bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐35: Clinical Performance Evaluation of a Phase II Proton CT Scanner
Authors: Mandapaka A , Ghebremedhin A , Farley D , Giacometti V , Vence N , Bashkirov V , Plautz T , Zatserklyaniy A , Johnson R , Sadrozinski H , Patyal B , Schulte R
Published: July 2014

Purpose:

To develop the methodology to evaluate the clinical performance of a Phase II Proton CT scanner

Methods:

Range errors on the order of 3%‐5% constitute a major uncertainty in current charged particle treatment planning based on Hounsfield Unit (HU)‐relative stopping power (RSP) calibration curves. Within our proton CT collaboration, we previously developed and built a Phase I proton CT scanner that provided a sensitive area of 9 cm (axial) × 18 cm (in‐plane). This scanner served to get initial experience with this new treatment planning tool and to incorporate lessons learned into the next generation design. A Phase II scanner was recently completed and is now undergoing initial performance testing. It will increase the proton acquisition rate and provide a larger detection area of 9 cm x 36 cm. We are now designing a comprehensive evaluation program to test the image quality, imaging dose, and range uncertainty associated with this scanner. The testing will be performed along the lines of AAPM TG 66.

Results:

In our discussion of the evaluation protocol we identified the following priorities. The image quality of proton CT images, in particular spatial resolution and low‐density contrast discrimination, will be evaluated with the Catphan600 phantom. Initial testing showed that the Catphan uniformity phantom did not provide sufficient uniformity; it was thus replaced by a cylindrical water phantom. The imaging dose will be tested with a Catphan dose module, and compared to a typical cone beam CT dose for comparable image quality. Lastly, we developed a dedicated dosimetry range phantom based on the CIRS pediatric head phantom HN715.

Conclusion:

A formal evaluation of proton CT as a new tool for proton treatment planning is an important task. The availability of the new Phase II proton CT scanner will allow us to perform this task.

This research is supported by the National Institute of Biomedical Imaging and Bioengineering of the NIH under award number R01EB013118. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH
SU‐E‐J‐38: Comparison of 6MV Photon Dose in a Perpendicular and Parallel Magnetic Field
Authors: Ghila A , Fallone B , Rathee S
Published: July 2014

Purpose:

Integrating a linac with an MRI system would allow for real time tumour tracking however the patient will be irradiated in the presence of a magnetic field. The present study experimentally investigates the magnetic field effects on entrance, exit, and interface dose for both transverse and parallel magnetic fields.

Methods:

Polystyrene was used to construct a set of phantoms for Gafchromic film measurements. One phantom had an adjustable air gap and four other phantoms had one surface at various angles. The linac‐MR prototype consisting of a biplanar permanent magnet coupled to a linac was used for the transverse magnetic field measurements. A couple of solenoid electromagnets, stacked on top of each other and irradiated along their bore, were used for the parallel field measurements.

Results:

All doses are relative to no magnetic field. The transverse magnetic field reduced the entrance dose for all surface angles by strongly deflecting the contaminant electrons. The exit dose in a transverse magnetic field was found to be significantly higher. The entrance dose with a parallel magnetic field present is higher due to the contaminant electrons being concentrated within the beam area. The air gap phantom measurements, done in a transverse magnetic field, show a significant increase of the dose at the proximal side of the air gap and a decrease at the distal side. The measurements, done in the parallel magnetic field, show the concentration of secondary electrons in the air gap.

Conclusion:

The radiation dose measurements of a 6MV beam in a parallel and transverse magnetic field presented here are currently being replicated using Monte Carlo simulations. This verified Monte Carlo system could provide the dose calculation basis for future linac‐MR systems.
SU‐E‐J‐39: Comparison of PTV Margins Determined by In‐Room Stereoscopic Image Guidance and by On‐Board Cone Beam Computed Tomography Technique for Brain Radiotherapy Patients
Authors: Ganesh T , Paul S , Munshi A , Sarkar B , Krishnankutty S , Sathya J , George S , Jassal K , Roy S , Mohanti B
Published: July 2014

Purpose:

Stereoscopic in room kV image guidance is a faster tool in daily monitoring of patient positioning. Our centre, for the first time in the world, has integrated such a solution from BrainLAB (ExacTrac) with Elekta's volumetric cone beam computed tomography (XVI). Using van Herk's formula, we compared the planning target volume (PTV) margins calculated by both these systems for patients treated with brain radiotherapy.

Methods:

For a total of 24 patients who received partial or whole brain radiotherapy, verification images were acquired for 524 treatment sessions by XVI and for 334 sessions by ExacTrac out of the total 547 sessions. Systematic and random errors were calculated in cranio‐caudal, lateral and antero‐posterior directions for both techniques. PTV margins were then determined using van Herk formula.

Results:

In the cranio‐caudal direction, systematic error, random error and the calculated PTV margin were found to be 0.13 cm, 0.12 cm and 0.41 cm with XVI and 0.14 cm, 0.13 cm and 0.44 cm with ExacTrac. The corresponding values in lateral direction were 0.13 cm 0.1 cm and 0.4 cm with XVI and 0.13 cm, 0.12 cm and 0.42 cm with ExacTrac imaging. The same parameters for antero‐posterior were for 0.1 cm, 0.11 cm and 0.34 cm with XVI and 0.13 cm, 0.16 cm and 0.43 cm with ExacTrac imaging. The margins estimated with the two imaging modalities were comparable within ± 1 mm limit.

