental Implementation of the Directed Coulomb Explosion Regime of Laser‐Proton Acceleration
Authors: Litzenberg D , Bulanov SS , Chvykov V , Brantov A , Bychenkov V , Kalintchenko G , Matsuoka T , Dollar F , Rousseau P , Reed S , Yanovsky V , Krushelnick K , Maksimchuk A
Published: April 2010

Purpose: To quantify the laser pulse requirements and target parameters required to achieve the Directed Coulomb Explosion (DCE) regime of laser‐target interaction for the acceleration of protons to therapeutic energies. Method and Materials: Particle‐in‐Cell (PIC) simulations of the planned experiments along the funded upgrade path of the HERCULES laser at the University of Michigan have predicted a new regime of attainable laser‐target interactions for proton acceleration. The laser was recently upgraded to 300 TW and a temporal pulse contrast ratio of 10−11, allowing intensities of 2×1022 W/cm2 to be achieved in a near diffraction limited, 1.3 micron, focal spot. The 2 ns long amplified spontaneous emission (ASE) pre‐pulse was suppressed by a factor 10−3 through the implementation of a cross‐polarized wave (XPW) pulse cleaner to prevent pre‐plasma creation on the front surface and preserve the physical integrity of the thin‐film target. Dual plasma mirrors are being characterized to reduce the prepulse at < 30 ps before the main pulse (caused by variations in the index of refraction through the optic path) below a contrast ratio of 10−11. This will allow experiments on thin foil targets (< 100 nm) up to 300TW with no significant pre‐pulse to compromise the target. Results: Preliminary measurements show an additional reduction of the contrast ratio of the ASE pre‐pulse by a factor of 10−3 after the addition of dual plasma mirrors. Additional work is required to optimize the setup and parameters of the plasma mirrors to account for polarization effects and wave front distortions and variable intensity levels. Conclusion: Implementation of dual plasma mirrors is progressing with promising results and will soon allow experimental implementation of the laser pulse characteristics required to test the DCE regime of proton acceleration.
MO‐EE‐A3‐03: Ordinary Least Squares and Partial Least Squares for Intra‐Fraction Lung Tumor Motion Modeling
Authors: Malinowski K , McAvoy T , George R , Dieterich S , D'Souza W
Published: April 2010

Purpose: For accurate operation, real‐time tumor tracking devices for radiation therapy require the real‐time position of the radiation target. In this study, we assess Ordinary‐Least‐Squares (OLS) and Partial‐Least‐Squares (PLS) modeling methods for inferring intra‐fraction motion from external markers. Method and Materials: We obtained the concurrent 3D positions of three optically tracked external markers affixed to the skin and the 3D centroid position of a set of three internal fiducials implanted in lung tumors localized with fluoroscopy by the Cyberknife system. We analyzed 134 treatment fractions from 63 patients, each including 40–112 (mean=62) samples spaced at approximately 1–2min. For each fraction, we used a randomly selected subset of N (4–35) points to train OLS and PLS models to infer tumor motion from the positions of the optical markers, and we repeated this process 40 times for each fraction and each N. We then tested the models against the remaining datapoints in that fraction to determine the position error. Results: The PLS mean(±standard deviation) errors decreased monotonically as N increased, from 0.3±2.6cm at N=4 to 0.2±1.4cm at N=35. In contrast, the OLS error peaked (mean=5.3cm) at N=10 training samples, a consequence of the Moore‐Penrose pseudo‐inverse regression technique. OLS errors at N=4 and N=35 were 0.4±4.6cm and 0.2±1.7cm, respectively. PLS and OLS mean and maximum errors converged for large N (approximately N⩾20). To achieve mean errors less than 0.25cm or 0.20cm over the entire dataset with PLS, at least 8 or 18 training samples, respectively, must be used. Conclusion: The results of this study indicate that PLS shows potential as an efficient (few image acquisitions) and accurate (2–3mm) intra‐fraction lung tumor motion modeling technique. Future work will focus on investigating methods for and consequences of non‐random training sample selection.
MO‐EE‐A3‐05: Improving the Temporal Resolution of Dynamic MRI by Deformable Alignment of the Peripheral K‐Space
Authors: Ahunbay E , Paulson E , Godley A , Li XA
Published: April 2010

