bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐97: Evaluation of Multi‐Modality (CT/MR/PET) Image Registration Accuracy in Radiotherapy Planning
Authors: Sethi A , Rusu I , Surucu M , Halama J
Published: June 2012

Purpose: Evaluate accuracy of multi‐modality image registration in radiotherapy planning process. Methods: A water‐filled anthropomorphic head phantom containing eight ‘donut‐shaped’ fiducial markers (3 internal + 5 external) was selected for this study. Seven image sets (3CTs, 3MRs and PET) of phantom were acquired and fused in a commercial treatment planning system. First, a narrow slice (0.75mm) baseline CT scan was acquired (CT1). Subsequently, the phantom was re‐scanned with a coarse slice width = 1.5mm (CT2) and after subjecting phantom to rotation/displacement (CT3). Next, the phantom was scanned in a 1.5 Tesla MR scanner and three MR image sets (axial T1, axial T2, coronal T1) were acquired at 2mm slice width. Finally, the phantom and center of fiducials were doped with 18F and a PET scan was performed with 2mm cubic voxels. All image scans (CT/MR/PET) were fused to the baseline (CT1) data using automated mutual‐information based fusion algorithm. Difference between centroids of fiducial markers in various image modalities was used to assess image registration accuracy. Results: CT/CT image registration was superior to CT/MR and CT/PET: average CT/CT fusion error was found to be 0.64 ± 0.14 mm. Corresponding values for CT/MR and CT/PET fusion were 1.33 ± 0.71mm and 1.11 ± 0.37mm. Internal markers near the center of phantom fused better than external markers placed on the phantom surface. This was particularly true for the CT/MR and CT/PET. The inferior quality of external marker fusion indicates possible distortion effects toward the edges of MR image. Peripheral targets in the PET scan may be subject to parallax error caused by depth of interaction of photons in detectors. Conclusions: Current widespread use of multimodality imaging in radiotherapy planning calls for periodic quality assurance of image registration process. Such studies may help improve safety and accuracy in treatment planning.
SU‐E‐J‐100: Feasibility of Dose Calculation Using Combined Information of Cone‐Beam and Multi‐Slice CT Images
Authors: Usui K , Ogawa K , Kunieda E
Published: June 2012

Purpose: The purpose of this study is to evaluate the feasibility of kilovoltage cone‐beam CT (CBCT) images that are obtained with the Varian On‐Board Imager in dose calculation at each radiation therapy. Methods: CBCT images are commonly degraded by scattered radiations originating in the patient's body, and so the CT numbers of the CBCT images depend on data acquisition conditions and the patient size. However, the anatomical shape of each organ is not likely affected by scattered radiations, and so we used only the shape of major organs such as lungs and bones in the CBCT images, and replaced these CT numbers with those of the multi‐slice CT (MSCT) images that were used for dose calculation in a treatment planning. As regards this alternative CT number we adopted the median of MSCT numbers in a segmented region of a major organ each corresponding to that in the CBCT images. We evaluated the validity of our segmented region (SR) method with images of eight patients with lung diseases. The number of irradiation beams was four. In this evaluation we used the distance‐to‐agreement (DTA) and y analysis, and the dose‐volume‐histogram (DVH) analysis. Results: The pass rates of the DTA analysis (2mm) and γ analysis (2mm, 2%) between the dose distributions calculated with our method were 90.4±6.0% and 99.1±1.1%, respectively. The results of the DVH analysis showed that the differences in doses (average, maximum and minimum) for a target volume were 1.3±0.5%, 0.9±0.8% and 3.4±3.0%, respectively. These results showed that our method was acceptable in the calculation of a dose distribution. Conclusion: We evaluated the dose calculation method with a combination of CBCT and MSCT images. This method could yield an accurate dose distribution and achieved an easier verification of radiation therapy on each treatment day.
SU‐E‐J‐107: Feasibility of Complete Brain Simulation Using Single MRI Acquisition
Authors: Traughber M , Meltsner M
Published: June 2012

Purpose: To evaluate the information available from a single MRI acquisition for a complete MRI‐based simulation in brain.Method and Materials: A 3.0T MRI scanner (Achieva TX, Philips Healthcare) was used to acquire a complete brain simulation data set in a single acquisition on four consenting volunteers. The acquisition consisted of collecting the FID signal (TE1 = 100μs) followed by two additional gradient echoes (TE2/TE3= 1.4ms/2.5ms) using a 3D volumetric excitation and radial read‐out toachieve 1.3mm isotropic voxels. The data from this single acquisition was used to reconstruct five volumetric data sets: Bone‐enhanced, fat‐only, water‐only, in‐phase and out‐of‐phase. The resulting image sets were assessed for image quality sufficient for organ delineation and used to generate digitally‐reconstructed radiographs (DRRs) (Pinnacle Workstation, Philips Healthcare). Results: Each volunteer study took less than 10 minutes to complete, and the single acquisition required less than 3 minutes. Images from all four volunteers had excellent image quality sufficient for organ delineation and complete cortical bone segmentation. In addition, the DDRs for all four volunteers were sufficient for 2D patient matching. Conclusion: This study confirms the feasibility of using a single acquisition MRI as a sole imaging modality for treatment planning simulation in the brain. To validate this method, we plan to use this imaging protocol in a group of patients and compare the DRRs and dose plans with those acquired during CT simulation. Both authors are employees of Philips Healthcare.
SU‐E‐J‐109: Accurate Contour Transfer Between Different Image Modalities Using a Hybrid Deformable Image Registration and Fuzzy Connected Image Segmentation Method
Authors: Yang C , Paulson E , Li X
Published: June 2012

