bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐G‐BRA‐04: Emission Guided Radiation Therapy: A Simulation Study of Lung Cancer Treatment with Automatic Tumor Tracking Using a 4D Digital Patient Model
Authors: Fan Q , Nanduri A , Zhu L , Mazin S
Published: June 2012

Purpose: Accurate tumor tracking, especially for lung cancer, remains a challenge ineffectively addressed. Many strategies including respiratory gating and fiducial implanting alleviate the problem to different extents however they are sub‐optimal due to indirect tracking. To track the tumor itself, the concept of Emission Guided Radiation therapy(EGRT) was recently proposed. This work serves to demonstrate the feasibility of the EGRT concept within the context of lung cancer treatment. Methods: EGRT is based on the physics principle that lines of response(LOR's) from positron emission events can define the lines of radiation projection passing through the emission sites. It enlightens the design of a radiation delivery system consisting of a linac and PET detectors on a fast rotating closed‐ring gantry. When treating radiotracer administrated patients, PET detectors collect LOR's from tumor uptake sites and the linac responds simultaneously with beamlets of radiation along the same LOR paths. Accurate direct tumor tracking can automatically be achieved with real‐time responses. To validate the EGRT concept, a treatment scheme is designed and implemented for the 4D XCAT phantom with a lung tumor. A conventional treatment is modeled for comparison. Attenuation correction is also implemented in EGRT. The emission process is simulated by Geant4 Application for Tomographic Emission package(GATE) and linac dose delivery is simulated using a voxel‐based Monte Carlo algorithm(VMC++). Results: EGRT, with or without attenuation correction, achieves over 25% and 40% relative dose increase to 100% and 50% of the tumor volume respectively compared to the conventional treatment with all cases normalized to have the same integral dose to lung. Attenuation correction helps achieve a better dose performance. Dose‐peaking in the tumor volume is observed in EGRT, demonstrating automatic tumor tracking. Conclusions: As a new radiation therapy modality with inherent tumor tracking, EGRT has the potential to substantially improve radiation therapy for lung cancer. This study was funded by RefleXion Medical, a company commercializing PET‐guided radiotherapy. SRM, ASN and LZ have financial interest in RefleXion.
TU‐G‐BRA‐07: Patient‐Specific Biomechanical Model of Human Lung Using Four‐Dimensional CT
Authors: Li Z , Wang J
Published: June 2012

Purpose: To develop patient‐specific lung biomechanical models for simulating lung deformation and predicting the tumor motion position during radiation therapy. Methods: A FEA/CFD (Finite Element Analysis/Computational Fluid Dynamic) model is built to simulate the deformation of the lung. The lung is assumed to behave as a poro‐elastic medium with uniform or heterogeneous elastic property. The method used a fluid‐structure interaction technique to model flow within the airway and deformation of the lobe. A slide boundary condition was applied between the ribcage and the lung surface. The 3D lung geometry is reproduced from the end‐of‐expiration phase of a 4D‐CT scan of a lung cancer patient. Three models of elasticity data (Young's Modulus: YM) distribution are analyzed: 1. Uniform YM distribution; 2. Major Branch YM distribution; 3. Spatial YM distribution calculated from the 4D‐CT. A linear increment air pressure is added to the trachea. The displacements of 135 landmarks at each time step are statistically compared with the manual registrated data from the 4D‐CT images. Results: Without applying the slide boundary conditions between the ribcage and the side lung surface, the standard errors for all these 3 YM models are larger than 4.5 mm. Appling the slide boundary conditions, the standard error of the displacement vector for the uniform YM model is 2.8mm, the standard error is reduced to 2.7 mm for the Major Branch model, and the standard error is further reduced to 2.5 mm for the spatial YM model. Conclusions: The standard error of landmark displacement is significantly reduced by applying sliding boundary conditions. Among three YM models investigated in this study, the spatially distributed YM model derived from 4D‐CT provides highest accuracy in simulating lung respiration process. This work was supported by Cancer Prevention and Research Institute of Texas (CPRIT) RP110562‐p2.
TU‐G‐217BCD‐01: Investigation of a Commercial OSLD System for CT Dosimetry
Authors: Scarboro S , Cody D , Followill D , Alvarez P , McNitt‐Gray M , Zhang D , Court L , Kry S
Published: June 2012

Purpose: With an increasing use of computed tomography (CT) in diagnostic procedures, there is a growing need for more accurate and patient‐specific dosimetry techniques. Optically stimulated luminescent dosimetry (OSLD), well‐suited for in‐vivo dosimetry with little if any impact on diagnostic image quality, offers a potential solution. We have characterized a commercially available OSLD system, provided CT calibration protocols, quantified uncertainties, and tested the system against ion chamber measurements for various CT applications. Methods: Landauer nanoDots were fully characterized through both measurements and theoretical approaches to quantify the effects of dose linearity, signal depletion, fading, angular dependence, and energy dependence specific to a CT environment. Three calibration approaches that included calibration (1) relative to a 60Co source, (2) relative to a 120kVp CT spectrum in air, and (3) using the vendor provided method were investigated along with their associated uncertainty. The OSL system and calibration procedures were tested and compared to ion chamber measurements using standard CTDI phantoms. The defined calibration protocols were used to measure an anthropomorphic head phantom's lens dose. Results: We determined the OSLD characteristics and calibration techniques appropriate for CT dosimetry. Most correction factors were less than 5% with the exception of energy dependence which, depending on the calibration method and specific scan parameters, was as large as 400% due to the OSL over‐response at low energies. The uncertainty budget for the dose calculations showed the uncertainties (2‐sigma) to range from 11% to 20% for a properly corrected system. More rigorous calibration approaches resulted in lower dosimetric uncertainties. Conclusion: The OSLD calibration protocols and correction factors described provide a precise and accurate patient dosimetry and documentation method for routine monitoring of CT patients, as well as for special procedures such as CT perfusion. Work supported by grant CA10953(NCI, DHHS)
TU‐G‐217BCD‐02: Evaluation of Dose Variability along the Z‐Axis in Helical CT Using Gafchromic Film
Authors: Al‐Senan R , Hatab M
Published: June 2012