Conclusion:

Verification of setup errors in the major axes by two independent imaging systems showed the results are comparable and within ± 1 mm. This implies that planar imaging based ExacTrac can yield equal accuracy in setup error determination as the time consuming volumetric imaging which is considered as the gold standard. Accordingly PTV margins estimated by this faster imaging technique can be confidently used in clinical setup.
SU‐E‐J‐40: Comparison of Two Head and Neck Immobilization Device Fabrication and Simulation Protocols: Effects On Setup Deviation and Intrafraction Motion During Treatment
Authors: Hosotani M , Lacey S M , Pafundi D H , Antolak J A , Foote R L , Herman M G , Garces Y I , Daniels T B , Brinkmann D H
Published: July 2014

Purpose:

To compare two protocols for head and neck immobilization device fabrication and simulation and their effect on daily setup deviation and intrafraction motion over the course of VMAT or static IMRT.

Methods:

Fifteen post‐surgical bilateral head and neck patients were immobilized with a custom‐fit dental mold attached to a 5–point thermoplastic mask and treated with VMAT or IMRT. After fabrication of the immobilization device, which included 5–10 minutes for mask hardening, the patient either was scanned immediately without any positioning adjustments (N = 10), or got off of the simulation table for approximately 1 minute and was repositioned in treatment position prior to scanning (N = 5). Patients were localized using kV orthogonal imaging matching to overall bony anatomy for 30–35 fractions. Translational setup deviations were determined retrospectively by matching pre‐ and post‐treatment kV orthogonal images to reference DRRs using bony anatomy near isocenter (typically C4) as well as gold fiducial markers embedded in the dental mold. Intrafraction motion was determined based on comparison of pre‐treatment kV orthogonal images with post‐treatment kV orthogonal images for each fraction. Margins were calculated using the pre‐ and posttreatment setup deviation data of each patient cohort.

Results:

Treatment position repositioning prior to simulation scanning decreased the patient group mean intrafraction motion near the dental mold (P < 0.02) and near isocenter (P < 0.04), but did not statistically significantly change the group mean setup uncertainty.

Conclusion:

Repositioning of the patient in treatment position prior to simulation reduced intrafraction motion, but did not affect patient setup uncertainty during head and neck treatment. These results indicate that on average repositioning the patient in treatment position decreases patient intrafraction motion over the course of treatment for post‐surgical bilateral head and neck patients immobilized with dental molds attached to a thermoplastic mask.
SU‐E‐J‐42: Customized Deformable Image Registration Using Open‐Source Software SlicerRT
Authors: Gaitan J Cifuentes , Kirby N , Lasso A , Chin L , Pinter C , Pignol J , Fichtinger G , Pouliot J
Published: July 2014

Purpose:

SlicerRT is a flexible platform that allows the user to incorporate the necessary images registration and processing tools to improve clinical workflow. This work validates the accuracy and the versatility of the deformable image registration algorithm of the free open‐source software SlicerRT using a deformable physical pelvic phantom versus available commercial image fusion algorithms.

Methods:

Optical camera images of nonradiopaque markers implanted in an anatomical pelvic phantom were used to measure the ground‐truth deformation and evaluate the theoretical deformations for several DIR algorithms. To perform the registration, full and empty bladder computed tomography (CT) images of the phantom were obtained and used as fixed and moving images, respectively. The DIR module, found in SlicerRT, used a B‐spline deformable image registration with multiple optimization parameters that allowed customization of the registration including a regularization term that controlled the amount of local voxel displacement. The virtual deformation field at the center of the phantom was obtained and compared to the experimental ground‐truth values. The parameters of SlicerRT were then varied to improve spatial accuracy. To quantify image similarity, the mean absolute difference (MAD) parameter using Hounsfield units was calculated. In addition, the Dice coefficient of the contoured rectum was evaluated to validate the strength of the algorithm to transfer anatomical contours.

Results:

Overall, SlicerRT achieved one of the lowest MAD values across the algorithm spectrum, but slightly smaller mean spatial errors in comparison to MIM software (MIM). On the other hand, SlicerRT created higher mean spatial errors than Velocity Medical Solutions (VEL), although obtaining an improvement on the DICE to 0.91. The large spatial errors were attributed to the poor contrast in the prostate bladder interface of the phantom.

Conclusion:

Based phantom validation, SlicerRT is capable of achieving comparable DIR accuracy to commercial programs such as MIM and VEL.
SU‐E‐J‐46: Development of a Compton Camera Prototype for Online Range Verification of Laser‐Accelerated Proton Beams
Authors: Thirolf PG , Aldawood S , Boehmer M , Bortfeldt J , Castelhano I , Gernhaeuser R , v.d. Kolff H , Lang C , Maier L , Schaart DR , Parodi K
Published: July 2014

Purpose:

Development of a photon detection system designed for online range verification of laser‐accelerated proton beams via prompt‐gamma imaging of nuclear reactions.

Methods:

We develop a Compton camera for the position‐sensitive detection of prompt photons emitted from nuclear reactions between the proton beam and biological samples. The detector is designed to be capable to reconstruct the photon source origin not only from the Compton scattering kinematics of the primary photon, but also to allow for tracking of the Compton‐scattered electrons.

Results:

Simulation studies resulted in the design of the Compton camera based on a LaBr3(Ce) scintillation crystal acting as absorber, preceded by a stacked array of 6 double‐sided silicon strip detectors as scatterers. From the design simulations, an angular resolution of ≤ 2° and an image reconstruction efficiency of 10−3 −10−5 (at 2–6 MeV) can be expected. The LaBr3 crystal has been characterized with calibration sources, resulting in a time resolution of 273 ps (FWHM) and an energy resolution of about 3.8% (FWHM). Using a collimated (1 mm diameter) 137Cs calibration source, the light distribution was measured for each of 64 pixels (6×6 mm2). Data were also taken with 0.5 mm collimation and 0.5 mm step size to generate a reference library of light distributions that allows for reconstructing the interaction position of the initial photon using a k‐nearest neighbor (k‐NN) algorithm developed by the Delft group.

