bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐363: Investigation of PRESAGE® Dosimeters for Proton Therapy
Authors: Grant R , Ibbott G , Zhu X , Carroll M , Adamovics J , Oldham M , Followill D 
Published: November 2011

Purpose: To evaluate a formulation of PRESAGE® intended for proton therapy and to use it to compare measurements with calculations for a spot scanning pencil proton beam and a passively scattered proton beam.Methods: Two 7.5 cm high by 9.5 cm diameter cylindrical PRESAGE® dosimeters were used. CT images were used to design two treatment plans with an Eclipse treatment planning system (TPS). The first plan used a single pencil beam of energy 153.2 MeV to provide a range of 16 cm in water. Four regions of the dosimeter were irradiated delivering doses in the peak of approximately 6, 10, 13 and 19 Gy(RBE) by rotating the dosimeter between spot deliveries. The second plan used a single passively scattered field with a spread out Bragg peak (SOBP) of 4 cm. This plan delivered approximately 10 Gy(RBE). The dosimeters were analyzed using an optical CT scanner. The measured optical densities were converted to dose via a calibration curve, exported to the CERR environment and fused to the treatment plan. Dose distributions were scaled to the SOBP plan. Dose profiles were taken along the axis of each spot and the SOBP and perpendicularly across the SOBP.Results: The dose measured in the peak of single spot irradiations increased proportionally to the MU setting. The distal falloff was steeper than predicted by the TPS. The cross profiles for the SOBP plan matched within 2 mm with the TPS. The depth profile was noisy within the modulated area. Noise decreased as dose increased for both dosimeters Conclusions: This formulation of PRESAGE® shows promise as a 3D dosimeter for proton therapy. A dose calibration specific to protons will facilitate further analysis and enable measurement of complex distributions.Work supported by PHS CA010953 and CA081647, awarded by NCI, DHHS.
SU‐E‐T‐416: Geometric and Dosimetric Effects of Residual Setup Error on the Cord and Larynx in Split‐Field Head and Neck Radiation Therapy
Authors: Yock A , Zhang L , Garden A , Dong L 
Published: November 2011

Purpose: In split‐field head and neck radiation therapy, image guided alignment of the superior IMRT field may result in large setup errors in the supraclavicular field. The goal of this study was to quantify geometric and dosimetric effects of residual setup error on the cord and larynx using the split‐field technique. Methods: Cord and larynx contours of 27 patients were propagated from a planning CT onto daily in‐room CTs using deformable registration. Cord contours were divided into superior and inferior structures at the match plane. Interfractional variations in the position of the larynx, superior cord, and inferior cord centroids were measured. Deformable registration allowed the calculation of cumulative dose delivered for each patient. The discrepancy between planned and delivered doses was compared for the maximum dose to the superior and inferior cord, mean dose to the larynx, larynx V50 and D60. Results: The group mean error, systematic error, and random error of the larynx centroid positions were 0.12cm, 0.06cm, and 0.08cm, laterally, and 0.15cm, 0.06cm, and 0.08cm in the anterior‐posterior direction. The lateral values for the superior cord were 0.04cm, 0.01cm, and 0.03cm, and for the inferior cord were 0.17cm, 0.06cm, and 0.12cm. Lateral and anterior‐posterior margins were 0.22cm and 0.20cm (larynx), 0.05cm and 0.08cm (superior cord), and 0.22cm and 0.35cm (inferior cord). Maximum cord dose was 43.8Gy. The average change in maximum dose was 0.3Gy (max=1.8Gy) for the superior cord, and −0.6Gy (max=1.2Gy) for the inferior cord. The increases in larynx mean dose, V50, and D60 averaged 1.6Gy (SD=2.5Gy), 3.24% (SD=3.52%), and 4.7Gy (SD=6.1Gy). Conclusions: While the inferior cord demonstrated the largest motion, it remained within the cord block. The increase in maximum cord dose and mean larynx dose were no more than 1.8Gy and 5.1Gy, respectively. The split‐field technique remains clinically viable.Funding provided by the University of Texas Graduate School of Biomedical Sciences at Houston.
SU‐E‐T‐774: on the Effects of Intrafraction Motion on TomoTherapy SIB Treatments of Lung Tumors: A 4D Monte Carlo Study including Non‐Rigid Registration and Beamlet‐Breathing Phase Correlation
Authors: Sterpin E , Orban J , Geets X , Goossens S , Wanet M , Mackie T , Vynckier S , Gregoire V , Janssens G 
Published: November 2011

