bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐D‐BRC‐01: Multi‐Fraction Dose Distributions for Image‐Guided IMRT of Prostate: Impact on TCP and NTCP
Authors: Battista J , Johnson C , Turnbull D , Kempe J , Bauman G , Van Dyk J
Published: November 2011

Purpose: IMRT of the prostate consists of multiple stages of treatment planning and dose delivery, each with inherent anatomical uncertainties. Differential filling of the bladder and rectum can displace the prostate during a course of treatment. The purpose of this study was to assess the effectiveness of adapting to these anatomical changes using various CT image‐guided adaptive (IGART) strategies. Methods: Our computer model is based on the Philips Pinnacle treatment planning system. A multi‐fraction simulation of 5‐field IMRT (76 Gy/35 fractions) yields the daily dose accumulation in individual tissue elements. Using megavoltage CT studies of 13 prostate cases, cumulated dose distributions are mapped onto the reference treatment plan. Total dose‐volume histograms are then processed to estimate the changes in tumor control probability (TCP) and normal tissue complication probability (NTCP) for various IGART scenarios. Results: Retargeting of the prostate generally maintains the intended TCP (typically 0.9 versus 0.8 with No Image Guidance) but is often associated with an enhanced risk of rectal toxicity (NTCP rises to 0.05 when Image Guidance is applied). This effect is due mainly to a systematic anterior shift caused by sag in the treatment couch (average 10mm). Without image‐guidance, this offset goes uncorrected, resulting in poorer coverage of the target with consistent avoidance of rectal exposure. Conclusions: Geometric repositioning without dose re‐planning is sufficient to maintain the intended TCP. IGART corrects for sag in the treatment couch and this results in greater risk of rectal toxicity, compared with no IGART. Smaller PTV margins could offset this effect, emphasizing the need for integrated image guided and intensity modulated delivery for optimal results. In the extreme, daily IMRT re‐planning based on in‐room imaging could exploit maximum benefits of this technology but this would require significantly more computing resources and streamlining of procedures at the treatment console.

Research funding was provided by the Canadian Health Research Institutes and the Ontario Research and Development Challenge Fund (OCITS Project), with Philips Medical Systems as an industry partner.
SU‐D‐BRC‐03: Spatial‐Temporal PET‐CT Features for Predicting Pathological Response of Esophagus Cancer to Chemo‐Radiation Therapies
Authors: Tan S , Chen W , Lu M , Kim G , Feigenberg S , DˈSouza W , Suntharalingam M , Lu W
Published: November 2011

Purpose: The purpose of this study is to develop new PET‐CT features for predicting the pathology response of esophagus tumor to chemo‐radiation therapies, and to compare their discriminant power with SUV‐max and SUV‐peak. Methods: Fifteen patients with locally advanced esophagus cancer and treated with tri‐modality therapies were studied. All patients underwent a Pre‐treatment and a Post‐treatment PET/CT. The Pre‐ and Post‐ CT images were first aligned with a rigid registration constrained in the chest region. All images were then projected into the Pre‐PET coordinate. Two different tumor regions of interest (ROI‐SUV2.5 and ROI‐SUVPeak) were produced. Various features capturing tumor shape, texture and intensity information were extracted, resulting in a total of 432 features for each patient. Receiver operating characteristic analyses were performed to investigate and compare the discriminant power of each feature. The ground truth was set to be the pathological response in the surgical specimen. Finally, trend analysis was conducted to examine whether a tumor is more likely a responder as the value of a feature increases or decreases. Results: Five among all 432 features have higher discriminant power than that of SUV‐max and SUV‐peak. These include two shape features, one intensity feature, one texture feature and one shape plus intensity feature. Among them, the Decline of Total Glycolytic Volume feature is extracted from the Diff‐SUV image. All five features were based on the larger tumor region ROI‐SUV2.5. Conclusions: Results demonstrated that shape, texture and intensity information are all important for predicting esophagus tumor pathological response to chemo‐radiation therapies. Integrating both spatial and temporal information is also important. Features based on a larger tumor region seem to be better than those based on a single point or a smaller tumor region.

This work is supported in part by NIH 1R21CA131979.
SU‐D‐BRC‐05: Characterizing Therapy‐Induced Brainstem Injury and Recovery with Serial Diffusion Tensor Imaging
Authors: Hua C
Published: November 2011

