bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐G‐137‐01: Proton Therapy Range Verification Using Prompt Gamma Rays: A Simulation Study with the Geant4 Monte Carlo Toolkit
Authors: Lau A , Chen Y , Ahmad S
Published: July 2013

Purpose: To simulate a coincidence detector system for in vivo range verification using prompt gamma (PG) emission technique for proton radiation therapy and to compare the results with the alternative technique utilizing the positron‐emitting nuclei (PEN). Methods: A coincidence detector system for characterizing both emitted and registered prompt gamma spectrum was simulated by Geant4 Monte Carlo toolkit version 9.4.9 p02. The interaction of 110 MeV protons with target phantom of PMMA (5 cm × 5 cm × 50 cm) was used in the simulation. A virtual detector (5 cm × 5 cm × 1 mm) was replicated 500 times to form a bank of detectors. A lower bank was placed 1 cm above the phantom while another bank was placed 1 cm above the lower bank. A coincidence requirement was met when a gamma had passed through both a bottom detector segment and the corresponding top detector segment directly above it. Our investigation used the built‐in physics list consisting of electromagnetic as well as nuclear interactions. Results: The depths corresponding to the maximum prompt gamma counts were found to be in close proximity to the range of protons as determined by the Bragg Peak. We noted that the PEN yields had their maximum and distal 50% yield more superficially than the Bragg Peak. This is clearly different compared to PG yields that showed their maximum in closer proximity to the Bragg Peak. The 50% distal PEN yields also lied shallower to the Bragg peak whereas the 50% distal PG yields lied deeper with respect to the Bragg Peak. Conclusion: This work shows clearly that the range of the incident protons can be measured in vivo via a suitable detector system utilizing the PG technique. More realistic simulations by implementing and optimizing various detector materials are now being planned.
MO‐G‐137‐02: Experimental Validation of Clinical as Well as Monte Carlo Dose Calculation for Proton Therapy of Lung Cancer Patients
Authors: Grassberger C , Daartz J , Dowdell S , Verburg J , Sharp G , Paganetti H
Published: July 2013

Purpose: Validate clinical pencil beam (PB) and Monte Carlo (MC) based dose calculations using a heterogeneous lung phantom and assess the clinical significance of these findings in lung patients. Methods: A modified IMRT lung phantom and a matrix‐array of ionization chambers was used to measure the distal fall‐off of the proton beam. The treatment was planned according to clinical protocols. We evaluated absolute and relative dose differences and the range where dose decreases to 50% of prescribed dose (range50). 10 patients treated with 32 beams were subsequently simulated using MC. Results: In the entrance region behind the ribs, the average deviation from the measured dose for MC and PB is 1.2% and 2.0%. Averaged over the 5 investigated depths in the distal falloff, the average error is 7.1% and 12.5% of prescribed dose for MC and PB respectively. Relative to the experimental point dose, the deviations in the distal falloff are 25.6%(MC) and 71.9%(PB). Discrepancies in relative dose in the distal falloff appear large due to the low absolute dose, sharp dose gradient and range differences. The average absolute error in range50 is 3.9mm(MC) and 7mm(PB) in lung tissue, which equals 1.3/2.3mm in water. Apart from differences in multiple Coulomb scattering caused by lateral inhomogeneities, MC generally predicts a larger low‐dose‐penumbra and lower target dose, confirmed by the measured dose profiles. These features also arise in the patients: mean dose and D95 in the clinical target volume are on average 1.8% and 2.3% lower for MC than PB, while normal lung V5 and mean lung dose increase by 5.1% and 2% respectively. Conclusion: For lung, MC increases dose calculation accuracy in the distal fall‐off significantly and reproduces measurements within experimental uncertainty. Differences in patient cases are small in the target, though at times significant in organs distal to the beam. This project was supported by the National Cancer Institute Grant No. R01 CA111590
MO‐G‐137‐04: Using Molecular Dynamics Simulation Algorithm to Overcome the Local Minima of Gradient Methods in IMPT Treatment Plan Optimization
Authors: Liao L , Cai B , Li Y , Cao W , Lim G , Li H , Zhang X
Published: July 2013

Purpose: The gradient optimization methods such as LBFGS are sensitive to starting conditions and can be trapped in local minima. Molecular dynamic (MD) simulation algorithm, a powerful computational technique used in material science, has the potential to overcome the local minima problem. The purpose of this study is to investigate whether MD algorithm can get out of the local minima, in which LBFGS will be trapped for the optimization problem in intensity modulated proton therapy (IMPT). Methods: A prostate cancer patient was selected for this study. Three different starting conditions was used to optimize the IMPT plans: (a) Forward wedge (FW), all beamlet weights are set to the same weight; (b) SOBP, beamlets weights are arranged to deliver a flat dose on the target; (c) Inverse wedge (IW), the weights are set to distal tracking like resulting very low dose on Femoral Heads. The dose‐based objective function, which only optimizes the uniformity of PTV dose, was used for both LBFGS and MD algorithms. Results: MD converged to the objective function value (OFV) of 3.46 regardless of different initial conditions. LBFGS converged to 3.68, 3.72 and 1082.6 starting with initial conditions FW, SOBP and IW, respectively. For PTV dose coverage, both MD and LBFGS achieved to similar results from FW and SOBP initial conditions. However, using IW initial condition, LBFGS was trapped into a local minimum reflected by a higher OFV and worse PTV coverage (D99=68.5 Gy) while MD converged to a lower OFV and better PTV coverage (D99=75.6 Gy). Conclusion: For the first time, we demonstrated that MD algorithm could be used in radiation therapy planning optimization to overcome the local minima problem which is a major shortcoming of gradient based algorithm widely adopted in radiation therapy optimization problem.
MO‐G‐137‐06: Evaluating Head‐And‐Neck 4pi Non‐Coplanar Plans From the Perspective of Proton Therapy
Authors: Sheng K , Dong P , Gautam A , Cheng C , Ruan D , Low D , Cao M , Lee S , Kupelian P
Published: July 2013

