bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐13: Radiobiological Model for Evaluation of Targeted Radionuclide Therapeutic Potential in Metastases Control
Authors: Martin‐Landrove R
Published: November 2011

Purpose: To provide a rabiobiological evaluation tool based on a mathematical model for control of metastases during treatment with the use of FDG beta emissions as therapeutic agent. Methods: Analytical and numerical solution of a nonlinear set of equations in order to describe the interaction between beta radiation and clonogenic transformed cells which are part of a primary tumor and related metastases. Under the consideration that beta emissions in this particular case can be taken as high LET radiation, the critical time and fraction number for local minima in the transformed cell population and can be found in closed form. Results: This theory can explain the observed behavior for the primary tumor and particularly for metastases in a mice‐melanoma experimental model, where 3 out of 7 of the treated animals showed no metastases. This result suggests the possibility of a fractionation scheme for total dose which can produce the same effect when repeated intravenous inoculations are provided at the proper critical time intervals. Conclusions: For metastases control with radionuclides, which are beta emitters like FDG as therapeutic agents, a treatment planning and follow up is possible from a quantitative point of view using a radiobiological kinetic model based on DNA damage mechanisms.

Funding was provided by the School of Physics, Faculty of Science and Consejo de Desarrollo Científico y Humanístico, Universidad Central de Venezuela and Física Médica C. A.
SU‐E‐T‐14: Predicted Biological Effectiveness of Treatments Delivered Using Dynamic MLC IMRT versus VMAT
Authors: Schmitt J , Wang Z
Published: November 2011

Purpose: Intensity Modulated Radiation Therapy (IMRT) is an effective method of maximizing dose conformity while minimizing damage to healthy tissue. The spatial effects of IMRT are commonly used as a technique to evaluate treatment quality. However, the use of spatial information alone neglects that cell survival is directly related to the temporal dose deposition. This study uses the linear quadratic (LQ) model, with the Lea‐Catcheside dose protraction factor in order to investigate the change in biological effectiveness between IMRT modalities, including sliding window (DMLC) and volumetric modulated arc therapy (VMAT). Methods: The dose‐time relationship was measured using Lucite phantom and an ion chamber. Measurements were taken for both prostate and head/neck plans. A specific coordinate was chosen in the tumor and the dose rate was measured as a function of time. The temporal dose deposition was used to calculate the dose protraction factor and the effective total dose (ETD) with varying repair half‐times and α/β ratios. The biological effectiveness was further studied using a Poisson model of tumor control probability (TCP). Results: Switching from VMAT to DMLC, for both the prostate and head/neck treatments, revealed a drop in the biological effects. A comparison of the DMLC and VMAT techniques showed a percentage loss of ETD for both anatomical sites. Differences in the protraction factor for DMLC and VMAT also contributed to a shift in the TCP model. The tumor control results revealed an overall increase in tumor control probability for VMAT compared to DMLC Conclusions: Comparing DMLC and VMAT techniques demonstrates that temporal dose deposition is an important characteristic in determining the biological effects from different treatment modalities. Although uncertainties in biological parameters prevents clinical application of these results this study still illustrates that the shorter treatment times characteristic of VMAT plans is preferable to the longer DMLC plans.
SU‐E‐T‐20: Differential Modulation of Antioxidant Defense System in Various Organs of Balb/c Mice by Whole Body Exposure to Low‐Dose Gamma Radiation
Authors: Pathak CM , Avti PK , Khanduja KL
Published: November 2011

Purpose: To evaluate the effect of low‐dose (< 50 cGy) whole body gamma irradiation on antioxidant defense system enzymes in the liver, lung and kidney of Balb/c mice at various post‐irradiation intervals. We examined the critical level of radiation dose and the degree to which these changes remain affected in these organs after irradiation. Methods: Young male Balb/c mice (5–6 wks), were divided into irradiated and non‐irradiated groups. Whole body irradiation was done with gamma rays from a, 60 Cobalt source at doses of 10, 25 and 50 cGy (48.78 cGy/min). Lipid peroxidation and antioxidant defense enzymes (reduced glutathione, superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase) were measured in liver, lung and kidney at 4, 12 and 24 hr after irradiation.Results: Lipid peroxidation increased by 1.38, 2.0 and 1.33 folds in lung, liver and kidney respectively at 12 hrs after exposure to 25 cGy. Reduced glutathione increased significantly in all these organs at 12 hrs after exposure of the animals at these doses as compared to control. Superoxide dismutase activity increased in liver and kidney up to 1.37 folds at 12 hrs of exposure at these doses. The antioxidant enzyme activities of catalase, glutathione peroxidase and glutathione reductase also increased between 1.1 and 1.3 folds in kidney and liver of mice at these doses. Interestingly, the activities of these enzymes remained unaltered in the lung after exposure of the animals at different doses Conclusions: Low‐dose whole body irradiation differentially modulates the antioxidant defense system in liver, lungs and kidneys of mice which may be due to variable sensitivities in activation of the related genes in these organs. The induction of endogenous glutathione immediately after exposure to low‐dose gamma irradiation, may be beneficial in protecting the cells from the reactive oxygen species (ROS) induced oxidative stress in various ROS‐related diseases

Funds for conducting this project were provided by Director, Post Graduate Institute of Medical Education and Research, Chandigarh, India.
SU‐E‐T‐33: Pydicom: An Open Source DICOM Library
Authors: Mason D
Published: November 2011