Introduction Dynamic MRI may be used to image motion that is needed for accurate radiotherapy treatment planning. The tradeoff between temporal and spatial resolution has been a major issue affecting the use of dynamic MRI. Here we propose to improve temporal resolution by reconstructing high spatial resolution components with deformably registered motion data. Dynamic MRI with increased temporal resolution without scarifying spatial resolution for several sites are presenting. Methods and Materials High and low spatial resolution components of the image typically move similarly, i.e. share most of the motion vector information. The motion vectors can be obtained by deformable registration of the central k‐space, and applied to the high spatial resolution data. This allows one to acquire the peripheral k‐space at a lower temporal resolution than the central k‐space therefore increase the overall sampling rate. We tested the possible gain by this method for 2‐dimensional dynamic MRIs (SIEMENS 3T Verio) of swallowing, breathing and peristalsis. Results The mean error in the displacement vectors obtained using only the central 20% of k‐space vs. using the full k‐space was less than 0.5mm, which reduced to 0.2mm if 50% of the radius is used. Peristalsis motion with sudden changes shared least information between central and peripheral k‐space. The reconstructed images with as low as central 20% of the k‐space radius are very similar to images reconstructed with full k‐space. The resulting probability distance histograms and regions of interest show minimal variation. Conclusion Temporal resolution can be improved considerably without compromising the spatial resolution if the low‐resolution vector information is used to construct high spatial resolution data as demonstrated in this work. The deformable registration accuracy is highly critical for the overall performance of the method. Conflict of Interest: This work is supported partially by Siemens Healthcare.
MO‐EE‐A4‐02: Metabolic Changes in Malignant Brain Tumors During Mid‐Course Radiation Therapy: Initial Findings of 3Tesla Volumetric Magnetic Resonance Spectroscopic Imaging
Authors: Muruganandham M , Bayouth J , Smith M , Buatti J
Published: April 2010

Purpose: Metabolic activity of tumors obtained non‐invasively by magnetic resonance spectroscopic imaging (MRSI) during mid‐course of radiation therapy (RT) can be useful in the evaluating tumor response as well as to design effective boost RT plans. The purpose of this work is to assess the changes in metabolic status of malignant brain tumors using 3Tesla volumetric proton MRSI at three weeks of radiation therapy. Method and Materials: The MRSI data from 11 patients with malignant brain tumors acquired during pre‐ and at 3rd week of RT were analyzed retrospectively. The 3D MRSI was performed on a Siemens 3T TRIO TIM scanner using PRESS (point resolved spectroscopy) sequence with TE/TR: 135/1510 ms, 16×16×8 matrix, FOV: 16×16×8 resulting in MRSI voxel size of 10×10×10 mm3. Linear combination (LC) model was used to analyze the acquired spectra. Tumor activity was determined from the values of metabolites ratio “Choline to N‐Acetyl‐Aspartate” (Cho/NAA). MRSI voxels segmented from metabolically active tumor regions were compared for further analysis. Results: The mean Cho/NAA values at 3rd week of RT compared to their pre‐RT values were found to decrease 26% to 79% in 7 out of 11 patients and increase73% in one case. Three patients had minimal changes (−6% to +17%). Voxels with higher tumor activity (i.e., larger Cho/NAA value) at pre‐RT were observed to show large decrease at 3 weeks of RT. The spatial patterns of metabolic abnormality considerably altered during 3 weeks of RT compared to that of pre‐RT. Conclusion: MRSI derived metabolic status of malignant brain tumors in patients undergoing RT obtained during mid‐course of treatment provides valuable functional tumor information that is not available from other conventional anatomical imaging methods and it could help to devise patient‐specific effective treatment interventions.
MO‐E‐213A‐02: Implementating In Vivo Perfusion Measurements Using DCE MRI
Authors: Cao Y
Published: April 2010

