bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐127: Two Dosimetric Methods of Measuring Linac Beam Spot Position
Authors: Nyiri B , Smale J , Gerig L 
Published: November 2011

Purpose: Two dosimetric methods of measuring the electron beam spot position of photon beams w.r.t. the Collimator Axis Of Rotation (CAOR) are described. Methods: Method 1 (SNG test) uses a cylindrical ion chamber (IC) (A1SL) in a phantom mounted on a jig co‐rotational with the collimator making the relationship among the chamber, phantom, jaws and CAOR fixed and independent of collimator angle. A jaw parallel to the IC axis is set to zero and the phantom adjusted so the IC signal is 65% of the open field value. cGy/mu is measured every 30 degrees of collimator rotation. The phantom is then translated normal to the IC axis until the signal is 35%. The shift is recorded to calculate sensitivity (%dose/mm). For a radially symmetric spot centred on CAOR, the IC signal is angularly constant. Deviation from constant indicates a displacement from the CAOR and a shape distortion. The displacement and spot shape are calculated using Fourier analysis and penumbra shape (sensitivity). The 2nd method uses a hard wedge instead of the jaw and sensitivity is obtained from wedge profiles. Test measurements were performed on an Elekta 6 MV: the In Plane beam spot position was measured before and after it was moved by changing bending magnet current (Bending Fine). Results: Independent beam spot measurement (Flexmap Image Registration) showed the initial beam spot, projected back to source, 0.29 mm from CAOR, moving to 0.91 mm (delta=0.62 mm) with steering. The SNG test reported the beam spot moving from 0.13mm to 0.92 mm from CAOR (delta=0.79 mm). The hard wedge test gave an initial position of 0.09 mm off axis and a final position of 0.79 mm (delta=0.7 mm) Conclusions: The methods described provide a quantitative measure of beam spot position, not requiring the user to independently define the CAOR.Jason Smale is an Employee of Elekta Canada
SU‐E‐T‐151: Application of a 2D Ionization Chamber Array for Monthly and Annual Linear Accelerator QA
Authors: Buckey C , Myers P , Mavroidis P , Esquivel C , Mihailidis D , Gutiérrez A , Papanikolaou N , Stathakis S 
Published: November 2011

Purpose: An evaluation of a commercially available 2D array for monthly and annual linear accelerator QA. Methods: The 2D‐ARRAY seven29 (PTW, Freiburg, Germany) is a two‐dimensional ion chamber array, consisting of 729 (27 × 27) vented ion chambers, with separately housed evaluation electronics. The parallel‐plate chambers are 5 × 5 × 5 mm in size, and have a center to center spacing of 10 mm. To increase resolution, the array can be shifted three times in increments of 5 mm, and the resulting 2916 measurement points can be summed into one image. The array was placed under 10 cm of water‐equivalent material, and irradiated to evaluate: flatness and symmetry, static MLC positioning, dynamic MLC positioning, and output. It was also irradiated without any buildup for the light field and radiation coincidence test. All deliveries were completed using a Varian 2100 C/D linear accelerator with a Millennium‐80 MLC. For improved accuracy, the static and dynamic MLC fields were delivered 4 times each, and were then summed using the “merge” function in the PTW VeriSoft software. Results: Over one month of data acquisition, output fluctuated less than 2%. For light field and radiation coincidence, reproducibility is excellent, with a maximum of 1% variation in asymmetric jaw settings. When using the “merge” function on dynamic MLC measurements, results were less than 4% for transmission and 0.5 mm for positioning errors. Measurements for flatness and symmetry and static MLC positioning also had good reproducibility. Conclusions: The PTW 2D‐Array seven29 can be used to evaluate many areas of monthly linear accelerator QA. Particularly in light of the trend for departments to go filmless, it is a viable alternative for obtaining flatness and symmetry, static and dynamic MLC positioning, light field and radiation coincidence, and for measuring output.This work partially supported by PTW (Freiburg, Germany).
SU‐E‐T‐268: The Evaluation of Dosimetric Characteristic of Radiophotoluminescent Glass Dosimeter According to Reading Methods of Reader
Authors: Son K , Shin S , Lee H , Lee S , Kim M , Ji Y , Kim K , Jung H 
Published: November 2011

