bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐J‐132: Estimate Absorbed Dose Using Micro PET Imaging of Rat Brain Tumor with I‐124 Infusion Followed by F‐18 Injection
Authors: Luo J , Jang S
Published: August 2010

OBJECTIVE: This study was to estimate absorbed dose using micro PET imaging of the rat brain tumor with I‐124 Infusion followed by F‐18 Injection METHOD: Two tumor‐bearing rats were infused intratumorally with 2.1 uCi I‐124 Gd Tagged Metallofullerenes. A 2‐hour post I‐124 infusion PET scan was performed on each animal to identify the infusion site and possible free I‐124 distribution. Following I‐124 imaging, 32 uCi and 182 uCi of F‐18 FDG were administered respectively by IP injection to highlight brain anatomy at different image contrasts. Each animal was imaged for 5 minutes using a uPET scanner, 350 – 550 keV energy window, without transmission scanning. F‐18 imaging started 5 and 45 minutes subsequently after the IP injection. Image reconstruction algorithms (FBP, 3D OSEM, 3D Re‐Projection with or without Hanning Filter) were used for comparison. Image processing and analysis were conducted on ASIPro VM platform. The infusion site and tumor were measured by FWHM from Gaussian fit of count profiles. Absorbed dose was estimated using MIRD based on RoI counts from the PET images. RESULT: The post infusion PET scan showed high I‐124 concentration in tumor and minimum free iodine in the rest of body. The 3D OSEM reconstruction improved spatial resolution and contrast compared with the FBP and 3DRP algorithms. The infusion site was 5.21 mm (FWHM). Tumor dose of I‐124 (19.8 Gy) was accurate because of high contrast of I‐124 image, and the dose for F‐18 depended on the RoI definition. CONCLUSION: Radiation dosimetry using PET scan depends on image quantification which is affected by the reconstruction algorithm selected and the acquisition or processing protocol. Radiation dosimetry using PET scan depends on image quantification which is affected by the reconstruction algorithm selected and the acquisition or processing protocol.
SU‐GG‐J‐133: Dosimetric Characterization of an Accessory Designed to Irradiate Rodents Using the Gamma Knife Perfexion Treatment System (PFX)
Authors: Wooten H , Tellez J , Drzymala R
Published: August 2010

Purpose: Dosimetric characterization of an accessory designed to irradiate rodents using the Gamma Knife Perfexion treatment system (PFX). Methods and Materials: A rodent holder assembly was designed to be compatible with the PFX for the irradiation of up to 6 anesthetized, immobilized mice in one session. The holder design includes modular plastic construction materials compatible with MR and CT image guidance. Rodent positions are aligned to the holder assembly through sighting of external features on each animal and are targeted using the stereotactic coordinate system of the PFX and the Leksell GammaPlan planning system (LGP). Currently, GammaPlan versions cannot easily model the mice on the rodent holder assembly. Co‐60 dose rates and isodose distributions for various radiation beam configurations and depths were determined using EBT radiochromic film and micro‐LiF TLDs in rodent‐sized polystyrene phantoms mounted on the assembly. Published tissue air ratios were spot‐checked using TPRs obtained in a special step‐wise tapered polystyrene phantom. Results: The measured dose rates using film agreed to within 7% of expected values computed from published TAR and Elekta output data. Dose rates are about 55–60% greater compared to Elekta 16cm sphere calibration. Maximum dose rates scale with the number of unblocked sources. Film dosimetry shows that the 4mm collimator irradiates an ellipsoidal volume with approximately a 3 mm diameter at the 90% isodose. Isodose distributions can be shaped by blocking sectors 3 and 7 to avoid specific rodent anatomy and the adjacent rodent positions on the holder assembly. Conclusion: Deviations from published data can be explained to result from attenuation of the dose rates by the rodent holder. Our dosimetric data supports the use of PFX for multiple‐rodent irradiation. The system can be used to determine response of rodent brain tissue and tumors to radiation and the effect of molecular radiation modifiers.
SU‐GG‐J‐134: Non‐Thermal Cell Damage and Therapeutic Potential of MR Guided High‐Intensity Focused Ultrasound
Authors: Ma C , Mu Z , Chen L
Published: August 2010

Purpose: High‐intensity focused ultrasound (HIFU) has garnered increasing interest in therapeutic applications for occlusion of blood flow, sealing of bleeding vessels, sonothrombolysis, myocardium revascularization channel creation, opening of the blood brain barrier and transdermal drug delivery. In this work, we investigate the non‐thermal cell damage and therapeutic potential of HIFU for treating non‐operable, radiation‐ and chemo‐resistant cancers. Method and Materials: An InSightec ExAblate 2000 with a 1.5T GE MR scanner was used in this study. MR thermometry was used to monitor the temperature elevation in real time to ensure non‐thermal (below 42°C) sonication. LNCaP and PC3 cells were placed in thin plastic vessels and inserted in an ultrasound gel phantom with the ultrasound beam focused on the tumor cells. Cells were exposed to pulsed ultrasound (1MHz; 6W and 10W acoustic power; 5Hz frequency; 0.5duty cycle: 0.1s power on, 0.1s power off) for 60sec. Cell viability was assessed by trypan blue dye exclusion and clonogenic assay. Results: Non‐thermal cell damage by HIFU exposure was observed for both LNCaP and PC3 cells. At 6W acoustic power, the cell‐death rate was 23.3+1.7% and at 10W it was 46.3+1.9% for the LNCaP cells (see table below). The control group has a 12.7+0.3% death rate. For PC3 cells, the cell‐death rate was 18.7+0.7% for the treated group and 9.0+0.6% for the control cells at 6W. The clonogenic assay results were consistent with the trypan blue dye analysis. Conclusions: Our in vitro experiments confirmed the non‐thermal effect of HIFU on prostate tumor cells. The exact mechanism for non‐thermal cell damage needs to be investigated. Further in vivo experiments are warranted to derive optimal ultrasound parameters for HIFU cancer therapy and to provide preclinical toxicity data. This work is supported by Focused Ultrasound Surgery Foundation, DOD PC073127 and Varian Medical Systems. Technical support from InSightec is acknowledged.
SU‐GG‐J‐137: Application of Unsupervised Spectral Clustering in 3D for PET Tumor Segmentation: A Digital Phantom Study
Authors: Yang F , Aristophanous M , Yang D , Low D , Lu W
Published: August 2010