Purpose: To develop and evaluate a tool that can improve the accuracy of contour transfer between different image modalities under challenging conditions of low image contrast and large image deformation, comparing to a few commonly used methods, for radiation treatment planning. Methods: The software tool includes the following steps and functionalities: (1) accepting input of images of different modalities, (2) converting existing contours on reference images (e.g., MRI) into delineated volumes and adjusting the intensity within the volumes to match target images (e.g., CT) intensity distribution for enhanced similarity metric, (3) registering reference and target images using appropriate deformable registration algorithms (e.g., B‐spline, demons) and generate deformed contours, (4) mapping the deformed volumes on target images, calculating mean, variance, and center of mass as the initialization parameters for consecutive fuzzy connectedness (FC) image segmentation on target images, (5) generate affinity map from FC segmentation, (6) achieving final contours by modifying the deformed contours using the affinity map with a gradient distance weighting algorithm. The tool was tested with the CT and MR images of four pancreatic cancer patients acquired at the same respiration phase to minimize motion distortion. Dice's Coefficient was calculated against direct delineation on target image. Contours generated by various methods, including rigid transfer, auto‐segmentation, deformable only transfer and proposed method, were compared. Results: Fuzzy connected image segmentation needs careful parameter initialization and user involvement. Automatic contour transfer by multi‐modality deformable registration leads up to 10% of accuracy improvement over the rigid transfer. Two extra proposed steps of adjusting intensity distribution and modifying the deformed contour with affinity map improve the transfer accuracy further to 14% averagely. Conclusions: Deformable image registration aided by contrast adjustment and fuzzy connectedness segmentation improves the contour transfer accuracy between multi‐modality images, particularly with large deformation and low image contrast.
SU‐E‐J‐119: Comparative Evaluation of Respiratory Motion‐Corrected Cone‐Beam CT Images Derived from Treatment‐Day Vs. Simulation‐Day Respiration‐Correlated CT Scans
Authors: Dzyubak O , Kincaid R , Yorke E , Hertanto A , Hu Y , Rimner A , Zhang Q , Mageras G
Published: June 2012

Purpose: Respiration‐induced motion artifacts in cone‐beam CT (CBCT) can be corrected using a model of patient motion obtained from respiration‐correlated CT (RCCT). This approach assumes that respiration‐induced organ deformations at simulation, when RCCT scans are normally acquired, are still valid at treatment. The purpose of this study is to compare lung tumor image quality in motion‐corrected CBCT images derived from treatment‐day RCCT(tx) to simulation‐day RCCT(sim) patient images. Methods: In an IRB‐approved study, lung cancer patients receive an RCCT at simulation, and an RCCT, gated CBCT and 1‐minute CBCT at one treatment session. CBCT projections from the 1‐minute scan are sorted according to breathing amplitude from an external monitor and reconstructed and warped to obtain a motion‐corrected MC‐CBCT at end expiration. Motion correction uses a model adapted from either RCCT(tx) or RCCT(sim), thus obtaining MC‐CBCT(tx) and MC‐CBCT(sim) images respectively. A gated CBCT, in which gantry rotation and projection acquisition occur within a gate at end expiration, serves as ground truth for comparison. Quality of MC‐CBCT images is evaluated from tumor‐to‐background contrast ratio (TBCR) values measured by delineating the tumor and annular volume around it on the gated CBCT then transferring the contours and aligning them to each MC‐CBCT. Results: TBCR is found tobe lower in MC‐CBCT(sim) images, relative to MC‐CBCT(tx), in four out of five patients with mean 21% reduction in a range 9–39%. In the remaining case, where there was no change in TBCR, tumor motion observed in the RCCT was small (2mm). Tumor motion extent relative to diaphragm is observed to change between RCCT(tx) and RCCT(sim) scans. Conclusions: Preliminary results indicate that deformation patterns in lung do change between simulation and treatment. Such variations may reduce the validity of using simulation data for motion‐corrected CBCT at treatment. The findings require confirmation with larger numbers of patients. NIH/NCI award R01 CA126993, research grant from Varian Medical Systems
SU‐E‐J‐185: 4DCT Geometrical Eigenmode Model for Inter‐Fraction Evaluation of Tumor Regression and Breathing Pattern Changes
Authors: Kearney V , Wang X , Jia X , Jiang S , Cervino L
Published: June 2012

Purpose: Evaluate the feasibility of using intra‐fractional respiratory dominant eigenmodes of lung deformation as a method to track inter‐fractional tumor regression and other physiological changes. Geometrical evaluation by dominant eigenmodes during free‐breathing may be implemented as an IGART tool for assessing inter‐fractional non‐respiratory anatomical variation. Methods: Intra‐fractional deformable image registration (DIR) is performed on 4DCT scans of lung cancer patients. Principal component analysis is conducted on a set of 10 deformation vector fields for each patient both with and without a lung mask. Leave‐one‐out cross‐validation (LOOCV) is used to assess intra‐fractional modeling error among a subset of respiratory phases. The first two dominant eigenmodes of PCA are compared across patients in axial, sagittal, and coronal slices. Results: Eigenvalues between the first and second dominant respiratory modes decay by a factor of ten for all patients. Intra‐fractional LOOCV maximum error is on the order of 1mm inside the lung and 4–6mm for the whole thorax for all patients using the first two dominant eigenmodes. Eigenvalue decay is fastest for patients where diaphragm motion is relatively larger in magnitude. The first two eigenmodes generally demonstrate a strong but smooth superior‐inferior motion component with a lesser lateral and anterior‐posterior component, while subsequent less dominant eigenmodes produce more random directional eigenvector fields. Conclusion: The two first principal components are consistent amongst patients. Inter‐fractional eigenmode comparison may provide a means to track tumor regression and breathing pattern or physiological changes. We expect that patients with more dominant diaphragmatic respiration will allow for more delineated eigenmode classification. Clear dominant eigenmode delineation may allow subsequent less dominant eigenmodes to be inter‐fractionally compared as a means to evaluate and compensate for tumor regression.
SU‐E‐J‐187: Evaluation of the Effects of Dose on 4DCT‐Calculated Lung Ventilation
Authors: Latifi K , Dilling T , Hoffe S , Stevens C , Moros E , Zhang G
Published: June 2012