Although it may appear relatively straightforward to extract quantitative metrics from static or dynamic imaging data, a variety of details are critical to the establishment of a data acquisition, analysis, and interpretation methodology that can significantly influence the fidelity of a clinical or fundamental investigation of imaging as a biomarker. While typical users will find available commercial tools and apply them, understanding these fundamental steps will help both the local investigator as well as national efforts to standardize the methodologies and understand the limits of information that can usefully be extracted by a given technique. As an example, the use of MRI‐based Dynamic Contrast Enhanced (DCE‐MRI) imaging and analysis of perfusion‐related metrics is described. The optimization of an image acquisition protocol, which varies by the tissue being studied, is presented. The steps to process this temporal data are described, including image registration for analysis of intrahepatic perfusion. The variables typically associated with DCE analysis, including Ktrans, blood flow, blood volume, and mean transit time, are defined. The dependence of these variables on image quality and temporal sampling are briefly mentioned. The step‐by‐step analysis of the data to extract regional information is presented. An example paradigm relating the analyzed metrics to external variables (e.g. local radiation dose) is shown.

Learning Objectives:

1. To understand practical issues to extract quantitative imaging metrics

2. To understand how to increase robustness and objectiveness in the analysis

3. To understand limitations of derived quantitative imaging metrics
MO‐FF‐A1‐01: Fluoroscopic Verification of Intensity‐Modulated Rotational Arc Therapy Delivery
Authors: Yi B , Han‐Oh Y , Lerma F , Berman B , Yu C
Published: April 2010

Purpose: Intensity modulated rotational arc technique requires verification of leaf positions, gantry angle and dose rate in the entire arc. This study shows how to achieve this with a detailed verification of Varian RapidArc using a fluoroscopic electronic portal imaging device (EPID). Materials and Methods: Three Rapid Arc plans (prostate 1, whole pelvis 1, and head and neck 1) are delivered on a Triology linac (Varian Medical Systems, CA). During delivery, approximately 600 fluoroscopic portal images are acquired (∼8 images/s) per arc with a PV‐aS1000 EPID, without use of secondary phantoms or blocks. Each leaf position of each gantry angle is calculated from the acquired EPID images offline. Gantry angle information of each portal image is acquired from the dynalog file generated during beam delivery. Leaf positions from the dynalog file are compared to scheduled positions from the DICOM RT plan file. Results: Online EPID image acquisition of Rapid Arc delivery is prompt, involving extension of the EPID system and beam delivery time. The measurement error depends on the displacement of EPID system relatively to the center of rotation, which is only 1mm–1.5 mm. Offline analyses show the accuracy of leaf positions for static leaf and gantry field are better than 1 mm. More than 98.5% of leaf sequences exhibit less than 3mm deviations, 83 % show 2mm and 56% for 1mm. Conclusions: Position of each leaf of each gantry angle for Rapid Arc delivery is verified within 1 mm accuracy with fluoroscopic portal images. Use of fluoroscopic EPID images can be considered as a practical QA tool for the verification of the Rapid Arc delivery.

This study is partially supported by Varian Medical Systems.
MO‐FF‐A1‐02: Calibration of a Novel 4D Diode Array for IMRT and VMAT QA
Authors: Yan G , Lu B , Kozelka J , Simon W , Liu C , Li J
Published: April 2010

Purpose: To develop calibration procedures for a novel 4D diode array for IMRT as well as arc therapy quality assurance (QA). Method and Materials: A novel 4D diode array (ArcCHECK) was designed for rotational therapy QA. Its cylindrical and isotropic design presents a consistent detector image in beam's eye view for all gantry angles. Signals were acquired every 50 ms, allowing for real‐time per‐beam QA as well as measuring composite dose distributions. An efficient calibration procedure was developed to obtain diode sensitivity and directional response dependence with one full gantry rotation. In this process, each diode was in turn irradiated under the same beam condition on beam central axis. The directional response was obtained using TPS‐calculated beam profiles, which were validated in rectangular geometry. A real time algorithm to derive beam angle based on beam edge back projections was developed to apply the corresponding directional response factors. Its clinical application for IMRT QA was demonstrated with 17 IMRT head and neck beams delivered with planned beam angles. Measured dose distribution was compared to TPS calculation in three dimensions with %diff and distance‐to‐agreement analysis. Its feasibility for VMAT QA was investigated with a prostate conformal arc plan. Results: For the IMRT beams, average passing rate was 94.3%±2.1% and 99.6%±0.8% with 1%/2mm and 1%/3mm, respectively. For the conformal arc plan, the passing rate was 97.7% with 1%/2mm and 100% with 1%/3mm. Conclusion: An efficient calibration procedure was developed to obtain both the diode sensitivity and directional response dependence. Real‐time gantry angles were derived accurately based on beam edge back projections, which were used to apply directional response factors. Excellent agreement with TPS calculation was achieved for both IMRT and VMAT plans. ArcCHECK is an efficient and valuable tool for both IMRT and VMAT QA.

