bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐121: Investigating the Optimal Scanning Resolution for Radiochromic EBT‐2 Films Using an Epson 10000XL Flatbed Scanner
Authors: Schoenfeld A , Poppinga D , Chofor N , Poppe B
Published: June 2012

Purpose: The purpose of this work is to determine the optimal scanner resolution of an Epson 10000XL scanner for the analysis of radiochromic EBT‐2 films. Using Fourier analysis and the Nyquist‐Shanon sampling theory, the highest frequency component required to sufficiently reproduce a previously measured step dose profile was investigated. Methods: A setup was created, in which one half of a 6×6cm2 EBT‐2 film was shielded on exposure using a 15×5×10cm3 lead block to obtain sharp step dose profiles. The film itself was placed between two 6cm RW3 stacks on top of which the lead block was placed. Using a Siemens Primus linear accelerator operating at 6/15MV nominal energies, the setup was exposed to 400MUs at 6MV and 500MUs at 15MV respectively. Preliminary investigations were performed without RW3 between the lead and film. Initial image acquisition was performed at 600dpi to minimize information loss. Using the average of five line profiles, a uniformity correction algorithm provided by the manufacturer was implemented prior to the Fast Fourier Transform (FFT) operation. In an iterative process, all frequency components above a cut‐off frequency wcut were successively removed and the original image reconstructed with the inverse FFT operation. The goodness of fit was evaluated by comparing the change in penumbra width on image reconstruction. Results: The minimum scanning resolution required to analyze the step dose profiles created without build‐up material was 52dpi for 6MV and 30dpi for 15MV. By adding build‐up material, in the areas of secondary electron equilibrium the required resolution reduces to 12dpi for 6MV and 8dpi for 15MV. Conclusions: For sufficient image reproduction within any information loss, resolutions as low as 52dpi at 6MV and 30dpi at 15MV are sufficient for evaluating EBT‐2 films. This is in compliance with 50dpi recommended by the manufacturer.
SU‐E‐T‐124: A Modified Winston Lutz Test Enabling Beam to Laser Angle Measurements
Authors: Haering P , Lang C , Schwahofer A , Echner G
Published: June 2012

Purpose: To present a modified Winston‐Lutz‐Test procedure able to measure beam and laser angles. Methods: Room lasers have not only to indicate the isocenter spot but should also be aligned to the central beam axis. Therefore a modified WL test, based on a cube phantom made of low density foam material was developed. The classical steel sphere in the center is surrounded by 8 additional smaller spheres located near the cube corners. Surface markers on the cube indicate the position of the spheres and are used for easy setup to the lasers. Measurements are made with a field size covering all spheres in the well known way, ideally with a gantry mounted EPID. Result is an image of in total 9 spheres that is influenced by the distances and incoming beam directions. An automated template based detection algorithm then searches the image for the spheres as well as for the outside field boundaries. Knowing the phantom geometry, it is now easy to calculate the following parameters: Position of center sphere and laser to central axis of the beam, beam angle to the orientation of the phantom and the distance of the cube to the radiation source. Calculation result s then can be used to correct the phantom position and orientation. A transfer device equipped with a finder sight then allows to set the lasers. Results: Test measurements were taken at a Siemens Artiste. Here the detection accuracy for angles and positions was tested. For smaller angles the automated detection works quite well within an accuracy of around 0.1° (max error 0.2°). Position detection was below 1/10mm and showed clearly the effects of Gantry and collimator sag. Conclusions: This method detects both, positions and angles of laser and beam, enabling a higher precision laser setup.
SU‐E‐T‐127: Feasibility Study for Using a 2D Array Detector for All Beam Measurements in Monthly Quality Assurance Procedure for a Uniform Scanning Proton Therapy System
Authors: Rains M , Mascia A , Ramirez E , Zheng Y , Ding X , Neuenschwander D , Harris B
Published: June 2012

Purpose: To develop a more efficient monthly quality assurance (QA) process by utilizing one detector with multiple setups instead of multiple detectors with multiple setups. Method: The Sun Nuclear IC Profiler was used to measure machine output, transverse profiles, and depth‐dose profiles. The IC Profiler contains 251 ionization chambers aligned in the X, Y, and diagonal axes, and was designed to measure machine output and transverse profiles. In order to measure depth‐doses, a Lucite compensator with an angled surface was fabricated. To test the capability of the detector, a proton beam of 10.5 cm range in water was used. The distal edge coincided with the overall water equivalent depth upstream of the detector on central axis. The measurement was repeated with an additional 1.0 mm of solid water placed in front of the detector. The measured profiles from both measurements were compared to quantify the IC Profiler response for a small range change. Results: The IC Profiler performs within vendor specification for measuring machine output and transverse profiles. When measuring depth‐doses with an angled compensator, the IC profiler measures a change in profile along central axis of 17.0% for a 1.0mm range change. Based on overall reproducibility of the beam delivery system, the IC profiler is capable of detecting 0.3 mm range shift. Therefore, the sensivity of the IC profiler response is suffficient to detect sub millimeter changes in delivered range. Conclusion: The Sun Nuclear IC Profiler is capable of measuring machine output, transverse profiles, and depth‐dose profile constancy with a high degree of accuracy and precision. Using a single detector for all beam measurements increases the overall QA efficiency by reducing multiple detector overhead while not sacrificing the accuracy and precision of the measurements.
SU‐E‐T‐135: Investigation of Commercial‐Grade Flatbed Scanners and a Medical‐ Grade Scanner for Radiochromic EBT Film Dosimetry
Authors: Syh J , Patel B , Syh J , Wu H , Rosen L , Durci M , Katz S , Sibata C
Published: June 2012