Purpose: Recent rapid development of non‐coplanar planning such as 4pi radiotherapy on robotic radiotherapy platform has shown marked improvements in the plan quality comparing against current coplanar plans. The efficacy of 4pi radiotherapy to significantly reduce radiation dose to normal tissue intrigues an evaluation from the proton therapy perspective. Methods: A post‐surgical head‐and‐neck patient with a tumor involving posterior right maxillary sinus was studied. A single‐level 60 Gy was prescribed to the PTV. Four treatment plans were developed including volumetric modulated arc therapy (VMAT, clinically used) using 2 partial arcs, two 4pi non‐coplanar plans using 30 1 MV and 6 MV beams, respectively, and a scanning 3‐field proton plan. The 4pi plans were generated using the convolution/superposition method and an in‐house optimization program. Both VMAT and the proton plans were generated on Eclipse (Varian). Results: All photon plans achieved 95% coverage of the PTV and less than 10% hot spots in the PTV. The proton plan showed greater dose heterogeneity in the PTV and greater high dose spillage to the surrounding normal tissue. The comparison of the maximum doses between VMAT, 6 MV 4pi and proton plans shows that for the left cochlea, it was reduced from 15.6 to 4.6 and 0 Gy; the chiasm, it was from 31 to 10.6 and 7.2 Gy; for the left lens, it was reduced from 6.2 to 1 and 1 Gy; for the left optical nerve, it was reduced from 31.5 to 16.4 and 10.9 Gy; for the brain stem, it was reduced from 28.6 to 14.5 and 14.2 Gy. Conclusion: The 4pi plan capacity to spare normal organs was benchmarked against the proton plan in a head‐and‐neck plan. 4pi plan showed remarkable potentials in approaching the proton therapy level of critical organ sparing while maintaining superior PTV coverage.
TU‐A‐103‐01: MRI QA
Authors: O' Shea M , Huff K , Reeve D , Jia G
Published: July 2013

MRI QAACR Annual Testing Requirements The ACR MRI accreditation program requires annual testing to be performed by a qualified medical physicist/MR scientist. Two of these tests are Magnetic Field Homogeneity and radio frequency Coil testing. Unfortunately, these tests are often not well understood by the medical physics community. They are often vendor specific, or require access to service protocols or passwords. In some cases they are cumbersome or impossible to perform on a particular unit. This session will give the medical physicist a better understanding of the value of these tests and guidance on how to perform them. Another portion of the annual testing is review of the technologist QA program. This is also subject to misunderstanding. Often the value of an individual test, or the proper procedures for their performance is not well understood. Guidance and recommendations for enhancing the review of the technologist QA program is also addressed in this session.

Learning Objectives:

1. Identify and understand the B0 homogeneity test tools available on manufactured MRI equipment sold today. Interpret the homogeneity field test results to ensure the magnet is shimmed properly.

2. Understand the acquisition and reconstruction of phase maps.

3. Identify the pitfalls when analyzing and subtracting phase maps.

4. Understand shimming values and how they relate to the magnetic field homogeneity.

5. Use of the Bandwidth Difference Methodology to evaluate the magnetic field homogeneity.

6. Describe different approaches to performing RF coil quality control testing.

7. Discuss methods of measuring SNR and the influence of acquisition parameters on the results.

8. Recommend information to include in the coil QC record.

9. Understand the technologist's role in the quality control program.

10. Obtain tips about the technologist's quality control test.

11. Identify common image quality problems of MRI scanners.

12. Understand the importance of efficient communication to Radiologists and Physicist Understand additional QC tests (MRS, Perfusion, Diffusion, fMRI, ADNI, etc).
TU‐A‐108‐04: An Investigation of Optimizing Proton Energies in IMPT Treatment Planning
Authors: Cao W , Lim G , Li X , Li Y , Zhang X
Published: July 2013

Purpose: In Intensity modulated proton therapy (IMPT), a set of different proton energies of pencil beams are used to create desired dose distributions. The selection of proton energies in the current clinical IMPT treatment planning is determined based on trial and error. In this study, we utilize an optimization approach to find an optimized subset of proton energies out of a given set of candidates. The treatment plan quality of IMPT plans with optimized and non‐optimized energy setups will be evaluated. Methods: A mixed integer linear programming based iterative optimization approach was introduced to find optimal proton energies from a given set of energies in IMPT treatment planning. Dosimetric measurements of treatment plans with optimized proton energies were compared with ones with conventional energy setups for four prostate cancer patients retrospectively selected at our institution for this study. Results: For four prostate cancer cases, no evident difference in dosimetric measurements was found between plans with optimized proton energies and ones with conventional energy setups, in terms of target coverage and critical structure sparing. Importantly, the number of optimized energies was approximately 20% less in average comparing with the number of energies used in conventional IMPT treatment planning. Thus, the IMPT delivery time can be shortened by reducing the energies used IMPT treatment Conclusion: With a reduction of proton energies that are used in the conventional IMPT treatment planning, we observed that there was no degrading effect in dosimetric performance of prostate IMPT plans in this study. Future studies on larger sized cancer sites may add a higher value to the research on the proton energy optimization problem in improving IMPT treatment delivery efficiency.
TU‐A‐108‐05: Quantification and Prediction of Dose Variation in Scanning Beam Proton Therapy From Setup and Anatomical Change for Single‐Field, Multi‐Field, and Robustly Optimized Plans
Authors: Li H , Park P , Zhang X , Liu W , Liao Z , Dong L , Gillin M , Zhu X
Published: July 2013

