bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐26: Automated Plan Evaluation System: Design and Implementation
Authors: Kapur Priyanka , Kapoor Rishabh , Kapoor S L
Published: November 2011

Purpose: To present software for a Radiation therapy facility that will simplify the process of dosimetric plan evaluation and will help clinicians and physicists to review the plan. Materials and method: Every treatment plan requires certain dosimetric characteristics or parameters to be evaluated, which are essential for the assessment of a treatment plan. One can automate this process with the software that can understand the treatment plan and DVH data and gives you the desired results. This software accepts DICOM RT data from IHE‐RO compliant Varian Eclipse v 8.6 and computes DVH. There is also a facility to define disease site, technique and fractionation specific templates for dose volume constraints. This software helps you to analyze the normal tissue tolerances with the data given in the literature and also gives user the freedom to use α/β ratios to modify the tolerance values in accordance with dose‐fractionation scheme. The dosimetric indices such as conformity index and homogeneity index can also be calculated and compared with the user defined criteria in the template. Results: The prototype system has been used to design various templates for different treatment sites such as head and neck and breast. These templates are used to evaluate plan and dosimetric parameters for several patients. Conclusion: This prototype software provides a simplified solution for an automated dosimetric plan evaluation. The dosimetric parameters used in the plan evaluation is stored in an database archive for all the patients and this data is intended to used for further analysis.
SU‐E‐T‐32: An Integrated IGART Planning Environment
Authors: Zhang B , Fatyga M , Sleeman W , Dogan N
Published: November 2011

Purpose: Open Radiological Archiving and Communication System(ORACS) relational research database, which stores images, projections, plans, trials and doses etc, is the backbone for Image Guided Adaptive Radiation Therapy (IGART) Research Project at VCU. Philips Pinnacle3 is being used by this project for IGART adaptive planning of Virtual Clinical Trials (VCT). Therefore, in order to establish a user‐friendly interactive environment and facilitate collaboration between different sub‐projects, seamless integration of these two systems will be a must. Methods: It is well‐known that Pinnacle3 lacks the capacity to interact with a database server. However, we take advantage of Pinnacleˈs configurability and scripting power to enhance Pinnacle with new GUI controls, which invoke a middleware layer to access ORACS database. Users can import images from ORACS database through remote web services or locally, and save contours and plans and doses and other derived Pinnacle data back to ORACS database by simply clicking these new GUI controls. Moreover, a Pinnacle database can be re‐created easily and entirely from ORACS database through these new GUI controls and the middleware layer. The same technique can be used to create connection between Pinnacle3 and other database servers. Also because ORACS database uses web services for data access, if a specific middleware is created, any Treatment Planning System can access ORACS database interactively. Results: We presented a software infrastructure for seamless integration of ORACS research database and Philips Pinnacle3, which created an integrated virtual clinical trial environment for IGART researchers at our institution. Conclusions: Contemporary IGART research imposes new demands on the IT infrastructure of Radiation Oncology departments. We created a data management system which takes first steps towards managing new and complex tasks of automated analysis of large data sets.

NIH Grant P01 CA11602
SU‐E‐T‐39: Volume Regression: An Appropriate Surrogate for Treatment Response in Locally Advanced Head and Neck Cancer?
Authors: Guerrero M , Hou J , DˈSouza W
Published: November 2011

Purpose: The purpose of this work was to evaluate whether GTV volume regression is an appropriate surrogate for treatment response during concurrent chemo‐radiation therapy in locally advanced head and neck cancer. The change in GTV volume during and after fractionated treatment was correlated with clinical outcome. Methods: We used a deformable image registration algorithm to register conventional CT images to weekly CBCT images. The image registration field was used to project GTV contours from the planning CT to the weekly CBCT images. We calculated GTV volume at different time points of the fractionated treatment for 29 patients. Patients were clinically classified as CR (complete response), PR (partial response) and NR (no response) by PET exam and clinical evaluation performed 3–4 months after the completion of therapy. The PR and the NR categories were pooled into one called NCR (non‐complete response). The initial GTV volume, final absolute GTV volume, early relative volume and final relative volume as well as a radiobiological parameter obtained by fitting the volume regression curves to a radiobiological model, were studied for correlation with outcome. Results: Of the four volume quantities studied, only the early volume regression showed a mean value with statistically significant difference between CR and NCR patients: 0.83±0.0.03 for CR and 0.95±0.04 for NCR (p=0.02). The radiobiological parameter had a mean of 0.86±0.03 for CR and 0.93±0.03 (p=0.03) for NCR. Conclusions: We studied volume regression in head and neck cancer patients by registering the planning CT and the weekly CBCT images. We found that while the final volume of the tumor is not a good predictor of clinical outcome, early relative volume (at about 3 weeks) showed a statistically significant difference between the CR and NCR groups. This result suggests that early volume regression could be a predictor for clinical outcome.
SU‐E‐T‐40: Exploring the Reproducibility of Tumor Volumes Measured by Radiologist, Computer‐Aided Radiologist and Computer Alone
Authors: Zhao B , Tan Y , Li Y , Guo P , Schwartz L
Published: November 2011