Purpose: To evaluate the characteristics of commercial‐grade flatbed scanners and medical‐grade scanners for radiochromic EBT film dosimetry. Methods: Performance aspects of a Vidar Dosimetry Pro Advantage (Red), Epson 750 Pro, Microtek ArtixScan 1800f, and Microtek ScanMaker 8700 scanner for EBT2 Gafchromic film were evaluated in the categories of repeatability, maximum distinguishable optical density (OD) differentiation, OD variance, and dose curve characteristics. OD step film by Stouffer Industries containing 31 steps ranging from 0.05 to 3.62 OD was used. EBT films were irradiated with dose ranging from 20 to 600 cGy in 6×6 cm2 field sizes and analyzed 24 hours later using RIT113 and Tomotherapy Film Analyzer software. Scans were performed in transmissive mode, landscape orientation, 16‐bit image. The mean and standard deviation Analog to Digital (A/D) scanner value was measured by selecting a 3×3 mm2 uniform area in the central region of each OD step from a total of 20 scans performed over several weeks. Repeatability was determined from the variance of OD step 0.38. Maximum distinguishable OD was defined as the last OD step whose range of A/D values does not overlap with its neighboring step. Results: Repeatability uncertainty ranged from 0.1% for Vidar to 4% for Epson. Average standard deviation of OD steps ranged from 0.21% for Vidar to 6.4% for ArtixScan 1800f. Maximum distinguishable optical density ranged from 3.38 for Vidar to 1.32 for ScanMaker 8700. A/D range of each OD step corresponds to a dose range. Dose ranges of OD steps varied from 1% for Vidar to 20% for ScanMaker 8700. Conclusions: The Vidar exhibited a dose curve that utilized a broader range of OD values than the other scanners. Vidar exhibited higher maximum distinguishable OD, smaller variance in repeatability, smaller A/D value deviation per OD step, and a shallower dose curve with respect to OD.
SU‐E‐T‐142: Evaluation of the Energy Dependence of Gafchromic EBT3 Film for Electron Beams
Authors: Inoue T , Sugimoto S , Fukata K , Kurokawa C , Ozawa S , Sasai K
Published: June 2012

Purpose: To evaluate the energy dependence of Gafchromic EBT3 film for establishing a quality assurance method of bolus electron conformal radiotherapy. Methods: We irradiated electron beam to EBT3 films, which were set in the water tank. The linear accelerator used was Varian Clinac 21EX. The energy of electron beams were 9 and 12 MeV. The irradiated field size was 10×10 cm2 and the source to surface distance was 100 cm. The depths of measurement were 22 (depth of dose maximum; dmax), 31, and 37 mm for 9 MeV and 28 (dmax), 43, and 50 mm for 12 MeV. The irradiated doses were 25, 50, 75, 100, 150, 200, and 300 cGy. EBT3 films were readout with a flat‐bed scanner 48 hours after irradiation, and the optical density (OD) curve was obtained for each beam energy and depth. The OD curves were approximated by a third‐order polynomial. The doses were evaluated at netOD 0.1 and 0.3 from the approximated curves. Results: The differences of the evaluated doses from those for 9 MeV at 22 mm depth were from 2 to 14 % for netOD=0.1, and from 1 to 13 % for netOD=0.3, respectively. The netOD curves of dmax for both energies showed good agreement, while large discrepancy was found in the deeper depths. Conclusions: The dependence of dose response of EBT3 film on electron beam energy was small at dmax, while it increased at deeper depth in the present study. It can be considered that the discrepancy was caused by setup error because dose gradient was steeper at the deeper region. In future work, we will perform more precise measurement with a solid phantom to evaluate the energy dependence of EBT3 film.
SU‐E‐T‐143: Effect of Physical and Virtual Wedges on the Surface Dose at Various SSD for 6 and 15 MV Photon Beam
Authors: Yadav Girigesh , Sinha SN , Ashokkumar S , Raman Kothanda , Mishra M , Thiyagarajan Rajesh , Yadav RS
Published: June 2012

Purpose: To study the effect of the virtual wedge and physical wedge filters on the surface and build‐up region doses for 6 and 15MV high‐energy photon beams for different field sizes and various source to surface distance(SSD). Methods: The measurements were made in water equivalent (PMMA) solid phantom in the build‐up region at various SSD for various field sizes using virtual and physical wedge filters having different angles. A parallel‐plate ion chamber (Markus) was used to measure the percent depth doses at surface and buildup region. Plane parallel ion chamber with fixed plate separation on the surface and buildup region would perturbate the dose measured, to get the proper dose over response correction factor was used. Results: The percentage depth dose at surface (PDD0) increased as the field size increased for open, virtual, and physical wedged beams. For open, 30 degree physical, and virtual wedged beams, the surface doses were found to be 15.4%, 11.2%, and 15.2% with 6‐MV photons and 11.2%, 9.4%, 11.2% with 15‐MV photons, respectively, at 10 × 10 cm2 field size at 100cm SSD.As SSD increases percentage depth dose at surface (PDD0) decreases for open,physical and virtual wedge field. Conclusions: Percentage depth dose at surface (PDD0) of virtual wedged beams were similar to those of open beams. PDD0 of physical wedged beams were lower than those of open and virtual wedged beams. Surface doses for both PW and VW increases with field size and small increase in surface dose for both PW and VW fields as wedge angle increases especially for large fields.
SU‐E‐T‐144: Daily and Monthly Quality Assurance with TomoDose
Authors: Terrell J
Published: June 2012