Purpose: Spectral clustering refers to a class of techniques which rely on the eigenstructure of a similarity matrix to partition pixels into disjoint clusters. This study intended to investigate the feasibility of using the unsupervised spectral clustering method for PET tumor segmentation. Method and Materials: In this study a digital PET phantom was adopted as the source to generate PET images with heterogeneous and/or irregular shaped tumors. The simulation was carried out by feeding the Zubal phantom as anatomical input to the SimSET (the Simulation System for Emission Tomography) software, which employs Monte Carlo techniques to model the underlying physical processes and imaging system to produce simulated emission tomography data. There were a total of 30 lung tumors with a variety of heterogeneous activities and/or irregular shapes simulated. The unsupervised spectral clustering algorithm was then applied to segment the simulated images. Segmentation accuracy was assessed with two metrics: volume detection error (VDE) and volume overlap measure (VOM). Results: The spectral clustering technique partitions the image volume into an optimal number of clusters according to the pair‐wise similarity measure between voxels. Upon segmentation, one can then select the segmented tumor regions for subsequent processing and analysis. Applying the spectral clustering technique on all the 30 simulated PET images shows that VDE ranges from −5.5% to 6.2%, and VOM ranges from 0.94 to 1.Conclusion: This study shows the potential of the unsupervised 3D spectral clustering method for PET tumor segmentation. Segmentation performance in terms of VDE and VOM on stimulated PET images shows this method may have the potential for accurate and consistent segmentation of tumors. Compared with thresholding‐based PET tumor delineation techniques, it segments the PET image without requiring any threshold‐volume relationship. Studies to further evaluate this method on patient data are planned.
SU‐GG‐J‐142: Investigation of MIP PET in Motion‐Encompassing Methods to Account for Respiratory Motion in Radiotherapy
Authors: Liu C , Schmitz R , Hendrickson K , Patel S , Jeraj R , Kinahan P
Published: August 2010

Purpose: Radiation treatment planning with PET/CT has been shown to be beneficial and leads to smaller variations in target delineation than using CT only. This study investigates the 3D maximum intensity projection (MIP) PET images derived from respiratory‐gated 4D PET as a complement to the MIP CT derived from a 4D CT dataset and their use in treatment planning as a means to account for respiratory motion in free‐breathing radiotherapy for lung and abdomen tumors. Methods and materials: 21 PET/CT patient datasets with 31 lesions were acquired. The patient respiratory motion was monitored by the Real‐time Position Management system. PET listmode data were phase‐binned into 5 frames and reconstructed. 3D MIP PET images were derived from the 5‐bin 4D PET datasets. Tumor volumes were determined by an automatic segmentation method and compared for the MIP PET and static PET images. The tumor motion amplitude was determined by measuring the centroid in phase‐gated images. The impact of tumor size and motion amplitude were investigated. In addition, PET data were binned into 10 frames to study the noise change in MIP PET. The comparison between the MIP PET and MIP CT is under study. Results: Compared to static PET, the tumor volumes in the MIP PET increased by 10% 14%, with a maximum increase of 44%. The volume increases are larger for the smaller tumors sizes and larger motion amplitudes. The image noise of the MIP PET is higher than in static PET and increases with number of phase bins. Conclusion: The MIP PET has a potential to complement MIP CT to inform the radiation treatment planning for motion‐encompassing radiotherapy by accounting for respiratory motion.
SU‐GG‐J‐145: PET Image Simulation of Isotopes Produced in Patient during Proton Therapy
Authors: Zou W , Dolney D , McDonough J , Surti S , Karp J
Published: August 2010