Purpose: To investigate the effect of the helical pitch, patient size, and beam width on point dose measurements of superficial organs in MSCT. Methods: Three sizes of cylindrical PMMA phantoms were utilized; 32cm (body), 16cm (adult head), and 10cm (pediatric head). For each phantom, helical scans were performed with different pitch factors (0.7, 1.0, and 1.3) and collimations (12mm and 24mm). In each scan, a strip of gafchromic film, measuring 12×1.5cm2, was taped onto the top of the phantom along its z‐axis. Film strips were scanned, red channel was extracted and pixel values were converted into optical densities from which doses (mGy) were obtained using a calibration curve. Results: The periodic pattern of peaks and valleys in dose profiles along the z‐axis of phantom surface was more obvious with the body phantom; the highest variation (% difference between peak and valley) was 56%. Adult and pediatric head phantoms showed significantly less variation; highest = 30% and 24%, respectively. These values were found with pitch 1.3 and collimation 24mm. When collimation was changed from 12mm to 24mm, the amount of variation was nearly doubled (at pitch 0.7 and 1.3). With pitch 1, dose variation was different; in the pediatric phantom the variation was similar in either collimation (7%). In adult and pediatric head phantoms it increased from 6% to 9% and from 17% to 39%, respectively. Conclusions: If point dose measurements were to be taken on patient surface or for superficial organs such as breast or thyroid using small dosimeters in anthropomorphic phantoms, the combined effect of helical pitch, patient size, and collimation on dose assessment accuracy should be taken into consideration. Variation of about 60% may result with large patients, high pitch, and wide collimation. Variations will be largely reduced with smaller patients, pitch close to 1 and narrow collimation.
TU‐G‐217BCD‐05: Enhanced CT Dose Reduction for a Pediatric Population Using Peak Tube Potential (kVp) Reduction Combined with ASiR™ Reconstruction
Authors: Brady S , Kaufman R
Published: June 2012

Purpose: To demonstrate enhanced CT dose reduction for a pediatric phantom population by implementing an iterative reconstruction (ASiR™) technique to compensate for added noise in reconstructed CT images from kVp reduction. Methods: (1) This study compared contrast to noise (CNR) for three contrast targets inserted into the abdomen of a 1, 5, and 10 yr anthropomorphic phantoms (CIRS). The contrast targets were the respective bone, brain tissue and spinal cord plugs manufactured for each phantom age. The phantoms were imaged using an abdomen protocol with 40% ASiR™at 120 kVp. The CNR and noise (standard deviation of ROI) for each phantom at 120 kVp were measured as a baseline from which subsequent scans at 80 and 100 kVp were compared. (2) MOSFET detectors were placed inside the major abdominal organs of the phantoms. Absorbed dose was measured and converted to effective dose. Results: Increased CNR and noise were found when the phantoms were imaged with 80 and 100 kVp compared to 120 kVp. Soft tissue and bone CNR increased by ∼0% and 7–10%, respectively, at 100 kVp and 10–22% and 7–25%, respectively, at 80 kVp. Increase in noise magnitude was held below 6% for both 80 and 100 kVp. Dose reduction on the order of 35–45% was demonstrated at 120 kVp when 40% ASiR™was introduced. Total dose reduction of 55–62% was demonstrated for the 1, 5, and 10 yr phantom when imaged at 100 kVp and 50% ASiR™, but only 49–54% for the 1 and 5 yr phantoms at 80 kVp and 50% ASiR™. Conclusions: CT dose reduction on the order of 55–62% was achieved for a pediatric phantom population when modifications of kVp were combined with ASiR™. Increases in bone and soft tissue contrast were demonstrated. Noise level increase was kept to = 6%.
TU‐G‐217BCD‐06: Reducing CT Dose during Routine Brain CT Using Attenuation Based Tube Current Modulation (TCM)
Authors: Angel E , Zhang D
Published: June 2012