Purpose: Examine the use of TomoDose for Tomotherapy quality assurance. Methods: Baseline TomoDose profiles are acquired annually in accordance with TG‐148. During monthly quality assurance, TomoDose is irradiated with a static beam and referenced to baseline. Differences between superimposed profiles are evaluated monthly. TomoDose is further utilized in verifying transverse laser alignment. The TomoDose is aligned to virtual isocenter lasers and statically irradiated with a 40cm × 5.02cm treatment beam. Next, the TomoDose's internal diodes are imaged using the MVCT. Transverse laser, imaging beam, and treatment beam field center are verified to less than 1mm coincidence difference. For daily TomoDose irradiation the couch is set to a fixed height and irradiated. The dose to the central axis and dose rate is recorded. To check energy, the measurement is repeated with an aluminum block placed centrally on the TomoDose. The output reading relative to the dose rate is compared to the baseline determined at the time of monthly verification. A ratio of the output and energy readings serves as a daily energy constancy check. Results: Over 28 months, for nominal field sizes of 1.05, 2.50, and 5.02cm, TomoDose measured an average field size of 1.10, 2.51, and 5.02cm with maximum deviations of 0.09, 0.09, and 0.10cm, respectively. For transverse laser alignment, TomoDose software calculates beam center location. We have found the alignment to be sensitive to sub‐millimeter changes. Our nominal daily energy ratio is 0.689. We have observed a decline from an estimated 0.693 to 0.680 with target wear, providing a good indicator of degradation. Conclusions: TomoDose serves as a reliable constancy device with added benefits of verifying transverse laser alignment and predicting target health. I own common stock in Accuray (Tomotherapy).
SU‐E‐T‐147: Film Dosimetry Verification for TSE Using An Epson Scanner
Authors: Timmerman J , Wang K , Tang S , Zhu T
Published: June 2012

Purpose: To commission and verify an Epson scanner for film dosimetry for total skin electron beam therapy (TSEB). Methods: Use data from an IBA PPC40 parallel‐plate ion chamber and Sun Nuclear QED skin diode detectors as standard; we have made comparisons to the film measurement using Kodak XV films. Hurter‐Driffield (HD) curve are established for 6 MeV total skin electron beams at a source‐to‐surface distance (SSD) of 5 m. Also HD curves are built for 6 MeV at a 100 cm SSD. Dose profiles for a series of oblique incident large electron fields are measured using the film for approximately 80 cGy dose delivered at the peak. The film is then scanned using two scanners, an Epson expression 10000 XL and a Vidar VXR‐16 Dosimetry Pro. The optimal scanning conditions (e.g., dot per pixel size, internal color correction scheme) are chosen for the Epson scanner. Matlab is then used to analyze the optical density (OD) of the scanned films. A transmission densitometer made by Tobias Associates transmission is used to analyze the films to give a classical standard. Results: The analysis of the Epson scanner is presented in two forms: one with and one without the HD correction from the established HD curve. The error analysis gives an uncertainty of 5% without the HD correction. An improved result of approximately 3% is found when an HD correction is applied to the analysis. Conclusions: A simple Epson scanner satisfies the commissioning standards for TSEB when an HD curve correction is applied.
SU‐E‐T‐154: Online Dose Verification with Gafchromic Film for Fixed‐Gantry and Rotational Intensity Modulated Radiation Therapy: A Phantom Study
Authors: Hu W , Zhao J , Ye J , Peng J , Zhang Z
Published: June 2012

Purpose: The patient specific quality assurance (QA) measurements for fixed‐gantry and rotational intensity modulated radiation therapy (IMRT and VMAT/RapidArc) are usually performed on a homogeneous phantom prior to the treatment. The purpose of this study is to develop an online method to verify the delivered dose to the patient on the treatment day. Methods: An anthropomorphic (Rando) head phantom was immobilized in treatment position with a thermoplastic mask to simulate a real patient. A sheet of gafchromic film (EBT2) was sandwiched between a 1‐cm‐thick solid water slab, which was fixed to the Type‐S extension board, and the patient's head hold (a pillow used here). The CT images of the Rando phantom were acquired and exported to the treatment planning systems. One step‐and‐shot fixed‐gantry IMRT plan and one RapidArc plan were generated and the dose distributions on the film plane were calculated. The two plans were delivered to the patient (Rando phantom in this study) in the treatment position on a Varian Trilogy linear accelerator with two new films. The films were scanned, and the measurements were compared with the planned doses. Results: The composite dose distributions measured on the film plane were the actual delivered dose for the treatment. The comparison between the measurement and planned dose profiles shows an agreement within 3% because of the good reproducibility of phantom positioning. Gamma pass rates (using 3mm and 3% criteria) for the IMRT and RapidArc plan were found to be 95% and 94%, respectively. Conclusions: The phantom study has demonstrated the feasibility of using gafchromic film for online dose verification. This simple method takes into account the patient heterogeneity and the treatment associated uncertainties such as setup error, intrafraction motions and machine related variations. It can be implemented as an online physics and/or clinical QA tool without taking additional machine time.
SU‐E‐T‐156: Robust Algorithms for Correction of Predicted Electronic Portal Imager Response
Authors: Bailey D , Kumaraswamy L , Podgorsak M
Published: June 2012