Conclusion:

The Compton‐camera approach for prompt‐gamma detection offers promising perspectives for ion beam range verification. A Compton camera prototype is presently being developed and characterized in Garching. Furthermore, an arrangement of, e.g., 4 camera modules could even be used in a ‘gamma‐PET’ mode to detect delayed annihilation radiation from positron emitters in the irradiation interrupts (with improved performance in the presence of an additional third (prompt) photon (as in 10C and 14O).

This work was supported by the DFG Cluster of Excellence MAP (Munich‐Centre for Advanced Photonics)
SU‐E‐J‐49: Distal Edge Activity Fall Off Of Proton Therapy Beams
Authors: Elmekawy A , Butuceanu C , Zhu L , Ewell L
Published: July 2014

Purpose:

To characterize and quantify the distal edge activity fall off, created in a phantom by a proton therapy beam

Method and Materials:

A 30×30×10cm polymethylmethacrylate phantom was irradiated with a proton therapy beam using different ranges and beams. The irradiation volume is approximated by a right circular cylinder of diameter 7.6cm and varying lengths. After irradiation, the phantom was scanned via a Philips Gemini Big Bore™ PET‐CT for isotope activation. Varian Eclipse™ treatment planning system as well as ImageJ™ were used to analyze the resulting PET and CT scans. The region of activity within the phantom was longitudinally measured as a function of PET slice number. Dose estimations were made via Monte Carlo (GATE) simulation.

Results:

For both the spread out Bragg peak (SOBP) and the mono‐energetic pristine Bragg peak proton beams, the proximal activation rise was steep: average slope −0.735 (average intensity/slice number) ± 0.091 (standard deviation) for the pristine beams and −1.149 ± 0.117 for the SOBP beams. In contrast, the distal fall offs were dissimilar. The distal fall off in activity for the pristine beams was fit well by a linear curve: R2 (Pierson Product) was 0.9968, 0.9955 and 0.9909 for the 13.5, 17.0 and 21.0cm range beams respectively. The good fit allows for a slope comparison between the different ranges. The slope varied as a function of range from 1.021 for the 13.5cm beam to 0.8407 (average intensity/slice number) for the 21.0cm beam. This dependence can be characterized: −0.0234(average intensity/slice number/cm range). For the SOBP beams, the slopes were significantly less and were also less linear: average slope 0.2628 ± 0.0474, average R2=0.9236.

Conclusion:

The distal activation fall off edge for pristine proton beams was linear and steep. The corresponding quantities for SOBP beams were shallower and less linear.

Philips has provided support for this work.
SU‐E‐J‐50: Does a Breathing Surrogate From a Point On the Abdominal Skin Represent the Organ Motion in Thorax for Phase‐Based 4D CT Sorting?
Authors: Lin M , D' Souza W , Lasio G , Lu W , Prado K , Feigenberg S , Yi B
Published: July 2014

Purpose:

This work aims (1) to determine the validity of the current practice of the phase‐based 4DCT sorting (abdomen signal) for thorax scans; (2) to assess the potential benefit of utilizing the 3D surface breathing surrogate of chest area for phase‐based 4DCT sorting.

Methods:

Dynamic 3D surface images over the chest and abdomen were acquired using 3D‐suface‐camera‐system (VisionRT Ltd., London, UK) for a total of 10 patients. The vertical motions of five regions‐of‐interest (ROIs): abdomen, mid‐sternum, lower‐, middle‐, and upper‐ ipsilateral‐chest were tracked. Based on our previous work, the main source of motion artifact is the variation‐of‐phase‐differences (VPD) between the breathing surrogate and the organ motion during scanning. Thus, we utilize VPD as a quantitative index of the variation of the resulting 4DCT images. The average VPD over a 60 second time‐period was calculated for each of the abdomen and ROI combination. A simulation study with a wire phantom was designed to demonstrate the resulting 4DCT images.

Results:

Simulation showed significant image distortion or motion artifacts when VPD is larger than 5% of breathing period. The average VPDs of individual ROIs of each patient indicates that 75%, 59% and 22% cases have VPD larger than 5%, 10% and 15% of period each cycle between the selected ROI and the abdominal motions patterns, respectively (10.1±6.0 %, minimum 1.0% to maximum 23.9 %). Overall, patients with less 3‐second breathing‐period present VPD larger than 10%. The correlations between the abdomen and individual chest ROIs motions as well as the motions among chest ROIs are highly case‐dependent.

Conclusion:

Abdominal motion does not represent the chest motions for some of the patients. This results in motion artifacts in the phase‐based 4DCT. Utilizing the surface surrogate of the chest region can potentially improve phase‐based 4DCT sorting for thorax 4DCT scan, especially for fast breathing patients.
SU‐E‐J‐52: Dosimetric Benefit of Adaptive Re‐Planning in Lung Cancer Stereotactic Body Radiotherapy (SBRT)
Authors: Jia J , Tian Z , Gu X , Yan H , Jia X , Jiang S
Published: July 2014

Purpose:

To investigate the dosimetric benefit of adaptive re‐planning for lung stereotactic body radiotherapy(SBRT).

