bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐197: A Comprehensive Variance Reporting System and an Analysis of Variances Reported at Our Institution
Authors: Miller B , Dickinson M , Nurushev T , Rasmusson R , Smith C , Orfali A , Wen N , Cormier A , Gifford L , Dragovic J , Movsas B , Aref I , Levin K , Ryu S , Ajlouni M , Walker E , Pradhan D , Chetty I
Published: June 2012

Purpose: It is essential for radiation oncology departments to have comprehensive patient safety and quality programs. Two years ago we undertook a systematic review of our safety/QA program. Existing policies were updated and new policies created where necessary. One crucial component of any safety/QA program is continually updating it based on current information, the ‘check’ and ‘act’ portions of the Deming Cycle. We accomplished this with a transparent variance reporting system and a safety/QA committee reviewing and acting on reported variances. Methods: With 5 radiation oncology centers in our institution, we needed to devise a system that would allow anyone to report a variance and provide our QA committee the ability to review variances system‐wide. We developed the system using web‐based tools. The system allows individuals to report variances, anonymously or named, specify the nature of the variance and indicate the tools used to identify the variance. Results: In 2011, 285 variances were reported, 102 were reported by physicists, 86 anonymously, 71 by therapists and 26 by dosimetrists. We realized the need to develop clear classifications for variances. We added a high priority category, defined as variances which resulted in or had the potential to result in harm to a patient or when a policy is purposely overridden. Of the 285 variances reported, 5 were high priority. We created a process variance category, defined as variances where a specific clinical process is not followed. Of the 285 reported variances 155 were process variances. Conclusions: Reporting of variances through a centralized database is central toward developing a robust patient safety/quality assurance program. Anonymous reporting fosters a non‐punitive environment, and promotes the ‘safety culture’. The goal of such a system is to review trends in clinical processes and ultimately to improve safety/quality by reducing variances associated with these processes.
SU‐E‐T‐199: The Radiological Physics Center's Credentialing Dosimetry Reviews: Their Effect on Clinical Trial Deviation Rates
Authors: Hollan A , Lowenstein J , Nguyen H , Hall F , Roll J , Harris I , Followill D
Published: June 2012

Purpose: To describe the Radiological Physics Center's (RPC) methods to evaluate an institution's ability to meet protocol guidelines in order to decrease NCI clinical trial deviation rate. Methods: The RPC's dosimetry group utilizes 3 methods of assessing an institutions ability to meet the protocol treatment specifications. These methods involve a clinical and dosimetric review of a treatment plan submitted by the institution prior to the first patient being treated on a protocol. The three evaluation methods include use of site/treatment modality specific benchmark cases, evaluation of a previous patient treated in a similar fashion and a rapid review of the first patient placed on a trial prior to start of treatment. The dosimetric review consists of an independent dose recalculation using RPC measured data or RPC standard dosimetry data. The clinical review assesses the patient's DVHs and contouring of the tumor volume and critical structures, typically in conjunction with a radiation oncologist. Results: Over the past 5 years the RPC has performed these QA reviews for several of the clinical trial groups for several different disease sites and treatment modalities. We have reviewed 1366 treatment plans as a part of credentialing (97 gynecological, 223 prostate, 1046 breast) where 222 failed the first submission requiring the RPC to interact with the submitting institution to resolve the discrepancy. The review of the benchmarks has resulted in 18% of the institutions requiring intervention by the RPC. Performing these reviews has identified potential clinical and dosimetric problem areas that could possibly have resulted in 17% of the charts reviewed to receive a minor or major deviation. Conclusions: The RPC's clinical and dosimetry review of submitted treatment plans before or early in the treatment process has helped to reduce the deviation rates on protocols. Work supported by PHS grant CA 10953 awarded by NCI, DHHS
SU‐E‐T‐202: Comprehensive Quality Assurance Procedures for Uniform Scanning Proton Therapy Machines
Authors: Zheng Y , Ding X , Mascia A , Hsi W , Kang Y , Ramirez E , Zeidan O , Schreuder N
Published: June 2012

Purpose: Quality assurance (QA) is essential in safe and accurate delivery of radiation therapy. However, QA in proton therapy is challenging due to complicated and often facility‐specific beam delivery systems and limited beam time for QA. The purpose of this study is to develop an efficient and comprehensive QA procedure for a multi‐room proton therapy center using uniform scanning beams. Methods: Our proton therapy center is comprised of a 230 MeV cyclotron, one fixed beam room, two inclined beam rooms, and one gantry room. Uniform scanning is employed exclusively in all treatment rooms. A rfDaily QA3 (Sun Nuclear Inc., Melbourne, Florida) together with home‐made devices is used for daily QA. Parallel plane chambers, a multi‐layer ionization chamber array (Zebra, IBA dosimetry, Schwarzenbruck, German), and an IC profiler (Sun Nuclear Inc., Melbourne, Florida) are used to QA the characteristics of the uniform scanning beams, including output, range, modulation width, flatness, symmetry, and penumbra, for both monthly and annual QA. QA procedures and acceptance criteria were developed, taking into account the likelihood and potential risk of failure, as well as the available equipment, personnel and other resources. Results: QA procedures and tolerances were developed for daily, monthly and annual QA at our proton therapy center. Daily QA is performed by radiation therapists, and can be completed within 30 minutes for all rooms. Monthly QA and annual QA are performed by physicists, taking about 4 hours and a weekend respectively. Trend analysis was performed for various machine characteristics, such as machine output, range, flatness, and symmetry. Conclusion: QA standards are desired in Radiation Oncology, but not many standards are developed and available for proton therapy. In the mean time, facility‐specific QA procedures should be developed based on the equipment failure modes and available resources.
SU‐E‐T‐208: The Secondary Malignancy Risk Estimation Due to the Neutron Contamination in 3D‐CRT and IMRT Treatment Techniques by Using Bubble Detectors
Authors: Biltekin F , Özyigit G , Celik D , Yeginer M , Akyol F , Cengiz M , Yildiz F
Published: June 2012

