bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐C‐211‐06: A New Treatment Plan Quality Index for NPC SIB‐IMRT
Authors: Jin X , Xie C , Yi J , Han C , Zhou Y
Published: June 2012

Purpose: To proposed a new plan quality index to fasten the evaluation and comparison of the competing multi‐isocenter SIB‐IMRT (intensity modulated radiotherapy with simultaneous integrated boost) plans for NPC (Nasopharyngeal Cancer) patients. Methods: Multi‐isocenter SIB‐IMRT plans at 2.5 Gy/fraction for GTV (gross tumor volume) and 2.0 Gy/fraction for CTVs (clinical tumor volume) with different OAR (Organ at Risk) constraint levels were generated with BrainSCAN 5.2 and m3 MLC. DVH (dose volume histogram) were read from treatment planning system by custom software (written with Matlab 7.1). Various items was read and calculated. A plan filter matrix with variable plan quality items was introduced to filter plans that fail to satisfy the customed criteria. PTV plan quality indices including TC (target coverage), V93, HI (homogeneity index), TCP (tumor control probability), and OAR plan quality indices including NTCP (normal tissue control probability), V26, and V32 of parotids were calculated for qualified plans. A unique composite plan quality index (CPQI) was proposed based on the relative weight of these indices to evaluate and compare plans. Plan ranking results were compared with physician's evaluation results to verify the accuracy of this new plan quality index. Results: The average CPQI values for plans with OAR constraint level of low, normal, high, and PTV only were 0.22±0.08, 0.49±0.077, 0.71±0.062, and −0.21±0.16, respectively. There were significant differences between these plan quality indices (One‐way ANOVA test, p<0.01). This consistent with physician's ranking results with 99.3% OAR high plans accepted. Conclusions: Plan filter matrix was able to fasten the plan evaluation process. The new matrix plan quality index CPQI showed good consistence with physician ranking results, it is a promising tool for optimal plan selection.
SU‐C‐213AB‐02: Independent 3D‐Dose Calculation Verification for High‐Dose Rate (HDR) Brachytherapy Using a Dicompyler Plug‐In
Authors: Lin J , Panchal A , Roeske J
Published: June 2012

Purpose: To implement an independent check on the 3D dose calculation for high‐dose rate (HDR) brachytherapy treatment planning using a custom plug‐in written for dicompyler. Methods: A plug‐in was developed for the open‐source program dicompyler that produces an independent 3D dose calculation based on DICOM‐RT files produced by BrachyVision (Varian Medical Systems, Palo Alto, CA). Using the DICOM‐RT files as input, dose is calculated to a 3D grid using a point source approximation. Dose volume histograms (DVHs) are then calculated and compared with those produced by the planning system. In order to evaluate the program, patient data was tested using four different parameter configurations for the independent dose calculation: Group 1 with average anisotropy set to 1 and no polynomial term, Group 2 with average anisotropy set to 1 and the Meisberger polynomial applied, Group 3 with average anisotropy set to 0.98 and the Meisberger polynomial applied, and Group 4 with average anisotropy set to 0.98 and no polynomial term. The tumor sites of the patients used in this study were: Prostate (n=10), Breast (n=10), Gynecological (n=10), Base of Tongue (n=4), and Sarcoma (n=3). DVHs computed using dicompyler and the original planning system were compared using differences in the area under the curve (AUC). Results: Comparison of original and independently calculated volumes showed good agreement with an average difference of 3.5%. Average differences in the AUC varied by group: +1.05%, +0.70%, − 1.36% and −0.95%, for Groups 1–4, respectively. The average time for a 3D independent dose calculation was ∼5 sec. Conclusions: With this custom plug‐in, dicompyler can be used to provide an independent, 3D dose calculation verification for HDR planning. Since it uses DICOM files directly, the approach is efficient, and it provides not only an independent dose check, but also validates the 3D positions of sources and surrounding organs.
SU‐C‐213AB‐03: Monte Carlo Computed KQmsr Correction Factors for Reference Dosimetry of Tomotherapy Beams for 7 Ion Chambers
Authors: Sterpin E , Mackie R , Vynckier S
Published: June 2012

Purpose: To compute kQmsr correction factors for various types of ion chamber (Exradin A1SL, A12; PTW 30006, 30010, 31014, MicroLion and NE‐2571) using Monte Carlo (MC) simulations according to the new formalism of Alfonso et al (Med. Phys. 35 2008) Methods: TomoTherapy units are not able to realize reference conditions specified in current codes of practice like IAEA/TRS‐398 and AAPM/TG‐51. To cope with this issue, Alfonso et al described a new formalism introducing machine‐specific (msr) factors kQmsr for reference dosimetry, applicable to static TomoTherapy beams. In this study, those factors were computed directly using MC simulations for Q0 corresponding to a simplified 60Co beam in TRS‐398 reference conditions (at 10 cm depth). Msr conditions were a 10×5 cm2 TomoTherapy beam, source‐surface distance of 85 cm and 10 cm depth. The chambers were modeled according to technical drawings using the egs++ package and the MC simulations were run with the egschamber user code. Phase‐space files used as the source input were produced using Penelope after simulation of a simplified 60Co beam and the TomoTherapy treatment head modeled according to technical drawings. Correlated sampling, intermediate phase‐space storage and photon cross‐section enhancement variance reduction techniques were used. The simulations were stopped when the combined standard uncertainty was below 0.2%. Results: All correction factors were close to one, from 0.991 for the PTW 31014 to 1.000 for Exradin A12 (+− 0.002). The factor obtained for Exradin A1SL (0.997 +− 0.002) confirmed previous findings. This work provides msr correction factors for additional chambers used in reference dosimetry. Conclusions: Global msr correction factors obtained in this study can be used directly for reference dosimetry of static tomotherapy beams. In the Alfonso et al formalism, intermediate factors are introduced to link the new formalism to existing protocols. Those intermediate factors are not needed here. This work has been partially supported by Accuray. Thomas Rockwell Mackie is a consultant of Accuray and has therefore a potential conflict of interest.
SU‐C‐213AB‐04: Dosimetry for Dynamic IMRT Photon Beams
Authors: Liang X , Zhu T
Published: June 2012