Purpose: Predicted electronic portal imaging device (EPID) response, as calculated by a commercial treatment planning system (TPS), is up to 15% lower than measured EPID response for off‐axis IMRT fields. Two original algorithms are presented to correct for EPID prediction errors. The EPID prediction algorithm and a recent image‐to‐dose conversion algorithm are each tested for ability to identify TPS dose calculation errors. Methods: By comparing test images to respective predictions, correction factors were calculated to modify the EPID diagonal calibration profile (applied via radial symmetry). Secondly, image/prediction comparisons were used to compute a 2D correction matrix for EPID predictions, to account for radially‐asymmetric errors. Over 50 IMRT fields of varying complexity were tested with each correction technique, and with a diode array. Absolute dose and beam‐profile errors were separately induced into the TPS and a number of IMRT plans were recalculated and measured with three systems ‐ an EPID prediction system, an EPID image‐to‐dose conversion system, and a diode array ‐ for comparison to verification plans. Results: With the profile correction, TPS predictions agree much better with EPID measurements, yielding improvement in gamma pass rates (3%,3mm) of over 30% on average for off‐axis IMRT fields. Since off‐axis prediction errors are not radially‐symmetric, the matrix correction further improves pass rates by 5% on average (up to 30%) for fields where the profile correction is limited. The EPID prediction system was unable to catch either induced TPS error, while both the image‐to‐dose conversion system and the diode array indicated both errors. Conclusions: Profile correction is effective and efficient though approximate, due to radial symmetry. The matrix correction is comprehensive but requires computational manipulation of DICOM images. Users must be aware that EPID prediction systems may be unable to catch delivered IMRT inaccuracies due to calculation errors downstream from the actual fluence calculation.
SU‐E‐T‐157: Reproducibility of CVD Diamond Detectors for Radiotherapy Dosimetry
Authors: Betzel G , Lansley S , McKay D , Meyer J
Published: June 2012

Purpose: Three diamond x‐ray detectors fabricated in‐house using films from the same batch of commercially‐available chemical vapor deposition (CVD) diamond were investigated for performance inter‐comparability under clinically relevant conditions. Methods: Detectors were based on single‐crystal CVD diamond films (0.5 × 3 × 3 mm̂3) with 0.4 mm^3 sensitive volumes, which were encapsulated with PMMA. Detectors were placed in a (30 × 30 × 30 cm̂3) PTW water phantom. Six‐MV photons from an Elekta Synergy linac were measured using an SSD of 90 cm and 10 cm phantom depth with a 10 × 10 cm̂2 field size in the central axis of the beam. Data acquisition was performed using a PTW UNIDOS E electrometer. Leakage current, priming dose, response dynamics, dose linearity, dependence on dose rate and angular dependence were used to evaluate differences between diamond detectors. Results: Differences were seen in leakage currents before (< 1.5 pA) and after (< 12 pA) irradiation. A priming dose of ∼7 Gy and rise and fall times of 2 s were found for all three detectors. Sensitivities differed by up to 10%. Dependence on dose rate was similar (Fowler fitting parameter, delta = 0.92‐0.94). Angular dependence was minimal (97‐102% average). Differences in detector performance appeared to be primarily due to film thickness, which can significantly change sensitivities and applied fields for detectors with small sensitive volumes. Conclusions: Although films were sourced from the same manufactured batch, small deviations were seen between detectors such that correction factors may be required much like natural diamonds used in existing commercial detectors. Differences in sensitivity and dependence on dose rate most likely originate from variation in film thickness due to manufactured tolerances. Preselecting films by thickness is important to help eliminate variability in detector response where small sensitive volumes are used.
SU‐E‐T‐158: Neutron Damage of Power Electronics Used during Image Guidance in Proton Therapy
Authors: Riley K , Cascio E
Published: June 2012

Purpose: A series of measurements were performed in a clinical proton therapy beam to assess the sensitivity of silicon‐based electronics in commercial x‐ray generators to single event burnout from the secondary neutron background in proton therapy treatments. Methods: Failure rates were nondestructively measured in various metal oxide semiconductor field‐effect transistors (MOSFETs) as a function of applied voltage using a dedicated test circuit board. Neutrons were produced by 230 MeV protons stopping in a brass beam target and high beam current was used to accelerate testing. Neutron fluences were measured by activation analysis of carbon and aluminum in both the test setup and in situ at the generator. Failure rates were determined by scaling results based on beam monitor output to the relevant neutron fluence rate. Results: Current pulses from the test board clearly indicated the onset of single event burnout without destroying the MOSFET. The neutron fluence measured on the test board was 4.3 ± 0.8×106 n cm‐2 MU‐1 and this is consistent with previous measurements. The MOSFET failure rate decreased rapidly with a reduction in the applied voltage and is 20‐30 times lower in higher‐rated components at the same voltage. Under nominal operating conditions the estimated failure rate is tens of failures per year for a generator 6m from the treatment position. Conclusion: The sensitivity of x‐ray generator power electronics to neutron‐induced single‐event burnout is significant and can affect the implementation of image‐guided techniques for proton therapy. Strategies and system designs to mitigate this phenomenon are being investigated to help enable x‐ray generators withstand the proton therapy environment. This research was supported by the NIH/NCI under grant number 6‐PO1 CA 21239
SU‐E‐T‐160: Response of EBT2 Gafchromic Film to Possible Stresses Associated with in Vivo Measures
Authors: Ashburn J
Published: June 2012