Purpose: In this study, the neutron measurements were performed in free in air and RW3 solid water phantom to estimate the secondary malignancy risk for three dimensional conformal radiotherapy (3D‐CRT) and intensity modulated radiotherapy (IMRT) techniques in prostate cancer treatment. Methods: Neutron dose were measured in 18 MV Elekta Synergy Platform and Varian Clinac linear accelerators by using bubble detector for personal neutron dosimetry (BD‐PND). To determine the neutron equivalent dose in different depths and different distance from the edge of treatment field RW3 solid water phantom was used and organs location was defined in Alderson Rando phantom with respect to target (prostate) position in the treatment field. By using these data, we determined the neutron equivalent dose and effective dose for the standard prostate cancer patient treated with 3D‐CRT and IMRT with 18 MV photon energy. The total dose was 70 Gy in 3D‐CRT and 76 Gy in IMRT treatment in the current study. For both of these treatment techniques, we estimated the risk of secondary malignancies due to the neutron contamination by using the International Commission on Radiological Protection (ICRP) report 103. Results: The equivalent dose and effective dose due the neutron contamination were considerably high in 18 MV IMRT technique. The secondary malignancy risk estimation for 3D‐CRT and IMRT were found to be 0.44% and 1.15% for Elekta Synergy Platform linear accelerator, 0.92% and 2.38% for the Varian Clinac DHX High Performance linear accelerator, respectively. Conclusions: Therefore, one should take care of the secondary malignancy risk in case of using 18 MV in IMRT applications.
SU‐E‐T‐210: Surviving a Visit by the Radiological Physics Center
Authors: Grant W , Mcgary J , Rosen I , Nitsch P , Davidson S
Published: June 2012

Purpose: To demonstrate an objective approach to determining if a negative report from the Radiological Physics Center (RPC) of greater than 10% error is valid or has clinical significance. Methods: The discrepancy involved the clinical activity (mgRaEq) of Cs‐137 sources, some manufactured by 3M and some by Amersham. Measurements were made in the proprietary RPC Well Counter calibrated by the MD Anderson ADCL and our Well Counter (CNMC, Model 44D) calibrated by the same laboratory as well as the University of Wisconsin ADCL. In addition, we possess an Amersham Cs‐137 Check Source that had been calibrated by the UW‐ADCL in 2002. All clinical sources were checked in both Well Counters on the first visit. One clinical source and the Check Source were measured in a second visit that occurred 51 days later. Results: On the initial RPC visit, 9 of 25 sources had a minimum of an 8% discrepancy between the RPC and the Institution, with a maximum of 11%. Contributing errors included using the incorrect straw position by us, an unexplained 2.3% error in the RPC data identified 73 days post‐visit, a 2% variation in Chamber Factors for our Well Counter from the two ADCL's. When we use the 2004 value of Air Kerma Strength for the Check Source to determine a Calibration Factor of the Well Counter, all sources were within 0.5% of their decayed value established in 2002. Conclusions: This work emphasizes the value of having simple Constancy Check systems in a Quality Assurance program as ‘Accuracy’ has error bars. The disagreement in calibration data between the ADCL Laboratories, which was at the 2% maximum quoted in their Calibration Reports, is a reminder that there is uncertainty in measurements. Constancy Checks allow one to sort out discrepancies and to answer challenges to the validity of your program.
SU‐E‐T‐211: Peer Review System for Ensuring Quality of Radiation Therapy Treatments
Authors: Kapoor R , Kapur P , Kumar SA , Alex D , Ranka S , Palta J
Published: June 2012

Purpose: To demonstrate a Web‐based electronic peer review system that has the potential to improve quality of care for radiation therapy patients. The system provides tools that allow radiation oncologists to seek peer review of target and critical structure delineation, treatment plans, and share clinical data with peers to optimize radiation therapy treatments. Material and Methods: Peer review of radiation therapy treatment planning data prior to its initiation improves the quality of radiation therapy and clinical outcomes. Web‐based access to radiation therapy treatment planning data and medical records mitigate existing geographical and temporal constraints. With internet access, the healthcare provider can access the data from any location and review it in an interactive and collaborative manner. Interoperability standard like DICOM‐RT and IHE‐RO compliant RT Systems have facilitated the design and implementation of PRS with Silverlight Web technology, .net Framework and SQL Server. Local DICOM‐RT archive and cloud based services are deployed to facilitate remote peer reviews. Results: To validate the PRS system, we tested the system for 100 patients with Philips Pinnacle v 9.0 and Varian Eclipse v 8.9 treatment planning system (TPS). We transmitted the DICOM RT data from the TPS to the cloud based services via the PRS local DICOM RT Archive. Various CT simulation based parameters such as orientation of CT, properties of RT structures etc. were compared between the TPS and PRS system. Data integrity of other parameters such as patient demographics (patient name, ID, attending physician etc.) and dose volume related parameters were also evaluated. Such rigorous testing allowed us to optimize the functionalities and clinical implementation of the PRS. Conclusions: We believe that the PRS will improve the quality and safety of a broad spectrum of radiation therapy patients treated in underserved areas while discouraging the overutilization of expensive radiation treatment modalities. This research and development project is supported by the James and Ester King Biomedical Research Program grant # RC1‐09KW‐09‐26829
SU‐E‐T‐212: Clinical Deployment of an Automatic Planning Interface for Overlap Volume Histogram Based Treatment Planning
Authors: Moore J , Herman J , Evans K , Yang W , McNutt T
Published: June 2012

