bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐D‐108‐09: Perturbation of Tissue Density Is An Important Metric to Be Considered When Planning for Respiratory Motion Management for Lung Proton Therapy
Authors: Park P , Matlney J , Mohlan R , Zlhu X , Dong L , Li H , Cheung J , Sahoo N , Yang J , Poenisch F , Liu W
Published: July 2013

Purpose: AAPM TG 76 report suggests 5mm tumor motion as the threshold of motion mitigating techniques such as gating or breath‐holding. However, for proton therapy, plan quality can change significantly due to change in tissue density along the beam path independent of tumor motion. In this work, we introduce our in‐house software used for respiratory motion assessment and demonstrate its application for selected patients. Methods: During the 4DCT simulation, an observer estimated the magnitude of tumor motion. Later, the max‐inhale (T0) and max‐exhale (T50) phases were registered using in‐house deformable image registration (DIR) software. The deformation vectors of voxels contained in the internal target volume (ITV) plus 5mm space were used to calculate the mean distance traveled by the tissue in direction that is both perpendicular and parallel to the beam axis. Furthermore, tissue density perturbation was measured as follow: the difference in water‐equivalent thickness (WET) between T0 and T50 were calculated by ray‐tracing along the beam path from the patent skin to the distal surface of the ITV. The observer and DIR measured tumor motion, and the absolute mean differences of WET were compared using Spearman rank correlation. Results: A total of 15 lung cases were studied. The observer measured motion was ranged from 6‐13mm while DIR measurement showed 4‐17mm. The average WET difference was range from 3–9mm. No correlation was observed between observer measured and WET change (rho = 0.16). A positive correlation was observed between DIR and the WET change (rho = 0.7). Conclusion: Our Result: indicates that the change in tissue density due to the breathing motion is as important as tumor motion itself when considering treatment planning strategy for lung proton therapy. Therefore, tissue perturbation due to breathing motion should be measured along with tumor motion when planning for respiratory management. This project is supported by grant P01CA021239 from the National Cancer Institute.
MO‐D‐108‐11: Implication of Spot Position Error On Plan Quality in Pencil‐Beam Proton Therapy
Authors: Yu J , Beltran C , Herman M
Published: July 2013

Purpose: To assess the dosimetric implication of spot position errors on intensity modulated proton therapy (IMPT) treatment plan‐quality and develop an analytical routine to aid in that assessment. Methods: IMPT plans with different spot spacing (SS) (3–6mm) were created on a water phantom and a patient CT using a commercial planning system. Spot position errors (PE) (1–2mm) were simulated by shifting spots away from their planned location using a custom built script. Various perturbations of single‐spot shift and multiple‐spot shift in a correlated and random manner were simulated. The resulting dose perturbations were compared to the original plans to calculate percent dose error (PDE (%)). Results: Spot shifts created hot and cold spots adjacent to the location of the error. In the phantom study of the single‐spot error, the PDE at the largest dose difference has been mapped out in SS and PE space to be a quadratic 3D surface, and the slope of the surface became less steep at the deeper depth. As the global dose distribution reduced from volume to plane and line the PDE increased substantially. For clustered multiple‐spot error the dose perturbation was significantly larger than single‐spot error, but there is saturation for the magnitude of PDE though the perturbation volume increased. In a patient plan, 5% of total spots were clustered which resulted in the PDE of 5 to 6 % and is decreased to 2% when the spots and shift direction are randomly chosen. Conclusion: The dose perturbation is a complex function of PE, SS, depth and global dose distribution. To quantitatively and systematically evaluate the impact of position errors on plan‐quality a simulation tool for both selective and random spot(s) position errors was developed.
MO‐D‐500‐01: Treatment Planning in Proton Therapy
Authors: Winey B , Lomax A
Published: July 2013

Proton therapy planning strategies differ in many aspects from traditional planning done for photon treatments. Both passive scattered and scanning proton treatment planning systems and protocols must account for proton specific uncertainties to deliver high fidelity plans to the patient. While many uncertainties have been discussed in the literature, clinical implementations of proton treatment planning systems require adequate procedures to address uncertainties. Some uncertainties are constant between passive scattered and scanning systems but other uncertainties, due to the differences in beam delivery methods, necessitate different approaches to accurately deliver the prescribed treatment. For example, range, LET, RBE, and patient position uncertainties are common to all particle therapies but the effects on the delivered treatment are dependent upon the delivery method. Passive scattered delivery techniques must account for field size effects, output factors, hardware uncertainties, air gaps and penumbras. Scanning beams encounter different uncertainties regarding spot size, scanning positional accuracy, beam spot dosimetry, and magnet calibration uncertainties.

