bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐143: Quality Assurance of Complex Rotational and Stereotactic IMRT Treatments Using Gafchromic EBT2 Film
Authors: Kairn T , Aland T , Hardcastle N , Hill B , Kenny J , Knight R , Meldrum R , Middlebrook N , Tome W
Published: November 2011

Purpose: The accurate completion of reliable quality assurance measurements of complex intensity‐modulated and rotational radiotherapy treatments demands the use of a dosimetry system with both high resolution and minimal angular dependence. This study demonstrates the utility of Gafchromic EBT2 radiochromic dosimetry film for the quality assurance of complex radiotherapy treatments. Methods: This study establishes that the dose‐response of EBT2 film has minimal angular and depth dependence and then demonstrates how the film can be used to perform quality assurance measurements for BrainLab stereotactic IMRT, Varian RapidArc and TomoTherapy treatments. Results: For all treatment plans, the proportion of dose points agreeing with the film measurements to within gamma(3%,3mm) was found to be above 95%, with all points agreeing within 5%, indicating that the treatments were delivered with an acceptable level of accuracy. The film images also provided additional information on low‐level dose variations including: the location and extent of dose from inter‐leaf leakage (for RapidArc); the location and extent of helical field junctioning effects, or threading (for TomoTherapy); and the existence of small regions of under‐dosage from very small treatment segments (for stereotactic IMRT). Conclusions: The fact that these film measurements detected small‐scale dosimetric effects that were not apparent in the dose planes exported from the treatment planning systems confirms both the value of high‐resolution dosimetry and the importance of designing complex radiotherapy treatments with the maximum achievable level of target dose homogeneity.
SU‐E‐T‐146: Uncertainty of Stopping Powers of Tissue Equivalent Materials in Uniformly Scanned Proton Beam
Authors: Butuceanu C , Athar B , Baillie N , Duvvuri S , Keppel C , Lee T , Nazaryan V , Shahnazi K
Published: November 2011

Purpose: To quantify uncertainties associated with the extraction of CT HU to stopping power conversion curve for tissue equivalent materials in uniformly scanned (US) proton beams. Methods and Materials: The Philips Gemini TF Big Bore PET/CT scanner at the Hampton University Proton Therapy Institute (HUPTI), was used to extract the HU numbers for several tissue equivalent materials in the CIRS M062 phantom. Proton stopping power for each material was extracted by measuring the range change with and without the material, in a US proton beam pristine Bragg peak, and comparing to its physical thickness. The in‐beam measurements were performed using a Multilayer Ionization Chamber device (IBA Dosimetry, Zebra). Data were analyzed using both IBA OmniPro Incline and an in‐house software analysis package. Several proton beam energies were used: 143 MeV, 175 MeV, and 210 MeV. For each material and energy the difference between measured and predicted value of the stopping power was quantified. Results: The difference between measured and calculated stopping power with proton energy was found to be within 1–2.5 percent. The upper value of this variation was added to the machine specific systematic error of the CT HU number and quantified as the uncertainty of the CT HU to proton stopping power conversion curve. It was added to the total uncertainties (proton range and lateral profile), when PTV margins were implemented in the TPS. Conclusions: The relative linear stopping powers of 9 different tissue equivalent materials were measured using a range of uniformly scanned proton beam energies. These values were compared with predicted stopping powers calculated using current prescriptions and quantified as uncertainties of the CT HU to proton stopping power calibration curve. This work supports the accuracy of the proton stopping power implementation in the TPS and implicit the accuracy of patient treatment at HUPTI.
SU‐E‐T‐149: 3D Proton Gel Dosimetry
Authors: Gorjiara T , Kuncic Z , Baldock C
Published: November 2011

Purpose: To evaluate the water equivalency of PRESAGE and genipin gel for 3D proton dosimetry. Methods: The GEANT4 Hadrontherapy example was modified to calculate depth doses in four different formulations of PRESAGE dosimeters and in water for a proton beam with a mean energy of 62 MeV. To compare the depth doses in each phantom, the water equivalent thickness (WET) was calculated for each PRESAGE dosimeter according to IAEA technical report 398. Results: Our GEANT4 results show that the maximum energy deposition occurs at 2.9 cm depth in water, at 2.7 cm in the two new chemical formulations of PRESAGE®, at 2.6 cm in the original formulation of PRESAGE®, at 2.55 cm in PRESAGETM and at 2.85 cm in genipin gel. The deposited energy in PRESAGETM is 15% higher than that in water, while it is approximately 5% higher than water in the new formulations of PRESAGE®. For the calculated relative dose versus WET, the new PRESAGE® dosimeters are in better agreement with the depth doses in water. At Bragg peak the maximum relative dose difference with that of water is up to 1% for the PRESAGE® formulation A and more than 2% for the PRESAGE® formulation B and C and the PRESAGETM dosimeter. For the genipin gel the maximum relative dose difference with water is less than 0.5%. Conclusions: The PRESAGE® dosimeters with the new chemical formulations are more water equivalent than the existing PRESAGE® and PRESAGETM dosimeters and are thus more suitable for accurate 3D dosimetry of proton beams. The depth dose in the genipin gel dosimeter shows better agreement with water than the PRESAGE dosimeters. Further experimental studies are planned to investigate possible saturation in the new PRESAGE® formulations and in genipin gel for high LET radiation fields.
SU‐E‐T‐153: Proton Linearity and Energy Dependence Studies of Optically Stimulated Luminescent Detectors for Remote Audits of Proton Beam Calibrations by the Radiological Physics Center
Authors: Cho J , Alvarez P , Followill D , Gillin M , Ibbott G
Published: November 2011