Purpose: To develop and deploy an interface to support automatic treatment planning which predicts achievable dose levels for organs at risk (OARs) from patients with similar or more complicated anatomies queried from a database. This interface will provide an easy to use method of selecting the best known achievable dose values for a given patient, and use them to automate the planning process. Methods: An overlap volume histogram (OVH) describes the distance a target structure can be expanded with the volume of the compared overlap structure. An OVH is generated for each target/critical structure pair and stored in a database with dose‐volume histograms (DVHs) for each patient. For all patients, structures are consistently named by mapping ROI names to a set of common names. For a new patient, the patient database is queried for the lowest achievable dose for each OAR from patients in the database with the same or lower overlap distance. The plan parameters and generated objectives are then automatically loaded into treatment planning system for optimization. The final clinical plan from each patient is added to the database to improve the results of future queries. Results: The system has been accepted by the dosimetrists for clinical use. Automatically generated plans required less dosimetrist interaction to achieve similar coverage to manually generated plans while OAR doses were reduced or no worse than the manually generated plans. Conclusion: Automatic planning tools can aid dosimetrists in quickly generating plans which maintain target coverage and produce comparable or reduced dose to OARs. Our interface has simplified the process enabling the broader use of the system across our dosimetry staff. Philips stock ownership Philips Sponsored Research Elekta Sponsored Research Elekta Patent License Accuray (Tomotherapy) Patent License
SU‐E‐T‐223: High‐Energy Photon Standard Dosimetry Data: A Quality Assurance Tool
Authors: Lowenstein J , Kry S , Molineu A , Alvarez P , Aguirre J , Summers P , Followill D
Published: June 2012

Purpose: Describe the Radiological Physics Center's (RPC) extensive standard dosimetry data set determined from on‐site audits measurements.Method and Materials: Measurements were made during on‐site audits to institutions participating in NCI funded cooperative clinical trials for 44 years using a 0.6cc cylindrical ionization chamber placed within the RPC's water tank. Measurements were made on Varian, Siemens, and Elekta/Philips accelerators for 11 different energies from 68 models of accelerators. We have measured percent depth dose, output factors, and off‐axis factors for 123 different accelerator model/energy combinations for which we have 5 or more sets of measurements. The RPC analyzed these data and determined the ‘standard data’ for each model/energy combination. The RPC defines ‘standard data’ as the mean value of 5 or more sets of dosimetry data or agreement with published depth dose data (within 2%). Results: The analysis of these standard data indicates that for modern accelerator models, the dosimetry data for a particular model/energy are within ï,±2%. The RPC has always found accelerators of the same make/model/energy combination have the same dosimetric properties in terms of depth dose, field size dependence and off‐axis factors. Because of this consistency, the RPC can assign standard data for percent depth dose, average output factors and off‐axis factors for a given combination of energy and accelerator make and model. Conclusions: The RPC standard data can be used as a redundant quality assurance tool to assist Medical Physicists to have confidence in their clinical data to within 2%. The next step is for the RPC to provide a way for institutions to submit data to the RPC to determine if their data agrees with the standard data as a redundant check. This work was supported by PHS grants CA10953 awarded by NCI, DHHS.
SU‐E‐T‐224: Dose Distribution of Oesophagus Stents Measured by EBT2 Film Dosimetry
Authors: Poppinga D , Schoenfeld A , Chofor N , Poppe B
Published: June 2012

Purpose: The purpose of this study is to investigate the dose enhancement at oesophagus stents made of nitinol. The material is a nickel titan alloy with an effective atomic number of 26. Because of the increased atomic number in comparison to the human body, dose enhancement in surrounding tissue is expected. Methods: The relative dose distribution around the stent was measured in a water phantom. To simulate the air cavity within the oesophagus, a styrodur cylinder was placed inside the stent. The stent was held with a circular PMMA holder. An EBT2 film was wrapped around the stent to measure the relative radial dose distribution.The setup was irradiated with a 6MV photon beam (Siemens Primus) and a field size of 5cmx5cm. The distance between source and centre of the stent was 100cm.The EBT2 films were digitized at a scanning resolution of 72dpi using an Epson 10000XL flatbed scanner with a transparency unit. Furthermore, the films were fixed in a frame to prevent Newton rings in the scanned image. Results: The dose increases in all directions around the stent. With approximately 18%, the highest increase is caused on the proximal side of the stent. On the backside the dose enhancement is approximately 10%. Conclusions: Dose enhancements around a stent are detectable and one should be aware of it's occurence in the radiotherapeutical treatment of oesophageal cancer. Because of the enhancement in all directions healthy tissue may be affected.
SU‐E‐T‐225: A Comprehensive Evaluation of Real‐Time Motion Tracking of a Surface Imaging System for Lung Treatment
Authors: Jin H , Su Z
Published: June 2012