Purpose: Attenuation based Tube Current Modulation (TCM) is used routinely for chest, abdomen, and pelvis CT studies, but is often not used for routine head CT exams. The aim of this study was to determine whether using TCM for routine brain imaging has the potential to reduce CT dose (CTDI). Methods: A Toshiba Aquilion ONE CT was used to image a head phantom. Two acquisitions were performed, one fixed tube current scan with 165mAs and one TCM scan with the appropriate SUREExposure SD setting selected to achieve image noise (HU standard deviation) of brain tissue in the posterior fossa region equivalent to that of the fixed tube current scan. Assuming the mA of the fixed tube current scan is limited by the noise level required for the posterior fossa (since posterior fossa is the most challenging head region to image), it is reasonable to assume other regions of the head are receiving unnecessarily low noise levels and can accept further mA reduction; TCM should correct for this. Image noise was measured as average standard deviation of CT number for three ROIs in the posterior fossa and four ROIs in each of two axial locations representing large and small diameter regions. CT dose difference was calculated using scanner reported CTDIvol. Results: Compared to fixed tube current, the TCM scan reduced CT dose by 38%. Compared to fixed tube current, image noise from the TCM scan was equivalent in the posterior fossa region (as designed), nearly equivalent (3% increase) in the large diameter region of the head, and as expected, image noise increased in the smaller diameter brain (24% increase). Conclusions: Tube Current Modulation (TCM) has the potential to reduce radiation dose for routine head CT. Future studies will investigate clinical image quality between fixed tube current and TCM head CT scans. EA, DZ ‐ Employee Toshiba America Medical Systems, Inc.
TU‐G‐217BCD‐07: Improving Size Specific Dose Estimates (TG 204): Extension to Tube Current Modulated CT Scans with Regional and Local CTDIvol Values
Authors: Khatonabadi M , Zhang D , Cagnon C , DeMarco J , McNitt‐Gray M
Published: June 2012

Purpose: The recently published TG 204 report established conversion factors based on measurements and Monte Carlo simulations, which adjust scanner‐reported CTDIvol for patient size, called size specific dose estimates (SSDE). However, those estimates were based on fixed tube current scans, while most performed clinical protocols make use of Tube Current Modulation (TCM). Therefore, the purpose of this study was to assess the performance of these conversion factors compared to Monte Carlo based simulated organ dose from fixed and TCM scans and to introduce region and organ specific CTDIvol to extend the calculated SSDEs to TCM scans. Methods: Using Monte Carlo based methods; liver doses were estimated from both constant tube current and TCM abdomen/pelvis CT exams. The effective diameter was calculated for each model and used to look up conversion factors which were then applied to scanner‐reported CTDIvol (CTDIvol,TCM)and CTDIvol based on constant tube current exam (CTDIvol,cTC) to calculate SSDEs. Calculated SSDEs were compared to liver dose estimates from constant tube current and TCM simulations. Additionally, regional and liver‐specific CTDIvol (CTDIvol,Abdomen and CTDIvol,Liver) were calculated and used to calculate TCM adjusted SSDEs. Results: Liver doses obtained from fixed tube current simulations were compared to SSDEs calculated using CTDIvol,cTC, and doses obtained from TCM simulations were compared to scanner‐reported CTDIvol,TCM. For these two datasets RMSE values of 3.0 and 3.3 mGy were calculated, respectively. RMSE value decreased to 1.5 and 1.3 mGy for SSDEs calculated based CTDIvol,Abdomen and CTDIvol,Liver, respectively. Conclusion: Conversion factors determined in TG 204 are based on fixed tube current measurements and Monte Carlo simulations and need further adjustments if they are being used to assess TCM exams. We have shown that region and organ‐specific CTDIvol can be used to adjust for TCM and to improve the performance of calculated SSDEs to estimate dose from TCM exams.
TU‐G‐217BCD‐09: Integration of Recent NEMA (MITA) XR‐25 CT Dose‐Check Standard into Clinical Practice
Authors: Zamora D , Kanal K , Dickinson R , Shuman W , Stewart B
Published: June 2012

Purpose: The aim of this work is to implement vendor mandated alert value (AV) and notification value (NV) Dose‐Check metrics into neuro radiology CT exams without adversely affecting clinical workflow and to evaluate these tools as a method of active dose monitoring. Methods: The NV represents an expected ‘reasonable’ CTDIvol (or DLP) value, and is assigned at the group level of the protocol prescription; projected surpassing of the NV displays a simple warning message. Preliminary NV implementation included neurological exams, which normally utilize manual (rather than modulated) tube current. Appropriate NV levels were established using internal population DLP metrics, ACR Dose Index Registry results, AAPM recommendations, and projected CTDIvol values. When an NV alert is issued, the technologist attains and documents radiologist approval and then proceeds with the exam. The AV is as a threshold that is compared to the maximum cumulative CTDIvol at any scan location for a given examination. If the forthcoming scan is projected to surpass the AV, login credentials are required to proceed with the scan. Our institution collectively established an AV of 1000 mGy to allow for expected high doses commonly observed for cerebral perfusion exams. Results: Effective implementation requires a balance of appropriate alerting and reasonable clinical interruption. After three months, we have received 6 NV alerts (2 T‐spine, 2 C‐spine, 2 Neck). Alerts came about from manual modification of the standard protocol by the technologist. On average, the projected CTDIvol exceeded the NV by 8.4% for spine and 18.5% for neck. No adverse effects on clinical workflow have been experienced. Conclusions: Active monitoring using AV and NV is a useful, non‐invasive tool in minimizing the likelihood of gross overdose (AV) and of abnormal incremental overdose (NV). Future work will involve implementing the NV values for the abdomen exams that use tube current modulation.
TU‐G‐217A‐02: Voxel‐Based Residual Analysis of High Spectral and Spatial Resolution (HiSS) MRI of Breast Lesions
Authors: Weiss W , Medved M , Karczmar G , Giger M
Published: June 2012