Purpose: In the context of lung tumor TomoTherapy treatments including a boost region based on a PET scan distribution, the clinical impact of neglecting intra‐fraction motion during dose computation was evaluated with 4D Monte Carlo (MC) simulations. Methods: The study includes ten lung tumor patients including a boost region defined using PET data and treated simultaneously with the remaining of the target volume (simultaneous integrated boost (SIB)) and planned according to the guidelines of ICRU Report 83. In this communication, we focus on one patient and vary temporal parameters to evaluate the potential effect of intrafraction motion interplay with sliding jaw and leaf motions. The 4D‐CT scan was acquired and temporally distributed over ten phases according to a breathing signal delivered by a motion detector, providing also an estimation of the breathing period. Dose was computed with the MC model TomoPen. for every projection, simulations were performed on a CT phase selected according to breathing period and initial phase. The 10 dose maps were accumulated using non‐rigid registration and then compared to the approved treatment plan. Parameters were varied as follows 1) variation of breathing period (from 3 to 8 sec) (motion interplay study) 2) variation in the initial phase (multiple fraction averaging effect) and 3) calculation with all the projections for every phase (only intra‐fraction motion).Results: Depending on the breathing period, all the simulations showed acceptable dose distributions on target volumes of the ten patients (0.3 to 1% for gEUDs of the boost tumor volume and the clinical target volume) indicating potential but minimal interplay effect Conclusions: For the patients studied, assuming regular breathing, the results showed that SIB treatments for a lung tumor with TomoTherapy including intra‐fraction motion delivered acceptable dose distributions. This ongoing study will be extended to more patients, including hypo‐fractionated stereotactic treatments.Tomotherapy Inc. has partially supported this research
SU‐E‐T‐785: Evaluation of HybridArc‐‐a Novel Treatment Planning and Delivery Approach
Authors: Robar J 
Published: November 2011

Purpose: This investigation focuses on possible dosimetric and efficiency advantages of HybridArc—a novel treatment planning approach combining optimized dynamic arcs with IMRT beams. Application of this technique to two disparate sites, complex cranial tumors and prostate, was examined. Methods: HybridArc plans were compared to either dynamic conformal arc (DCA) or IMRT plans, in order to determine whether HybridArc offers a synergy through combination of these two techniques. Plans were compared with regard to target volume dose conformity, target volume dose homogeneity, sparing of proximal organs at risk, normal tissue sparing and Monitor Unit (MU) efficiency. Results: HybridArc produced improved and comparable dose conformity for cranial and prostate cases, respectively, compared to IMRT. Using the DCA technique produced inferior results on average in this regard, for both sites. For prostate cases, HybridArc also offered the advantage of improved dose homogeneity in the target volume compared to IMRT. Both arc‐based techniques distribute peripheral dose over larger volumes of normal tissue compared to IMRT, while HybridArc involved slightly greater volumes of normal tissues compared to DCA. Compared to IMRT, cranial cases required 38% more MUs, while for prostate cases, MUs were reduced by 7%. Conclusions: HybridArc is capable of improving dose conformity and dose homogeneity for cranial and prostate cases, respectively. MU efficiency may depend on the complexity of the case.This work results from a collaboration with Brainlab, AG but no financial support has been received by this company during the course of the investigation.
SU‐E‐T‐843: Direct Segment Optimization of Conformal Plans: Achieving Equivalence with Beamlet IMRT
Authors: Fraass B , Steers J , Matuszak M , McShan D 
Published: November 2011

