bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐A‐217A‐07: Predicting Residual Disease for NSCLC Using Pre‐Radiotherapy 4D PET/CT
Authors: Yue Y , Aristophanous M , Chen A , Killoran J , Yap J , Berbeco R
Published: June 2012

Purpose: To quantify PET treatment response using a novel image registration approach, and to investigate the impact of 4D PET/CT pre‐ radiotherapy scan for predicting residual high‐uptake areas toward dose‐ boosting in adaptive radiotherapy. Methods: 3D and 4D FDG‐PET/CT scans were obtained from ten patients with non‐small cell lung cancer (NSCLC) for approximately two weeks before radiotherapy (pre‐RT) and approximately one month after therapy (post‐RT). The 4D scan was taken immediately following a 3D PET scan. The areas of high uptake in the pre‐ RT scans were aligned with those in the post‐RT scans using a novel rigid‐ penalized deformable registration. The global lung bronchi and chest wall were non‐rigidly transformed to minimize the respiration effects while the target lesion is rigidly transformed to preserve the volume and SUV values. A region of interest (ROI) was defined by a threshold of 40% of the maximum SUV for both 3D and 4D PET scans. The maximal SUV within the ROI were measured. Volumetric overlap fraction (VOF) was calculated as the overlap volume of pre‐RT and post‐RT target volumes divided by the residual volume in the post‐RT scans. Results: The maximal SUVs for 4D pre and post PET have a 16.3% increase compared to those in 3D PET. The pre‐to‐post maximal SUV variations showed 57% lesions has nontrivial residual uptake (SUVmax>2.5) for 3D PET, and 64% for 4D PET. The results of the VOFs showed that the residual metabolic‐active areas are mainly located within the primary tumor volume, 92% for 3D and 89% for 4D. Conclusions: Residual metabolic‐active areas have strong physiological and geometric correspondence to the primary tumor. With better signal recovery than standard 3D PET, high uptake areas of 4D PET pre‐RT can predict areas where residual metabolic activity will be found after radiotherapy.
WE‐A‐217A‐09: Evaluating Radiation‐Induced White Matter Changes in Patients with Recurrent Malignant Gliomas under Treatment of Stereotactic Radiosurgery Using Diffusion Tensor Imaging
Authors: Chang Z , Kirkpatrick J , Cai J , Wang Z , Yin F
Published: June 2012

Purpose: Stereotactic radiosurgery (SRS) has been an effective treatment for brain tumors; however, few data are available regarding radiation‐ induced white matter (WM) damage by SRS. WM is generally vulnerable to radiation, which may compromise sensory and neurocognitive functions. In this work, diffusion tensor imaging (DTI) was used to assess WM changes following SRS. Methods: In this study, 15 patients with recurrent, unifocal malignant gliomas were enrolled. The prescription dose ranged from 16Gy to 26Gy. Patients were scanned with MRI 1–4 days before and 7‐day and two‐month after SRS treatment. All MR scans including DTI were acquired on a 1.5T clinical scanner. DTI scans were acquired axially using a spin‐ echo echo‐planar imaging sequence (TR = 9,100ms, TE = 98ms, field‐of‐ view = 30×30cm2, matrix size = 128×128, slice thickness = 5mm, b = l,000s/mm2). Diffusion tensors were calculated and fiber tracking was performed. Tract seeding is performed within a defined volume of interest (VOI). In the study, the volumes of WM receiving dose > 5Gy were contoured as VOIs. Diffusion coefficient , fractional anisotropy (FA), number of fibers (NF) were statistically calculated. Wilcoxon signed‐rank test was used to assess the differences, with statistical significance at p < 0.05. Results: After 7 days of SRS,  increased by approximately 1% (p= 0.53), and FA decreased by 1.8% (p = 0.17) with 24% decline of NF (p = 0.12). After two months of SRS,  increased by 2.3% (p= 0.36), and FA decreased significantly by 6.8% (p <0.01) with nearly 40% decline of NF (p = 0.02). Conclusions: DTI data indicated compromise of WM fiber integrity after SRS, which shall not be ignored. These preliminary results suggest that dose sparing to white matter should be considered in SRS, particularly when the target is close to white matter fiber bundles such as genu and splenium.
WE‐A‐218‐02: Assessing the Repair of DNA Damage from Multi‐Pass CT Protocols
Authors: Elgart SR , Khatonabadi M , McNitt‐Gray M , Ruehm S , Adibi A , Iwamoto K
Published: June 2012