Purpose: To extend CADx techniques for High Spectral and Spatial Resolution (HiSS) breast MRI, and to assess the ability of the Lorentzian‐fit‐ subtraction residual maxima of the water resonance spectra to distinguish between benign and malignant breast lesions on a voxel‐by‐voxel basis. Methods: HiSS high resolution spectroscopic MR images were collected under an IRB‐approved protocol. To analyze HiSS data, we fit a Lorentzian curve to a 25 bin (140 Hz) region of the proton‐resonance spectra in each lesion, centered at the water resonance and normalized to the water peak height. After subtracting this fit from each spectrum, the maximum residual value in nine spectral bins from +22.4 to +67.2 Hz to the right of the water peak was recorded with its corresponding frequency bin. We automatically excluded voxels in each lesion with maximum residual lower than 60% of the maximum residual in the entire lesion in order to eliminate voxels with off‐peaks close to or below the noise floor. These residual maxima were evaluated on a voxel‐by‐voxel basis, for each frequency bin based on the known diagnosis (9 malignant; 8 benign cases) and the performance of this single feature was assessed using ROC analysis. Results: In the task of distinguishing between voxels in malignant and benign lesions, analysis across all nine spectral bins yielded an AUC value of 0.96 ± 0.007. AUC values within specific spectral bins ranged from 0.72 at 5.6 Hz from the water peak to 1.0 at 60.6 Hz ‐ noting that the latter could be artificially high due to our limited database. Conclusions: We have presented a technique utilizing a voxel‐based approach to HiSS spectral analysis, with potential for use in the diagnosis of cancerous breast lesions. We are currently extending this method to include lesion‐based classification rather than voxel‐based evaluation. M.L. Giger is a stockholder in R2 Technology/Hologic, has equity in Quantitative Insights, and receives royalties from Hologic, GE Medical Systems, MEDIAN Technologies, Riverain Medical, Mitsubishi and Toshiba. G.S. Karczmar has an institutional research agreement with Philips Healthcare. It is the University of Chicago Conflict of Interest Policy that investigators disclose publicly actual or potential significant financial interest that would reasonably appear to be directly and significantly affected by the research activities.
TU‐G‐217A‐06: Accelerated 3D Lung MRI Using Compressed Sensing
Authors: Sarma M , Hu P , Ennis D , Thomas M , Sheng K
Published: June 2012

Purpose: High temporal resolution volumetric thoracic MRI is needed to accurately describe the lung and lung tumor motion. The main aim of the present study is to substantially increase 3D acquisition speed of lung MRI with k‐space under‐sampling along the phase encoding directions and subsequent image reconstruction using Compressed Sensing (CS). Method and Materials: CS was simulated using fully sampled thoracic breath‐ holding MRI of a lung cancer patient. The imaging resolution is 1.8×1.8×2.6 mm. Biased random under‐sampling was imposed in the k‐space by selecting more points near the center, and fewer points near the bottom left and bottom right corners. An unbiased random under‐sampling scheme was performed for comparison. The data was reconstructed using the Split Bregman method for L1 regularized problems, which solve the unconstrained optimization problem iteratively by spliting the L1 and L2 components. The method removes the artifacts due to the non‐uniform under‐sampling by minimizing the total variation (TV) while maintaining fidelity with the sampled measurements. Results: We were able to reconstruct the data sub‐sampled with different under‐sampling factors (2×2 − 4×4 folds). Images reconstructed with very low sampling ratio of 13.05% were acceptable. The biased under‐sampling strategy required 30% fewer samples than the unbiased under‐sampling technique for equivalent results. The overall quality and resolution of the reconstructed image was comparable to the fully sampled dataset in the conspicuity of fine lung features and organ shapes, which are degraded by noise in images reconstructed from same dataset without using the CS method. Conclusions: We have successfully demonstrated the application of CS to high‐resolution 3D MRI of the lung, providing an acceleration factor up to 4×4. While higher acceleration factor is needed for real‐time full thoracic imaging, the current method would enable real time imaging of a subvolume of the lung for regional motion study.
WE‐A‐BRCD‐01: Stereotactic Radiosurgery: State of the Art Technology and Implementation
Authors: Yenice K , Petti P , Dieterich S , Solberg T
Published: June 2012

Since its introduction nearly 60 years ago, stereotactic radiosurgery has become the standard of care for the noninvasive destruction of intracranial tissues or lesions that may be inaccessible or unsuitable for open surgery. Today, modern stereotactic radiosurgery is practiced using advanced image guided treatment planning and specialized delivery systems including micro‐ MLC equipped linacs, CyberKnife, and Gamma Knife machines. Stereotactic radisourgery delivers a large dose to a precisely defined volume in a short time, and as such requires the utmost attention to precision and quality assurance. Also critical is the meticulous design of treatment processes that eliminate the possibility of potentially disastrous errors. In this presentation we review the fundamental aspects of stereotactic targeting and delivery, the technologies for stereotactic localization and treatment of cranial targets, and the quality assurance aspects associated with establishing and maintaining a clinical radiosurgery program. Examples of radiosurgery cases will be presented from the best practice sites utilizing Gamma Knife, CyberKnife, and linac delivery systems, followed by an expert panel discussion of quality measures for treatment planning and delivery.

Learning Objectives:

1. Differentiate how radiation is delivered for Gamma Knife, CyberKnife and Linac‐based (conventional and robotic) stereotactic radiosurgery.

