bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐237: Patient Safety Improvement with a Software Tool to Prevent Isocenter Errors
Authors: Ford E , Nyflot M , Jordan L , Carlson J
Published: July 2013

Purpose: Based on one year of departmental experience with near‐miss incident learning, issues with isocenter placement were identified as a significant potential risk. Motivated by this, we initiated a patient safety improvement intervention which employs modern concepts in human factors engineering, error prevention, and software design. Methods: In February 2012 a departmental electronic incident learning system was launched that is unique in three respects: the high volume of near‐miss/no‐harm reports (20 per week or ∼1 per patient), the ability to tag each event by category type, and ranking of events by potential severity (0‐to‐4 point scale). Data over ten months (774 reports) indicate that near‐miss events related to isocenter placement have a significantly higher potential severity compared to other events: 3.0+−1.3 vs. 1.5+−1.0 (p<0.001). We therefore developed a custom software interface to manage the placement of isocenters through the clinical workflow. The approach draws from concepts in the psychology of human factors design and usability, including forcing functions and automatic error checking. Results: The custom software interface is designed to accommodate all common workflow scenarios for isocenter placement. The user is presented with a single screen containing all relevant information and is guided with a color‐coded status scheme. The software checks for common error pathways (e.g. isocenter point inadvertently moved during planning) and changes the interface status accordingly. Further evaluation is ongoing, after which wider distribution may be possible. Conclusion: Incident learning is a valuable method for objectively identifying areas for safety improvement. The critical safety issue identified here, isocenter placement, was addressed with a custom software interface that utilizes approaches not commonly employed by the vendor community such as user‐centered design. The design bridges the gap of execution and evaluation which lies at the root of most errors.
SU‐E‐T‐240: Risk Assessment for Stereotactic Intracranial Radiosurgery (SRS) in Brazil Using FMEA
Authors: Teixeira F
Published: July 2013

Purpose: The purpose of this work is develop a study capable of help the radiotherapy centers to apply a quality management program based on a process analysis methods with the application of failure mode and effect analysis (FMEA) to stereotactic radiosurgery. Methods: This (FMEA) methodology has been tested initially in two radiotherapy centers, both of which perform SRS with a linear accelerator Novalis using a 6 MV of photon beam.The FMEA method allows documenting potential failure modes, determining its effects, identifying causes of failures, developing plans, documenting team concurrence and actions taken.The FMEA method determines a value to the risk probability number (RPN) for each potential cause of failure using the product of three categories: O, the probability that a specific cause will Results in a failure mode; S, the severity of the effects resulting from a specific failure mode; D, the probability that the failure mode will be detected. Results: This work presents preliminary results and shows that the most failures are somewhat related of the human factors issues. It have been already found values 38 sub process and it was identified 59 different potential failure modes and 140 potential causes of failure. Among the potential cause of failure mode 40,7% can be considered an error associated to human factors issues. The larger value for RPN was 432 and the lower was 12. Conclusion: Although FMEA contains a very subjective component, it is a useful and simple tool for prospective risk assessment with respect to patient care. This work is still in development but it is already possible to conclude that some conditions for operating are indispensable to achieving a high quality in patient care, such as: adequate training, clear procedures, clear level of the responsibility.
SU‐E‐T‐245: A Physics Database for a Multi‐Institutional Quality Consortium
Authors: Moran J , Feng M , Benedetti L , McMullen M , Matuszak M , Nurushev T , Hess M , Griffith KA , Hayman J , Fisher J , Brossard S , Grubb M , Pierce L
Published: July 2013

Purpose: A collaborative quality initiative (CQI) has been developed in the state of Michigan to assess physician and patient reported outcomes to compare conformal and IMRT techniques for a specific cohort of breast and lung cancer patients. Here, we present a web‐based database that was designed to collect planning and delivery information to facilitate analysis of outcomes for the CQI. Methods: A web‐based database was built to capture key physics information, including dose that may be related to acute toxicities. An annual institutional questionnaire captures the technology available for these patients. A patient‐specific survey collects simulation, planning, and delivery information. To overcome differences in DVH file formats, a simple interface was developed where the user selects from a structure list, submits numeric data, and reviews the data summary. To analyze the delivery type, DICOM‐RT plan files are uploaded via a web interface. The data are anonymized and displayed for the user to verify that no protected health information is submitted. Results: Initial partner institutions tested and provided feedback on all aspects of the physics data collection. Institutions have shared customized programs for extracting DVH and DICOM‐RT data and documents for electronic workflow. Data submission began via the web portal in April 2012. There are 4 planning systems represented among the 14 institutions. Delivery techniques include static, dynamic and segmental MLC, Tomotherapy, and VMAT. As of February, data have been submitted for approximately 80% of the 815 eligible cases. Centers will be audited for data quality once per year. Conclusion: A system has been designed to capture high integrity simulation, plan, and delivery data for a CQI focused on breast and lung cancer. This information will be used to quantitatively evaluate the use of IMRT techniques in the state of Michigan and to permit dose‐based correlations to physician and patient‐rated toxicities. This work was funded by Blue Cross Blue Shield of Michigan.
SU‐E‐T‐246: On Augmented DVH Analysis
Authors: Loveless A , Roy A , Das I , Nohadani O
Published: July 2013