Purpose: Applicability of the AlignRT surface imaging system was extensively investigated for real‐time motion tracking in radiation therapy of lung cancer. Methods: A 4D computer‐controlled motion phantom was employed to simulate a human breathing motion. An anthropomorphic thoracic phantom (a coronal cross‐sectional area: ∼1,200 cm2) was monitored during the 4D motion tracking. A breathing cycle from a healthy subject (breathing frequency: 0.2 Hz; maximum amplitude: vertical 7 mm, longitudinal 6 mm, and lateral 1.2 mm) was monitored and fed into the phantom control system. The real time monitoring was investigated by modifying a region of detection (the whole, a half, and a quarter of the area) and combination of 3 cameras (patient left, middle, and right). Results: The real‐time tracking errors (detected breathing motion ‐ the input of the subject's breathing) of the phantom motion using one camera (lateral, longitudinal, vertical) were (0.02±0.14 mm, −0.23±0.48 mm, −0.10±0.48 mm) with ipsilateral halves of the area (frame rate: 1.52 Hz), (0.06±0.10 mm, −0.30±0.30 mm, ‐0.03−0.35 mm) with ipsilateral quarters (frame rate: 1.95 Hz), and (0.19±0.96 mm, 0.29±1.50 mm, −0.46±1.58 mm) with contralateral quarters (frame rate: 3.04 Hz). The detection errors using 2‐camera combinations (left‐middle and right‐middle) were (−0.06±0.06 mm, −0.43±0.21 mm, 0.00±0.22 mm) for the ipsilateral quarters and (−0.62±0.18 mm, −1.20±0.37 mm, 0.03±0.30 mm) for the contralateral quarters, respectively. The 3‐camera tracking using halves of the area presented an error of (−0.04±0.12 mm, −0.69±0.35 mm, −0.08±0.38 mm) with a frame rate of 0.62 Hz. Conclusions: To guarantee a sub‐millimeter accuracy of realtime motion tracking in the lung treatment, combination of 2 cameras or less, a frame rate of greater than the Nyquist frequency (in this study fN = 2B (breathing frequency) = 0.4 Hz), and a tracking area of less than an ipsilateral half of thoracic area is highly recommended.
SU‐E‐T‐231: Comparison of Beam Characteristics of Small Field 6 MeV Electrons as Replacement for Superficial X Ray Beam
Authors: Avadhani J , Sasidharan S , Carton C , Lowen M , Klapproth T , Licitra C
Published: June 2012

Purpose: To compare beam characteristics of superficial X‐rays with 6 MeV Electrons for the purpose of replacing superficial treatments with electron fields for skin lesions. Methods: Electron beam cutouts were made with 12mm thickness cerrobend in diameters 2–5 cm to match superficial X‐ray machine cones. Central axis depth doses and profiles were generated using 0.007 cc Exradin A‐16 ion chamber, in PTW water phantom at 1mm steps, at 96 and 100cm SSD for electron beams, and at 15cm SSD for superficial X‐rays. From the beam data, radiation penumbra 90‐10%, 90% profile width, peripheral dose and percentage depth dose were obtained for comparison. Results: The 90‐10% radiation penumbra was ranging 7.4–13.7 mm, 12.6–17.6 mm for 6 MeV electrons at 96 and 100cm SSD respectively, and 4.2–11.4 mm for 2–5 cm superficial X‐ray cones. For 90% treatment width, a margin ranging 5‐7 mm, 6–9 mm is needed around the periphery of target for 6 MeV Electrons at 96 and 100cm SSD respectively, and 2–3 mm for superficial X‐ray cones. For 96cm SSD, the peripheral dose from the geometrical field edge were 3.9% at 1cm and 0.5% at 2cm. It was 2.6% at 1cm and 0.7% at 2cm for 100cm SSD. For superficial, it was 6.2%, 7.5%, 9.1% at 1cm, and 3.4%, 4.3%, 5.6% at 2cm for 100 kV, 120 kV and 150 kV respectively. The electron surface dose was below 90%. Conclusion: 6 MeV Electron beam shows high superiority with rapid fall off of dose beyond target with lower peripheral dose compared to superficial X‐rays. However, the electrons need higher margin around the target and also need appropriate bolus thickness to increase skin dose. The dose at depth beyond 2cm makes very significant advantage using electrons compared to superficial X‐rays.
SU‐E‐T‐233: Evaluation of Superficial Doses for Postmastectomy Radiotherapy
Authors: Shiau A , Chiu M , Chen T , Chiou J , Shueng P , Chen S , Chen W , Kuan W
Published: June 2012

Purpose: To measure and to evaluate the surface and superficial doses for patients requiring postmastectomy radiotherapy (PMRT) with different treatment techniques. Methods: An elliptic cylinder cork and super‐flab boluses were used to simulate the lung and the chest wall, respectively. Sets of CT images with chest wall thicknesses of 5, 8, 10, 13, and 15 mm were acquired. Hypothetical clinical target volumes were outlined and modified to fit a margin of 1 –3 mm away from the surface. The planning target volume was initially created by expanding an isotropic 3 mm margin from CTV and then a margin of 1–3 mm was shrunk from the phantom surface. Treatment techniques using a pair of tangential wedged fields (TWF) and 4‐field IMRT were designed with a prescribed fraction dose (Dp) of 180 cGy. Superficial dose profiles around the phantom circumference at depths of 0, 1, 2, 3, and 5 mm were obtained for each treatment technique using radiochromic external beam therapy (EBT) films. Results: The TWF plans show a dose buildup about 3 mm at the median and lateral tangential incident regions with a surface dose of about 52% of Dp. Dose profiles were more uniform in the PTV region for the 4‐F IMRT plans. Most of the PTV region had doses higher than 94% of Dp at depths larger than 1 mm. The mean surface dose was about 65% of Dp for the 4‐F IMRT plans. The maximum dose for the 4‐F IMRT plans was less than 118.4% of Dp. Conclusions: The dose variations caused by the oblique incidence and a thin chest wall are modulated and reduced in the IMRT plans. More uniform dose distributions within the PTV are obtained with the 4‐F IMRT plans.
SU‐E‐T‐235: Dosimetry Study within a Millimeter from Beam Exiting Air‐Tissue Interface Using Film and Monte‐Carlo Simulation on a Co‐60 Beam
Authors: Tailor R , Yang J
Published: June 2012