Purpose: The use of volumetric CT as an imaging metric to better assess cancer response to treatment requires knowledge of measurement reproducibility. This study was designed to explore the reproducibility of tumor volumes obtained by radiologist manual delineation (MAN), computer‐aided method (CAM) and computer alone (CA) using a same‐day repeat CT dataset of 32 non‐small cell lung cancer (NSCLC) patients. Methods: We used a publicly accessible repeat CT dataset aimed at studying cancer treatment response. Briefly, each patient was scanned twice within 15 minutes using the same imaging protocol and CT scanner (16‐ or 64‐row). Patients were repositioned before the second scan. Thin‐sectional images of 1.25mm slice interval were reconstructed using a shaper filter. Thirty‐two lesions (one per patient) were analyzed using the following three Methods: (1) MAN‐an experienced radiologist manually drew tumor contours on two repeat scans in a side‐by‐side mode, (2) CAM‐an operator applied a home‐grown algorithm to segment the tumors and the computer‐generated contours were reviewed/edited by the same radiologist, also in a side‐by‐side mode, and (3) CA‐an operator applied a different, also homegrown, algorithm to delineate tumor contours (no edit). Bland‐Altman plots were constructed to assess the agreement between volumes measured by each method on the two repeat scans. Volume difference between MAN and CA on each patientˈs first scan was analyzed using a paired t‐test. Results: The 95% limits of agreements for the tumor volumes made by MAN, CAM and CA on two repeat scans were (−19.9%, 19.6%), (−12.1%, 13.4%) and (−11.8%, 16.0%), respectively. The difference between tumor volumes measured by MAN and CA was not statistically significant (p=0.497). Conclusions: MAN is the least reproducible method for measuring tumor volumes compared to CAM and CA. The recommended way to obtain tumor volumes is to use a computer algorithm to segment tumors followed by radiologistˈs supervision.

This work is supported in part by R01CA125143 from National Cancer Institute
SU‐E‐T‐108: EBT2 Film Based Dosimetry Incorporating Correction for Spatial‐Temporal Dose Response Variation
Authors: Tenn S , Ruan D , Dou T , Low D
Published: November 2011

Purpose: Implementation of radiochromic film, such as GafChromic EBT2 film, as a quantitative 2‐dimensional dosimeter requires an array of equipment calibrations and corrections. We have developed a holistic model‐based calibration/correction mechanism for radiochromic film dosimetry. Methods: One challenge of using radiochromic film is that most of the densitometry scanners in use are designed for qualitative, not quantitative use. We performed careful characterization and quantification of the systematic and random components of all temporal and spatial optical density variations. In the proposed workflow, the spatial‐dependent dose response is estimated in the calibration stage under a novel model‐based optimization framework. A benchmark calibration process has been developed for the full (optical density, space) calibration map. For improved robustness, a simplified model that assumes separability of spatial variation and dose dependence was developed. The corresponding QA tool utilizes a consistent correction principle and maps the observed pixel intensity value based on the estimated spatially varying calibration map. The developed method has been tested on seven plans (both IMRT and VMAT) and compared with commercial software correction results. Dosimetry accuracy was validated against EDR2 film by comparison with treatment planning system calculated dose distribution using 3%‐3mm gamma criterion.Results: Under equivalent test conditions, the proposed method achieves gamma passing rates with EBT2 that are comparable to or better than a correction method of a commercial counterpart. Such corroboration is consistent for both IMRT and VMAT plans under gamma tests Conclusions: We have developed a systematic approach to comprehensively calibrate and use EBT2 film, accounting for temporal and spatial dose response variations. Specifically, a formal generative model and an estimation methodology was developed to achieve good balance between measurement sensitivity and robustness. This process has been implemented with in‐house software.

Research supported in part by AACR career development award.
SU‐E‐T‐112: 18 MV X‐Ray Beam Commissioning with the IC Profiler: A Fast 3D Relative Dosimetry Technique Using An Ion Chamber Array in a Solid Tissue‐Equivalent Phantom
Authors: Leduc V , Furstoss C , Pater P , Munger P , Wierzbicki W
Published: November 2011

Purpose: To devise a technique of 3D relative dosimetry using an ion chamber array with solid phantom to significantly reduce overall measurement time needed for photon beam modeling. Methods: Measurement setup of the array was determined by comparison of acquired profiles in the array and in a water tank. Software was developed to queue measurements in step‐and‐shoot sequences and process the resulting IC array data. Beam profiles and PDDs necessary for beam modeling were acquired with the IC array for 18 MV. A model was created with the IC array data using the Pinnacle TPS and compared to a model created from water tank measurements. Both models were first compared by measuring differences between profiles and PDDs. Secondly, 3D dose distributions predicted by both models were compared using a gamma metric for a pair of treatment plans. Results: The IC array model was found to match the water tank model for most profiles. Due to fixed chamber depth in the IC array, PDDs near the surface differed in the IC array model from the water tank model. For a prostate case treatment plan, comparison of 3D dose distributions from both models showed that 90.4 % of voxels agreed within a gamma of (1%, 1 mm). This tolerance was violated near air‐tissue interfaces due to differences in the measured PDDs between both models. The devised technique allowed most measurements necessary for beam modeling, except for output factors, to be made for a single energy in under 8 hours. Conclusions: The IC array with solid phantom setup allows substantially faster beam acquisition than a water tank. Further investigation is required for measuring exact PDDs in the IC array setup. Future work will study lower photon energies and electron beam modeling with IC array acquisitions.