2. Define the treatment planning parameters, imaging requirements and workflow for Gamma Knife, CyberKnife and Linac‐based stereotactic radiosurgery.

3. Discuss measures for assuring accuracy in stereotactic localization and dose delivery for Gamma Knife, CyberKnife and Linac‐based stereotactic radiosurgery.

4. Discuss uncertainties and limitations associated with Gamma Knife, CyberKnife and Linac‐based stereotactic radiosurgery
WE‐A‐211‐01: Medical Physics in Latin America ‐ How Can the AAPM Help?
Authors: Pipman Y
Published: June 2012

Purpose: 1) To examine current clinical and educational needs in Medical Physics in Latin America and recent AAPM efforts to meet them. 2) To assess how can AAPM be more effective in Latin America. Methods: Data from the region are used to update the needs for training and education of Medical Physicists vis‐à‐vis current and projected staffing needs. Developments in the state of practice, and upgrades of equipment, are considered in the assessment of needs. Activities and resources of the AAPM are appraised for their specific requirements and their potential effectiveness. Results: Several programs and local resources have been added or expanded in a number of countries since the last update in 2010. These concentrate mainly in Radiation Oncology Physics, where the perceived need is most evident. Current and projected staffing necessitate more extensive education, training and certification in most countries in Latin America. There is marked difference in utilization of Medical Physics services in imaging between the region and North America. Regulatory requirements and adoption of practice standards are uneven between and within countries. AAPM, and a considerable number of its members, have supported, participated and contributed to a variety of educational and professional activities carried out by local and regional organizations. Several of these involved collaboration with international organizations such as IAEA and IOMP. A smaller number of projects involved individual commitments for longer durations. These provide an insight into ways of enhancing and further developing regional capabilities. Conclusions: There is measurable growth in the regional capabilities to educate and train Medical Physicists in Radiation Oncology, with a slower pace of growth in Imaging. The introduction of new technologies and methods requires this pace to be accelerated in order to meet current and projected needs. The AAPM has significant human and organizational resources to offer and can make a meaningful contribution to expand this local capacity. There is a need to leverage its resources by increased collaboration and coordination with international organizations and to explore funding mechanisms from companies to augment these resources. Longer term projects and partnerships need to be developed.

Learning Objectives:

1. Understand the current needs for Education and Training in Latin America

2. Assess the resources that the AAPM and its members can offer to support the regional programs

3. Discuss ways for leveraging the AAPM resources for a sustained and effective effort to meet the regional needs
WE‐A‐211‐04: AAPM International Outreach Programs ‐ Collaboration with IOMP
Authors: Wu Raymond
Published: June 2012

Introduction. The purpose of the AAPM International Affairs Committee (IAC) is to advise the AAPM Board through the Administrative Council on matters related to activities of an international nature conducted on behalf of the Association. The charges of the IOMP Professional Relations Committee are to promote and support international cooperation to promote the standards of practice in medical physics and professional conduct. Purpose: The various programs of AAPM and IOMP developed over many decades will be presented. The AAPM international outreach programs will be described. The opportunities for collaboration will be explored. Methods: Many of the AAPM programs, including the Partner in Physics (PIP), International Affiliate, Developing Country Educational Associate, and International Library (ILP), are intended to assist the medical physics community in developing countries to have access to the latest literature and other information to improve the quality of medical physics practice. Other programs, including the Delegates to IOMP, the Liaisons to countries in all regions, and the International Portal are serving as the global link for medical physicists. Since 1992, IAC raised funding to deliver the International Scientific Exchange Program (ISEP) courses in developing countries. Results. Recently, AAPM has provided budgets for two ISEP courses every year, and created the International Educational Activities Committee to take over the program under the Education Council. All medical physics organizations in developing countries are encouraged to host such courses in partnership with AAPM. Since about ten years ago, the IOMP banner started to appear in the ISEP certificates presented to all participants. Conclusions. This joint activity in education will continue to improve the quality of medical physics globally. This and other opportunities for collaboration between the two organizations, including the ILP, PIP, Exchange Scientist Program, and Equipment Donation Program will be explored in this presentation.
WE‐A‐213AB‐01: Second Cancers from Radiation Therapy Procedures
Authors: Kry S , Howell R
Published: June 2012

Second Cancers are the most common late effect among long‐term cancer survivors. Radiation has been a known risk factor for cancer induction based on atomic bomb survivor follow‐up. Over the last few decades, there has also been increasing data on second cancers in medically exposed populations, particularly radiotherapy patients. As treatments become more successful and patients survive longer after treatment, long‐term patient health considerations must play an increasing role in the selection of treatment. To this end, it is important that the field of medical physics become well educated in issues related to long‐term radiotherapy sequelae, including second cancers. The session chair will give an overview of retrospective dose reconstruction method commonly used in these large cohort studies second cancers in patients treated with radiation therapy. Understanding the dosimetry in these studies will provide a better understanding of the results of the studies, the dose response models, and gaps in knowledge regarding dose volume effects. In the remainder of the presentation, the speaker will focus on the current state of knowledge of second cancers, specifically focusing on information and limitations of the available literature. This will include the magnitude of risk of second cancers, including the impact of different demographics. It will also include etiological discussions, focusing on the risk attributable to radiation. This presentation will include the available data on the dose response of second cancers, including the large uncertainties inherent to both low and high dose regions. It will also highlight dosimetry for advanced radiotherapy techniques, and what associated doses might mean for the second cancer risk. Finally, the presentation will discuss examples of how second cancer risk can be reduced in routine clinical practice. Learning Objectives: increase the knowledge of clinical medical physicists regarding radiation‐ induced second cancers as well as stimulate further research in this broad and increasingly important area.