Purpose: The purpose of this study is two‐fold: 1) to study proton dose variation due to weekly patient setup and anatomy change; and 2) to evaluate the effectiveness of robustness optimization and robustness evaluation techniques. Methods: For a given patient, single‐field optimized (SFO), multi‐field optimized (MFO) and multi‐field optimized with robustness constrains (MFO‐Robust) plans were generated on a simulation CT (CT0). The robustness of the plans was evaluated on CT0 with a statistical technique to compute standard deviation of the dose‐volume histogram (SD‐DVH) of the target volumes and critical structures for 600 combinations of setup and range uncertainties. The original plans were recalculated on subsequent weekly CTs (CTn), and the dose distributions on weekly CTs were deformed onto CT0 using the Velocity (Velocity Medical Solutions) software. The DVHs of weekly doses, as well as the accumulated dose were compared on CT0 with the anticipated SD‐DVH variations predicted by the statistical plan robustness evaluation system. Results: The mean standard deviation of weekly doses for voxels within the GTV is <2%, for all techniques, the standard deviation of dose difference between the accumulated dose and the planned dose is <1% in GTV for all techniques. The DVH deviations of weekly and accumulated doses were within the 2SD‐DVH confidence interval. Conclusion: This study quantifies the weekly variation of the patient dose, and the accumulated dose variation due to setup uncertainty and anatomy change. The SD‐DVH, which is calculated at the time of planning, could be a good predictor of dose variation over the course of treatment.
TU‐A‐108‐06: Computing Proton Dose to Irregularly Moving Targets
Authors: Phillips J , Gueorguiev G , Shackleford J , Grassberger C , Dowdell S , Paganetti H , Sharp G
Published: July 2013

Purpose: While 4DCT and deformable registration can be used to assess the dose delivered toregularly moving targets, there are currently few methods available for irregularly moving targets. This study describes a method for computing the dose delivered to irregularly moving targets basedon 1D or 3D waveforms captured at the time of delivery. Methods: The procedure requires 4DCT images for dose calculation, and 1D or 3D respiratorywaveforms to estimate target position at time of delivery. Dose volumes are converted from their Cartesian geometry into a beam‐specific radiological depth space, parameterized in 2D by the beamaperture, and longitudinally by the radiological depth. In this water‐equivalent depth space, the proton doses are translated according to the motion found in the 1D or 3D trajectory. These translated dose volumes are weighted and summed, then transformed back into Cartesian space,yielding an estimate of the dose that includes the effect of the measured breathing motion. Results: The method was validated using a synthetic lung CT phantom with a mobile tumor. Simulated 4DCT was generated for the phantom with 2 cm peak‐to‐peak motion. A passively‐scattered proton treatment plan was generated using a 7 mm smearing radius. The method wastested without motion, and with two simulated breathing signals: a 2 cm amplitude sinusoid, anda 2 cm amplitude sinusoid with 3 cm linear drift. Motion‐corrected dose was computed based onthe mid‐ventilation CT image. Gamma evaluation (3 mm, 3%) was 98.7% without motion, 92.9%for 2 cm sinusoidal motion, and 98.0% with 3 cm drift. Conclusion: We have demonstrated a method for accurately reproducing proton dose to anirregularly moving target from a single CT image. We believe this algorithm could prove a usefultool to study the dosimetric impact of baseline shifts either before or during treatment.
TU‐A‐108‐07: Design and Verification of a Heterogeneous Proton Equivalent Thorax Phantom for Use in End‐To‐End Assessment of Pencil Beam Proton Therapy
Authors: Neihart J , Sahoo N , Balter P , Summers P , Palmer M , Kerr M , Followill D
Published: July 2013

Purpose: Design and commission a dynamic proton‐equivalent lung phantom for implementation as an end‐to‐end audit tool for credentialing proton therapy centers participating in proton lung clinical trials. Methods: Phantom materials were tested and chosen with relative stopping powers (RSP) similar to those found on the Eclipse tissue calibration curve. One material was determined to be in good agreement with the Eclipse HU vs. RSP calibration curve to simulate bone. A phantom was designed with materials that could be imaged, planned, and treated without need for manual adjustment of HU. The lung target was designed to simulate 2cm respiratory motion. The phantom was simulated on a 4DCT and planned on the resulting average CT images. A proton pencil beam plan was generated to cover the ITV and spare other structures, and was verified by 2‐D ion chamber array QA measurements. Image‐guided spot scanned therapy was delivered to the phantom. The film and TLD within the moving dosimetry insert were read and registered to the planned 3D dose distribution. Using TLD for absolute dose and film for dose distribution, a gamma analysis was performed in the sagittal, coronal, and axial planes. Results: A bone equivalent material was found with an agreement of 0.9% to Eclipse calculation. For the two initial spot scanned proton beam treatment deliveries, the Gamma index ranged from 86% to 73% at ±5%/5mm about an RPC/Institution ratio of 0.97 for all film planes. The regions of highest failure were found to be in the distal region beyond the target volume. The measured vs. calculated dose ratio ranged from 0.96–1.01 with an average of 0.98. Conclusion: A proton‐equivalent lung phantom, with a dynamic thoracic target, was designed and tested as an audit tool for credentialing proton therapy centers. Spot scanned therapy without motion management was determined inadequate for 2cm motion. This work was supported by Public Health Service grants CA010953, CA081647, and CA21661 awarded by the National Cancer Institute, United States Department of Health and Human Services.
TU‐A‐108‐08: Comparison of Full Intensity Modulated and Single Field Uniform Dose Proton Beam Scanning Lung Treatments
Authors: Dowdell S , Grassberger C , Paganetti H
Published: July 2013