Purpose: To develop a model accounting for differences of dose per monitor unit between dynamic and stop‐and‐shoot IMRT. Methods: For IMRT photon beams, treatments can be divided into stop‐and‐shoot mode and dynamic mode based on the movement of the multileaf collimator (MLC) during the photon delivery. However, dose measurements from a Varian photon beam based on these two different types of treatments are varied for at least 8%. We propose a model to compensate for this discrepancy, based on the physical parameters of both the MLC shape and moving pattern. In this model, A MLC minimum width is developed to explain the cause of the discrepancy, and dose calculation is implemented by convolving the source kernel with the multi‐leaf profile function with different moving patterns. Thus, dose calculation under stop‐and‐shoot mode and dynamic mode are both obtained using this convolution method. Results: Analytical models have been obtained for stop‐and‐shoot and dynamic modes for IMRT. The theory predicts that doses from dynamic mode are higher than dose from the stop‐and‐shoot mode, which reflects the experimental results. MLC minimum widths for different photon beam energies are also obtained. Conclusions: This work models the MLC shape and movement pattern for IMRT dose calculation, and explains the dose difference between two modes. The theory, as well as the results in this work provides a useful tool for photon beam IMRT dose calculation.
SU‐C‐BRCD‐01: Spatial Variation of Dosimetric Leaf Gap and the Impact in Dose Delivery
Authors: Kumaraswamy L , Schmitt J , Podgorsak M
Published: June 2012

Purpose: To evaluate the variation of dosimetric leaf‐gap (DLG) along the travel path of each MLC leaf pairs. Furthermore, dosimetric implication of this variation is studied for several dynamic MLC fields. Methods: During dose calculation, the treatment planning systems (TPS) retracts the MLC leaf positions by half of the DLG value (measured at CA) for all leaf positions in a Dynamic MLC plan to accurately model the rounded leaf ends. The 6 MV DLG values were measured, for all leaf pairs, in increment of 0.5 cm at Dmax, in the direction of leaf motion. The measurements were performed on three Varian Linacs, employing the Millennium 120‐leaf MLCs. Measurements were performed using both the Sun Nuclear MapCheck device and the PTW pinpoint ion chamber. Measurements with an ion chamber were also performed with varying leaf gaps to determine % change in dose with leaf gap discrepancy. Results: The measured DLGs for all leaf pairs were very similar along the in‐plane direction; varying maximally only by 0.3 mm. But in the in the leaf travel direction, the DLG increases gradually from CA to 6.0 cm off‐axis, reaching to a maximum variation of 1.6 mm for a particular leaf pair. Varying gap measurements indicate that DLG deviation of about 1 mm can cause a dose difference of about 5.0 % for a fluence with 1.5 cm leaf width sweeps and significantly increases to about 12.5 % difference for 0.5 cm sweeps. Conclusions: The spatial variation in DLG is caused by the variation in beam spectrum as well as MLC motion across the field. Fields with dynamic MLC centered on the CAX would not be affected since DLG does not vary as much; but any field residing significantly off‐axis with narrow sweeping leafs can exhibit significant dose differences due to large DLG differences.
SU‐C‐BRCD‐03: Recommendations for Quality Control of Prostate Brachytherapy with I‐125 Seeds, Based on a Survey of Current Practice in the Netherlands and Belgium
Authors: Koedooder C , Rijnders A , Aalbers A , de Brabandere M , Moerland M , Schaeken R , Thissen B , van 't Riet A , Vynckier S
Published: June 2012

Purpose: Giving guidelines and recommendations for Quality Control of prostate brachytherapy with I‐125 seeds, based on an inventory of current practice in the Netherlands and Belgium. Methods: A Working Group of the Dutch Commission on Radiation Dosimetry performed a written survey of current QC practice in 34 hospitals, of which 31 were also visited. For 2–4 of the locally used seeds Air Kerma Strength was measured with an SI IVB1000 well chamber and a PTW SourceCheck and compared with manufacturer's stated values and, if applicable, with a measurement with local equipment. With the locally used TPS's, calculations for 5 different representative configurations were performed and compared with calculations based on the AAPM TG‐43 formalism. Results: About 40% of the institutes responding to the written survey reported doing no verification measurements prior to clinical use of seeds. The remaining 60% only performed a constancy check, based on an average source strength value, obtained over a certain period of time. For lack of calibrated equipment, only few were able to perform measurements in terms of Air Kerma Strength. Three measurement devices were ADCL traceable, four were calibrated by the manufacturer. For the two most frequently used seed types (Oncura Oncoseed 6711 and IBt Intersource 1251L) the lowest and highest measured ratio between manufacturer's stated value and value measured by the visiting team was 0.943 (Oncoseed/SourceCheck) and 1.047 (Intersource/Sourcecheck) respectively. The majority of measurements, however, showed a discrepancy <3%. Four different TPS's were in use. The tests showed variations in dose calculations due to incorrect application of anisotropy models and application of obsolete source data. Conclusions: In a report of the Dutch Commission on Radiation Dosimetry, the AAPM recommendations to perform seed measurements prior to the implantation procedure, using traceably calibrated equipment, are endorsed and QC recommendations for TPS's are formulated.
SU‐C‐BRCD‐04: Development of An Efficient and Effective Patient Specific QA Program for IMPT
Authors: Zhu X , Li H , Li Y , Lii M , Taylor M , Zhang X , Poenisch F , Frank S , Gillin M , Sahoo N
Published: June 2012