Purpose: To investigate the effects of radiation therapy (RT) treatment dose on ventilation. Methods: Optical flow deformable image registration of the normal end‐expiration and end‐inspiration phases of 4DCT images was used to correlate the voxels between the two phases. 4DCT sets from before and after RT were used to derive ventilation for 3 SBRT lung patients. Planning dose and normalized ventilation were superimposed on the CT volume resulting in each voxel having a volume, a normalized ventilation and a dose. From these values a 3D dose‐ventilation‐volume surfaces was created. The surface was integrated over dose to reduce the 3D surface to a 2D histogram that is easier to interpret. Results: For lung tissue regions receiving more than 20 Gy, a decrease in ventilation was observed in the three patients. Patient A (time between scans, T=26 months) showed an increase in ventilation for regions receiving a dose smaller than 20 Gy, whereas patients B (T=3 months) and C (T=6 months) did not show any change for these regions. Mean ventilation within the 20 Gy region for patient A was 0.57 before RT and 0.51 after RT; and 0.54 before and 0.48 after RT for the 30 Gy region. Mean ventilation for the 20 Gy region for patient B was 0.49 before RT and 0.47 after RT, for the 30 Gy region mean ventilation was 0.49 Gy before and 0.45 Gy after RT. Patient C's mean ventilation for the 20 Gy region was 0.54 before RT and 0.50 after RT, for the 30 Gy region mean ventilation was 0.54 before RT and 0.49 after RT. Conclusions: Ventilation before and after radiation therapy can be measured using 4DCT and deformable image registration techniques. In a preliminary application of this approach for three patients, changes in ventilation were observed with a weak correlation between ventilation change and dose. Partially supported by a grant from Varian Medical Systems.
SU‐E‐J‐210: Lung Tumor Target Volume Contours on EPID Cine Mode Images
Authors: Bryant JH , Yue Y , Rottmann J , Lewis JH , Berbeco RI
Published: June 2012

Purpose: While real time imaging of treatment through an electronic portal imaging device (EPID) is a powerful tool to monitor treatment, limited field of view and lower contrast from an MV beam can make assessment difficult for physicians. This work will develops a method to register and project contour outlines for the internal target volume (ITV) and planning target volume (PTV) of lung tumor cases onto cine mode EPID images to help physicians in interpretation during treatment. Methods: A sequence of EPID images, acquired during treatment, was registered to treatment planning computed tomography (CT) by machine geometry and patient setup with cone‐beam computed tomography (CBCT). The planning CT was converted from Hounsfield scale to electron density by calibration curves of our CT simulator and digitally reconstructed radiographs (DRRs) were produced to match the EPID geometry, pixel for pixel. ITV and PTV structures as defined on the planning CT were then projected onto the DRRs. The DRRs were registered to the EPID images using cross correlation of a single template defined within the treatment aperture of each image. Once registered, the contours from the DRR were transferred to the EPID. Results: We were able to successfully register MV DRRs to EPID images and display the projected target volumes. Without introduced motion, geometric registration and CBCT guided patient setup up were sufficient to register the contours within a single pixel, as normalized cross correlations produced no additional shift. We expect the DRR/EPID registration to be an important step when looking at cases with substantial tumor movement. Conclusions: The visualization of target volumes provides a tool for physicians to interpret EPID images and assess treatment, especially in cases with tumor movement. The methods developed will serve as the basis for a clinical tool providing real time contours.
SU‐E‐T‐07: Edema Induced Changes in Tumor Cell Survival Fraction and Tumor Control Probability in 131Cs Permanent Prostate Implant Patients
Authors: Kehwar TS , Huq MS , Smith RP
Published: June 2012

Purpose: The purpose of this study is to estimate the effect of edema, developed during implant procedure, on tumor cell surviving fraction(SF) and tumor control probability(TCP) in the patients of prostate cancer who underwent 131Cs permanent seed implants. Methods: The impact of edema on SF and TCP, was calculated using LQ equation extended to account for exponential nature of edema decay, dose delivered to dematous prostate and inhomogeneous dose distribution. Where (1) S(D)=(1/V)Σi=1n [Vpi{1+M0exp(−λet)}Si(D)] Si(D)=exp[−αRi(0)∫0t[exp(− λt)/{1+M0exp(−λet)}τ/3]dt −βq(t){Ri(0)∫0t[exp(−λt)/{1+M0exp(−λet)}τ/3]dt }2] and (2) TCP=exp[−ρVpS(D)] Following parameters, α=0.15Gy−1, β=0.05Gy−2, α/β=3.0Gy, Tp=42days, μ=61.6d−1 and ρ=1×106 are used to calculate SF and TCP for 31 patients of 131Cs permanent seed implants for edema half lives(EHL) ranging from 4 days to 34 days and for edemas of magnitudes(M0) varying from 5% to 60% of the actual prostate volume. Results: The dose reductions in 131Cs implants varied from 1.1% (for EHL=4 days and M0=5%) to 32.3% (for EHL= 34 days and M0 = 60%). These are higher than the dose reduction in 125I implants, which vary from 0.3% (for EHL= 4 days and M0 = 5%) to 17.5% (for EHL= 34 days and M0 = 60%). As edema half life increased from 4 days to 34 days and edema magnitude increased from 5% to 60% the SF increased by 4.57 log, and the TCP decreased by 0.80. Conclusions: Compensation of edema induced increase in the SF and decrease in the TCP in 131Cs seed implants should be carefully done by redefining seed positions with the guidance of post needle plans. The presented model in this study can be used to estimate the SF or the TCP for pre plan or real time permanent prostate implants using day 0 post implant CT images.
SU‐E‐T‐08: Simple Governing Equations for Tumor Growth
Authors: Watanabe Y , Dahlman E
Published: June 2012