Purpose: pydicom is an open source package for reading and writing DICOM files using the python programming language. Methods: pydicom was first publicly released in Oct 2008, and has since had five version releases. Pydicom is a pure python package, installing and running on any platform on which python runs. DICOM structures are read and parsed into python data types, with the values and full details of the data elements accessible. Pydicom is hosted on a google code website (http://pydicom.googlecode.com), in a Mercurial distributed version control system, and is released under an MIT license. The website has an active issues list for requesting features and reporting bugs, a wiki section documenting how to install and use the code, example files, and a test suite. Performance profiling of reading files was improved greatly in the 0.9.4 release. Profiling of the code was analysed to find code bottlenecks and rework the slower sections. Results: Pydicom can read and write all standard DICOM files, including nested sequences such as found in DICOM RT files or in structured reports. The code has approximately 1200 downloads per release, and about 80 subscribers in an online discussion group. It is an installable module in the pythonxy distribution, and is used by other open source projects such as dicompyler, DiPy and RadPy. Performance profiling yielded an approximate three‐fold reading speed improvement, to approximately 3 seconds per hundred images, comparable to python file reading with no parsing. Conclusions: Pydicom is a mature library offering a reliable, simple reading and writing of DICOM files from python code. It has been actively developed over several years and has a solid base of users in imaging and therapy projects.
SU‐E‐T‐36: Sensitivity of Tumor Control Probability to Changes in Radiobiological Parameters
Authors: Knaup C , Mavroidis P , Stathakis S , Swanson G , Papanikolaou N
Published: November 2011

Purpose: Radiobiological parameters used to calculate tumor control probabilities (TCP) are known to vary among patients. It then becomes important to explore the effects different parameters have on TCP calculations. Here, the effect of different parameter combinations on TCP for several prostate seed implant treatments was explored. Methods: Forty‐four patients were evaluated. All patients were treated with Pd‐103 seeds and were planned on the Spot system. The prescription dose was 120 Gy. A post‐implant CT was taken for each patient and was used to create a tumor DVH. Using this information and different biological parameters, the linear‐quadratic model was used to calculate the biological effective dose (BED). The BED was then used to calculate the TCP. Combinations of the following biological parameters were evaluated: alpha/beta = 2, 3, 4 Gy; D50 = 30, 50, 70 Gy; and maximum normalized dose‐response gradient (gamma) = 2, 3, 4. The TCP for each patient was calculated for each of the twenty‐seven different combinations.Results: Combinations with the highest TCP at a given low BED were those were alpha/beta and gamma were high and D50 was low. Combinations with the lowest TCP at a given high BED levels were those were alpha/beta and gamma were low and D50 was high. Parameter values of alpha/beta = 2 Gy, D50 = 50 Gy and gamma = 4 provided TCP values that are consistent with realistic patient outcomes. These parameters yield an α value that was consistent with newer findings Conclusions: In this work, the sensitivity of TCP calculations on choice of biological parameters was evaluated for prostate seed implant patients. This was done by calculating the BED and TCP for the tumor. The parameters that best matched realistic clinical results were alpha/beta = 2 Gy, D50 = 50 Gy and gamma = 4.
SU‐E‐T‐43: Calculation of the Risks of Second Cancer and Cardiac Toxicities for a Pediatric Patient Treated with Photon and Proton Radiotherapies
Authors: Zhang R , Howell R , Giebeler A , Taddei P , Mahajan A , Newhauser W
Published: November 2011

Purpose: Although advanced radiation treatment methods deliver highly conformal primary dose, they will expose patients to stray radiation doses, which increases patientsˈ risks of radiation‐induced late effects. Second cancer and cardiac toxicity, two chief late effects of concern, can be physically and psychologically devastating to patients that survive their first cancer. There are limited comparative studies about second cancer risk for patients following photon and proton craniospinal irradiation (CSI), and there is a lack of predicted risk of cardiac toxicities for those patients. The purpose of this work was to calculate the risks of second cancer and cardiac toxicities after receiving photon and proton CSI therapies, based on realistic patient data, accurate dose calculation and latest dose‐response models. Methods: Treatment plans were created for both modalities for a pediatric patient with medulloblastoma. The risks of second cancer for radiosensitive organs and normal tissue complication probabilities (NTCP) for the heart sub‐structures were calculated using existing models and dose volume histograms (DVH) from commercial treatment planning system (TPS). Primary doses were taken from TPS directly, and stray radiation doses were obtained from measurements or Monte Carlo simulations. Sensitivity tests were carried out to test the sensitivity of the final results to the changes of dose‐risk relationship, NTCP model parameters and neutron radiation weighting factor. Results: The preliminary results showed that proton therapy generated much lower risks of second cancer and cardiac toxicities compared to conventional photon therapy, regardless of the changes of potential uncertainties in plausible ranges. Conclusions: The findings of this study suggest that proton therapy will confer lower risks of second cancer and cardiac toxicity compared to conventional photon therapy for children receiving CSI. Sensitivity tests strengthened our conclusion. This study is the prototype of an evidence‐based approach for selecting best treatment modality for pediatric patients.
SU‐E‐T‐45: Rectal Motion Simulations ‐ Exploring the Associations with Rectal Toxicity
Authors: Thor M , Apte A , Deasy J , Væth M , Muren L
Published: November 2011