Purpose: Intensity modulated proton therapy (IMPT) patient specific quality assurance (QA) program based on measurement alone could be very time consuming due to highly modulated dose distributions of IMPT fields. In this work, we present our efforts for developing an efficient and effective patient specific QA program for IMPT. Methods: The improved QA program, based on a previously reported one for single field uniform dose (SFUD), consists of three components: measurements, independent dose calculation and analysis of patient specific treatment delivery log files. Measurements included two‐dimensional (2D) measurements for each field delivered at the planned gantry angles with electronic medical record (EMR) system in the QA mode and the accelerator control system (ACS) in the treatment mode and additional depths for each field with ACS in physics mode without using the EMR. Dose distributions in a water phantom for each field were calculated independently using a recently developed in‐ house pencil beam algorithm and compared with the results of TPS. The treatment log file for each field was analyzed in terms of deviations in delivered spot positions from their planned positions using various statistic analysis methods. Results: With the improved patient specific QA program, we are able to verify (1) the dose calculation of TPS, (2) integrity of the data transfer from TPS to EMR to ACS and (3) treatment delivery including dose delivered and spot positions. We estimated that the in‐room measurement time required for each complex IMPT patient like head and neck patients would be less than 2 h. Conclusions: We have developed an efficient and effective QA program for IMPT patients with the equipment and resources available in our clinic.
SU‐C‐BRB‐01: Radiogenic Second Cancer Risk Differences in Female Hodgkin Lymphoma Patients Treated with Proton versus Photon Radiotherapies
Authors: Homann K , Howell R , Giebeler A , Eley J , Randeniya K , Newhauser W
Published: June 2012

Purpose: To determine the significance of neutron and scatter dose in comparing the predicted risk of developing a radiogenic second cancer (RSC) to the breast and lungs of a female Hodgkin Lymphoma (HL) patient irradiated at 30 years old when treated with photon Intensity Modulated Radiotherapy (IMXT) versus Passive Scatter Proton Therapy (PSPT). Methods: Clinically approved IMXT and PSPT treatment plans were designed and prescribed 36 Gy to the treatment volume. For both plans, the therapeutic dose was calculated using a commercial treatment planning system (TPS). To account for inaccuracies in the TPS, the stray and neutron dose was calculated using an in‐house Monte Carlo code for IMXT and with an analytical model fit to Monte Carlo data for PSPT. The mean equivalent dose was calculated for the breasts and lungs for both techniques, input into the BEIR VII Excess Relative Risk (ERR) models, and RSC risk compared at subsequent 10 year intervals. Results: Mean dose to the patient's breast, including neutron and scatter dose, was 6.5 Sv for both the PSPT and IMXT plans which led to nearly equivalent ERR values. Sparing of the lungs was seen from PSPT (4.5 Sv) compared to the IMXT plan (8.4 Sv), however, which led to a reduction in ERR of nearly 50% for PSPT compared to IMXT. For the PSPT plan, the mean neutron equivalent dose contribution for the breast was 0.38 Sv (5% of the ERR contribution) and 0.28 Sv (6% of the ERR contribution) for the lungs. The IMXT plan had no neutron dose since it was planned with a 6 MV beam. Conclusions: Mean breast dose was nearly equivalent for both plans leading to equal ERR to the patient. The mean lung dose, however, was reduced by a factor of two for PSPT, even taking into account the dose from neutrons. Work supported by the National Cancer Institute (awards 1 RO1 CA131463‐01A1)
SU‐C‐BRB‐04: Isotoxic Hypofractionation for Liver Cancer Radiobiologically Optimized Schedules and Normal Tissue DVH Metrics for NTCP
Authors: Wang L , Bkaer C , Uzan J , Fan J , Jin L , Hayes S , Ma C , Nahum A
Published: June 2012

Purpose: To investigate optimal fractionations to achieve high tumor control probabilities (TCPs) while maintaining acceptable normal‐tissue complication probability (NTCP) using radiobiological models with new parameters derived from recent clinical data for hypofractionated liver‐ cancer patients. Methods and Materials: Biological parameters for the Marsden TCP model were derived from reported outcomes of a multi‐ institutional Phase I/II trial. TCP and NTCP (using the LKB model with Dawson's parameters) were calculated for 8 liver cancer patients treated with different hypofractionation regimens. The correlation between tumor size, the normal liver volume receiving at least 15 Gy and NTCP were examined. Using the BioSuite software, we determined the range of fractionation regimens that achieve high TCP for 5% NTCP. Results: The TCP parameters for liver tumors are: alpha= 0.217 Gy‐1, alpha spread is 0.067 Gy‐1, assuming alpha/beta = 10 Gy and 107 tumor clonogens cm‐3. For any given fractionation we have found that NTCP is not correlated with the absolute liver volume receiving at least 15Gy, nor with the dose received by the hottest 700‐cc of the normal liver; these constraints are widely used in liver hypofractionation treatment planning. Instead, the parameter which correlates best with NTCP is the percentage liver volume receiving at least 15Gy. For 5 of the 8 patients, no more than 3 fractions were required to achieve a TCP over 96%; for 2 patients TCP increased gradually with number of fractions (from 3 to 10) to 95.2% and 92.2% respectively. The remaining patient had a small liver and larger target volume which resulted in high NTCP for any fractionation. Conclusions: A range of different hypofractionated regimens from 3×12Gy to 5×12 Gy is found to ensure excellent outcomes. However, the commonly used dose‐volume metrics for normal liver do not correlate well with NTCP. A new metric is proposed in this study.
SU‐C‐BRA‐02: Evaluation of 2D DIR from CBCT to 4DCT Projections as a Tool for IGART
Authors: Kearney V , Wang X , Gu X , Yan H , Zhen X , Jia X , Jiang S , Cervino L
Published: June 2012