Purpose: To determine differences in motion interplay effects between single‐field uniform dose (SFUD) and intensity modulated proton therapy (IMPT) treatments for lung patients. Methods: SFUD and IMPT treatment plans were generated for 10 lung cancer patients. The spot spacing was set to 0.7σ for all treatment plans and all plans used 2 fields delivered to the planning target volume (PTV). Treatment plans required that at least 95% of the PTV and 99% of the ICTV received the prescription dose. The ICTV was defined as the IGTV+8mm and covered the CTV in all 10 phases of the 4DCT. SFUD plans require each field homogeneously, within a given tolerance, cover the PTV, whilst IMPT has no such constraint. Monte Carlo simulations were performed using the detailed timing structure of the proton fields and the patient 4DCT for 2.5Gy(RBE) and 12Gy(RBE) fractions using 2 different spot sizes (σ ∼8–17mm and ∼2–4mm). Simulations were performed on the different phases of the patient 4DCT. The 4D dose distribution was generated via deformable image registration, using the 50% phase as the reference. Degradation in the dose distributions due to motion and interplay effects was quantified via equivalent uniform dose (EUD), V95 and dose homogeneity. Results: All values are quoted as percentages of the dose per fraction. For 2.5Gy(RBE) fractions, the average EUD loss due to interplay is 3.7+/−3.6% and 4.4+/−3.3% for IMPT and SFUD respectively for the larger spot size. For the smaller spot size, the average EUD loss for IMPT and SFUD treatments is 12.2+/−10.5% and 15.1+/−12.2% respectively. The average EUD loss for 12Gy(RBE) fractions is within 1% of the 2.5Gy(RBE) values. No significant differences between the SFUD and IMPT plans were observed for V95 and target dose homogeneity. Conclusion: No significant difference in motion effects was observed between SFUD and IMPT treatments. This project was supported by the National Cancer Institute Grant No. R01 CA111590
TU‐A‐WAB‐01: Characterization of Vascular and Proliferative Flare in Anti‐Angiogenic Therapy Using FLT PET/CT and Circulating VEGF
Authors: Scully P , Liu G , Simoncic U , Jeraj R
Published: July 2013

Purpose: Previous studies observed significant rebound of tumor proliferation and vascularization following cessation of anti‐angiogenic therapy. In this study we characterize this phenomenon in a novel anti‐angiogenic agent, using both [18‐F]FLT PET/CT and circulating VEGF. Methods: Seventeen patients with solid tumors of various histologies were treated for two weeks with Axitinib, a molecularly targeted anti‐proliferative and anti‐angiogenic agent, 5mg twice daily, followed by a one‐week treatment break. Dynamic FLT PET scans were acquired at peak drug concentration (day 12–14), and washout (day 20–21). Vasculature status was quantified using a two‐compartment kinetic model (blood volume, Vb; blood‐to‐tissue transfer constant, K1). Proliferation was quantified using both kinetic analysis (net uptake rate, Ki) and SUV‐based metrics (SUVmean, SUVmax, SUVpeak, SUVtotal). Relative change in each of these metrics during washout was assessed. Blood samples obtained pre‐treatment and at each imaging time point were analyzed for the pro‐angiogenic factor VEGF (vascular endothelial growth factor). The change in VEGF during therapy was also assessed. Results: Seven of seventeen patients showed unambiguous proliferative flare, with all four SUV metrics increasing >20% during washout. Median increases of 30% SUVmean, 50% SUVmax, 60% SUVpeak, 70% SUVtotal, and 75% Ki were observed in these patients. Increase in vascular parameters were also observed in these patients (medians 30% Vb, 80% K1). Vascular and proliferative flare were correlated across all seventeen patients (ΔSUVpeak vs. ΔK1, R = 0.59). A highly significant increase in circulating VEGF (p<0.001) occurs during the treatment period, followed by a highly significant drop (p<0.001) during the withdrawal period, to a level indistinguishable from baseline (p=0.9).Conclusion: Substantial proliferative and vascular flare were observed in many patients during Axitinib withdrawal. These phenomena were correlated, suggesting Axitinib withdrawal may open a window for effective combination therapy. Axitinib treatment strongly impacts VEGF expression levels, suggesting it successfully targets the VEGF receptor. Research funded in part by the U.W. Radiological Sciences Training Grant: 5T32CA009206‐34. Research funded in part by Pfizer.
TU‐A‐WAB‐02: Arterial Perfusion Imaging‐Defined Aggressive Subvolume of Intrahepatic Cancer for Radiation Therapy
Authors: Wang H , Farjam R , Feng M , Ten Haken R , Lawrence T , Cao Y
Published: July 2013