Purpose: The process of IMRT planning is an iterative inverse process, where a planner seeks to attain a desired dose distribution, specified for tumors and OARs, hence creating a plethora of competing objectives. However, the final product is rather the unpredictable outcome of a series of trial‐and‐error attempts at meeting these objectives. A key tool to inspect the quality of plans is the DVH. This inspection, however, is primarily conducted visually, hence, the chosen treatment plan is ultimately clinician dependent. In this study, we propose a quantitative method for DVH comparison based on historical data. Methods: The treatment of one prostate case was planned by seven planners, while imposing the same clinical objectives for PTV and OARs. The resulting seven test DVHs were compared based on their deviation of from the ideal coverage, namely 100% of PTV receiving 100% of the dose. A deviation function L is proposed to measure the weighted area between the ideal and realized DVH. The weights are formed based on the distribution of past data of 100 comparable prostate cases. The frequencies were interpolated to form a continuous surface using tensor product piecewise cubic hermite interpolation. While only the dose distribution to PTV was subject to this study, the proposed method is universal and applies to other organs and/or combinations of criteria as well. Result: Even though none of the seven test DVHs appeared visually preferable, we measured significantly different L values: Planner 2 exhibited the lowest deviation, while the deviations of Planners 1 and 7 were far higher. Conclusion: The proposed method of quantitative DVH comparison can distinguish DVHs that might otherwise visually appear similar in a clinical setting. Furthermore, the outcomes from our method are independent of planning personnel biases, providing a quantitative way of evaluating DVHs and augmenting decisions in IMRT. Joint Purdue‐IU Seed Grant
SU‐E‐T‐248: A Patient Data Management System for Philips Pinnacle‐3 TPS
Authors: Zhang B
Published: July 2013

Purpose: This abstract presents a Pinnacle TPS data management system for patient data sharing and long‐term archiving. Methods: For institutions deploying Philips Pinnacle‐3 as TPS, data management, such as, patient data sharing and long‐term archiving, is always challenging. Most institutions have multiple cancer centers, each of which has its own separate Pinnacle database. With increasing cooperation and personnel mobility, there is a high demand for patient data sharing among these cancer centers. Meanwhile, for the sake of patient data safety and integrity, once a patient is done with treatments, patient data should be moved out of Pinnacle database instead of continuing to consume limited disk space. In addition, for re‐treatment and research purposes, patient data should be retrievable and searchable. To address these needs, we implemented a solution, which uses a centralized database system with rich web interfaces. In this system, every operation is executed simply by mouse clicks through web and all data is transferred over secure network channels. Any Pinnacle database can join the system as a member. Within its user access control scheme, each user belongs to a user group associated with a specific Pinnacle database. That is, once a user logs on to the system, s/he can only access patient data from the Pinnacle database of which the user has privilege. Patient data in the database can be searched through a variety of criteria and also can be easily retrieved and restored to Pinnacle and other TPS. Furthermore, due to its rich web interfaces, this system can be accessed by mobile devices (e.g., iPad/Android). Results: Conclusion: Our system provides a comprehensive solution for Pinnacle patient data management, which greatly enhances patient data safety/integrity and facilitates cooperation. Its centralized infrastructure also opens up possibilities of advanced features, such as, online planning and patient data visual search.
SU‐E‐T‐255: Monte Carlo Quantification of Dose Distributions Around Thin Lead Foils
Authors: Warmington L , Watanabe Y
Published: July 2013

Purpose: Patients are increasingly undergoing radiotherapy procedures, in which small metals are implanted in the body for target localization in IGRT or dose enhancement. Previously we proposed the polymer gel dosimetry technique for measurement of 3D dose distributions around small metallic materials including thin foils. The purpose of this study is to determine the effect of separation between thin metallic objects and 3D dose distributions using a Monte Carlo method and to provide theoretical data which will be compared with the measurement data. Methods: DOSxyz was used to perform Monte Carlo simulations of a two lead foil setup. The Mohan 24MV spectrum was used as a radiation source with 5cm x 5cm collimation at a 100 SSD. The foils had dimensions 1cm × 1cm × 0.5mm and had separations of 2mm, 5mm, 7mm, 10mm and 15mm. The phantom size was 16cm × 16cm × 28cm. Simulations were performed on custom Intel I7 machines with various histories (100 million to 1 billion). Percent depth dose curves were determined, then the minimum dose between the foils was recorded and compared to the dose without the foil. The plots were normalized against the maximum dose point. Results: The minimum dose enhancement ratios between two foils were 1.47, 1.29, 1.18, 1.13 and 1.08 for the separation of 2, 5, 7, 10, and 15 mm, respectively. The dose enhancement ratio exponentially decreased with the separation. The Monte Carlo simulation results were in agreement with experimental data previously obtained with films. Conclusion: The degree of dose enhancement around thin lead foils was determined by the Monte Carlo method. It is expected that other high Z materials such as gold will behave in similar manner. The results would be used to identify optimal placement of materials for measurement by a polymer‐gel dosimeter.
SU‐E‐T‐256: Evaluation of Silver Dressing as Bolus
Authors: Hipp E , Becker S , Osterman K
Published: July 2013