Purpose: To demonstrate 2D parallelized DIR as a method to correct for anatomical changes of patient anatomy and respiratory motion. CBCT to simulated 4D‐CT projections using DIR can be used in real time for respiratory phase determination, patient setup or as a retrospective analysis to track inter‐ and intra‐fractional deformations. Methods: Ten phases of simulated 4DCT respiratory projections were individually registered to pulmonary CBCT projections using a modified 2D‐DIR demons algorithm implemented on GPUs. An automated global image‐preprocessing algorithm of the simulated projection was implemented to account for the relative local inter‐modality intensity mismatch. The deformation vector field intermodality congruence was inspected using bony structures, diaphragm position, and tumor position. A phase prediction matrix was constructed by choosing the lowest sum absolute value of the ten deformation vector fields generated by DIR. Results: For AP projections SI and tangential respective deformation maximum displacements were 4.8mm and 4.78mm with a mean displacement of 1.71mm +/− 1.17mm and 1.07mm +/− 0.94mm. For Lateral projections SI and tangential respective deformation maximum displacements were of 3.67mm and 3.07mm with a mean displacement of 0.6mm +/− 0.73mm and 0.72mm +/− 0.64mm. The phase prediction model performs better for AP projections than for lateral projections as lateral patient thickness shrouds respiratory motions. Conclusion: Respiratory motion can still be accurately reconstructed even in the presents of large bony structure deformations. The phase determination matrix nullifies respiratory deformation in the AP projections as SI and tangential maximum and mean deformations are nearly equal and respiration produces large SI motion. Larger non‐respiratory deformations typically occur in the AP projections as the couch helps maintain rigidity in lateral projections. Implementation of parallelized DIR increases spatial accuracy of the integration between multimodality imaging and as an automated tool to assess geometrical changes intra‐ and inter‐fractionally.
SU‐C‐BRA‐04: Determination of the Optimal X‐Ray Monitoring Angle for Creating a Correlation Model in Dynamic Tumor Tracking Irradiation with Vero4DRT(MHI‐TM2000)
Authors: Akimoto M , Nakamura M , Mukumoto N , Yamada M , Ueki N , Matsuo Y , Mizowaki T , Sawada A , Kokubo M , Hiraoka M
Published: June 2012

Purpose: The Vero4DRT(MHI‐Tm2000) can perform dynamic tumor tracking (DTT) irradiation using two special features; orthogonal kV x‐ray imaging subsystems and a gimbaled x‐ray head. Prior to DTT irradiation a correlation model between the tumor position estimated from implanted fiducials and IR marker position on the abdomen is required. The purpose of this study was to estimate an optimal x‐ray monitoring angle for creating the correlation model utilizing CT images. Methods: A water equivalent path length (WEPL) on CT images was employed as an indicator to estimate the optimal angles. First, the relationship between the WEPL on 4D‐CT images at the end‐exhalation phase (4D‐CT EE) and an intensity ratio of the fiducial to its surroundings on fluoroscopic images was examined to assess the validity of our proposed methods. Subsequently, the optimal angles were calculated on 4D‐CT EE images for 11 patients with 3 to 5 implanted fiducials as follows; (1) detection of fiducials on CT images, (2) exclusion of angles at which a fiducial was overlapped with other fiducials, (3) calculation of WEPLs on the orthogonal lines passing the fiducials, and (4) determination of the monitoring angles by minimizing the sum of the WEPLs. The determined optimal angles were also applied to 4D‐CT images at the end‐inhalation phase and other 4D‐CT sets. Results: The WEPL was highly correlated with the logarithm of the intensity ratio (R=−0.89 [95%CI: −0.86‐0.91], p<0.01). The optimal gantry and ring angles depended on the geometric arrangement between fiducials and anatomical structures. The inter‐ and intrafractional variations in the intensity ratios estimated from WEPLs were observed; however, the intensity ratios exceeded a threshold level to detect fiducials. Conclusions: We demonstrated that the optimal x‐ ray monitoring angles for the correlation model were determined by minimizing the WEPLs on CT images. This research was supported by the Japan Society for the Promotion of Science (JSPS) through its Funding Program for World‐Leading Innovation R&D on Science and Technology (FIRST Program). Research sponsored in part by Mitsubishi Heavy Industries, Ltd.
SU‐C‐213CD‐02: The Use of Optically Stimulated Luminescent Dosimeters in a Cone Beam Quality Assurance Testing
Authors: Lovelock D , Lim S , LoSasso T
Published: June 2012