Purpose: to assess the response of EBT2 Gafchromic filmast; to stresses that might be imposed on the film when used as an in‐vivo dosimeter. The following stress factors were investigated: bending the film; compression; and the shearing that occurs when cutting the film. Methods: For bending stress, the film was rolled into cylinders of various radii, submerged in water, and exposed to X‐rays. For compression, 64 cm̂2 pieces of the film were sandwiched within a stack of solid water and weights were placed on top of the solid water in order to compress the film while being exposed to X‐rays. For artifacts that arise from cutting the film, pieces of the film were cut either with scissors or a paper cutter. The cut film was then exposed uniformly and shearing artifacts introduced from cutting the film were identified. The effects of ‘light piping’ from the cut edges of the film were also investigated. A felt tip pen was used to darken the cut edges in order to mitigate light piping. The film was scanned with an Epson 10000 XL scanner in transmission mode and images in the red spectrum were analyzed. Results: At 200 cGy exposures, a compression corresponding to 0.6 kg/cm̂2 ‘weight pressure’ had less than a 2% influence on the film's response. Bending the film had a larger influence, >5%, when the radius of curvature was 1 cm. Also, larger artifacts were identified when the film was cut with scissors and the cut edges were not darkened with a pen. Conclusions: EBT2 film can readily be used as an in‐vivo dosimeter within the compression and dose ranges investigated. The user should avoid cutting the film with scissors, and also avoid excessively bending the film. No COI.
SU‐E‐T‐161: SOBP Beam Analysis Using Light Output of Scintillation Plate Acquired by CCD Camera
Authors: Cho S , Lee S , Shin J , Min B , Chung K , Shin D , Lim Y , Park S
Published: June 2012

Purpose: To analyze Bragg‐peak beams in SOBP (spread‐out Bragg‐peak) beam using CCD (charge‐coupled device) camera ‐ scintillation screen system. We separated each Bragg‐peak beam using light output of high sensitivity scintillation material acquired by CCD camera and compared with Bragg‐peak beams calculated by Monte Carlo simulation. Methods: In this study, CCD camera ‐ scintillation screen system was constructed with a high sensitivity scintillation plate (Gd2O2S:Tb) and a right‐angled prismatic PMMA phantom, and a Marlin F‐201B, EEE‐1394 CCD camera. SOBP beam irradiated by the double scattering mode of a PROTEUS 235 proton therapy machine in NCC is 8 cm width, 13 g/cm2 range. The gain, dose rate and current of this beam is 50, 2 Gy/min and 70 nA, respectively. Also, we simulated the light output of scintillation plate for SOBP beam using Geant4 toolkit. Results: We evaluated the light output of high sensitivity scintillation plate according to intergration time (0.1 ‐ 1.0 sec). The images of CCD camera during the shortest intergration time (0.1 sec) were acquired automatically and randomly, respectively. Bragg‐peak beams in SOBP beam were analyzed by the acquired images. Then, the SOBP beam used in this study was calculated by Geant4 toolkit and Bragg‐peak beams in SOBP beam were obtained by ROOT program. The SOBP beam consists of 13 Bragg‐peak beams. The results of experiment were compared with that of simulation. Conclusions: We analyzed Bragg‐peak beams in SOBP beam using light output of scintillation plate acquired by CCD camera and compared with that of Geant4 simulation. We are going to study SOBP beam analysis using more effective the image acquisition technique.
SU‐E‐T‐162: Rapid Assessment of Cyberknife IRIS Variable Collimator Performance Using a Commercial Diode Array
Authors: Gibbs G , White G , Bulz G
Published: June 2012

Purpose: To describe an efficient method for verifying the size and centering of the radiation field from the Cyberknife IRIS variable collimator with sub‐millimeter accuracy using a general purpose commercially available diode array. Methods: We present a technique using a conventional diode array (Sun Nuclear Profiler) with the array at an extended distance of 320 cm. The projection of the 4 mm diode spacing back to the 80 cm field definition distance gives an effective spacing of 1 mm, sufficient to confirm proper operation of the IRIS. We describe the data acquisition process and present data comparing the Profiler measurements to scanned measurements for both profile and FWHM analysis and reproducibility of the technique over repeated measurements. Results: Average difference between original water scanner measurements and diode array measurements over the 12 aperture sizes) from 5 mm to 60 mm) were ‐ 0.14 mm (range 0.03 mm to 0.83 mm). Reproducibility and centering measurements had a similar range of accuracy. Conclusions: A general purpose commercially available diode array can be used to quickly and accurately characterize the field size and centering of the Cyberknife IRIS variable collimator system with sub‐millimeter accuracy subsequent to service, software recalibration, software upgrades or associated with routine QA. This technique avoids the time consuming and cumbersome water tank scanning with a diode and the difficulties associated with image based measurements (CR or radiochromic film) that require time consuming and careful calibration and choice of threshold values.
SU‐E‐T‐163: Thin‐Film Organic Photocell (OPV) Properties in MV and KV Beams for Dosimetry Applications
Authors: Ng SK , Hesser J , Zhang H , Gowrisanker S , Yakushevich S , Shulhevich Y , Abkai C , Wack L , Zygmanski P
Published: June 2012