Purpose: Anti‐microbial silver wound dressing may be useful as a bolus material. This study measures the water‐equivalent‐thickness of a silver wound dressing to characterize it for clinical use. This nylon‐mesh dressing, with its permanently plated silver surface (546 mg Ag/100 cm2) may meet the need for bolus with fine variability of thickness and self‐sterilization. Methods: A percent depth dose (PDD) curve was measured in plastic water (CNMC Best Medical) using a parallel plate chamber (PTW N34001) for an 8×8 cm field size, 6 MV beam, 100 cm SSD with a linear accelerator. Measurements were repeated under varying thicknesses (0.5 mm, 1mm, and 2 mm) of silver dressing material, 10 cm × 11 cm (Silverlon™ Antimicrobial silver wound contact dressing WCD‐466). Control measurements were also made in a small water tank. Results: For every layer of dressing added (∼0.5mm) the PDD shifts to the left along the depth axis. A 2 mm offset applied to the position values of the 2 mm (4‐layers) PDD curve causes superposition with the control PDD. This suggests that 2 mm of silver dressing performs similarly to 2 mm of plastic water. This was verified with measurements under clinical setup conditions, 100 cm to the top of the parallel plate chamber, ie. to skin, with bolus placed on top, under 2 mm plastic water (73.40%) and under 2 mm silver dressing (73.41%). Measurements in a water tank for this equivalent depth agree within 1%. Conclusion: The bolus properties of silver‐mesh dressing appear to be water‐equivalent. Silver dressings can be used as bolus and may be particularly beneficial when fine variations are desired or when maintaining an anti‐microbial environment is of particular value.
SU‐E‐T‐257: A Monte Carlo Simulation Study of Photon Beam with Energies 6X, 10X, 6FFF, 10FFF From a TrueBeam Linear Accelerator
Authors: Johnson D , Chen Y , Schnell E , Ahmad S
Published: July 2013

Purpose: To compare the quality of Monte Carlo simulation results of photon beams with multiple energies with the corresponding measured beam commissioning data from a Varian TrueBeam accelerator. Methods: IAEA phase space files for photon beam energies 6X, 10X, 6FFF, 10FFF from TrueBeam linear accelerator provided by Varian were implemented as source files in the GEANT4 Monte Carlo code. The simulation geometry consisted of upper and lower tungsten alloy jaws and a cubic water phantom (50 × 50 × 50 cm3). Central axis depth dose curves (PDD) for multiple field sizes (1×1, 2×2, 4×4, 6×6, 10×10, 20×20, 30×30 cm2) and radial and transverse dose profiles for identical field sizes at 5 different depths (Dmax, 5, 10, 20, 30 cm) for all four energies were recorded in the phantom. Each simulation was performed with 2.0E9 incident particles. The results of PDD and profiles from simulations were then compared with the corresponding beam commissioning data collected with a Wellhoffer Blue Phantom using a 0.13cc ion‐chamber and a 0.8 × 0.8 mm2 diode. Results: The GEANT4 simulated PDD curve for photon beam compared favorably well, within ∼2%, against the corresponding measured ion‐chamber PDD for all energies and field sizes. The simulated in‐plane and cross‐plane profiles also compared well, within 2 mm, at the 50% level against the measured profiles for all energies, field sizes and depths. Conclusion: For the commissioning of a linear accelerator, the feasibility of utilizing Monte‐Carlo simulated beam data has been demonstrated in this study. The increase of computer speed and capabilities may Result in the adoption of Monte‐Carlo techniques for future machine commissioning and dose calculations.
SU‐E‐T‐259: Dosimetric Comparison of Cs‐131 Vs. I‐125 Vs. Pd‐103 Intraoperative Brachytherapy in Patients with Resected Brain Metastasis
Authors: Nedialkova L , Sabbas A , Trichter S , Kulidzhanov F , Delamerced M , Parashar B , Nori  , Chao K , Yondorf M , Wernicke G
Published: July 2013

Purpose: Cs‐131, I‐125 and Pd‐103, have been used for permanent implant brachytherapy. Cs‐131 has shorter half‐life — 9.7 days as compared to I‐125 and Pd‐103 — 59.4 and 17.0 days, respectively. It is likely more biologically efficient for tumor cell kill as the initial dose rate from Cs‐131(23.9 cGy/h) is 4 times higher than that of I‐125(5.8 cGy/h) and twice of Pd‐103(13.62 cGy/h). These isotopes differ in their average gamma‐ray energies (30.4keV, 28.5keV and 20.8keV, respectively). This study examines the dosimetric differences amongst these isotopes when used as a permanent implant for patients with resected brain metastasis with regard to exposure of normal brain tissue and the potential for developing radiation necrosis (RN). Methods: 24 patients with a single newly diagnosed and resected brain metastasis were implanted with Cs‐131. Post‐op dosimetry plans were generated for Cs‐131, I‐125 model #6711 and Pd‐103 model #200. The prescription dose was 80 Gy to 5mm depth from the surface cavity. The mean air kerma strength for the Cs‐131, I‐125 and Pd‐103 seeds were 2.4U, 0.6985U and 2.11U respectively. The volume of brain tissue exposed to radiation at 100%, 80% and 50% isodose lines were compared for each isotope. Results: Significantly larger volume of brain tissue exposed to radiation, with the use of I‐125 when compared to both Cs‐131 (p less than 0.00005) and Pd‐103 (p less than 0.00004). There is no significant difference when comparing Cs‐131 to Pd‐103 (p=0.26605). Conclusion: In this analysis, we report that Cs‐131 and Pd‐103 expose less normal brain tissue to radiation when compared to I‐125, thus providing a dosimetric superiority and subjecting less tissue to RN. In addition, Cs‐131 has the shortest T1/2 and in our trial with a median follow up of 10 months, all 24 patients have 100% local control while experiencing 0% incidence of RN.
SU‐E‐T‐267: Preliminary Study of Development of the Respiratory Training System by Using the MEMS Acceleration Sensor for the Radiation Therapy
Authors: Sung J , Yoon M , Chung W , Shin D , Bae S , Kim D
Published: July 2013