Methods:

Five lung cancer patients with SBRT treatment were retrospectively investigated. Our in‐house supercomputing online re‐planning environment (SCORE) was used to realize the re‐planning process. First a deformable image registration was carried out to transfer contours from treatment planning CT to each treatment CBCT. Then an automatic re‐planning using original plan DVH guided fluence‐map optimization is performed to get a new plan for the up‐to‐date patient geometry. We compared the re‐optimized plan to the original plan projected on the up‐to‐date patient geometry in critical dosimetric parameters, such as PTV coverage, spinal cord maximum and volumetric constraint dose, esophagus maximum and volumetric constraint dose.

Results:

The average volume of PTV covered by prescription dose for all patients was improved by 7.56% after the adaptive re‐planning. The volume of the spinal cord receiving 14.5Gy and 23Gy (V14.5, V23) decreased by 1.48% and 0.68%, respectively. For the esophagus, the volume receiving 19.5Gy (V19.5) reduced by 1.37%. Meanwhile, the maximum dose dropped off by 2.87% for spinal cord and 4.80% for esophagus.

Conclusion:

Our experimental results demonstrate that adaptive re‐planning for lung SBRT has the potential to minimize the dosimetric effect of inter‐fraction deformation and thus improve target coverage while reducing the risk of toxicity to nearby normal tissues.
SU‐E‐J‐53: Dosimetric Evaluation at Volumetric Modulated Arc Therapy for Treatment of Prostate Cancer Using Single Or Double Arcs
Authors: Silva D , Salmon H , Pavan G , Nardi S , Anderson E , Fairbanks L , Junior J , Cursino F , Colodette K
Published: July 2014

Purpose:

Evaluate and compare retrospective prostate treatment plan using Volumetric Modulated Arc Therapy (RapidArc™ – Varian) technique with single or double arcs at COI Group.

Methods:

Ten patients with present prostate and seminal vesicle neoplasia were replanned as a target treatment volume and a prescribed dose of 78 Gy. A baseline planning, using single arc, was developed for each case reaching for the best result on PTV, in order to minimize the dose on organs at risk (OAR). Maintaining the same optimization objectives used on baseline plan, two copies for optimizing single and double arcs, have been developed. The plans were performed with 10 MV photon beam energy on Eclipse software, version 11.0, making use of Trilogy linear accelerator with Millenium HD120 multileaf collimator. Comparisons on PTV have been performed, such as: maximum, minimum and mean dose, gradient dose, as well as the quantity of monitor units, treatment time and homogeneity and conformity index. OARs constrains dose have been evaluated, comparing both optimizations.

Results:

Regarding PTV coverage, the difference of the minimum, maximum and mean dose were 1.28%, 0.7% and 0.2% respectively higher for single arc. When analyzed the index of homogeneity found a difference of 0.99% higher when compared with double arcs. However homogeneity index was 0.97% lower on average by using single arc. The doses on the OARs, in both cases, were in compliance to the recommended limits RTOG 0415. With the use of single arc, the quantity of monitor units was 10,1% lower, as well as the Beam‐On time, 41,78%, when comparing double arcs, respectively.

Conclusion:

Concerning the optimization of patients with present prostate and seminal vesicle neoplasia, the use of single arc reaches similar objectives, when compared to double arcs, in order to decrease the treatment time and the quantity of monitor units.
SU‐E‐J‐54: Dosimetric Evaluation of Amplitude‐Based Gating in Volumetric Modulated Arc Therapy (VMAT)
Authors: Lee Chang Yeol , Huh Hyun Do , Kim Woo Chul , Kim Hun Jeong , Min Chul Kee , Ji Young Hoon , Kim Kum Bae
Published: July 2014

Purpose:

The purpose of this work is to evaluate the dosimetric influence in the gated volumetric modulated arc therapy.

Methods:

This study is performed in three liver cancer patients. Execution of 4D CT simulation and plan deliveries on one‐dimensional respiratory motion phantom were based on patient's respiratory trace data sets. We chose the regular and irregular respiratory amplitude patterns among the patient respiratory‐gated treatment log file. Dose distributions were evaluated using EBT3 film by comparing the gated delivery with static delivery.

Results:

The presented results of static measured and calculated dose distributions showed good agreement with gamma‐index passing rates above 97% for 3%/3 m dose accuracy/distance‐to‐agreement criteria. In regular respiratory amplitude pattern, the results of two in three patients evaluated gamma‐index passing rates above 92% except for another patient who was evaluated of 87.16%. Patients whose plans had the largest percentage failing the gamma statistics exhibited irregular respiratory amplitude pattern that evaluated less than 70%. Minimum passing rate was 37.40%. This results showed that the correlation of between sorted 4D CT phase and irregular patient respiratory amplitude pattern may results in considerable dosimetric difference.

Conclusion:

The effort to maintain regular patient respiratory amplitude pattern between 4D CT simulation and treatment is the most important in gated volumetric modulated arc therapy.
SU‐E‐J‐55: Dosimetric Evaluation of Centrally Located Lung Tumors: A Monte Carlo (MC) Study of Lung SBRT Planning
Authors: Pokhrel D , Badkul R , Jiang H , Saleh H , Estes C , Park J , Kumar P , Wang F
Published: July 2014

Purpose:

To compare dose distributions calculated using the iPlan XVMC algorithm and heterogeneities corrected/uncorrected Pencil Beam (PB‐hete/PB‐homo) algorithms for SBRT treatments of lung tumors.