Purpose: To derive a set of simple differential equations, which can represent temporal growth of typical tumors, by taking into account the effects of the tumor microenvironment on cell proliferation. Methods: Cause‐effect relationships between cell proliferation and nutrients contained in blood stream, which included oxygen and glucose, were modeled. By formulating a set of rate equations and simplifying those, we finally obtained two differential equations. One equation represents the change of the tumor mass and included time‐varying growth rate, which was a solution of another equation relating the growth rate with the blood volume in the tumor. The set of differential equations were numerically solved by varying a parameter, kappa, which represented the growth rate of the blood volume relative to the tumor mass. Results: Through numerical experiments we showed that the tumor volume increased exponentially if the blood volume increased at the same rate as the tumor. However, the blood volume did not increase rapidly enough as the tumor grew, the tumor showed the saturation in the growth when the tumor grew by 1000‐fold. Such a retardation of tumor growth was experimentally observed and the function representing the growth curve is called as Gompertz equation. One of solutions also showed that the tumor stopped growing when the blood supply was shut off (or kappa = 0). Conclusions: A solution of simple differential equations derived in this study could reproduce the tumor growth which can be represented by the well known Gompertz equation. Using these equations we were able to theoretically show that the saturation of tumor growth observed often for larger tumors could be explained by a relative lack of blood supply which leads to a decrease in the cell proliferation rate. In a future study the effects of radiation on the tumor growth will be included in the model.
SU‐E‐T‐14: Modeling of 3D Positron Emission Activity Distributions Induced by Proton Irradiation: A Semi‐Empirical Method
Authors: Lopatiuk‐Tirpak O , Su Z , Hsi W , Zeidan O , Meeks S
Published: June 2012

Purpose: to present and validate a method for modeling three‐dimensional positron emission (PE) activity distributions induced by proton beam irradiation for PET/CT delivery verification studies in homogeneous media. Methods: the method relies on modeling the 3D proton flux distribution by combining the analytical expression for the depth reduction of proton flux with the empirically obtained lateral distribution. The latter is extracted from the corresponding dose distribution under the assumption that the projectile energy is nearly constant in the lateral plane. The same assumption allows calculating the 3D induced activity distributions from proton flux distributions by parameterizing the energy‐dependent activation cross‐sections in terms of depth via the energy‐range relation. Results of this modeling approach were validated against experimental PET/CT data from three phantom deliveries: unmodulated (pristine) beam, spread‐out Bragg peak (SOBP) delivery without a range compensator, and SOBP with a range compensator. BANG3‐Pro2 polymer gel was used as a phantom material because of its elemental soft‐tissue equivalence. Results: the agreement between modeled and measured activity distributions was evaluated using 3D gamma index analysis method, which, despite being traditionally reserved for dose distribution comparisons, is sufficiently general to be applied to other quantities. The evaluation criteria were dictated by limitations of PET imaging and were chosen to correspond to count rate uncertainty (6% value difference) and spatial resolution (4 mm distance to agreement). With these criteria and the threshold of 6%, the fraction of evaluated voxels passing the gamma evaluation was 97.9% for the pristine beam, 98.9% for the SOBP without compensator, and 98.5% for SOBP with compensator. Conclusions: results of gamma evaluation indicate that the activity distributions produced by the model are consistent with experimental data within the uncertainties of PET imaging for clinical proton beams deliveries. This work was supported by the Bankhead‐Coley Florida Biomedical Research Program under Grant No. 1BD10‐34212.
SU‐E‐T‐20: Removal of Electron Contamination in Longitudinal Field MRI‐Linac Systems: A Monte Carlo Study
Authors: Oborn BM , Metcalfe P , Butson M , Crozier S , Keall P
Published: June 2012

Purpose: The prototype inline MRI‐linac system has some advantages over perpendicular models including avoiding the electron return effect. One of the disadvantages of the inline approach is the increased skin dose, estimated to be 400–1000% of the dmax dose. The purpose of this work was to design a feasible method to reduce this skin dose to acceptable levels. Methods: Magnetic modeling of proposed MRI‐linac designs have been simulated with the inclusion of an optimized permanent magnet system to purge/deflect the electron contamination. The region of air above the phantom was also replaced with a helium bag (region of helium gas) and a beam scrapper below the deflector was added to collect deflected off‐axis contamination. Monte Carlo simulations were then performed including the accurate 3D magnetic field maps. Surface dosimetry was recorded to verify the changes to the skin doses. Results: Magnetic modelling showed that an optimized NdFeB permanent magnet system located outside the MRI coils (below the MLC's) can provide a strong enough region to purge/deflect a significant portion of the electron contamination from the x‐ray beam. The impact on the MRI uniformity is around 100 ppm and hence is correctable via active/passive shimming of the MRI. The helium region also significantly limits the production of contamination traveling towards the phantom surface. Entry doses near CAX are predicted to be similar to the 0 T case. Conclusions: Magnetic and Monte Carlo modeling were performed to estimate the effect that a permanent magnet purging system, beam scrapper, and helium bag would have on lowering the skin doses in an inline MRI‐Linac system. MRI non‐uniformities introduced by the deflector could be corrected, contamination is mostly purged or blocked, and the helium bag minimizes air‐generated contamination. As a result skin doses are comparable to having zero magnetic field.
SU‐E‐T‐26: Evaluation of New Pre‐Treatment In‐Air Patient Specific QA Software for TomoTherapy Treatments
Authors: Levinson L , Chen Q , Ding K , Renner W , Benedict S , Read P
Published: June 2012