Purpose: Rectum is the main dose‐limiting organ in radiotherapy (RT) of prostate cancer (PC). This organ displays considerable motion leading to uncertainties in the rectum dose‐volume histogram (DVH), which is likely to also influence the associations between rectal DVHs and toxicity. The aim of this study was to improve the understanding of how rectum motion influences these associations by introducing and applying a rectum motion model to generate ˈmotion‐inclusiveˈ DVHs. Methods: Varying amounts of random and systematic organ motion (“shifts”) were generated by altering the standard deviations (SDs) of normal distribution from 0.1 cm to 1 cm in steps of 0.1 cm. In order to simulate random shifts, we perturbed each dose fraction with a unique value of shift drawn from a normal distribution whose SD was proportional to the simulated random shift. The systematic shift was simulated similarly but with a normally distributed shift that remained constant over the entire course of trial. The delivered DVHs (dDVHs) were generated as a number of pseudo DVHs. The dDVHs were associated with prospectively registered late rectal larger than Grade 2 RTOG toxicity (dichotomized; minimum 5 year follow‐up) for a cohort of 232 PC patients treated using 35 dose fractions and compared to the planned rectum DVH (pDVH). The Spearmanˈs rank correlation coefficient (Rs) was used as a measure of the associations. Results: Systematic errors reduced the association at rectum volumes receiving doses above 40 Gy (V40) and doses less than the dose max. The Rs (V40) was insensitive to the magnitude of systematic and random errors. Random errors smoothed out the curve describing Rs vs. Vx. Conclusions: A model for simulating rectal motion has been presented and the corresponding DVHs investigated in relation to rectal toxicity. Systematic errors reduced the association above V40 and doses less than the dose max.
SU‐E‐T‐46: Evaluation of Different Cancer Risk Models on Second Cancer Risk Calculation for Conventional Breast Cancer Radiation Therapy
Authors: Joosten A , Bochud F , Matzinger O , Moeckli R
Published: November 2011

Purpose: To determine the influence of different cancer risk models on second cancer risk when these models are applied to full‐body dose distribution of two conventional breast treatments computed by Monte Carlo. Methods: Two conventional breast treatments (2‐fields and 4‐fields) were simulated in a full‐body voxelised anthropomorphic phantom with a Monte Carlo model of the Siemens Primus 6MV linac. Dose distribution for each organ at risk was extracted. Linear risk models from the ICRP 103 and BEIR VII were applied to the average dose of specific organs. Both cancer incidence risk and cancer mortality risk were determined for the BEIR calculations. Risks were determined when considering all organs together and out‐of‐field organs exclusively. In addition to these linear models, cancer risks were determined with non‐linear dose risk models applied to the full body dose distribution yielding “Organ Equivalent Doses” (OED). for all models used, both the absolute risks were determined for the two treatments and the relative risk between the two treatment plans. Results: The radiation‐induced second cancer risk ranged from 0.12% to 145% for the 2‐field treatment and from 0.84% to 458% for the 4‐field treatment depending on the choice of models. The calculated risks can be much higher than the values reported by epidemiological studies (2–4%). The ratio of risks between the two treatments varied from 1.2 to 9.1. Conclusions: Risk models should be applied with great caution. Great uncertainties underlie absolute risk calculations yielding unrealistic risks; therefore many investigators use the ratio of risk to compare different treatments. However, the ratio of risk between two treatments may also greatly vary depending on the risk models used. This may explain inconsistent findings on the potential increase in risk of IMRT techniques compared to conventional treatments.

This work was supported by the Swiss National Science Foundation FNRS 320000‐114101
SU‐E‐T‐117: Absorbed Dose to Water Measurement with a Sandwich Method for High Dose‐Rate Ir‐192 Brachytherapy Sources
Authors: Araki F , Yoshiyama F , Ohno T , Kakei K , Wulff J
Published: November 2011

Purpose: This study aimed to establish a standard dosimetry protocol for HDR Ir‐192 sources using an ion chamber calibrated with a Co‐60 beam. We developed a dedicated device for ion chamber measurements with a sandwich method and examined its measurement accuracy. Methods: A microSelectron‐v2 HDR Ir‐192 source was modeled with the EGSnrc/egs_chamber code. The accuracy of modeling was confirmed by comparing calculated results for gL (r) and F(r, angle) with those of TG‐43. First, an optimal source‐to‐chamber (SCD) separation for Ir‐192 dosimetry was determined from measurements with a PTW 31010 chamber at distances of 1.5–5 cm from the source center in water. The measured ionization chamber reading was corrected with the Monte Carlo‐calculated energy response for Co‐60 and Ir‐192, and was converted to the absorbed dose to water. The measured doses were compared with TPS values based on TG‐43. We developed a dedicated device for ion chamber measurements with a sandwich method at the optimal SCD separation. The average dose measured with two EXRADIN A1SL chambers was compared with the TPS value. Results: Calculated gL (r) and F(r, angle) values agreed well withthose of TG‐43. The absorbed dose to water measured with the PTW31010 chamber was 3% lower than that of TPS at a distance of 5 cm and was 3%– 7% lower at distances less than 5 cm. This was addressed to the uncertainty of the chamber positioning. We made a sandwich measurement device with the separation of 5 cm, considering the uncertainty of positioning and measurement time. The dose to water with the sandwich method was in agreement with that of TG‐43 within −1.2%. Conclusions: The optimal distance for ion chamber measurements was at 5 cm from the Ir‐192 source. The dose to water measurement with the sandwich method is useful for daily dose management for Ir‐192 sources.
SU‐E‐T‐121: A New Procedure That Simultaneously Measures Beam Energy and Beam Symmetry
Authors: Hsu H , Johnsen S
Published: November 2011