Funding for the presenting author was provided for this study by Sun Nuclear Corporation during the summer of 2010.
SU‐E‐T‐120: Characterization of EBT2 Film for Absolute Dosimetry in Proton Beams
Authors: Devaraju V , Slopsema R
Published: November 2011

Purpose: The objective of this work is to fully characterize Gafchromic EBT2 film for absolute dose measurement (in‐vitro and in‐vivo) in the spread out Bragg peak (SOBP) of both scanned and scattered proton beams. Methods and Materials: The OD‐vs‐dose calibration curve is determined by irradiating film at different depths (0, 5, 10, 15, 20, and 25 cm) to different dose in a calibration field (range 28 g/cm2, modulation 15 g/cm2). Solid water slabs are used as phantom; 4x5 cm films are irradiated to nine dose levels spanning from 10 cGy to 1000 cGy. Beam output is measured using parallel plate ionization chamber both to calculate the specific doses delivered to the film and to compare the measured dose with the calculated dose from the film. The films are digitized with EPSON scanner and the net optical density computed. Measurement done at different depths (different average energy) are combined to create a single calibration curve. Verification measurements are performed for different range and modulation combinations, at various depths, and using both double‐scattering and uniform‐scanning delivery, thus validating the use of single sensitometric plot for different proton energy and delivery technique. In addition, reproducibility, angular response, and film uniformity are investigated. Results: Using the single calibration curve, the accuracy of absolute dose measurements using EBT2 film is found to be within 5% for any point within the SOBP excluding the distal fall off region and at very low dose level (<15cGy). No difference in response to scattering or scanning beams is observed. The day‐to‐day reproducibility is better than 1%. The uncertainty introduced by angular response, film nonuniformity and different delivery techniques are found to be insignificant. Conclusions: EBT2 film is a viable option for absolute dose measurements both for in‐vitro and in‐vivo.
SU‐E‐T‐128: Characterizing the Uniformity of Gafchromic EBT2 Film Response in a Cobalt‐60 Field
Authors: McCaw T , Micka J , DeWerd L
Published: November 2011

Purpose: The goal of this work is to evaluate the uniformity of International Specialty Products Gafchromic EBT2 film with a high‐resolution metric. The effect on uniformity of the marker dye (blue‐channel) correction and time post‐exposure are investigated. Methods: Film uniformity was quantified by using EBT2 and Kodak EDR2 film to measure the flatness of a cobalt‐60 field. EBT2 films were digitized 24, 48, and 72 hours post‐exposure and analyzed using three Methods: the manufacturer‐recommended blue‐channel correction, an in‐house blue‐channel correction, and a net optical density (OD) measurement in the red color channel. The field flatness was calculated from the horizontal and vertical dose profiles taken through the center of the cobalt‐60 field for each analysis method and compared to the EDR2 results. Results: The blue‐channel correction methods improved the flatness measured with EBT2 film by up to 1% over the net OD method. Additionally, the percent standard deviations of the flatness measurements with the blue‐channel correction methods were up to 0.7% (1‐sigma) lower than the net OD method. The flatness measured with EDR2 film was 1.4% to 1.8% better than the flatness measured with EBT2 film using the net OD method. The flatness did not exhibit any unidirectional change with time and showed a maximum change of 0.4%. Conclusions: Using field flatness as a metric for response uniformity, EBT2 film analyzed with the net OD method demonstrates substantial non‐uniformities relative to EDR2 film. The blue‐channel correction considerably improves the uniformity of EBT2 response and reduces the film‐to‐film response variation relative to the net OD method. The uniformity of EBT2 is independent of post‐exposure time. The blue‐channel correction can be used to reduce uncertainty in relative dosimetric measurements with EBT2 film.
SU‐E‐T‐130: Evaluation of Optically Stimulated Luminescent Dosimeters as An In‐Vivo Dosimeter for Breast Surface Dose Measurement
Authors: Harrop S , Cao F , Kohli K , Harvey E , Dubrowski P
Published: November 2011