Research sponsored by Sun Nuclear Corporation.
MO‐FF‐A1‐04: Toward a True Real‐Time in Vivo Dosimetry System Using Plastic Scintillators
Authors: Archambault L , Briere T , Poenisch F , Beaulieu L , Beddar S
Published: April 2010

Purpose: Plastic scintillation detectors (PSDs) have shown great promise for offline applications such as IMRT QA. Because of their fast response and high sensitivity they could also be used as in vivo detectors. In this work we present and validate a PSD system designed for multi‐probe in vivo measurements with an electron‐multiplying CCD for real‐time photodetection. Method and Materials: The detectors were built with a dose sensitive volume of 0.4 cubic millimeters. Individual PSDs were assembled in modular detector patches each containing 5 closely packed detector elements. Continuous dose readings were performed every 150 ms (1.5 cGy) with a dead time of less than 0.3 ms between consecutive readings. We first studied the signal‐to‐noise ratio for different electron multiplication gain factors. We then analyzed the precision and accuracy of the detectors in acrylic and anthropomorphic pelvic phantoms. Results: The PSDs were found to be compatible with two clinical models of rectal balloons and could easily be inserted into the anthropomorphic phantom. A twofold increase in signal‐to‐noise ratio was seen by setting the electron‐multiplication gain factor to 40 therefore making near real‐time dosimetry feasible. Under calibration conditions, the PSDs agreed with ion chamber measurements to 0.08%. Precision was a function of the total dose delivered, ranging from 2% at 2 cGy to 0.4% at 200 cGy. Conclusion: We have shown PSD read in 150 ms with high accuracy and precision. We have also shown that these detectors can be mounted on different types of rectal balloons therefore transforming these clinical devices in dose detectors without modifying current clinical standard of practice and care. Real‐time monitoring of the dose delivered close to the rectum during prostate treatments will be invaluable to protect this sensitive normal structure while keeping small margins around the prostate.

Supported by the NCI (1R01CA120198‐01A2)
MO‐FF‐A2‐01: Neural Stem Cell Sparing Radiation Therapy—A Feasibility Study
Authors: Redmond K , Grossman S , Kleinberg L , Ford E
Published: April 2010

Purpose: Neural stem cells (NSC) are found in two regions of the adult brain: the subventricular zone (SVZ) of the lateral ventricles and the dentate gyrus (DG) of the hippocampus. These cells are thought to be involved in injury repair and tumor inhibition. This study assesses the feasibility of sparing NSC niches during radiotherapy. Method and Materials: 33 patients treated with IMRT for brain tumors were evaluated (10 glioblastoma multiforme (GBM), 10 low grade gliomas, 10 meningiomas, 3 pituitary macroadenomas). IMRT treatment plans were reconstructed using the Pinnacle treatment planning system (v.8.0m). SVZ and DG were contoured on fused MRI scans. A second IMRT plan using the NSC regions as an avoidance structure was created for each patient. The change in D70 to the contralateral NSC niches and PTV‐1 was recorded. Results: The mean (range) reduction in D70 for the contralateral DG was: 8.3 Gy (0.7–14.3 Gy), 1.8 Gy (−0.15–5.42 Gy), 1.2 Gy (−1.46–7.28 Gy), and 0.5 Gy (−0.4–1.27 Gy) for GBM, low grade gliomas, meningiomas and pituitary adenomas respectively. The mean (range) reduction in D70 for the contralateral SVZ was: 7.3 Gy (2.5–13.4 Gy), 4.2 Gy (−0.5–10.4 Gy), 3.7 Gy (0.43–7.02 Gy), and 5.61 Gy (2–8.34 Gy) for GBM, low grade gliomas, meningiomas and pituitary adenomas respectively. There was no clinically relevant change in the coverage of the PTV‐1. Conclusion: This study demonstrates that it is possible to spare some of the NSC containing regions of the brain using IMRT in patients with brain tumors. This is the first study to date to demonstrate feasibility of this technique in numerous patients with multiple tumor histologies.
MO‐FF‐A2‐04: Pulsed Reduced Dose‐Rate Radiotherapy On a Helical Tomotherapy Unit
Authors: Rong Y , Howard S , Paliwal B , Welsh J
Published: April 2010