Purpose: To demonstrate a quality assurance procedure using a flat‐panel array that simultaneously measures the beam energy and beam symmetry, with one single measurement setup. Methods: The energy and symmetry of x‐ray and electron beams from TrueBeam (Varian Medical Systems) were measured at various bend magnet currents and steering coil currents, using a water phantom (Blue Phantom, IBA) and an ion chamber array (IC Profiler, Sun Nuclear). With IC Profiler, the energy was measured along the diagonal; simultaneously, the symmetry was measured along the transverse as well as the radial. For x‐ray, changes in energy were manifest as changes in the maximum off‐axis ratios along the diagonals at Dmax (“horns”). Horns were measured with IC Profiler and Blue Phantom, and compared to the depth dose scans. For electron energy, the “field size” was measured using IC Profiler with an aluminum wedge placed along the diagonal; the results were compared to the depth dose scans by Blue Phantom. The beam symmetries measured by IC Profiler were compared to the standard measurements by Blue Phantom. Results: For x‐rays, the diagonal “horns” changed approximately 1.2% measured by IC Profiler and approximately 1% measured by Blue Phantom. The same energy range changed the relative dose at 10 cm depth in water less than 0.4%. For electrons, the “field size” measured by IC Profiler increased 4 mm, versus R50 in water increased less than 2 mm, for the same energy change. Symmetries of x‐ray and electron measured by both devices were comparable. Conclusions: A single setup to measure beam profiles, accomplished with a flat‐panel array, can simultaneously detect whether the beam energy and symmetry are correct. The ease of setting up the array suggests that this technique could be made as part of routine QA procedures.
SU‐E‐T‐129: Angular Dependence and Its Correction of the MatriXXEvolution System for IMRT and VMAT Dose Verification
Authors: Shimohigashi Y , Araki F , Tominaga H , Sakata J
Published: November 2011

Purpose: The purpose of this study was to evaluate the angular dependence of the MatriXX Evolution and establish its correction method to improve the dose verification accuracy of IMRT and VAMT. Methods: The CT study was performed by inserting the MatriXX into the MULTICube, which was exported to iPlan. The regions of interest that correspond to the size and locations of the MatriXX detectors were configured in CT images. The angular dependence for the MatriXX detectors was measured with gantry angles 0°–180° at a field size of 30cm×10cm for 6 and 10MV photons. The correction factor (CF) was calculated as the ratio of the MatriXX dose to the Monte Carlo (MC) calculated dose for central detectors and detectors of every line, and was normalized at the gantry angle 0°.To verify two correction methods (central and entire correction), the MatriXX detectors was irradiated with gantry angles 0°–180° at different field sizes for 6 and 10MV photons. The results were compared with MC calculations by gamma index with 2% and 2mm using the OmniPro IˈmRT. Absolute doses for central and off‐axis locations were measured with a PTW31010 chamber inserted into the MULTICube, and were compared with the MatriXX doses. Results: The angular dependence of the MatriXX detectors reached up to14% and 11% for 6 and 10MV photons, respectively. The difference in CF between central and off‐axis detectors was up to 7% and 5% for 6 and 10MV photons, respectively. The entire corrected MatriXX doses agreed within 1.5% with those of a PTW31010 chamber for central and off‐axis regions. The passing rate for gantry angle 90° shows a significant deviation between central and entire correction methods. Conclusions: The dose verification accuracy of the MatriXX Evolution improved gamma index up to 10% by the use of the entire correction method that includes off‐axis detectors
SU‐E‐T‐131: Iterative Deconvolution of Dose Profile Measurements with Ionization Chambers Based on Lorentz‐Type Lateral Response Functions of the Detectors
Authors: Poppe B , Stelljes T , Foschepoth S , Looe H , Willborn K , Harder D
Published: November 2011

Purpose: In this work it is shown that the volume effect of ionization chamber can be corrected by the application of a van‐Cittert iterative deconvolution algorithm. Methods: Due to their volume effect the reading of an ionisation chamber s(x) can be considered as a convolution of the true dose distribution d(x) with the lateral response function r(x) of the detector. A prominent effect of this convolution is the broadening of profile measurements in the penumbra region. For the analysis a Lorentz‐type response function a bell shaped function with wide tails and free parameter l is assumed. Representations of the “true” dose distribution are measured with a diode detector (detector with minimal spatial spread of r(x)). The free parameter for the response function l is found by systematical variation and subsequent application of an iterative deconvolution algorithm. The iterative procedure consists of a sequence of approximations for n(x) which quickly converges towards the desired true d(x). Each n(x) is numerically convolved with r(x) and from the comparison of the result with s(x), the next approximation n+1(x) is derived. The best estimate for r(x) is found for the 1 resulting in the best approximation of d(x). Results: For cylindrical ionisation chambers with different radii and volume effect the lateral response functions for 6 and 15 MV photon radiation and a variety of field sizes have been analyzed. It is shown that the penumbra broadening can be revoked with a sufficient accuracy. Conclusions: By an iterative deconvolution algorithm with a pre‐defined Lorentz‐shaped lateral response function can calculate an approximation of the true dose distribution from ionization chamber measurements. The resulting corrected dose profiles may act as the input for base data determination for treatment planning systems and may thus improve the accuracy of calculated dose distributions.
SU‐E‐T‐140: Experimental Determination of the Effective Point of Measurement for Various Detectors Used in Photon and Electron Beam Dosimetry
Authors: KLooe H , Harder D , Poppe B
Published: November 2011