Purpose: In this study, we developed and estimated the home‐made patient‐respiration‐training‐system (PRTS) by using the micro‐electromechanical‐system (MEMS) which can help to avoid the problems for the limitation of the RGRT applicable patient cases. Methods: We compared the response of the PRTS with period of real movement and commercially introduced real time patient monitoring (RPM) system. We measured the response of the PRTS by using the respiratory gating platform (RGP) for a 2.5, 3.0 and 3.5 second of the period and a 20, 30, 40 mm of the amplitude. Under the same condition, we measured the response of the RPM system by using the RGP. Results: The period error from the PRST was measured as 0.6∼6.0% compared with period of real movement. Considering the overall shape of the graphs, the uncertainty of the signal of the RPM system measured about 1% in an amplitude for each interval, on the other hand, MEMS signals had 3∼11% of the error in amplitude. Conclusion: In term of simplicity and convenience, we found the possibility of PRTS as the patient training system and we expect more detail of study for more realistic situation can be established, in near future.
SU‐E‐T‐269: Trends in Medical Physics Research
Authors: Keyes R
Published: July 2013

Purpose: Electronic publication of present and archival journal materials has aided medical physics research by decreasing the effort necessary to locate relevant articles. Additionally, ease of access via electronic publishing has improved the prospect for meta‐studies. The purpose of this meta‐study is to investigate the past, present, and emerging trends in medical physics research. Methods: Keyword analysis was performed on abstracts from the journal Medical Physics from January 1994 — February 2013. Keywords were chosen by article authors. Similar keywords were reconciled via manual and clustering techniques. Frequency and trend analysis was performed. Keywords were weighted by article and total keyword occurrence over time. Results: Major and minor keyword trends were apparent along with the overall increase in number of articles published per month and change in keywords per article. Conclusion: While keyword data may not be sufficient to enable strong statistical prediction of emerging research trends, visualization of keyword trends allows for a better qualitative understanding of these trends. Full access to the journal article corpus would enable stronger predictive analytic techniques to be successfully performed.
SU‐E‐T‐272: Cochlea Dose Tolerance for Acoustic Neuroma Patients Treated with CyberKnife Stereotactic Radiosurgery
Authors: Rashid A , Pang D , Karam S
Published: July 2013

Purpose: In this study, a predictive model was generated to estimate the probability of hearing loss as a Result of acoustic neuroma radiosurgey in five fractions, since we have not seen any other published cochlea dose response model for five fractionsMethods: Cyberknife stereotactic radiosurgey at the Medstar Georgetown University Hospital was used in the treatment of 44 acoustic neuroma patients from 2003 to 2012. Toxicity was scored using Common Toxicity Criteria for Adverse Events (CTCAE) 3.0. Grade 1 toxicity was experienced by 2 patients; Grade 2 by 3 patients; and Grade 3 by 2 patients.The maximum cochlea doses and grade of the complications from cochlea were imported into the DVH Evaluator where the probit dose response model was fitted using the maximum likelihood algorithm. The model fitting parameters were optimized to provide the best fit to the observed complication data for hearing loss in one ear for acoustic Neuroma patients. Results: The two standard maximum point dose tolerance limits for cochlea in five fractions are Timmerman's 27.5Gy limit and the TG‐101 25Gy limit. From this dataset for Grade 3 complications the predicted risk level of these dose tolerance limits are 13.3% and 7.9%, respectively. For Grade 2 or higher events, the 5%, 10%, and 25% risk levels were estimated to be 11.4, 18.4, and 30.0Gy, respectively. For Grade 3 events, the 5%, 10%, and 25% risk levels were estimated to be 23.1, 26.1, and 31.2Gy. Conclusion: NTCP using cochlea maximum doses can be used to estimate the rate of hearing risk analysis from acoustic Neuroma Radiosurgery. More clinical data and further study will lead to refinement of the dose tolerance estimates.
SU‐E‐T‐337: Intensity Modulated Brachytherapy for Rectal Cancer Using A Novel Grooved Shielding Design
Authors: Webster M , Devic S , Vuong T , Scanderbeg D , Han D , Song W
Published: July 2013

Purpose: To create a novel HDR (192‐Ir) brachytherapy applicator for treatment of rectal carcinomas that uses tungsten shielding to make it dosimetrically superior to all commercially available applicators, despite being no larger than them. Methods: A set of 16 new applicators were designed and simulated using Monte Carlo (MCNPX). All designs were made of a 16‐mm diameter, high density tungsten alloy cylinder with inset grooves running along its length for the source to travel along. The designs varied regarding the number and depth of these grooves. Each design was optimized on 36 clinically treated plans (using 8‐channel Intracavitary Mold Applicator (Nucletron)) with asymmetrical CTVs, on in‐house written intensity modulated brachytherapy planning optimization software. Additionally, a 10 channel device with two channels per groove at varying depths was considered. All results were compared against the clinically treated plans. Results: First, all device designs outperformed the Intracavitary Mold Applicator in EVERY metric, except the total dwell times (about 30% increase). There were clear but relative tradeoffs regarding both the number of channels and the depth of each channel. Overall, the 12‐channel, 1‐mm depth design had the best results of the simpler designs, sparing the healthy rectal tissues the most while achieving comparable CTV coverage. All designs significantly outperformed the clinically treated plans using the Intracavitary Mold Applicator. Conclusions: Our extensive simulations and planning showed that our device designs have the ability to conform to the CTV and spare OAR with previously unmatched quality compared to existing commercial brachytherapy devices.
SU‐E‐T‐339: Dosimetric Verification of New Accuboost Applicators
Authors: Garcia‐Cobian J , Lee S , Curran B , Sternick E
Published: July 2013

