bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐T‐548: An Extraction Method for Correction of Detector Volume Effect in Small Field Profile Measurement
Authors: Chiu T , Yang B , Law M , Lam W , Kong C , Geng H , Cheung K , Yu S
Published: July 2016

Purpose:

To investigate the appropriateness of Gaussian detector response function in SRS profile measurement.

Methods:

In‐air profile data for a 6MV beam were collected by using ionization chambers and radiochromic film. Two ionization chambers (FC65‐G(IBA) and PinPoint(PTWTW31009)) were used to scan the beam profile. Film was used to measure the beam penumbra. A half‐blocked beam was acquired with stepping size of 0.2mm and gradient of the measured profile represents the detector response function. The field widths of 2cm and 3cm were measured at SAD. Two detector response functions were evaluated, i.e. a traditional single Gaussian and a three‐Gaussian symmetric function. Two corresponding models were used to fit measured data. One was error functions with one shaping parameter. The other model was a symmetrical superposition of three sets of error functions with fixed separation and two different shaping parameters. In both fitting, resultant Gaussian kernels and corresponding σs could be calculated analytically. SNR of the fitted curves were obtained and compared.

Results:

Our measured data indicated that the ionization chambers had a three‐peak response function. From the first modeling, SNR for FC65‐G were 36.0dB and 38.3dB for 2cm and 3cm field respectively. The corresponding SNR for the PinPoint were 43.6dB and 42.5dB. From the second modeling, SNR for FC65‐G were 42.5dB and 47.4dB for 2cm and 3cm field respectively. The corresponding SNR for the PinPoint were 44.0dB and 44.5 dB. Three‐gaussian model had an observable improvement for FC65‐G chamber. Film measured penumbra was 3–5 times smaller than that of ionization‐chambers.

Conclusion:

Superposition of three Gaussian kernels resembles the detector response due to central electrode and chamber wall and results in a better fitting to the measurement data than a single Gaussian kernel. Our study indicated that the Three‐Gaussian model was more suitable for the detector with sigma comparable to penumbra width.
SU‐F‐T‐553: Sector Output Uniformity of the Perfexion Gamma Knife
Authors: Volotskova O , Jozsef G , Osterman K , Han K , Xu A
Published: July 2016

Purpose:

To study the uniformity of single‐sector outputs from the 3 collimators of the Perfexion Gamma Knife (PGK) unit and investigate the potential impact on Gamma Knife treatment planning.

Methods:

An A16 ion chamber and a SFD diode detector were used to measure both the output factors and the single‐sector outputs from a PGK unit. The detectors were placed in custom inserts in the center of a spherical solid water phantom and connected to a Max 4000 electrometer during the measurements. For single‐sector outputs, a treatment plan with a prescription dose of 1 Gy at the focal point was generated for each sector of the 16 mm, 8 mm, and 4 mm collimators and was exported to the console computer for dose delivery. The procedure was repeated 3 times for each sector and an average value was taken as the sector output.

Results:

The differences between the output factors from the diode measurements and the clinical values for the 8 mm and 4 mm collimators were −0.4% and −2.1% respectively. The corresponding values for the A16 ion chamber were −3.5% and −17.1%. The maximum differences among the 8 single‐sector outputs for the 16 mm, 8 mm, and 4 mm collimators were 4%, 3.7%, and 4.6% respectively. Variations of the sector outputs (defined as the standard deviation‐to‐mean ratio) among the 8 single‐sector outputs for the 16 mm, 8 mm, and 4 mm collimators were measured at 1.16%, 1.32%, and 1.81%. Measurements using the ion chamber were similar to those acquired with the diode for the 16 mm and 8 mm collimators.

Conclusion:

Single‐sector outputs for the 8 sectors of the 16 mm, 8 mm, and 4 mm collimators of the PGK differed by less than 5% and are within the specified range of planning accuracy.
SU‐F‐T‐629: Effect of Multi‐Leaf Collimator (MLC) Width On Plan Quality of Single‐Isocenter VMAT Intracranial Stereotactic Radiosurgery for Multiple Metastases
Authors: Kraus J , Thomas E , Wu X , Fiveash J , Popple R
Published: July 2016

Purpose:

Single‐isocenter VMAT has been shown able to create high quality plans for complex intracranial multiple metastasis SRS cases. Linacs capable of the technique are typically outfitted with an MLC that consists of a combination of 5 mm and 10 mm leaves (standard) or 2.5 mm and 5 mm leaves (high‐definition). In this study, we test the hypothesis that thinner collimator leaves are associated with improved plan quality.

Methods:

Ten multiple metastasis cases were identified and planned for VMAT SRS using a 10 MV flattening filter free beam. Plans were created for a standard (std) and a high‐definition (HD) MLC. Published values for leaf transmission factor and dosimetric leaf gap were utilized. All other parameters were invariant. Conformity (plan and individual target), moderate isodose spill (V50%), and low isodose spill (mean brain dose) were selected for analysis.

Results:

Compared to standard MLC, HD‐MLC improved overall plan conformity (median: Paddick CI_HD = 0.83, Paddick CI_std = 0.79; p = 0.004 and median: RTOG CI_HD =1.18, RTOG CI_std =1.24; p = 0.01), improved individual lesion conformity (median: Paddick CI_HD,i =0.77, Paddick CI_std,i =0.72; p < 0.001 and median: RTOG CI_HD,i = 1.28, RTOG CI_std,i =1.35; p < 0.001), improved moderate isodose spill (median: V50%_HD = 37.0 cc, V50%_std = 45.7 cc; p = 0.002), and improved low dose spill (median: dmean_HD = 2.90 Gy, dmean_std = 3.19 Gy; p = 0.002).