Purpose: Math Resolutions, LLC, has extended their Dosimetry Check quality assurance software to include TomoTherapy treatments. Data collected from TomoTherapy's MVCT detectors is processed and compared to the planned treatment dose allowing for pre‐treatment QA without the use of phantoms and other detectors. This study presents an overview of our experience at the University of Virginia developing, implementing, and verifying this novel QA strategy. Methods: Low modulation and high modulation cheese phantom plans as well as patient plans (prostate, GYN, and vertebra) were used to test the Dosimetry Check in‐air software. For all evaluations the treatment table was removed from the XML file of each plan using software provided by Accuray and the resulting in‐air calibration plan was delivered. The exit detector sinogram was extracted from the machine and imported into Dosimetry Check along with the TomoTherapy calculated planned dose. The fluence maps were reconstructed and used to recalculate the dose. Results: The percent difference between the planned dose and the dose calculated from the exit detectors by Dosimetry Check ranged between 0.62% for a simple low modulation cheese phantom plan with a cylindrical target to 7.3% for a high modulation 2.5cm prostate plan. The gamma indices reported range from 94.7% to 97.8% <1 over the overall calculation area for the plans tested using a gamma of 3% and 3mm. For the area receiving over 80% of the prescribed dose, the gamma ranged from 80.7% to 92.9% <1. Conclusions: The results of our investigation of Math Resolutions' new product in development, Dosimetry Check's pre‐treatment in‐air QA software, demonstrate that it has the potential be a very useful and practical tool for TomoTherapy QA. Further testing is being performed in which various errors are intentionally introduced in the delivered dose to test the limits of Dosimetry Check's sensitivity. Research Grant from Math Resolutions LLC 01/12/2012–01/11/2013 Math Resolutionsâ€™ Dosimetry Check software was given to UVa to assist with evaluating the precision of the product in reconstructing dose from the TomoTherapy exit detector data.
SU‐E‐T‐87: The Effect of Bleaching Wavelengths on the Regeneration of the Optically Stimulated Luminescence Signal of NanoDot Dosimeters Pre‐Exposed to High‐Doses
Authors: Omotayo A , Cygler J , Sawakuchi G
Published: June 2012

Purpose: To investigate the effect of bleaching wavelengths on the regeneration of optically stimulated luminescence (OSL) signals in Al2O3:C nanoDot dosimeters pre‐exposed to high doses. Regeneration is the increase in the OSL signal during storage of a bleached nanoDot that was previously pre‐exposed to a high dose. This phenomenon affects the accuracy of a calibration protocol proposed by Jursinic 2010 (Med. Phys. 37:102) in which pre‐exposure of nanoDots to a high‐dose was used to minimize changes in the sensitivity of the detector as a function of accumulated dose. Methods: Al2O3:C OSLDs of the type nanoDot were used throughout this study. Readout was performed using the microStar reader. Bleaching of the OSLDs was performed with four 26 W fluorescent light bulbs in two modes: (i) directly under the lamps; and (ii) with the aid of a long‐pass optical filter placed over the nanoDots, partially blocking wavelengths below 495 nm. Eighteen nanoDots were pre‐exposed to 1 kGy dose. Then the pre‐exposed nanoDots were bleached in two sets of 9 to very low residual OSL signals using bleaching modes (i) and (ii) for 12 h and 45 h, respectively. The nanoDots were then stored in dark and readout after various time intervals to monitor the regeneration of the OSL signal. Results: We fitted the regeneration of the OSL signal using a saturation function and obtained rise‐time values of 563 h and 630 h, for bleaching modes (i) and (ii), respectively. At the saturation level, the equivalent doses were about 1.18 Gy and 0.38 Gy for modes (i) and (ii), respectively. Conclusions: The regeneration rates of nanoDot OSLDs pre‐exposed to high doses depend on the bleaching light wavelength used to reset the detectors. A bleaching source that has a low component of wavelengths below 495 nm can minimize the regeneration of the OSL signal. Natural Sciences and Engineering Research Council of Canada
SU‐E‐T‐90: Investigation of Different Bleaching Wavelengths on the Absorbed‐Dose Sensitivity of NanoDot OSLDs Exposed to 6 MV X‐Ray Beams
Authors: Omotayo A , Cygler J , Sawakuchi G
Published: June 2012