Purpose: To characterize therapy‐induced changes in normal‐appearing brainstems of childhood brain tumor patients by serial diffusion tensor imaging (DTI). Methods: We analyzed sequential DTI of 20 brain tumor patients, aged 4–23 years, with normal‐appearing brainstems included in the radiation treatment fields. Prescribed tumor doses ranged from 54 to 59.4 Gy. Parametric maps of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were computed and registered to three‐dimensional radiation dose data. Volumes of interest included corticospinal tracts, medial lemnisci, and the pons. Serving as an age‐related benchmark for comparison, DTI studies from 20 healthy volunteers, aged 6–25 years, were included in the analysis. Results: The median DTI follow‐up was 3.5 years (range, 1.6–5.0 years). The median mean dose to the pons was 56 Gy (range, 7–59 Gy). Three distinctive patterns of temporal changes in FA and ADC were observed in the pons: (1) a stable or normal developing time trend similar to those observed in healthy children, (2) initial deviation from normal with subsequent recovery, (3) progressive deviation without evidence of complete recovery. In this group of patients without severe brainstem necrosis, maximal decline in FA often occurred 1.5 to 3.5 years after the start of radiation therapy. A full recovery time trend could be observed within 4 years. Patients with incomplete recovery often had a larger decline in FA within the first year. Radiation dose alone did not predict long‐term recovery patterns. Conclusions: Longitudinal DTI analysis revealed variation among individual patients in diffusion properties of brainstems reflecting therapy‐induced white matter injury and recovery. Early response in brainstem anisotropy may serve as an indicator of the recovery time trend over 5 years following radiation therapy. Attention should be given to patients with pronounced early changes since DTI suggested their recovery was slower and less complete than other patients.

Acknowledgement: NIH grant HD049888.
SU‐D‐214‐06: Designing Simulators for Studying Medical Physics: From CT Imaging to Radiotherapy Treatment Planning and Quality Assurance
Authors: Kum O , Choi W , Park K , Chung Y , Han Y
Published: November 2011

Purpose: Designing simulators for studying medical physics ranging from CT imaging to radiotherapy treatment planning and quality assurance will be very valuable for students, educators, and medical professionals to learn and teach radiation physics principles and to perform virtual practicing of the patient diagnosis and treatment based on physical principles. Methods: A Monte Carlo method is the best to simulate the radiation transport phenomena. Thus, in this project, we used our in‐house Monte Carlo code, PMCEPT code, to simulate directly the interactions between the radiation and the patient body. However, for better understanding of the complex physical phenomena involved in the radiation interactions with matter, some augmenting novel computational approaches such as ray‐tracing and medical image segmentation algorithms are included. Specifically, fast ray tracing method is useful for better understanding the CT images and the near future IGRT treatment planning. For the real time simulations, parallel algorithms adaptive to PC cluster and GPU‐accelerated algorithms were employed. Results: The CBCT simulator with a set of ray beams emitting towards every pixel center of the detector from the X‐ray source was developed. Semi‐automatic segmentation of CT image using watershed algorithm and graphical user interface was developed for analyzing the DICOM data to provide ASCII data file which is readable. The external beam accelerator operated with keyboard and mouse was developed. Conclusions: The important benefits of these virtual simulators may be the replacement of the conventional laborious procedures which are required for the expensive hardware simulator units, the efficiency increment, the accuracy improvement of radiation treatment procedure, and the cost reduction in terms of time and physical patientˈs presence. A more extensive assessment of the efficiency improvement provided by these simulators is still under investigation and will be presented in future articles.

This research was supported by BSR program through NRF funded by the MEST (grant # 2010‐0003983)
SU‐D‐110‐02: Evaluation of the Differences between Locoregional Lung Ventilation Estimation Methods Using a Single Deformable Image Registration Algorithm
Authors: Latifi K , Zhang G , van Elmpt W , Hoffe S , Dilling T , Stawicki M , Dekker A , Forster K
Published: November 2011

Purpose: Three methods of calculating ventilation from 4D CT image sets have been explored by several research groups. This study is to investigate the differences of these three local ventilation calculations. Methods: Optical flow (OF) deformable image registration of the normal end expiration and inspiration phases of 4D‐CT images was used to correlate the voxels between the two phases. The OF was validated using a 4D pixel‐ based and point‐validated breathing thorax model, consisting of a 4D‐CT image data set along with associated landmarks. Ventilation derived from 4D‐CTs from 20 esophageal patients were retrospectively analyzed. Differences between the ventilation images generated by three methods, the Jacobian, the DeltaV, and the HU, were examined on a voxel‐to‐voxel basis. The Jacobian method uses the first derivative of the deformation field to approximate the change in volume of voxels. The DeltaV method directly calculates the volume change. The HU method uses the change in Houndsfield Units (HUs) of corresponding voxels to calculate ventilation. Results: The target registration error (TRE) for the deformable image registration was an average of 1.6±0.68 mm and maximum of 3.1 mm. Average difference between the DeltaV and the Jacobian ventilation as a percentage of the maximum ventilation value was 0.51±0.3% (range 0.33% to 1.32%). Average difference between the DeltaV and HU ventilation was 2.4±4.5 % (range 0.4% to 19.2 %). A small number of voxels show significant differences. We speculate that the larger differences were due to some image registration variances. Regions of highest and lowest ventilation matched well for all methods. Conclusions: Highs and lows in ventilation were more pronounced in the DeltaV method compared to the Jacobian. In general the differences between the two ventilation methods were small. However, the differences between the DeltaV and the HU methods were considerably larger.
SU‐D‐301‐02: Increase of Generalized 2D NEQ for the Microangiographic Fluoroscope (MAF) System Using the Medium Rather than the Small Focal Spot
Authors: gupta S , Bednarek D , Rudin S
Published: November 2011