Purpose: To determine whether radiation damage is additive for fractionated doses at diagnostic levels using mouse tumor infiltrating lymphocytes (Til) in an in vitro assay. Methods: Til cells placed in the center chamber of a CDTI head phantom were irradiated using a Multidetector row CT scanner (Siemens Sensation64). 20mGy, 40mGy or 60mGy (reported CTDIvol values) irradiations were performed by either a single pass or multiple passes of 20mGy separated by 2 minutes. The cellular response to DNA double strand breaks (DSBs) was quantified by flow cytometric quantitation of gammaH2AX foci 1hr post‐irradiation at room temperature. Non‐irradiated controls were included for each sample. Collected flow cytometry data, corrected for debris and dead cells using side and forward scatter gating, were analyzed with CellQuest Pro Software. Fluorescence histograms were generated and median fluorescence of each treatment sample was compared to respective controls and excess gammaH2AX signal was reported. Results represent the average from three independent experiments. Results: A linear, dose‐dependent response of excess gammaH2AX signal was observed for single pass doses of 20– 60mGy. However, in cells exposed to multiple passes of 20mGy, a significant decrease (P<0.05) in excess gammaH2AX signal was observed compared to equivalent single pass doses. Conclusion: These preliminary results suggest multi‐pass CT protocols may alter the biological response to DNA DSBs in vitro, with significantly reduced gammaH2AX signal when the same total dose is fractionated, even with very short inter‐fraction intervals (minutes), rather than delivered as a single exposure. Kinetic analysis is necessary to determine whether this reduction is due to increased repair rate or decreased repair capacity. This altered response could have marked implications for current diagnostic procedures and thus underscore the importance of understanding how imaging protocols may affect the biological response in order to accurately assess risk estimates and biological dose. This work is partially supported by a SIEMENS Corporation research grant.
WE‐A‐218‐06: A Practical Method of CT Radiation Dose Adjustment for Patient Size and Tissue Composition
Authors: Lu Z , Nickoloff E , Dutta A , So J
Published: June 2012

Purpose: The CTDIvol displayed on CT scanners is not patient specific. A practical method to estimate CT dose corrected for patient size, tissue composition, and anatomical location is presented. Methods: The measured CTDIvol of acrylic cylindrical phantoms of diameters from 6–32 cm on a CT scanner revealed a logarithmic relationship with the phantom mass. The relationship has been used in 25 cases of each category of adult head, chest, abdomen and pelvic CT exams. Actual patient CT images have been used to measure the average CT numbers within image slices which are subsequently related to the total tissue mass. By applying the relationship between the actual CTDIvol and the total mass, the CT radiation dose has been adjusted for patient size and tissue composition. Results: Overall, dose underestimation by the scanner dose report is well demonstrated in all 25 cases of adult chest exams (ranging from 9% to 80% under‐estimation) because the lung tissue density is significantly lower. Even in the abdomen, which has a more consistent soft tissue density, there are adipose tissues and voids that complicate the dosimetry. The pelvis contains considerable amounts of bone, which has a much higher attenuation coefficient than soft tissues, complicating the estimation of radiation doses. Also, there is a significant variation in actual patient sizes even among adult patients; thus leads to a spread in actual CTDIvol delivered to these patients. Conclusions: There is a nationwide effort to monitor patient CT dose. Because the current scanner‐reported dose may underestimate the patient dose when the patient size is smaller than the assumed standard or the tissue density is lower, excessive dose outliers may be undetected. This is more likely to happen to pediatric patients. We present a practical method to provide a more accurate estimate of patient CT radiation dose.
WE‐A‐218‐07: Linear Relationship between Average (global) and Regional Average Tube Current (mA) in Tube Current Modulated CT Scans
Authors: Khatonabadi M , McNitt‐Gray M
Published: June 2012

Purpose: Previously we have shown the importance of implementing region and/or organ‐specific CTDIvol values for tube current modulated (TCM) scans to better quantify scanner's output at a specific table location in TCM CT scans. Extracting and averaging organ‐specific mA values from the DICOM header is a tedious task. Therefore, the purpose of this study was to investigate the relationship between average mA over the entire scan and regional and organ‐specific average mA. Methods: Within a scanner the TCM algorithm performs equally across patients and similar TCM trend is usually been observed among patients, unless there are certain improper positioning of the patient, e. g. arms within the scan FOV in thoracic scans. This suggests a possible high correlation between global and regional average mA. A MatLab code was written to extract tube current values and table location for all of our voxelized patient modes. For specific organs and regions table locations were looked up and average mA values were calculated. For five organs these organ‐specific mA values were compared to the global, scanner‐reported average mA by conduction regression analyses. Results: Regional average mA is linearly proportional to the global average and can be estimated using regression equations instead of extracting every single value from the image and averaging them. The R2 values of the linear regression equations are 0.80, 0.85, 0.90, 0.90, 0.92, and 0.99 for spleen, kidneys, liver, abdomen, breasts, and lungs, respectively. Conclusion: We have shown that region‐ and organ‐specific average mA calculations, from which a region‐ and organ‐specific CTDIvol can also be calculated, can be estimated using the global average mA. Furthermore, the calculated correlations can be increased if the organ‐specific average mA are calculated using detail TCM function, which includes the angular modulation of tube current as well, rather than utilizing the image data.
WE‐A‐218‐10: The Tradeoff between Diagnostic Performance and Radiation Dose for CT Imaging in the Diagnosis of Appendicitis Across Observers with Various Levels of Experience
Authors: Zhang D , Khatonabadi M , Jude C , Zaragoza E , Kim H , Lee M , Andrews‐Tang D , Poon C , Douek M , Patel M , Doepke L , McNitt‐Gray S , Cagnon C , DeMarco J , McNitt‐Gray M
Published: June 2012