Purpose: To determine experimentally the effective point of measurement, Peff, for various detectors used in clinical dosimetry. Materials and methods: Peff was determined for six ionization chambers, the parallel‐plate Roos and Markus chambers and the cylindrical “PinPoint”, “Semiflex” and “Rigid‐Stem” (0.3 cm3 and 1 cm3) chambers, also for the 2D‐Array and an E‐type Si diode from PTW‐Freiburg. The tissue‐phantom ratio (TPR) curves of these detectors, measured with water‐equivalent RW3 plates (PTW‐Freiburg), were compared directly or indirectly with the “true” TPR curve acquired with radiochromic film (EBT 1), a detector of almost vanishing thickness. The shifts along the absorber thickness axis, needed to put these curves into the best possible coverage with the “true” TPR curve, is used to determine the shift Dz of the Peff from the detectorˈs reference point. TPR curves were obtained for 6 and 15 MV photon beams and 6 and 9 MeV electron beams. Results: For both the Roos and the Markus chamber: Dz = (0.4 +/− 0.1) mm. The cylindrical chambers show a systematic increase of quotient Dz/r with chamber radius r. Their Dz values: − 0.30 r, − 0.36 r, − 0.47 r and − 0.58 r for chamber radii 1.0, 2.5, 2.75 and 3.95 mm. For the 2D‐Array and the Si diode: Dz = (0.5 +/− 0.2) mm and Dz = (0.6 +/− 0.1) mm respectively. Conclusions: Our major finding is that Dz depends on the detector construction but remains invariant under changes of radiation quality and depth. This invariance can be shown theoretically to result from the premise that the displacement effect of a detector is caused by a perturbation of the measured value proportional to the gradient of the fluence of the directly ionizing particles.
SU‐E‐T‐141: Leaf Position Verification during Dynamic Beam Delivery of Volumetric Modulated Arc Therapy Using Electronic Portal Imaging Device
Authors: Sarkar B , Manikandan A , Holla R
Published: November 2011

Purpose: Volumetric‐modulated arc therapy is a technique for delivering intensity‐modulated radiation therapy using rotational beams. During delivery of the rotational beam, the field shape, created by a multileaf collimator (MLC), changes continuously. The objectives of this study were to verify the MLC positional error at some arbitrary intermediate point during delivery for different dose rates and MLC speeds. Methods: The Elekta Synergy‐S has a discreet dose rate, forty pairs of MLC. Dose rate, gantry speed, MLC speed is constant between two Control Points. The MLC Positions were verified with AmSi portal imaging. The leaf speed depends on three factors: ‐ dose rate, delivered MU and distance traveled by MLC. The leaf positions were verified for all combinations of available dose rates 35, 70, 140, 280, 560 MU/min and MLC speed of 0.5, 1, 1.5, 2, 2.5 cm/sec for a dynamically varying field size from 20×16 cm2 to 10×16 cm2 for a 0– 10 degree gantry rotation. Results: The largest MLC Leaf positional error found for 2.5 cm/sec speed for 35MU/min was −1.1±0.26 mm (95% Confidence Intervals‐CI). The minimum leaf positional error encountered for 1.5cm/ sec and 140MU/min was 0.03± 0.16 mm (95% CI). The single highest positional error was −1.31 mm. The maximum and minimum leaf positional error of all 25 sets results mean error of 0.36±0.72mm and − 0.08±0.67mm respectively with 95% CI. The MLC positional error depends on the MLC speed as well as dose rate also. Conclusions: 3.4% tested leaf positional errors found more than tolerance limit (±1 mm). It can be concluded that MLC positional error is higher in case of lower dose rate and highest MLC leaf Speed. The largest three errors (in descending order) encountered for highest speed 2.5 cm/sec and dose rate 35, 70 and 140 MU/min respectively. This clearly indicates lower delivered MU increases the Leaf positional error.

No Funding, support and no conflict of interest
SU‐E‐T‐144: Study of the Effect of the Optical Density to Dose Conversion Calibration Curves on the Measurement of Transverse Lateral Dose Profiles of Proton Beams Using Kodak XV Films
Authors: Sahoo N , Anand A , Martin C , Ciangaru G , Poenisch F , Li H , Gillin M , Zhu X
Published: November 2011