Introduction — During proton therapy, positron emitting radio‐isotopes are produced along the track where incident proton beam interacts with human tissue. The isotope activity profile is related to the proton dose distribution and can be imaged using a PET scanner. Many factors affect the obtained PET images, such as various patient geometry, time interval between proton therapy and PET scan, the PET scan duration, and PET scanner design. In order to quantitatively relate the obtained PET image to the dose delivered in patient, an understanding of these factors in the PET image is necessary. This work is to develop a simulation pathway to facilitate such study. Method — The simulation starts with proton beam irradiating the patient geometry, obtains isotopes distribution, records in list‐mode gammas from positron annihilations arriving at PET ring geometry, and finally reconstructs the PET images. The patient DICOM CT are input to GEANT4 code to construct the geometry. Experimental isotope cross‐section data are built into the simulation. The positron emitter 3D map is used as the source in the PET scanner simulation. The PET scanner geometry, crystal detector type and its cross‐section are the input parameters. The received signals in PET crystals are output in list‐mode. Image reconstruction is performed with iterative TOF image reconstruction together with data corrections for scatter and attenuation. Results — The 3‐D proton dose and isotope distributions are obtained. The reconstructed isotope distribution from PET simulation correlates with the original isotope map generated from proton beam irradiation. Some of the factors affecting the obtained PET images will be addressed. In the future, the simulation can be used to quantitatively correlate to the proton dose. It can also facilitate the design of a PET system that can yield an accurate and efficient reconstruction of the isotope activities and verify the proton dose.
SU‐GG‐J‐148: Evaluation of Performance of a Conceptual Time‐Resolved Proton Range Telescope for In‐Room Respiration Monitoring Using Monte Carlo Simulations and 4DCT Patient Data
Authors: Han B , Ding A , Xu X , Bednarz B , Sharp G , Choi N , Chen G , Riper K
Published: August 2010

Purpose: To demonstrate the feasibility to perform and optimize a time‐resolved proton range telescope (TRRT) in localization of moving lung tumors and quantification of proton range variations. Method: A TRRT is designed to detect transmission protons and provide a fluoroscopic image showing tumor location and range perturbations prior to or during treatment. MCNPX code with a particle‐tracking feature was used to simulate and evaluate the TRRT performance, especially in visualizing and quantifying the proton range variations during respiration. Monoenergetic protons, 235 MeV in a 15cm × 15cm field, were tracked one by one as they pass through position detectors, 4DCT phantom, and finally scintillators that measured position and residual energies. Mass density and elemental composition of tissues were defined from a set of 4DCT of a lung patient. Radiological pathlength in the patient was determined by an energy‐range algorithm. Effects of multiple Coulomb scattering on image quality were determined by comparison with a pure ray‐tracing algorithm in Aqualyzer. Results: Interesting water equivalent length (WEL) maps for 10 respiratory phases were obtained to form fluoroscopic sequences. Appropriate color‐map windowing was used to visualize and measure tumor trajectories. The tumor trajectory extracted from the proton fluoroscopic simulation agreed with ground‐truth established by 4DCT to about 1mm. WEL difference maps were reconstructed to quantify respiration‐induced range changes. The maximum proton range pullback for the tumor target was measured to be 2.29 cm. Rejection of wide angle scatter events was found to effectively sharpen the image. Clinical applications to track the tumor during proton therapy using the range telescope are discussed. Conclusion: The performance of a TRRT is systematically studied and demonstrated by Monte Carlo simulations. When parameters are optimized, localization of a 2cm tumor is possible with an accuracy of about 1mm. Technical requirements for an operational device are discussed, including GPU acceleration.
SU‐GG‐J‐153: Voxel‐Based Phenomenological SUV‐Dose Response Model for the Human Parotid Glands
Authors: Cannon B , Tucker S , Chambers M , Garden A , Martel M , Schwartz D , Dong L
Published: August 2010

Purpose: The goal of this study is to evaluate SUV as an imaging biomarker of parotid function following radiotherapy (RT) and to develop a phenomenological model of SUV‐dose response, enabling prediction of the biomarker prior to RT. Method and Materials: As part of an ongoing study, patients (n = 8) with head and neck cancer (HNC) had 18F‐FDG PET/CT studies performed before (within 30 days) and following RT (∼50 days). In addition, resting and stimulated whole mouth saliva was collected. Next, a deformable image registration algorithm was utilized to map parotid contours from planning CT (PCT) images to pre‐ and post‐RT PET/CT studies, separately. Mean SUV was then calculated for the parotid glands at both time points and compared to collected saliva. The SUV‐dose response relationship was assessed in a separate cohort (n = 60) also treated for HNC. Pre‐ and post‐RT PET/CT images were deformably aligned to PCT images to achieve correspondence between SUV and planned dose. SUV response was then modeled using a single parameter, incorporating planned dose and pre‐RT SUV; defined as metabolic dose. Results: Post‐RT stimulated saliva and SUV decreased (59% and 20%, respectively) in seven patients. For one patient, stimulated saliva and SUV increased (14% and 11%, respectively). Fractional SUV correlated significantly with xerostomia grade, P < 0.01 and Spearman's ρ = −0.964. A second order polynomial provided an adequate fit to the log transformed SUV‐dose response curve, adjusted R2 = 0.95. Post‐RT SUV was predicted within 3% for an exemplary patient, but overestimated (50%) in the worst case. Conclusions: Pilot data suggest that SUV is significantly correlated with parotid saliva output. Furthermore, the feasibility of predicting reductions in SUV, prior to treatment delivery, has been demonstrated.