Purpose: To investigate the tradeoffs between radiation dose and diagnostic performance in CT for a challenging clinical task (diagnosis of appendicitis). Methods: This IRB approved study utilized data for 20 patients undergoing clinical CT exams for indications of appendicitis. Medical records were reviewed to establish true diagnosis and identified 10 positive and 10 negative cases. Original (100%) and simulated reduced dose levels (70%, 50%, 30%, 20% of original) were created with a validated software tool using raw projection data from each scan. An observer study was performed with 6 radiologists (of different training and cross‐sectional reading experience) reviewing each case at each dose level in stratified random order over several sessions. Readers assessed image quality and provided confidence in their diagnosis of appendicitis, each on a 5 point scale. Receiver Operating Characteristics (ROC) curves were generated for each dose level using all rating levels and from the resulting ROC curves, the AUC (Area under curve) was calculated for each dose level. This analysis was repeated for groups of readers with different experience levels. Results: The ROC curves averaged over all 6 observers and corresponding AUC values showed indifferent performances for all the dose levels. For the 2 non‐abdominal trained, occasional CT readers, the performance did not decrease until 30% dose level. For the 2 non‐abdominal trained, routine CT readers, the performance did not decrease until 20% dose level. For the 2 abdominal trained, routine CT readers, the performance is consistent across all the dose levels. Conclusions: This preliminary study demonstrated the tradeoffs between radiation dose and diagnostic performance and indicated that: (a) There is essentially no difference between diagnostic performance of 100%, 70%, and 50% dose level for all 6 observers. (b) For abdominal CT specialists, the diagnostic difference is not substantially compromised even at 20% dose levels. (c) For non‐abdominal trained CT readers, the performance declines at 30% and 20% dose levels. For Michael McNitt‐ Gray: Institutional research agreement, Siemens AG Recipient research support Siemens AG
WE‐B‐213AB‐01: AAPM TG1S7: An Overview of Source Modeling and Beam Commissioning for Clinical Monte Carlo
Authors: Ma C
Published: June 2012

The Monte Carlo method is the most accurate dose calculation method for radiotherapy treatment planning and several commercial vendors have implemented Monte Carlo dose calculation algorithms for photon and electron radiation therapy treatment planning. The AAPM task group 157 was formed to deal with the source modeling and beam commissioning issues for the clinical implementation of Monte Carlo algorithms and a report has been produced to summarize the source models used by the commercial vendors and the beam commissioning recommendations by TG 157. This is the first presentation of this educational session on the TG 157 report and related topics. A brief introduction will be given of the basics of Monte Carlo dose calculation and methods developed for source modeling and beam commissioning for clinical Monte Carlo dose calculation. This will be followed by a brief introduction to the TG157 report that will provide some background information on the two following presentations.

Learning Objectives:

1. Understand the basics of Monte Carlo radiation transport

2. Understand the methods for Monte Carlo source modeling and beam commissioning

3. Understand the goals and scope of the AAPM Task Group 157
WE‐B‐213AB‐02: AAPM TG‐157 Recommendations on Beam Commissioning for Clinical Monte Carlo Dose Calculation
Authors: Chetty IJ , Faddegon B , Ma C
Published: June 2012

Monte Carlo (MC) dose calculation algorithms are currently available for routine clinical planning in several commercial treatment planning systems. As noted in the AAPM Task Group Report No. 105 on issues associated with clinical implementation of MC dose algorithms, there are several fundamental differences between MC and other algorithms that need to be considered in the clinical commissioning process. The AAPM Task Group 157 was formed to provide comprehensive information on the factors relevant to source modeling and beam commissioning of MC dose algorithms. The TG‐157 report was charged to provide prescriptive guidelines to medical physicists as they embark on acceptance testing and clinical commissioning of these algorithms prior to clinical use. This lecture will focus specifically on the topic of beam commissioning

Learning Objectives:

1. Understand the basic components of the MC dose algorithm which need to be considered during clinical commissioning. Understand the beam commissioning requirements associated with different beam models.

2. Understand the types of verification measurements necessary for accurate clinical commissioning of MC beam models and the criteria for acceptable agreement between calculations and measurements.

3. Understand the issues associated with accurate benchmark measurements for beam modeling, especially under circumstances of charged particle disequilibrium.
WE‐B‐213AB‐03: AAPM TG‐1S7: Commercial Implementation of Source Modeling and Beam Commissioning for Clinical Monte Carlo Dose Calculation
Authors: Faddegon B , Ma C , Chetty I
Published: June 2012

Monte Carlo simulation for dose calculation is available in several commercial treatment planning systems. A range of source models and beam commissioning methodology is available with the different systems. Source models are currently analytical or hybrid models, combining Monte Carlo simulation with analytical approaches. The models are characterized by measurement. In this lecture, source modeling and beam commissioning for dose calculation with the Monte Carlo method employed in 5 commercial treatment planning systems will be reviewed. For x‐rays: iPlan (BrainLAB), Monaco (Elekta), and Multiplan (Accuray). For electrons: Eclipse (Varian Medical Systems), and Oncentra MasterPlan (Nucletron). The beam modeling approaches will be compared and contrasted, based on published source models and information provided by the vendors.

Learning Objectives:

1. Understand the different source models used in commercial planning systems for dose calculation with the Monte Carlo method.