Purpose: Implement Optically Stimulated Luminescent Detectors (OSLD) into Radiological Physics Centerˈs (RPC) remote audit quality assurance (QA) program for protons. Methods: The OSLDs were aluminum oxide (Al2O3:C) nanoDots™ from Landauer, Inc. (Glenwood, IL.). A standard RPC remote audit electron phantom with detector inserts at two different locations with three scatter rings and slabs of water equivalent plastic phantom, added on top of the phantom to place both dosimeter locations within the SOBP, were used. Two nanoDots™ were placed in each detector insert of the phantom. For the linearity study, a 250 MeV proton beam with reference setup (FS = 10 × 10 cm2, 10cm SOBP) was used with the beam isocenter located between the two detector depths. Doses of 25, 50, 100, 200, 300, 350 cGy at isocenter were delivered. For the energy dependence study, doses of 200 cGy each were delivered with the reference setup for 250, 200, and 160 MeV proton beams. Co‐60 measurement was performed as a standardization process. The OSLDs were read on a MicroStar reader from Landauer between 5 to 7 days after irradiation. Results: The OSLD irradiated had a linear dose response of y=−8.3513E−5x+1.0084 with an R2 = 1.000 over the dose range where y=Kl (dose linearity factor) and x=dose. The energy dependence of the OSLD for the three different energies was less than 3% for the irradiation conditions and fluctuation for different OSLDs less than 1% for the same energy used for the RPC remote audit program. Conclusions: The OSLD showed a linear dose response and consistent energy dependence for three proton energies at the MD Anderson Cancer Center Proton Center. OSLD can be used to replace the TLD for RPCˈs remote audit QA program for proton beam output.

Work supported by PHS CA0 10953 and CA081647 awarded by NCI, DHHS
SU‐E‐T‐155: Evaluation of An in Vivo Device for Daily Patient Treatment Delivery Measurements Using a Varian Linear Accelerator
Authors: Buckey C , Myers P , Esquivel C , Mihailidis D , Mavroidis P , Gutiérrez A , Papanikolaou N , Stathakis S
Published: November 2011

Purpose: A clinical evaluation of a commercially available dosimetric device for in‐vivo monitoring of IMRT and VMAT treatments. Methods: The Device for Advanced Verification of IMRT Deliveries (DAVID) system (PTW, Freiburg, Germany) is a transparent multi‐wire harp chamber that can slide into the wedge slot of a Varian linear accelerator. Its 40 measurement wires correspond to the positions of the leaf pairs of a Millennium‐80 MLC, with a projected spacing at isocenter of 5 mm. The DAVID was inserted into the beam during deliveries of clinically approved IMRT and VMAT treatments. The ability of the DAVID to detect errors in MLC positions was tested by introducing small errors into the plans. The reproducibility of measurements was tested for several disease sites over a series of deliveries. Results: The reproducibility of IMRT and VMAT plans is good. The maximum deviation of any one leaf among all plans and all deliveries was 3.11% (IMRT) and −2.09% (VMAT). The maximum total deviation among all plans and all deliveries was 3.41% (IMRT) and −1.99% (VMAT). The average total deviation among all plans and all deliveries for IMRT was 1.35% ± 1.06% and for VMAT was 0.40% ± 1.35%. When intentional errors were introduced, the DAVID could consistently detect leaf position errors when the resulting gap differed from the plan by great than or equal to 1 mm. Conclusions: The DAVID system is a useful, reliable tool for daily in‐vivo monitoring of patient treatments. It is capable of detecting errors as small as 1 mm, and requires no additional time or effort by the treatment staff for data collection. The DAVID system can provide assurance that every fraction of an IMRT or VMAT treatment is being executed as planned.

This work partially supported by PTW (Freiburg, Germany).
SU‐E‐T‐162: Dosimetric Comparison of Radiochromic Film and Diode Array Measurements for Quality Assurance of Small IMRT Fields
Authors: Ivanova T , Kassaee A
Published: November 2011

Purpose: To evaluate the effect of the dose distribution sampling on the outcome of the Intensity Modulated Radiotherapy (IMRT) Quality Assurance (QA) for the small fields. Methods: MapCHECK diode array (Sun Nuclear, Melbourne, FL) is routinely used for IMRT plans verification in our clinic. Dose distributions for ten plans with small field sizes ranging from 3 to 6 cm were measured using MapCHECK, satisfying our 3% and 3 mm distance‐to‐agreement (DTA) criterion for more than 90% of points above 10% threshold. The spatial resolution of 0.7 cm diagonally in the central region of the MapCHECK may result in as few as 20 or less sampling points. To increase the spatial resolution, we delivered the same plans to the MapCHECK, shifted 0.5 cm orthogonally, and merged the two dose distributions. Same fields were also delivered to the EBT2 radiochromic films (International Specialty Products, Wayne, NJ). Films were scanned using Epson Expression 10000XL flatbed film scanner with a resolution of 0.3 mm and calibrated for absolute dosimetry. The dose distributions with 3% and 3 mm DTA criterion were compared for as follows: plan with film, plan with MapCHECK and direct comparison of MapCHECK and merged MapCHECK distributions with film. Results: MapCHECK shows a slightly better agreement with plan than film dosimetry (mean percentage of passing points is 98.3% vs. 96.0%). The average percentage of passing points is 98.3% with standard deviation (SD) of 2.4% when comparing film with single MapCHECK measurements. This average is 97.7% with SD of 2.1% for MapCHECK measurement with merged fields. The increase of MAPCHECK sampling does not always results in improvement in agreement with film. Conclusions: The diode matrix may effectively replace the film dosimetry for small field sizes ranging from 3 to 6 cm.
SU‐E‐T‐164: Determination of Response Factors for Si‐Diode Detectors in Photon Fields
Authors: Sauer O , Parczyk M
Published: November 2011