Purpose: The number of cone beam techniques available on LINACs and the large variation of dose with position means that a large number of measurements would be required to perform the annual QA as recommended by TG142. We evaluate the accuracy of a more efficient method of measuring the imaging dose of cone beam scanning modes using optically stimulated luminescent (OSL) (Microdot, Landauer) dosimeters. Methods: Special inserts were constructed to hold OSL dosimeters at the 5 standard points of measurement (1 central, 4 peripheral) of a commercial CT dose phantom. The phantom was loaded with OSLs and scanned for each of four cone beam modes: two half‐fan modes (pelvis, low dose thorax) and two full fan modes (head, pelvis spot‐light). KVP and mAs settings were at default values, the head technique used 100KVP, the others used 125 KVP. All scans were then re‐measured using a 0.6cc ion chamber positioned at the same points. Ion chamber and OSL results were compared. A single calibration point, the measurement with the highest dose, was used to convert the readout to cGy. Results: Doses measured by the ion chamber varied from 0.17 cGy to 4.6 cGy. The correspondence between the PMT reading and the chamber reading (RADCAL 9096) was linear, the correlation coefficient being 0.996. The average absolute difference between the chamber and the OSL dose was 0.13 cGy. Conclusions: The use of OSLs was found to be of sufficient accuracy to permit their use for the annual QA recommended by TG 142. The number of scans required for a comprehensive set of dose measurements for 4 scans modes and five measurement points was reduced from 20 to 5, including a single calibration scan. This is a significant reduction in the time needed for TG 142 QA.
SU‐C‐217BCD‐01: Breathing Maneuvers Result in Regional Changes in Ventilation as Assessed by 4D‐CT
Authors: Mistry N , Pokharel S , Diwanji T , Feigenberg S , D'Souza W
Published: June 2012

Purpose: Different breathing maneuvers typically Result in slightly different tidal volumes that can lead to changes in alveolar recruitment. Recently, there has been tremendous interest in utilizing 4D‐CT based measurements of regional ventilation for treatment planning and treatment assessment. In this work, we wanted to demonstrate the effect of different breathing maneuvers on fractional regional ventilation (FRV) extracted using 4D‐CT. Methods: In this work, we evaluate the effect of different breathing maneuvers: a) free‐breathing (FB), b) audio‐visual assistance (AV), and c) active breathing control (ABC), on FRV. We measured these changes using a 4D‐CT based technique that quantifies changes in CT characteristics of the pulmonary parenchyma. Five subjects were imaged using 4D‐CT during a single session under 3 different breathing maneuvers. 4D‐CT images were used to extract fractional regional ventilation by applying a ‘mass correction’ that is estimated using the ratio of the global inhale‐mass and end‐exhale mass. A subtraction of the corrected images is performed by spatially matching the images at each phase of the respiratory cycle using a deformable image registration algorithm in Insight Toolkit. A distribution of the fractional regional ventilation values is used to estimate a ratio of tidal volume to functional residual capacity. Results: Increased fractional regional ventilation is observed in all the subjects when they were breathing using the ABC maneuver. Statistically significant difference (p=0.079) in fractional regional ventilation was observed when we compared the means for the FB and ABC breathing maneuvers. These global differences were also reflected on a regional level when we compared the fractional regional ventilation maps. Conclusions: This is the first study to report that breathing pattern changes can significantly impact the recruitment of alveoli resulting in marked changes in the fractional regional ventilation.
SU‐C‐217BCD‐04: Application of Statistical Process Control to Long Term CT Constancy Testing
Authors: Fredriksson J , Olafsdottir H , Kristbjornsson A , Healy A , Levy J , Goodenough D , Kristinsson S
Published: June 2012

Purpose: To validate how a reliable Statistical Process Control can be implemented, using routine scanning of a test phantom and automatic QA program, to establish effective long term performance monitoring of CT imaging systems. Methods: A data set of 21474 QA images acquired on 1565 distinct days was collected on a CT system from 2002 until 2011, during a large population based quantitative imaging study with a longitudinal component, using the Catphan® 500 phantom. The image data was processed with the ImageOwl Catphan®QA software. Tolerances for CT imaging quality parameters were selected from IEC‐61223‐3‐5 and other sources. Process capability, Cp, describes the ratio of tolerance range to observed standard deviation. Cpk additionally weighs in closeness to one side of specification limits. A process capability equal to 1 means 99.7% chance of correctly observing a single measurement within specification, i.e. 3 sigma. Results: While slice thickness measurement can be an extremely reliable process (Cp=4.5, 5.1), image uniformity at standard +/−4HU limits, though generally reliable (Cp=2.1), showed relatively high probability of reporting false positive system out of specification (Cpk=0.8), due to measurements being near lower limit. Tube aging is manifested by changes in effective energy, causing changes in readings of sensitometric targets. This is confirmed by an effective energy value reset at tube renewal. Conclusions: By monitoring modern CT scanners with today's test systems using commonly accepted control limits, reliable go/no‐go signals can be generated for most CT QA variables. However, physicists implementing a monitoring system have to pay special attention to low process capability caveats when establishing monitoring action rules. This is especially important when implementing monitoring of large scale clinical or research operations requiring high reliability and cost effective QA solutions. Funding provided by The Phantom Laboratory, Incorporated and Image Owl, Incorporated
SU‐C‐217BCD‐05: Computed Tomography X‐Ray Tube (CTXT) Life Analysis: A Multi‐ Year Study
Authors: Erdi Y
Published: June 2012