Learning Objectives:

1. To provide general overview of the dose reconstruction methods used in epidemiological retrospective cohort studies of radiation related late effects.

2. To improve the understanding of the magnitude of the second cancer risk faced by radiotherapy patients.

3. To improve the understanding of the etiology of second cancers.

4. To present an overview of current knowledge on dose response for radiation induced second cancers.

5. To discuss the impact of advanced radiotherapy techniques on the risk of second cancers

6. To provide examples of how second cancer risk can be reduced in routine clinical practice.
WE‐A‐BRB‐01: Robotic Brachytherapy Demonstration: Implant of HDR Brachytherapy Needle Configuration Computer‐Optimized to Avoid Critical Structures Near the Bulb of the Penis
Authors: Cunha JA , Siauw T , Garg A , Zhang N , Goldberg K , Stoianovici D , III M Roach , Hsu I‐C , Pouliot J
Published: June 2012

Purpose: To develop a robotic system to implant high dose rate brachytherapy (HDR‐BT) needle configurations meeting clinical dose objectives while avoiding puncture of non‐target structures. This system consists of (1) a robotic needle insertion device, (2) needle and dose planning software, and (3) a human with no clinical experience. Methods: Acubot‐RND is a joy‐stick controlled 7‐DoF stereotactic needle insertion robot with a remote center of motion (RCM) allowing needle pivot around the RCM point. For this project, a digital needle coordinate input and execution system was developed to replace the analog joy‐stick control. Custom pelvic phantoms were built, CT imaged, and contoured. A custom needle‐geometry optimization engine was used to generate a planned needle configuration (PNC) within the robot workspace and tailored to the phantom anatomy. Configurations of parallel and angulated needles (up to 53 deg. from parallel) were instructed to avoid puncture of the critical structures near the penile bulb (CSNB). The PNC was transferred to Acubot for sequential insertion. After each insertion, the robot released the needle in place. Needle stylets were passed through the needle and deposited in the phantom during needle retraction by the human user making the implanted needle configuration (INC). Results: Two phantoms were implanted using the robotic system. Post‐implant CT were obtained, puncture avoidance of the CSNB, pubic arch, and urethra confirmed, and the INC digitized for treatment plan generation. Satisfaction of RTOG‐0321 clinical dose objectives was verified and quantitatively compared against a phantom implant performed by an experienced physician. Conclusions: A clinically‐ relevant robotic brachytherapy workflow able to avoid the CSNB and guide needles behind the pubic arch while meeting clinical dose requirements was demonstrated. Operation of this system mitigates some reliance on brachytherapy implant expertise. This workflow is valid for both PPI and HDR‐BT. Supported by American Cancer Society Grant #IRG‐97‐150‐13.
WE‐A‐BRB‐03: A Fiber Optic Dosimeter to Calibrate P‐32 Conformal Brachytherapy Sources
Authors: Pursley J , Mauceri T , Sliski A
Published: June 2012

Purpose: Conformal brachytherapy plaques are used to irradiate the dura for paraspinal tumors. The plaques consist of Phosphorus‐32 chemically bonded to a flexible polymeric film. Radiochromic film has been successfully used to calibrate P‐32 plaques, but this method is time consuming due to the film characteristics. We investigate using a commercial fiber optic dosimetry system as a more efficient calibration method. Methods: A calibration curve for the radiochromic film was determined using an ADCL calibrated Strontium‐90 source, and this film is used to measure the dose rate of a P‐32 plaque. The Orbital Therapy system consists of a small cylindrical plastic scintillator coupled to a fiber optic cable. The dosimeter, controlled by a LabView‐based user interface, counts scintillation photons during a set time period and provides an immediate readout. Custom plastic phantoms hold the dosimeter probe in contact with a P‐32 plaque. The counts from the fiber optic dosimeter are plotted against the expected surface dose and modeled with a linear function to extract the dose deposited per count. Different measurement designs are considered to select a measurement time with accurate and reproducible results. Results: The fiber optic dosimeter is observed to have a linear dose response curve to both P‐32 and Sr‐90 sources. For a P‐32 plaque each count corresponds to 1.5 microGy, while for a Sr‐90 source each count corresponds to 1.16 microGy. We average 10 consecutive 6‐second measurements of the P‐32 plaque for a standard deviation of 0.1% and precision within 1%. Conclusions: The Orbital Therapy fiber optic dosimeter is acceptable for calibrating P‐32 conformal brachytherapy plaques. Initial calibration of the dosimeter requires a calibrated source of the same isotope, as the dose response depends on the beta energy spectrum. Once calibrated, the dosimeter is faster, simpler, and less error‐prone than using film for P‐32 plaque calibration.
WE‐A‐BRB‐08: Dosimetric Investigation of Praseodymium‐142 Microspheres for Microsphere Brachytherapy of Nonresectable Hepatic Tumor
Authors: Ferreira M , Podder T , Jung J
Published: June 2012