Purpose: While for air filled ionization chambers an approximately energy invariant response leads to an approximately position invariant calibration factor, silicon diodes express over response for low energy photons. This results in too high signals at large depth inside a photon field and outside the geometric field. However use of a silicon diode is appropriate due to its high spatial resolution. We measured the behaviour of the calibration factor for different commercially available Si‐detectors and compared it with the behaviour of a small ionisation chamber (IC). The aim was to find a position dependent correction for Si‐diodes. Methods: Depth dose curves and profiles were measured for five different Silicon diodes; i.e. the Scanditronix field photon (ye) and the stereotactic detector (gr), the PTW electron (pe) and photon diodes (pp) and the Sun Nuclear edge detector (se). The standard field size, 10 × 10cm2 and a 0.8 × 0.8cm2 field were investigated. The energies were 6MV and 10MV. Results: To compare the depth dose measurements the signal ratios at 20cm and 10cm depth were calculated. The difference between the diode signals was less than 3%. The “pp” and the “pe” signals were the closest to the ionization chamber signal ratio at the 10cm field. for the profiles, besides the penumbra, the signals outside the geometrical field differed significantly form the IC signal. By appropriate averaging of the diode signals and division with the IC signal we could derive correction factors for the different detectors. For the large field this correction was smaller 1. For the small field the correction became greater than 1, but only at points blocked by the MLC only. Conclusions: We propose to measure virtually simultaneously with a diode and an IC in order to correct the energy and hence spatial dependent diode response factor. This correction is otherwise hardly predictable.
SU‐E‐T‐167: IMRT Pre‐Treatment Verification in the Build‐Up Region: Comparison of IˈmatriXX and EDR‐2 Film
Authors: Sharma S , Manigandan D , Subramani V , Julka P , Rath G
Published: November 2011

Purpose: Aim is to evaluate the response of IˈmatriXX and EDR‐2 films for the pre‐treatment verification of IMRT dose distribution in the build‐up region for superficially located targets such as carcinoma parotid. Methods: IMRT plans (6MV X‐rays, sliding window technique) were created for three previously treated patients of post‐operative carcinoma parotid using Eclipse treatment planning system (TPS). Generated fluence was transferred to previously scanned solid water phantoms by placing IˈmatriXX and EDR‐2(Extended dose rate) films at 0.5, 1.0 and 1.5cm depth. Six verification plans were created for each patient. Fluence was delivered by Varian CL2300C/D linac at 99.5cm, 99.0cm and 98.5cm source to detector distance (SSD) for 0.5cm, 1.0cm and 1.5cm build‐up depth. Dose distributions obtained with IˈmatriXX, EDR‐2 film and TPS were rescaled at 0.1cm resolution using OmniPro IMRT analyzing software. Initially, IˈmatriXX and films were calibrated at corresponding measurement depth. All measured fluence was compared with TPS dose plane by 2D gamma evaluation using 3% dose difference and 3mm distance‐to‐agreement (DTA) criteria. Results: The gamma function tests for IˈmatriXX and TPS were 98.30±0.81%, 99.97±0.60% and 99.97±0.62% for 0.5cm, 1.0cm and 1.5cm build‐up, respectively. The gamma function tests for EDR‐2 film and TPS were 98.58±0.84%, 99.92±0.14% and 99.96±0.14% for 0.5cm, 1.0cm and 1.5cm build‐up. The difference between point dose at the central axis for IˈmatriXX and TPS were 17.69±0.27%, 6.75±0.30% and 0.36±0.86%. IˈmatriXX was overestimating the dose than TPS at lesser depths and difference was decreasing with the increase of depth. For EDR‐2 Vs TPS, the point dose difference at the central axis was 0.52 ±0.18%, 4.5±2.0%, and 9.69±0.32% for 0.5cm, 1.0cm and 1.5cm build‐up. EDR‐2 was underestimating the dose than TPS, which increased with depth. Conclusions: IˈmatriXX results are comparable to EDR‐2 and may be used for the pre‐treatment verification of IMRT for superficially located targets.
SU‐E‐T‐172: Output Factors of a Cyberknife System : Comparison Between Measurements and Monte Carlo Calculations
Authors: Huet C , Bassinet C , Derreumaux S , Moignier C , Baumann M , Lacornerie T , Trompier F , Roch P , Clairand I
Published: November 2011