Methods:

Ten patients with centrally located solitary lung tumors were treated using MC‐based SBRT to 60Gy in 5 fractions for PTVV100%=95%. ITV was delineated on MIP‐images based on 4D‐CT scans. PTVs(ITV+5mm margins) ranged from 10.1–106.5cc(mean=48.6cc). MC‐SBRT plans were generated with a combination of non‐coplanar conformal arcs/beams using iPlan‐XVMC‐algorithm (BrainLABiPlan ver.4.1.2) for Novalis‐TX consisting of HD‐MLCs and 6MV‐SRS(1000MU/min) mode, following RTOG 0813 dosimetric criteria. For comparison, PB‐hete/PB‐homo algorithms were used to re‐calculate dose distributions using same beam configurations, MLCs/monitor units. Plans were evaluated with isocenter/maximal/mean doses to PTV. Normal lung doses were evaluated with V5/V10/V20 and mean‐lung‐dose(MLD), excluding PTV. Other OAR doses such as maximal spinal cord/2cc‐esophagus/max bronchial tree (BT/maximal heart doses were tabulated.

Results:

Maximal/mean/isocenter doses to PTV calculated by PB‐hete were uniformly larger than MC plans by a factors of 1.09/1.13/1.07, on average, whereas they were consistently lower by PB‐homo by a factors of 0.9/0.84/0.9, respectively. The volume covered by 5Gy/10Gy/20Gy isodose‐lines of the lung were comparable (average within±3%) when calculated by PB‐hete compared to XVMC, but, consistently lower by PB‐homo by a factors of 0.90/0.88/0.85, respectively. MLD was higher with PB‐hete by 1.05, but, lower by PB‐homo by 0.9, on average, compared to XVMC. XVMC max‐cord/max‐BT/max‐heart and 2cc of esophagus doses were comparable to PB‐hete; however, PB‐homo underestimates by a factors of 0.82/0.89/0.88/0.86, on average, respectively.

Conclusion:

PB‐hete significantly overestimates dose to PTV relative to XVMC ‐hence underdosing the target. MC is more complex and accurate with tissue‐heterogeneities. The magnitude of variation significantly varies with ‘small‐island‐tumor’ surrounded by low‐density lung tissues ‐PB algorithms lacks later electron scattering. Dose calculation with XVMC for lung SBRT is routinely performed in our clinic, its performance for head' neck/sinus cases will also be investigated.
SU‐E‐J‐56: Dosimetric Impact of Patient Roll Variability in Peripheral‐Lung SBRT
Authors: Casto B , Ying J , Ku L
Published: July 2014

Purpose:

Positional variation about the patient longitudinal axis may introduce deleterious effects to clinical treatment plans, the effects of which are exacerbated by hypo‐fractionated treatment regimens. Our goal is to evaluate the dosimetric impact of rotational setup error in stereotactic body radiation therapy (SBRT) for peripherally‐located lung lesions.

Methods:

Six patients who had been treated for peripheral lung lesions using varying SBRT techniques were analyzed. Each patient's planning CT was processed using custom in‐house software to simulate 1, 3, and 5 degree roll in both directions about their longitudinal axis. The original plan was fused and re‐calculated. Agreement between planned and error‐simulated dose distributions was quantified using 3%, 3mm criteria for the 3‐dimensional gamma metric, and changes in target coverage and adjacent normal anatomy were also quantified.

Results:

Increased rotational setup error resulted in reduced target coverage, with changes in equivalent uniform dose ranging from −1.24% to −6.11% for simulated roll greater than or equal to 3 degrees, increasing with magnitude of error and skewed for roll directed toward the involved side. Changes to normal tissue metrics are linearly related to simulated roll, with rib D(1cc) changes ranging from −4.23% to 3.27% relative to the original treatment plan. Error‐simulated dose distributions demonstrate agreement by the gamma metric in the planned target of 72.56%, 81.02%, and 99.52% for 5, 3, and 1 degree simulated roll scenarios, respectively. Corresponding agreement for the regional dose in excess of 50% of the maximum were 65.71%,70.77%, and 97.88%.

Conclusion:

This study suggests that the ability to detect and compensate for rotational positioning variations beyond a threshold level may improve care for patients with peripherally‐located lesions beyond that which may be accomplished using only translational axes. Positional error of one degree of roll had little influence, though three or more degrees of error introduced significant discrepancy.
SU‐E‐J‐58: Dosimetric Verification of Metal Artifact Effects: Comparison of Dose Distributions Affected by Patient Teeth and Implants
Authors: Lee M , Lee J , Park J , Park H , Lee B , Kang S , Lee S , Suh T
Published: July 2014

Purpose:

Implant‐supported dentures seem particularly appropriate for the predicament of becoming edentulous and cancer patients are no exceptions. As the number of people having dental implants increased in different ages, critical dosimetric verification of metal artifact effects are required for the more accurate head and neck radiation therapy. The purpose of this study is to verify the theoretical analysis of the metal(streak and dark) artifact, and to evaluate dosimetric effect which cause by dental implants in CT images of patients with the patient teeth and implants inserted humanoid phantom.

Methods:

The phantom comprises cylinder which is shaped to simulate the anatomical structures of a human head and neck. Through applying various clinical cases, made phantom which is closely allied to human. Developed phantom can verify two classes: (i)closed mouth (ii)opened mouth. RapidArc plans of 4 cases were created in the Eclipse planning system. Total dose of 2000 cGy in 10 fractions is prescribed to the whole planning target volume (PTV) using 6MV photon beams. Acuros XB (AXB) advanced dose calculation algorithm, Analytical Anisotropic Algorithm (AAA) and progressive resolution optimizer were used in dose optimization and calculation.

Results:

In closed and opened mouth phantom, because dark artifacts formed extensively around the metal implants, dose variation was relatively higher than that of streak artifacts. As the PTV was delineated on the dark regions or large streak artifact regions, maximum 7.8% dose error and average 3.2% difference was observed. The averaged minimum dose to the PTV predicted by AAA was about 5.6% higher and OARs doses are also 5.2% higher compared to AXB.