Purpose/Background: Pulsed reduced dose‐rate radiotherapy (PRDR) re‐irradiation has the potential to reduce late normal tissue toxicity while yielding nearly identical tumoricidal effect. A typical method using a conventional linac is to deliver a series of 20cGy pulses separated by 3‐minute intervals to give an average dose‐rate of 6.67cGy/min. Dissimilarly, PRDR done via helical tomotherapy would not require an interlude if the sub‐fraction time is approximately 3 minutes, since the top of the PTV will have had a 3‐minute “rest” by the time the bottom is finished. However, intrinsic MLC leaf open time (LOT) limitations in tomotherapy deteriorate plan quality and deliverability when attempting to deliver very low doses (<40cGy). We investigated various means to overcome this limitation to deliver PRDR with a helical tomotherapy device. Method and Materials: Two different cases (central and non‐central targets) were studied. Plans were generated with different combinations of jaw‐width (1.05cm and 2.5cm), pitch (0.43 and 0.86), and modulation factor (MF) (1.5 and 2.5) to administer eight 25cGy sub‐fractions as part of 2Gy to PTV for 20 fractions, giving a total of 40Gy dose. Plans were compared using dose‐volume histogram (DVH), homogeneity indexes (HI), conformation number (CN), and treatment time. DQA for each plan was performed to assess deliverability. Results: Clinically acceptable DVHs with a ∼3 minute treatment duration are achievable with several combinations of jaw width and pitch. However, dose discrepancies were >3% in those plans where average LOT is <70msec, which falls into the high‐error region in the MLC latency curve. The combination of small jaw‐width (1cm), low MF (1.5) and large pitch (0.86), as well as using directional blocks gives clinically acceptable results in dose distribution, beam‐on time, and delivery accuracy (<3%). Conclusion: With a careful selection of planning parameters, PRDR re‐irradiation is deliverable in an efficient fashion on a tomotherapy unit.
MO‐FF‐A3‐05: Tools and Methods for Consensus Generation From Experts' Contours for Radiotherapy Structure Definition
Authors: Apte A , Deasy J , Bosch W , Naqa I El
Published: April 2010

Purpose: The aim of this work is to develop software tool to that is capable of analyzing and estimating consensus contour for target volumes and critical structures from experts' contours for radiotherapy treatment planning. Materials/Methods: The tool was developed as an add‐in for CERR (A Computational Environment for Radiotherapy Research). The tool can obtain consensus contour based on two statistical methods as well as apparent intersection between experts' structures. The two statistical approaches include (i) Kappa‐corrected algorithm and (ii) Expectation‐maximization (EM) algorithm for simultaneous truth and performance level estimation (STAPLE). The tool was used to obtain consensus contour for two studies: (i) Clinical target volume (CTV) definitions of post‐operative prostate cancer patient contoured by 11 radiation oncologists and (ii) CTV and normal structures in rectal cancer contoured by 6 radiation oncologists. Results: The consensus contouring module was developed in Matlab/CERR. The users can choose structures to obtain consensus from and the tool provides graphs of consensus contours at any desired CT slice in any of the transverse, saggittal or coronal views. Users can interactively set the confidence level to obtain desired consensus estimate using any of the three available methods. The tool offers an option to generate basic statistics report about minimum, maximum, mean, median intersection volumes, and estimates of agreement levels, and export this information to an excel file for further analysis of data. Conclusions: We have developed a tool that can be used to guide radiotherapists to obtain estimates of different contours consensus at selected statistical confidence levels. It allows for better quantification of the differences in contour definition among oncologists and their effects on treatment outcomes. It can also be used as a learning tool for residents, where they can draw contours and compare them with experts' consensus.
TU‐SAM‐BRB‐02: Monte Carlo for Radiotherapy Treatment Planning
Authors: Ma C
Published: April 2010