Purpose: To evaluate the dosimetric parameters of Praseodymium‐142 (1 4 2Pr) glass microspheres and its potential application in microsphere brachytherapy of nonresectable hepatic tumor for faster dose delivery and facilitated quality assurance, while maintaining comparable dose distribution of the currently used radionuclides. Methods: Dose profiles for a 1 4 2Pr point source were obtained using BRAIN‐DOSE dose point kernel code and MCNPX2.6 Monte Carlo simulation. Microspheres containing 14 2Pr were studied and their dose distributions were compared to the doses of the currently used radionuclide Yittrium‐90 (9 0Y). Dose distributions due to glass microspheres ensembles within different sizes of spherical tumors were simulated. Physical properties, e.g. time to deliver 90% of the total dose for 1 4 2Pr and 9 0Y, were studied. Results: Dose rates from BRAIN‐ DOSE calculation for ‘ 1 4 2Pr and 9 0Y were 4.42 mGy/hr and 5.53 mGy/hr at 0.5 cm away from a 1 μCi source. From MCNPX2.6 the beta dose per decay at the tumor center for 142Pr and 9 0Y were 2.02 × 10−12 Gy and 2.36 × 10−12 Gy, respectively, for a tumor of 2.5 cm radius. For this case, simulation showed that the total dose in the tumor vicinity and therefore to adjacent organs due to the gamma yield was small, e.g. 0.03 Gy at 10 cm from the tumor center for 150 Gy total physical dose. Conclusions: Total dose per decay due to beta emissions were similar for both 1 4 2Pr and 9 0Y. Shorter half‐life is an advantage of ‘ 1 4 2Pr, enabling faster dose delivery. The physical properties of 1 4 2Pr make it suitable for microsphere brachytherapy. Total gamma contribution of 1 4 2Pr was small, therefore may not be clinically relevant. Gamma radiation, however, opens possibilities for quality assurance, biodistribution imaging and dose distribution assessments.
WE‐A‐BRA‐03: Towards Real‐Time Ultrasound Image‐Guided Abdominal Radiotherapy
Authors: van der Meer S , Wong J , Bloemen E , Fontanarosa D , Lachaine M , Verhaegen F
Published: June 2012

Purpose: Accurate tumor positioning in stereotactic body radiotherapy of abdominal lesions is often hampered by organ motion and set‐up errors. The problems of the daily variation (interfractional motion) in tumor position can be partially corrected with on‐line soft‐tissue image‐guided radiotherapy. However, a greater challenge is to also capture the movement during treatment (intrafractional motion). Methods: To study the feasibility of abdominal real‐time volumetric soft‐tissue image‐guidance with ultrasound (US) imaging, we are investigating several aspects each with their own challenges: 3DUS volumetric imaging, 2DUS time series of the organ motion, robotic US probe placement, US auto‐contouring and contrast enhanced US (CEUS). Results: Currently, 3DUS imaging is used first to correct for the set‐up errors as well as interfractional organ motion. One of the conditions for reliable and accurate results in this part is acquiring US images without artifacts due to breathing motion. For interfractional corrections, this can be realized by imaging during breath hold. In order to track intrafractional tumor and organ motion, including breathing induced, we are moving towards acquisition of temporal 3D image series. As an interim step, we discuss acquisition of temporal 2D datasets. As opposed to prostate, where the US probe can be placed on the perineum during treatment to avoid interaction with the radiation beam, the probe positions required for liver are more complex. Therefore, we are developing robot‐ assisted positioning of the probe. Not all abdominal lesions are clearly visible on US images. By introducing CEUS, more tumors will have increased contrast allowing tracking them. With real‐time tumor tracking it is impossible to manually delineate structures. Therefore auto‐contouring algorithms for this specific application are under investigation. Conclusion: By combining all the investigated technologies we aim to develop a reliable real‐time volumetric soft‐tissue US image‐guidance system for clinical implementation. Research sponsored by ElektaLearning Objectives:1‐ understand the challenges of in‐vivo real time motion monitoring2‐ understand the role of ultrasound imaging in in‐vivo real time motion monitoring3‐learn about our efforts to develop a system for ultrasound‐ based in‐vivo real time motion monitoring
WE‐A‐213CD‐01: Molecular Imaging of the Breast
Authors: O‘Connor M
Published: June 2012