Purpose: To investigate the effect of the optical density (OD) to dose conversion calibration curves on the measurement of transverse lateral dose profiles of proton beams using Kodak XV films. Methods: A number of XV films were exposed to different doses in a 10 cm × 10 cm field of passively scattered range modulated beams of different incident energies. The films were placed at the center of spread out Bragg peak of the beam inside plastic water phantoms. The films were scanned by a Vidar Scanner using Scanditronix/ Wellhofer OmniPro‐Accept6.4 software. Different OD‐dose calibration curves were generated and compared. Transverse lateral dose profiles were obtained from an irradiated film using different OD‐dose calibration curves and were compared to evaluate the differences. The lateral dose profiles of proton pencil beam spots (PPBS) were also obtained using the XV films and one of these OD‐dose calibration curves and were compared with ion chamber measurement. Results: OD‐dose calibration curves obtained by giving same doses, but with beams of different incident energies were found to have differences in all dose regions. But, the relative lateral dose profiles (LDP) were not affected by the differences in the calibration curves. Thus, the incident energy of the range modulated beam is not an important consideration for obtaining the film OD‐dose calibration curves for relative LDP measurements. The XV film measured relative LDP of the PPBS agreed well with that from ion chamber measurement in the high dose region, but was seen to be noisier in the long tail region. Conclusions: OD‐dose calibration curves created with given doses from any range modulated passively scattered beam, irrespective of the energy of the incident beam, are found to be suitable for measuring the relative LDP of broad fields of passively scattered proton beams and PPBS with XV films.
SU‐E‐T‐154: Evaluation and Improvement of the ArcCHECK 3D Dosimeter
Authors: Kozelka J , Robinson J , Zhang G , Nelms B , Feygelman V
Published: November 2011

Purpose: To address important questions regarding calibration and use of the ArcCHECK (Sun Nuclear Corp) detector resulting from its hollow shape and cylindrical array geometry. The goals are to investigate how accurate different treatment planning algorithms are with the phantom containing a large air‐density inhomogeneity; to establish a method of calibrating the detector against an isotropic, energy‐independent dosimeter; and to develop a robust virtual inclinometer capable of providing uninterrupted beam angle information during arc deliveries. Methods: A PMMA shell accommodating an ion chamber at the diode position was designed to replicate the dimensions of the ArcCHECK phantom. The ratio of entrance to exit dose was measured and compared to calculations by five sophisticated commercial algorithms. Field size dependence of the diode response was measured at different locations in the phantom. A novel virtual inclinometer algorithm was designed based on the coincidence of dose grid images projected with attenuation on a common plane. A formalism of reading to dose conversion accounting for the field size and detector position dependence was developed. A practical method of measuring the positional dependence factors against an ion chamber in the actual phantom geometry was designed.Results: Philips Pinnacle CCC, CMS XiO Superposition and Monaco algorithms disagreed with the ion chamber by no more than 1.5%. XiO Convolution and Varian Eclipse AAA were off by >11%. Field size correction is position‐dependent and varies between the hollow and plugged phantom configurations. Virtual inclinometer is robust and deviates no more than 0.5±0.7° from the Dynalog record. An average disagreement is 0.5% between the diode and ion chamber dose measurements in a wide field Conclusions: Using hollow ArcCHECK phantom configuration with Eclipse AAA is not recommended. A robust positional correction based on the novel virtual inclinometer is feasible. Diode “reading to dose” formalism must include field size dependence.

This work was supported in part by Sun Nuclear Corp.
SU‐E‐T‐156: Fast Cone‐Beam Optical CT Scanning of a Radiochromic Solid Dosimeter for Clinical 3‐D Dose Verification
Authors: Hoogcarspel S J , Xu Y , Wuu C
Published: November 2011

Purpose: There is an urgent need for fast 3‐D dose verification for advanced radiotherapy techniques such as IMAT. This study is to evaluate the accuracy and clinical relevance utilizing a fast cone‐beam optical CT scanner with a radiochromic solid dosimeter, PRESAGE®. Methods: A first‐generation laser optical CT scanner, in conjunction with gels and radiochromic solid dosimeters, has been successfully used for 3‐D dose verification of complex treatments such as IMRT and radiosurgery. However, a major limitation with this type scanner is the long scanning time (8‐hours), which makes same‐day dose verification for treatment impossible. In this study three radiochromic dosimeters (PRESAGE®) were irradiated with 12Mev electron beam, 6MV photon beam, and 5‐field IMRT, respectively. Dose readout was performed using a Vista™ cone beam optical scanner (Modus Medical Devices Inc.). This scanner utilizes a LED diffuse light panel and a lens based CCD camera to capture a series of 2D optical projections through the region of interest while the object is being rotated 360°. Feldkamp filtered back projection was used to reconstruct the 3D dose map, with a spatial resolution of 1×1×1mm. Each dosimeter was scanned both before and after irradiation in order to eliminate artifacts caused by light scattering and dosimeter un‐uniformity. Dose distributions were compared with results from a first‐generation laser optical CT scanner and Eclipse planning system. Results: The PDDs measured with PRESAGE® and the beam data from Eclipse agree within 3% and 1mm. Comparison of the IMRT dose distributions between PRESAGE® measurements and Eclipse calculation shows 93% Gamma index passing rate (3%, 3mm criteria). The scanning time for a 3‐D dose map is less then 30 minutes. Conclusions: The Vista™ cone‐beam optical CT scanner and radiochromic dosimeter, PRESAGE®, has shown the potential for fast 3‐D dose verification.
SU‐E‐T‐159: Average and Maximum Doses in Thin Fricke Layers Irradiated with Soft X‐Rays
Authors: Austerlitz C , Campos D , Benhabib S
Published: November 2011