Accurate dose calculation is essential to the success of modern radiation therapy especially for treatment planning involving heterogeneous patient anatomy. This presentation will facilitate participants with the clinical implementation and application of Monte Carlo dose calculation algorithms in treatment planning and dosimetry verification for advanced radiation therapy treatments. Following a brief introduction to the Monte Carlo method for radiation transport and radiotherapy applications we will discuss the radiotherapy process and the dose calculation requirements for treatment planning. Detailed descriptions will be given of the important steps and procedures for the clinical implementation and commissioning of Monte Carlo dose calculation software including clinical accelerator simulation, radiation source modeling, clinical beam commissioning, patient CT data conversion, beam modifier simulation, patient dose calculation, dose display and statistical analysis for Monte Carlo dose calculation. We will also discuss a few issues that are Monte Carlo specific such as dose prescription, energy cutoff values for Monte Carlo electron transport, voxel size effect on dose calculation accuracy and techniques to improve computation efficiency. Finally, we will describe the current status of commercially available Monte Carlo dose calculation systems for radiotherapy treatment planning.
TU‐SAM‐304A‐02: Clinical Considerations of the ACR MRI Accreditation Program
Authors: Branham T
Published: April 2010

In October, 2008, the ACR MRI Accreditation Program was updated to a more flexible, modular process. The ACR MR Accreditation process includes the initial application, and the submission of clinical and phantom images and forms.

The medial physicist plays a critical role in the accreditation process, along with the lead technologist and the supervising radiologist. A team approach is necessary to ensure that all information is accurate and appropriate for the examinations (both clinical and phantom) submitted for accreditation. The medical physicist should assist the facility in assessing the condition of the scanner as well as optimizing the clinical protocols.

This lecture will provide a brief overview of the application steps, and some of the most common problems encountered during clinical portion of the accreditation submission.

Learning Objectives:

1. Understand the basics of the ACR MR Accreditation process.

2. Understand the relationship of the medical physicist in this process as it relates to clinical protocols.

3. Understand some of the most common pitfalls and misconceptions in the accreditation process.
TU‐A‐BRC‐01: Monte Carlo Treatment Planning: Implementation of Clinical Systems
Authors: Popple R , Cygler J
Published: April 2010

Monte Carlo (MC) based treatment planning systems are already commercially available for both photon and electron beams and more users are implementing them in a clinical setting. Therefore it is important that strategies and paradigms for clinical commissioning and implementation of such systems be formulated and discussed. The purpose of commissioning tests for MC based treatment planning systems is not only to evaluate the accuracy of the system, but also to define the optimum calculation parameters, such as number of histories, calculation voxel size, etc., which will be applied in clinical use of the system. This in turn requires that medical physicists responsible for clinical implementation of such systems are well educated in principles of Monte Carlo algorithms.

We provide a brief review of AAPM Task Group Report No. 105 (Med. Phys. 34 (2007) 4818–4853), a document which outlines the important aspects of a MC‐based dose calculation algorithm, from the basic aspects of the use of the MC method for radiation transport to the application of this approach in routine clinical photon and electron beam treatment planning. We also describe possible clinical implementation issues, including dose‐to‐medium vs. dose‐to‐water differences and give comparison of computation times for typical patient anatomies and calculation parameters.

Learning Objectives:

1. To provide an educational review of the physics of the MC method.

2. To discuss the factors associated with MC dose calculation within the patient‐specific geometry, such as statistical uncertainties, approximations of the underlying physics model, CT‐number to material density assignments, and reporting of dose‐to‐medium versus dose‐to‐water.