Conflict of Interest: Research partially sponsored by Varian Medical Systems.
SU‐GG‐J‐158: Functional Diffusion Map Analysis in Assessing Brain Tumor Response to Therapy
Authors: Wang J , Curtis W , Chandler A
Published: August 2010

Background: DTI has been used as a functional imaging tool in the assessment of tumor response to therapy, mostly by monitoring the changes in DTI matrices such as ADC and FA during the course of treatment. In this study, we studied the predictive value of various functional diffusion maps (fDM) generated using the ADC, FA and transverse diffusivity that were acquired pre‐ and post‐ anti‐VEGA therapy in brain tumor patients. Materials and Methods: Functional diffusion maps were generated by comparing the pre‐ and post‐ therapy DTI studies and the changes of DTI matrices such as ADC, FA and the transverse diffusivity. Prior to the creation of the fDMs, all images including the anatomical images (T1, T2, FLAIR and post‐contrast T1) for each patient were co‐registered to the DTI images for each visit and then across all visits. All fDMs were compared and correlated with the status of radiographic response. Results: For core tumor volume defined by post‐contrast T1 images, fDMs generated with ADC values correlated the best with the radiographic response, while there was no obvious difference between the fDMs generated with ADC (Fig1a) and those with the transverse diffusivity. The fDM generated with FA differed from those with ADC and may have predictive value in the direction of tumor progression. Conclusion and Discussion: The fDMs are useful tools in the assessment of tumor response to therapy. fDM analysis of the pretumoral white‐matter area may have the potential to assess the tumor cell progression in the WM tract.
SU‐GG‐T‐161: Effect of Leaf Motion Calculator Parameters in Head and Neck IMRT
Authors: Das KJ Maria , Mani KR , Yoganathan SA , Agarwal A , Kumar S , Gandhi Sanjay
Published: August 2010

Purpose: To investigate the dosimetric effect of the Leaf Motion Calculator (LMC) parameters using sliding window technique in head and neck IMRT. Materials and Methods: Two head and neck IMRT patients (T1/T2,N0) were selected for this study. The actual fluence of the IMRT plans were calculated by varying the LMC parameters which includes, dose rates from 100 to 600 MU/min, MLC limiting leaf speed (0.5 to 3.0 cm/sec) and minimum dynamic leaf gap (0.05 to 0.2cm) from the same optimal fluence. The doses to OAR, total monitor unit (MU), low and high dose volumes were analyzed. Results: The doses to OAR, low and high dose volume (10%, 50% & 95% of isodose) increases with increase in dose rate and decreases with increase in limiting leaf speed. The total MU also increases with increase in dose rate and decreases with increase in leaf speed. When the dose rate increases from 300 MU/min to 600MU/min, the total MU significantly increase by 12% at a limiting leaf speed of 2.5cm/sec. There was no significant difference in doses to OAR, total MU, low and high dose volumes for minimum dynamic leaf gap between 0.05 to 0.10 cm. Conclusion: OAR sparing is observed with lower dose rate and higher leaf speed. There is no significant difference in PTV coverage and high dose volumes with dose rate as well as limited leaf speed. However, in the low dose volumes significant difference was observed for leaf speed less than 1.5cm/sec.
SU‐GG‐T‐162: Using Tumor Motion Trajectory as a Constraint for 4D‐IMRT Treatment Planning
Authors: Qin L , Zhang J
Published: August 2010

Purpose: To develop a 4D‐IMRT treatment planning technique by adding a tumor motion trajectory (TMTJ) as a constraint in a commercially available Treatment Planning System (TPS). The goal is to create an IMRT plan with a set of MLC segments catering for the motion of the patient anatomy extracted from 4D‐CT images. Method and Materials: 4D‐CT images were obtained from three lung cancer patients. The 4D protocol divided the breathing cycle into ten phases followed by a Maximum Intensity Projection (MIP) volume reconstruction. ITVs were contoured based on the MIP volumes. GTVs were contoured on all ten CT phases to generate a TMTJ, defined as the position of the centroid of the GTV on all phases. A tube shaped contour (TBC) with about 1 cm diameter along the TMTJ and inside the GTV was generated. TBC was added to the objective function as a constraint with minimum dose‐volume histogram (DVH) set to prescribed dose. IMRT plans were generated by using Pinnacle DMPO with and without the TMTJ constraint. Results: The IMRT plans generated with TMTJ constraints optimized the MLC segment shapes and weights for each beam with the TBC being forced/encouraged to inside of the segmented fields. The percentage of total MUs delivered to the largest area segments in each beam increased from 16.4% of the total MUs to 21.5%. The MU weight increased up to 20% by using TMTJ constrain. The DVHs for PTV and ORs, dose distributions and total MUs for plans with/without TMTJ constraints were very similar. Conclusion: The 4D tumor motion trajectory information can be used as a constraint in the Pinnacle DMPO to obtain tempospatially optimized IMRT plans. The method shows the potential to significantly reducing the dosimetric inaccuracies introduced by the interplay between organ motion and multileaf collimator (MLC) motion for IMRT.
SU‐GG‐T‐164: Population Dose Volume Histograms: An Institutional Analysis of An Uniform Sample of IMRT Plans for Prostate Treatments
Authors: Neves‐Junior W , Casagrande T , Alves T , Mancini A , Pelosi E , Haddad C , Silva J
Published: August 2010