Learning Objectives:

1. To understand the fundamentals of treatment planning for passive and scanned proton therapy, including Intensity Modulated Proton Therapy

2. To understand the proton specific strategies in treatment planning for passive scattering and scanning

3. To understand uncertainties of proton therapy and their implications on proton treatment planning

4. To understand the limitations of current proton treatment planning techniques.
MO‐D‐141‐03: Characterization of a One‐Ring Small‐Animal PET Prototype
Authors: Miranda A
Published: July 2013

Purpose: 1) To experimentally characterize a one‐ring small‐animal PET prototype currently being developed at Instituto de Fisica, UNAM. 2) To develop a software engine for data rebinning and image reconstruction from list mode raw data. Methods: The prototype detectors are an assembly of 16×16 LYSO scintillation crystals (1×1×10 mm3) coupled to position sensitive photomultiplier tubes (PS‐PMT) Hamamatsu H7546B, placed in a ring of 9.8 cm inner diameter. PS‐PMT output signals are reduced with resistive chains and digitized with a multichannel acquisition board based on FPGAs using a coincidence window of 6 ns and 12 bits encoding depth. Corrections for spatial distortions, decay, center of rotation and detector normalization have been implemented and are part of our data processing protocol. Energy resolution is measured for each individual crystal using a normalization phantom (hollow cylinder containing 18F mixed with water). Spatial resolution is measured with line sources at different radial distances. Sinograms are obtained from list mode data using different rebinning algorithms (SSRB, MSRB and FORE). Image reconstruction is performed using analytical (FBP, ART) and iterative algorithms (ML‐EM, OSEM). Data analysis and processing have been implemented in MATLAB. Results: The energy resolution of individual crystals has a typical value of 21±3% around the photopeak. The reconstructions of the line sources show different quality depending on the reconstruction technique used. Among the rebinning methods, FORE shows best results producing a spatial resolution of 1.36 mm when using FBP. FORE followed by ML‐EM iterative algorithm provides the best spatial resolution (1.05 mm), but with great computational effort. Conclusion: A one‐ring small‐animal PET prototype has been built and characterized in terms of spatial and energy resolution. Different rebinning and reconstruction methods have been successfully implemented. Future work will involve phantoms studies (microDerenzo, NEMA NU4‐2008) to determine other performance characteristics. DGAPA‐UNAM PAPIIT IN105913
MO‐D‐141‐07: X‐Ray Activated Gold Nanoparticles for Tumor‐Specific Molecular Imaging
Authors: Volotskova O , Osakada Y , Pratx G , Sun C , Cui B , Xing L
Published: July 2013

Purpose: X‐ray radiography and computed tomography are commonly used anatomical imaging modalities still have significant shortcomings in sensitivity and specificity. Molecular imaging based on tumor‐specific nanoparticles that can probe biochemical processes in vivo can provide characterization and identification of benign and malignant lesions on the cellular level. In particular, radioluminescent nanoparticles (RLNPs) are the ideal platform for X‐ray‐mediated imaging and synergistic therapy during radiation treatment. These unique particles can emit visible light under X‐ray irradiation. However, existing RLNPs based on lanthanides may cause toxicity in vivo. Here we report new intriguing radioluminescent properties of a new type of nanoparticles made by arranging a small number of gold atoms. The objective of this work is to examine practical aspects of a new imaging modality: light emission and spectral emission characteristics. Methods: Bare gold nanoparticles (4 and 1.8 nm) and conjugated gold nanoparticles with size less than 2 nm (25 atoms size) were synthesized. Imaging was performed by irradiating the samples with X‐ray (30–80 kVp, 10–30 mA) while acquiring 10 s frames with an EMCCD camera (Princeton Instruments, 300–900 nm). The samples were further characterized by using a custom PMT‐based system. The spectral properties of the emission were measured under both optical and X‐ray excitation using a sensitive spectrometer. Results: It was found that tested gold nanoparticles had different responses to x‐ray excitation. Au25‐BSA is the most promising candidate for x‐ray luminescence imaging, with up to 4‐6‐fold increase in the optical signal compared to the controls. Conclusion: In this work, it was first time demonstrated the optical detection of small atom number gold nanoparticles excited by x‐ray source. Development of a new optical imaging probes will allow us to take advantage of the desirable features of optical molecular imaging and achieve substantially improved spatiotemporal resolution, sensitivity and specificity for tumor detection.
MO‐D‐134‐01: K‐Factors for Overweight and Obese Patients in CT Examinations as a Function of Body Mass Index
Authors: Gao Y , Ding A , Caracappa P , Xu X
Published: July 2013

Purpose: To generate Dose Length Product to Effective Dose conversion factors (k‐factors) for a series of overweight and obese patients and to establish a functional form for k‐factors in relation to body mass index. Methods: Using the Monte Carlo code MCNPX 2.5.0 and a validated model of the CT source, CT scans were simulated on a series of overweight and obese adult male and female phantoms with fixed height and body mass index (BMI) ranging from 23 to 45. For several CT scan protocols simulations generated the organ doses and effective doses using ICRP 103 tissue weighting factors. The k‐factors were then derived using the dose length product (DLP) for each protocol and the effective dose from pairs of phantoms with the same BMI. For each protocol, a regression analysis was performed for k‐factors to BMI. Results: The calculated k‐factors showed a consistent trend of decreasing with increasing BMI for each of the protocols. In the pelvic scan protocol, for example, the k‐factor for patients with a BMI of 45 is 42% of that for an average sized individual. The k‐factor equations in terms of BMI fit an exponential function regression for all protocols with R‐squared values greater than 0.99 in every case. Conclusion: Where patient height and weight are available, the BMI‐dependent k‐factor equations can provide more accurate effective dose estimation for overweight and obese patients. While they do not provide the patient‐specific dose information that is the purpose of some modern CT dose tracking software, they provide easy access to more appropriate risk estimation and a better metric for performance tracking of a diverse patient population than DLP alone. One member was funded by the 2012‐2013 J. Newell Stannard Fellowship Award from Health Physics Society.
MO‐D‐134‐05: Size Specific Dose Estimation in Abdominal CT: Impact of Longitudinal Variations in Patient Size
Authors: Leng S , Shiung M , Duan X , Yu L , Zhang Y , McCollough C
Published: July 2013