Purpose: Objective is to assess dose accuracy and uniformity to cells in a well‐plate irradiated on Co‐60 beam using film (EBT2) and Monte‐Carlo simulation. Methods: Situations are encountered where dosimetry near beam‐exiting air‐interface is needed. Typical example is irradiation of cells in well‐plate. Small amount of cell emulsion may amount to as small as 1 mm thickness which results in leaving large air space above the cells. Due to contamination concerns, air space above cells can not be avoided. Preferred geometry for irradiation is to place cell‐plate on a build‐up slab (water‐equivalent), and point the beam upward. On Co‐60 beam, film EBT2 was employed to measure doses 0.1, 0.4, 0.7, 1.2 mm upstream from air‐ interface. Film optical‐density (OD) was measured with a pocket densitometer, and converted to dose using film‐calibration specific to film‐batch. To validate film data, Monte‐Carlo code DOSXYZNRC was employed for simulation. Doses were calculated employing (i) calculation grid 0.1–1.0 mm along beam direction, and (ii) 15000 million incident particles to achieve < 0.2% precision. Results: Doses measured with film close to beam‐exiting air‐interface are ∼16% lower than the maximum doses 1.2 mm up‐stream and beyond. Monte‐Carlo calculations validate the doses measured with film within measurement uncertainty (2%). Dose variation is steep in the first 0.1 mm zone near air‐interface, but it is within 10% further up‐stream. Conclusions: In cell irradiations, dose in‐homogeneity in the top 1mm zone is significant. Layer close to air‐interface receives ∼16% lower dose than the layer 1.2mm up‐stream. Dose homogeneity with the stated geometry can be improved by having (i) larger amount of cells to provide emulsion thickness > 3mm, and (ii) non‐homogeneous emulsion for cells to settle at the bottom. Since dose in‐homogeneity is primarily due to air interface, results are expected to be qualitatively similar for other beams (Cs‐137 or 6 MV.
SU‐E‐T‐239: In Vivo Dosimetry with Surface Diodes during Total Body Irradiation: A Patient Thickness Factor to Correct Midline Dose
Authors: Nyflot M , Holdsworth C , Kalet A , Chvetsov A , Sandison G
Published: June 2012

Purpose: In vivo dosimetry (IVD) assessment of treatment dose is important when delivering total body irradiation (TBI). One method is to average AP and PA surface diode measurements and compare them to prescribed midline doses. We designed phantom studies to examine the impact of patient thickness on surface IVD measurements under TBI conditions. Methods: Phantom studies were designed to assess the effects of patient thickness on diode IVD. Sun Nuclear QED diodes with inherent buildup were placed on anterior and posterior surfaces of a solid water phantom. Phantom thickness was varied between 20 and 40 cm. A PTW farmer chamber was inserted in the center of the phantom at 425 SSD to reflect prescribed midline dose, and 50 cGy was delivered to midline with 18 MV photons. Averaged entrance and exit diode doses were then compared to farmer chamber measurements of phantom midline dose. Results: A trend of increased deviation with increasing umbilicus thickness was observed between averaged surface diodes and midline farmer chamber measurements. Averaged surface diode dose ranged from 49.6 cGy (20 cm thickness) to 52.1 cGy (40 cm thickness). Interpolation of diode measurements to midline resulted in linear overestimation of delivered dose relative to farmer chamber measurements at midline, up to 6.8% at 40 cm umbilicus thickness. Conclusion: Accurate in vivo dosimetry at time of patient TBI is important to allow individual correction of MU exposure and tissue compensation. Without patient thickness correction, overresponse of surface diodes may lead to unnecessary clinical intervention to treatment MU or compensation and insufficient midline dose. Additionally, SAD setup is preferable to SSD setup to minimize thickness non‐linearity. In conclusion, thickness correction factors should be used to generate expected diode readings for patients with thickness greater than 30 cm.
SU‐E‐T‐247: Dose‐Volummetrics in the Prediction of Pulmonary Function Changes after Radiotherapy in Patients with Non‐Small Cell Lung Cancer
Authors: Zhu S , Li Y , Liu Z , Cao Y , Qiu R , Su J
Published: June 2012