Purpose: To characterize dosimetric properties of low‐cost thin film organic‐based photovoltaic (OPV) cells to kV and MV x‐ray beams for their usage as large area dosimeter for QA and patient safety monitoring device. Methods: A series of thin film OPV cells of various areas and thicknesses were irradiated with MV beams to evaluate the stability and reproducibility of their response, linearity and sensitivity to absorbed dose. The OPV response to x‐rays of various linac energies were also characterized. Furthermore the practical (clinical) sensitivity of the cells was determined using IMRT sweeping gap test generated with various gap sizes. To evaluate their potential usage in the development of low cost kV imaging device, the OPV cells were irradiated with kV beam (60‐120 kVp) from a fluoroscopy unit. Photocell response to the absorbed dose was characterized as a function of the organic thin film thickness and size, beam energy and exposure for kV beams as well. In addition, photocell response was determined with and without thin plastic scintillator. Results: Response of the OPV cells to the absorbed dose from kV and MV beams are stable and reproducible. The photocell response was linearly proportional to the size and about slightly decreasing with the thickness of the organic thin film, which agrees with the general performance of the photocells in visible light. The photocell response increases as a linear function of absorbed dose and x‐ray energy. The sweeping gap tests performed showed that OPV cells have sufficient practical sensitivity to measured MV x‐ray delivery with gap size as small as 1 mm. Conclusions: With proper calibration, the OPV cells could be used for online radiation dose measurement for quality assurance and patient safety purposes. Their response to kV beam show promising potential in development of low cost kV radiation detection devices.
SU‐E‐T‐166: Use of an in Vivo Dosimeter to Assess the Implications of Daily Prostate Rotations
Authors: Studenski M , Gardner S , Yamoah K , Buzurovic I , Showalter T , Den R
Published: June 2012

Purpose: It is well established that using image guidance for prostate motion allows reduction of margin, dose escalation, decreased toxicity and recently improved outcomes. However, current methods only account for translational motion, not rotational variations. The purpose of this study is to assess whether rotations in anatomy lead to significant changes in the delivered dose for prostate patients. Methods: Under an IRB approved protocol, 11 consecutive patients underwent prostate IMRT using IGRT with implanted metal‐oxide semiconductor field‐effect transistors (MOSFETs); the Dose Verification System (DVS) manufactured by Sicel Technologies. Two dosimeters were implanted per patient. From conebeam CT (CBCT) registration, corrections were applied to all translational errors. For rotations larger than 3 degrees, patient were repositioned and realigned to attempt to correct the rotation. Both translational and rotational errors based on the CBCT were documented. The daily DVS readings were compared to CBCT rotations about each axis (pitch, roll and yaw) and the root‐mean square (RMS) rotation. Results: 372 CBCT images were acquired. The correlation between rotation and DVS measurement was analyzed using linear regression. The R2 value for pitch was 0.059 and 0.144 for each dosimeter, respectively. For roll, the R2 values were 0.049 and 0.001. For yaw, the values were <0.001. For the RMS rotation, R2 was 0.034 and 0.038. As it could confound results, the angular dependence of the dosimeters was measured during commissioning and found that it was approximately 0.5% for 5 degree rotations. Conclusions: We did not find any significant correlation between prostate rotation around any axis and discrepancy in DVS reading. These results show that rotations seen clinically do not have a substantial effect on the dose delivered to the prostate. Further studies will attempt to determine at what angle rotations begin to affect the dose distribution, if at all.
SU‐E‐T‐171: Missing Dose in Integrated EPID Images
Authors: King B , Seymour E , Nitschke K
Published: June 2012

Purpose: A dosimetric artifact has been observed with Varian EPIDs in the presence of beam interrupts. This work determines the root cause and significance of this artifact. Methods: Integrated mode EPID images were acquired both with and without a manual beam interrupt for rectangular, sliding gap IMRT fields. Simultaneously, the individual frames were captured on a separate computer using a frame‐grabber system. Synchronization of the individual frames with the integrated images allowed the determination of precisely how the EPID behaved during regular operation as well as when a beam interrupt was triggered. The ability of the EPID to reliably monitor a treatment in the presence of beam interrupts was tested by comparing the difference between the interrupt and non‐interrupt images. Results: The interrupted images acquired in integrated acquisition mode displayed unanticipated behaviour in the region of the image where the leaves were located when the beam interrupt was triggered. Differences greater than 5% were observed as a result of the interrupt in some cases, with the discrepancies occurring in a non‐uniform manner across the imager. The differences measured were not repeatable from one measurement to another. Examination of the individual frames showed that the EPID was consistently losing a small amount of dose at the termination of every exposure. Inclusion of one additional frame in every image rectified the unexpected behaviour, reducing the differences to 1% or less. Conclusions: Although integrated EPID images nominally capture the entire dose delivered during an exposure, a small amount of dose is consistently being lost at the end of every exposure. The amount of missing dose is random, depending on the exact beam termination time within a frame. Inclusion of an extra frame at the end of each exposure effectively rectifies the problem, making the EPID more suitable for clinical dosimetry applications. The authors received support from Varian Medical Systems in the form of software and equipment loans as well as technical support.
SU‐E‐T‐172: Ion Recombination Correction Factor in Medium Dose Rate for Advanced Markus Ionization Chamber
Authors: Ghorbanpour M , Martini P , Simiantonakis I
Published: June 2012