Purpose: Evaluation of the optically stimulated luminescence (OSL) system for surface dose measurement for breast radiation therapy techniques. Methods: Landauer InLight OSL were calibrated on a Varian 21EX linac using an ion chamber with 6 MV beam. The response of OSL, TLD and a parallel plate chamber were compared at the surface of a solid water phantom and also under reference conditions (10×10cm2 at depth 5cm). OSL angular dependence, reproducibility, linearity, and inter‐OSL variability were investigated. Radiation therapy treatment plans were generated for an anthropomorphic breast phantom (RANDO). Eleven locations were identified and 2 OSL and 3 TLD were placed at each location. Treatment was delivered under clinical conditions. The OSL and TLD were evaluated for dose response. Results: The average response of the OSL to dose as compared to the ion chamber was found to be within 6% under reference conditions and the TLD within 2.5%. The factor of surface response to response at depth was found to be 0.284 for the Markus chamber, 0.425 for the OSLˈs and 0.434 for the TLD. No angular dependence was found for the OSL. The reproducibility of the batch response given 100 cGy was within 1%. The linearity of the OSL displayed an R2 value of 0.9997. The OSL given 100 cGy under reference conditions had a maximum deviation from average of 2.6%. Discrepancies on the IMRT plan between TLD and OSL ranged from 0.1% to 6.5% for the dose>50cGy and between 3.5% and 38.9% for the dose≤50cGy Conclusions: OSL and TLD are over‐responding to surface dose with respect to the parallel plate ion chamber. OSL have been found to respond similarly to TLD at the surface of an anthropomorphic phantom.
SU‐E‐T‐132: Commissioning Integrated System in High‐Dose‐Rate (HDR) Brachytherapy
Authors: Saw C , Juliano J , Wagner H
Published: November 2011

Purpose: Because of the delivery of large doses in a few fractions, any deviation generally results in a medical event for HDR brachytherapy. NRC Section §35.633 on full calibration measurements requires among others, the determination of (a) source positioning accuracy, (b) length of transfer tubes, (c) length of applicators, and (d) function of the transfer tubes, applicators, and transfer tube ‐ applicator interface. While the determination of the individual parameters may be acceptable, the use as an integrated system may fail resulting in medical events reported to NRC. Methods: A treatment plan was designed to check the integrity of the integrated system consisting of the applicator connected to the HDR remote afterloader unit via designated transfer tubes. In this fashion, data entry of both the length of the applicator and the dwell positions must be entered into the treatment planning system. The first dwell position was set at the extreme end of the applicator. A series of dwell positions of equal or unequal spacing was set to track the pathway of the applicator. During dose delivery, the applicator was placed over a film or digital radiograph. Results: The successful completion of the dose delivery assures that there are no obstructions and confirms the integrity of the interconnectivity of the HDR unit, transfer tubes, and applicator. The radiograph allowed an evaluation of the maximum extent of the travel of the source relative to the applicator and thereby validating the data entry on the length of the applicator, dwell positions, and dwell spacing. In addition, the radiograph also revealed the travel of the source within the applicator. Conclusions: Commissioning using end‐to‐end testing of an integrated system should be applied to HDR brachytherapy. This process would have eliminated a number of medical events recently reported.
SU‐E‐T‐136: Measure the Actual Radiation Dose Delivered for Prostate IMRT Treatment Using An Implantable MOSFET Dosimeter
Authors: Cao J , Showalter T , Buzurovic I , Peng C , Harrison A , Xiao Y , Yu Y
Published: November 2011

Purpose: To report the initial clinical experience using an in‐vivo, implantable metal oxide semiconductors field effect transistors (MOSFET) dosimeters for the daily dose verification of prostate IMRT treatment.Methods: The dose verification system (DVS) from Sicel Technologies was used to measure the actual dose delivered for prostate IMRT patients. Fifteen patients (10 prostate IMRT; 5 Sequential IMRT, pelvis then prostate) were implanted with two DVS dosimeters in the prostate gland: one on the right and the other on the left. The location of the DVS dosimeters were identified on the CT images and the expected doses were calculated. The measured readings of the dosimeters were compared to the expected dose values. Daily orthogonal portal film or CBCT was used for patient setup.Results: The average difference between predicted and measured doses was 1.1% for all 15 patients (30 dosimeters) over the whole course of treatment. The range of the difference between the measured cumulative doses to the planned doses for the whole treatment course was from −5.3% to 5.1%. For three out of fifteen patients, a new plan was created as the measured doses disagreed with the expected value for the original plans. For those three patients, the difference between measured and the predicted doses was as large as 11.3%. The discrepancies were much smaller after replanning. The average dosimeter measurement for the nine prostate IMRT treatment (exclude one prostate IMRT patient who had been re‐planned) over the course of treatment was decreasing signifying a possible decrease in the sensitivity of the dosimeters Conclusions: This study demonstrated DVS dosimeters could provide valuable information about actual dose delivered and actual dose fluctuations of the daily treatment. The DVS dosimeters could serve as a patient specific quality assurance and guidance for adaptive radiation therapy.
SU‐E‐T‐139: Note on the Underestimation of the Dosimetrical Significance of Detected IMRT Verification Deviations Using the Gamma‐Index Method and a Global Acceptance Criterion Based on the Number of Passing Points
Authors: Poppe B , Looe H , Luellau T , Willborn K , Allgaier B , Harder D
Published: November 2011