Purpose: To confirm dose, dose coverage, and dose homogeneity for two new types of Accuboost™ applicators. Methods: Measurements were performed with the newly designed Skin Dose Optimized (SDO) and Dose Rate Optimized (DRO) Accuboost™ applicators used with an Elekta High Dose Rate (HDR) after‐loader. 5 cm, 6 cm, and 7 cm diameter applicators were tested for both the SDO and DRO designs. Landauer nanoDot dosimeters (OSLD) were placed along the central axis of the applicators at a depth of 2 cm. Dwell times determined for a dose of 200 cGy and a separation of 40 mm were calculated for the standard parallel‐opposed setup. A single posterior applicator was then used to deliver 100 cGy. Dose measured using a parallel plate Markus chamber and the earlier applicator design (7 cm round) was used to normalize the measurements. The Markus chamber was then used to further verify doses from the new applicator designs. Relative film dosimetry was also performed to assess the dose distribution. Gafchromic film was sandwiched between solid water plates at a depth of 2 cm. Results: nanoDot‐measured dose differences ranged from −4.9% to 2.4% for both SDO and DRO applicators across all sizes. Ion chamber measurement differences ranged from −2.76% to 1.1% and from — 2.21% to 0.17% for DRO and SDO applicators, respectively. Gafchromic films were normalized such that the 100% value was consistent with nominal dimension of the applicator. Maximum doses ranged from 130% — 150% and showed reasonable dose distributions in both axial and coronal irradiated films. Conclusion: All applicators showed good dose distribution as well as absolute dose values. Treatments with these applicators should deliver the prescription doses and coverage as intended.
SU‐E‐T‐340: Predictive Models for Dosimetry of the Organs‐At‐Risk in Interstitial Gynecologic Brachytherapy
Authors: Damato A , Viswanathan A , Cormack R
Published: July 2013

Purpose: In this work, mathematical models for the prediction of the D2cc of rectum and bladder in interstitial gynecologic brachytherapy based on geometric information, without the generation of a treatment plan, are discussed and validated. Methods: Previous plans were used to establish the relationship between D2cc and the overlapping volume of the organ‐at‐risk with the targeted area (C0) or a 1‐cm expansion of the target area (C1). Three mathematical models were evaluated: D2cc = a*C1+b (LIN); D2cc = a — exp(‐b*C0) (EXP); and a mixed approach (MIX), where both C0 and C1 were inputs of the model. The model's parameters were optimized on a training set, and the model predictive error (predicted D2cc — real D2cc) was calculated on a validation set. The data of 20 patients treated with interstitial gynecologic brachytherapy were used to perform a K‐fold cross validation analysis, with K = 2, 4, 6,8, 10, and 20. Results: MIX was associated with the smallest mean prediction error with error <6.4% for an 18‐patient training set; LIN had an error <8.5%; EXP had an error < 8.3%. Best‐case‐scenario analysis showed that an error <5% could be achieved for a 10‐patient training set with MIX, error <7.5% for LIN and error <7.0% for EXP. The error decreases with the increase in training set size, with the most marked decrease observed for MIX. Conclusion: Ten training cases allow the MIX model to predict D2cc for the organs‐at‐risk with an error <5%. While clearly specific to clinical practice, the model can be used in the development of quality assurance tools to identify treatment plans with sub‐optimal sparing of the organs‐at‐risk. It can also be used to improve preplanning and in the development of real‐time intra‐operative planning tools.
SU‐E‐T‐342: Differences of Dose to Pelvic Organs at Risk (OAR) with Use of Vaginal Multi‐Channel Cylinder Applicator for Adjuvant High‐Dose Rate (HDR) Brachytherapy to the Vaginal Cuff
Authors: Neicu T , Valakh V , Chan P , Charpentier P , Li S
Published: July 2013

Purpose: We reviewed the use of Vaginal multi‐channel cylinder applicator (VCMC) in adjuvant HDR brachytherapy with the goal of reducing dose to OAR while completely covering the entire proximal vaginal cuff. Methods: Two patients underwent total hysterectomy for endometrial carcinoma and received combined 5 fractions of Ir‐192 HDR brachytherapy to the vaginal cuff as a portion of their postoperative regimens. Treatment was delivered using a commercially available Nucletron CT/MR compatible VCMC. The dwell time distribution for multiple lumens was optimized to maintain at least 95% of CTV within 95% of isodose line (V95 > 95%) while keeping dose to all OAR as low as possible. For comparison, plans were created using the central channel only simulating single‐channel (SC) cylinder treatments. Related samples Wilcoxon signed rank test was used to test for statistical significance. Results: Average CTV V200 was 39.7 ± 1.5 % of prescribed dose for VCMC plans vs. 32.5 ± 0.5 % for SC (p=0.04). Average CTV V150, V95, and V90 were 58.4 ± 2.0 %, 98.1 ± 1.0 %, and 99.4 ± 0.5 % for VCMC and 51.1 ± 0.3 % (p=0.04), 96.5 ± 0.6 % (p=0.04) and 98.8 ± 0.4 % (p=0.08) for SC. Average maximum point vaginal surface dose as a percentage of prescribed dose was similar: 294.5 ± 62.4 % for VCMC and 295.9 ± 79.7 % for SC. We also calculated the average D0.1cc, D1cc, D2cc and D10cc for bladder, rectum, sigmoid, and small bowel. Conclusion: Use of VCMC reduced D0.1cc, D1cc and D2cc for the rectum; however bladder D0.1cc and D10cc were lower for SC. While CTV V200 and V150 were higher for VCMC, maximum dose to vaginal surface was similar. Additional dosimetric and clinical studies of VCMC use are necessary.
SU‐E‐T‐343: Dosimetric Analysis of Catheter Displacement in High Dose Rate Prostate Brachytherapy
Authors: Park S , Kamrava M , Banerjee R , Demanes D
Published: July 2013