Purpose: Size specific dose estimates (SSDE) represent the mean dose to a patient of a specific size. However, patient size can vary significantly within the scan range, affecting the choice of conversion factor and, with tube current modulation, CTDIvol. The purpose of this study was to evaluate the impact of patient size variations in the abdomen on SSDE. Methods: Images from 100 consecutive abdominal CT exams (top of liver to top of crest) were evaluated. A Matlab program was used to automatically remove the patient table and calculate water equivalent diameter (Dw). SSDE was calculated in two ways and compared: 1) The mean CTDIvol over the scan range was used with the conversion factor corresponding to Dw at the middle of the scan range. 2) The mean mAs(z) and the CTDIvol/mAs were used to calculate the CTDIvol(z); Dw(z) used to determine the conversion factor(z); SSDE(z) and mean SSDE over the scan range calculated, where z=longitudinal position. Results: A range of body sizes was included, with BMI ranging from 14.9 to 41.5. However, the standard deviation of Dw within each patients' scan range was on average only 1.3cm (range: 0.4–2.9cm), indicating a high degree of uniformity in patient size over the abdomen. The difference between the two groups of SSDE values ranged from −0.3 to 1.9mGy, with root mean square difference of 0.3 mGy. A paired t‐test showed no significant difference between these two groups of SSDE values (p<0.001). Conclusion: For abdominal CT, there was no significant difference between the mean SSDE values calculated using 1) the mean CTDIvol over the scan range and Dw at the middle of the scan range and 2) the CTDIvol and Dw at each position in the scan range. In body regions with greater longitudinal variation in attenuation, this may not be the case. This work was supported in part by NIH grant R01 EB071095 from the National Institute of Biomedical Imaging and Bioengineering.
MO‐D‐144‐01: Ultrasound Guided RT Intervention & Novel Technologies
Authors: Beaulieu L , Cunha J , Libby B , Wong J
Published: July 2013

Significant advances were made over the past decade in ultrasound (US) imaging and new therapeutic applications are emerging. Used alone or in combination with other imaging modalities, US imaging is also well suited for robot‐assisted interventions. This session will feature invited presentations on (1) the use of US and robot for interstitial breast implant high dose rate (HDR) brachytherapy, (2) the possibilities of electromagnetic tracking system for interactive needle navigation, 3D‐printed patient‐specific skewed‐needle template, and co‐robots for interventional brachytherapy, (3), the real time US guidance, dosimetry and treatment optimization for novel HDR brachytherapy such as single fraction partial prostate treatment for early stage disease, and (4) the development of an integrated 3D x‐ray/ultrasound imaging system for on‐board guidance of soft tissue targets for external beam radiation therapy.

Learning Objectives:

1. Understand the improvements made on ultrasound imaging technology

2. Understand the possibilities of real‐time imaging for a wide range of applications

3. Identify new applications for medical physicists of ultrasound imaging for image‐guided interventions.

Part of this work is supported by NCI R01 CA 161613, and another part by a research contract with Philips Medical Systems.
MO‐F‐108‐05: Treatment Planning Study of Volumetric Arc Therapy for Spine Stereotactic Radiosurgery Using Flattening Filter Free Beams
Authors: Chin K , Wen N , Huang Y , Jin J , Chetty I , Ryu S
Published: July 2013

Purpose: To evaluate the potential usage of flattening filter‐free (FFF) with volumetric modulated arc therapy (VMAT) in the treatment of spine radiosurgery. Methods: VMAT plans were retrospectively generated for six patients treated with intensity modulated radiotherapy (IMRT) according to the RTOG 0631 protocol. The VMAT plans were developed in the Eclipse treatment planning system on a Varian Truebeam equipped with a Millennium 120 MLC system, using the flattening‐filter‐free mode with a maximum dose rate of 1400 MU/min. The plans were prescribed to either 16 or 18Gy in one fraction to cover at least 90% of the target. Planning target volume (PTV) coverage, conformity index (CI), dose to spinal cord, distance to fall off between the prescription and maximum isodose line of the cord, as well as plan delivery efficiency were evaluated. Results: PTV coverage was better for VMAT compared to IMRT plans. The ratios between VMAT and IMRT for PTV coverage were 1.06 for D99% and 1.01 for D95%. The hot spots were comparable; the ratios of D10% and D5% were both 0.994. The VMAT plans were more conformal than the IMRT plans (CI of 1.13 vs. 1.28, p= 0. 0004). The VMAT plans also had shorter distance to fall off between the prescription and max cord isodose line (0.28 vs. 0.38 cm, p=0.0006). The average cord dose is 4.72 Gy in the VMAT plans, relative to 5.77 Gy in the IMRT plans. Finally, the VMAT treatments required slightly less MUs than the IMRT plans (8236 vs 9410, p=0.116). Conclusion: The VMAT plans had better PTV coverage compared to the IMRT plans. Furthermore, VMAT allowed for lower mean dose to the spinal cord, a sharper dose gradient between the PTV and the cord, and required fewer MUs, thus reducing the treatment time.
MO‐F‐108‐09: Single Fraction Spine SBRT End to End Testing On TomoTherapy and Vero Treatment Platforms Using a Novel Anthropomorphic Phantom
Authors: Gallo J , Kaufman I , Bossenberger T , Powell R , Ramirez E , Reynolds R , Solberg T , Burmeister J
Published: July 2013