Purpose: Small photon beams used in radiotherapy are characterised by high dose gradients and a lack of lateral electron equilibrium. Thus, the measurement of output factors (OF) of these beams is problematic and OF measurements with different detectors for similar irradiation conditions can lead to a deviation up to 30% (Derreumaux et al., 2010). The aim of this study is to accurately determine the OF of a Cyberknife system thanks to measurements and Monte Carlo data. Methods: OF were measured on a Cyberknife for the 5, 7.5, 10, 20 and 60 mm diameter field sizes using active detectors (high resolution diodes (IBA SFD, PTW 60016, PTW 60017, Sun Nuclear EDGE), PTW 31014 Pinpoint chamber and PTW 60003 natural diamond) and passive dosemeters (EBT2 radiochromic films and TLD micro‐cubes). Correction factors for diodes (EDGE, PTW 60016, PTW 60017) and for the PTW 31014 chamber were calculated thanks to a recent methodology based on Monte Carlo data (Francescon et al., 2008 and 2009). The Cyberknife used in this study was modelled with Penelope and MCNPX Monte Carlo codes in order to determine the “true” OF. Results: For the smallest field size, a deviation of nearly 20% was observed between the values of the OF measured with the different detectors. The agreement between the passive dosemeters was better than 2%. After correction for diodes and for the chamber, the OF obtained with these active detectors agreed within 2% with the passive OF measurements. Conclusions: This study is encouraging concerning the determination of the output factors of the Cyberknife system. For the active detectors, the use of correction factors improves the accuracy in the OF measurements. The results obtained with the passive dosemeters in this study as well as in another study performed on a Novalis system (Bassinet et al., 2011) are promising.
SU‐E‐T‐173: Design, Development, and Evaluation of a Modified, Anthropomorphic, Head and Neck, Quality Assurance Phantom for Use in Stereotactic Radiosurgery
Authors: Faught A , Kry S , Luo D , Molineu A , Galvin J , Drzymala R , Timmerman R , Sheehan J , Gillin M , Ibbott G , Followill D
Published: November 2011

Purpose: To design, construct, and evaluate a modified anthropomorphic head phantom for evaluation of stereotactic radiosurgery (SRS) dose planning and delivery, for protocols developed by NCI funded cooperative groups. Methods: A phantom was constructed from a water equivalent, plastic, head‐shaped shell. Modifications from an original phantom design containing only a spherical target included the addition of structures resembling a nonspherical target (pituitary) and an adjacent (within 2mm) organ at risk (OAR) (optic chiasm) simulating structures encountered when treating acromegaly. A separate insert for treatment delivery contained two thermoluminescent dosimeters (TLD) for absolute dosimetry and radiochromic film in the sagittal and coronal planes for relative dosimetry. The target and OAR proximity provided a more realistic treatment planning and dose delivery exercise than the original design. To create an achievable planning criterion, the volume of the OAR receiving ≥8Gy was limited to 10%. The rigor of the treatment planning process, reproducibility of the dosimeters, and agreement with calculated doses were assessed through three GammaKnife irradiations. Results: The TLD results from the three irradiations agreed with the calculated target dose to within 4.3% with a coefficient of variation of 2.0%. Gamma analysis in the film planes showed an average passing rate of 99.9% and 99% using 5%/3mm distance to agreement criteria in the coronal and sagittal planes, respectively. A gamma analysis using 3%/2mm criteria showed the percent of total pixels passing to be 87% and 79% respectively. Conclusions: A modified anthropomorphic SRS phantom has been designed that provides a more realistic clinical planning and delivery challenge that can be used to credential institutions wanting to participate in NCI funded clinical trials.

Work supported by PHS CA010953, CA081647 and CA21661 awarded by NCI. DHHS
SU‐E‐T‐174: First Results from an Epid Based MLC QA Program on a Siemens Artiste
Authors: Haering P , Lang C , Schwahofer A , Stahl‐Arnsberger C , Schwamm F
Published: November 2011

Purpose: To present first results from an Epid based MLC QA Program done on a Siemens Artiste. Methods: In September 2010 a new MLC QA program started in our institute to replace previously film based positioning tests with Epid measurements. The tests were done on a weekly basis using a scatterblock and the Artisteˈs Epid. A SSD of 100cm was chosen to allow for the full maximum field size. A nineteen 2cm stripes MLC pattern was found be an optimum. Data evaluation was done with MLCSoftepid, PTW, Germany. This tool analyses the Epid data for all pictured leafs and is intended for a comparison to a reference data set, but can also check for nominal positions, which was employed here. To validate this new method, film based tests were done in parallel, although a comparison was difficult due to a different geometry and the film size used. MLC position data derived by MLCSoftepid were analyzed and plotted for different parameters. Results: The new workflow was easy to adapt and makes film processing and scanning dispensable. Also the evaluation was simplified as data were analyzed automatically. The evaluation distinguished a somehow wrong MLC calibration for the X1 side which was immediately corrected and would have been missed from the film evaluations. In contrast to that, the overall comparison of detected to nominal MLC positions showed a characteristic trend that was not seen in the film data. Detected positions varied strongly over the field position (up to .9mm) and were also different for both MLC sides. As this effect is not reported in literature for other MLCs, this behavior might be unique to the Siemens MLC and its special leaf end design. Conclusion: Epid based MLC QA is a feasible approach even if there are some limitations in absolute leaf position detection.
SU‐E‐T‐175: 3D Dose Verification of Varian RapidArc Treatment Plans by BANG Polymer Gel Dosimetry
Authors: Watanabe Y , Malmin R , Hayashi N
Published: November 2011