Molecular imaging of the breast using either SPECT or PET based radiopharmaceuticals is a relatively new area of focus for nuclear medicine and has grown in importance over the last few years with the development of specialized small field of view gamma cameras and small PET systems designed to provide high resolution functional images of the breast. Molecular Breast Imaging (MBI) / Breast Specific Gamma imaging (BSGI): MBI and BSGI are currently performed with Tc‐99m sestamibi and have shown a high sensitivity for the detection of small breast lesions, with reported sensitivities of ∼90%. Sensitivity is lowest for tumors < 5 mm in size. This talk will review the technology behind both MBI and BSGI and the primary clinical applications. It will also review the potential use of MBI as a screening technique. Recent studies have shown that it may be considerably more sensitive than mammography in women with dense breast tissue. A significant issue with MBI / BSGI is radiation burden and this talk will review efforts to increase the sensitivity of these technologies to allow a reduction in the administered dose of radiopharmaceutical, and thereby achieve a comparable radiation burden to mammography. Positron Emission Mammography (PEM): PEM is currently performed on a dual detector system incorporating 2 scanning arrays of BGO crystals providing limited angle tomographic imaging. Studies using F‐18 FDG have shown PEM to have comparable sensitivity to MRI for the detection of breast cancer. It is a useful tool in the preoperative assessment of disease extent and in evaluating response to neoadjuvant therapy. As with single photon systems, sensitivity is lowest for tumors < 5 mm in size. Current systems employ doses of 10 mCi F‐18 FDG. Recent technical developments have seen the emergence of systems using small ring detectors or rotating planar detectors that provide full tomographic views of the breast. Clinical studies are expected to show improvements in spatial resolution and a reduction in the administered dose of F‐18 required. COI: The author and Mayo Clinic receive royalties from patents licensed to Gamma Medica Ideas, a manufacturer of MBI systems. Learning Objective:1) Understand the different technologies (PEM,MBI, BSGI) and detector configurations now available for molecular imaging of the breast. 2) Understand the potential applications for molecular imaging of the breast in both the diagnostic and screening environments. 3) Compare the strengths and weakness of molecular imaging techniques with other breast imaging modalities. 4) Appreciate the potential future applications of this technology in the understanding of breast disease. 5) Demonstrate understanding of the radiation dose implications of current radiopharmaceuticals and how the dose can be reduced with new technologies and radiopharmaceuticals.
WE‐A‐217A‐02: The Impact of Fluorodeoxyglucose Positron Emission Tomography (FDG‐PET) Variability on the Assessment of Treatment Response in Head‐And‐Neck Cancer Patients Undergoing Chemoradiotherapy
Authors: Das S , Hoang J , Choudhury K Roy , Yoo D , Brizel D
Published: June 2012

Purpose: To compare intrinsic, temporal variability of tumor glucose metabolism versus early treatment‐induced change. This assessment is necessary to use changes in imaging parameters during therapy to properly segregate metabolic responders from non‐responders Methods: As part of an IRB‐approved study, 12 patients underwent 2 baseline PET scans (mean separation: 11 days) prior to chemoradiotherapy (70 Gy, 2 Gy/fraction). The intra‐RT PET scan was acquired at 10‐20 Gy (mean 14 Gy) into therapy. For each patient, the two baseline scans were analyzed using Bland‐Altman analysis to determine the PET repeatability coefficient as a function of average baseline voxel SUV (repeatability coefficient for any voxel is the treatment‐induced SUV change from the average baseline value required for the change to be deemed significantly higher than baseline variation). Using the repeatability coefficient, the intra‐treatment PET nodal/GTV volume was divided into 3 groups of voxels: significantly reduced SUV, no significant difference, significantly increased SUV. A volume difference metric, defined as the difference in the percentages of node/GTV voxels with significantly decreased and increased SUV, was matched against each patient's post‐RT assessment of residual/no‐residual disease. Results: The PET repeatability coefficient decreased from 49–17% as the baseline voxel SUV increased from 2–12. The repeatability coefficient identified large volumes of the nodes (mean:52;std:35%) and GTV (mean:49;std:26%) as not having significant change. One patient had clinically‐assessed residual disease. The node/GTV volume metric for this patient was positive (22%/46%), compared to an average node/GTV volume metric of −36%/– 40% for patients without residual disease. Among the patients with no residual disease, only one had a positive nodal volume metric and one other had a positive GTV volume metric. Conclusions: The repeatability coefficient can be used in future head‐and‐neck studies with only one baseline PET. A positive volume metric on an early intra‐treatment scan may identify patients with residual disease post‐RT.
WE‐A‐217A‐05: Lung Deformations and Airway Stenosis with Distal Atelectasis in Patients Treated with Stereotactic Body Radiation Therapy for Lung Tumors
Authors: Diot Q , Kavanagh B , Gaspar L , Miften M
Published: June 2012

Purpose: To investigate the possibility to use lung deformations to differentiate between radiation‐induced fibrosis and potential airway stenosis with distal atelectasis in patients treated with stereotactic body radiation therapy (SBRT) for lung tumors. Methods: Planning and follow‐ ups CT scans were reviewed for 46 patients who received lung SBRT treatment at our institution between 2002 and 2009, in 3 or 5 fractions, and a median total dose of 54Gy (range, 30–60). Vector lung tissue displacements were studied for patterns of parenchymal deformation only in patients with follow‐up CT scans > 6 months. Planning CT lung surface contours were matched to the follow‐up scans and at least 50 anatomical landmarks inside the lung (vessel or airway branches) were identified on both scans to guide the deformation of the lung structure. Parenchyma displacements maps for the whole lung were interpolated from the landmark deformations and analyzed to identify tissue migrations towards the observed hyperdense region consistent with distal atelectasis. Results: Out of 46, only 24 patients demonstrated lung density changes with sufficient follow‐up time and image quality. Fifteen patients (62%) displayed converging deformation patterns and their average Hounsfield Unit change for the hyperdense region was 344HU and significantly higher than for the other patients (247HU, p = 0.03) supporting an alternate consolidation mechanism. The mean maximum dose to proximal airways was 38Gy for the converging pattern group versus 20Gy (p = 0.003) and a maximum likelihood Probit fit yielded TD50 = 24Gy, m = 0.56. The mean minimum dose to the hyperdense region was 15Gy versus 18Gy (p = 0.23). Conclusions: A correlation between converging deformation patterns and lung density changes was observed suggesting the possibility of an additional mechanism for lung density increase in addition to fibrosis. Correlations between converging patterns and dose to proximal airways also suggest a 24Gy dose‐threshold effect.