Purpose: Evaluate an Institutional sample of prostate IMRT results, constructing a Population based Dose Volume Histogram (DVHp) to compare with literature and use it as an internal benchmark for plan approval and quality assurance. Finally, seek for relations between dosimetric plan results with anatomic variables to create predictive parameters. Method and Materials: Retrospective analysis of 40 patients that received the following treatment: IMRT with 5 beams (60Gy to the prostate and 54Gy to the seminal vesicles SV) + 3DCRT boost with 3 beams (20Gy to the prostate), 10mm isotropical PTV margins. Technical details: Step‐and‐Shoot, 18MV beam energy, Siemens KonRad treatment planning system, 10mm MLC leaf width. Structures analyzed: bladder, rectum, femur heads, penile bulb, PTV80Gy (prostate+ margin), PTV54Gy (prostate +SV +margin). Main DVH points for each structure were used to build the DVHp. Results: For Bladder, the V80Gy was 11±7%. The V75Gy, V70Gy, V65Gy, were, respectively, 17±11%, 21±14%, 23±16% for bladder and 13±3%, 18±4%, 22±5% for rectum and its V60Gy was 28±6%. The Dmax, was 86±1Gy for bladder, 85±1Gy for rectum, and 50±4Gy for femur. For penile bulb, the average dose was 44±9Gy. For targets, the D95%, Average Dose, Dmin and Dmax were, respectively 79.4±0.6Gy, 83.9±0.8Gy, 71±4Gy and 88±1Gy for the PTV80Gy and 64±6Gy, 80±2Gy, 53±5Gy and 88±1Gy for PTV54Gy (which includes the PTV80Gy). The rectum doses have weak correlation with its volume (r=−0.29±0.02), but a moderate to strong correlation with its PTV overlap (r=0.71±0.05) ‐ more than 20% Rectum‐PTV overlap means 66% chance of violating the V75Gy<15% constraint. The bladder doses have a moderate correlation with its volume (r=−0.62±0.04) and a strong correlation with its PTV overlap (r=0.80±0.01). Conclusion: In general, the DVHp meets literature recommendations regarding prescription and dose limits. This analysis allows evaluating future plans based on Institutional acceptance criteria, more detailed and restrictive than literature.
SU‐GG‐T‐172: Dosimetric Comparison of Low Dose Region (V5) for Tomotherapy versus Conventional IMRT Plans of Lung Cancer
Authors: Jang S , Krafft S , Hamilton R , Watchman C , Nguyen N
Published: August 2010

Purpose: To compare clinical Tomotherapy plans for lung cancer with conventional IMRT plans in terms of mean lung/ventricle dose, heterogeneity index, V5, V10, V15, and V20 for total lung. Method: The conventional IMRT plans for 16 patients treated with clinical Tomotherapy plans were made retrospectively with Pinnacle 8.0 for Varian 6EX. We designed the conventional plans to achieve comparable target coverage as well as maximum spinal cord dose of the clinical Tomotherapy plans. To minimize any planning‐related subjective issue, nine‐beam angles aligned through anterior‐posterior directions were chosen for all cases. Multiple iterative processes were performed until the objective functions were minimized and the treatment planning goals were met. Dosimetric parameters of the two types of plans were compared in terms of avoidance of normal tissues (i.e., total lung and ventricle). Results Median differences in lung between the Tomotherapy plans and conventional IMRT plans for 16 patients were 7.4%, 4.4%, 3.0%, and 1.9% for V5, V10, V15, and V20, respectively. Median ratios of mean lung dose and mean ventricle dose between the Tomotherapy plans and conventional IMRT plans were 1.2 (range, 0.97∼1.41) and 1.6 (range, 0.86∼2.55), demonstrating that dose to normal tissues for conventional IMRT plans, especially in low dose region (V5∼V10), was considerably lower than Tomotherapy plans for lung cancer. However, median ratio of heterogeneity index defined as D5%/D95% was 0.96 (range, 0.86∼2.55) indicating better dose‐uniformity of Tomotherapy plans, which resulted from the difference in number of beam angles for the two different plans. Conclusions Median V5 of conventional IMRT plans was lower than that of Tomotherapy plans, showing that conventional IMRT plan appears to be effective in low dose region (V5) for lung cancer. However, Tomotherapy plans showed better dose‐uniformity in terms of target coverage.
SU‐GG‐T‐173: Dosimetric Verification of IMRT Fields Using GafChromic® EBT‐2 Film
Authors: McLawhorn R , Ter‐Antonyan R , Benedict S , Wijesooriya K
Published: August 2010

Purpose: Film based dosimetry often has advantages over detector based dosimetry when measurements with high spatial resolution are needed. We present comparisons of dosimetric verification measurements using GafChromic® EBT‐2 film with IBA Dosimetry® I'mRT MatriXX with MultiCube. Methods and Materials: Dosimetric measurements of IMRT treatment fields for 5 patients were performed using GafChromic® EBT‐2 film and compared to measurements performed using IBA Dosimetry® MatriXX. The measurement results from both systems were analyzed using IBA Dosimetry® OmniPro‐I'mRT software. GafChromic® films (8”×10”) were scanned both pre‐ and post‐irradiation using an Epson® 10000XL flatbed scanner. The pre‐irradiation films were used for background subtraction in the OmniPro software. The films were placed in a solid water phantom for irradiation. The MatriXX system uses a 32×32 array of 0.08 cc ion chambers with a center to center spacing of approximately 0.76 cm to measure absolute dose distributions within a solid phantom. Verification plans were created in Pinnacle treatment planning software for both the MatriXX and solid water phantoms. The results were analyzed by comparison of the measured central axis dose, gamma analysis (3 % and 3mm agreement), and evaluation of dose profiles and isodose distributions. Results: Better agreement with the planned central axis dose is seen for the measurements with the MatriXX system over those measured with GafChromic® EBT‐2 film. However, the film‐based measurements show improved agreement in the dose profiles and isodose distributions. These improvements result in better gamma analysis agreement, increasing the average gamma from 97.39% to 99.49%. Conclusion: GafChromic® EBT‐2 can effectively be used for film‐based dosimetry and may provide superior results for small fields, areas with steep gradients, or beam delivery geometries where detector based measurements are limited. Some dosimetry software, such as IBA Dosimetry® OmniPro‐I'mRT, may allow users to analyze GafChromic® EBT‐2 film without purchasing additional software.
SU‐GG‐T‐181: Effects of the MLC Characteristics on IMRT Dose Distribution
Authors: Li J S , Lin T , Chen L , Price R , Ma C‐M
Published: August 2010