Purpose: Single fraction spine SBRT involves very high doses delivered to targets adjacent to the spinal cord. Highly conformal planning and accurate delivery of such plans is imperative for successful treatment without catastrophic adverse affects. End to end testing is an important practice for evaluating the entire treatment process from simulation through treatment delivery. We performed end‐to‐end testing for a set of representative spine SBRT targets planned and delivered using different treatment planning systems (TPSs) and delivery systems. Methods: An anthropomorphic E2E SBRT phantom (IMT, Troy,NY) accepting ion chambers in the thoracic region and film in the lumbar region was simulated and treated to evaluate agreement between measured and calculated doses. Four representative targets were developed within each region (thoracic and lumbar) to represent different presentations of spine metastases and planned according to RTOG 0631 constraints. Plans were created using the TomoTherapy TPS for delivery using the Hi‐ART system (Accuray, Sunnyvale,CA) and the iPlan TPS for delivery using the Vero system (BrainLAB, Feldkirchen,Germany). Delivered doses were measured using 0.007cc ion chambers (Standard Imaging, Middleton,WI) in the thoracic region and EBT3 Gafchromic film (Ashland, Wayne,NJ) in the lumbar region. Results: Both treatment platforms met all dose constraints required by RTOG 0631. Ion chamber measurements in the 4 thoracic targets delivered on TomoTherapy all agreed within 2.2%, with an average difference of 0.8%. Similar measurements on the Vero system agreed within 3.3%. Film measurements for the 4 lumbar targets resulted in gamma index passing rates over 99.7% at 3%/3mm, 99.2% at 2%/2mm, and 90% at 1%/1mm for all plans on both platforms. Conclusion: In spite of the complexity of the representative targets and their proximity to the spinal cord, both treatment platforms were able to create plans meeting all RTOG dose constraints and produced exceptional agreement between calculated and measured doses.
MO‐F‐108‐11: 3D Verification for Multifocal Single Isocenter SRS
Authors: Thomas A , Niebanck M , Wang Z , Kirkpatrick J , Oldham M
Published: July 2013

Purpose: Recent trends in SRS use multifocal VMAT plans to simultaneously treat several, distinct targets. Conventional verification often involves low resolution measurements in a single plane, cylinder, or intersecting planes of diodes or ion chambers. This work presents an investigation into the accuracy, consistency and reproducibility of this treatment technique using a high‐resolution 3D dosimetry system (PRESAGE/Optical‐CT). Methods: A complex VMAT plan consisting of a single isocenter but 5 separate targets was created in Eclipse for a head phantom containing a cylindrical PRESAGE dosimetry insert of 10cm diameter and height. The plan contained 5 arcs delivering doses from 12–20 Gy. The treatment was delivered to four separate dosimeters positioned in the head‐phantom. Each delivery was performed after IGRT positioning using 2D and 3D kilovoltage images. A final delivery was given to a modified insert containing a pin‐point ion chamber enabling calibration of Presage data to dose. Dosimetric data was read out in an optical‐CT scanner. Consistency and reproducibility of the treatment technique (including IGRT set‐up) was investigated by comparing the dose distributions in the 4 inserts, and with the predicted TPS distribution. Results: Dose distributions from the 4 dosimeters were registered to find the mean and standard deviation at all points throughout the dosimeters. They showed less than 3% standard deviation within voxels of similar dose regions. 3D gamma maps show the calculated delivered dose matched output to within expected tolerances and errors ‐ passing rate was 98.0% (3%, 2mm). Conclusions: The deliveries of the irradiation were found to be consistent and matched the treatment plan, demonstrating high accuracy and reproducibility of the treatment machine, the IGRT procedure, and the 3D measurement. The complexity of the treatment (multiple arcs) and dosimetry (multiple strong gradients) pose a substantial challenge for comprehensive verification. 3D dosimetry can be uniquely effective in this scenario.
MO‐F‐108‐12: Evaluation of the Planar Ion Chamber and the Cylindrical Diode Arrays for Extracranial Cyberknife Patient Specific QA
Authors: Lin M , Veltchev I , Li J , Price R , Fan J , Jin L , Koren S , Ma C
Published: July 2013