Purpose: To determine the effect of different bleaching wavelengths on the luminescence response of Al2O3:C optically stimulated luminescence detectors (OSLDs) exposed to accumulated doses of 6 MV photon beams. Methods: OSLDs of the nanoDot type were used and readout with a microStar InLight reader. To determine the effect of different bleaching wavelengths on the luminescence response of nanoDot OSLDs, we optically reset (bleached) the OSLDs with 26 W fluorescent lamps in two modes: (i) directly under the lamps for 10, 120 and 600 min; and (ii) with a long pass filter for 55, 600 and 2400 min. The long pass filter blocks wavelengths below 495 nm, hence the longer bleaching duration to attain equivalent OSL signals as bleaching directly under the lamps. Changes in the sensitivity of the nanoDot OSLDs were determined for an irradiation‐readout‐bleaching‐readout cycle, after irradiations with 1 and 10 Gy dose fractions. Results: The nanoDot OSLDs presented a linear response to dose up to 2 Gy and supra‐linear response afterwards. They produced different OSL signal loss and fading behaviors for doses of 1 and 10 Gy. OSLDs bleached for 120 min and 600 min without and with the filter in 1 Gy fractions, did not exhibit any significant change in sensitivity over an accumulated dose of 7 Gy. The OSLDs exposed with 10 Gy fractions exhibited a small under‐response when bleached with filter, and an over‐response when bleached directly without filter. Conclusions: The nanoDot OSLDs may be reused without a significant sensitivity change for accumulated doses below 7 Gy. However, for accumulated doses beyond 10 Gy, nanoDot OSLDs show significant sensitivity change and hence, need to be recalibrated for reuse. We also concluded that the light spectrum used to reset the OSLDs has an influence on the sensitivity of the detectors. Natural Sciences and Engineering Research Council of Canada
SU‐E‐T‐92: on the Use of High‐Sensitivity Thermoluminescent Dosimeters (TLDs) for Dosimetric Characterization of Low‐Energy Brachytherapy Sources
Authors: Chen Z , Bongiorni P , Donahue W , Hearn R , Rodgers J , Nath R
Published: June 2012

Purpose: To investigate the utility and accuracy of high‐sensitivity TLD for dosimetric characterization of low‐energy brachytherapy sources. Methods: One hundred high‐sensitivity (TLD‐100H) and 100 normal‐sensitivity (TLD‐100) TLDs were used in this study. The TLD‐100s were annealed at 400°C for one hour and then kept at room temperature for 45 minutes followed by 80°C heating for 24 hours. To prevent temperature overshot from reducing the sensitivity of TLD‐100Hs, a novel thermal reservoir was built, tested, and used to anneal TLD‐100H at 240 0C for 15 minutes and then kept at room temperature for 45 minutes followed by 100 0C heating for one hour. These TLDs were then irradiated uniformly in a large cavity Cs‐137 irradiator for biomedical research (Shepherd, Mark III) to test their reproducibility and to establish their relative sensitivities. The radial dose function of a Model AgX100 125I source was measured using both types of TLDs in water‐equivalent solid phantoms as a test case. The radial dose function measured by the TLD‐100H was compared with that measured by TLD‐100 to determine its utility in brachytherapy dosimetry characterization. Results: Consistent and accurate annealing of high‐sensitivity TLDs was achieved by using a custom‐built thermal reservoir system. TLD‐100H was found to be about 18 times more sensitive than TLD‐100. For a 125I source with a source‐strength of 2.7U, the irradiation time for radial dose function characterization up to 7 cm can be cut down from 38 days to 3 days. The radial dose function measured by TLD‐100H agreed well (within ±6%) with that measured by TLD‐100. Conclusions: A novel thermal reservoir was used for consistent annealing of high‐sensitivity TLDs. TLD‐100H can significantly shorten the irradiation time needed for a complete characterization of radial dose function. Investigation of TLD‐100H for complete brachytherapy source characterization is in progress. Supported in part by NIH grant R01‐CA134627
SU‐E‐T‐98: Towards Cell Nucleus Microdosimetry: Construction of a Confocal Laser‐Scanning Fluorescence Microscope to Readout Fluorescence Nuclear Track Detectors (FNTDs)
Authors: McFadden C , Bartz J , Akselrod M , Sawakuchi G
Published: June 2012

Purpose: To construct a custom confocal laser scanning microscope (CLSM) capable of resolving individual proton tracks in the volume of an Al2O3:C,Mg fluorescent nuclear track detector (FNTD). The spatial resolution of the FNTD technique is at the sub‐micrometer scale. Therefore the FNTD technique has the potential to perform radiation measurements at the cell nucleus scale. Methods: The crystal volume of an FNTD contains defects which become fluorescent F2+ centers after trapping delta electrons from ionizing radiation. These centers have an absorption band centered at 620 nm and an emission band in the near infrared. Events of energy deposition in the crystal are read‐out using a CLSM with sub‐micrometer spatial resolution. Excitation light from a 635 nm laser is focused in the crystal volume by an objective lens. Fluorescence is collected back through the same path, filtered through a dichroic mirror, and focused through a small pinhole onto an avalanche photodiode. Lateral scanning of the focal point is performed with a scanning mirror galvanometer, and axial scanning is performed using a stepper‐motor stage. Control of electronics and image acquisition was performed using a custom built LabVIEW VI and further image processing was done using Java. The system was used to scan FNTDs exposed to a 6 MV x‐ray beam and an unexposed FNTD. Results: Fluorescence images above the unexposed background were obtained at scan depths ranging from 5 – 10 micrometer below the crystal surface using a 100 micrometer pinhole size. Conclusions: Further work needs to be done to increase the resolution and the signal to noise ratio of the images so that energy deposition events may be identified more easily. Natural Sciences and Engineering Research Council of Canada
SU‐E‐T‐103: Three‐Dimensional Measurements of Dose and LET from a Proton Beam via Polymer Gel Dosimetry
Authors: Vredevoogd K , Ibbott G , Gillin M , Sahoo N , Kry S , Gifford K , Maryanski M
Published: June 2012