Purpose: To evaluate the dosimetric effect of catheter displacement on target coverage and doses to organs at risks (OARs) in high dose rate prostate brachytherapy. Methods: CT simulations from 21 prostate cancer patients treated with HDR monotherapy (7.25 Gy × 6 fractions) were used. The prostate CTV and OARs were contoured on the 3D‐CT. Treatment plans were optimized using an inverse planning simulated annealing algorithm and graphical optimization to ensure dosimetry objectives: target coverage (CTV D90=100–115%, V100 >97%, and V150 <35%) and OAR dose constraints (D0.1cc <85% (rectum), 80&–95% (bladder), and <110% (urethra)). Craniocaudal catheter movements from 1 to 10 mm in 1 mm increments were simulated by simultaneously shifting all active dwell positions in the initial treatment plan using catheter offset in the Oncentra MasterPlan (Nucletron). Target coverage (D90 and V100) and OAR doses (D0.1cc and D1cc) were evaluated and compared to no displacement plans. Results: The mean prostate CTV volume was 74.7±22.8 cc (range: 24.8–113.7 cc). Initial treatment plans provided target D90 = 107.7±2.0% (103.0–111.2%) and V100 = 98.5±0.8% (97.1–99.5%). The D0.1cc to OARs was 77.3±2.3% (rectum), 84.2±2.0% (bladder), and 106.8±1.6% (urethra). The mean target coverage was not significantly different for 1–2 mm shifts. Shifts between 3 and 6 mm still met most dosimetry objectives, but provided progressively less good target coverage and doses to OARs. Displacements of greater than or equal to 7 mm resulted in dosimetry that did not meet our dosimetry objectives. Conclusion: Small changes in catheter position Result in significant alterations in dosimetry and treatment delivery. The target coverage (D90 and V100) and bladder dose are reduced and the rectal and urethra doses are higher in direct proportion to the degree of displacement. It is essential to check and correct interstitial catheter positions before each HDR fraction to accurately deliver the planned radiation dose.
SU‐E‐T‐344: Interfractional Needle Displacement During HDR Brachytherapy for Patients with Gynecological Cancer Using Interstitial Needle Template
Authors: Benhabib S , Kim R , Duan J , Burnett L , Popple R , Wu X , Cardan R , Brezovich I , Shen S
Published: July 2013

Purpose: HDR Brachytherapy using interstitial needle templates for gynecological cancer is commonly delivered in 4–5 fractions. Potential movement of afterloading needles between fractions requires verification before each treatment. The current study analyzed the interfractional displacement of the implant needles relative to implanted fiducial markers (for tumor border) positions. Methods: 15 patients with interstitial needle implants were reviewed. Treatment plans were based on CT images and the superior and inferior borders of the target volumes were defined by fiducial markers. The implant position was verified with kV orthogonal images before each treatment. The 3D positions of the needle tip and fiducial markers were determined from the orthogonal images. Needle displacement was defined by the change of the 3D distance between needle tip and 2 fiducial markers between planning and before the last fraction. The relative 3D distances between 2 fiducial markers were also measured to assess possible markers migration. Results: The median needle was 1.1 mm and the displacement ranged from 0.2–7.8 mm for the needle that near superior fiducial marker, and was typically in the inferior direction. One patient had significant needle displacement (7.8 mm) and positions were corrected before treatment. The needle displacements in the remaining patients were less than 4 mm and were not corrected because of adequate treatment margins. The displacement between 2 fiducial markers changed from 0.2–4.9 mm with a median change of 1 mm. Conclusion: There was detectable displacement of implant needles between HDR fractions, typically in the inferior direction. Pretreatment verification using orthogonal imaging is required and used to correct needle position based on implanted fiducial markers and needle tip positions.
SU‐E‐T‐348: Dosimetric Characteristic of Zeiss IntraBeam Flat and Surface Applicators
Authors: Xu Y , Lam S
Published: July 2013

Purpose: To verify the dosimetric characteristics of Flat and Surface applicators (two of each, 2cm and 4cm in diameters) for Zeiss Intrabeam systemMethods: Dose rate vs. distance from surface of the applicators were measured with the 1D water tank and PTW ion chamber provided by IntraBeam system. Gafchromic films and solid water were used to determine the 2D dose distribution and beam divergence of the applicators. Results: The highest dose rate is from 2cm Surface applicator (3.4Gy/min at 1.6mm from applicator surface, it drops to 0.52Gy/min at 10mm). The 2cm Flat applicator dose rate is 1.47Gy/min at 1.6mm; it drops to 0.36Gy/min at 10mm. The lowest dose rate is from the 4cm Flat applicator (0.49Gy/min at 1.6mm; it drops to 0.18Gy/min at 10mm). The 4cm Surface applicator dose rate is 1.36Gy/min at 1.6mm; it drops to 0.29Gy/min at 10mm. All the data were verified and confirmed with the manufacture factory measurements.Two dimensional dose profiles (parallel to applicator surface) at different depths were plotted from scanned Gafchromic films. Dose divergence of approximately 85 degree for 4cm applicators; and 65 degree for 2cm applicators; can also be seen from exposed films perpendicular to the applicator surface. Conclusion: Dosimetric characteristic were studied for both Flat and Surface applicators from Intrabeam system. Although all the applicators in this study are still pending FDA approval for clinical use, the data collected thus far can serve as a framework for both radiation oncologists and medical physicists to build the future clinical trials and treatment programs.
SU‐E‐T‐353: Feasibility of 3D Dosimetry for Prostate LDR: Monte Carlo Simulations of Pd‐103,I‐125, and Cs‐131 Seeds in Deformable PRESAGE
Authors: Yang Y , Oldham M , Adamovics J , Adamson J
Published: July 2013