Purpose: To verify 3D dose distributions predicted by Eclipse treatment planning software (with AAA version 8.2.23) with those measured by polymer gel dosimeters for RapidArc intensity modulated arc radiation therapy. Methods: Treatment plans were created for RapidArc therapy of two prostate cancer patients. The daily fraction size was 180 cGy for both plans (R and E). The treatments used 10MV photon beams from a Varian iX linear accelerator. Two cylindrical phantoms (15 cm diameter and 15 cm long) containing BANG3‐PRO polymer gel were used. For dosimetric verification, QA plans were created using the CT images of the polymer gel phantom, which were obtained using 3‐mm thick slices. The phantoms were irradiated using the dose delivery techniques identical to those used for the patient treatments. After irradiation, the phantoms were scanned using a 32 spin‐echo technique with a 3T MRI scanner. The major imaging parameters were as follows: 1 mm × 1mm pixels, 45 2‐mm thick slices, and the echo spacing of 13.6 ms. The MRI images were processed to obtain 3D dose distributions using in‐house MATLAB programs. 3D dose distributions of measurements and calculations were compared using gamma index (3 % and 3 mm criteria), dose volume and dose difference diagrams, line dose profiles, and planer dose distributions. Results: Mean percentage differences between the measured and calculated doses in the 3D volumes containing PTVs were −3.1±11.9 % and 1.6±9.8 % for Plans R and E, respectively. The passing rates of the gamma index analyses were 90% and 84% for doses greater than 80% of the maximum doses of those plans. Conclusions: The current study has demonstrated a potential usefulness of polymer gel dosimetry for 3D dose verification of RapidArc plans. However, the agreement of measured and calculated doses was not satisfactory. The causes of the disagreements need to be investigated.

Japanese Society of Radiological Technology
SU‐E‐T‐178: Can a Portal Monitor Be Used for Screening of Population from Radiological Terrorism Events?
Authors: Fredrickson M , Yoshizumi T
Published: November 2011

Purpose: The purpose of this study is to obtain physics characteristics of a portal monitor and to study the feasibility of its use in a radiological emergency, more specifically from radiological dispersal devices (RDDs).Methods: Two Cs‐137 sources with activity of 0.953 μCi and 1.50 mCi were used. Two physics characteristics were investigated: (a) angular dependence outside of the portal monitor, and (b) distance dependence from sources outside of the portal monitor. Queue theory was applied to the physics characterization measurements in order to evaluate the utility of the portal monitor in a radiological emergency. Results: The portal monitor detected the low activity source outside of the portal monitor at various angles at distances between 0.2 m and 0.3 m. It also detected the low activity when it was 0.25 m from the center of the portal monitor. This measurement was repeated with the 1.50 mCi Cs‐137 source. We found that the 1.50 mCi Cs‐137 source could be detected 3.0 m from the center of the portal monitor and the exposure rate was measured to be 30 μR/hr at the center of the portal monitor. Assuming collective contamination with 100 mCi of Cs‐137 in the RDD scenario, the portal monitor would have to be placed approximately 40 m away from people waiting to be scanned. Additionally, portal monitors should be 10 m from each other if multiple are used Conclusions: The portal monitor is designed for the detection of small amount of contamination (∼1 μCi) for screening employees in commercial nuclear facilities. The portal monitor could be improved by adding shielding and collimation around the detectors and by decreasing the sensitivity for RDD applications. Without these improvements, the portal monitor cannot be deployed in a radiological emergency in urban areas because of the space needed to avoid false positive readings.
SU‐E‐T‐183: Validation of COMPASS System for RapidArc Patient‐Specific QA
Authors: Huang H , Tsai P , Huang Y , Yeh C
Published: November 2011

Purpose: Patient specific QA, one of important QA in radiotherapy, was performed with different devices in hospitals. It was commonly conducted with 2D array devices. To quickly and accurately verify 3D dose delivered is a big issue in clinic. The aim of this study is to validate the COMPASS system for dose verification for rotational and conventional IMRT technique as part of our clinical RapidArc QA program. Methods: Several RapidArc and IMRT cases with different treatment sites were chosen in this study. Each case was measured with MatriXX mounted on the gantry to reconstruct the 3D dose distribution in MultiCube phantom. In order to verify the COMPASS system, 3D dose measured in phantom was compared to that calculated in TPS. The MatriXX was setup on the treatment couch to obtain the 2D dose distribution as well. The OmniPro IˈmRT software was used to compare the measured 2D dose distribution with the results from COMPASS. Results: With 3D dose study, the average GAI (gamma agreement index) was 99.4+−1.0 (96.9∼100.0) for the comparison between COMPASS and TPS. The comparison results showed GAI was 96.5+−3.0 (87.8∼99.6) without detectorˈs angular correction and 98.4+−1.3 (95.2∼99.9) with the correction for the comparison between COMPASS calculation and 2D dose measurements. Conclusions: The COMPASS was validated by 3D dose studies in phantom. And, MatriXX was mounted and fixed on accessory holder of gantry which rotated with gantry to take fields responses; there is no gantry angular correction of detectors. Although the detectors in the MatriXX are ionization chambers, it combined with OmniPro IˈMRT software which implemented with function to correct angular dependence. We applied the angular dependence in our studies to improve the measurement accuracy. In conclusion, the COMPASS system is reliable and can be used in clinical QA program.
SU‐E‐T‐185: Passing Rates of 83 Patient‐Specific IMRT QA Measurements with ArcCHECK Using Various Gamma Criteria
Authors: Sintay B , Ramer T , Wiant D
Published: November 2011