Conclusion:

The results of this study showed that AXB dose calculation involving high‐density materials is more accurate than AAA calculation, and AXB was superior to AAA in dose predictions beyond dark artifact/air cavity portion when compared against the measurements.
SU‐E‐J‐59: Effective Adaptive DMLC Gated Radiotherapy with OAR Sparing
Authors: Chen Y , Wu H , Zhou Z , Sandison MinGeorge
Published: July 2014

Purpose:

Patient respiratory motion degrades the effectiveness of cancer radiation treatment. Advanced respiratory gating delivers radiation dose accurately yet with elongated treatment time. The goal of this research is to propose a novel adaptive dMLC dynamic gating with high delivery efficiency and precision.

Methods:

The dose delivery of dMLC is aided by simultaneous tracking of tumor and organ at risk (OAR). The leaf opening/closing will follow the motion trajectory of the tumor while sparing the OAR. The treatment beam turns on only when there is no overlapping between OAR and tumor in BEV. A variety of evaluation metrics were considered and calculated, including duty cycle, beam toggling rate, and direct irradiation avoidance to OAR, under various combinations of different tumor margins and the distance between the centers of the tumor and OAR in BEV (expressed as dx).

Results:

Retrospective simulation was performed to investigate the feasibility and superiority of this technique using four groups of synchronized tumor and OAR motion data. The simulation results indicate that the tumor and OAR motion patterns and their relative positions are the dominant influential factors. The duty cycle can be greater than 96.71% yet can be as low as 6.69% depending different motion groups. This proposed technique provides good OAR protection, especially for such cases with low duty cycle for which as high as 77.71% maximal direct irradiation to OAR can be spared. Increasing dx improves the duty cycle (treatment efficiency) and provides better OAR volume sparing, whereas, that of the tumor margins has the opposite influence.

Conclusion:

This real‐time adaptive dMLC gated radiation treatment with synchronous tumor and OAR tracking has inherent accurate dose delivery to tumor with reduced treatment time. In addition, the OAR protection capability make it an outstanding potential treatment strategy for mobile tumors.
SU‐E‐J‐60: Efficient Monte Carlo Dose Calculation On CPU‐GPU Heterogeneous Systems
Authors: Xiao K , Zhou B , Chen D. Z , Hu X. S
Published: July 2014

Purpose:

It is well‐known that the performance of GPU‐based Monte Carlo dose calculation implementations is bounded by memory bandwidth. One major cause of this bottleneck is the random memory writing patterns in dose deposition, which leads to several memory efficiency issues on GPU such as un‐coalesced writing and atomic operations. We propose a new method to alleviate such issues on CPU‐GPU heterogeneous systems, which achieves overall performance improvement for Monte Carlo dose calculation.

Methods:

Dose deposition is to accumulate dose into the voxels of a dose volume along the trajectories of radiation rays. Our idea is to partition this procedure into the following three steps, which are fine‐tuned for CPU or GPU: (1) each GPU thread writes dose results with location information to a buffer on GPU memory, which achieves fully‐coalesced and atomic‐free memory transactions; (2) the dose results in the buffer are transferred to CPU memory; (3) the dose volume is constructed from the dose buffer on CPU. We organize the processing of all radiation rays into streams. Since the steps within a stream use different hardware resources (i.e., GPU, DMA, CPU), we can overlap the execution of these steps for different streams by pipelining.

Results:

We evaluated our method using a Monte Carlo Convolution Superposition (MCCS) program and tested our implementation for various clinical cases on a heterogeneous system containing an Intel i7 quad‐core CPU and an NVIDIA TITAN GPU. Comparing with a straightforward MCCS implementation on the same system (using both CPU and GPU for radiation ray tracing), our method gained 2‐5X speedup without losing dose calculation accuracy.

Conclusion:

The results show that our new method improves the effective memory bandwidth and overall performance for MCCS on the CPU‐GPU systems. Our proposed method can also be applied to accelerate other Monte Carlo dose calculation approaches.

This research was supported in part by NSF under Grants CCF‐1217906, and also in part by a research contract from the Sandia National Laboratories.
SU‐E‐J‐68: Evaluation of Liver Deformation During Breathing Using Deformable Image Registration: A Comparison Between 4D CT and 4D MRI
Authors: Liang X , Czito B , Palta M , Bashir M , Yin F , Cai J
Published: July 2014

Purpose:

It is of clinical interest to study liver deformation during breathing by applying deformable image registration (DIR) on respiratory correlated 4D images. This study aims to evaluate and compare the accuracy of DIR‐derived liver deformation based on 4D CT and 4D MRI.

Methods:

4D CT, 4D MR and cine MR images of liver region were acquired from 5 patients with liver cancer under an IRB‐approved protocol. Tumor trajectories were tracked from cine MR images. DVFs from 4D CT and 4D MR were generated via DIR implemented in Velocity AI. To enable comparison between DVFs and tumor trajectories from cine images, deformation vectors from each frame were linked together, forming DVF‐based trajectories. All DVF‐based trajectories within each tumor region were averaged. Absolute difference, relative difference and correlation coefficient between each pair of averaged DVF‐based trajectory and trajectory from cine MR images were calculated.