Purpose: The robotic‐radiosurgery‐system (Cyberknife) has been increasingly employed for extracranial treatments. The recent development of the MLC‐equipped ‐ Cyberknife emphasizes this application more, especially for larger treatment volumes. This work is aimed to study the feasibility of the ArcCHECK and the MatriXX systems for CyberKnife patient‐specific QA and co mpare their performance. Methods: Fiducial markers were implanted in both systems to enable image‐based setup. The output factors measured by them were co mpared with co mmissioning data. The impact of angular dependency on the Cyberknife measurements and the sensitivity of detecting the translational (1–3mm) and the rotational (1–3 degree) delivery errors were also evaluated for both systems. Single‐beam‐plans, isocentric‐plans and ten extracranial Cyberknife patient plans (PTV 5–136cm3) were measured and co mpared with calculated QA plans. The plan dose distributions were calculated with Ray‐tracing and the Monte Carlo (MC) method, respectively. The gamma‐passing‐rates with different criteria were evaluated and co mpared. Results: With the 0.8×0.8 mm2 diodes, the output factors measured with the ArcCHECK co mpare better with co mmissioning data. The maximum angular‐co rrection for a given beam is 8.2% for the MatriXX and 2.4% for the ArcCHECK. Both systems demonstrate a co mparable sensitivity of detecting the translational targeting errors while the ArcCHECK is more sensitive to the rotational targeting error. MC calculations are necessary for the ArcCHECK calculations since the Ray‐tracing‐algorithm fails to handle the heterogeneity. For all the studied Cyberknife patient plans, the ArcCHECK system demonstrates 100% (3%/3mm) and >96% (2%/2mm) passing‐rates. In co ntrast, the MatriXX system demonstrates >92% (3%/3mm) and ∼80% (2%/2mm) passing‐rates and the passing‐rates decrease with PTV/co ne sizes. Co nclusions: The feasibility of using the ArcCHECK or the MatriXX systems for Cyberknife patient‐specific QA has been demonstrated. The gamma‐passing‐rate is higher for the ArcCHECK system. The custom angular co rrection is necessary as proven by the improved passing‐rate, especially with the MatriXX system.
MO‐F‐WAB‐02: Constancy of Time Lag Relationship Between External and Internal Signal in Abdominal Tumor Sites
Authors: Regmi R , Lovelock D , Zhang P , Pham H , Xiong J , Yorke E , Goodman K , Wu A , Mageras G
Published: July 2013

Purpose: To investigate constancy, within a treatment session, of the time lag relationship between implanted markers in abdominal tumors and an external motion surrogate. Methods: Six gastroesophageal junction and three pancreatic cancer patients (IRB‐approved protocol) received a respiration‐correlated CT (RCCT), and two cone‐beam CTs (CBCT), one before and one after the treatment. Time between initial and final scan varied from about 1 to 3 h. Each patient had at least one implanted fiducial marker near the tumor. In all scans, abdominal displacement (Varian RPM) was recorded as the external motion signal. In‐house software tracked fiducials, representing internal signal, in CBCT projection images and amplitude‐sorted RCCT. For each set of projection images, time lag between internal and external signals was found by maximizing the correlation coefficient in each breathing cycle and averaging over all cycles. For the RCCT, these quantities were calculated for the 1 –2 cycles during which the fiducial was imaged. Results: Mean ± standard deviation in time lag, over all scans and patients, was 0.10 ± 0.07 s (range 0.01 – 0.36 s). External signal lagged the internal in 20/27 scans. Change in time lag between pre‐and post‐RT CBCT was 0.06 ± 0.07s (range 0.01 – 0.22 s), corresponding to 3.1 ± 3.7% (range 0.6 – 10.8%) of the gate width (range 1.6 – 3.1 s). Including the RCCT scan, change in time lag increased to 6.5 ± 5.4% (range 0.2 – 16.1%) of the gate width, and in three patients, change in time lag exceeded 10% of the gate width. Conclusion: Time lag between internal and external signal is small compared to the treatment gate width in all patients. Change in time lag within a treatment session, inferred from pre to post‐RT measurements is also small, suggesting that a single measurement at the session start is adequate.

NIH/NCI award R01 CA126993 and a research grant from Varian.
MO‐F‐WAB‐05: Predictor Model Training for Real‐Time Motion Management of Lung Tumors
Authors: Rottmann J , Berbeco R
Published: July 2013

Purpose: Real‐time image guided radiotherapy requires tumor motion prediction to compensate for system specific latencies caused by image acquisition, motion estimation, hardware control and other factors. The performance of prediction models depends strongly on the amount of patient specific data available for training. This may be problematic if additional imaging dose is associated with the training data acquisition. To solve this problem, we investigate the use of chest wall motion data as a surrogate to train a linear predictor for lung tumor motion. Methods: A dataset containing both lung tumor and chest wall motion trajectories for 172 beams/fractions of lung radiotherapy (11 patients) is used. We implement a linear prediction model and estimate the average geometric tracking error as a function of latency. Each trajectory is split into a dataset used for training the predictor model and one used for verification. In a second study we compare two training scenarios for a fixed system latency value of 250 ms. In the first scenario tumor motion is used for training directly, while in the second scenario the external surrogate motion trajectory is used. Verification is performed in both scenarios with the tumor motion trajectory as the reference. Results: For latencies of 0–500ms, the average error without using a predictor increases approximately linearly to 4 mm and at 250 ms we observe 1.8 mm. Using the linear predictor model the error is reduced by an average of about 50%. Training the predictor model with external surrogate data provides similar results. Conclusion: A linear prediction model can reduce latency induced tracking errors by an average of 50% in real‐time image guided radiotherapy systems with system latencies of about 250 ms. External surrogate data is suitable to train the prediction model yielding similar prediction performance as training with lung tumor motion data directly. The project described was supported, in part, by Award Number R21CA156068 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health.
MO‐F‐WAB‐12: Quantification of Intrafractional Tumor Motion in the Upper Lung Using An Electromagnetic Tumor Tracking System
Authors: Schmitt D , Nill S , Roeder F , Herth F , Oelfke U
Published: July 2013