Purpose: Use of inverse planning to improve conformal treatment plan quality has concentrated on optimization of beamlet‐based IMRT plans. The few direct aperture‐based optimization methods are all based on optimizing a beamlet‐based plan, followed by sequencing which identifies the many apertures to be optimized. In contrast, direct segment optimization (DSO), described here, directly optimizes conformal and few‐segment plans using inverse planning. This work compares DSO‐optimized plans versus beamlet IMRT and forward‐planned 3DCRT plans for a series of clinical sites. Methods: Our in‐house beamlet‐based inverse planning system has been enhanced to support DSO with an improved and reimplemented perturbational version of the Edge/Octree calculation algorithm and a multilayer search strategy. DSO optimizes MLC segment shapes, weights and/or jaw positions for multiple field plans (including VMAT). In our inverse planning infrastructure, beamlet, multi‐segment and conformal plans can all be optimized using the same cost functions, dose points, and plan evaluation metrics, making quantitative comparisons between techniques straightforward. Inverse planned DSO 3DCRT plans are compared to forward planned 3DCRT and beamlet IMRT plans for brain, liver, lung, and other sites. Results: For many tested patient geometries, DSO achieves equivalent plan quality to the beamlet IMRT plan optimized with the same cost function, though there are certain situations where IMRT is expected to (and does) perform better. The DSO plans use significantly fewer MU, require less treatment time, are less sensitive to motion, and do not require pre‐treatment IMRT QA checks, so they may be significantly easier to implement in the clinic. Conclusions: Optimization of 3DCRT and multi‐segment plans using DSO results in plan evaluation metrics virtually equivalent to beamlet IMRT plans optimized with the same cost function and beam directions, for many geometries. DSO may potentially lead to important efficiency savings for many clinical protocols.Supported in part by NIH P01‐CA59827
MO‐D‐BRC‐08: Improving the McKinnon‐Bates 4D‐CBCT Reconstruction Algorithm through Prior Destreaking
Authors: Sun M , Star‐Lack J 
Published: November 2011

Purpose: On‐board 4D cone‐beam computed tomography (CBCT) is being actively pursued to help guide radiotherapy treatments of lung tumors. Among the existing 4D‐CBCT methods, the McKinnon‐Bates algorithm (MKB) has the advantage of being computationally efficient and not requiring additional scan time compared to a conventional 3‐D acquisition taking on the order of 1 minute. The resulting images, however, can suffer from temporal hysteresis and ghosting artifacts that hinder tumor delineation and determination of motion trajectories. This work describes an improvement to the MKB algorithm that reduces or eliminates the ghosting artifacts and restores tumor conspicuity in the lungs. Methods: Temporal blurring and ghosting are identified as being caused by motion‐induced streaks in the 3D image that serves as the MKB prior and which, ideally, should be a time‐averaged image of all respiratory phases. A prior destreaking method, using tissue thresholding and boundary erosion operations, is then proposed to remove the streaks without introducing new artifacts in the final phase images. The method is tested on simulated data using the XCAT phantom and on in vivo data from lung tumor patient. Image quality improvements are assessed in moving and static tissue. Results: The prior destreaking technique successfully removed motion‐induced streaks from the prior images, and the subsequent MKB reconstructions provided accurate spatial and temporal information. The lung tumor patient exhibited +/ −6 mm of diaphragm motion that was not seen in the original MKB reconstruction, but was clearly recorded after prior destreaking was employed. Phantom images were similarly improved. Conclusions: The MKB algorithm is enhanced by destreaking the prior image, and the proposed thresholding‐ and erosion‐based technique is proven to be effective and efficient. This approach enables 4D‐CBCT images to be acquired and reconstructed in a sufficiently short period of time forIGRT.All authors are employees of Varian Medical Systems.
MO‐D‐220‐02: Assessing Intra‐Tumor Hemodynamics and Oxygen Concentration Using Photoacoustic Computed Tomography
Authors: Stantz K , Cao N , Shaffer M 
Published: November 2011