Results:

All metrics did not give consistent indications of which modality can provide more accurate DVFs. In superior‐inferior (SI) direction, averaging over all the five patients, 4D CT trajectories exhibited smaller absolute (2.05±0.52mm) and relative difference (0.43±0.14) and larger correlation coefficient (0.92±0.06) than 4D MR trajectories (2.54±1.45mm, 0.47±0.18, 0.88±0.10) whereas 4D MR (1.02±1.20mm, 0.90±0.69, 0.59±0.30) surpassed 4D CT (1.35±1.42mm, 1.35±1.25, 0.12±0.64) in every metric in right‐left direction. In anterior‐posterior direction, 4D MR trajectories has smaller absolute (1.17±0.74mm) and relative difference (0.50±0.18) with slightly smaller correlation coefficient (0.72±0.23) than 4D CT trajectories (1.51±0.64mm, 0.69±0.09, 0.75±0.26).

Conclusion:

We have implemented a novel approach for evaluating accuracy of DVFs based on 4D imaging for studying liver deformation. Initial results indicate that DVFs from 4D CT and 4D MRI are comparable. Further study on more patients is warranted and is undergoing to determine whether there is significant difference between 4D CT and 4D MRI.
SU‐E‐J‐75: Importance of 4DCT for Target Volume Definition in Stereotactic Lung Radiotherapy
Authors: Goksel E , Cone D , Tezcanli E , Kucucuk H , Senkesen O , Yilmaz M , Garipagaoglu M , Aslay I , Sengoz M
Published: July 2014

Purpose:

We aimed to investigate the importance of 4DCT for lung tumors treated with SBRT and whether maximum intensity projection (MIP) and free breathing (FB) images can compansate for tumor movement.

Methods:

Six patients with primary lung cancer and 2 patients with lung metastasis with a median age of 69.5 (42–86) were included. Patients were positioned supine on a vacuum bag. In addition to FB planning CT images, 4DCT images were obtained at 3 mm intervals using Varian RPM system with (Siemens Somatom Sensetion 64). MIP series were reconstructed using 4DCT images. PTV‐FB and PTV‐MIP (GTV+5mm) volumes were contoured using FB and MIP series, respectively. GTVs were defined on each of eight different breathing phase images and were merged to create the ITV. PTV‐4D was generated with a 5 mm margin to ITV. PTV‐MIP and PTV‐4D contours were copied to FB CT series and treatment plans for PTV‐MIP and PTV‐FB were generated using RapidArc (2 partial arc) technique in Eclipse (version 11, AAA algorithm). The prescription dose was 5600cGy in 7 fractions. ITV volumes receiving prescription dose (%) and V95 for ITV were calculated for each treatment plan.

Results:

The mean PTV‐4B, PTV‐MIP and PTV‐FB volumes were 23.2 cc, 15.4cc ve 11cc respectively. Median volume of ITV receiving the prescription dose was 34.6% (16.4–70 %) and median V95 dose for ITV was 1699cGy (232cGy‐5117cGy) in the plan optimized for PTV‐FB as the reference. When the plan was optimized for PTV‐MIP, median ITV volume receiving the prescription dose was 67.15% (26–86%) and median V95 dose for ITV was 4231cGy (1735cGy‐5290cGy).

Conclusion:

Images used in lung SBRT are critical for treatment quality; FB and MIP images did not compensate target movement, therefore 4DCT images should be obtained for all patients undergoing lung SBRT or the safety margins should be adjusted.
SU‐E‐J‐82: Intra‐Fraction Proton Beam‐Range Verification with PET Imaging: Feasibility Studies with Monte Carlo Simulations and Statistical Modeling
Authors: Lou K , Mirkovic D , Sun X , Zhu X , Poenisch F , Grosshans D , Clark J , Shao Y
Published: July 2014

Purpose:

To study the feasibility of intra‐fraction proton beam‐range verification with PET imaging.

Methods:

Two phantoms homogeneous cylindrical PMMA phantoms (290 mm axial length, 38 mm and 200 mm diameter respectively) were studied using PET imaging: a small phantom using a mouse‐sized PET (61 mm diameter field of view (FOV)) and a larger phantom using a human brain‐sized PET (300 mm FOV). Monte Carlo (MC) simulations (MCNPX and GATE) were used to simulate 179.2 MeV proton pencil beams irradiating the two phantoms and be imaged by the two PET systems. A total of 50 simulations were conducted to generate 50 positron activity distributions and correspondingly 50 measured activity‐ranges. The accuracy and precision of these activity‐ranges were calculated under different conditions (including count statistics and other factors, such as crystal cross‐section). Separate from the MC simulations, an activity distribution measured from a simulated PET image was modeled as a noiseless positron activity distribution corrupted by Poisson counting noise. The results from these two approaches were compared to assess the impact of count statistics on the accuracy and precision of activity‐range calculations.

Results:

MC Simulations show that the accuracy and precision of an activity‐range are dominated by the number (N) of coincidence events of the reconstructed image. They are improved in a manner that is inversely proportional to 1/sqrt(N), which can be understood from the statistical modeling. MC simulations also indicate that the coincidence events acquired within the first 60 seconds with 10^9 protons (small phantom) and 10^10 protons (large phantom) are sufficient to achieve both sub‐millimeter accuracy and precision.

Conclusion:

Under the current MC simulation conditions, the initial study indicates that the accuracy and precision of beam‐range verification are dominated by count statistics, and intra‐fraction PET image‐based beam‐range verification is feasible.

This work was supported by a research award RP120326 from Cancer Prevention and Research Institute of Texas.
SU‐E‐J‐83: Ion Imaging to Better Estimate In‐Vivo Relative Stopping Powers Using X‐Ray CT Prior‐Knowledge Information
Authors: Dias M , Collins‐Fekete C , Riboldi M , Doolan P , Hansen D , Baroni G , Seco J
Published: July 2014

Purpose:

To reduce uncertainties in relative stopping power (RSP) estimates for ions (alpha and carbon) by using Ion radiographic‐imaging and X‐ray CT prior‐knowledge.