Purpose: To determine the ion recombination correction factor using different methods in medium dose per pulse electron beams for Advance Markus ionization chamber (AMC) Methods: Two different methods were applied to obtain ion recombination correction factor. Conventional Boag's two voltage analysis (TVA) recommended in IAEA TRS‐398 dosimetry protocol and recently modified Boag's TVA expressions which consider the effect of free electron contribution on ks value. High energy electron beams of a dedicated linear accelerator, NOCAC7 (NRT, Italy), for intraoperative radiation therapy were applied. Dose per pulse in medium range of 4 to 41 mGy/pulse was investigated. Radiochromic films (ISP Gafchromic EBT2, USA) have been exploited as reference dose rate independent method. Dose measurement was performed by AMC in a small water phantom (IBA Dosimetry, Germany). Results: At reference conditions (9 MeV, 100 mm applicator, SSD 80 cm (27 mGy/pulse)), ks values derived from IAEA TRS‐ 398 dosimetry protocols deviates 0.3% from reference value. From 4–35 mGy/pulse TVA yielded acceptable result (in average 1.0% deviation). For dose rate more that 35 mGy/pulse, conventional two voltage analysis (TVA) might be applied with caution (4.2% deviation at 41 mGy/pulse). In this range first model in the new modified Boag's expressions yielded acceptable accordance (average deviation 1.3%) in comparison with dose rate independent reference dosimeter (EBT2, Gafchromic film). The deviation in ks value among Boag's modified expressions increased when the dose rate raised. Conclusions: Authors concluded that AMC could be employed for absorbed dose determination of medium dose per pulse electron beams. The accuracy of TVA which is recommended currently in dosimetry protocol IAEA‐TRS‐398 is dependent on the range of applied dose rate. It is proper to be used for dose rate less than 35 mGy/pulse. First expression in Boag's modified formulas is proper for ks determination in high dose rate values (> 35 mGy/pulse).
SU‐E‐T‐173: TomoTherapy Treatment Couch Velocity Verification Using TomoDose
Authors: Chen C , Bichay T
Published: June 2012

Purpose: Accurate TomoTherapy treatment is dependent on multiple parameters, including the accuracy of couch velocity during beam delivery and gantry rotation. The recent TG‐148 protocol recommends quarterly film tests to verify the constancy of couch velocity. We determined the feasibility of using TomoDose, a quality assurance device, to detect the variation in couch velocity from baseline by a deviation of one or two percent. Methods: The TomoDose unit was rotated 90 degrees clockwise so that the long axis, consisting of 107 detectors, would translate across the TomoTherapy ‘Y’ jaws. The collimator field size used was the 1 cm mode and the table velocity was set to 0.5 mm/sec to establish a baseline. The velocity was then varied by 1% or 2% from nominal. The five tested velocities were 0.495, 0.490, 0.500, 0.505 and 0.510 mm/sec. The total translation time was kept at a constant 400 sec. The field was progressively painted during the scans and was shortened if table velocity was decreased, and lengthened as velocity was increased. Results: The baseline field size was 20.03 cm (400 sec × 0.05 cm/sec). A 2% increase in velocity translated to an increase in the field size to 20.39 cm and a 2% decrease in velocity resulted in a decrease in field size to 19.64 cm. Similarly, a 1% increase in velocity increased the field to 20.18 cm, and a 1% decrease velocity decreased the field to 19.76 cm. Conclusions: An increase or decrease in the couch velocity, for a fixed beam delivery time, resulted in an altered radiation field size. The field size results are approximately as expected for both the baseline scans as well as the modified velocity scans. This study demonstrates that, under these conditions, TomoDose can be used to determine small variations in table velocity as small as 1 %.
SU‐E‐T‐176: Improved Collimator Scattering Factor (Sc) Measurements for Small Fields Using Build‐Up Caps in Robotic Radiosurgery
Authors: Lee S , Tien C , Curran B , Sternick E
Published: June 2012

Purpose: The Monte Carlo calculation algorithm in the MultiPlan (Accuray, Palo Alto, CA) treatment planning system used for CyberKnife (Accuray) robotic radiosurgery requires in‐air measurements. In this study, results were compared for the impact of build‐up caps using a diode detector for small field in‐air measurements. Methods: Two acrylic caps custom‐made for the SFD diode detector (IBA, Germany) of two thicknesses were compared against free‐in‐air measurements. The 1.5 and 5 cm thicknesses correspond to Dmax and a depth beyond the range of electron contamination, respectively. A Blue Phantom (IBA) was used to position the diode 80 cm SAD. Measurements were made for all 12 fixed cones ranging from 5 to 60 mm. Results: For the 5 mm cone, there is a 15.6% and 20.0% difference in the Sc factor between the 1.5 cm and 5 cm buildup caps, respectively, versus the free‐in‐air measurement. For the 7.5 mm cone, the difference is 6.3% and 10.4% for the 1.5 cm and 5 cm buildup caps, respectively, versus the free‐in‐air measurement. While generally decreasing, the Sc factor for either buildup cap does not agree within 2% to free‐in‐air measurements until the cone used is larger than 40 mm. Overall, the two buildup caps yield similar Sc factors and the differences observed are attributed to electron contamination. Conclusions: The Monte Carlo calculation algorithm used by the CyberKnife planning manual does not refer to any build‐up caps. This study has shown that, particularly for small fields, there are large differences in Sc factors measured with and without buildup caps. In general, for fields smaller than 10 mm, build‐up caps should be carefully chosen, especially in commissioning data.
SU‐E‐T‐181: Development of a Single‐Marker‐Based Optical Tracking System to Enhance Patient Safety in Radiotherapy
Authors: Yan G , Lu B , Mittauer K , Liu C , Li J
Published: June 2012