Purpose: Prolonged CT x‐ray tube (CTXT) life is always in the interest of health‐care provides for lowering the operating costs. However, long CTXT life is a function of many conditions, such as, mA, heat loading, environmental, anode material, pulse duration, scan length and mechanical failures. In this multi‐year study, we investigated actual CTXT life versus manufacturer warranty coverage limits. Methods: Ten GE Lightspeed CT (GE Healthcare, Waukesha, WI) scanners with 33 Performix‐Ultra and 3 GE VCT scanners with 8 Performix‐Pro tube changes over the 5 year period (2006–2011) included in the study. These CT scanners located at main campus and various satellite locations of our radiology department. CTXT life measurements were performed by analyzing log files of the CT units after a CTXT change. Results: Company warranty coverage indicates 6000 exams/12 months (whichever comes first) for Performix‐Pro and 70kAs/12 months for Performix‐Ultra tubes. Our measurements for 33 Ultra CTXT showed a range from 7 months to 48 months and from 16.7 kAs to 239.9 kAs. Mean values for Ultra CTXT are 16.5 ± 9.9 months and 81.2 ± 46.9 kAs. For 8 Pro CTXTs, the measured logs indicated 19.0 ± 7.0 months of CTXT life. Among the 33 Ultra CTXTs, 7 of them did not meet the company warranty coverage limits. Those 7 CTXTs had an average life of 8.0 months and 48.1 kAs. All 8 Ultra‐Pro CTXTs exceeded company warranty coverage limits. Conclusions: Overall 7 out of 41 CTXTs failed to meet company warranty period. None of these tubes were Pro type. Since clinical demand from a CT scanner varies, it is difficult to reason for the failed CTXTs. Mechanical, environmental conditions and usage related choices can reduce the life expectancy of a CTXT.
SU‐C‐218‐01: Comparison of Single‐View and Dual‐View Digital Chest Tomosynthesis
Authors: Zhong Y , You Z , Liu X , Wang T , Shen Y , Lai C , Shaw C
Published: June 2012

Purpose: Digital tomosynthesis (DTS) has been applied to chest imaging to crudely separate objects at different depth levels. However, the spatial resolution in the posterior‐anterior (PA) direction is very poor. We implement a dual‐view DTS technique to improve the spatial resolution along the PA direction and compare the results with the single‐view DTS technique and the cone beam CT (CBCT) technique. Methods: Computer simulations and experiments were conducted with the CBCT, dual‐view DTS and single‐view DTS techniques using the same geometry. For simulations, clinical CT images obtained at 120 kVp were used to generate a digital chest phantom, with which the projection images were computed. For imaging experiments, an anthropomorphic chest phantom was scanned with a bench top experimental CBCT system. 300 projections were obtained for CBCT imaging using the FDK algorithm for reconstruction. 51 projections covering 60 degrees in the PA direction were used for single‐view DTS imaging using the iterative algorithm for reconstruction. 25 projection over 60 degrees in the PA direction and another 25 images over 60 degrees in the lateral direction were used for dual view DTS. Results: For sagittal slice images, the CBCT image closely resembled the original phantom image. The dual‐view DTS images were fairly accurate in depicting the shape and dimensions of the anatomy in the fulcrum, despite the presence of some artifacts. With the single‐view DTS images, the anatomy was poorly depicted in the PA direction. For coronal slice images, the single‐view DTS images appeared less blurred but were much more affected by artifacts from the off‐fulcrum objects, resulting in severe distortion. The dual‐view DTS images, while not free from artifacts, provides more accurate rendition of the anatomy. Conclusions: Our results show that the dual‐view DTS technique substantially improved the spatial resolution of the reconstructed images in the PA direction. This work was supported in part by grants CA104759, CA124585, and CA138502A1 from NIH‐NCI, a research grant CA00117 from NIH‐NIBIB, and a subcontract from NIST‐ATP.
SU‐D‐211‐01: Effect of Immobilization/support Devices and Air Gap on Skin Doses for Stereotactic Body Radiotherapy with Abdominal Compression Device
Authors: Peng Y
Published: June 2012

Purpose To evaluate the effects of the couch, the immobilization/support devices, and air gap on the skin dose for SBRT treatment with abdominal compression device and to investigate strategies to minimize skin dose by phantom measurementMaterial and methodsSkin‐sparing comes from lower dose in buildup region, anything added between tissue and air may change buildup PDD curve hence skin dose increases. To investigate such effects due to different buildup materials and air gap between the buildup material and the surface, we employed EBT2 film in slab and water phantoms to measure doses at depths varying from surface to dmax, field sizes (4×4 to 10×10 cm2), and air gaps from 5 to 15 cm for 6 MV photons. Measured dose was normalized to dose at dmax for a 10×10 cm2 field. The buildup materials included table tops (tennis net, Exact Couch and Indexed Immobilization table tops), vacuum bags (Civco Vac‐Lok and Med‐Tec cushions), and body frames (Elekta stereotactic body frame and Civco Body Pro‐Loc). ResultsThe relative doses at depth of 1.00 mm were 0.63 with no buildup, 0.90 with couch+6cm bag, 0.91 with bodyframe+bag, and 0.96 with couch+bodyframe+bag for a 4×4 cm2 field. With a 10×10 cm2 field, the above values changed to 0.67, 0.94, 1.01, and 0.97, respectively. Thick bag (6.0cm) increased skin dose by 10% comparing to the thinner bag (1.5cm). For a buildup (couch + body frame) plus air gap, the relative doses were 0.73, 0.84, and 0.91 for air gap of 15.0, 10.0, and 5.0 cm, respectively, for a 10×10 cm2 field. Conclusions: The skin dose increases by up to 40% if patient was treated through the immobilization device or couch. Skin dose also increased with increasing field size. Introduction of large air gap may recover much of the lost buildup effect.
SU‐D‐211‐02: A Framework for 4pi Radiotherapy
Authors: Sheng K , Romeijn E , Dong P , Long T , Low D , Ruan D
Published: June 2012