Purpose: The purpose of this study is to investigate the characteristics of the Multi‐leaf collimator (MLC) including the leaf thickness, leakage and the tongue‐and‐groove structure and their effects on the dose distribution of intensity‐modulated radiation therapy (IMRT) and patient‐specific IMRT quality assurance (QA). Methods: Monte Carlo dose calculations were performed based on intensity maps that were built from the actual deliverable IMRT leaf sequences with and without considering the characteristics of MLC using our in‐house Monte Carlo software. Intensity maps with a fine resolution (0.1×0.1mm2 pixel size) were used for IMRT dose calculation. The mean dose of the treatment target and the voxel doses in high dose regions of 7 IMRT plans generated by different treatment planning systems for Varian 21EX and Siemens Primus linear accelerators were used for comparison and evaluation. Results: The MLC leaf thickness, leakage and the tongue‐and‐groove structure can change the mean dose by up to 4.5%, 5.6% and 5.3%, respectively, when these factors are considered separately. They also cause significant uncertainties in the voxel doses with standard deviations of up to 0.7%, 2.1% and 1.3%, respectively. The fudge factors applied in treatment planning systems (TPS) can only compensate the mean dose change partially because the effects are different for individual IMRT plans. The uncorrected mean dose change and the voxel dose uncertainties are shown as the difference between the TPS calculation and measurements in measurement‐based IMRT QA. Conclusions: It is concluded that the MLC characteristics can affect the mean target dose and cause significant uncertainties in individual voxel doses. The dose uncertainties caused by MLC characteristics are a major source of dose discrepancies for measurement‐based IMRT QA because they are not fully considered in the TPS.
SU‐GG‐T‐182: Two Years of Clinical Experience with DAVID ‐ A Translucent Multi‐Wire Detector for On‐Line Verification of Patient Treatments
Authors: Poppe B , Looe H , Harder D , Upphoff Y , Ruehmann A , Willborn K
Published: August 2010

Purpose: The DAVID system is used as an independent monitor system positioned between MLC and patient to assure the correct application of IMRT deliveries. In this work we report on our two year clinical experience with the system and will discuss detected treatment deviations and errors. Material and Methods: The DAVID system (PTW‐Freiburg, Germany) is a translucent multiwire transmission ionisation chamber, placed in the accessory holder of the linear accelerator. Each detection wire of the chamber is positioned in the projection line of a MLC leaf pair, resulting in a signal proportional to the line integral of the ionisation density (MLC opening). After the dosimetric verification of an IMRT plan, the values measured by all detection wires of the system are stored for each segment as reference values. During daily treatment the signals are re‐measured and compared to the reference values. A visual display of the readings and reference levels allows a fast overview about the correctness of the irradiation. Additionally a warning occurs if the predefined deviation level is exceeded. Results: The system is especially useful for all cases in which the MLC reproducibility is an issue such as in highly complex treatment deliveries. The permanent visual display of the signal in the control room has been established in our clinic as a reliable and fast tool, helping to identify errors that might not have been detected without this method. So far our experience with the system is based on the verification of approximately 50 IMRT plans with a total irradiated number of more than 60.000 sub‐segments over approximately 2 years. The main recorded deviations have been drifts of the linear accelerator output as well as block‐jaw and MLC decalibrations. In one case lost MLC segments resulting in a possible irradiation of open fields have been detected.
SU‐GG‐T‐187: Impact of Breathing Irreproducibility on Dose Delivery for Phase and Amplitude Gating
Authors: An S , Jung J , Yeo I , Lee R , Yi B
Published: August 2010

Purpose: Gated radiation therapy (gRT) reduces the effect of organ motion during treatment. Once internal margin due to residual motion is determined by four‐dimensional computer tomography, it is used throughout entire treatments. However, patient's breathing is not completely reproducible during treatments, so dose distribution within internal target volume (ITV) can change from planned distribution. Therefore, we aim at evaluating effect of breathing changes on dose delivery of gRT. Methods: Each of nineteen patients with lung cancer was given five respiratory sessions,* and each session included free‐breathing (FB), audio‐instruction (A), and audio‐visual biofeedback (AV). We assumed that the first session generates breathing traces for ITV determination, and others traces for delivery determination. A computational model was developed for calculating delivered dose under motion for phase and amplitude gating: dose at virtual detectors was expressed as a function of phases and positions. The doses in clinical target volume and normal tissue within ITV were evaluated using the volume receiving >90% of the prescription dose (V90). Results: As we used a maximum extent of residual motion from the first session, CTV coverage did not show visible change during treatments. However, increases of 21.6% (range: −49.00% ∼ 211.61%) and 2.51% (−45.65% ∼ 45.27%) in V90 of normal tissue in ITV were observed for phase and amplitude gating, respectively. Phase gating showed that V90 of FB was higher than that of AV (FB: 27.23% and AV: 16.28%), while amplitude gating did not show notable differences. The amplitude gating saved more normal tissue than phase gating overall and particularly for FB. Use of maximum residual motion in ITV over the entire trace may not be possible, and CTV coverage is questionable. Conclusion: This study quantified dose delivery for gRT. *We thank R. George for providing data. In part supported by Nuclear R&D project from MEST, Korea
SU‐GG‐T‐191: DynaLog File Analysis for IMRT Delivery Verification
Authors: Aydogan B , Smith B , Li J
Published: August 2010