Purpose: To increase the generalized NEQ (GNEQ) for the new high‐ resolution Microangiographic Fluoroscope (MAF) by using the increased tube‐loading capacity of the medium focal spot compared to the small focal spot. Methods: Generalized MTF (GMTF), generalized NNPS (GNNPS) and GNEQ were calculated for the MAF at a fixed object magnification of 1.11 for the medium and small focal spots on the central axis and the medium focal spot on the anode side. Due to increased tube‐loading capacity of the Toshiba Infinix system for the 0.5‐mm medium focal spot compared to the 0.3‐mm small focal spot, the 2D NNPS was calculated at 3.125 times higher dose on the central axis and 2.85 times higher dose on the anode side (considering a 9% reduction in intensity due to the Heel effect) for the medium spot. Results: The GNEQ ratio of medium‐to‐small focal‐spot at the central axis is much greater than 1.0 at low frequencies, with a rapid drop at higher frequencies in the tube axis direction, becoming less than 1.0 above 7 cycles/mm. The GNEQ of medium focal spot at the anode side is higher at nearly all frequencies below the Nyquist due to the reduced effective focal spot size, becoming less than 1.0 above 9 cycles/mm. Conclusions: Improvements in GNEQ can be obtained for the MAF using the medium focal spot as compared to the small focal spot at the central axis position at low frequencies, whereas the GNEQ is improved for almost all frequencies for the medium focal spot at the anode side. There is a clear benefit to utilizing the increased tube output for the medium focal spot, while decreasing the effective anode angle to reduce focal spot size but maintain sufficient FOV for the MAF. Support: NIH Grants R01‐EB008425, R01‐EB002873
SU‐D‐220‐02: Optimal Transducer Position for 4D Ultrasound Guidance in Cardiac IGRT
Authors: Bruder R , Ernst F , Stender B , Richter L , Schweikard A
Published: November 2011

Purpose: Currently effort is taken to use radiation therapy to cure arrhythmia. In this circumstance the left atrium and the pulmonary veins have to be irradiated. While the precise robot system placing the beam onto a moving target already exists, sensory information for target movement acquisition and heart‐beat motion compensation still have to be analyzed. One possibility for real‐time, direct target localization during treatment is three‐dimensional, transthoracic ultrasound requiring a transducer to be positioned on the patientˈs chest. The imaging and ‐as a result ‐tracking quality highly depends on this positioning choice. Especially when a patient lies in treatment position on his back, it is difficult to find a transducer position, which allows suitable imaging quality. Methods: We present an automatic algorithm which calculates the patient‐specific ultrasound imaging quality from a given CT scan. A quality function is executed in real‐time on the graphics card calculating the target reflectivity in beam direction as well as the distance and the absorption in the line of sight from transducer to the chosen target. The optimal transducer position is found as the area on the skin with the best results of the quality function and at least the area of the size of the ultrasound transducer. Results: We have tested the algorithm with 10 CTs. For general cardiac imaging the calculated transducer positions mostly fit with the typical ultrasound views found in literature. Nevertheless, the acquisition of special targets, such as the atria and pulmonary veins, often requires or at least profits from an off‐standard transducer placement. Conclusions: We have found a reliable method to calculate an optimal transducer position for a specific target inside the heart without the need to iteratively search and optimize it. In this way electronic (e.g. robotic) transducer placement during treatment becomes possible.
SU‐D‐220‐03: Inter‐ and Intra‐Fraction Verification with Integrated On‐Board Xray CBCT and 3D Ultrasound Imaging: A Feaibility Study
Authors: Xia P , Lachaine M , Kazanzides P , Iordachita I , Stephans K , Wallace J , Herman J , Wong J
Published: November 2011

Purpose: CBCT and 3D Ultrasound (3DUS) provide complementary information on bony landmarks and soft tissues, particularly for abdominal sites. Furthermore, 3DUS can potentially track intra‐fractional motion of soft tissues. In this study, we investigate the feasibility of integrating these two modalities to provide a comprehensive image guidance procedure that corrects for both inter‐and intra‐fractional motion. Methods: The ultrasound probe will be operated under robotic control to enhance reproducible placement. We investigated the effect of potential CT artifacts caused by the probe and the subsequent effect on treatment plan dose calculation. We then measured the effect on ultrasound image quality due to an 18 MV radiation beam in close proximity to the probe. A phantom was constructed by imbedding markers in gel. The reproducibility of the marker positions under controlled repeat compressions, mimicking robotic placement, was measured. The effect of removing a beam to allow probe placement during treatment was studied by comparing optimized liver plans with or without the specific beam. Results: CT artifacts associated with probe placement affected treatment planning dose by 20%. The artifacts can be avoided with a CT‐compatible model probe. Radiation dose delivered 1 cm from the probe did not affect the ultrasound image quality. When the same compression was used to compress the gel phantom, the positions of the fiducial markers were reproducible to within 0.3 mm. The reoptimized liver plan with the omission of one beam was not noticeably different from the original plan. Conclusions: On‐board x‐ray CBCT is highly effective for patient setup based on bony landmark. 3DUS is a non‐invasive, non‐ionizing means to continuously monitor soft tissue motion. Our studies indicate that it is feasible to combine both systems during treatment. Their integration, enhanced by robotic repositioning, provides a highly complementary approach for IGRT of soft tissue sites in the abdomen.