3. To briefly review the vendor transport codes currently used for clinical treatment planning.

4. To discuss the issues associated with experimental verification of MC algorithms.

5. To briefly review the potential clinical implications of MC calculated dose distributions.

6. To provide example timing comparisons of the major vendor MC codes in the clinical setting.
TU‐A‐210A‐01: Quality Assurance for Digital Radiography
Authors: Willis C
Published: April 2010

Diagnostic medical physicists have traditionally played a key role in the radiology department's Quality Assurance (QA) program. Procedures for QA of digital radiography (DR) systems are less well‐established than those designed for conventional screen‐film radiography. Some methods that were appropriate for conventional systems do not yield accurate results for digital systems. Methods that rely on images on film cannot be performed in a facility devoid of chemical processing. Methods that do not consider effects of all stages of the digital imaging chain from acquisition to display are likely to provide erroneous results. Digital systems often do not provide data in a convenient form for assessing performance. Nevertheless, medical physicists are responsible for designing and directing efforts to assure the safety and efficacy of DR.

Development of standards for performance verification of digital radiographic systems has been outpaced by commercialization of the technology. Practitioners, operators, vendors, and medical physicists are uncertain as to how to configure, calibrate, and verify systems for the best diagnostic quality images at the lowest practical radiation exposure to the patient. Several manufacturers have fielded commercial systems for performance verification, but long term data indicating trends and action limits is rare. Sources of definitive information on practical clinical methods are also scarce in the scientific literature. This has led to the current situation where clinical imaging operations are routinely conducted using systems that are not optimized.

The good news is that methods in common practice for conventional radiography can be applied with modification to digital radiography. Some of these methods are described in recent literature. The AAPM has recognized the dilemma and has initiated an effort to provide practical guidance to clinical physicists, i.e. Task Group 150.

This lecture will discuss some components of a QA program for DR, including adaptation of conventional QA processes. The lecture will discuss methods of evaluating system performance and provide examples of potential interferences. The lecture will review commercial devices for performance evaluation and their limitations. Finally, some ongoing standardization efforts will be described.

Learning Objectives:

1. Review components of a QA program and show how they apply to DR.

2. Understand how some conventional tests should be modified for a digital radiographic system integrated into an electronic image management system.

3. Identify key references and standards that can be useful in QA of DR.
TU‐B‐BRC‐01: Promise and Challenges of PET for Target Definition and Treatment Response Evaluation
Authors: Jeraj R , Kirov AS
Published: April 2010

Positron Emission Tomography (PET) images show physiological and biological information through the in vivo distribution of radioactive, positron‐emitting agents. PET imaging shows focal and distributed regions of cancer and its metastases. Initial PET uses in oncology include diagnosis and staging, which are important for determining treatment decisions. Current PET uses now include target definition for radiation planning followed by PET‐based assessment of treatment. Hybrid PET‐CT devices are becoming attractive radiation treatment simulators.

PET imaging has coarse spatial resolution compared to CT and MR. PET's clinical use is valued because of its great sensitivity for cancer detection. While F‐18‐labled Fluoro‐deoxyglucose (FDG) remains the most promising agent for tumor diagnosis and staging, other, biologically more specific agents (e.g., FMISO, CuATSM for hypoxia imaging or FLT for cell proliferation imaging) might be more appropriate for target definition and treatment assessment.

Although PET brings to radiation therapy of cancer the critical advantage of defining the tumor based on its molecular properties, delineating the gross tumor volume (GTV) with PET is problematic due to the uncertainties in the biological and physiological processes governing the tracer uptake and due to physical limitations for the accuracy of PET images. The main PET image degrading factors, including limited resolution, photon scatter and attenuation will be described and some of the current correction strategies will be introduced. A brief summary of the PET image segmentation methods will be presented.

This course reviews PET‐CT hybrid scanning devices, uses of FDG and non‐FDG PET for oncology imaging, and quantitative aspects for PET‐based radiation target definition and treatment assessment. Example images demonstrate the potential contributions and limitations of FDG and non‐FDG PET oncology imaging. This review course is intended for both imaging and radiation oncology physicists.