Purpose: To assess whether subvolumes of tumors extracted from hepatic arterial perfusion images can predict treatment outcome in radiation therapy (RT) of intrahepatic cancer. Methods: 21 patients who had 25 unresectable intrahepatic cancers and underwent focal RT were enrolled in a prospective IRB‐approved study of dynamic contrast‐enhanced (DCE) MRI. DCE MRI scans of the patients were acquired prior to RT, after delivering ∼60% planned doses and 1 month after the completion of RT. Hepatic arterial perfusion images were quantified by using a dual‐input single‐compartment pharmacokinetic model of DCE MRI. Each treated tumor was classified into the subvolumes with low‐normal, or high hepatic arterial perfusion. The changes in the subvolumes with high hepatic arterial perfusion and in the volumetric means of hepatic arterial perfusion over the whole tumors from pre‐RT to during‐RT were evaluated for differentiation of responsive and progressive tumors using Mann‐Whitney U test. The performance of the early changes in the new metrics for predicting tumor progression following treatment was evaluated by receiver operating characteristic (ROC) analysis. Results: Of the 25 tumors, 6 tumors in 5 patients progressed 5–21 months after the completion of RT, the other tumors responded to treatment. From pre‐RT to during‐RT, the tumor subvolumes with high hepatic arterial perfusion significantly increased (118%, p=0.007) in the progressive tumors compared to responsive ones. For predicting tumor progression, the change percentage in the tumor subvolume with high hepatic arterial perfusion had an area under curve (AUC) of 0.87 ± 0.09, while the change in mean hepatic arterial perfusion over the whole tumors had AUC of 0.85 ± 0.10. Conclusion: The tumor subvolume with high hepatic arterial perfusion could be an early predictor for treatment outcome in RT of intrahepatic cancer, and could be a candidate for radiation boost. (Supported by NIH grant RO1CA132834)
TU‐A‐WAB‐03: BEST IN PHYSICS (JOINT IMAGING‐THERAPY)‐Application of Raman Spectroscopy for Diagnosis of Adult and Pediatric Cancers
Authors: Devpura S , Naik R , Thakur J , Naik V , Sethi S , Sarkar F , Sakr W , Poulik J , Rabah R , Klein M , Barton K , Siddiqui F , Chetty I
Published: July 2013

Purpose: To investigate the feasibility of Raman spectroscopy for diagnosis of pre‐invasive and invasive head and neck squamous cell carcinoma (HNSCC), prostate cancer, and pediatric cancers. Methods: Human tissues were used for each tumor type and normal tissues corresponding to the respective anatomic site were included for baseline analysis. Raman spectroscopic data was compared against pathological diagnosis, for assessment of accuracy. Formalin fixed paraffin processed (FFPP) tissues were used in HNSCC and prostate cancer investigations, while both frozen and FFPP tissues were used in pediatric research. A total of 2550 Raman spectra were collected; 401 from HNSCC tissues; 1220 from prostate tissues, and 929 from pediatric tissues (normal, neuroblastoma, and ganglioneuroma). Principal component analysis (PCA) and discriminant function analysis (DFA) were carried out to classify the data. Results: In HNSCC, the Raman bands assignable to L‐tryptophan showed an increase while keratin bands showed a reduction relative to corresponding normal tissues signals. PCA/DFA analysis predicted 89% accuracy for invasive SCC relative to pathological diagnosis. Accuracy for predicting in carcinoma‐in‐situ and differentiating normal tongue tissues was 91%. For prostate cancer, distinguishable Raman spectral changes were noted for each of the following pathological states: benign epithelia, prostatic intraepithelial neoplasia, prostate cancer, and the stroma surrounding these stages. In pediatric cancers, β‐carotene, fat, and cholesterol are key biochemicals differentiating normal tissues from neuroblastoma and ganglioneuroma and, although these chemicals were impacted by the paraffin‐fixing process, Raman spectra were able to classify each category with greater than 90% accuracy in the FFPP tissues. Conclusion: These initial results demonstrate the promise for Raman spectroscopy in the diagnosis and staging of cancer at various stages of progression. We are currently investigating the potential for the use of Raman spectroscopy in the assessment of tumor and normal tissue response following radiation therapy, using animal models and human tissues.
TU‐A‐WAB‐04: A Prospective Longitudinal Study with Ultrasound Nakagami Imaging to Evaluate the Relationship Between Acute and Late Normal‐Tissue Toxicity in Breast‐Cancer Radiotherapy
Authors: Liu T , Yang X , Liu Y , Wang Y , Curran W , Torres M
Published: July 2013

Purpose: Radiation‐induced normal‐tissue toxicity is heterogeneous in nature and manifests in a wide range of severities across women who undergo breast‐cancer radiotherapy (RT). Numerous studies have investigated the relationship between acute and late toxicity based on patient‐and physician‐conducted assessments, and the results have been conflicting. We carried out a prospective longitudinal study to examine whether acute toxicity can predict late toxicity in breast‐cancer RT using quantitative ultrasound Nakagami imaging. Methods: Twenty‐two patients were enrolled following lumpectomy and all participants received whole‐breast external‐beam RT (50Gy plus a 10Gy boost). Each participant received up to 6 ultrasound scans. A baseline ultrasound scan was performed 1 week prior to RT and followed by a scan at week 6 of RT. Four additional scans were taken post‐RT at 6‐week, 3‐month, 6‐month, and 1‐year follow‐ups. Patients were imaged on both breasts with a 10‐MHz ultrasound. Nakagami shape parameter was used as a surrogate for acute and late toxicity. A Nakagami shape parameter ratio (NSPR) was generated using measurements from the irradiated breast over the contralateral breast. Clinical assessment of normal‐tissue toxicity was conducted by a radiation oncologist using RTOG toxicity scheme. A linear regression model was used to examine the relationship between acute and late toxicity. Results: The NSRP measurements correlated with RTOG toxicity. For most patients, NSPR increased during RT and up to 3 months post RT, reached the highest value between 3 and 6 months, and then started to recover. The linearregression model indicates the NSPR during RT are correlated with NSPR measured at 3‐month, 6‐month and 1‐year post‐RT (p<0.05). Conclusion: Our results based on ultrasound Nakagami imaging suggest that acute normal‐tissue toxicity predicts late toxicity (up to 1 year) following breast RT. Therefore, interventions designed to limit acute toxicity may Result in less late toxicity and improved quality‐of‐life of breast‐cancer survivors.
TU‐A‐116‐05: Evaluation of Relative X‐Ray Imaging Detector Performance Using the Metric of Relative Object Detectability (ROD)
Authors: Singh V , Jain A , Nagesh S Setlur , Bednarek D , Rudin S
Published: July 2013