Martin Lachaine is the Director of Research at Resonant Medical.
SU‐D‐220‐05: Dynamic Ultrasound Evaluation of Radiation‐Induced Vocal Cord Injury in Head and Neck Cancer Patients
Authors: Chen H , Beitler J , Tridandapani S , Yoshida E , Walter C , Liu T
Published: November 2011

Purpose: Curative radiation for oral cavity, oropharyngeal, hypopharyngeal and nasopharyngeal cancers can injure the vocal cords which can adversely affect speech and quality of life. Vocal cords are difficult to image with conventional MRI, CT or ultrasound. Currently, no imaging technique is available in the clinic to visualize and evaluate such injury. The purpose of this study is to develop a dynamic ultrasound technology to quantify radiation‐induced vocal cord injury. Methods: Eight healthy volunteers and five post‐radiation patients were enrolled under IRB approval. Each participant was scanned using a clinical ultrasound scanner (Sonix Touch) with a 14‐MHz linear array transducer. The ultrasound probe was placed in the transverse plane approximately parallel to the vocal foldˈs mucosal wave propagation. Each participant was asked to phonate the vowel sound “a” and sustain the phonation for 5 seconds while 315 dynamic (consecutive) ultrasound images of the vocal fold were recorded. Vocal cord vibration patterns were obtained through these consecutive images. Vibration frequency and 2‐D dimensions were computed to measure vocal cord performance. Results: The vocal cords were clearly visualized using dynamic ultrasound in all participants. Vocal cord vibration patterns of the healthy volunteers revealed smooth sinusoidal wave propagation. In contrast, the patterns of post‐radiation vocal cords presented irregular wave propagation. M‐mode videos parallel and vertical to vocal cord vibration direction were generated. The vocal cord vibration pattern was most disrupted in the patient with clinically‐identifiedvocal cord injury. Aliased frequency estimated from M‐mode video could be used to distinguish damaged vocal cord injury from normal vocal cord. Conclusions: In the effort to develop a noninvasive imaging technique for evaluating vocal cord injury post radiotherapy, we identified dynamic ultrasound as a promising tool. Ultrasound is safe, simple, and cost‐effective. This study demonstrated its feasibility in imaging the vocal cords and quantifying the vocal cord condition.

Part of this research is supported by Susan Komen Grant (KG101373).
SU‐D‐220‐06: Non‐Contact (Air‐Coupled) Ultrasound Applied to Cortical Bone Phantoms
Authors: Ganezer K , Halcrow P , Bulman J.
Published: November 2011

Purpose: The purpose was to take the first steps towards applying Non‐Contact Ultrasound (NCU) to the in‐vivo monitoring of osteoporosis and to skeletal quantitative ultrasound imaging (QUS) using cortical bone. The goals of this study focused on the possible advantages of NCU such as its lack of reliance on a technologist and a layer of acoustical coupling gel, its ability to use methods similar to those in x‐ray imaging, and the likely reduction in statistical and systematic errors. This project pursued additional applications of NCU beyond its usage in assessing the severity of third degree burns. Methods: An NCU imaging system, a pair of broadband, 1.5 MHz, non‐contact transducers, and cortical bone phantoms were used to determine bone mineral density (BMD), speed of sound (SOS), integrated acoustical response (IR), and ultrasonic transmittance. Air gaps of greater than 3 cm, two transmission and reflection paths, and a digital signal processor were used to collect data from phantoms of nominal mass density and (BMD) from 1.17 g/cm3 to 2.25 g/cm3 and from 0 g/cm3 to 1.7 g/cm3. Results: Good correlations between known BMD and measured SOS, IR, and transmittance were obtained for all 14 phantoms. Repeated measurements of the speed of sound (SOS), thickness, and IR for the phantom set show a small variation of plus or minus 1–2 %. These NCU data were shown to be in agreement with similar results from contact ultrasound to within 1–2%. Attenuation images of cortical bone phantoms showed discernible differences as a function of BMD. Conclusions: The results suggest that NCU might find additional applications beyond burn assessment. Since the NCU and conventional gel‐coupled measurements yield similar results, our air‐coupled methods might be able to reach levels of accuracy close to those attained with gel, while avoiding the disadvantages of contact.

The authors would like to express their gratitude to the National Institutes of Health who supported this research through Grant Number GM 08156‐22 and its supplements which included funding for obtaining an NCU system and other ultrasound hardware used in this study.
SU‐E‐E‐01: Hands‐On Treatment Planning Education for Medical Physics Students and Radiation Oncology Residents
Authors: Smilowitz J , Gondi V , Tome W
Published: November 2011