Learning Objectives

1. Understand the principle and the current physical limitations of PET

2. Become familiar with the types of PET‐based tumor segmentation methods

3. Discuss quantitative aspects of PET imaging for treatment assessment
TU‐C‐BRD‐02: Applications of Millimeter Precision Small Animal Radiation
Authors: Ford E
Published: April 2010

Recent technical advances in small animal radiation devices allow laboratory irradiation of rodents under cone‐beam CT guidance with, in some cases, sub‐millimeter precision. This provides the opportunity for novel avenues of radiobiological research. Examples include radiation‐enhanced immunotherapy, normal tissue radiation response modeling, and localized radiation ablation of neural stem cell populations. Highlights from recent experiments will be reviewed and future proposed technical developments will be discussed.
TU‐C‐BRB‐02: Dose‐Response Analysis of Radiation‐Induced Sensory Neural Hearing Loss
Authors: Bhandare N , Song W , Moiseenko V , Mendenhall W
Published: April 2010

Purpose: To evaluate the the effect of total radiation dose received by cochlea on the risk of radiation induced sensory‐neural hearing loss (RI‐SNHL) using the Lyman NTCP model. Methods and Materials: A retrospective analysis for RI‐SNHL (audiology, otolaryngology, and radiation oncology records) of 410 patients (820 total ears) treated for selected treatment sites of head and neck cancers were performed. Due to the small volume of the organ, the dose volume analysis was not performed, instead the response was evaluated as a function of the average dose to cochlea. RI‐SNHL was defined as 10 dB loss at high freq (4 kHz) or low freq (average of frequencies between 0.5–2.0 kHz). The Lyman NTCP model was used to describe the dose response. Parameters of clinical significance were estimated using the maximum‐likelihood method with confidence intervals determined from the asymptotic covariance matrix (95% CI). Results: The average doses to cochlea varied between 0.5 – 81 Gy. The estimated values of TD50, m, and TD5 (calculated) for high frequency hearing loss were 63.1±1.9 Gy, 0.263±0.043, and 36.0 Gy and those for low frequency loss were 81.3±5.5, 0.168±0.041, and 59.0 Gy, respectively. The calculated γ50 for high and low frequency SNHL were 1.52 and 2.38, respectively. Conclusion: Lyman NTCP model fit to the RI‐SNHL data for high and low frequency hearing loss showed significant variation in pattern of incidence of hearing loss with increase in the dose to cochlea. The probality of incidence of RI‐SNHL at high frequency starts at lower dose (TD5 = 36 Gy) and increases relatively slowly (γ50 = 1.52) compared with that for low frequency RI‐SNHL (TD5 = 59 Gy, γ50 = 2.38). The NTCP model fit to the clinical data suggests that the dose to cochlea be limited to 36 Gy to reduce the possibility of any RI‐SNHL complications.
TU‐C‐BRB‐09: Estimate of the Uncertainty in Relative Secondary Cancer Risk Calculations Following Proton Therapy and Intensity Modulated X‐Ray Therapy
Authors: Fontenot J , Bloch C , Followill D , Titt U , Zhang M , Newhauser W
Published: April 2010

Purpose: To determine the uncertainty in calculations of the ratio of relative risk (RRR) of developing a secondary malignant neoplasm (SMN) from proton therapy compared to that of IMXT for prostate cancer by examining the sensitivity to key input parameters. Methods and Materials: The RRR and associated uncertainties were examined for a typical patient treated for early‐stage prostate cancer. Proton therapy and IMXT plans were developed using clinical protocols. Baseline risk of SMN was estimated using primary doses from treatment planning calculations, stray doses from Monte Carlo simulations and available data, radiation weighting factors (wR) values from ICRP Publication 92, and the linear no‐threshold model for SMN risk. The sensitivity of RRR to wR was estimated by re‐computing the RRR using various scaled wR values. The influence of uncertainties in the dose‐response model was estimated by re‐computing the RRR with various available models. The influence of inter‐patient variation in primary dose was determined using the standard deviation of mean dose in organs at risk over a patient population, while variation in stray dose was determined with Monte Carlo simulations. Results: The baseline RRR for the selected patient was 0.66, suggesting that proton therapy can reduce the calculated incidence of SMN by 34% compared with IMXT. Changes in wR and the shape of the dose‐response model introduced uncertainties of ±10%, and ±7%, respectively. Inter‐patient variations in primary and stray dose produced RRR values that deviated greatly from the baseline value; however, a strong positive correlation coefficient was observed, resulting in a net uncertainty in the baseline RRR of ±30%. Thus, the total uncertainty in the baseline RRR was 0.22 (2‐σ). Conclusion: Proton therapy can reduce the incidence of SMN compared with IMXT for a population of prostate patients, independent of uncertainties in wR and the shape of the dose response model.