Purpose: Statistical checks of system parameters and follow up of readerˈs behavior will give a broader understanding into the operational characteristics of the reader and may help for proper maintenance of the system. The purpose of this study is to suggest effective use of reading methods for reducing the uncertainty in dose measurements through the investigation of characteristics of GD‐based reader system. Methods: To evaluate the characteristics of readerˈs, we performed measurement such as reproducibility of repeated reading, readout variation according to the number of GD loading on readout magazine, and deviation depending on each magazine position. To evaluate dose reproducibility we made a try to do repeated reading up to 200 times for each 15 GDs. Also, to evaluate readout variation characteristic, 80 GDs are irradiated one by one under the same irradiation conditions. Reading process was measured with 4 different cases. Lastly, to measure the deviation magazine position, we examine the readout values according to each loading position.Results: According to measurement result, reproducibility shows 1.3% lower measurement from total 200 times. Readout sensitivity of GD on magazine values is normalized to 1st position response. 1 to 5th position measured 1.015, also 1 to 10th position examined 1.022, and 1 to 20th position presented 1.035. Lastly, at all position except for 20th position of magazine, response is tend to increase gradually. It was overestimated on 2.0% of average rather than response at reference position (first position). Conclusions: According to the result, we should put each GD in consecutive order from 1st space of magazine to get accuracy value of dose and it is recommended that reading process should be performed the only first position of magazine with regard to absolute dosimetry.This work was supported by Nuclear Research & Development Program of the National Research Foundation of Korea(NRF) grant funded by the Korean government(MEST).
SU‐E‐T‐284: Quantifying Respiratory Hysteresis via an Inter‐Cluster Distance Metric
Authors: Ruan D 
Published: November 2011

Purposes: Understanding the degree of respiratory hysteresis is important for motion adaptive radiotherapy, as patients with significant respiratory hysteresis may require different motion models and/or management techniques. This work aims to develop a quantitative hysteresis index, that has the right metric property and robust towards observation settings. Methods: The proposed method herein is a data‐driven, clustering‐based approach. It stems from the intuition that hysteresis manifests via the discrepancy between the inhalation and exhalation segments of the respiratory trajectory. Therefore, a semi‐supervised clustering method is first applied to partition the trajectory data into inhalation and exhalation stages, and hysteresis is characterized by an inter‐cluster distance metric that intrinsically associates the corresponding displacement at these two stages. This metric is designed to be robust to scale, dynamic range, and data size, to permit comparison of hysteretic behavior across datasets acquired under different observation protocols and/or modalities. In the absence of any existing objective characterization of hysteresis, the proposed index was computed for simulation data to corroborate with human judgment. The robustness of the proposed index is tested with cross‐validation, applied to 159 patient‐derived respiratory trajectories. Results: The proposed hysteresis index is stable, and corroborates well with human judgment. Distribution of the hysteresis index among the patient cohort shows a small subgroup of trajectories with noticeably high hysteresis. Conclusion: For the first time, a quantitative index for hysteresis has been proposed. It is a proper metric and reflects the insight as a measure of discrepancy between corresponding inhalation and exhalation segment. The presence of a small population with high hysteresis alludes to the potential to “differentiate” patients based on such index and customize the motion management strategy. We will continue to develop unsupervised clustering schemes with built‐in outlier detection, and endeavor to incorporate physiological/biomechanical insight.Research supported in part by AACR.
SU‐E‐T‐321: Whole Brain Irradiation Technique for Radiation‐Induced Cognitive Impairment
Authors: Bourland J , Robbins M , Deadwyler S 
Published: November 2011