2. Understand how these source models are commissioned.
WE‐B‐213CD‐01: International Actions on Radiation Safety in Fluoroscopic Procedures Performed Outside Radiology Departments
Authors: Rehani M
Published: June 2012

Fluoroscopic guided procedures are increasingly being performed outside main radiology departments particularly in operation theatres. In some procedures the patient dose per procedure falls in the range of 5 to 30 mSv of effective dose and in some others local radiation is high enough with risks of radiation induced skin injuries. Generally most fluoroscopy machines used in operation theatres do not have protective lead glass screens for operators and other staff and thus there is possibility of higher exposure to staff. There has been general lack of training in radiation protection of doctors performing these procedures. Medical physicists are often asked to provide training or advice in such situations. International Commission on Radiological Protection (ICRP) has recently finalized a publication under the chairmanship of the presenter which is going to be published as Annals of ICRP 117. It deals with radiological protection aspects in vascular surgery, urology, orthopaedic surgery, obstetrics and gynaecology, gastroenterology, anaesthetics & pain management and sentinel lymph node biopsy. The IAEA has made available training materials as ppt slides on this subject that can be downloaded free and members of AAPM can effectively use. The IAEA has conducted training programs in which specialists from more than 35 countries have participated. The presentation shall review the work of ICRP and IAEA in this area in many countries.

Learning Objectives:

1. To understand radiation doses and risks to patients and staff in fluoroscopic guided procedures performed outside radiology such as in operation theatres

2. To become familiar with recent international resources in this area

3. To understand radiation protection methods as applicable in specific situation of procedures in operating theatres
WE‐B‐213CD‐02: NCRP‐168 as a Training and Operational Resource
Authors: Balter S
Published: June 2012

NCRP Report 168 provides guidance on facilities as well as on patient and worker radiation safety during fluoroscopically guided interventions (FGI). Fluoroscopy is widely used in surgical settings in ways that can be comparable to its use in other FGI procedures. Surgical fluoroscopes range from simple mobile analog C‐arms, heavy mobiles with most of characteristics of a fixed system, to state of the art fixed systems. Patient and worker radiation safety concerns along with training, credentialing, and privileging of surgical staff are similar to those for all other FGI procedures. Recommendations relevant to the surgical setting will be reviewed. Two key recommendations are: An FGI procedure shall be performed or supervised only by a physician or other medical professional with fluoroscopic and clinical privileges appropriate to the specific procedure. An FGI procedure shall be performed or supervised only by a physician or other medical professional with fluoroscopic and clinical privileges appropriate to the specific procedure. Other topics such as responsibilities of all workers for their own radiation protection, those of the attending surgeon for patient dose management and follow‐up, and those of the facility for providing necessary resources will also be briefly discussed.

Learning Objectives:

1. To understand the responsibilities of surgeons and others working in a FGI environment toward patient and worker radiation safety.

2. To understand radiation protection requirements and actions necessary for personal safety while radiation is in use in a surgical environment

3. To gain familiarity with the knowledge base needed to safely perform or supervise FGA procedures in the surgical environment.
WE‐C‐211‐03: IOMP Role on the International Stage
Authors: Nuesslin F
Published: June 2012

The Senegalese Authority for Radiation protection and Nuclear Safety (ARSN), placed under the supervision of the Prime Minister, was setting up by the Law 2009‐14 relating to nuclear security and to radiation protection which repeals and replaces the opposite measures of the Law 2004‐17 relating to protection against ionizing radiations. The implementation of the ARSN enters within the scope of the international commitments of the Senegalese Government. Indeed, the member states of the International Atomic Energy Agency, the IAEA, participate collectively, through the structures of the Agency or in bilateral cooperation, in the implementation of the programs of radioprotection. Furthermore, from the moment a state makes a commitment in the implementation of nuclear programs, it has to set up the adequate legal framework. So, the global aim of ARSN is to regulate activities involving nuclear materials or radioactive sources and to control the traffic of such materials within the country. To that effect, all activities involving radiation exposure are subjected to regulatory control by a system of notification, authorization by registration or licensing and inspection. ARSN has the mandate to advise the Government on matters relating to radiation protection and disposal of radioactive waste; and to provide an effective national framework for the safety and security of radioactive sources and radiological installations, including physical protection. While the ARSN is specific to Senegal, other countries within Africa may have similar laws pertaining to local regulations that will also most likely be different. We will provide a brief overview of ARSN and how it applies to some of the activities within Senegal, including industrial and medical. When possible, notifications and/or comparison with other similar authorities within the African continent will be made.
WE‐C‐BRB‐04: Fast and Accurate Hybrid Source Model for Modulated Electron Radiotherapy
Authors: Papaconstadopoulos P , Seuntjens J
Published: June 2012

Purpose: To develop a highly accurate and fast method for calculating electron beam dose distributions in Modulated Electron Radiation Therapy (MERT). Method: An algorithm has been developed for creating phase‐ space files at the exit of a linear accelerator for any arbitrary intensity and energy electron beam without the need of full Monte Carlo simulations. The model assigns each particle to one of the 3 following sources: primary, secondary collimator and electron collimator scatter. The primary component is derived by fast MC transport in air. The scatter components are derived by the use of MC pre‐calculated leaf kernels. Each kernel includes the fluence distribution, energy distribution and scatter probability of generating an electron from a leaf. The original position is sampled from Gaussian or uniform distributions. The direction is estimated by geometrical means. According to the projection of the direction, a particle is rejected if it is expected to suffer a leaf‐hit. A leaf‐hit counter is used to calculate the output of scatter particles based on the pre‐calculated scatter probabilities. To account for multiple coulomb scattering in air a MC‐corrected version of the Fermi‐Eyges scattering theory was implemented. Results: Depth and profile dose distributions were derived for the largest and smallest square field sizes, as well as for irregular and off‐axis fields. The model agreed with full MC dose distributions within 3% in all cases. Output at the depth of maximum dose exhibited discrepancies less than 2.6% in all cases. The model was 16–22 times faster in generating a phase‐space file than a full MC simulation with the BEAMnrc code. Conclusions: Fast, dynamic electron beam calculations open up the possibility for real time delivery of MERT in the clinic and renew interest in electron beam therapy.
WE‐C‐BRB‐06: Clinical Impact of Uncertainties in the Mean Excitation Energy of Human Tissues during Proton Therapy
Authors: Besemer A , Paganetti H , Bednarz B
Published: June 2012