Purpose: To determine the relative detectability performance of two x‐ray imaging detectors for specific clinical objects and devices. Methods: The relative object detectability (ROD) can be defined as the ratio of the integral of the detective quantum efficiency (DQE) of a detector weighted by the square of the Fourier Transform (or frequency spectrum) of the object to the same integral for a second detector. Three different detectors, namely the micro‐angiographic fluoroscope (MAF), the solid state x‐ray image intensifier (SSXII) and a flat panel detector (FPD), were assessed for their relative performance with respect to the detectability of wires and spheres. The RODs were calculated for three sets of detectors: MAF‐FPD, MAF‐SSXII and SSXII‐FPD, for wires of a fixed length of 20 mm and solid spheres made of different materials (aluminum, titanium and nickel) ranging in diameters from 100 micron to 1.0 mm to simulate endovascular devices. Results: For the 100‐micron diameter, the ROD is 1.4 [2.0] for the MAF‐SSXII and SSXII‐FPD sets and 1.9 [3.9] for the MAF‐FPD for the wire [sphere] indicating superior performance of the MAF over the FPD and SSXII and of the SSXII over the FPD for small sized objects. However, the ROD decreased monotonically as the object diameter increased and showed equivalent performance for wires with diameter over 300 microns and spheres with diameters above 400 microns. Conclusion: The ROD depends upon the physical geometry of the object and is useful in quantifying the relative performance of detectors regarding detectability of specific objects. Because of their higher spatial resolution both the MAF and the SSXII perform better than the FPD for viewing wires with diameters under 300 microns and spheres with diameters under 400 microns; however, the MAF performance is shown to be superior to the SSXII as well. NIH Grant 2R01EB002873
TU‐A‐116‐07: Comparison and Evaluation of Commercially Available CMOS X‐Ray Detectors for Neurological Endovascular Image Guided Interventions (neuro‐EIGI' s)
Authors: Loughran B , Jain A , Singh V , Nagesh S Setlur , Ionita C , Bednarek D , Rudin S
Published: July 2013

Purpose: To evaluate three commercially available CMOS x‐ray detector systems as potential dual fluoroscopic and angiographic, high‐resolution, ROI detectors for neuro‐endovascular image‐guided interventions (neuro‐EIGIs) and to compare them to other experimentally evaluated or simulated neuro‐EIGI detectors. Methods: Each CMOS detector was exposed to a standard RQA5 x‐ray spectrum obtained by adding 21 mm of aluminum to a 70 kVp x‐ray beam. Flat‐field images were acquired by each detector and exposure per frame was determined using an ion chamber. From these images and exposures, sensitivity in digital numbers (DN/μR) and instrumentation noise‐equivalent exposure (INEE) was found for each detector. These values were used to compare the three commercial detectors to other neuro‐EIGI detectors previously built or simulated. Results: Detector A has a 12‐bit ADC, a pixel size of 100 μm, and a full well capacity (FWC) of 2.2 million electrons (Me‐). The sensitivity was found to be 5.8 DN/μR and the INEE was found to be 7.58 μR. Detector B has a 14‐bit ADC, a pixel size of 75 μm, and a FWC of 0.36 Me‐for the high sensitivity mode and 1.4 Me‐for the high saturation mode. The sensitivity was found to be 28.9 DN/μR and the INEE was found to be 2.04 μR in the high sensitivity mode. Detector C has a 14‐bit ADC, a pixel size of 100 μm and a FWC of 1.5 Me‐. The sensitivity was found to be 15.1 DN/μR and the INEE was found to be 3.04 μR. The previous neuro‐EIGI detectors had similar sensitivities of 10s–100s DN/μR, but much lower INEEs of <0.2 μR. Conclusion: While the commercial CMOS x‐ray detectors are improving, it remains a desirable goal to further reduce the commercial detector pixel size and instrumentation noise to approach the values seen with the previously built and simulated neuro‐EIGI detectors. Supported by NIH Grant 2R01EB002873 and an equipment grant from Toshiba Corporation.
TU‐A‐116‐09: Real‐Time Plastic Scintillation Dosimeter for Fluoroscopically‐Guided Interventional Procedures
Authors: Boivin J , Guillemette M , Beaulieu L
Published: July 2013