Purpose:The goal is to develop a method to non‐invasively assess intra‐ tumor pO2 using photoacoustic imaging. It is well established that the oxygen status of a tumor plays a critical role in the therapeutic response and resistance, resulting in treatment failure and poor disease‐free and overall survival. Clinical techniques, such as polarographic electrode, photoluminescence‐quenching, or pimonidazole, are invasive and lack the patho‐physiological etiology leading to hypoxia. A biophysical model is proposed to determine local pO2 based on fusing hemodynamic measurements acquired from dynamic contrast‐enhanced and spectroscopic photoacoustic imaging (DCE‐PCT and PCT‐S). Methods: MCF7 and MCF7/VEGF xenograft breast tumors were first scanned within a prototype PCT scanner to obtain parametric maps of oxygen saturation and hemoglobin concentration and within a clinical CT scanner to obtain dynamic contrast‐enhanced data (DCE‐CT) to obtain parametric maps of perfusion, fractional‐plasma‐volume, and fractional‐interstitial‐volume. These maps were fused based on a mathematical model of tissue oxygen delivery, and compared to measurements taken with an OxyLite probe. To replace DCE‐CT, a new generation of PCT scanner was developed to acquire DCE‐PCT data and realize physiological maps. Mice with MDA‐ MB‐231 xenograft breast tumors were i.v. injected with ICG, and scanned prior to and every 12‐seconds for up to 4‐minutes and at 15‐minutes post‐ injection. These contrast‐enhance curves were fit compartmental models to obtain maps of tumor perfusion and fractional plasma volumes. Results: Preliminary results comparing pO2 measurements implementing biophysical models and PCT‐S and DCE‐CT and OxyLite probe measured a linear correlation of R2=0.82, and a slope of 0.975(±0.10) and an intercept of − 0.093(±2.2)mmHg. The first parametric maps of tumor perfusion and fractional plasma volume using DCE‐PCT will be presented and compared to DCE‐CT, and ICG kinematics identifying regions of high extravasation. Conclusions: A biophysical model of pO2 based on hemodynamic data and physiological maps in breast tumors obtained from photoacoustic imaging has been demonstrated.NIH/SBIR Funding from OptoSonics, Inc, OptoSonics, Inc., 108 Straight Road, Oriental, NC 28571; Consulting for Endra, Inc, 35 Research Drive, Suite 100, Ann Arbor, MI 48103.
MO‐F‐BRA‐05: Comparison of Organ Dosimetry for Astronaut Phantoms: Earth‐Based vs. Microgravity‐Based Anthropometry and Body Positioning
Authors: Bahadori A , Shavers M , Baalen M Van , Semones E , Bolch W 
Published: November 2011

Purpose: To use NASA radiation transport codes to compare astronaut organ dose equivalents resulting from solar particle events (SPE), geomagnetically trapped protons, and free‐space galactic cosmic rays (GCR) using phantom models representing Earth‐based and microgravity‐based anthropometry and positioning. Methods: The University of Florida hybrid adult phantoms were scaled to represent male and female astronauts with 5th, 50th, and 95th percentile heights and weights as measured on Earth. Another set of scaled phantoms, incorporating microgravity‐induced changes, such as spinal lengthening, leg volume loss, and the assumption of the neutral body position, was also created. A ray‐tracer was created and used to generate body self‐shielding distributions for dose points within a voxelized phantom under isotropic irradiation conditions, which closely approximates the free‐ space radiation environment. Simplified external shielding consisting of an aluminum spherical shell was used to consider the influence of a spacesuit or shielding of a hull. These distributions were combined with depth dose distributions generated from the NASA radiation transport codes BRYNTRN (SPE and trapped protons) and HZETRN (GCR) to yield dose equivalent. Many points were sampled per organ. Results: The organ dose equivalent rates were on the order of 1.5–2.5 mSv per day for GCR (1977 solar minimum) and 0.4–0.8 mSv per day for trapped proton irradiation with shielding of 2 g cm−2 aluminum equivalent. The organ dose equivalents for SPE irradiation varied considerably, with the skin and eye lens having the highest organ dose equivalents and deep‐seated organs, such as the bladder, liver, and stomach having the lowest. Conclusions: The greatest differences between the Earth‐based and microgravity‐based phantoms are observed for smaller ray thicknesses, since the most drastic changes involved limb repositioning and not overall phantom size. Improved self‐shielding models reduce the overall uncertainty in organ dosimetry for mission‐risk projections and assessments for astronauts.This research was supported by NASA GSRP Grant NNX09AK14H and NASA Bioastronautics Contract NAS9‐02078.
MO‐F‐BRC‐02: A Method for 4D Tumor Tracking Using Dynamic 2D Orthogonal MRI
Authors: Tryggestad E , Roland T , Shea S 
Published: November 2011