Purpose: Uncertainties in the estimated mean excitation energies (I‐value) needed forcalculating proton stopping power can be in the order of 10–15%, which introduces afundamental limitation in the accuracy of proton range determination. Previous efforts havequantified shifts in proton depth dose distributions due to I‐value uncertainties in homogenoustissue phantoms. This study is the first to quantify the clinical impact of I‐value uncertainties onproton dose distributions within patient geometries. Methods: A previously developed Geant4 based Monte Carlo code was used to simulate aproton treatment plan for prostate cancer with varying tissue I‐values. A total of five cases weresimulated using nominal I‐values as well as I‐values modified by ±5% and ±10% of the nominalvalues. Dose volume histograms were generated for the GTV, CTV, PTV and relevant organs‐at‐risk (OARs). Results: Modification of tissue I‐values impacted both the proton range and SOBP width. D90range shifts up to 4 mm from the nominal range were recorded whereas D80 range shiftsreached up to 2 mm. For an increase in I‐value of 10% of the nominal value, the increase inrange and SOBP width resulted in a 1.4% decrease in the CTV mean dose. Inversely, decreasing the I‐value by 10% increased the CTV mean dose by 0.8%. The difference in themean dose to the OARs was relatively small except for the rectum that differedby up to 5%. Conclusions: This study demonstrated that the impact of I‐value uncertainties on patient dosedistributions. Clearly, sub‐millimeter precision in proton therapy would necessitate reduction in I‐value uncertainties to ensure an efficacious clinical outcome.
WE‐C‐BRB‐07: Benchmarking of the TOPAS Monte Carlo System against Phantom Dose Measurements in Proton Therapy
Authors: Testa M , Schuemann J , Paganetti H
Published: June 2012

Purpose: To validate the accuracy of Monte Carlo (MC) simulations performed with TOPAS (TOol for PArticle Simulation; to be released to the proton therapy community) against phantom measurements in proton therapy. Methods: We used TOPAS, a new MC simulation tool that provides a user‐friendly interface to the Geant4 package, to simulate proton depth‐dose curves from the MGH gantry treatment heads in double‐ scattering mode. Simulations were compared to QA measurements of SOBPs. Field flatness and field symmetry from all clinical options (i.e. combinations of double‐scattering system, range modulator wheel and beam current modulation settings) have been simulated and benchmarked against measurements performed with 2D dose detectors. A step‐compensator consisting of two sections of different thickness was placed upstream a water phantom in which we measured lateral and longitudinal dose profiles. Results: For all treatment options TOPAS depth‐dose curves are within clinical required accuracy, the range being within +1/−1.5 mm and the modulation within ±3 mm of the requested specifications. SOBP simulations also validate time‐dependent geometry and beam current in TOPAS, as the modulator wheel is rotating with the beam current modulation changing at the same time. The field flatness of simulated protons is within ±2% the average dose measured in a plane transverse to the beam axis. Field symmetries show slight discrepancies compared to measured data. In the case of the step‐compensator, TOPAS correctly predicts the lateral width of the beam and longitudinal profiles at different transverse positions. In the transverse profiles, the edge scattering effects due to multiple Coulomb scattering were correctly reproduced by TOPAS. Conclusions: We demonstrated TOPAS accuracy to reproduce measured dose profiles in a variety of homogeneous phantom setups relevant for proton therapy. The accuracy in the benchmarking achieved with TOPAS simulations provides the basis for routine clinical dose calculations. NIH/NCI P01 CA021239
WE‐C‐BRB‐08: A GPU/CUDA Based Monte Carlo Code for Proton Transport: Preliminary Results of Proton Depth Dose in Water
Authors: Su L , Liu T , Ding A , Xu X
Published: June 2012