Purpose: To determine the relationship between maximum and average doses in thin Fricke layers irradiated with soft x‐rays. Methods: The MC code PENELOPE was used to modeling a Fricke solution pillbox‐like volume 0.30 cm thick and 1.5 cm diameter embedded in the center and flushing the surface of a 0.50‐cm thick, 1125 cm3 solid water thank filled with water. The pillbox was covered with a 0.0030 cm thick polystyrene film and the reference point for the absorbed dose calculations was its geometric center for all the simulations performed at a source‐detector distance of 30.0 cm using the PTB (Physikalisch‐Technische Bundesanstalt‐Germany courtesy: R. Kramer) calibration therapy TW30 kV, TW50 kV TW 70kV and TW100 kV spectra. The same procedure was followed with pillbox thickness varying from 0.0010 to 0.40 cm. For each x‐ray quality, the average energy per unit mass (average dose) in the pillboxes were normalized for the 0.30 cm thick Fricke solution and their maximum average dose values were assigned as being the CPE region. The effect of the beam divergence on the average dose and the water/Fricke dose relationship are being investigated. Results: As the thickness of the pillbox increases, the average dose increases, reaching a maximum after descending due to attenuation in the solution. With an uncertainty of ±0.3%, a deviation between the maximum and average doses of 17.0% (0.010‐cm depth), 5.2% (0.025‐cm depth), 0.23% (0.15‐cm depth) and 0.00% (0.30‐cm depth) were observed for 30, 50, 70 and 100 kV, respectively. Conclusions: As expected, different thickness of Fricke solution are required to determine the absorbed dose under CPE condition. Nevertheless, the data provided in this work may serve for absolute calibration of the Fricke solution using a similar setup, radiation qualities and the calculated relationship between maximum and average dose presented herein.
SU‐E‐T‐169: Modification and Implementation of the RPC Heterogeneous Thorax Phantom for Verification of Proton Therapy Treatment Procedures
Authors: Blatnica A , Ibbott G , Zhu X , Balter P , White R , Followill D
Published: November 2011

Purpose: To modify the existing RPC heterogeneous thorax phantom to assess lung tumor proton beam therapy procedures including patient simulation, treatment planning, and treatment delivery. Methods: A new dosimetry/imaging insert was designed for use with the RPC thorax phantom. The insert was constructed of extra heavy balsa wood with density from 0.30 – 0.34 g/cm3 and average HU of −670. A relative linear stopping power of 0.313 was measured. A tapered compression technique eliminated air gaps around the dosimeters. TLDs were positioned in the superior and inferior aspects of a unit density target and EBT2 radiochromic film was placed in three orthogonal planes. The phantom was imaged with a 16 slice CT scanner. A treatment plan with fields at 10 and 80 degree gantry angles and a 15 degree couch kick was designed with an Eclipse TPS utilizing apertures (expanded 10mm) and compensators (smeared 6mm). The plan was delivered three times with new dosimeters for each irradiation.Results: The ratio of measured dose to calculated dose was 0.947±0.009 (superior point) and 0.937±0.003 (inferior point). Gamma analysis utilizing 5%/5mm criteria showed 3 trial average pass rates of 86.7% (axial), 90.0% (coronal), 90.1% (sagittal) and 88.9% (3 plane average). DTA ranged from 0.9 – 2.4mm (axial), 0.4 –1.8mm (coronal), 0.6 – 1.9mm (sagittal). Conclusions: This work indicated that modifications to the existing RPC thorax phantom allowed the evaluation of proton therapy procedures. The differences in measured/calculated doses were higher than expected but consistent with previous experience with this phantom. Gamma analysis and DTA showed good results, with poor correspondence in the distal low dose regions of the treatment fields. Further analysis is underway to determine if the discrepancies reflect inadequacies of the TPS or limitations of the dosimetry system.

Work supported in part by PHS grants CA010953 and CA081647, awarded by NCI, DHHS.
SU‐E‐T‐177: RPLGD: A Navel Tool for TBI in Vivo Dosimetry
Authors: Lin C , Lin C , Huang Y
Published: November 2011

Purpose: After implementing a new total body irradiation (TBI) technique in clinic, in vivo dosimetry check is essential. We use a navel tool, radiophotoluminescent glass dosimeter (RPLGD), for in vivo dose measurement. It has superior physical and dosimetric characteristics than thermoluminenscent dosimeter (TLD). Method and Materials:Bilateral TBI is performed with the Siemens Prius Linac with a nominal energy of 6 MV photon beam. The patient is at the lying position and the source to midpoint of the patient is 415 cm. Water bags are used to compensate the change in body thickness and arms are positioned laterally at the mid AP‐thickness level to block the lungs. In vivo dose measurements were performed with RPLGDs placed bilaterally at five levels to obtain the entrance dose and exit dose : on brain, chest, abdomen, thigh and lower legs. The midline dose is the average of entrance dose and exit dose. The prescribed dose is 120 cGy per fraction to the umbilicus to a total of 1200 cGy. Results: The absolute dose measured on dose prescribed point is 123.6 cGy and the difference between the prescription and measurement is 3%. The dose at five different levels are normalized to that at the abdomen level. The relative doses of brain, chest, thigh and lower legs are 89%, 99%, 1.03% and 88% respectively. The absorbed doses at brain and lower leg levels may be overcompensated and these can be adjusted by modifying the thickness of water bags. Conclusions: In our preliminary result, RPLGD is an ideal dosimeter to perform the in vivo dose measurement, not only the better physical and dosimetric characteristics but the easy process without annealing and the ability to be readout repeatedly. Conclusion, the RPLGD is a useful tool to for in vivo dosimetry in clinic.
SU‐E‐T‐181: IMRT Quality Assurance ‐Evolution from 2D to 3D
Authors: Fan E , Qin L , Chaudhari S
Published: November 2011