Purpose: Possible underestimations of the dosimetrical impact of Gamma‐Index detected dose deviations due to the choice of the maximum dose in the analysis plane as the reference value are analyzed. It is shown that clinical relevant deviations can be thereby missed in possible projections of organs‐at‐risk as low dose regions. Furthermore global criteria based on the number of points passing a verification procedure may be not sufficient to guarantee the detection of dose deviations within relevant areas of the patient. Methods: Clinical relevant dose deviations are introduced in some IMRT plans. Measurements are performed with the 2D‐ARRAY and analyzed by the Gamma Index method by normalization to the maximum and local dose in the plane. The acceptance procedure is performed according to guidelines recommending a fraction of approximately 95% accepted points to accept the plan. A point‐by‐point evaluation is performed to further analyze if the failing chambers may have a relevant impact on organs‐at‐risk. Results: Referencing relative doses to the “maximum dose in plane” tends to underestimate the deviations in the low dose regions. These regions are often in the beam projection of organs‐at‐risk, therefore possible impacts may be overseen. Even under tight acceptance criteria for the “global fraction” of points failing the analysis, relying on only this criterium may not be sufficient. We have started to re‐evaluate the dose deviations on a chamber‐by‐chamber basis, regarding them as screening values for detection of relevant deviations. Conclusions: In situations in which deviations in low dose regions may indicate a dosimetrical impact on critical structures, a local normalization procedure should be used. In addition to the global acceptance criterion of an IMRT treatment plan verification, we consider the single‐chamber failings of the Gamma‐Index analysis as screening values for actual dosimetrical impacts in the patient.

One of the co‐authors works for PTW. However there was no funding for this study.
SU‐E‐T‐147: Scintillating Fiber Array to Determine the Proton Beam Range
Authors: Hwang U , Shin D , Song M
Published: November 2011

Purpose: To develop the scintillating fiber array dosimeter to determine the proton beam range for the purpose of quality assurance of the patient in the proton therapy. Methods: A scintillating fiber dosimeter was composed of a commercial scintillating fiber optically coupled with organic based optical fiber. An array of scintillating fibers was settled inside a water bath. The scintillating light was amplified by photo multiplier tube before being gathered by commercial data acquisition system. Bragg peak and SOBP was measured with scintillating fiber dosimetry. The correction of the signal between the dosimeters and quenching effect of each dosimeter itself were conducted in home‐made software. The results were compared with the ion chamber.Results: The signals from each scintillating fiber dosimeter showed randomly distributed along the depth. After calibrating between the dosimeters, the signals showed similar curve to Bragg peak and SOBP. Then correcting the quenching effect made the signal to coincident with the icon chamber results Conclusions: We improved the scintillating fiber optic dosimetry system which is previously developed in scanning type to the array type. The developed dosimetry system can provided more applicable and faster way to determine the proton beam range.
SU‐E‐T‐163: Characterization of the Response of Active Detectors and Passive Dosemeters Used for Dose Measurement in Small Photon Beams
Authors: Derreumaux S , Bassinet C , Huet C , Chea M , Boisserie G , Brunet G , Baumann M , Trompier F , Roch P , Clairand I
Published: November 2011

Purpose: To characterize the response of detectors used for the dosimetry in small photon beams, especially for stereotactic radiation therapy. Methods: Measurements were performed with active detectors dedicated to the dosimetry in small fields (high resolution diodes IBA SFD, Sun Nuclear EDGE, PTW 60016 and PTW 60017; PTW 31014 0.015 cm3 PinPoint chamber, PTW 31018 microLion liquid chamber and PTW 60003 natural diamond) and with passive dosemeters suitable for small fields (TLD micro‐cubes, EBT2 radiochromic films). They were irradiated in a Cobalt 60 beam for investigation of reproducibility and drift and for study of the response as a function of the dose, in X‐ray linac beams ranging from 4 to 18 MV for study of the response as a function of the beam energy and as a function of the dose rate, and in small and large 6 MV X‐ray beams of different irradiating systems for study of the influence of beam size. Results: Regarding the reproducibility of the detector response, diodes give the best results, especially the EDGE and the PTW 60016 diodes with reproducibility better than 0.3%. The SFD diode reveals problem of stability, with sudden unexplainable large drift of the response. Both the PTW diodes undergo a slight variation of the response as a function of the dose rate. The detectors showing the highest variation of the response as a function of beam energy are the unshielded diodes. On the contrary, shielded diodes reveal more important impact of their non tissue equivalent composition on the measurement of output factors in very small fields (Huet et al., 2011; Bassinet et al., 2011). Correction factors depend on the measurement depth. Conclusions: This study will help to determine an optimized methodology for the measurement of the data characterizing the small photon beams used in radiotherapy.
SU‐E‐T‐168: Variations in Dose Response of Gafchromic EBT2 Film Scanned in Transmission and Reflection Mode
Authors: Park S , Kang S , Cheong K , Hwang T , Lee M , Kim K , Oh D , Bae H
Published: November 2011