Purpose: To obtain and assess the accuracy of 3D dose distributions and LET maps from a passively‐scattered proton beam through the use of LET‐dependent and LET‐independent polymer gel formulations. Methods: Dose measurements were performed with BANG3‐Pro2 (MGS Research, Inc, Madison, CT) polymer gel dosimeters. The dosimeters were mixed from kits and were poured into 14.5 cm high by 15 cm diameter acrylic cylinders. For LET measurements, a new BANG3‐Pro variant intended for use as an ‘LET‐ meter’ was employed. Initial irradiations were performed using a 200 MeV passively scattered proton beam with a 4 cm spread out Bragg peak (SOBP), delivering a physical dose of 3 Gy to the center of the SOBP. Dosimeters were read out using the OCTOPUS‐IQ (MGS Research, Inc, Madison, CT) optical CT scanner. The optical densities measured in the gel were compared against ion chamber data to assess the accuracy of the dosimeter. Results: Initial analysis indicates 80% of points measured along the central axis agreed with ion chamber data at the ±5%/±3mm level in the sensitive region of the gel. An artifact in the reconstructed image produced inaccurate readings beyond the depth of 50% dose on the distal edge of the SOBP, resulting in the majority of the agreement failures. Conclusions: BANG3‐Pro2 polymer gel dosimeters demonstrate promise as a 3D dosimeter for use in proton therapy. The dosimetric data obtained to date will be used as the baseline measurement against which the LET‐sensitive BANG3‐Pro formulation will be compared for the measurement of proton LET.
SU‐E‐T‐106: Evaluation of Sensitivity and Uniformity of New Radiochromic Film with Two Commercial Scanners
Authors: Kamomae T , Miyabe Y , Sawada A , Oita M , Fujimoto T , Yano S , Nakata M , Nakayama S , Hiraoka M
Published: June 2012

Purpose: A newly introduced radiochromic film, the GAFCHROMIC EBT3, has been expected as much useful device for the IMRT dosimetry. The purpose of this study was to investigate the sensitivity and the uniformity of the films between an Epson ES‐10000G flatbed scanner and a Vidar DosimetryPRO Advantage (Red) scanner. Methods: Doses ranging from 1 cGy to 1600 cGy with 15‐MV photon beam was irradiated to the film in a solid water phantom, respectively. All of the films were then digitized after irradiation using both two scanners. Sensitivities, local fluctuations of the film with two scanners were evaluated. Local fluctuations were defined as the relative (percent) standard deviation of the film response in ROIs (3 cmx3 cm). Results: As to the Vidar scanner, the sensitivity of the film was higher for low dose range (below <400 cGy). While, as to the Epson scanner, the sensitivity using the red color channel was higher than others for low dose range. At high dose range (above >400 cGy), the green color channel had higher sensitivity than others. The Vidar scanner exhibited the lower local fluctuations than the Epson scanner for all dose ranges. For the Epson scanner, the red color channel had the lower local fluctuations than the green and blue color channel for all dose ranges. Conclusions: This study shows the characteristics of the new EBT3 films, in conjunction with the Epson ES‐10000G flatbed scanner and the Vidar DosimetryPRO Advantage (Red) scanner.
SU‐E‐T‐107: Uncertainty Estimate of a Practical EBT‐2 Film Dosimetry Approach: Transpose‐And‐Scan Technique
Authors: Kim J , Huang Y , Chin K , Bellon M , Glide‐Hurst C , Smith C , Altman M , Li H , Kim S , Gopal A , Liu C , Chetty I
Published: June 2012

Purpose: To estimate the uncertainty of a practical EBT2 film dosimetry approach that has been established at our institution and used for routine patient‐specific plan verifications, particularly for SBRT and RapidArc, as well as planning system commissioning. Our technique is unique from other common dosimetry protocols with respect to calibration, irradiation and scanning. Methods: Film dosimetry for patient‐specific quality assurance of 29 patient plans were retrospectively reviewed. For each case, four films were irradiated; two for calibration and two for treatment plan. Each pair of two films were irradiated together in a phantom with one film transposed (rotated 180 degrees relative to the other) to compensate for asymmetric film response. After a minimum of 12 hrs post‐irradiation, each film was scanned in four different orientations to mitigate non‐uniform response of the scanner light and detector elements. The scanned 8 calibration and 8 plan images were averaged into one calibration and one plan film image, respectively. Each color channel of the calibration film was correlated to the reference dose matrix to produce a 3rd order polynomial calibration curve. Finally, each color channel of the plan film was converted to a dose map using the corresponding calibration curve. Average dose maps of the red and green channels were correlated to the treatment planning dose matrix, and the mean dose differences at the center of dose distributions (5×5mm̂2 area) as well as a gamma analysis were evaluated. Results: The absolute dose differences were −0.8±1.7% (range=−4.5–3.0%). The gamma pass‐rates (3%/3mm) were 94±7% (min.=74%). The pass rate increased to 99±3%(min.=87%) with the film scaled relatively to the plan doses. Conclusions: Based on a large number of cases, our approach appears to be robust to non‐uniform film and scanner responses, and is shown to have an uncertainty (1SD) of less than 2% for absolute film dosimetry.
SU‐E‐T‐110: Small Electron Field Surface Dosimetry Using Solid State Detectors
Authors: Tanny S , Gautam B , Pearson D , Parsai E
Published: June 2012