Purpose: Inclusion of highly non‐coplanar treatment angles increases radiations dose conformality and critical organ sparing. However, implementation of this treatment strategy has been hampered by inaccurate solution space modeling, limited automated beam selection methods, the lack of efficient beam sequencing program and integrated collision prevention. The aim is to develop a 4pi radiotherapy paradigm that takes full advantage of modern computer‐controlled robotic C‐arm linear accelerators. Methods: The beam geometry solution space was modeled by 3D surface scanning of the couch, gantry and patient. In order to utilize the entire solution space and optimize MLC resolution, variable source‐to‐tumor distances were introduced. Conformai radiation doses were computed using convolution/superposition from uniformly distributed solid angles. Beam orientation optimization was performed using a column generation and pricing approach, which was also used to optimize beam fluence intensity modulation. A level set method was then employed to automatically sequence beams so the treatment time and couch motion can be minimized while avoiding collision on the path. Results: The machine and patient surface was accurately measured and a cocoon shaped solution space was created with an integrated gap buffer of 4 cm. 14 conformai beams were typically selected to maximize target dose coverage and minimize critical organ doses. Compared with manual non‐coplanar and coplanar volumetric modulated arc therapy plans, an average 20% improvement was observed in high dose spillage, defined as the 50% isodose volume divided by the target volume, in a wide range of clinical cases including brain, lung, liver and partial breast cancer. Conclusions: We have established a framework that overcomes major technical difficulties associated with automated planning and delivery of highly non‐coplanar treatment on the widely available C‐arm linacs. Compared with coplanar volumetric modulated arc therapy plans, 4pi plans improve nearly all aspects of the dosimetry while remain highly deliverable.
SU‐D‐213AB‐01: Dosimetry Improvement and Needle Number Reduction in Prostate Brachytherapy Using Electromagnetically Guided Needle Placement
Authors: Zhou J , Sebastian E , Yan D
Published: June 2012

Purpose: To investigate dosimetry improvement in prostate brachytherapy by conforming needles to urethral and prostate shape using an electromagnetic tracking device. Methods: We have reported a needle tracking system using an electromagnetic sensor embedded inside the tip of the needle to improve needle reconstruction accuracy and efficiency in conventional prostate HDR brachytherapy. Utilizing the same system, we propose to guide needle insertion following pre‐optimized tracks based onthe target shape. In this study, we investigate possible dosimetry improvement and needle number reduction by comparing plans using the conventional implant method and the proposed method. Twelve prostate brachytherapy patients were selected and studied retrospectively. New virtual plans were created using the proposed method and conforming needle tracks to the urethral and prostate shapes. Same optimization constraints were applied to both the conventional and the new plans. DVH parameters and total needles used have been analyzed to quantify dosimetry improvement and potential toxicity sparing due to reduction in implant needles. Results: Prostate volumes are 41.16±13.27 cc. Number of needles used for the conventional plan is 16.6±1.2, vs. 13 for all the new plans. The prostate volume receiving 100% (V100), 125% (V125), and 150% (V150) of the prescription dose in conventional plans vs. those in the new plans are 99.48%±0.21% vs. 99.53%±0.20%, 53.90%±5.61% vs. 50.30%±5.23%, and 25.37%±4.91% vs. 20.96%±3.41%, respectively. The corresponding urethra V100 and V110 are 90.96%±3.10% vs. 85.78%±7.76% and 2.06%±1.23 vs. 0.46%±0.28%. Conclusions: The needle numbers and the urethral V110 in the new plans are significantly lower than those in conventional plans(p<0.001 and p=0.004, respectively), with no significant changes in doses tothe prostate. Conformai needle implant following pre‐optimized tracks with electromagnetic guidance may significantly reduce acute and late toxicities in prostate brachytherapy by reducing the number of needles and theurethral doses.
SU‐D‐213AB‐03: Design Optimization of a HDR Ir‐192 Brachytherapy Skin Applicator Using Monte Carlo‐Based Dosimetry
Authors: Yang Y , Rivard MJ
Published: June 2012

Purpose: AccuBoost® applicators are designed to deliver boost dose after whole breast irradiation in substitution for electron boost. By augmenting the current design through adding a wedge inside the applicator and atungsten window above the skin surface, the AccuBoost applicators can be used to treat skin cancer. This study aimed to design a skin applicator that could deliver brachytherapy in a conformai and homogeneous manner to the skin while minimizing OAR dose. Methods: The 6 cm round AccuBoost applicator served as the foundation for variations of an internal cone, internal wedge, and external window. Monte Carlo (MC) methods (MCNP5)were used for dose characterization and design optimization of these tungsten‐alloy components. Specifically, the cone, wedge, and window dimensions were iteratively varied in MC simulations based on HDR Ir‐192 dose distributions having (0.5 mm)̂2 voxels in a soft tissue phantom. The design goal was an applicator that can protect tissue > 5 mm while providing lateral dose conformity and a homogeneous dose distribution for tissue < 3 mm. Results: The internal wedge angle governed field size to be irradiated, limiting depth‐dose spread into the phantom. Dose conformity was enhanced by the internal cone and collimating window. Window thickness increased required treatment time, where 3 mm was determined to be optimal when considering tradeoff between depth dose and dose rate. With a lesion thickness of 3 mm and setup uncertainty of 1 mm, the optimal design provided better lateral coverage at d = 5mm. Here, the dose was less than 30% of that within the treatment aperture. Conclusion: Standardized criteria were established for dose optimization of a skin applicator. Using these criteria and MC methods, an optimized design was obtained. Optimization is underway for other applicator diameters. Clinical evaluation within a 3D treatment planning system and comparison with other brachytherapy skin applicators is ongoing. Prof. Rivard is a stakeholder of Advanced Radiation Therapy, LLC.
SU‐D‐213AB‐05: Commissioning a CT Compatible LDR T&O Applicator Using Analytical Calculation with ID and 3D Dosimetry
Authors: Adamson J , Newton J , Steffey B , Cai J , Adamovics J , Oldham M , Chino J , Craciunescu O
Published: June 2012