Purpose: To investigate the amount and variation of 3‐dimensional intrafractional tumor motion in the upper lung. Methods: We analyzed motion data for seven patients, who were enrolled by our institution in a multicenter trial evaluating investigational anchored Calypso beacons (Varian Medican Systems Inc.) in lung cancer. Beacons were placed bronchoscopically close to the tumor prior to radiotherapy. Tumors were located in a middle or upper lobe of the lung. Two patients received a hypofractionated 3D conformal irradiation and five a conventionally fractionated IMRT treatment. Average fraction time was 4.5 min and 9.8 min, respectively. In total, 162 fractions were analyzed. After patient setup using cone‐beam CT, the Calypso system monitored the beacon centroid positions during all fractions with 10 Hz update rate. The centroid midline was calculated by a sliding mean of the positions in all directions with a window of 10 s, covering 2–3 breathing cycles. The midline at the time irradiation starts, called initial midline, was used as reference for intrafraction motion in general. As amplitude the average distance between each peak (inhale and exhale) and the current midline was assessed. Results: The mean 3D distance from the initial midline over all patients was measured as (2.4+−1.3) mm. The mean of the individual patient intrafractional 3D midline drift ranges from (0.8 to 3.4) mm. Lateral, longitudinal and vertical mean amplitude was calculated to (0.9+−0.5) mm, (1.5+−1.3) mm and (1.2+−0.9) mm, respectively. Mean longitudinal motion range was up to 15 mm for 2 patients. Conclusion: The analyzed motion data covers only tumors in the middle or upper lobes of the lung, therefore the amplitudes are biased towards smaller values. Nevertheless remarkable midline drifts could be detected. Electromagnetic tracking of lung tumor motion can provide validation of motion range assumptions from the planning 4D CT and information on midline drifts. This work was partially supported by Siemens Healthcare and Varian Medical Systems Inc.
MO‐F‐134‐02: Project‐Based Learning ‐ Expanding Course Content with a Broad‐Scope Project
Authors: Howell R , Kry S , Titt U
Published: July 2013

Purpose: We set out to revise/improve the Radiation Detection Instrumentation and Data Analysis course at our institution due to negative student evaluations of this course. Initially, we began with changes to the syllabus, adding important topics that were not being covered and expanding the teaching faculty to include board‐certified physicists with practical clinical experience. Although this led to improved student course evaluations compared to the previous years, we were still not satisfied that enough material was being covered in the course. Because the time in the semester was limited, we considered alternative teaching methodologies in an effort to broaden the scope of the course. Methods: We implemented project‐based learning because it allowed us to keep instructor‐led lectures, which provide the students with fundamental knowledge that we believe essential for a core course. We also expanded the breadth of the topics covered in the course through assignment of a class project. The class project broadly aims to provide opportunities for each group of students to investigate meaningful real‐world topics related to radiation detection in medical physics. For this assignment, the students assume the role of director of the medical physics radiation therapy department at a comprehensive cancer treatment center and are asked to develop a capital equipment list of detectors and associated equipment to perform all necessary QA for this department. They are expected to submit a detailed report and give a presentation to the class. Results: The class project was first assigned in 2010 and has been required every year since. The project has increased the breadth of the course and student course evaluations have improved (82% positive compared to 36% positive). Conclusion: Overall, our students are learning more material in the revamped course and are exposed to one of the many facets of a career in clinical medical physics.
MO‐F‐134‐05: Physics Education to Enhance CT Image Quality Optimization and Dose Management: Model, Method, and Materials
Authors: Sprawls P
Published: July 2013

Purpose: To enable physicists to contribute to more effective and optimized CT imaging procedures and dose management by providing applicable physics education for medical professionals, including residents, who have direct responsibility for the procedures. Methods: The program model recognizes the values and limitations of the different physics learning activities, from classroom to direct clinical experience, and provides open access resources to enrich and enhance each. Classroom presentations and discussions provide an opportunity for physicists to interact directly with medical professionals guiding the learning experience and sharing their knowledge. A limitation is that many physicists do not have practical knowledge and experience in CT procedure optimization and dose management and the ability to create effective teaching materials. This can be overcome by using visuals available at http://www.sprawls.org/resources/CTIQDM/visuals.htm and the self‐study module at http://www.sprawls.org/resources/CTIQDM/. The CT clinic is also a highly effective environment for learning applied physics because the medical professional is interacting directly with and observing the process. Although the physicists are not present they can add a valuable physics learning opportunity by managing a program in which the module is assigned for review at the beginning of a CT rotation and used as a reference after that. An additional enhancement is to encourage the radiology clinical faculty to engage in physics discussions with the residents as images and protocols are being reviewed. These can be guided by questions and talking points provided by physicists. Results: A highly‐effective clinically focused physics education project with the potential of producing more optimized CT procedures and dose management. Conclusion: Physics education based on collaboration among physicists and radiologists, using shared open access resources, combining and enriching the different learning activities, and focused on a specific topic (such as CT) is an innovative model that can be applied in a variety of other areas.
MO‐G‐137‐05: Improving Passive Scattering Proton Therapy Plan Quality by Optimizing Compensator Parameters
Authors: Taylor M , Liao Z , Bluett J , Kerr M , Li H , Sahoo N , Gillin M , Zhu X , Zhang X
Published: July 2013