Purpose: We aim to supplement the didactic education of medical physics graduate students with a laboratory course on treatment planning systems (TPS.) TPS are ubiquitous in clinical practice and research. Physicists are responsible for development, commissioning, maintenance and QA of these increasingly complex systems. Oncologists rely on physicist expertise for the safe and efficacious TPS use. Hands‐on training has been limited due in part to access to clinical TPS. Methods: A teaching laboratory was developed to train medical physics graduate students with 6 workstations running commercially available TPS. An upper level special topics graduate course was designed around the laboratory. It has a clinical focus and is structured by disease site to reinforce physics topics with practical relevance. Commissioning and dose algorithms are taught after students have system familiarity, enabling less software focus and greater understanding using plans to illustrate the effects of beam model parameters. Results: Based on student evaluations and enrollment, the class is a success. Our initial class had 11 students, and in 4 years it has doubled in size. It has become a popular staple of our graduate curriculum. The average student evaluation score (out of 5) of lecture and lab respectively are 4.74 and 4.52. These are among the highest for our department. Improvements in content and structure have been made each year based on student feedback. Additions included exercises on a third TPS and physician‐taught clinical lectures to complement disease sites. Conclusions: This course will be a regular timetable offering. This innovative approach has been so well received so we are expanding this model to radiation oncology residents. An RSNA Education Grant has been applied for. Just as graduate students have honed their skills using the lab, medical residents will benefit from simulation exercises involving radiotherapy field design, optimization and dose evaluation.
SU‐E‐E‐02: The Affect of Backscatter and Later Phantom Dimension on Dosimetry of Radiographic Film
Authors: Srivastava R , De Wagter C
Published: November 2011

Purpose: The aim of this study is to determine the optimal backscatter thickness and later phantom dimension beyond the field size on the dosimetry verification with radiographic film when irradiating large volumes. Methods: The experiments were conducted for 6 and 18 MV 20 × 20 cm2 field sizes with XV2 and EDR2 films positioned at 10 cm depth inside (30 × 30 cm2) polystyrene and Virtual Water™ phantoms by varying the phantom backscattered thickness and changing the table height accordingly. A constant 100 cGy dose was delivered to EDR2 film for 6 and 18 MV by adapting the MU setting. A Farmer‐type ionization chamber was inserted centrally in a dedicated slab so that chamber position was kept at the same depth as the film. A laterally increased phantom studies were done by symmetrically increasing the lateral dimension in the gun‐target direction of the linear accelerator. Results: For 6 MV beam at 20 cm backscatter thickness, EDR2 film response in polystyrene is 20% higher than in Virtual Water™ phantom. Approximately the same difference exists between the XV2 results. The results show 11.4% and 6.4% over‐response of the XV2 film when compared to the ion chamber for 6 MV 30 × 30 cm2 and 10 × 10 cm2 field sizes respectively when the backscatter phantom thickness is 5 cm. For the same setup, measurements with EDR2 films indicate 8.5% and 1.7% over‐response. The film response on later scattered phantom study show nearly firm within 5 cm of lateral thickness and it increases when lateral thickness increases due to more multiple scatter of low energy photons. Conclusions: The backscattered phantom should not exceed more than 7cm for film accuracy. The lateral extension of the phantom should not be more than 5 cm from the field boundary in the case of large volumes.
SU‐E‐E‐08: Rotational IMRT Is No Turnkey Technique Yet: The Upcoming Challenge of Integral Dose in Head‐And‐Neck Cancer Treatment
Authors: De Hertogh O , Boukour Y , Viard R
Published: November 2011

Purpose: Rotational IMRT for HNC raises new challenges regarding the dose homogeneity within the PTV, and the dose delivered to the non‐tumour tissue (NTT). The purpose of this study is to: 1. develop a new parameter to assess PTV dose homogeneity. 2. evaluate the impact of the physicistˈs experience on the dose conformity to the PTV and containment away from the PTV. 3. calculate the resulting integral dose (ID), and subsequently propose an optimisation method using the ID as primary endpoint. Methods: Ten locally‐advanced HNC cases were contoured according to the EORTC‐RTOG consensus. DICOM studies were sent to 9 TomoTherapy European users. Planning was performed to 50Gy prophylactic dose and 70Gy therapeutic dose. Results: 1. The improvement in dose homogeneity achieved by each plan was calculated with respect to a reference DVH (minimally compliant with the ICRU‐62 requirements), using an AUC calculation. Hi‐ART planning increased dose homogeneity by 44 to 82%. 4. Dose conformity to the PTV was quantified by the Overlap Ratio (OR) and Dice Similarity Coefficient (DSC). Experienced users achieved higher conformity, i.e. 0.75 to 0.80 OR values and 0.85 to 0.90 DSC values. 5. Dose containment outside the PTV was evaluated by the Dose Gradient (DG). Experienced TomoTherapy users achieved sharper dose fall‐offs (2.5%/mm for bilateral volumes). 6. Improvement in dose conformity and fall‐off reduced the ID by a mean 20% (up to 30% in some patients) Conclusions: An AUC calculation assesses the IMRT‐related improvement in dose homogeneity, allowing separate analysis of the under‐ and overdosage regions. Dose to the NTT is a challenge. Experience in IMRT planning allows a consistent 20% decrease in ID. OR, DSC and DG have to become primary endpoints during optimisation. Further trials investigating rotational IMRT should encompass these parameters, as undisclosed discrepancies in ID will impact on treatment outcome and patient late complications.
SU‐E‐E‐16: Quality Assurance Check on Tomotherapy and Precalculation of Time
Authors: Sriramulu H Erra , Sharma A , Muruganandham M
Published: November 2011