Purpose: Although several studies have reported the use of GPUs to accelerate Monte Carlo calculations for x‐ray imaging and treatment planning, there is little effort to demonstrate the utility of this highly parallel yet affordable computing tool for proton treatment planning and dose verification. This paper describes a preliminary project to design a GPU/CUDA based proton transport MC code and to evaluate the timing for proton dose depth distribution. Methods: The proton transport in media was modeled by condensed history method, in which the effect of many interactions was grouped into single condensed step. The Moliere distribution and Valilov distribution were employed to calculate angular deflection and energy loss. The CPU code was written in C++ and GPU‐ based code was developed in CUDA C 4.0. The hardware platform was a desktop with Intel Xeon X5660 CPU and NVIDIA Tesla™ m2090 GPU. Nuclear interactions were not included in the preliminary study and the transport medium was limited to water. Results: The depth dose distributions of proton of different energies were simulated. It was found that 98% of the tallies had relative error less than 1%. The code was benchmarked against MCNPX and GEANT4 codes. For 200 MeV proton pencil beam incident on the water phantom, the dose difference between our code and GEANT4 (nuclear interaction disabled) was within 2% for 95% of all depths. The speedup factor of our GPU code over CPU code was x57. While compared with MCNPX (nuclear interaction on), the GPU code was x620 times faster. Conclusions: This is one of the first reported efforts to demonstrate a GPU/CUDA‐based proton transport MC code for dose calculations. Despite some limitations, this preliminary project was able to show significant gains in the GPU computing time, thus suggesting a promising role of such Monte Carlo tools in the future. This project was funded in part by National Institutes of Health (National Library of Medicine R01LM009362)
WE‐C‐BRA‐01: Best in Physics (Joint Imaging‐Therapy) ‐ Modeling Pathologic Response of Locally Advanced Esophageal Cancer to Chemoradiotherapy Using Spatial‐Temporal FDG‐PET Features, Clinical Parameters and Demographics
Authors: Zhang H , Tan S , Chen W , Kligerman S , Kim G , DSouza W , Suntharalingam M , Lu W
Published: June 2012

Purpose: To develop tumor response models using quantitative spatial‐temporal FDG‐PET features to accurately and precisely predict pathologic response to concurrent chemoradiotherapy (CRT) for locally advanced esophageal cancer patients. Methods: Data from 20 patients who underwent tri‐modality therapy (CRT plus surgery) were retrospectively evaluated. Patients underwent FDG‐PET/CT scans before initiation of CRT and 4–6 weeks after completion of CRT but prior to surgery. Three types of image features were examined for their ability to predict pathologic tumor response: (1) conventional PET/CT response measures (SUVmax, SUVpeak, tumor diameter); (2) clinical parameters (TNM stage, histology, etc) and demographics (patient age, sex, etc.); (3) spatial‐temporal PET features, which characterize the FDG uptake distribution, spatial variation (texture), geometric properties of a tumor and their temporal changes. Recursive feature selection was used to identify an optimal subset of features from the full feature set. Support vector machine (SVM) and logistic regression models were constructed for the prediction using the optimal subset as input. Cross‐validation with randomized training and testing data were used to avoid over‐fitting. Model accuracy was assessed via sensitivity, specificity and receiver operating characteristics (ROC) curve analysis. Model precision was assessed via confidence intervals of the mean. Results: Highly accurate pathologic tumor response was obtained using SVM with an area under the ROC curve (AUC) of 0.95, (100% sensitivity and 90% specificity). The 95% confidence interval was [0.92, 0.98], suggesting high precision as well. The improvements using spatial‐temporal PET features over only using conventional PET/CT response measures (AUC=0.82) or clinical parameters and demographics (AUC=0.77) were significant (p<0.0001). Conclusions: By using quantitative PET/CT image features we were able to accurately and precisely predict pathologic tumor response in esophageal cancer patients undergoing concurrent CRT. This prediction has the potential to alter current clinical practice standards by identifying patients in whom surgery may be safely deferred.
WE‐C‐BRA‐03: Best in Physics (Joint Imaging‐Therapy) ‐ Registration of Magnetic Resonance, Reconstructed 3D Ultrasound Imaging and Whole‐Mount Breast Pathology for Therapy Assessment of Breast Cancer
Authors: Vlad R , Samavati N , Moseley J , Tadayyon H , Iradji S , Stanisz G , Czarnota G , Brock K
Published: June 2012

Purpose: To develop a procedure to register 3D whole‐mount histology of the breast with multimodality imaging, including MRI and ultrasound. This work provides a platform for developing methods for therapy assessment in breast cancer using cell death characterized through quantitative ultrasound. Methods: Ultrasound scans, DCE‐MRI, MRI‐exvivo mastectomy sample and whole‐mount histological slices were obtained. The ultrasound scans were collected using a freehand 2D‐ultrasound probe and a tracking tool affixed to the probe for coordinate determination. These coordinates were used to reconstruct the 3D‐ ultrasound volume. All image data sets were rigidly registered, the tumor was contoured on each data set, and each set of contours was converted to a volumetric mesh. There are considerable deformations between imaging modalities due to different breast positions at the time of scanning and between imaging and pathology. Part of these deformations were estimated using the MRI exvivo scans of the breast collected before histological processing, and applying a biomechanical‐based model deformation algorithm to calculate the deformation map from DCE‐MRI‐invivo to MRI‐exvivo. Results: The rigid registration method resulted in large differences between the residual tumor volumes estimated from DCE‐MRI(147%), US(56%) and histology(100%), considering the histology representation as the ground truth. After applying the deformation map to the DCE‐MRI, the volume of the residual tumor in DCE‐MRI decreased by 30% approaching the representation of the residual tumor in histology and ultrasound. Modest improvements to the Dice Index were seen from DCE‐MRI‐to histology and from DCE‐MRI‐to‐US after applying the deformation map. Conclusions: The project provides metrics of comparison between the volumes of residual tumor assessed from ground truth histology and the volumes assessed from ultrasound and DCE‐MRI in breast cancer patients. Since tumors are stiffer than surrounding breast tissue, future work will need to consider including tumor elastic properties in calculating the deformation map from MRI‐invivo to MRI‐exvivo. Terry Fox New Frontiers Program Project in Ultrasound for Cancer Therapy. Dr. Brock has financial interest in deformable registration technology through the licensing of Morfeus to RaySearch Laboratories
WE‐C‐BRA‐04: Stability of FLT and Cu‐ATSM PET in Canine Patients during Radiotherapy: Possible Targets for Dose Painting
Authors: Bradshaw T , Jallow N , Forrest L , Jeraj R
Published: June 2012