Purpose: This aim was to explore the relationship between dose‐volummetrics and changes of pulmonary function tests (PFTs) and provide criteria of dose‐volummetrics to predict these changes of PFTs after radiotherapy with NSCLC. Methods: Between March 2008 to November 2009,39 patients (male 30,female 9, median age 66 years) with inoperable NSCLC received definitive 3DCRT or IMRT treatment were included in this study. The GTV included primary tumor and metastasis lymph node in hilar or mediastinum, and delineated the PTV from GTV 1.5 to 2.0 centimeter outside. The prescription doses ranged from 60–68Gy with a median dose of 66Gy. The forced vital capacity(FVC), forced expiratory volume in one second (FEV1.0) and diffusion capacity of carbon monoxide(DLCO) were checked for each patient two times, one week pretreatment and 2 to 4 months after radiotherapy. dose‐volummetrics of lungV10,V15,V20,V25,V30,V35,V40, lung mean dose and GTV100,GTV95, GTV90,GTV80 were analyzed. Statistical methods of Pearson and Line regression were used to determine whether correlation existed between these metrics and the changes in PFTs. Results: This investigation showed that FVC went down 2.4±1.6 from 77.2±18.7 to 74.1±18.5, FEV1.0 went down 5.9±3.2 from 74.1±20.5 to 70.9±20.2 P=0.065and DLCO went down 17.9±6.3 from 70.4±20.5 to 59.8±16.0 P=0.000 after radiotherapy. No correlation was found between dose‐volummterics and the changes in PFTs. Excluding patients(n=15)with pretreatment atelectasis, significant correlation was retained between dose‐volummetrics (lungV20,V25,V30,V35,V40, Lung mean dose and Veff) and the PFTs changes (P=0.05).Multivariate analysis showed that lung V30 was risk factor for the changes of FEV1.0 and DLCO(P=0.046 and 0.041).Furthermore analysis by stratifies, compared lung V30=18% and <18%, the dropped values of FVC, FEV1.0, DLCO were 6.9±2.5 and 4.5±1.8 P=0.061, 15.2±4.0 and 6.1±2.3 P=0.033, 22.8±2.0 and 11.6±1.4 P=0.000 respectively, showed PFTs became more worse with lungV30=18%. Conclusions: lungV30 is risk factor to affect PFTs changes in patients with NSCLC excluding those who have had pretreatment atelectasis. Our funding support received from National Natural Science Foundation of China (30870743).
SU‐E‐T‐249: Theoretical Analysis of the Effects Uncertainties Have On Treatment Outcomes
Authors: Harry T , Whitaker M , Pawlicki T
Published: June 2012

Purpose: Mathematical models are used in Industrial & Systems Engineering to analyze complex integrated operational systems. Adapting this approach to radiation therapy can help quantify the precision and accuracy necessary to achieve optimal outcome of radiation treatment. The purpose of this work is to develop such a model using clinical data and assess the effect uncertainties have on treatment outcomes. Methods: The Taguchi Loss Function (TLF) is adapted to radiation therapy using conventional radiobiological models for tumor control probabilities (TCP) and normal tissues complication probabilities (NTCP) based on the equivalent uniform dose. The TCP and NTCP curves are combined to create a failure probability function for a given treatment plan. The composite effects of all uncertainties involved in treating a patient are modeled by a normal distribution. The standard deviation and mean of the normal distribution represent the precision and accuracy of a treatment. The failure probability function is convolved with the normal distribution to arrive at an expected failure probability. Precision was varied from 0.5% to 25% while accuracy ranged from ±5% to investigate uncertainties effects on complication‐free local tumor control. 3D 4‐field box plans where compared to IMRT plans for 18 prostate patients using this method. Results: The average expected failure probability at the prescription dose for the 3D 4‐field box plans was 30.02% and 18.13% for the IMRT plans at zero uncertainty. At 25% uncertainty the expected failure probabilities were 76.85% and 64.36%, respectively. On average the IMRT plans failure probability was 14.84% less than the 3D 4‐field box plans for all uncertainty levels. Conclusion: This study demonstrates that uncertainty in radiotherapy procedures has a quantifiable effect on treatment outcome. To further improve complication‐free local tumor control we must both improve treatment technologies and improve quality to minimize the uncertainties in radiation therapy.
SU‐E‐T‐250: Dose‐Response Curves for the Esophagus
Authors: Court L , Wang J , Lin S
Published: June 2012

Purpose: To determine the dose‐response curve for the esophagus, using esophageal thickening as a surrogate for radiation injury. Methods: 15 esophageal cancer patients were selected who had received weekly 4DCT images throughout their course of concurrent chemo‐radiotherapy (IMRT) to a total of 50.4Gy. Each patient had a length of at least 4cm of esophagus that was outside the GTV but received the full prescription dose. The weekly CT images were registered with the original treatment planning CT images using deformable registration techniques, and the esophagus contours mapped to the weekly images. The relative change in esophagus size was calculated as the average ratio of the cross‐sectional area of the esophagus (minus air) in the weekly images to the area in the planning images for a 1cm long region of the esophagus in the center of the CTV (i.e. away from the GTV and field edge). We are considering this region to be ‘normal esophagus.’ Results: Thirteen of the 15 patients experienced mild esophagitis. The average relative expansion increased as the treatment progressed. For all patients the esophagus was thicker at the final week of treatment than its pre‐treatment size. For 7/15 patients the esophageal expansion was larger than 1.3. The average relative expansion of the esophagus was 1.30±0.19 (range: 1.04 – 1.67). We will present dose‐response curves calculated from the weekly 4DCTs. Conclusions: The esophagus expands in response to radiation, reaching approximately a 30% increase in cross‐sectional area during the final week of a 50.4Gy treatment, although there is much variability between patients.
SU‐E‐T‐251: Analysis of Irradiated Induced Lung Injury in Non‐Small Cell Lung Cancer (NSCLC) Treated by Three‐Dimensional Conformal Radiotherapy(3DCRT)
Authors: Liu Z , Su J , Shen W , Li Y , Li S , Zhu S
Published: June 2012