Purpose: We evaluated the performance of a 3D diode device ArcCHECK (Sun Nuclear) for IMRT patient plan verification and compared the results with our current IMRT QA 2D diode array device MapCHECK (Sun Nuclear). Methods: The ArcCHECK QA device consists of 1386 diodes of 0.8×0.8 mm2 size geometrically arranged in 21 adjacent rings spaced 1 cm apart. An acrylic insert with an ionization chamber holder was plugged into ArcCHECK to form a 26.6 cm diameter cylindrical phantom. A compact ion chamber was placed inside the holder to measure dose. Seven IMRT patient plans generated using Pinnacle 9.0 were evaluated for this study, including 3 Head & Neck, 3 prostate and one whole pelvis. Actual beam angles were used for ArcCHECK QA plans, but set to 0 degrees for MapCHECK. Gamma criteria of 3%/3mm were used for analysis. Results: Results using our gamma criteria fall between 90.4% to 96.8% for ArcCHECK and 96% to 100% for MapCHECK. For 3 Head & Neck plans ArcCHECK achieved 96% or above pass rate using our gamma criteria, very similar to our MapCHECK result. 90.4% of ArcCHECK measurements passed the gamma analysis for the whole pelvis while 100% of MapCHECK measurements passed. The gamma analysis for three prostate plans was 91.5%, 95% and 96.7% using Arc Check measurements and 98.2%, 96% and 99.2% using MapCHECK. Doses between ion chamber measurement and calculation were in good agreement (0.89%∼2.44%) for all 7 plans. Conclusions: ArcCHECK achieved above 90% pass rate using gamma criteria of 3%/3mm. ArcCHECK measurements produced very similar results to MapCHECK for most plans. Using ArcCHECK in the clinic for IMRT QA can mimic patient dose delivery and examine gantry angle and couch transmission effects.
SU‐E‐T‐199: Three‐Dimensional Dose Verification Using Normoxic Polymer Gel Dosimeters for Tomotherapy
Authors: Huang T , Zhang G
Published: November 2011

The aim of this study is to evaluate the feasibility of using MAGAT as a near real‐time 3‐dimensional dose measurement device for tomotherapy. MAGAT is a new type of normoxic polymer gel dosimeter, which responses well to absorbed dose and can be easily made in the presence of normal oxygen surroundings. Its dose response was measured by irradiating MAGAT‐gel‐filled testing vials with tomotherapy and its linear relationship with dose was present from 0 to 6.5 Gy. One group of gel samples were measured in near real‐time, in which the gel phantom was read right after the irradiation. The other group was measured 12 hours after irradiation so the gel phantom can be exposed to oxygen. Several post‐imaging processing filters including Nagao, Guess, median, mean, min and max, were applied on megavoltage computed tomography (MVCT) images for better discrimination on dose responses. Our results show that dose responses for MVCT with real‐time and 12‐hour delayed measurement were 4.76 and 4.69 ΔSI．cGy‐1, respectively, and show no significant difference (p‐value = 0.72). For study of the filtering effects, Gauss, median and mean filters offer better linear correction coefficients of dose response. In conclusion, the MAGAT polymer gel dosimeter read from MVCT imaging is a promising method for dose verification in clinical tomotherapy.
SU‐E‐T‐209: Testing of Prototype Delta4AT Diode Array for In‐Vivo Radiotherapy Dosimetry
Authors: Riley S , Matzen T , Carver A
Published: November 2011

Purpose: The Delta, 4AT, (ScandiDos, Sweden,) is a head‐mounted diode‐array detector that is intended to be used during a patientˈs treatment. The device currently only exists in prototype form. By introducing MU and MLC errors into radiotherapy plans, the ability of the hardware and software to detect errors was measured. The closest separation of the diodes, (when projected to the isocentre plane,) is 8mm in the prototype, but it is intended to reduce this to 2mm in the final device. Methods: The Delta, 4AT is calibrated for each patient by taking a simultaneous measurement with the existing Delta, 4PT phantom. The Delta, 4AT then reports subsequent measurements of the same plan as predicted doses on the two perpendicular diodes arrays within the cylindrical Delta, 4PT phantom. To test the accuracy of the Delta, 4AT, the Delta, 4PT was left on the couch for the subsequent beam deliveries and the predicted doses in the Delta, 4PT were compared to the actual doses. The Delta, 4AT was calibrated with known good conformal and RapidArcTM plans, (Varian Medical Systems.). MU errors of −1.5%, −3%, +1.5% and +3% were used and MLC errors of +1.5 mm to the X1 bank, +3mm to the X1 bank and +1.5mm and +3mm to an individual MLC. Results: For a RapidArc plan and MU errors, the Delta, 4AT measurements were within gamma <1 (0.5%/0.5mm) of the Delta, 4PT for >99% of diodes, (detectors above 20% included). For a RapidArc plan and smaller MLC errors (+1.5mm), the Delta, 4AT measurements were within gamma < 1 for > 95% of diodes at 3%/3mm. For a conformal plan and a +3mm X1 bank error the Delta, 4AT measurements were within gamma <1 of the Delta, 4PT for >95% of diodes at 2%/2mm. Conclusions: The prototype Delta4, AT has been shown to produce accurate measurements and will allow verification throughout a patientˈs treatment.

Thomas Matzen is employed by ScandiDos, the manufacturer of the Delta, 4AT. The meeting registration fees and travel costs of the presenting author may or may not be partly paid by ScandiDos.