Purpose: Development of an easily reproduced, fractionated whole brain irradiation technique for the study of radiation‐induced cognitive impairment in nonhuman primates. Methods: A nonhuman primate (NHP) irradiation technique has been developed that replicates the fractionated whole brain irradiation technique for humans. Right and left lateral 6MV x‐ray beams are used, with opposed central axes matched at the level of the outer canthi. An eye block shields both eyes for each lateral beam. Monitor unit calculations to mid‐brain are based on anatomical measurements with a mid‐field slant distance incorporated. Total dose is 40 Gy, delivered at 5 Gy/fraction × 8 fractions, two fractions/week for four weeks. A clinical linear accelerator is used, with personnel procedures, room preparation, and clean‐up per research animal and human care requirements. Results: NHP positioning and beam parameter choices (eg, gantry and collimator rotation) allow for flexibility at the time of irradiation, based on anesthesia requirements and individual animal anatomy. Computed monitor units scale with NHP cranial measurements, which scale with NHP weight. A record/verify system facilitates set‐up and dose recording for each animal. Each right and left lateral radiation field is delivered via image‐guidance by the use of pre‐irradiation electronic portal imaging to verify positioning immediately before irradiation. Portal imaging dose, also performed at 6 MV, is recorded as irradiation dose. The portal image record enables post‐irradiation assessment of each fraction as well as cumulative dose. Room readiness techniques include preparations to minimize potential contamination of clinical equipment, and clean‐up procedures for return of equipment to human use. Conclusions: A simple, reproducible approach has been devised to replicate human fractionated whole brain irradiation of NHP cohorts to enable research studies of radiation‐induced cognitive impairment. Our irradiation techniques and experience are reviewed for the safe and efficient irradiation of this unique animal species.Supported in part by the Brain Tumor Center of Excellence, the Kulynych Interdisciplinary Cancer Research Fund, and the Sticht Family Foundation at Wake Forest University Health Sciences.
SU‐E‐T‐349: Evaluating a Stochastic Reconstruction Algorithm for Compton Camera Based Prompt Gamma Imaging during Proton Therapy
Authors: Mackin D , Polf J , Peterson S , Gillin M , Beddar S 
Published: November 2011

Purpose: Prompt gamma photons emitted during proton radiotherapy may provide a method to measure dose delivery and range. The utility of this method depends on how well the gammas can be detected and reconstructed. The purpose of this study is to demonstrate the feasibility of the stochastic origin ensemble (SOE) algorithm for reconstructing images of the origins of prompt gammas emitted during proton therapy and to introduce a metric for quantifying the accuracy of this image. Methods: Using Geant4 we simulated a Compton camera detecting prompt gamma emission from proton irradiated tissue phantoms. The information recorded by the simulated detector is used as the input to the SOE reconstruction algorithm, which iteratively determines the likely gamma emission origin. We introduce a metric to quantify the accuracy of the reconstruction and use the metric to provide a quantitative analysis of the SOE reconstructions. Results: We show both qualitatively and quantitatively that the SOE algorithm can reconstruct images which accurately predict the origins of prompt gammas emitted during proton therapy. We also show that the distal falloff of gamma production based on the reconstructed image agrees with the distal falloff in Monte Carlo calculated gamma origin distribution to within 1 mm for both the 50% and 20% regions. Conclusions: The SOE algorithm was able to reconstruct usable images of prompt gamma emission during proton irradiation. We believe these results justify further investigation of this technique for in‐vivo prompt gamma imaging.This work was supported by Award Number R21CA137362 from the National Cancer Institute.
SU‐E‐T‐350: Calibration of a Prototype Proton CT Scanner
Authors: Hurley F , Schulte R , Bashkirov V , Wroe A , Ghebremedhin A , Patyal B , Penfold S , Rykalin V , Sadrozinsk H 
Published: November 2011