Purpose: The aim of this study was to analyze the affect factors with radiation induced lung injury of NSCLC treated by 3DCRT, in order to supply reference criteria for optimize the treatment planning, further to improve the local control rate and the quality of life of NSCLC patients.Methods: From August 2000 to December 2004, 107 NSCLC patients received 3DCRT were retrospectively enrolled in this study. All of patients received the prescription doses ranged from 60‐68Gy with a median dose of 66Gy. Dosimetric parameters of dose‐volume histograms from 3DCRT plans was recorded. The lung injury were assessed for each patient during the treatment and follow‐up within 3 months after treatment completion. Acute radiation induced pneumonitis were graded by one radiation oncologist according to the RTOG/EORTC criteria. The correlation between dosimetric parameters with lung injury was evaluated by univariate and multivariate analysis using Logistic Regression Model of SPSS11.0 software. Results: In the 107 patients of NSCLC, the rate of irradiated induced lung injury was 62.6% and the rate of =2 grade radiation induced pneumonitis was 38.3%. Twenty‐three cases were classified in grade 2, fourteen cases in grade 3, four cases in grade 4. Univariate analysis showed chronic obstructive pulmonary disease(COPD), number of beams field, lung mean dose, lung V5‐V40 were important parameters on radiation induced lung injury. The rate of =2 grade lung injury was 56.3%(18/32) in patients accompany COPD, compared with 30.7%(23/75) of those without COPD. In the same way,the rate of =2 grade lung injury was 61.9%(26/42) in patients of lung mean dose=20Gy, which higher than 19.4%(12/62) of lung mean dose<20Gy. Further more, lung mean dose, lung V20 and COPD were likely to be the independent factors of radiation induced lung injury by Logistic Regression Model. Conclusions: lung mean dose, lung V20 and COPD were the independent affect factors on irradiated induced lung injury. Our funding support received from National Natural Science Foundation of China (30870743).
SU‐E‐T‐262: Treatment Room Activation after 15 MV Single Fraction Radiation Treatments Delivered Using Varian's TrueBeam and Trilogy Linear Accelerators
Authors: Yan M , Fanchon L , Williamson M , Hunt M , Kirov A
Published: June 2012

Purpose: To measure radiation levels in treatment room due to activation after 15MV single fraction radiation treatment (SFRT) delivered to a solid water phantom. Methods: We performed radiation surveys of two LINAC treatment rooms immediately after 15 MV SFRT. We delivered a sequence of two 15 MV single fraction IMRT treatments to a phantom at the end of a typical treatment day. The first treatment delivered was 6201MU (about 12 Gy) and the second one, 15 minutes later was 12711 MU (24 Gy). Both were delivered to the pelvic region of a solid water anthropomorphic phantom. In a second technique, a 15 MV VMAT SFRT (4326 MU) was delivered using the Varian TrueBeam LINAC. Radiation measurements were recorded repetitively at four locations using a thin windowed Geiger Muller detector, a sodium iodide photon spectrometer and a pressurized ionization chamber. The four locations surveyed were: the top of the collimator head, the collimator window surface, the isocenter, and the inferior end of the patient support assembly. Results: Radiation levels at the isocenter at the end of the treatment day and before the two IMRT SFRTs varied from 0.06 to 0.1 mR/h. Within 2‐3 minutes after finishing the second IMRT SFRT the radiation levels were approximately 10 and 1.4 mR/h at isocenter for the TrueBeam and Trilogy rooms respectively and around 0.6 mR/h for the TrueBeam VMAT SFRT. Closing the MLC and the jaws significantly reduces the radiation level at isocenter. The average half life of the mixture of radionuclides produced is about 10 minutes. Conclusions: High dose single fraction IMRT treatments with 15 MV photons produce elevated treatment room activation as compared to conventional IMRT. In addition, activation levels varied between the TrueBeam and Trilogy for similar SFRT schemes. There is no funding support, disclosures, or conflict of interest.
SU‐E‐T‐271: Irradiating a Single Hippocampus in a Small Rodent Using VMAT‐ RapidArc SRS: Preliminary Data
Authors: Lin Y , Limoli C , Acharya M , Christie L , Bosch O , Kumar V , Hamamura M , Roa D
Published: June 2012

Purpose: To develop and optimize the procedures for the precise irradiation of the hippocampal region in a rodent with minimum radiation dose to the remainder of the brain. For this purpose, VMAT‐RapidArc SRS was used to irradiate one hippocampus of athymic nude (ATN) rats. Prescribed dose was verified through TLD measurements and spared brain region(s) were confirmed through immunohistochemical analysis postmortem.Methods: Seven ATN rats, 10–12 weeks old underwent human‐like radiation treatment planning followed by SRS. MRI and CT axial images of 0.8 mm thickness of the rat's skull were acquired and transferred to ECLIPSE treatment planning software where brain, right and left hippocampi were contoured. A VMAT‐RapidArc plan consisting of two 3600 axial arcs and two 1200 vertex arcs irradiated the left hippocampus only to a dose of 10 Gy. Treatment was delivered using a 6 MV photon beam from a Trilogy Linac equipped with OBI. TLD measurements were performed prior to treatment using a custom made phantom that simulated the rat's brain and body. Orthogonal x‐ray images taken with the OBI and co‐registered to DRR images were used to adjust the rat's treatment position. One month post‐ irradiation, rats were sacrificed and brain dissection was performed to verify the radiation effects in the targeted and non‐targeted regions. Results: Percent differences between calculated and measured dose were ∼12% which was expected due to the small field sizes (<2cm) used. Immunohistochemistry analysis revealed a significant reduction in cell population in the ipsilateral hippocampus while cell populations comparable to those in a non‐irradiated subject were observed in the contralateral hippocampal region. Conclusions: Present results demonstrate that precise irradiation of small volumes within a rat's brain can be achieved with human‐like image‐guided VMAT‐RapidArc treatment. Postmortem analysis of the rat brain provides evidence of high‐precision targeted radiation damage and dose sparing.
SU‐E‐T‐272: Commissioning an Orthovoltage Unit Used for Radiobiology Research
Authors: Azimi R , Alaei P , Hui S
Published: June 2012