Purpose: Current methods for deriving tumor motion in the pre‐treatment setting, e.g. 4D‐CT or planar x‐ray fluoroscopy, fail to address breathing motion variability and result in imaging dose to the patient. “4D” treatment planning and delivery methods, most of which are under development, typically rely on a robust characterization of motion. Implementation of these beneficial 4D methods may be hindered by deficiencies in pre‐ treatment imaging. To characterize motion and associated variability over extended durations, we have developed a technique employing 2D dynamic MRI acquired in orthogonal planes intersecting the tumor. Methods: 2D balanced steady‐state free precession (bSSFP; TR=2.9 ms; TE=1.22 ms; flip angle=77–79°) MRI was acquired continuously over >4 minutes with interleaved sagittal and coronal planes in two healthy (lung and abdomen) volunteers at 1.5 T using a MAGNETOM Espree MRI (Siemens). In‐plane resolution was 2 mm and the slice thickness was 5 mm. The imaging grid was 160×160 and 176×176 for the lung and abdominal volunteer, respectively. The resulting frame rate was 4 frames/sec. Synchronous with image acquisition, an external respiratory trace was collected at 50 Hz. Results: 4D tracking of normal anatomy was successfully performed using custom software (Matlab, The Mathworks Inc.). Rectangular template matching was employed via normalized cross‐correlation‐based optimization. MRI frames were up‐sampled (4×) to provide improved tracking resolution (0.5 mm). Image feature positions in 3D as a function of time were derived by interpolating 2D data from each plane onto a regular temporal grid according to the frame rate. Conclusion: In patients, this technique will be employed to derive the mean tumor trajectory and the breathing phase‐dependent tumor position uncertainty over the imaging duration. The external respiratory trace provides important data, allowing for careful study of its viability as a surrogate. Future efforts will involve modifications to the bSSFP sequence for significant improvements in speed.This work was made possible, in part, by research personnel support from Siemens.
MO‐F‐214‐07: Online Monitoring of Radiotherapy Treatments Using a Novel Optical Attenuation‐Based Transmission Detector
Authors: Goulet M , Gingras L , Beaulieu L 
Published: November 2011

Purpose: To present and characterize a fluence monitoring transmission detector for the online quality control of radiotherapy treatments. This work presents extended detection capability of the detector using a new formalism for the representation of the beam quality control. Methods: Sixty 27‐cm scintillating fibers were aligned in the direction of motion of each of the 60 leaf pairs of a 120 leaves Millenium MLC on a Varian Clinac iX. Because of the significant light attenuation in scintillating fibers, combined information from the two sides of each fiber allowed for both position coding and integral fluence information of the incident fluence passing thought each MLC leaf pair. The whole device was placed in the accessory tray of the linac to enable fluence verification during the treatment delivery. The impact of a wide range of delivery errors was evaluated using a graphical representation of the treatment validity. The influence of the transmission device on the radiation beam was also evaluated. Results: The presented online detector allowed the detection of MLC leaf positioning errors below 1 mm, symmetric leaf displacement of 1.6mm, blocking jaws errors of 2mm and absolute dose rate de‐calibration of less than 1 %. The formalism used for the graphical representation of the beam quality control allowed the instantaneous detection of critical delivery errors such as deleted segments or wrong energy selection. The fluence monitor also achieved a uniform beam transmission of 98.3%. Conclusions: This work shows that an optical attenuation—based detector can be used to monitor both intuitively and precisely the incident fluence during radiotherapy delivery. The performance of such a system would enables real‐time quality control of the incident fluence both in current MLC‐driven treatments and in future adaptive radiotherapy procedures where new treatment plans will have to be delivered without passing thru the current standard quality control chain.This research is supported in part by the Natural Sciences and Engineering Research Council of Canada (NSERC) support Grant No.262105