Purpose: To develop a method based on the analysis of the Varian DynaLog files as part of the routine IMRT QA procedure. Method and Materials: The DynaLog files of a Varian Millennium MLC were analyzed using an in‐house software. The expected and actual locations of each MLC leaf at a number of time intervals were extracted from the DynaLog files and were used to calculate the expected and delivered fluence maps. A pixel‐by‐pixel Gamma‐comparison consisting of leaf position deviation and fluence discrepancy between the expected and the delivered values was performed. A pixel is accepted to pass this Gamma‐test if the leaf position deviation is within 1.0 mm at the plane of the isocenter and the fluence discrepancy is no greater than one dose fraction. A pass rate (RP) is defined for each IMRT field as the ratio of the number of pixels that pass the Gamma‐test to the total number of pixels. Retrospective studies of 183 patients with various forms of cancers who underwent IMRT were carried out. A total of 45,270 individual IMRT fields were analyzed. Results: More than 99.9% of the 45,270 IMRT fields showed RP > 95%, indicating excellent agreement between the delivered and the expected IMRT leaf positions as well as the dose fractions for the cases studied. Detailed investigation of the few fields that showed lower than 95% pass rate is underway. Conclusion: This work indicates that the information stored in the DynaLog files of the Varian MLC system can be exploited and used as a part of the routine IMRT QA. Furthermore, when integrated within the record and verify system, it may be used to alert whether an IMRT plan is being delivered correctly real‐time.
SU‐GG‐T‐192: Automatic Ionization Chamber Measurement Points Selection for IMRT Point Dose QA
Authors: Yang D , Goddu S , Rangaraj D
Published: August 2010

Purpose: This work is about a method to automatically select IC (ion‐chamber) QA measurement points. As a IMRT patient specific QA method, IC measurement is used to determine the absolute dose for delivery verification and monitor units (MU) correction purposes. Because of steep dose gradients, the locations of IC measurement points are critical. Manually selecting IC measurement points is a laborious and difficult work especially for highly modulated fields. Poor IC point selections often result in unnecessary failed measurements, or even inaccurate MU corrections. We therefore have developed a new and automatic method to determine the best IC measurement points. Methods: The key idea of the method is to rank the possible IC measurement points according to their local dose variations, and then to pick the best points. The local dose variation for a point is defined as the dose value range inside a 1 cm diameter sphere centered by the point. A composite ranking method is developed to include the local dose variation ratio, the absolute dose value, point location in the water phantom box, spatial distances and dose value differences from other good measurement points. In this way, the best multiple IC points can be determined not only based on the goodness of single point, but also to meet other dosimetry and physical requirements between the points. Results and conclusion: The method was firstly implemented and verified in MATLAB. we have ported it to Pinnacle scripts combined with C program, so to make it fully automated in Pinnacle TPS. It has been routinely used in our clinic for months. The results show that this method can speed up the IC QA planning process and reduce the rate of IC QA failures.
SU‐GG‐T‐195: On the Correlation of Conventional IMRT QA Metrics to Clinical Impact in Per‐Patient Dose QA
Authors: Zhen H , Nelms B , Tome W
Published: August 2010

Purpose: Per‐patient IMRT QA is often performed by comparing measured planar phantom dose to calculated planar phantom dose, per beam. The most common analysis metric is percent passing 3%/3mm (DTA). Similarly, TG‐119 reports utilizes a metric of 3%/3mm (Gamma) when discussing IMRT commissioning. In this work, we analyze the correlation of conventional per‐beam IMRT QA metrics to: 1) patient dose comparisons (3D %diff/DTA), and 2) important clinical dose endpoints in volumetric regions‐of‐interest. Method and Materials: For 24 Head/Neck IMRT plans, an accurate TPS beam model was error‐induced (four unique ways) to simulate IMRT calculation and/or delivery errors. The error‐free beam models were used to generate “virtual planar QA measurements” and analyzed in conventional ways against the error‐induced beams. The error‐free 3D patient doses were compared against the error‐induced 3D patient doses. This method produced a robust simulation (high precision, high data density of 3D patient dose) which is necessary given the practical inability to measure dose inside complicated patient anatomy. The 96 error‐induced plans were compared to the error‐free plans to quantify the correlation of conventional Planar QA metrics with relevant clinical endpoints such as: max cord dose, mean parotid dose, and D95 of the principal CTV. Results: No correlation was found between 3%/3mm conventional IMRT QA criteria and all clinical endpoints studied (R‐squared values of: 0.0314, 0.0272, 0.0899, and 0.0248 for predicting errors in the cord max, left parotid mean, right parotid mean, and CTV D95). There was also no correlation when considering 2%/2mm and 1%/1mm metrics. In addition, there were many examples of both false positives and false negatives using conventional IMRT QA methods/metrics to predict accurate patient dose. Conclusion: The location and magnitude of the errors was far more important than the quantity of the errors, and moving to patient ROI‐based error simulations is strongly recommended.
SU‐GG‐T‐200: Comparison of a Novel Transmission Detector to a Standard Measurement Technique for Patient IMRT Quality Assurance
Authors: McCurdy B , Malkoske K
Published: August 2010