Purpose: To monitor and measure, in real‐time, patient skin dose during fluoroscopically‐guided interventional (FGI) procedures using a novel plastic scintillation dosimeter (PSD). Methods: A clear optical fiber of 1 mm diameter, 10 m long, is optically coupled to a plastic scintillation fiber (BCF‐60) of 1 mm diameter, 10 mm long. On its other end, the clear fiber is connected to an avalanche photodiode, APD (C4777‐01, Hamamatsu). An electrometer collects the APD charge and displays live graph and dose values. Initial calibration is achieved with a NRC calibrated Farmer‐type ionization chamber (Exradin A12, Standard Imaging). The PSD and the chamber are set on an Allura Xper Fd10/10 (Philips) intervention table at the Air Kerma reference point, 150 mm below isocentre. In compliance with TG‐125 data collection methodology, slabs of solid water are gradually added over the instruments. In order to preserve image quality, the automatic controls increase tube current and kVp accordingly. Acquisitions are made in both cine‐fluorography and fluoroscopy operation modes, at 15 frames/s. Measurements were repeated by replacing the solid water by an Alderson RANDO phantom, with image intensifier as close as possible of the surface to replicate clinical protocols. Results: The calibration curves indicate that PSD response is linear below 80 kVp, but exhibits a quadratic behavior above, with a rate of 20–40 pA/mGy over Air Kerma Rate range of 0.10–16 mGy/s. The PSD can read dose rate as low as 1.7 mGy/s ± 5 %. However, uncertainties rise above 10 % for dose rate less than 1 mGy/s. Phantom measurements indicate that the dosimeter is accurate for clinical applications. Conclusion: A PSD has been calibrated and tested in order to monitor and measure low dose rates involved in FGI procedures in real‐time. The next steps will include Monte Carlo calculations to assess accuracy before starting clinical procedures.
TU‐C‐108‐08: Characterization of a Fiber‐Taper CCD Photo‐Counting System for Plastic Scintillation Dosimetry and Comparison to the Traditional Lens System
Authors: Gagnon L , Beddar S , Beaulieu L
Published: July 2013

Purpose: To build a lens‐less CCD photo‐counting system for plastic scintillation dosimeters (PSDs), characterize its signal‐to‐noise ratio (SNR), its dose and dose‐rate sensitivity, and compare it to traditional CCD+lens optical systems. Methods: The detector used in this study is made of a 1 mm diameter by 2 mm long BCF60 scintillating‐fiber coupled to a 2.6 meters clear plastic fiber. This PSD is coupled to two different photon‐counting systems. The first is composed of a fiber‐taper system (FTS) of a 2048 × 2048 pixels attached to an uncooled Alta (Apogee) 4020 polychromatic CCD‐camera and a second one consisting of a 1600 × 1200 pixels, Alta (Apogee) 2020 polychromatic CCD‐camera (cooled to ‐ 18°C) using a 50 mm lens of F#=1. The same identical dose measurements were made under the same irradiation conditions. For both systems, the chromatic Cerenkov removal method is used to account for the stem effects. Results: The FTS increases the light collection by a factor of 4. This gain is possible because we are no longer restricted by the geometric limitation or the optical aberration of a lens system. Despite a difference of 45°C in operating temperature, we observed a SNR 1.8 times higher. This produces a good stability of measure vs. integration time with at most 1% difference on low‐dose measurements. This also reduces by at least a factor of 2 the uncertainties, allowing us to realize low‐dose measurements of 1.0 and 0.5 cGy with accuracy of 3.4% and 5.6% vs. 5.8% and 15.9% for the lens‐based system. Conclusion: This study demonstrates the superiority of the simpler FTS over a lens‐based system. It opens the possibility of using PSDs of smaller radii (125 micron) to obtain greater spatial resolution. Reducing the size of PSDs could further simplify their use for in‐vivo monitoring and small field dosimetry. Development and funding supported by Standard Imaging.
TU‐C‐108‐10: Development of An Absorbed Dose to Water Primary Standard for HDR Ir‐192 Brachytherapy Based On the Fricke Dosimetry System
Authors: El Gamal I , Cojocaru C , Mainegra‐Hing E , Ross C , McEwen M
Published: July 2013

Purpose: To develop a Fricke based absorbed dose standard for HDR Ir‐192 brachytherapy that will give a significantly lower uncertainty on the dose to water at 1 cm compared to methods based on air‐kerma standards. Methods: A ring shaped PMMA Fricke holder was developed to allow measurements to be conducted in a water phantom with the Fricke volume centred at 1 cm from the source. The seed was positioned at the ring centre to allow for a uniform irradiation geometry. The radiation chemical yield of Ferric ions, or G‐value, was determined at 250KVp X‐ray and at Co‐60 and a linear interpolation of effective photon energies allowed the determination of the G‐value at Ir‐192. Using this interpolated G‐value the radiation induced change in the Fricke solution's optical density could then be related to the absorbed dose to water at 1 cm. Results: The G‐value experiments yielded values for 250 KVp X‐ray and Co‐60 of 1.56 umol/J and 1.61 umol/J respectively. The uncertainty in the G‐value for Ir‐192 photon energies is estimated to be around ±1%. The absorbed dose to water using the Fricke system was calculated and compared with the value obtained via an air‐kerma measurement and TG‐43 agreement was obtained within the combined uncertainties. An uncertainty analysis of the Fricke system indicates an overall uncertainty of 1.2% to 1.5% (for dose at 1 cm) is achievable. Conclusion: This work demonstrates the ability to reduce the standard uncertainty for Ir‐192 HDR brachytherapy sources by using a Fricke chemical dosimeter that measures the absorbed dose to water directly and allows measurements to be conducted in the quantity of interest. The overall uncertainty is on par, or better than current water calorimetry based methods.
TU‐C‐108‐12: A New Technology for Fast Two‐Dimensional Detection of Proton Therapy Beams
Authors: Hollebeek R , Newcomer M , Mayers G , Delgado B , Shukla G , Maughan R , Dolney D
Published: July 2013