Purpose: Orthovoltage X‐ray units are used to irradiate cell cultures or small animals in research. Beam characteristics of these units are often not well understood and only nominal dose specified is used by researchers in their studies. This work describes commissioning of an orthovoltage unit similar to that of a linear accelerator. Methods: The X‐Rad 320 Orthovoltage unit is a self‐contained x‐ray system which can be operatedwithin a wide range of kVp and mAs settings. This work characterizes the beam produced by this system. Various beam data, including depth dose, cross profiles, collimator and total scatter factors, have been measured. Collimator and total scatter measurements were done with cylindrical farmer chambers (0.6 cc and 0.057 cc volumes) for field sizes ranging from 2×2 to 20×20 cm2. Sc measurements were done in air at 50 cm SCD and Sc,p measurements were done in 2 cm depth of phantom at 50 cm SSD.The depth dose curves were generated for three different field sizes for depths up to 15 cm. A parallel plate chamber was used for surface and near surface dose measurements while the cylindrical chamber was used for other depths. Results:
Measurements of Sc and Sc,p indicate minimal variation of these factors with field size, except for very small fields. The results of depth dose measurements produce results comparable with published data for similar beams and indicate a very small dose buildup at shallow depths. Conclusions: Proper characterization of an x‐ray beam and accurate dosimetry is of importance in radiobiology investigations which may lead to advent of new therapies for humans. This work investigates the beam characteristics of an orthovoltage unit to ensure accurate irradiation of samples. The data collected here could further be used for simulation of dose distribution within irradiated volume.
SU‐E‐T‐279: A Novel Electron‐Beam Combined with Magnetic Field Application for Radiotherapy
Authors: Alezra D , Nardi E , Koren S , Bragilovski D , Orion I
Published: June 2012

Purpose: The new beam and delivery system consists of an electron accelerator and a system of magnets (one or more). Introducing a transverse magnetic field in and near the tumor, causes the electrons to spiral in this region, thereby producing an effective peak in the depth dose distribution, within the tumor volume. Although the basic idea is not new, we suggest here for the first time, a viable as well as a workable, magnetic field configuration, which in addition to focusing the beam does not interfere with its propagation to the target. Methods: The electron accelerator: can be a linear accelerator or any other type electron accelerator, capable of producing different electron energies for different depths and dose absorption accumulation. The Field size can be as small as a pencil beam and as big as any of the other standard field sizes that are used in radiotherapy. The scatter filter can be used or removed. The dose rate accumulation can be as higher as possible.The magnets are able to produce magnetic fields. The order, direction, width, place, shape and number of the magnetic fields define the shape and the Percentage Depth Dose (PDD) curve of the electron beam. Prototypes were successfully tested by means of computer simulation, using:COMSOL‐Multiphsics for magnetic fields calculations. FLUKA package, for electron beam MC simulation. Results: Our results suggest that by using an electron beam at different energies, combined with magnetic fields, we could modify the delivered dose. This is caused by manipulating the electron motion via the Lorentz force. The applied magnetic field, will focus the electron beam at a given depth and deposit the energy in a given volume and depth, where otherwise the electron energy will have spread deeper. The direction and magnitude of the magnetic fields will prevent the scattering of the electron beam and its absorption in remote volumes. In practice, we get a pseudo Bragg peak depth dose distribution, applying a relatively low cost system. The therapeutic efficiency induced by the system is of similar efficiency as the ion beam therapy techniques. Conclusions: Our novel concept demonstrates treatment that is almost similar to proton therapy and in some parameters even better performance.Unlike the current high‐energy electron therapy, our system's beam deposit almost all of its energy on its target, with a low amount of radiation deposited in tissues from the surface of the skin to the front of tumor, and almost no “exit dose” beyond the tumor. This property will enables to hit tumors with higher, potentially more effective radiation doses, while being considerably less expensive.
SU‐E‐T‐284: Surface Dose Evaluation for Beams with and without Flattening Filter in Breast Cancer Treatment
Authors: Xie J , Chen W , Cui Y , Giaddui T , Galvin J , Yu Y , Xiao Y
Published: June 2012

Purpose: To evaluate surface doses for beams with and without flattening filter (FF and FFF) in breast cancer treatment plans. Measurements were performed for validation. Delivery:TrueBeam, used in this study, is a linear accelerator newly designed to deliver both flattened and flattening filter free beams. Planning: Eclipse treatment planning system (TPS) is commissioned and utilized. We used 6 MV half beams from FFF mode to plan standard tangential breast treatments due to its similar shape to wedged FF beams. We compare these plans with those from 6MV flattened beams with 30° wedges. Measurement Validation: We used a Rando phantom and InLightTM nanoDots Optically stimulated luminescence dosimetry(OSLD) system to measure surface doses from FFF beams. Medial, apex and lateral locations from central plane, as well as positions from caudal and cranial regions, were included. Results:Planning comparison: surface doses from plans with FFF beams were2.2%–4.7% lower than those with flattened beams with wedges, when doses at deeper depth from central axis stay close in value. Measurement validation: In the apex region of central plane,the OSLD readouts are 4.5% – 6.3% higher than calculated. In the caudal, cranial and medial regions, TPS underestimated the surface dose from 7.2–8.7%. Conclusions: For standard tangential breast plans, surface doses are lower with FFF beam than with flattened beams with wedges. The surface doses from FFF beams were validated with OSLD measurements, taking into account the uncertainty of the dosimeter and its angular dependence.