Purpose: Recent innovations in 3D dosimetry include deformable polyurethane dosimeters (PRESAGE) and high resolution optical CT (∼50 microns). These developments enable 3D dosimetry in deformation conditions present during prostate LDR brachytherapy. However, water equivalence for the deformable dosimeter formulations has not been quantified. The purpose of this study was to characterize the dose distributions of Pd‐103, I‐125, and Cs‐131 in different PRESAGE using Monte Carlo (MC) simulations. Methods: Dose distributions from models 200(Pd‐103), 6711(I‐125), and CS‐1 Rev2(Cs‐131) seeds were simulated using the MCNP5 radiation transport. Geometric function g(r) and anisotropy function Φ(r) from TG43 were calculated from MC results in water and compared to published results to verify the MC technique. Dose distributions were then simulated in 5×5×10 cm^3 cylindrical PRESAGE with (0.1cm)^3 resolution. Current formulations of both conventional (rigid, 1.065 g/cm^3) and deformable (1.02 g/cm^3) PRESAGE with effective Z of 7.61 and 7.48 were simulated and g(r) and Φ(r) were calculated in X‐Y and X‐Z planes respectively. The 2×10^9 histories gave a typical statistical uncertainty (k=1) of ∼3% at 6 cm on the transverse plane. Results: Conventional PRESAGE over‐attenuated all three sources. Relative to water, g(r) in conventional PRESAGE decreased linearly ∼2.5%/cm within a radius of 1–6 cm for Pd‐103, and 1–10 cm for I‐125 and Cs‐131. Deformable PRESAGE under‐attenuated Pd‐103 but was water equivalent for I‐125 and Cs‐131, with g(r) within 5% and 1% of water within a radius of 0–10 cm, respectively. Differences for Φ(r) were <1% for Pd‐103 and Cs‐131, and <5% for I‐125 for both conventional and deformable PRESAGE. MC results indicated underdose >10% at dosimeter surface, while <2% with 2 cm backscatter. Conclusion: Dose distributions for Pd‐103, I‐125, and Cs‐131 have been characterized in PRESAGE and show great potential for water equivalent 3D dosimetry and further deformable formulations optimization. Research efforts at Duke University and Rider University were partially supported by National Institutes of Health (NIH) Grant No. R01 CA100835‐01. Dr. John Adamovics is the owner of Heuris Inc.
SU‐E‐T‐354: Dosimetry Parameters Revisited for the IsoAid Model IAI‐125A Brachytherapy Seed
Authors: Aryal P , Molloy J , Rivard M
Published: July 2013

Purpose: Investigate and analyze TG43 dosimetry parameters for the IsoAid I125 model IAI 125A seedMethods: We revisited dosimetry for the IsoAid advantage I125 model IAI 125A seed to verify the published TG43 parameters. The IsoAid seed was examined based on manufacturer data and detailed information published in literature. The MCNP5 Monte Carlo radiation transport code was used. Sensitivity of these dosimetry parameters was assessed by changing a total of 10 geometric and computational variables, including source coating thickness, capsule design, photon emission spectrum, and cross section library. The calculated dose rate constants and radial dose functions were then compared with published literature values. Results: Compared to the reference simulation conditions of a 0.5 um source coating, recent capsule design data, the NNDC photon spectrum, and the ZAID.04p MCNP5 cross section libraries, the highest dose rate constant variation was +3.1% and the lowest was −4.0% compared to our value of 0.922 cGy/h/U. Calculated values by Solberg et al. (2002) and Meigooni et al. (2002) were 0.962 and 0.98 cGy/h/U respectively. There were significant differences (>10%) between the published values for the radial dose function and those calculated herein, becoming increasingly disparate as radial distance increased. These differences could be explained within a few percent by performing simulations with their photon emission spectrum and using older cross section libraries. For the similarly designed model 6711 seed, our dose rate constant results agreed within 0.2% and within 0.5% for gL(0.5<r<10cm) with Kennedy et al. (2010). Conclusion: A modern investigation of the TG43 dosimetry parameters for the I125 IsoAid seed indicates clinically‐significant differences with published results used for the AAPM consensus values. We suggest that the AAPM revisit dosimetry for this and other seeds included in the 2004 and 2007 reports.
SU‐E‐T‐358: Double‐Ends Quasi‐Breath‐Hold (DE‐QBH) Technique for Respiratory Motion Management
Authors: Kim S , Park Y , Lee J , Choi K , Ye S
Published: July 2013