Purpose: To demonstrate the importance of optimizing compensator parameters in passive scattering proton therapy (PSPT). Method:We examined the plans of four patients treated for lung tumors at MD Anderson Cancer Center. Comparable IMRT and PSPT plans had been created for each of these patients. The clinical PSPT plans were calculated using 5 mm drill bit compensators with smearing values of 0.5 to 0.9 cm. Two new plans were created for each patient: one with a smearing value of 0 cm and a second with 0 cm smearing and smooth compensators. The prescribed isodose line of each plan was changed so that PTV D95 was equal in a given patient's plans and robustness analysis was performed to evaluate the impact of the compensator changes. A plan was considered robust if ITV D95 remained greater than 95% of the prescribed dose in the worst case scenario for target coverage. The robust plan with altered compensator parameters and most improved normal tissue sparing was considered to be the compensator optimized plan. Results: Mean lung dose for the 4 patients is 19.8, 12.7, 11.9 and 12.4 Gy in the compensator optimized plans compared to 21.8, 14.2, 12.9 and 13.6 Gy in the clinical plans; esophagus V60 is 39.2%, 13.4%, 7.7% and 17.7% compared to 48.6%, 18.1%, 11.6% and 20.7%; mean heart dose is 23.3, 1.2, 8.2 and 4.6 Gy compared to 24.7, 2.4, 9.5 and 8.3 Gy. Conclusion: Robustness analysis allows reduction of the smearing parameter while keeping confidence that the plan is robust against range and setup uncertainties. Compensator parameters should be individually optimized if PSPT plans are to display maximum advantage over IMRT plans in terms of dose volume data.
TU‐A‐137‐01: High Energy Brachytherapy Dosimetry as It Applies to Accelerated Partial Breast Irradiation (APBI)
Authors: Richardson S , Mourtada F
Published: July 2013

Report 229 is the newest report on high energy brachytherapy dosimetry. It investigates many known issues with accurately doing brachytherapy dose calculations and modeling of TG43 parameters for sources with photon energies >50keV. Two issues that are described in the report are the presence of tissue heterogeneities and scatter corrections when doing brachytherapy treatments. Both of these issues are well manifested when doing partial breast brachytherapy. The applicators for breast brachytherapy are either filled with high Z contrast material (Mammosite or Contura) or are filled with air (Savi) which can create either a dose decrease or dose increase in the PTV compared to a standard TG43 calculation. Often times when these devices are used, the applicators are in close proximity to the skin surface which results in a loss of CPE and can actually decrease the dose compared to what one would expect when doing a TG43 calculation. The applicators are also sometimes near the lung or ribs which also creates a dose discrepancy compared to treatment planning systems. The purpose of this talk will be to describe the physics behind these issues and provide an overview of published literature which investigates the nature of the dose discrepancies encountered with partial breast brachytherapy. It will also describe the magnitude of the dose discrepancy for a variety of clinical cases.

Learning Objectives:

1. To understand the physics behind high energy brachytherapy as applied to APBI

2. To understand when TG43 calculations may not accurately describe the clinical situation

3. To understand the nature of these dose discrepancies and be able to provide magnitudes for clinical approximations

4. Some of the research presented was funded by an MRA with Varian Medical Systems.
TU‐A‐108‐01: Four‐Dimensional Monte Carlo Using the TOPAS TOol for PArticle Simulation
Authors: Perl J , Shin J , Schuemann J , Paganetti H , Faddegon B
Published: July 2013

Purpose: As the number and diversity of 4D radiation therapy treatment modalities increases, with techniques from IMRT, VMAT, SBRT, IGRT and IMPT to proton and ion beam scanning, the value of a comprehensive 4D Monte Carlo dose calculation tool has become evident. In silico experiments provide a powerful platform to study sensitivity of dose calculation techniques to motion errors, beam instabilities and interplay effects. We present a comprehensive system to meet this growing need. Methods: We have provided rich 4D capabilities within the TOPAS TOol for PArticle Simulation. TOPAS allows any one or more simulation parameter to vary over time, such as a beam current, the geometrical position of a treatment head component, a magnetic field, a 4D CT time slice or a gating signal for scoring. In use at 25 research institutions, TOPAS has been brought to bear on a wide range of 4D problems. We present 4D capabilities, including modulator wheel rotation during beam current modulation, beam scanning, MLC leaf motion, gantry rotation and 4D CT. Results: It is imperative that 4D simulation tools provide 4D‐scoring capabilities, such as scorers that can be gated by time, or phase space output that can associate time to each saved particle. Only with such tools can one confirm that the simulation is accurate in not just three dimensions but four. We show such results that confirm TOPAS 4D performance, both as time‐sliced histograms and through simulated 4D radiography (simulated films darkening as dose accumulates over time). Conclusion: TOPAS has proven to be a comprehensive 4D simulation tool. While current users are mainly in proton therapy, TOPAS is being extended for use in ion, x‐ray, electron and brachytherapy. While there are many excellent MC tools already for some of these modalities, TOPAS is unique in the 4D domain.
TU‐A‐108‐02: A 4D Monte Carlo Study Quantifying Changes in the Interplay Effect as a Function of Treatment Delivery Parameters in Proton Beam Scanning for Lung
Authors: Dowdell S , Grassberger C , Sharp GC , Paganetti H
Published: July 2013