Purpose: In order to find treatment time prior to the calculation since tomotherapy takes very long time for calculation and checking quality assurance on input parameters like modulation factor, field size, pitch experimentally. Methods: Cheese phantom was scanned and the target, organ at risk(inner circle and outer ring) were delineated concentrically. The target was sandwiched between OAR(organ at risk) and calculated the gantry rotation time and treatment time for various input parameters modulation factor(M), pitch(P) and field size(fs). Experimentally verified all these input parameters from the gantry speed and treatment time. The relation of dR/dT(rotation time/treatment time) against pitch and dM/dR(mod factor/rotation) against pitch were verified. Moreover by evaluating constancy c in the formula D = c Dr R/(PM) helps to calculating treatment time prior to planning in order to know the time in advance. Results: The field size verification from the graph dR/dT against pitch was done and obtained experimentally 2.52, 1.15, 4.97 for the field sizes set at the beginning of the experiment 2.48, 1 and 5. dM/dR with respect to pitch also verified which shows smooth power fit. The constancy c value obtained when gantry rotation speed saturates at 15s at the pitch value 0.143. Further decrease in pitch only alters treatment time, not the gantry speed. When R and t are constant and c is linearly proportional to M and P by referring above formula. If we evaluate experimentally the second order partial differentiation of c with respect to modulation factor and pitch, is given by 0.0151. The c is given by when rotation period is more than15s is 0.008=M*P*0.0151 and c varies when speed attains 15 according M and P variation. Conclusions: The quality assurance of input parameters can be assured. Calculation sheet was developed for particular thickness by knowing c and will vary if gantry speed attains constant. I am working as Medical Physicist in Kuwait Cancer Control Center. I worked this project by taking interest and spent my money for everything, boarding and lodging. I am very much thankful to Dr. Anil Sharma who has helped me in this project. I can work any sort of Medical Physics project.
SU‐E‐E‐19: Focal Therapy for Prostate Cancer with Permanent Prostate Brachytherapy
Authors: Moran B , Tack K , Keyes K , Banghart K , Braccioforte M
Published: November 2011

Purpose: Treatment outcomes for prostate cancer are intimately tied to the ability to locate the disease; current standard clinical practice utilizes DRE, PSA, and transrectal ultrasound (TRUS) extended systematic sextant biopsy for staging. Some speculation about enhanced diagnostic techniques such as MRI spectroscopy for triangulating disease has suggested that treating the prostate in its entirety may not be necessary. Methods: Stereotactic transperineal prostate biopsy (STPB) provides tissue evidence from all sections of the prostate, and itˈs accurate Gleason scoring ability has been correlated to surgically removed prostate pathology in over 74% of cases (n=85 prostates removed with previous STPB staging). Additionally, STPB was 95% accurate in predicting the location in those patients (81/85). Utilizing the comprehensive sampling of STPB pathological findings, focal therapy of prostate cancer is the next logical step. Seeds are then planned and implanted only in the areas of disease identified on STPB. Results: Figure 1 shows sample focal therapy loading in four such patients treated in the last year at Chicago Prostate, (the total prostate is contoured in orange, the yellow contour is the “target as delineated by BJM using STPB outcomes). Focal therapy may then provide a reduction in dose to the surrounding normal tissues (depending on the location within the gland to be treated). Conclusions: This treatment is tolerated well by patients and further follow up will continue. Focal therapy also shows promise for local treatment failure when it is most important to restrict dose to critical normal tissues which have already experienced radiation insult. Dose escalation to demonstrated disease cites is the goal of radiation therapy and in the new era of tissue‐proven disease location through STPB — focal therapy may further spare the surrounding normal tissues as well.
SU‐E‐I‐02: Automated Detection of Bifurcations in CT Images of the Lung
Authors: Xiong G , Xing L
Published: November 2011

Purpose: Vessel and bronchial bifurcations are ubiquitous in the lung and their respiration‐induced motions are visually apparent in 4D CT images. Manual and semi‐automated identification of bifurcations has been done previously, but this procedure is labor‐intensive, subjective, and not practical for routine use. Here, we propose a novel fully‐automated method for this task. Methods: Given a reference image, we first segment the lung region by adaptive thresholding and morphological operations. The blood vessels in the lungs are then segmented by a multi‐scale enhancement filtering and region growing. With the segmented vessels, we analyze the local shape profiles within the concentric spheres for all voxels. If the number of disconnected components is more than three, the particular voxel is classified as a bifurcation candidate and its distance to the vessel boundary is recorded as the candidate size. Since several bifurcation candidates can associate with one bifurcation, two candidates are selected to merge if their corresponding regions overlap. Finally, the candidate which has the largest bifurcation size among all candidates of the same bifurcation is labeled as the bifurcation point and its size is treated as the bifurcation size. We implement our method in parallel. Results: We tested our method in 5 cases. All detections are completed in less than 1 minute. On average, we are able to detect more than 500 bifurcations with accuracy greater than 90%, as determined by a quantitative comparison with the data identified by an experienced human observer. The number of bifurcations is far more than that can be accomplished by manual and semi‐automated approaches within the same time. Conclusions: The proposed approach can detect the bifurcations in lung CT images fast and accurately. The technique provides a prerequisite step for studying 4D motion of tissues in the different parts of the lungs using bifurcations as landmarks.
SU‐E‐I‐03: Evaluation of CT Texture Feature Changes Following Deformable Lung Registration
Authors: Cunliffe A , Al‐Hallaq H , Labby Z , Pelizzari C , Sensakovic W , Armato S
Published: November 2011