Purpose: To determine the characteristics of a new commercially available CT‐compatible LDR Tandem and Ovoid (T&O) applicator using 3D dosimetry. Methods: We characterized source attenuation through the asymmetric gold shielding in the buckets by measuring dose with diode and 3D dosimetry and compared to an analytical line integral calculation. For 3D dosimetry, a cylindrical PRESAGE dosimeter (9.5cm diameter, 9.2cm height) with a central 6mm channel bored for source placement was scanned with the Duke Large field of view Optical CT‐Scanner (DLOS) before and after delivering a nominal 7.7Gy at a distance of 1 cm using a Cs‐137 source loaded in the bucket. The optical CT scan time lasted approximately 15 minutes during which 720 projections were acquired at 0.5° increments, anda 3D dose distribution was reconstructed with a 0.5mm3 isotropic voxel size. The 3D dose distribution was applied to a CT‐based T&O implant to determine effect of ovoid shielding on the dose delivered to ICRU 38 Point A as well as D2cc of the bladder, rectum, bowel, and sigmoid. Results: Dose transmission through the gold shielding at a radial distance of 1–3cm from midplane of the source was 86.6%, 86.1, and 87.0% for analytical calculation, diode, and 3D dosimetry, respectively. For the gold shielding of the bucket, dose transmission calculated using the 3D dosimetrymeasurement was found to be lowest at oblique angles from the bucket witha minimum of ∼51%. For the patient case, attenuation from the buckets leadto a decrease in average Point A dose of ∼4% and decrease in D2cc to bladder, rectum, sigmoid, and bowel of 2%, 15%, 2%, and 7%, respectively. Conclusions: The measured 3D dose distribution provided unique insight to the dosimetry and shielding characteristics of the investigated applicator, the technique for which can be applied to commissioning of other brachytherapy applicators. John Adamovics is the owner of Heuris Pharma LLC. Partially supported by NIH Grant R01 CA100835‐01.
SU‐D‐213AB‐06: Surface Texture and Insertion Speed Effect on Needle Friction
Authors: Abdullah A , Golecki C , Barnett A , Moore J
Published: June 2012

Purpose: High frictional forces between the needle surface and tissue cause tissue deflection which hinders accurate needle placement for procedures such as brachytherapy and needle biopsy. Accurate needle placement isimportant to maximize procedure efficacy. This work investigates how needle surface roughness and insertion speed affect the frictional forcebetween a needle and tissue. Methods: A friction experiment was conducted to measure the force of friction between bovine liver and three 11 gauge needles having Ra surface roughness of 3.43, 1.33, and 0.2 μm. Each of the three needles were mounted on a linear slide and were advanced and retracted through bovine liver at speeds of 50, 100, 150, and 200 mm/s for a total of 12 trials. In each trial the needle was advanced and retracted in 10 cycles producing a steady state insertion force and a steady state retraction force for each cycle. A force sensor connecting the needle to the linear slide recorded the resistance force of the needle sliding through the liver. The liver was mounted in a box with a pneumatic cylinder which compressed the liver sample by 11.65 kPa. Results: The roughest needle (Ra = 3.43 μm) on average produced 68, 73, 74, and 73% lower friction force than the smoothest needle (Ra = 0.2 μm) for the speeds of 50, 100, 150, and 200mm/s, respectively. The second roughest needle (Ra = 1.33 μm) on average produced 25, 45, 60 and 64% lower friction force than the smoothest needle (Ra = 0.2 μm) for the speeds of 50, 100, 150, and 200 mm/s, respectively. Conclusions: Rougher needle surface texture and higher insertion speed reduced frictional forces between the tissue and the needle. Future studies will examine how frictional forces can be modeled and predicted given surface texture and insertion speed.
SU‐D‐BRCD‐02: A Novel Cylindrical 3D Water Scanner for Beam Data Collection: I. Validation of the Automatic‐Setup
Authors: Li J , Lu B , Yan G , Huang Y , Liu C
Published: June 2012

Purpose: To determine the accuracy and reproducibility of the automatic‐ setup procedure of a 3D water scanner (3D SCANNER, Sun Nuclear Corp). The procedure automatically aligns the scanner's coordinate system to the Linac coordinate system. A unique off‐center detector holder extends the scan range to 630 mm, eliminating the need for scanner shifts for large‐field scans. Methods: The automatic‐setup procedure provides means to automatically (1) level the tank; (2) zero the detector position to water surface; (3) align the scanner's coordinate system to the Linac system; and (4) correct motor hysteresis. After automatic‐setup, (1) and (2) were evaluated visually by three physicists. Step (3) was tested by moving one of the jaws to the isocenter and scans were made along the jaw edge. Angular misalignment between the scanner and the Linac would Result in a noticeably tilted profile. Step (4) was tested by scanning with the chamber moving forward and then backward five times. The accuracy of the off‐center detector holder was tested by comparing scans made using the regularand the off‐center detector holders. All tests were repeated three times. Results: All tests of the water surface and horizontal chamber movementwere acceptable from the nine independent evaluations. Scans along the jawedge resulted in < 1% in profile tilt, corresponding to < 0.05 degree in angular misalignment. Same direction scans resulted in field edge differences < 0.05 mm, and < 0.2 mm when compared to scans in thereverse direction. There was no difference in accuracy when different scan speeds were used. Profiles obtained using the regular and the off‐centerdetector holders were identical. Conclusions: The automatic‐setupprocedure resulted in accurate alignment of the 3D SCANNER to the Linac. These results were user‐independent. It also provides the ability to scan large fields without the need to change tank setup. This work was partially supported by a research grant from Sun Nuclear Corp., Melbourne, FL.