Purpose: 2D planar dosimeter, radiochromic film has commonly been used to perform patient quality assurance (QA). It is our aim to investigate the properties of new EBT2 film scanned in transmission and reflection scanning mode. Method: We compared the transmission and reflection scanning mode of EBT2 (Lot No. A07160901) film with an EPSON expression 1680 pro flatbed scanner. Films were cut up into 3×3cm, 2 and irradiated from 20cGy to 700cGy using a 1 0 × 10cm, 2 field size with 6MV and 10MV photons for calibration. The red channel was confirmed to provide the greatest sensitivity and was used for all measurements. We investigated the effect of an absolute dose and film orientation using film pieces which were delivered 100cGy, 300cGy, and 500cGy at the depth of maximum dose in a phantom. The EBT2 films were irradiated with 6MV and 10MV photons for intensity modulated radiotherapy (IMRT) QA and compared with the films which have left under different room light conditions. Result: A maximum dose variation was −9.7% in transmission mode and 6.6% in reflection mode respectively. The maximum standard deviation in a region of interest (ROI) was 2.2% in transmission and 3.6% in reflection mode. The transmission scanning readings show strong film orientation dependency compared with reflection readings. In addition to, readings in transmission scanning mode are more sensitive to room light than that in reflection mode. Conclusion: Transmission scanning mode is conventionally used for the purpose of patient QA using EBT2 film. However, the mode is sensitive to the orientation of the film nd room light. Reflection scanning mode has the long term stability of the film readings and a relatively low orientation effect on EBT2 film. On the other hand, the large standard deviation of absolute dose in reflection mode is a drawback in providing high‐precision dosimetric information.
SU‐E‐T‐170: Development and Testing of a Single Exposure Film Calibration Procedure
Authors: Niedzielski J , Kry S , Childress N
Published: November 2011

Purpose: To develop and test the sensitivity of a single exposure film calibration procedure using a dynamic wedge. Method and Materials:A 60o dynamic wedge was used to expose EDR2 film and generate optical density (OD) to dose calibration curves in DoseLab Pro. Doses between 50 and 500 cGy were examined. Dosimetric data was generated from a Profiler2 diode array. This calibration curve was compared to one generated by the standard approach of irradiating 8 separate sheets of film to known doses. The sensitivity of the wedged‐film calibration procedure was also tested through the following 4 investigations. First, film measurements were repeated 10 times to determine the variability of the film response. Second, profiler measurements were repeated 10 times to determine the variability of the profiler response. Third, positional offsets of the profiler were investigated (up to 4mm off‐center — the size of the diode spacing). Fourth, different amounts of solid water build‐up were used (between 1 and 10cm) above the profiler and corresponding film. Results: The calibration curve generated with the wedge exposure compared very well to that generated with the standard 8‐film approach, being less than 2.5% locally different (0.8% relative to maximum) at doses above 50 cGy. Irradiation of multiple films introduced a maximum deviation of 1.2%, while multiple profiler measurements introduced a maximum deviation of 0.5%. Shifts in the position of the profiler introduced a maximum error of 3.0%. These deviations represent good robustness of the calibration procedure. Consistent calibration curves were generated regardless of the extent of build‐up material used. Each film exposure and software analysis was completed in 1 minute and 5 seconds, respectively. Conclusions: This work has developed a single exposure film calibration procedure. This offers physicists a rapid and robust film calibration method.
SU‐E‐T‐184: Usefulness of Triple Channel Correction for Gafchromic EBT2 Film on Patient Specific Quality Assurance of IMRT and IMAT
Authors: Hayashi N , Watanabe Y , Malmin R , Micke A , Kato H
Published: November 2011

Purpose: Triple channel correction acquisition (TCCA) is a model‐based method for obtaining the characteristic curve of Gafchromic EBT2 film (EBT2). In this study the TCCA method was applied to EBT2 film dosimetry of intensity modulated radiation therapy (IMRT) and intensity modulated arc therapy (IMAT). Method and Materials:EBT2 films were calibrated by a field‐by‐field method in 13 steps. All films were scanned by using flat‐bed scanners at one day after the irradiation. Seven characteristic curves obtained by the TCCA method were compared with those of a single channel acquisition (SCA) method. For clinical applications, the planar dose distributions of IMRT and IMAT plans were compared with dose distributions measured with EBT2 films. The film analyses were performed by applying both TCCA and SCA. We chose two IMRT plans and two Varian IMAT (RapidArc) plans, which were created by the BrainLAB i‐plan and Eclipse Varian treatment planning systems for IMRT and RapidArc, respectively. Results: The constancy of the characteristic curves obtained by TCCA was better than that of SCA. The most significant difference between the characteristic curves of TCCA and SCA was observed in a low dose range between 25 cGy and 100 cGy. The results of clinical cases demonstrated that the dose difference between the measured and planned doses in high dose gradient regions was smaller with TCCA than that with SCA. Conclusions: We showed that characteristic curves obtained by the TCCA method have a good constancy compared with those of SCA. The potential advantage of TCCA was seen in high dose gradient regions in clinically relevant IMRT and IMAT cases. Hence, EBT2 film dosimetry with the TCCA method can be used for high precision patient specific QA.
SU‐E‐T‐186: Evaluation of Optical Density Growth and Sensitivity of EBT1 and EBT2 Gafchromic Films on the Dosimetry for IMRT Quality Assurance
Authors: Hu Y , Ahmad S , Ali I
Published: November 2011