Purpose: A new measurement‐based, pre‐treatment IMRT composite quality assurance (QA) procedure was compared to a standard QA method. The standard QA method consisted of delivering the treatment to a cuboidal IMRT phantom containing dose measuring media. This standard measurement employed Gaf‐chromic film sheets for relative dosimetry and an ion chamber for absolute dosimetry. The new method examined here used a novel transmission detector measurement (IBA Dosimetry) designed for in vivo patient dosimetry. However, before in vivo application, we compare to our standard QA method, which is the focus of this work. Method and Materials: Treatment plans for ten previously‐treated, head and neck IMRT patients were used. All treatment plans were QA'd with the standard method at the treatment beam angles. Measurements with the transmission detector (an array of 1600 IC's) were also performed at the treatment beam angles. The COMPASS software (IBA Dosimetry) converts these 2D‐array measurements to incident fluence, and then forward calculates dose in a patient model (ie. CT data). In this work the patient model was a cuboidal shaped solid‐water IMRT phantom (MedTec). Absolute doses were compared using isocentre location for the COMPASS/planning system, and a low dose gradient point location for the IC/planning system comparison (near isocentre, but not necessarily due to alignment needs during measurement). Results: On average, the standard QA method results for absolute dosimetry were different by 1.4±1.8% compared to the planning system (measured above planning system). On average the transmission detector based QA method results for absolute dosimetry were different by 0.3±1.6% compared to the planning system (measured above planning system). Conclusion: QA results using the COMPASS software with the transmission detector were comparable to the standard QA method.

Conflict of Interest: CancerCare Manitoba has a collaborative research agreement with IBA Dosimetry, although there is not direct financial support.
SU‐GG‐T‐201: Managing the Transition of IMRT QA Systems: From Radiographic Films to Detectors Array
Authors: Neves‐Junior W , Alves T , Casagrande T , Mancini A , Pelosi E , Haddad C
Published: August 2010

Purpose: This study aims to evaluate the results of intensity modulated radiotherapy quality assurance (IMRT QA) obtained with the MatriXX Evolution system and compare them to those previously obtained with, in order to implement this new technology in clinical routine, turning it more practical and still reliable. Materials and methods: Three moments are being compared: (i) an “Old Standard”, when the IMRT QA was performed with a polymethylmethacrylate slabs phantom, ionization chamber and radiographic film in the coronal plane; (ii) “Transition”, when the use of MatriXX system was initiated, but still in conjunction with a film simultaneously and (iii) “New Standard”, with MatriXX alone. The measurements were performed in linear accelerators with step‐and‐shoot technique. OmniPro‐I'mRT software was used to obtain the measured dose distributions (MatriXX and digitized film) and to compare them to calculated dose distributions ‐ by two treatment planning systems, Helax TMS and Oncentra MasterPlan. The percentage of points that meet the criteria of 3% dose difference and 3mm distance to agreement using the gamma function (γ) was evaluated, denoted here as γ≤1. Results: The IMRT QA with the “Old Standard” (141 patients) provides 2.1%±1.6% average dose difference and 95%±5% of γ≤1. During the “Transition” (48 patients), the average dose difference was 2.6%±1.4%, and the γ≤1 were 98%±2% with MatriXX and 99%±1% with films. Finally, with the “New Standard” (116 patients) a 2.2%±1.8% average dose difference and 98%±2% of γ≤1 where obtained. Conclusions: The results indicate a learning curve along this whole experience, as well as equivalence between film and MatriXX measured dose distributions, despite the distinct resolutions. IMRT QA performed with MatriXX Evolution system can properly substitute the ionization chamber and film pattern, reducing the time spent to execute these processes in clinical routine.
SU‐GG‐T‐203: Dosimetric Properties of a Transmission Detector in a 6 MV Photon Beam
Authors: Nakaguchi Y , Araki F , Saiga S
Published: August 2010

Introduction: The objective of this study was to investigate dosimetric properties of a new transmission dosimeter system. The system, COMPASS (IBA Dosimetry, Germany), contains 1600 plane parallel ionization chambers with a detector spacing of 6.5 mm and an active volume of 0.02 cm3. The COMPASS detector is mounted on the gantry of the linear accelerator to perform on‐line dose vilification during treatment. We checked capability of the system for dose verification in clinical intensity modulated radiotherapy (IMRT) plans. Methods and Materials: Fist, the COMPASS system was modeled by dosimteric data (percent depth dose, off‐axis ratio, and output factor) for a 6 MV photon beam. The dosimetric properties for simple square fields and various MLC test patterns were checked by comparison with those of MapCHECK and EDR2 films. The Monte Carlo simulations were also used as needed. The system was also compared for dose verification in clinical IMRT plans of neck cases. Results and Discussion: The influence of a transmission detector for radiation fields was insignificant except for buildup regions. For MLC test patterns, the COMPASS dose profiles agreed within 3% with those of MapCHECK, EDR2 films, and Monte Carlo simulations, except for complex MLC test patterns. Monte Carlo simulations agreed within 2% with EDR2 in the region more than 50cGy. In clinical examples, COMPASS agreed well with EDR2. COMPASS is a detector having the same accuracy as ion chambers in output measurements and is similar to a film for the dose profiles. The reason is because COMPASS dose distributions are based on measured fluence maps. Conclusions: The COMPASS system is useful for dose verification for IMRT plans. The system can use with the similar accuracy to traditional film measurements and 2D detectors. The beam model needs to be improved for complex dose profiles.