Purpose: To calibrate a novel proton CT scanner using polystyrene degraders of accurately known thickness and relative stopping power.Methods: A prototype proton CT scanner was constructed and installed on a horizontal proton research beam line for further study of this novel, potentially low‐dose tomographic imaging modality. The proton CT scanner registers individual protons up to a maximum rate of about 10̂5 protons/sec, recording their entry and exit coordinates and directions with high‐resolution silicon strip detectors, as well as their residual energy by stopping them in an augmented 18‐crystal CsI calorimeter. To avoid uncertainties in the mean excitation energy (I) of water when converting energy loss to water equivalent path length (WEPL) via the Bethe‐Bloch equation, the response of the calorimeter was calibrated using polystyrene plates of known water‐equivalent thickness (WET). Stacks of polystyrene plates of variable thickness were placed between the proton CT detectors and about 3 × 10̂5 protons were recorded for each thickness. For each proton event, the calorimeter response was derived from the weighted sum of the response of the 18 crystals, taking into account variations in the sensitivity of each crystal. A Gaussian distribution function was fitted to the response data at each WET, and the mean of each distribution was used to establish the WEPL calibration curve. Results: For protons of 100 MeV and 200 MeV, the mean response of the calorimeter was obtained for 7–8 different WET values (including zero) and the WEPL vs. response calibration curve was fitted with a quadratic polynomial with an excellent goodness of fit. A WEPL measurement accuracy of 1 mm or better can be achieved by measuring the calorimeter response of about 150 protons Conclusions: This work is an important step towards a thorough investigation of proton computed tomography for therapeutic and imaging applications.Funded in part by DOD Contract W81XWH‐08‐1‐0205 and the Department of Radiation Medicine, Loma Linda University Medical Center
SU‐E‐T‐357: Development of An Anthropomorphic Head Phantom for the Assessment of Proton Therapy Treatment Procedures
Authors: Summers P , Followill D , Sahoo N , Poenisch F , Tucker S , Gillin M , Riley B , Ibbott G 
Published: November 2011

Purpose: Develop an anthropomorphic head phantom for the evaluation of proton therapy treatment procedures from simulation to treatment planning and treatment delivery. Methods: A head phantom was designed and constructed from materials tested specifically with proton beams to match stopping powers and Hounsfield Units of corresponding human anatomy. Separate MR (water‐filled)‐ and CT (polyethylene)‐compatible inserts were designed for imaging (including target delineation) and dosimetry verification. The dosimetry insert contained radiochromic film and TLD dosimeters. The phantom was imaged with MR to outline the target and fused with a CT image for the dose distribution calculation. Passive scattering and spot scanning treatment plans were designed using the Eclipse proton planning system per M.D. Anderson Proton Centerˈs standard brain protocol. The phantom was irradiated according to each treatment plan three separate times. The dose distributions and absolute point doses determined with film and TLD were compared to calculated points, dose profiles and dose distributions, using a gamma analysis with pass criteria of 5%/3mm and 5%/5mm, to determine agreement and reproducibility. Results: The average passive scatter plan pixel pass rates were 91.9% and 97.4% for 5%/3mm and 5%/5mm criteria, respectively. The average lateral shift ‐ mean(standard deviation) ‐ was 2.5mm(1.8mm); the average longitudinal shift was −2mm(1.9mm); the average transverse shift was 1.7mm(2.8mm). The average spot scan plan pass rates were 90.4% and 98.4% for 5%/3mm and 5%/5mm criteria, respectively. The average lateral shift was 2.2mm (1.4mm); the average longitudinal shift was −1.6mm(1.1mm) on the inferior side and 3.1mm(4.3mm) on the superior side; the average transverse shift was −0.9mm(0.4mm). Conclusions: A proton head phantom made of proton suitable plastics was developed that can verify the agreement between treatment plans and measurement that can be used to credential proton therapy facilities for participation in NCI‐funded clinical trials.Work supported by PHS CA010953 and CA081647, awarded by NCI, DHHS and Massachusetts General Hospital Federal Share Funds.
SU‐E‐T‐367: Cervix Brachytherapy Dosimetry: Inconsistencies in Defining Bladder and Rectal Points
Authors: Lowenstein J , Roll J , Harris I , Hall F , Hollan A , Followill D 
Published: November 2011