Purpose: To assess the impact of delivery parameters of a pencil beam scanning proton therapy system on the dosimetric interplay effect during lung treatments. Methods: 4D Monte Carlo simulations were performed using TOPAS for 5 lung cancer patients with varying tumor sizes (50.4–167.1cc) and superior‐inferior (SI) motion amplitudes (2.9–30.1mm). Each patient was planned based on a 4DCT scan. The complete time structure of the proton fields was incorporated into the simulation framework by including the time required to deposit dose, scan the beam laterally, change the beam energy and the time required for magnet settling. Changes in the 4D dose distribution resulting from altering the spot size, energy switch time, magnet settling time, initial breathing phase, spot spacing, scanning direction, scanning speed, beam current and breathing period were determined using deformable image registration. The metrics used for analysis were mean dose, minimum dose, maximum dose, dose homogeneity, equivalent uniform dose (EUD), lung V 5, V 20 and mean lung dose. Results: In general, longer delivery times led to less interplay and the interplay effect could not be predicted using motion amplitude alone. Larger spot sizes (σ ∼9–16mm) gave a EUD of 99.0% + 4.4% (1 standard deviation) of the prescription dose in 1 fraction compared to 86.1% + 13.1% for smaller spots (σ ∼2–4mm). Smaller spot sizes gave EUD values as low as 65.3% in 1 fraction. Target dose homogeneity improved with reduced spot spacing. The interplay effect can vary significantly with initial breathing phase. No definitive benefit was observed when scanning predominantly parallel or perpendicular to the SI axis. Conventional fractionation reduced interplay, giving EUD values of at least 84.7% and 100.0% for the small and larger spot sizes respectively. Conclusion: The interplay effect is highly patient specific and varies based on the motion amplitude, tumor location and various delivery parameters. This project was supported by the National Cancer Institute Grant No. R01 CA111590
TU‐A‐108‐03: Validation and End‐To‐End Testing of a New Proton Treatment Planning System
Authors: Su Z , Slopsema R , Li Z
Published: July 2013

Purpose: To perform validation of a novel Spread‐Out‐Bragg‐Peak (SOBP) modulation table method and to perform commissioning and end‐to‐end testing of the Pinnacle proton treatment planning system (TPS) for dose algorithm accuracy and clinical functionality. Methods: Beam model parameter values were determined using measurements in air and water. The effective‐SAD, virtual‐SAD, effective‐source‐size, and Bragg Peaks (BP) were calculated for each nozzle option for double‐scattering delivery in an IBA system. We then generated SOBPs for specific modulation values using a subset of BPs which produce a full plateau SOBP. Tables of modulation and BP cumulative weights were used to produce the SOBP functions for each option. Patient treatment plans for brain and prostate sites and corresponding apertures and range compensators were generated. The patient plans were copied onto a water phantom using built‐in TPS tools. Central axis depth dose profiles were measured using 1D scanning inside a water tank. Planar doses were obtained using a MatriXX 2D ion‐chamber array located at isocenter, and 2 cm upstream and downstream from isocenter. Corresponding planes and profiles were calculated and compared with measurements. Results: Comparisons between measured SOBPs for various sub‐options confirmed the novel beam model approach was clinically acceptable to within 1–3% error at the SOBP entrance region. The measured ranges and modulations were within 1 mm of calculated ones. The agreement between measured and calculated 2D planar dose data is 98% at the three different depths using 3 % and 3 mm gamma criteria. Conclusion: A novel modulation table method was validated through end‐to‐end testing of a commissioned Pinnacle proton TPS for an IBA delivery system. This approach covers all sub‐options for a given option. Analysis of agreement between calculated and measured profiles indicates that the Pinnacle proton dosimetric accuracy is comparable to our currently used commercial proton TPS. Philips Medical Systems
TU‐A‐WAB‐05: Using 4DCT‐Ventilation Based Multi‐Modality Imaging to Assess Lung Function and Optimize Radiation Therapy for Lung Cancer Patients
Authors: Vinogradskiy Y , Schubert L , Castillo R , Castillo E , Martel M , Guerrero T , Miften M
Published: July 2013

Purpose: A new form of imaging has been developed to assess ventilation‐based lung function using 4DCT. Because 4DCTs are acquired as part of thoracic simulation, calculation of 4DCT‐ventilation maps enables exciting opportunities to assess pre‐treatment lung function and create functional avoidance radiotherapy plans. The purpose of our work was to use 4DCT‐ventilation to evaluate lung function differences between stage I and III lung cancer patients and investigate strategies to adapt plans to a patients ventilation profile. Methods: We retrospectively analyzed 40 stage I and 69 stage III lung cancer patients collected from 2 different institutions. Pre‐treatment ventilation maps were calculated using the simulation 4DCT, deformable image registration, and a density‐change based model. To assess ventilation homogeneity of stage I and III patients we studied visually observed ventilation defects, an ipsilateral/contralateral ventilation ratio, and the standard deviation (SD) of lung ventilation. Plans for both stage groups were created using ventilation‐based functional avoidance maps. The feasibility and quality of plans was assessed using dose‐volume and dose‐function metrics. Results: Fifteen percent of the stage I cohort and 33% of the stage III cohort had ventilation defects. The ipsilateral/contralateral ventilation ratio was significantly different (p=0.005) between stage I (ratio=1.06) and stage III (ratio=0.83) patients. Similarly, the SD of stage I and stage III patients was significantly different (p=0.023). Representative functional avoidance plans are presented for both stage I and III groups that improve dose sparing of functional lung. Conclusion: Patients at varying stages of lung disease have different functional profiles and require unique strategies to create functional avoidance plans. We present quantitative data to highlight the impaired lung function of advanced disease patients and explore the potential of using that functional information to adapt plans to a patients ventilation profile. Our study presents an important step of incorporating 4DCT‐based ventilation imaging into the clinic.