Purpose: The purpose of this study was to quantify the effect of deformable registration on the values of lung texture features extracted from chest computed tomography (CT) scans. Methods: Two clinical chest CT scans (slice thickness=1mm, pixel spacing<0.9mm, time between scans: 1 week–3 years) were collected for each of nine patients with no evidence of abnormal lung pathology. Automated lung segmentation was performed, and a deformable registration algorithm (“demons”) was employed to register each patientˈs follow‐up scan to their original baseline scan. Deformation accuracy was evaluated through inspection of a difference image and measurement of the mean Euclidean distance between landmarks in the baseline scan and deformed follow‐up scan. Over 1,500 spatially‐matched region‐of‐interest (ROI) pairs were extracted from each scan pair. First‐order, fractal, Fourier, Lawsˈ filter, and gray‐level concurrence texture features (196 total features) were computed for each ROI, and the percent change of each feature between matched ROIs was calculated. Because scans contained normal pathology, we expected texture changes to be introduced primarily by deformation. Fourteen features with a percent change standard deviation less than 10% across patients were identified. Analysis of variance (ANOVA) was performed to determine whether percent changes in texture features between patients were statistically different. Results: ANOVA showed mean percent changes in texture values to be significantly different between patients for all fourteen features (p<0.001); nevertheless, percent changes in texture features between baseline and follow‐up deformed scans were consistently small across patients. Twelve of fourteen features selected demonstrated mean percent differences less than 5%. These features were distributed among first‐order, fractal, and Lawsˈ filter classes. Conclusions: For some texture features, deformable registration may be performed without altering the feature value by more than 5% on average. These “invariant” features have potential for use in texture‐based evaluation of progressive lung disease using serial scans requiring registration.
SU‐E‐I‐07: Average Cross Sectional Dose for a CT Phantom through Fourth Order and Implications for 180° + Fan Angle Acquisition
Authors: Bakalyar D , Feng W
Published: November 2011

Purpose: To determine spatial average dose over the central plane of a cylindrical phantom through the 4th order from three measurements and also to determine spatial average dose for an arbitrary angle of irradiation. This has general applicability but is especially important for those cone beam CT installations where the irradiation angle is restricted to less than a full rotation. Methods: Assuming a uniform cylindrical cylinder and cylindrically symmetric conditions of irradiation, the dose distribution can be described using a radial function. Because of symmetry, the function must be even and thus when expanded as a polynomial can only have terms with even powers of the radial coordinate. Expanding to the fourth power and integrating leaves us with an expression for average dose which we have compared to our own measurements and Monte Carlo calculations. Application to cone‐beam CT presents a difficulty because oftentimes less than a full rotation is used during the irradiation process. Results: The results show that there is often an improvement over the use of a second order function; however, the additional complexity requires dose measurements at three radii instead of two. Though these results apply to all CT phantom measurements, sub full‐rotation acquisitions common in cone beam CT violate the symmetry in the irradiation pattern. However, we are interested only in the average dose and not the details of the dose distribution throughout the cross sectional area. With this restriction, we provide a proof along with recommended methodology that allows for the determination of average dose even if it is not possible to perform a full gantry rotation. Conclusions: The accuracy of phantom calculations has been extended to fourth order but at the expense of an additional measurement. The validity is extended to partial rotations.
SU‐E‐I‐08: Impact of Adaptive Statistical Iterative Reconstruction on Paediatric CT Protocols
Authors: Protik A , Ford N
Published: November 2011

Purpose: Dose optimization in CT is crucial in paediatrics since children are at higher risk for developing secondary cancer from medical exposure compared to adults. We examine the possibility for systematic dose reduction in clinical CT protocols with Adaptive Statistical Iterative Reconstruction (ASIR) technique. Methods: Utilizing a Catphan‐600 phantom and the Discovery CT750 HD (64‐slice CT) scanner we documented the effect of applying 0% or 50% ASIR on image quality (IQ) parameters over a wide range of kVp (80–140) and mA(10–400) settings. We assess the following parameters noise, spatial and contrast resolution, MTF, CNR and Wiener spectrum. For reconstruction we used axial 0.625 mm slices and both axial and coronal 5 mm MPR slices. We also studied the effect of varying amount of ASIR (0%, 30%, 50%, 70% and 100% ASIR) on image quality for 80kVp/150mA, 100kVp/150mA and 120kVp/150mA. By comparing the variable ASIR images to baseline images we have assessed the stepwise changes in the IQ parameters. Results: Improvements in image quality were demonstrated by using 50% ASIR for axial slices and their multiplanar reformats. On average this technique reduces noise by 30% for 0.625 mm axial, 26% for 5mm axial MPR and 28% for coronal MPR. However, it also reduces spatial resolution by 2.3% for 0.625 mm axial and 8.1% for 5 mm Axial MPR and 5.7% for Coronal MPR. ASIR improved the low contrast detectability by 30%. The CT number accuracy is not affected by the algorithm. Conclusions: Improved low contrast detectability and reduced image noise with ASIR in CT images could result in dose reduction in current paediatric protocols without compromising image quality or diagnostic objective. This study also provides quantitative assessment of the applicability and utility of ASIR for different diagnostic tasks.
SU‐E‐I‐09: Image Quality Evaluation on Reduced Doses in Brain CT Scans ‐ Anthropomorphic Phantom Study Using Adaptive Statistical Iterative Reconstruction
Authors: Zhou Y , Scott A
Published: November 2011