Purpose: The Radiological Physics Center (RPC) reviews patient records on brachytherapy cervix trials for completeness, consistency with the protocol and dosimetric accuracy to minimize patient dose delivery and reporting uncertainty for NCI funded clinical trials. Within cervical protocols, bladder and rectum doses are specified to limit toxicity to these normal tissues. However, bladder and rectal doses reported by institutions often disagree with the RPCˈs calculated doses. The RPC has investigated the sources of these disagreements. Methods: The RPC reviewed 182 HDR brachytherapy (tandem and ovoids (T&O)/tandem and ring (T&R)) implants and compared the institutionˈs bladder and rectum point locations and doses to those determined by the RPC strictly adhering to protocol specifications (ICRU 38) for point location and using its independent dose calculation algorithm. The RPC also analyzed its own uncertainty in defining these two points. A dose agreement criterion of ±15% was used as agreed upon by the study group and RPC. Results: The RPC disagreed with the bladder and rectal doses in 25% and 45%, respectively, of the 182 implants. The RPCˈs own uncertainty in defining the bladder and rectal points was 1mm±0. 1(STDEV), respectively which in a worst case scenario might account for 7% of the dose disagreement. The majority of the dose disagreements were due to the institutionˈs incorrect localization of the bladder and rectal points, by greater than 5mm and 4mm, respectively, away from the ICRU 38 defined location. There were no differences noted whether the applicator used was a T&O or T&R. Conclusions: Most errors resulted from institutions incorrectly defining the bladder and rectum dose calculation points per ICRU 38. Additional education, timely reviews of implant data and communication with institutions are needed to reduce the number of discrepancies.Work supported by PHS grant CA 10953 awarded by NCI, DHHS
SU‐E‐T‐373: Treatment Plan Validation of the XPS (Interstitial) Applicator for Use with the Xoft Axxent 50kVp X‐Ray Source
Authors: Kelley L , Rusch T 
Published: November 2011

Purpose: To determine the dosimetric properties of a new interstitial applicator designed for the Xoft 50 kVp X‐ray Electronic Brachytherapy (eBx) system. Methods: A 0.64 cm diameter polymer sheath applicator interfaces with the Xoft 50kVp x‐ray source to provide radiation treatment to interstitial and other small target areas using eBx. Measurements of the dose profiles in a plane parallel to the applicator axis were determined. The absolute dose delivered to a prescription point at 90° off the central axis 1 cm from the source center, was determined using GafChromic EBT‐2 radiochromic film. The dose distribution measured in this parallel plane is compared to the distribution determined by the treatment planning software (Varian Brachyvision V8). Three x‐ray sources were paired with three interstitial applicators for the tests. Results: Using a single position treatment plan, the absolute dose at the defined prescription point was determined from calibrated film images. The measured dose agreed with the dose predicted by the treatment plan to within ±5%, with the actual range from −4.6% to +3.1% for the three samples. The measured isodose contours, including the 1 cm prescription point contour, agreed with the contours predicted by the treatment plan to within 5% (1 sigma) and the applicator does not perturb the water‐based dose distribution. The absolute dose determined from each of these contours agreed with the predicted dose to within +1/−6%. Conclusions: The XPS applicator can be used to treat small cavities using eBx with the Xoft X‐ray source. The applicator delivers dose profiles in good agreement with those predicted from the treatment planning software. It can be used for treatment in lightly shielded rooms due to the low energies employed. There are also intriguing possibilities for this applicator to be used intra‐operatively.Research supported by Xoft, Inc. — an iCAD Company