Purpose: The authors have developed a novel detector technology for proton therapy dosimetrywith fine spatial and time resolution. New dosimetry technology tailored to proton therapy willreduce the uncertainties in beam characteristics, assist in the development of new and moreadvanced therapy‐supporting technologies, facilitate more rapid delivery and commissioning ofnew particle therapy facilities, and allow more comprehensive Quality Assurance measurements. Methods: The Micromesh Gaseous Structure, or Micromegas, is a technology developed for highcount‐rate applications in high‐energy physics experiments. Presented here are tests using aMicromegas chamber and specially designed amplifiers and readout electronics adapted to therequirements of the proton therapy environment and providing both excellent time and high spa‐tial resolution. Several iterations of Micromegas prototypes have been fabricated and assembled.Data has been collected with these prototypes in proton therapy beams to demonstrate the capa‐bilities and limitations of this new technology. Results: The digitized ionization signal from the chamber is found to be reproducible to betterthan 0.8%. Spatial resolution is determined to be 1.1 mm (1σ) at 1 ms time resolution. We resolvethe range modulator wheel rotational frequency and the thicknesses of its segments and showthat this information can be quickly measured owing to the high time resolution of the system. Oursystem resolves the high dose rate within a proton Bragg peak and measurements agree with aparallel‐plate ionization chamber (PTW 34070) to better than 1%. Conclusion: We have demonstrated an adaptation of Micromegas as a beam monitor for protontherapy, and the data indicates that Micromegas holds promise as a high spatial and time resolu‐tion measurement device. Systems of this type will be useful in future treatment methods involvingbeams that change rapidly in time and spatial position.
TU‐C‐141‐09: An Automated Workflow for Patient‐Specific Verification of Deformable Image Registration
Authors: Kirby N , Morin O , Ueda U , Nie K , Chen J , Pouliot J
Published: July 2013

Purpose: To develop an automated workflow for patient‐specific verification of deformable image registration (DIR). Methods: The central concept behind this verification process is digitally applying test deformations to patient images and comparing to those returned from clinical DIR algorithms. The patient‐specific nature of these test deformations is the novel feature of this workflow. First, a set of different test DIR algorithms is applied to the original clinical images. The deformations produced by these algorithms represent plausible deformations and are applied to the clinical moving image, producing a set of test fixed images. A combination of computed‐tomography images of a water phantom with frequency‐domain image filtering is utilized to first remove image noise and then reintroduce distinct noise fluctuations on the moving and fixed test images, which would otherwise skew DIR error evaluation. The clinical algorithm is then applied to the set of test images, which yields a set of theoretical deformations. For each image voxel, the set of theoretical deformations are compared to those actually applied. The maximum discrepancy in each direction becomes the theoretical uncertainty for that voxel on the clinical image. This creates an uncertainty vector field, which can be applied to patient contours and dose to evaluate potential clinical errors from DIR uncertainty. The results of this process are benchmarked against an anthropomorphic pelvic phantom, which possesses a measured ground‐truth deformation. Results: The theoretical DIR uncertainties from the workflow gave an accurate indication for the spatial location of the actual errors, but tended to overestimate the error magnitude. The maximum theoretical uncertainties in the anterior and lateral directions were 15.4 and 11.5 mm, respectively, compared to the maximum measured errors of 12.6 and 3.0 mm, respectively. Conclusion: This workflow demonstrates the ability to perform automated patient‐specific verification for DIR. Further work to develop the method is ongoing.
TU‐C‐141‐11: Dosimetric Consequences of Deformable Image Registration Errors for Lung SBRT Patients
Authors: Zhong H , Kim J , Glide‐Hurst C , Chetty I
Published: July 2013

Purpose: To quantify the consequence of deformable image registration (DIR) errors on the total dose calculated for lung SBRT patients. Methods: 4DCT images were acquired from three lung SBRT patients who had lesions in the upper, middle and lower lobes of lungs. From their end‐inhale (EI) CT image, finite element models were developed to generate different sets of displacement vector fields (FEM‐DVFs). With these DVFs, mid‐and end‐exhale (EE) phase images were created from the EI images using a subvoxel‐based, mass mapping method. The simulated images were registered to the EI image using Elastix software, and the resultant DVFs were compared with the FEM‐DVFs to quantify registration errors at each image voxel. IMRT plans were developed with Pinnacle on simulated maximum intensity projection (MIP) images, and recalculated on each simulated phase image. The resultant dose was warped back to the EI image using both FEM and Elastix DVFs. Relative dose error was quantified via the difference between the two warped doses divided by the prescribed target dose. The dosimetric impact index was then calculated as the ratio of the relative dose error to the registration displacement error at each image voxel. Results: The mean registration errors evaluated in PTV for the three patients were 1.6, 1.9 and 1.7 mm, and their corresponding dosimetric impact indices were 4.2, 6.1 and 4.9%, respectively. The dosimetric impact indices averaged in PTV, ITV, lung and patient volume for these patients were 5.1, 4.4, 0.4 and 0.7%, and their corresponding standard deviations were 8.1, 7.0, 3.3 and 4.3%, respectively. Conclusion: The impact of DIR errors on dose accumulation has been quantified with patient‐specific FEM‐based breathing models. The dosimetric impact indices derived could help assess the quality of dose mapping for lung SBRT patients. The research was supported by NIH/NCI R01CA140341.