Purpose: To investigate the effects of optical density (OD) sensitivity and growth with time post‐irradiation on intensity‐modulated radiation therapy (IMRT) dosimetry with gafchromic films (EBT1 and EBT2). Method and Materials:EBT1 and EBT2 films were used to perform IMRT quality assurance, which were exposed to IMRT plans created in treatment planning system using 6 MV photon beam from a Trilogy Varian linac. Calibration films were exposed to graded doses from 78–399cGy in order to convert OD to dose. The films were scanned using a flat panel scanner several times starting from 4 to 480 hours post‐irradiation. Gray scale and red colors for both EBT1 and EBT2 films were used to evaluate film sensitivity on IMRT analysis. The IMRT films were analyzed with calibration films that were scanned synchronously and at different times post‐irradiation to quantify the effect of OD growth. Dose difference and gamma analysis of the dose distributions measured by film and calculated by treatment planning system were used to evaluate the effects of OD growth and sensitivity. Result: OD variations show that EBT1 grows slower, however, reaching higher values (14%) than EBT2 (13%) after long time post‐irradiation. The gray color values grow higher (13–14%) than red values (6%) for both EBT1&2 films after 480 hours. The results of dose difference and gamma parameter with more than 85% and 97% passing rates, respectively, using acceptance criteria (5%, 5mm) were better for films analyzed with synchronized calibration and red color values than non‐synchronized calibration and grayscale. Conclusion: The measurement of dose distributions agrees well with those calculated by treatment planning for synchronized IMRT and calibration films where variation due to OD growth is minimized. Red color values provide better gamma for IMRT analysis with EBT1&2 films because of lower OD growth and high sensitivity than gray color values.
SU‐E‐T‐187: A Dedicated Phantom for Electron Density Calibration and Image QA of Linac Cone Beam CT Options
Authors: Cossmann P
Published: November 2011

Purpose: In order to use linac Cone‐Beam‐CT (CBCT) data for dosimetric planning an electron density calibration is compulsory. Studies on available phantoms for CT performance checks/QA have shown that these are not sufficient for an adequate HU calibration. Therefore we designed a new dedicated phantom and carried out a planning study to determine the usability of such calibrated CBCT data in comparison with diagnostic CT data. Methods: Available linac CBCT options acquire in a single gantry rotation a volumetric CT data set. In order to 3D‐calibrate the system with regard to HU a special phantom has been designed to include the whole imager area. Removable inserts allow flexible positioning of the probes in x‐z as well as z‐direction. Furthermore a performance and image QA part according AAPM recommendations No. 1 has been integrated and evaluated. We compared 20 plan setups (10 in the pelvic and 10 in the thoracic region). Results: Within the field of view the HU variation is up to 5%. Towards the imager edges hounsfield units show small deviations relative to the imager center (max. 8%). Relative dose distributions in CBCT‐based plans show minor differences to plans calculated using a diagnostic CT image dataset (p=0.002) and absolute dosage deviations are within 1% (p=0.001). Image quality comparisons using the performance and image QA part showed that CBCT images are of lower quality than diagnostic images, i.e. spatial and low contrast resolution are 2–3 levels below. Conclusions: The newly designed phantom allows real 3D‐calibration of linac CBCT. It is made of water equivalent material and consists of probes with tissue equivalent materials. The phantom has additional scatter material to simulate a real patientsˈ situation. CBCT data can be used for treatment planning. Furthermore the image QA part allows to carry out recommended constancy checks in straightforward approach.

We received financial support from Varian Medical Systems to manufacture the prototypes.
SU‐E‐T‐188: Patient Specific Quality Assurance for Volumetric Modulated Arc Therapy (RapidArc) Using COMPASS 3D Dosimetry System
Authors: Arun G , Subramanian V Shanmuga , Swamy S Thirumalai , Kathirvel M , Ramalingam K , Kala S , Kumar S Ashok , Karthikeyan K , Anantharaman A , Kumar N Jagdish , Arivarasan I , Babaiah M.
Published: November 2011

Purpose: To implement the COMPASS (IBA, Inc) quality assurance (QA) system as a patient specific QA tool for Volumetric Modulated Arc Therapy. Methods: RapidArc is a treatment technique which produces conformal dose distribution by delivering the dose in a rotational fashion while simultaneously changing MLC position, dose rate as well as gantry speed. The COMPASS has the potential to calculate and display the delivered 3D dose distribution on a patient CT data by using beam modeling, dose map from detector measurements (I‐MatriXX Evolution) and dose map reconstruction using Collapsed Cone Convolution Algorithm. Dose maps for 10 Ten RapidArc plans were measured using I‐MatriXX Evolution with a gantry mount (SSD=76.2cm) along with gantry angle sensor. This device captures the RapidArc plan delivery in real‐time in a pre‐treatment QA context. The measurement data were read directly by the control software, which provides the ability to import patient plan data from the treatment planning system via DICOM export. The COMPASS software also provides the user a dose calculation engine, including a physics based head fluence model. The doses and dose‐volume histograms reconstructed from the fluence measurements were compared to the TPS calculated plans.Results: Maximum and minimum deviation of PTV Volume receiving 95% of the prescribed dose(V95%) was found to be −2.89% and 0.16% respectively and mean deviation −1.12%. Average deviation of maximum and mean doses of OARˈs (organ at risk) were −0.5880±0.012% and − 0.6952±0.011% respectively. Average 3D mean gamma for 3mm and 3% criteria was found to be 0.067±0.0013 and Maximum absolute dose deviation at isocentre was 1.3573% Conclusions: Compass system can be used as an accurate and visually enhanced patient specific QA tool for VMAT plans to provide a complete clinical relevance of dose discrepancies for better patient treatment.
SU‐E‐T‐191: Evaluation of a Commercial QA Device for Daily Output Check for a Large Multi‐LINAC Institution
Authors: Gao S , Balter P , Pollard J
Published: November 2011