Methods:

A 36×36 phantom matrix composed of 9 materials with different thicknesses and randomly placed is generated. Theoretical RSPs are calculated using stopping power (SP) data from three references (Janni, ICRU49 and Bischel). We introduced an artificial systematic error (1.5%, 2.5% or 3.5%) and a random error (<0.5%) to the SP to simulated patient ion‐range errors present in clinic environment. Carbon/alpha final energy for each RSPs set (theoretical and from CT images) is obtained with a ray‐tracing algorithm. A gradient descent (GD) method is used to minimize the difference in exit particle energy, between theory and X‐ray CT RSP maps, by iteratively correcting the RSP map from X‐ray CT. Once a new set of RSPs is obtained for a direction a new optimization is done over other direction using the RSPs from the previous optimization. Theoretical RSPs are compared with experimental RSPs obtained with Gammex Phantom.

Results:

Preliminary results show that optimized RSP values can be obtained with smaller uncertainties (<1%) than clinical RSPs (1.5% to 3.5%). Theoretical values from three different references show uncertainties, up to 3% from experimental values. Further investigation will consider prior‐knowledge from RSP obtained with CT images and ion radiographies from Monte Carlo Simulations.

Conclusion:

GD and ray‐tracing methods have been implemented to reduce RSP uncertainties from values obtained for clinical treatment. Experimental RSPs will be obtained using carbon/alpha beams to consider the existence of material dependent systematic errors. Based on the results, it is hoped to show that using ray‐tracing optimization with ion radiography and prior knowledge on RPSs, treatment planning accuracy and cost‐effectiveness can be improved.
SU‐E‐J‐93: Parametrisation of Dose to the Mucosa of the Anterior Rectal Wall in Transrectal Ultrasound Guided High‐Dose‐Rate Brachytherapy of the Prostate
Authors: Aitkenhead A , Hamlett L , Wood D , Choudhury A
Published: July 2014

Purpose:

In high‐dose‐rate (HDR) brachytherapy of the prostate, radiation is delivered from a number of radioactive sources which are inserted via catheter into the target volume. The rectal mucosa also receives dose during the treatment, which may lead to late toxicity effects. To allow possible links between rectal dose and toxicity to be investigated, suitable methods of parametrising the rectal dose are needed.

Methods:

During treatment of a series of 95 patients, anatomy and catheter locations were monitored by transrectal ultrasound, and target volume positions were contoured on the ultrasound scan by the therapist. The anterior rectal mucosal wall was identified by contouring the transrectal ultrasound balloon within the ultrasound scan. Source positions and dwell times, along with the dose delivered to the patient were computed using the Oncentra Prostate treatment planning system (TPS). Data for the series of patients were exported from the TPS in Dicom format, and a series of parametrisation methods were developed in a Matlab environment to assess the rectal dose.

Results:

Contours of the anterior rectal mucosa were voxelised within Matlab to allow the dose to the rectal mucosa to be analysed directly from the 3D dose grid. Dose parametrisations based on dose‐surface (DSH) and dose‐line (DLH) histograms were obtained. Both lateral and longitudinal extents of the mucosal dose were parametrised using dose‐line histograms in the relevant directions.

Conclusion:

We have developed a series of dose parametrisations for quantifying the dose to the rectal mucosa during HDR prostate brachytherapy which are suitable for future studies investigating potential associations between mucosal dose and late toxicity effects. The geometry of the transrectal probe standardises the rectal anatomy, making this treatment technique particularly suited to studies of this nature.
SU‐E‐J‐95: Predicting Treatment Outcomes for Prostate Cancer: Irradiation Responses of Prostate Cancer Stem Cells
Authors: Wang K
Published: July 2014

Purpose:

Most prostate cancers are slow‐growing diseases but normally require much higher doses (80Gy) with conventional fractionation radiotherapy, comparing to other more aggressive cancers. This study is to disclose the radiobiological basis of this discrepancy by proposing the concept of prostate cancer stem cells (CSCs) and examining their specific irradiation responses.

Methods:

There are overwhelming evidences that CSC may keep their stemness, e.g. the competency of cell differentiation, in hypoxic microenvironments and hence become radiation resistive, though the probability is tiny for aggressiveness cancers. Tumor hypoxia used to be considered as an independent reason for poor treatment outcomes, and recent evidences showed that even prostate cancers were also hypoxic though they are very slow‐growing. In addition, to achieve comparable outcomes to other much more aggressive cancers, much higher doses (rather than lower doses) are always needed for prostate cancers, regardless of its non‐aggressiveness. All these abnormal facts can only be possibly interpreted by the irradiation responses characteristics of prostate CSCs.

Results:

Both normal cancer cells (NCCs) and CSCs exiting in tumors, in which NCCs are mainly for symptoms whereas killing all CSCs achieves disease‐free. Since prostate cancers are slow‐growing, the hypoxia in prostate cancers cannot possibly from NCCs, thus it is caused by hypoxic CSCs. However, single hypoxic cell cannot be imaged due to limitation of imaging techniques, unless a large group of hypoxic cells exist together, thus most of CSCs in prostate cancers are virtually hypoxic, i.e. not in working mode because CSCs in proliferating mode have to be normoxic, and this explains why prostate cancers are unaggressive.

Conclusion:

The fractional dose in conventional radiotherapy (∼2Gy) could only kill NCCs and CSCs in proliferating modes, whereas most CSCs survived fractional treatments since they were hypoxic, thus to eliminate all CSCs and achieve disease‐free, much more fractionations are needed.