Purpose: Three‐dimensional diode arrays are an important tool in patient‐specific intensity modulated radiotherapy quality assurance (IMRT QA) for arc therapy. We investigated the results of 83 patient‐specific IMRT QA measurements made on TomoTherapy using the Sun Nuclear ArcCHECK. Methods: Our ArcCHECK setup consists of a water‐equivalent plug and ion chamber at the center of the device. Planned dose is recalculated for ArcCHECK using the TomoTherapy planning workstation on the “Normal” setting creating dose voxels sized 4.8mm in each dimension. Patient‐specific IMRT QA measurements are made for all patients on TomoTherapy using megavoltage computed tomography to register the device. Analysis is performed in Sun Nuclearˈs MapCHECK software using various dose difference and distance gamma criteria using absolute dose (AD). The average passing rates, uncertainty, and upper/lower quartiles (UQ and LQ) of the data were computed. Four measurements deemed unacceptable were left in the data to determine the number of false negatives (FN) and false positives (FP) given when using various passing thresholds. Results: The average passing rates using gamma criteria 5%/5mm, 5%/3mm, 3%/5mm, 3%/3mm, 2%/5mm, 2%/3mm, 1%/5mm and 1%/3mm were 99.7 +/−0.5%, 98.4 +/−1.9%, 98.6 +/−1.5%, 94.9 +/−3.5%, 97.0 +/2.5%, 90.4 +/−5.1%, 94.1 +/−4.6% and 83.6 +/−7.1% respectively. The distribution of points passing using 2%/5mm (UQ 98.8 LQ 95.8) was significantly better than the typical criteria of 3%/3mm (UQ 97.8 LQ 92.7). 2%/5mm were the only criteria that gave no FN or FP using a percentage of points passing threshold of 93%. At this threshold 3%/3mm produced 21 FN and 1 FP. Conclusions: The performance of various criteria at or below the 3% dose difference threshold demonstrates improved results using 5mm as the distance parameter. This is likely due to the “Normal” dose voxel size in TomoTherapy and has led us to investigate using the “Fine” dose grid of 2.4mm.
SU‐E‐T‐190: Measuring Patient Cone Beam CT Dose Using a Commercial 4D Diode Array
Authors: Qin L , Alaei P , Zhang J , Chaudhari S
Published: November 2011

Purpose: To investigate the feasibility of measuring dose to patient from kilovoltage CBCT with the Sun Nuclear ArcCHECK device. Methods: The ArcCHECK QA device consists of 1386 diodes of 0.8×0.8 mm2 size geometrically arranged on a cylindrical phantom. The diodes are situated at depth of 2.85 cm acrylic build up and spaced 1 cm apart. A compact ion chamber was placed in the center of the ArcCHECK. A MV x‐ray based array calibration file was applied to our measurement. To validate the array calibration file in kV x‐ray range, an axial scan dose distribution from a CT‐scanner was measured using ArcCHECK. Absolute dose was calibrated according to AAPM TG61 protocol. Doses of different CBCT modes from VARIAN OBI were measured using ArcCHECK and ion chamber, including half scan (high‐quality head, pelvis spotlight) and full scan (pelvis, low‐dose thorax). Dose for pelvis mode was also calculated using Pinnacle Treatment Planning System (TPS) and compared with measurements. Results: For CBCT pelvis mode full scan, more than 80% of diode readings are in agreement with the calculation. The ion chamber measurement agrees with the calculation within +/−10% uncertainty. The doses from ion chamber measurement at the iso‐center are 1.3 cGy, 3.1 cGy, 3.0 cGy, and 0.8 cGy for high quality head, pelvis spotlight, pelvis, and low dose thorax scans respectively. The average reading of diodes at y=0 cm circle are 5.5 cGy for pelvis and 1.8 cGy for low‐dose thorax. The ratio between doses at center of the phantom to doses at depth of the diode‐position is 0.56 for pelvis mode (125 kV) and 0.44 for low‐dose thorax mode (110 kV). Conclusions: The CBCT doses measured using ArcCHECK for different CBCT scan modes are within diagnostic dose accuracy. With careful calibration ArcCHECK can be used as dosimeters for measuring CBCT patient doses.
SU‐E‐T‐193: EPID IMRT QA for Brain, and Head‐Neck Treatment Plans in Radiation Therapy
Authors: Vazquez‐Quino L , Fitzpatrick M , Chen X , Alkhatib H , Mavroidis P , Papanikolaou N
Published: November 2011

Purpose: Since amorphous‐silicon electronic portal imaging devices (EPIDs) availability the interest for radiation dosimetry use increases. In clinical quality assurance (QA) program, EPIDs has the potential to be used to verify IMRT plans in radiation therapy. The present study purpose is to test the use of an EPID phantom‐less method in clinical applications for IMRT. Methods: EPID images were acquired using a aS1000 EPID in the integrated mode, 6 MV beam, 600 MU/min dose rate (IMRT) . Signal intensity of EPID images were converted to dose map using a calibrated linear signal‐dose relationship. An EPID‐based QA system was designed, which includes IMRT Quality Assurance (QA). For IMRT and VMAT QA, a phantom‐less method was proposed, which used fluence maps reconstructed from EPID‐measured fluences as input to treatment plan system for dose calculation and comparison Results: Comparison of the calculated dose using EPID‐measured fluence to the plan dose for IMRT to a point and plane dose calculated by the TPS and measured by Ion Chamber were made for 16 patient specific QA plans. The EPID‐based IMRT method was able to verify the treatment plan and capture the reasonable plan‐versus‐QA comparison with a gamma analysis (3% maximum dose, 3mm) resulting in >99 % of points with a gamma <1 . EPID‐based QA dose matches well to the plan dose with similar contours. Point dose between EPID and Ion chamber measurements for IMRT plans were in average 2.24% for 16 plans including brain and Head/Neck cases. Conclusions: The results show that EPID may be properly used as a tool for clinical QA tasks and the developed EPID‐based QA system may be used for IMRT patient specific QA. Our method for EPID IMRT QA indicates the feasibility to use EPID measurements for daily patient QA verification.