Purpose: To introduce double‐ends quasi‐breath‐hold (DE‐QBH) technique and evaluate its feasibility. Methods: It was previously demonstrated QBH, a hybrid technique combining free‐breathing‐gating (FBG) and breath‐hold, could provide less motion uncertainty and shorter treatment time than conventional FBG. While QBH uses only one phase, either end‐of‐exhalation (EOE) or end‐of‐inhalation (EOI), DE‐QBH utilizes both phases to further improve delivery efficiency. DE‐QBH is realized using an audiovisual biofeedback system (AVBFS) and a respiratory motion management program (RMMP). The in‐house developed AVBFS, consisting of two infrared stereo cameras and a head mounted display, provides dynamic feedback to patients. The RMMP establishes a personalized DE‐QBH model by adding a short quasi‐breath‐hold period to both EOI and EOE phase. Then the patient is guided to follow the model. A simulation study for 6 different maneuvers (2−2, 3−3, 4−4, 5−5, 7−5, and 9−5 sec for EOI‐EOE combination) was performed with 3 volunteers. External motion signals were analyzed to obtain mean absolute error (MAE) between the measured and guided. Duty cycle was also estimated. Results: MAEs were smaller than 1 mm for all maneuvers except 9−5 combination [0.9(+/−)1.3, 0.7(+/−)1.2, 0.6(+/−)1.1, 0.7(+/−)1.1, 0.6(+/−)1.0, and 1.1(+/−)0.8 mm for 2−2, 3−3, 4−4, 5−5, 7−5, and 9−5 combination, respectively]. Estimated duty cycles were 43, 52, 57, 62, 64, and 71% for 2−2, 3−3, 4−4, 5−5, 7−5, and 9v5 combination, respectively. Conclusion: The proposed DE‐QBH technique was feasible for respiratory motion management. It showed excellent feasibility with minimal motion uncertainty and significantly improved delivery efficiency, reaching up to 70% duty cycle.
SU‐E‐T‐370: To Study the Impact of Energy Variation On Cone Ratio, PDD, TMR and IMRT Doses for Flattening Filter Free (FFF) Beam of TomoTherapy Hi‐Art(TM)
Authors: Tolakanahalli R , Robeck L , Tewatia D
Published: July 2013

Purpose: To study the effect of energy variation on standard IMRT plans, MU chamber ratio (MU1/MU2) and cone ratio (CR) for non‐flattened beam e.g., Tomotherapy. Methods: In this controlled experiment, we varied the energy (PDD10) on TomoTherapy Hi‐ARTTM from −1.6 % to +1.6% in six steps while keeping calibrated output unchanged. For achieving this, injector current (Injl) and pulse forming network (pfn) voltage were adjusted. The effect of this variation in energy(δE) on standard IMRT plans and energy indicators were studied. To quantify sensitivity of standard IMRT plans with δE, cheese phantom was used with multiple calibrated ionization chambers. ΔD was calculated as a percent variation of measured vs. expected dose. Ratio of ΔDon‐axis with ΔDoff‐axis for each commissioned field width (FW) was tabulated against δE. The effect of this on other energy indicators was also studied to verify the sensitivity of TMR20 10 MU chamber ratio, and detector data‐based‐CR. Results: Good agreement between PDD10 vs TMR20 10 (R2=0.97, slope=1.01) and PDD10 vs MU chamber ratio(R2=0.99, slope=−0.9) was observed. CR is more sensitive to energy change with slope =−2.5 than PDD10. Ratio of ΔDon‐axis with ΔDoff‐axis for FW 2.5 cm (R2=0.91, slope =0.63) and FW 1 cm (R2=0.94, slope =0.80) of standard IMRT plan also agreed well with PDD10. Conclusion: CR is more sensitive to energy changes compared to PDD10, thus CR with MU1/MU2 can definitely be used as quality measure on a daily/weekly basis. Though the on‐axis vs off‐axis variation is not as sensitive, output across the 6 standard IMRT plans can vary up to 2% for a 1% increase in energy. Hence, it is of utmost important to manage the PDD10 tightly around +/− 0.5%. This study can be easily extended to monitor the calibration and beam quality for other emerging technologies based on flattening‐filter‐free (FFF) delivery mode e.g., TrueBeamTM.
SU‐E‐T‐381: The Step‐And‐Shoot IMRT Overshooting Phenomena: A Novel Method to Mitigate Patient Overdosage
Authors: Pompos A , Zhen H , Ouyang L , Bao Q , Stojadinovic S
Published: July 2013

Purpose: To demonstrate a method to mitigate the step‐and‐shoot (S&S) IMRT overdose phenomenon for set of patients which initially failed IMRT QA process. Methods: Five S&S IMRT patients treated on Varian 2100C‐EX linacs with larger than +4.5% phantom IC point dose difference relative to planned dose were investigated. For every patient plan, five fractions (Fx) were delivered. Dynalog files were recorded and centiMU pulses from dose integrator board for every control point (CP) were counted using a BK1856D (B&K Precision Corp.) pulse counter (PC). The recorded MUs were imported to Pinnacle9.2 (Philips Healthcare), the 3D dose was recalculated and compared to the planned dose distribution. The initial plans were then modified by adding one starting segment to every beam. This segment consisted of an MLC aperture of 0.5x1cm2 hidden under the jaws with 1MU. For each patient, five Fx of the modified plan were delivered, recorded and the delivered 3D dose recalculated. Individual voxels' dose in high dose region, isocenter point dose, segment MUs, PTV D95 and OAR D2cc were compared between the original plan and the results of both deliveries. Results: The PC recorded total number showed the delivered beam MUs exceeded the plan by only ∼0.2%. For all initial plans, the first CP on average overshot by 0.6MU. It was determined that this on average translated to an increased dose to isocenter, PTV D95, bladder D2cc and high‐dose‐region voxels' dose by 2.66% (2.21%–3.12%), 2.06% (1.59%–2.48%), 2.57% (1.97%–3.11%), and 2.19% (1.75%–2.75%) respectively. All modified plans had inconsequential 0.05MU overshoot in first unmodified CP and 0.04%(−0.45% −0.55%), −0.07%(−0.44–‐0.48%), 0.08%(−0.28%–0.33%) and −0.07%(−0.31%–0.20%) differences for dosimetric parameters listed above. Conclusion: Our proposed method of attaching a special aperture 1MU CP to each beam was experimentally verified by using centiMU pulse counts to successfully eliminate the overdosage.