Purpose: In dose painting, functional imaging is used to identify and target radiotherapy‐resistant regions of the tumor. It is important to know if target locations remain stable during radiotherapy, otherwise dose plans will need to adapt to mid‐therapy changes. This study investigated the spatio‐temporal stability of FLT and Cu‐ATSM PET after a few fractions of radiotherapy. Methods: Nineteen canine patients with nasal tumors (12 carcinoma and 7 sarcoma) were imaged prior to accelerated hypofractionated radiotherapy with [F‐18]FLT PET/CT for proliferation and [Cu‐61]Cu‐ATSM PET/CT for hypoxia. FLT scans were repeated after two fractions (8.4 or 10 Gy) and Cu‐ATSM scans after three fractions (12.6 or 15 Gy). Patients were immobilized with custom bite blocks and vacuum mattresses for reproducible positioning. Mid‐treatment scans were rigidly registered to pre‐treatment scans. Spearman correlation coefficients quantified the voxel‐by‐voxel SUV correlations between pre‐ and mid‐treatment scans. Population and histology averaged correlation coefficients were determined using Fisher transformations. SUVmax, SUVmean, SUVpeak, and SUVtotal were also compared between pre‐ and mid‐treatment scans using paired t‐tests. Results: Pre‐ and mid‐treatment scans were highly correlated, for both FLT and Cu‐ATSM PET distributions. The Fisher‐weighted mean Spearman correlation coefficient was 0.87[range: 0.57–0.95] for Cu‐ATSM and 0.79[0.18–0.90] for FLT. On average, sarcomas had slightly higher correlations (0.88) than carcinomas (0.78). We observed significant reductions (p<0.05) in FLT SUVmax, SUVmean, and SUVpeak at mid‐treatment for both histologies. For Cu‐ATSM, carcinomas showed significant reductions in SUVmean, SUVpeak, and SUVtotal, while no significant differences (p>0.20) were observed in sarcomas. Conclusion: Spatial distributions of hypoxia and proliferation were stable after a few fractions of radiotherapy. The magnitude of proliferation reduced significantly in both sarcoma and carcinoma tumors. The magnitude of hypoxia only reduced significantly in carcinoma tumors. With high spatial stability early during radiotherapy, pre‐treatment FLT and Cu‐ATSM PET are potential candidates for dose painting targets.
WE‐C‐BRA‐05: Physiological Imaging‐Defined Response‐Driven Subvolumes of a Tumor
Authors: Farjam R , Tsien C , Feng F , Gomez‐Hassan D , Hayman J , Lawrence T , Cao Y
Published: June 2012

Purpose: To develop an image analysis framework to delineate the physiological imaging‐defined subvolumes of a tumor in relating to treatment response and outcome. Methods: Our proposed approach is designed to delineate subvolumes of a tumor based upon its heterogeneous distributions of physiological imaging parameters. The method assigns each voxel a probabilistic membership function belonging to the physiological parameter classes based upon a sample of tumors, and then calculates the related subvolumes for each tumor. We applied our approach to regional cerebral blood volume (rCBV) and Gd‐DTAP transfer constant (Ktrans) images of patients who had brain metastases and were treated by whole brain radiation therapy (WBRT). Forty five lesions were included in the analysis. Changes in the rCBV (or Ktrans)‐defined subvolumes of the tumors from pre RT to 2 weeks (2W) after the start of WBRT were evaluated for differentiation of responsive, stable and non‐responsive tumors using Mann‐Whitney U test. Performance of the newly developed metrics for predicting tumor response to WBRT was evaluated by Receiver Operating Characteristic (ROC) analysis. Results: The percentage decrease in the high‐CBV defined subvolumes of the tumors from pre‐RT to 2W was significantly greater in the group of responsive tumors than in the group of stable and nonresponsive ones (p<0.007). The change in the high‐CBV defined subvolumes of the tumors from pre‐RT to 2W was a predictor for post‐RT response significantly better than the change in gross tumor volume observed during the same time interval (p=0.0124), suggesting the physiological change occurs prior to the volumetric change. Also, Ktrans did not add significant discriminatory information for assessing response with respect to rCBV. Conclusions: The physiological imaging‐defined subvolumes of the tumors delineated by our method have the potential to be a new imaging response‐predictor and a candidate for intensified treatment. NIH grant RO1 NS064973
WE‐C‐BRA‐06: In Vivo Detection of Proton End Range Effect in Human Lungs: Intra‐Subject Dose Response Comparison
Authors: McCurdy M , Castillo E , Castillo R , Echeverria A , Guerrero T
Published: June 2012