Potential for Conflict of Interest: Research sponsored by Oncology Data Systems, Inc, Oklahoma City, OK
SU‐E‐T‐204: Real‐Time Monitoring of Age‐Related Macular Degeneration Radiosurgery Using Plastic Scintillation Dosimetry
Authors: Tien C , Cantley J , Hintenlang D , Bolch W , Firpo M , Chell E
Published: November 2011

Purpose: Age‐related macular degeneration (AMD) is the leading cause of vision loss and blindness among those over age 65. In its wet form, blood vessels grow from the choroid, causing macular tension and sometimes retinal displacement. As an alternative to monthly direct‐injection methods, Oraya Therapeutics has developed the IRayTM stereotactic radiosurgery device. This table‐top system has been validated in Monte Carlo simulations, human cadaver eye studies, pre‐clinical animal studies, and a phase 1 clinical trial. A plastic scintillation dosimetry (PSD) system was developed to monitor dose delivery in real‐time and provide measurement of total dose delivered. Methods: The IRayTM uses 100 keV x‐rays to deliver 24 Gy of macular dose, divided into three positions along the inferior pars plana. The PSDˈs small volume (0.5 mm diameter and 2 mm height), allows placement within the machine head. The PSD is fiber‐optically coupled to a photomultiplier tube via a plastic waveguide. Before direct characterization of the IRayTM, the preliminary PSD performance was tested using a portable x‐ray unit, mobile c‐arm fluoroscopy unit, and an ion chamber. Results: In order to avoid buffering issues, real‐time measurements used 250 ms bins, but can be adjustable to 10 ms. A calibration factor (CF) from PSD percent‐depth‐dose to ion chamber percent‐depth‐dose was 1.06 at a depth of 1.5 cm in solid water, the typical macular target depth. Counts‐to‐exposure CF varied less than 1% from 0.862 to 15.26R. Counts‐to‐exposure CF remained linear with R2 of 0.999 up to 16R even with varying dose rate (.002 R/s to 1.0 R/s). Conclusions: The PSD demonstrated linear dose measurements even at high dose and high dose rates. This study demonstrates the feasibility, accuracy, and precision of a PSD for clinical implantation in the IRayTM, a device for treatment of AMD.

This research was supported by a grant from Oraya Therapeutics, Inc.
SU‐E‐T‐205: Physical Model for in Vivo Dose Image Prediction
Authors: Chytyk K , Van Uytven E , Van Beek T , Greer P , McCurdy B
Published: November 2011

Purpose: To create a physical fluence model for portal dose image prediction that will be used to verify patient radiation treatment delivery. Methods and Materials: A physical fluence model was created to predict portal dose images. This model utilized Monte Carlo simulation and linac‐specific engineering schematics of the MLCs to create as accurate a model as possible. The fluence model consists of a focal and extra‐focal source, determined to be a Gaussian and Gaussian‐like function, respectively. The MLC transmission is calculated by attenuating a pre‐MLC BEAMnrc spectrum through the leaves; the MLC leaf‐tip and tongue‐and‐groove are modeled using the schematics. Incident energy fluence profiles from BEAMnrc are used to account for the field shape and beam horns. The asymmetric backscatter from the EPID arm is also modeled. The energy fluence is converted to dose using a superposition of EPID‐specific dose kernels. Scatter from the patient or phantom is approximated using Monte Carlo calculated scatter fluence kernels. The model is tested on simple slab phantoms for a variety of field sizes, thicknesses and air gaps. It was also tested on one field acquired during a patientˈs prostate IMRT treatment. Results: Predicted images with phantoms in the beam agreed within 2%, 2 mm in relative comparison with the measured images. After calibration of measured and predicted images to absolute units, the images agreed within 3% and 3 mm. The patient IMRT field predicted image was not ideal when compared to the measured image, mainly because the patient is heterogeneous. Conclusions: The physical fluence model, in conjunction with the patient scatter model, is accurate and could be used to verify patient treatment. The algorithm is versatile and can be applied to a variety of treatment scenarios.
SU‐E‐T‐206: A Patient Dose Monitor for a Proton Uniform Scanning Gantry
Authors: Nichiporov D , Klyachko A , Solberg K , Kunkler B , Eads A , Ball M
Published: November 2011

Purpose: Discontinuation by the manufacturer of construction materials and several known design imperfections of the existing patient dose monitor (PDM) in our gantry nozzle prompted a redesign of the PDM. We fabricated and tested a replacement prototype detector with an improved design that uses widely available materials and new fabrication techniques. For continuity of clinical operations, the prototype detectorˈs output factor and beam range attenuation are kept virtually unchanged. Methods: After fabrication, the prototypeˈs performance was tested for stability as a function of humidity. Contribution to signal from electrode leads (stem effect) was studied. Total detector thickness was measured by the beam range attenuation and detector response as a function of gantry angle was studied. The prototype PDM linearity in dose rate, charge collection efficiency, reproducibility of response, and output stability over the week were also measured. Results: After temperature correction, the response of the redesigned PDM is constant within +/− 2 % in the 20 % – 80 % relative humidity range. The stem effect is less than 1 %. The total water‐equivalent thickness of the new detector is 0.5 mm, reducing beam range by only 0.15 mm compared with the original PDM. The new detectorˈs output as a function of gantry angle is constant within +/− 0.5 % and the response is linear with dose rate in the 0.25 — 25 Gy/s range while charge collection efficiency is 0.999 +/− 0.002. Stability of the detector output throughout the week is 0.7 % and reproducibility for ten consecutive measurements is 0.16 %. Conclusions: The redesigned patient dose monitor has been tested to meet design goals, has improved performance characteristics, and can be used in a proton gantry uniform scanning nozzle.
SU‐E‐T‐213: Preliminary Testing of a 2‐D Fluence Measurement Prototype Device (Delta4‐AT) for In‐Vivo Patient Verification Dosimetry
Authors: Calvo O , Matzen T , Wright R , Gutiérrez A
Published: November 2011