Purpose: To quantify for brain CT scans the image quality difference under various dose reduction and adaptive statistical iterative reconstruction (ASIR) blending options, and to find the optimal combination without experimenting on patients. Method and Materials: An anthropomorphic phantom (Atom, CIRS) was utilized with inserts for low‐ and high‐contrast resolution. The low‐contrast insert has various sized spherical (2 — 10 mm, 1–2% contrast) and cylindrical (1.2 — 7 mm, 1–2% contrast) targets. The high contrast insert contains line pair targets (6–12 lp/cm). Axial scans were conducted using a GE VCT with settings 120 kVp, 1 sec rotation, and 5 mm thickness. The baseline was set at 280 mA (CTDI_vol = 54 mGy) without ASIR. Other protocols utilized a combination of dose reduction rates between 20% and 50% and ASIR blending between 10% and 50%. The contrast‐to‐noise ratio (CNR) was computed for the biggest targets. The contrast detailed analysis was also conducted. To compare spatial resolution, a rectangular ROI was applied to the 6 lp/cm target. The resulting standard deviation was used as a descriptor for spatial resolution. Results: For each dose level, CNR improved linearly with ASIR blending fraction but spatial resolution decreased linearly albeit at a lower rate. As the dose was reduced to 33 mGy or less, the spatial resolution reduction rate increased significantly (50%) while the contrast improvement rate was relatively stable. At the same ASIR blending fraction, the images at the lower dose showed lower contrast and spatial resolution. Conclusions: Applying ASIR improves low contrast but reduces spatial resolution. As compared to the baseline (54 mGy), the overall image quality may be at optimal at 43 mGy or 37 mGy with 20% or 30% ASIR. The image quality at 33 mGy or less is appreciably decreased. The analysis on the low contrast detectability showed similar results
SU‐E‐I‐11: Extraction of Blood Flow Patterns and Calculation of Heart function Parameters in Dual Source CT Angiography
Authors: Chen S , Wei D , Gao M
Published: November 2011

Purpose: A new approach is presented to extract the coronary artery blood flow patterns from the angiographic data and to calculate the parameter to evaluate the heart function. Methods: This method uses five patientsˈ coronary angiographic data. Firstly, use a ˈseedˈ method to extract the coronary artery in a completely automatic way. Secondly, acquire the blood flow patterns from the angiographic data with a ‘dynamic registration’ method and save the result image sequence as an AVI file. Finally, calculate the heart function parameter (velocity of blood flow) by frame counting method. Results: The accurate boundary of the coronary artery and the blood flow is clearly presented, and the velocity of blood flow is similar to the Dopller ultrasound measurement. Conclusions: This method is shown with good performance, particularly in modeling the blood flow patterns and calculation of heart function parameter. It provides not only an automatic, fast, real‐time and accurate method in precise diagnosis and treatment of coronary disease, but also a complementary criterion to evaluate the heart function, and then predict the recovery.
SU‐E‐I‐13: A Model for CT Contrast Agent Evaluation
Authors: Bonvento M , Jambawalikar S , Button T
Published: November 2011

Purpose: A model is presented that has been designed to evaluate and optimize the use of CT based contrast agents. Initial validation of the model was undertaken and presented here. Methods: The model employs computed spectra from the x‐ray tube at a specified kilovoltage, attenuation correct ion applied to the spectra for filtration and projection of the spectra through a cylindrically symmetric phantom which may also contain a virtual contrast agent filled target at its center. Noise was applied to computed projection data based on photon counting and standard filtered back projection applied to provide a simulated image from which signal‐to‐noise (SNR) can be computed. In the case of a virtual contrast agent filled target, the contrast‐to‐noise ratio (CNR) can be determined as well. Dose at the center of the phantom is computed from the calculated photon fluence. In this model, the CNR per unit radiation dose and/or per unit of contrast agent may be computed. The impact of kilovoltage and filtration on this parameter may be assessed allowing for optimized imaging conditions. In this initial validation of the model a uniform water equivalent plastic phantom was assumed and the CT number and radiation dose were computed for a CT system operating at 120 kVp and 100 mAs. The results were compared to direct measurement for a GE CT system under these conditions.Results: The CT number and dose provided by the model was ‐ 0.04 and 0.440 cGy respectively. This agreed within 3.5 H.U. and 11% of measured value when scatter is added to the model Conclusions: Computed tomography dose, and with further refinement, SNR and CNR may be accurately computed using this model. Placing a virtual contrast agent containing target at the phantom center will allow for prototype contrast agent evaluation and allow for the optimization of technical parameters.