Purpose: To quantify the difference between the daily output readings of a Daily QA device and monthly output readings and to determine at what frequency these devices need recalibration. Methods: Daily QA 3 (Sun Nuclear, Melbourne, FL) devices were used on 17 Clinac 6EX and Varian 2100C/D/EX LINACs to measure daily output over a period of 6 months for 2 photon energies and 5 electron energies for each machine. These devices measure output using an open ionization chamber that is corrected for temperature and pressure by internal sensors. The daily output was averaged each month across all days and compared to the monthly output readings taken using a temperature/pressure corrected farmer chamber and PMMA blocks. Results: The average difference across all energies and all machines across all months was 0.3% ±0.7%, indicating a good level of stability for slope was found to be consistent with a −.07% per month change in Daily QA 3 readings over the 6 month time period investigated. This change was not found to be a function of energy or radiation type (X‐rays or electrons). However, device‐dependent variation was noted in drift with values from ‐ 0.3%/month to + 0.1%/month. Conclusions: The data collected in this study indicates that although the Daily QA 3 device is a robust and simple to use machine capable of several tests, it would be prudent to verify these devices against a transfer quality dosimetry system monthly and recalibrate as necessary, with an expected frequency between 3 months and 1 year.
SU‐E‐T‐192: Spatial Accuracy Considerations in the Development of a Gamma Knife Quality Assurance Program
Authors: Vorndran L
Published: November 2011

Purpose: Spatial accuracy in a Gamma Knife SRS treatment plan is of utmost importance because of the single fraction high doses of ionizing radiation intended to be delivered to small volumes often times at close proximity to critical brain structures. Methods: Leksell‐Gamma Knife head frames and associated fiducial marker box attached to a phantom, as well as the MRI scanner were studied in this regard. Three phantoms with known geometrical accuracy were scanned. These included the ACR MRI accreditation phantom, GE MRI standard calibration phantom, and a specifically designed MRI phantom. The latter phantom consists of known size and positional coordinates of structures including a cone, cube, cylinder, and sphere. Observed measurements were made using a GE 1.5 tesla MRI scanner. Scanning was done following our standard protocol, i.e. T1 imaging, 512×512 pixels, 28×28 cm fov, and 1.5 mm slice thickness with no gap. All data was analyzed after being dicom transmitted to our Gamma Knife Treatment Planning computer. Results: We will show that over many applications of the head frame to patients, warping of the head frame can and does occur. Fiducial marker boxes are unlikely to warp or change the parameters of the copper sulfite tracks. The MRI scanner remains spatially accurate as long as a gradient field test is done routinely and attention is closely paid to the head coil and its associated small field gradient. This is generally accomplished during routine PMI by the manufacturer. Conclusions: Head frame alignment parameters dictate where the fiducial markers are actually found. If the fiducial marker parameters measured do not agree with the known position of the fiducial markers as stored in the treatment planning computer errors occur in the “Leksell” coordinate frame space. Clues will be provided indicating that the head frame has warped out of allowed tolerances.
SU‐E‐T‐195: Determination of Standard TG‐51 Calibration Factors for Matched Therapy Beams Over a Three Year Period
Authors: Rosenzweig D P , Meiler R , Gray A , Matloubieh A , Cavanaugh D , Clark D , Schell M C
Published: November 2011

Purpose: Analyze the calibration data, beam data and RPC dosimeter checks of x‐ray and electron beam data at the University of Rochester Medical Center over a three year period. The goal is to assess the accuracy and precision of patient dose delivery at the four radiation therapy sites in the system. Methods: The University of Rochester Medical Center operates a total of six dual‐energy Varian accelerators which have had their beam characteristics matched. Dose output is determined using four Exradin model A12 ion chambers. The values of the dose calibration factors defined by the Task Group 51 report are determined annually, where they exhibit small variations year‐to‐year and machine‐to‐machine. These variations are anticipated to be due predominately to measurement uncertainties. A study was initiated to extract useable standard values, as a means of improving our overall calibration uncertainty. We report on the measurements of the TG‐51 factors and an appropriate standard set of values determined from that data, for photon beams of 6 and 16 MV and for electron beams of 6, 9, 12, 16, and 20 MeV. Independent calibration measurements using the Radiological Physics Centerˈs services are correlated with our analysis to shed light on how using a standard set of chamber factor values affects overall calibration uncertainty. Results: The TG‐51 parameters vary typically by less than 0.5%. The x‐ray and electron beam characteristics vary by an average of 0.5% and the RPC dosimeter results averages are less than 2%. Conclusion: As a member of the Radiation Therapy Oncology Group, the University of Rochester data undergoes rigorous quality assurance through annual internal and external audits. Using standard values for TG‐51 factors, the dose delivery is accurate to between 1.5 to 2%, excluding uncertainties in the treatment planning systems.