Purpose: Preclinical studies have measured an increase in the relative biological effectiveness (RBE) at the distal end of proton therapy beams, however, no clinical consequences have been reported. This study compares the radiation pneumonitis dose response in lungs that received a terminating proton beam with their contralateral lung. Methods: Thirty‐four patients treated with proton therapy for esophageal cancer who received restaging [18F]‐fluorodeoxyglucose positron emission tomography (FDG PET) were selected. Each received a proton field arrangement that included a lateral beam terminating in one lung. The pulmonary radiation inflammatory dose response was quantified for each lung separately as the slope of the FDG uptake versus dose using regression modeling. The dose‐response was compared within subject between the entrance and end‐range containing lungs using the related sample Wilcoxon signed rank test. Results: The spatial distribution of the regions that received between 1 and 10 Co‐60 Gy Equivalents (CGE) corresponded to the proton beam lateral and distal edges. The mean and range of SUV for the entire end range lung (0.65, 0.40 – 1.09) was lower than the entry lung (0.72, 0.40 – 1.17) (p=0.009). For the 1 to 10 CGE regions the dose response was higher in the end range lung (19.2 × 10‐ 2, range 0.8‐50 × 10‐2) versus the entry lung (10.2 × 10‐2, 0.03‐39 × 10‐2) (p < 0.001). Conclusions: This study found an enhanced radiation dose response in lungs that received radiation from the proton beam end‐range. This spatial variation in the dose response contradicts the prevailing isodose equals isoeffect assumption. This quantifiable enhancement represents a clinical manifestation of the increase in the RBE at the end range of proton beams.
WE‐C‐BRA‐08: Using 4DCT‐Based Ventilation Imaging to Correlate Lung Dose and Function with Clinical Outcomes
Authors: Vinogradskiy Y , Castillo R , Castillo E , Tucker S , Zhongxing L , Guerrero T , Martel M
Published: June 2012

Purpose: An exciting form of ventilation imaging is being developed based on 4‐dimensional computed tomography (4DCT) data. Because 4DCTs are routine for thoracic radiation therapy, calculating ventilation maps from 4DCT data does not add extra dosimetric or monetary cost. Studies have discussed designing treatment plans to avoid highly‐ventilated areas of the lung. However, the hypothesis that using ventilation in treatment planning can reduce thoracic toxicity remains to be tested. The purpose of our work was to determine whether incorporating ventilation‐based functional information could improve prediction for clinical thoracic toxicity. Methods: The study used 96 lung cancer patients, 17 of whom developed radiation pneumonitis (CTCAE 3.0 Grade>=3). Pre‐treatment 4DCT data, spatial registration, and a density‐change based model were used to compute pre‐treatment ventilation maps for each patient. Using dose and ventilation, we calculated dose‐volume and dose‐function histograms, mean lung doses (MLD), and ventilation‐weighted MLD (fMLD). The ventilation‐weighted dosimetric values were compared between the pneumonitis group and the non‐pneumonitis group using a two‐sample t‐test. The ventilation‐based functional data were incorporated into a predictive dose‐response model and maximum likelihood was used to determine whether incorporating functional data could significantly improve the model fit to clinical toxicity data. Results: Specific patient examples illustrate that using functional dose metrics can lead to better estimates of toxicity. The fMLD was higher for patients that developed pneumonitis (20.8 Gy) than for those that did not (18.9 Gy), however, the results were not significant (p=0.251). Although fMLD improved model fit over using MLD, the difference in fits was not found to be significant (p=0.312). Conclusions: This is the first study that has attempted to link irradiating ventilated portions of the lung to clinical outcomes. Although promising data were presented, the results were not statistically significant. Future work will include more patients and further functional information with perfusion imaging.
WE‐G‐BRCD‐05: Evaluation of Localization Errors for CSA Delivery Using VMAT
Authors: Myers P , Stathakis S , Esquivel C , Gutierrez A , Mavroidis P , Papanikolaou N
Published: June 2012

Purpose: To dosimetrically evaluate the effects of improper patient positioning in the junction area of a VMAT cranio‐spinal axis irradiation technique consisting of one superior and one inferior arc. Methods: Five (n=5) cranio‐spinal axis irradiation patients were planned with 2 arcs: one superior and one inferior. The plans were then recalculated with inferior isocenter shifted, in order to mimic patient setup errors, eight times: lmm, 2mm, 5mm, and 10mm superiorly, and 1mm, 2mm, 5mm, and 10mm inferiorly. Plans were then compared to the original, non‐shifted arc plan based on target metrics of conformity number and homogeneity index, as well as several normal structure mean doses. Results: Percent differences were calculated in order to compare each of the eight shifted plans to the original arc plan without shifts, which would be the ideal setup of patient without error. The conformity number was on average 0.87%, 2.74%, 5.75%, and 9.10% lower for the 1mm, 2mm, 5mm, and 10mm inferiorly‐ shifted plans and 0.41%, 0.82%, 2.75%, and 5.99% lower for the respective superiorly‐shifted plans. The homogeneity indices were, averaged among the five patients, 0.03%, 0.26%, 0.97%, and 2.84% for the inferior shifts and 0.23%, 1.17%, 6.31%, and 15.29% worse, or less homogenous for the superior shifts. Overall the mean doses to the organs at risk were less than 2% different for the 1mm, 2mm, and 5mm shifted plans. The 10mm shifted plans, however, showed percent differences from original plan of up to 5.6% on average. Conclusions: Setup errors when shifting isocenters should be minimized in order to provide the patient with the best treatment possible. Errors of 1 to 2mm can negatively affect patient treatment, most notably in the arc junction area, but are not as problematic as larger errors of 5 to 10mm.