Purpose: Solid state detectors from two independent systems have shown similar over‐responses to small electron fields used for treatment of surface lesions. We propose to evaluate the accuracy of solid state detector systems for highly blocked electron fields as a method for clinical dosimetry and determine the cause for any deviations from expected dose‐delivery calculations. Methods: A QED Diode detector system and a Best‐Medical MOSFET dosimeter system were used to measure relative output factors (ROF's) for a range of blocked electron fields with 3 different electron energies. Measurements were taken on the surface of a Solid‐Water phantom as well as under varying thicknesses of bolus (surface to dmax) to determine the extent of this effect with increasing depth. Measurements were compared with expected results obtained during machine commissioning with an A‐14 micro‐ionization chamber. Results: Field sizes larger than 4×4 cm2 showed little significant deviation from expected output factor values. However, fields smaller than this threshold showed as much as a 30% over‐response of the solid state detectors compared to ion chamber measurements on the surface. This deviation was consistent over multiple measurements using both systems. The degree of over‐response is both energy and effective field size dependent. As the effective depth of measurement increases, the relative differences in responses decrease and eventually converge. Conclusions: Surface dosimetry using solid state detectors is a straightforward method of verifying dosimetric calculations. Care must be taken when using these systems for surface dosimetry with highly blocked fields as their non‐tissue equivalence makes these detectors overly sensitive to low‐energy scattered electrons and bremsstrahlung photons produced from the block edge. Measurements taken near dmax will not show a significant deviation from the actual dose and do not need to account for this effect.
SU‐E‐T‐115: A Novel Cylindrical 3D Water Scanner for Beam Data Collection: II. Dosimetric Characteristics
Authors: Li J , Yan G , Lu B , Huang Y , Liu C
Published: June 2012

Purpose: To study the dosimetric characteristics of a commercial three‐dimensional water scanner (3D SCANNER, Sun Nuclear Corp). The novel cylindrical scanner uses a compact electrometer mounted on the side of the tank, eliminating the need for chamber extension cables. The electrometer has a wide dynamic range, requiring no gain adjustment as scanning conditions change, e.g., field size, dose rate, wedge field, etc. Methods: Measurements from the 3D SCANNER were compared against those from another commercial scanner (Blue Phantom, IBA Dosimetry). Comparable collection intervals and scanning speeds were used on both systems. Profile and depth measurements were performed for open field beams (6 and 18 MV; 10‐cm and 30‐cm squared fields; depths of dmax, 10, and 30 cm) and wedged fields (6 and 18 MV; 30‐cm squared field; depth of 10 cm). Electron beam profile and depth measurements were performed for a 20‐cm squared applicator (6, 12, and 20 MeV; depth of dmax). The root mean square (RMS) values were determined for each scanner's measurements. Results: The measured field sizes were within 0.06 cm and 0.05 cm for photon and electron beams, respectively. The photon D10/D20 ratios differed by < 0.4% and the electron I50 values were within 0.02 cm. The RMS of the profiles was approximately 0.1% for both the 3D SCANNER and Blue Phantom measurements. Between the two scanners, all measurements agreed within RMS, excluding the penumbra region. Two exceptions occurred: a 0.5% difference was observed in the shoulder of the 12 MeV profiles, and a 0.8% difference was observed in the 6 MeV depth measurements near the surface. Conclusions: The quality of the scanned profile and depth measurements from the 3D SCANNER is comparable to that of another commercial scanner. Both scanning systems have similar levels of scanning noise. This work was partially supported by a research grant from Sun Nuclear Corp., Melbourne, FL
SU‐E‐T‐118: Characterization of EBT3 Films in Photon and Proton Beams
Authors: Sorriaux J , Rossomme S , Kacperek A , Bertrand D , Vynckier S , Sterpin E
Published: June 2012

Purpose: To measure the calibration curves of EBT3 dosimetry films in photon and proton beams and to quantify the related uncertainties from one beam type to another. Methods: EBT3 Gafchromic films have similar properties than EBT2 with a symmetric construction and a matte polyester substrate to prevent Newton's ring artefacts. Films from a same batch were exposed in three different beam qualities, an Elekta SL25 6 MV photon beam, a 100 MeV 5×5cm2 proton beam delivered by pencil‐beam scanning dedicated system from IBA and a 60 MeV fixed proton beam (2.5cm in diameter) at Clatterbridge Center for Oncology (CCO), UK. The films were read using an EPSON 10000 XL/PRO scanner. Film calibration curves were acquired for all modalities within a range of 0.05 to 20 Gy. Influence of increasing linear‐energy transfer (LET) on film response was investigated by comparing dose measured by EBT3 to a silicon diode detector in depth for a fully‐modulated beam using the CCO beam line (homogeneous dose with distal end at 3.1cm in water). A comprehensive uncertainty budget (reproducibility, uniformity'¦) was estimated on films irradiated by Elekta SL25. Results: The main source of uncertainty was the non‐uniformity of the scanner response. By placing all the irradiated films at the center of the scanner, the uncertainty could be reduced from 5.8% to 1.9% (1 sigma). For all beams and energies, the calibration curves were matched within uncertainties. Along the fully‐modulated depth dose curve, diode and EBT3 measurement were in a 4% agreement point‐to‐point, indicating films weak dependence with LET. Conclusions: The weak influence of LET, beam type and energy on film response as well as its small uncertainty make EBT3 suitable for relative dosimetry and a promising candidate for measuring correction factors (quality, recombination,'¦) for reference dosimetry with ion chambers of non‐standard beams (e.g pencil‐beam scanning proton‐therapy). â€œThis work is supported by the Walloon Region under the project name InVivoIGT, convention number 1017266.â€