Purpose: To perform preliminary sensitivity testing on the performance of a prototype device (Delta4‐AT) that measures the 2D linear accelerator photon fluence during IMRT treatments. The measured fluence is then projected onto the Delta4 phantom to assess the dosimetric impact. Methods: Two Smart‐Arc patient treatment plans were delivered on the Delta4 for pretreatment dose (PT) verification with the At‐treatment (AT) Delta4 prototype. The measurement process of Delta4‐AT is the same as the Delta4‐PT. Delta4‐AT acquires the fluence data and reconstructs a semi‐measured dose in the Delta4 geometry based on daily changes such as MLC position and output. To assess the sensitivity, MLC patterns for the two patients were modified to introduce two sets of known errors: 1) Systematic error—all leaves moved relative to isocenter, and 2) Random error— selected leaves shifted. Data was collected and an inter‐comparison of the TPS calculated dose, AT semi‐measured, and PT semi‐measured dose was performed. All data was analyzed using the Delta4 software. Results: Measurements showed a good gamma index (GI) agreement of 90.0% (3%/3mm) between the Delta4‐AT and Delta4‐PT when small discrepancies were introduced. When larger errors were present, a larger discrepancy existed between both measurement devices partly due to the decreased resolution of the prototype Delta4‐AT. Relative to the TPS dose, both showed good agreement within the GI criteria. Conclusions: The Delta4‐AT prototype together with the Delta4‐PT is a promising solution for the quantification of the dosimetric impact of daily variations in linear accelerators during IMRT delivery. The Delta4‐PT can serve as a vital, addon tool for patient dose verification.
SU‐E‐T‐214: Volumetric Particle Beam Quality Assurance
Authors: Utsunomiya S , Klein E , Karasawa K
Published: November 2011

Purpose: Quality assurance (QA) and dose output measurements for particle therapy, where the range varies across the field is a challenge. Our goal was to devise a system that was both accurate and efficient. Methods: We have utilized a MatriXX(IBA) device in a protective sleeve within water to measure absolute dose and profiles. The MatriXXcan be positioned remotely to various depths in water. For high energy electrons (using a custom compensator‐CC) and protons (range compensator) depths may be chosen according to the therapeutic ranges across the field. Measured data was compared to phantom calculated profiles using the IˈmRTsoftware (IBA). Two CC were constructed, CT scanned, and calculated, on top of a test phantom. The CC in front of a water phantom was irradiated with 20 MeV electrons. One CC was intentionally altered (added plastic narrow ring) to ensure a deviation could be detected. Setup and measurement times were recorded. Results: We found good agreement between measured absolute dose/profiles and calculations for two CCs at three depths (6.17, 8.17 and 10.17 cm). The Gamma index (3 mm, 3%) was calculated to be met over the majority of irradiated field. The MatriXX accurately detected the intentionally altered CC by for the measurement vs. the calculated plan. Setup and measurement times were reasonable for routine patient specific QA (∼5 min. per CC tested) excluding setup. Conclusions: The results indicate our measurement system using the MatriXX device in water was sufficient for measuring dose and profiles for electrons. We plan on performing dose output and profile measurements for proton patients when we go clinical in 2012. We anticipate performing QA for as many as 6 proton fields in <1hour. We have devised a measurement system that is accurate, efficient and sensitive to deviations.
SU‐E‐T‐216: Investigation of the System Performance of An Online Dose Verification Device
Authors: Asuni G , Rickey D , McCurdy B M
Published: November 2011

Purpose: To measure the detector response function of an online dose verification device and to validate our measurement by applying the detector response to Monte Carlo (MC) derived incident fluence. Methods: A transmission detector array (IBA Dosimetry, Schwarzenbruck, Germany) was recently developed as an IMRT quality assurance tool. To understand the detector system performance for verification of IMRT fluence, the detector response function at 6MV of a single ion chamber in the detector was measured with a narrow slit collimator. The narrow slit was formed by two 24 × 72 × 152 mm3 lead blocks, which provided a slit of 0.25 × 10 mm2. The LSF of the detector was obtained by laterally translating it in 0.25 mm steps underneath the slit. Two head‐and‐neck IMRT fields were also measured using the device. The same fields were simulated in our BEAMnrc MC model, and the MC incident fluence was convolved with the 2D detector response to obtain calculated dose. The measured and calculated dose distributions were then quantitatively compared using chi comparison (3%/3mm) for in‐field points (defined as those above 10% maximum dose). Results: The FWHM of the measured detector response for a single chamber is 4.3 mm which is comparable to the chamber diameter of 3.8 mm. For both examined IMRT fields, the Chi comparison between measured and calculated data show good agreement with 100% of in‐field points below a chi of 1.0 (chi <0.6 for IMRT field 1 and <0.12 for IMRT field 2). Conclusions: The detector response function for a new novel online detector has been measured at 6 MV using a narrow slit technique. The good comparison shown between measured and calculated dose of the two IMRT fields is a validation of our response function measurement.