Purpose: To develop an accurate and efficient single‐marker‐based optical tracking system to enhance patient safety and quality of care in radiotherapy. Methods: The optical tracking system consists of a Polaris camera as well as in‐house software. The camera is mounted inside the treatment room and detects the location of a single infra‐red (IR) reflective marker affixed on patient skin in real‐time. The tracking system safeguards patient from treating wrong sites by comparing real‐time marker position to the position predicted by virtual simulation, which is independent of couch or any indexing system. The deviation of marker position is shown in color (red or green) to indicate accuracy of patient positioning. The system works in concert with record‐and‐verify (R&V) system to further enhance patient safety and smooth clinic work flow. Marker information matching the patient under treatment is automatically loaded by the tracking system when a setup or treatment field is loaded in R&V. In non‐coplanar treatment, the system automatically adjusts expected marker coordinators by accounting for each beam's couch angle extracted from R&V. Results: Accuracy of the developed tracking system on a pelvis phantom has been verified against a CBCT system to be within 1.0 mm for coplanar treatment. In non‐coplanar treatment, uncertainty of the system increases as the distance of the marker relative to treatment isocenter. The system precisely and automatically loads in patient and marker information for each beam, in concert with our R&V system. Conclusions: We have developed an accurate and efficient single IR marker‐based optical tracking system for patient treatment position verification. It significantly enhances patient safety with streamlined clinic work flow. The system can be readily upgraded for high‐precision radiotherapy with the use of multiple markers (>4).
SU‐E‐T‐187: Clinical Use of the Software for the Automation of Treatment Field Parameters Verification Prior to Radiation Delivery
Authors: Kriminski S , Lysiuk I , Sansourekidou P , Pavord D
Published: June 2012

Purpose: Verification of treatment field parameters by therapists take place prior to every or first fraction. Such verification or field timeout should be completely independent from record‐and‐verify system. It is performed manually via reading treatment parameters from linac screen and comparing them to treatment plan. We evaluate clinical use of software allowing automation of field timeout. Methods: The program for automated timeout performs three tasks.Plan information is extracted from PDF printouts generated by Eclipse (Varian Medical Systems, Palo Alto, CA) treatment planning system. User selects patient, plan and field to be compared with the field moded‐up at the linac. Information from the Varian (Varian Medical Systems) linac's screen is extracted using video signal splitter and VGA2USB converter (Epiphan Systems, Ottawa, CA). Image farther undergoes character recognition, which works reliably for 1X, Trilogy and 2100C linacs used in out tests.The plan and linac screen information are output to the computer screen and user is alerted if mismatch is observed. The software uses tolerances established in out clinic. The program also outputs auxiliary information, e.g. bolus, which is not well alerted by or can be omitted in the record and verify system. In the workflow tested, PDF printouts are uploaded for the software during second check and automatic timeout is performed for all treatments except v‐sim and first fraction (of each treatment plan). Results: The software has friendly user interface and is easily included in clinical work flow. With the error rate being extremely low, we don't have data yet to claim that automated timeout provides higher safety than manual; however, it definitely cuts timeout time to 2‐3sec per fields versus 10sec, if done manually. Conclusions: Field timeout automation is practicable and fits well into clinical workflow. It improves patient throughput and is expected to improve patient safety. Conflict of interest: S. Kriminski and I. Lysiuk: provisional patent application is submitted to United States Patent and Trademark Office
SU‐E‐T‐191: PITSTOP: Process Improvement Techniques, Software Tools, and Operating Principles for a Quality Initiative Discovery Framework
Authors: Siochi R
Published: June 2012

Purpose: To develop a quality initiative discovery framework using process improvement techniques, software tools and operating principles. Methods: Process deviations are entered into a radiotherapy incident reporting database. Supervisors use an in‐house Event Analysis System (EASy) to discuss incidents with staff. Major incidents are analyzed with an in‐house Fault Tree Analysis (FTA). A meta‐Analysis is performed using association, text mining, key word clustering, and differential frequency analysis. A key operating principle encourages the creation of forcing functions via rapid application development. Results: 504 events have been logged this past year. The results for the key word analysis indicate that the root cause for the top ranked key words was miscommunication. This was also the root cause found from association analysis, where 24% of the time that an event involved a physician it also involved a nurse. Differential frequency analysis revealed that sharp peaks at week 27 were followed by 3 major incidents, two of which were dose related. The peak was largely due to the front desk which caused distractions in other areas. The analysis led to many PI projects but there is still a major systematic issue with the use of forms. The solution we identified is to implement Smart Forms to perform error checking and interlocking. Our first initiative replaced our daily QA checklist with a form that uses custom validation routines, preventing therapists from proceeding with treatments until out of tolerance conditions are corrected. Conclusions: PITSTOP has increased the number of quality initiatives in our department, and we have discovered or confirmed common underlying causes of a variety of seemingly unrelated errors. It has motivated the replacement of all forms with smart forms.