Conclusion:

For the single‐isocenter VMAT SRS of multiple metastasis plans examined, use of HD‐MLC modestly improved conformity, moderate isodose, and low isodose spill compared to standard MLC. However, in all cases we were able to generate clinically acceptable plans with the standard MLC. More work is need to further quantify the difference in cases with higher numbers of small targets and to better understand any potential clinical significance.

This research was supported in part by Varian Medical Systems.
SU‐F‐T‐634: Feasibility Study of Respiratory Gated RapidArc SBRT Using a 6MV FFF Photon Beam
Authors: Dou K , Jacobs M , Laser B , Safaraz M , Rodgers J
Published: July 2016

Purpose:

To conduct a feasibility study on retrospective respiratory gating and marker tracking for lung stereotactic body radiotherapy (SBRT) with a gated RapidArc delivery using a 6MV flattened filter free photon mode.

Methods:

A CIRS dynamic thorax phantom Model 008A with different inserts was used for treatment planning and respiratory gating. 4D CT had a free breathing simulation followed by a respiration gated, ten phased CT using a Philips Brilliance CT with a Varian RPM respiratory gating system. The internal target volume was created from the ten phase gated CT images, followed by exporting to a Varian Eclipse TPS v11 for treatment planning on the free breath images. Both MIP and AIP were also generated for comparison of planning and target motion tracking. The planned dose was delivered with a 6MV FFF photon beam from a Varian TrueBeam accelerator. Gated target motion was also verified by tracking the implanted makers during delivery using continuous kV imaging in addition to CBCT, kV and MV localization and verification.

Results:

Gating was studied in three situations of lower, normal, and faster breathing at a respiratory cycle of 5, 15 and 25 breaths per minute, respectively. 4D treatment planning was performed at a normal breathing of 15 breaths per minute. The gated patterns obtained using the TrueBeam IR camera were compared with the planned ones while gating operation was added prior to delivery . Gating was realized only when the measured respiratory patterns matched to the planned ones. The gated target motion was verified within the tolerance by kV and MV imaging. Either free breathing CT or averaged CT images were studied to be good for image guidance to align the target.

Conclusion:

Gated RapidArc SBRT delivered with a 6MV FFF photon beam is realized using a dynamic lung phantom.
SU‐F‐T‐643: Feasibility of Performing Patient Specific VMAT QA On Single Linac for Plans Treated in Beam‐Matched Elekta Agility Linacs
Authors: Leung R , Lee V , Cheung S , Lee K , Law G , Wong M , Chan M , Mun Tuen
Published: July 2016

Purpose:

The increasing application of VMAT demands a more efficient workflow and QA solution. This study aims to investigate the feasibility of performing VMAT QA measurements on one linac for plans treated on other beam‐matched Elekta Agility linacs.

Methods:

A single model was used to create 24 clinically approved VMAT plans (12 head‐and‐neck and 12 prostate using 6MV and 10MV respectively) on Pinnacle v9.10 (Philips, Einhoven, Netherlands). All head‐and‐neck plans were delivered on three beam‐matched machines while all prostate cases were delivered on two beam‐matched 10MV Agility machines. All plans were delivered onto PTW Octavius 4D phantom with 1500 detector array (PTW, Freiburg, Germany). Reconstructed volume doses were then compared with the Pinnacle reference plans in Verisoft 6.1 under 3%/3mm gamma criteria at local dose. Plans were considered clinically acceptable if >90% of the voxels passing the gamma criteria.

Results:

All measurements were passed (3D gamma passing rate >90%) and the result shows that the mean difference of 3D gamma of 12 head‐and‐neck cases is 1.2% with standard deviation of 0.6%. While for prostate cases, the mean difference of 3D gamma is 0.9% with standard deviation of 0.7%. Maximum difference of 3D gamma of all measurements between beam‐matched machines is less than 2.5%. The differences of passing rates between different machines were statistically insignificant (p>0.05). Conclusion. The result suggests that ther

Conclusion:

The result suggests that there exists a 3D gamma threshold, in our case 92.5%, above which the VMAT QA performed in any one of beam‐matched machine will also pass in another one. Therefore, VMAT QA efficiency may be increased and phantom set up time can be saved by implementing such method. A constant performance across all beam matched machines must be maintained to make this QA approach feasible.
SU‐F‐T‐647: Linac‐Based Stereotactic Radiosurgery (SRS) in the Treatment of Trigeminal Neuralgia: Detailed Description of SRS Procedural Technique and Reported Clinical Outcomes
Authors: Pokhrel D , Sood S , Badkul R , Jiang H , Stepp T , Camarata P , Wang F
Published: July 2016

Purpose:

SRS is an effective non‐invasive alternative treatment modality with minimal‐toxicity used to treat patients with medically/surgically refractory trigeminal neuralgia root(TNR) or those who may not tolerate surgical intervention. We present our linac‐based SRS procedure for TNR treatment and simultaneously report our clinical outcomes.

Methods:

Twenty‐eight TNR‐patients treated with frame‐based SRS at our institution (2009–2015) with a single‐fraction point‐dose of 60‐80Gy to TNR were included in this IRB‐approved study. Experienced neurosurgeon and radiation oncologist delineated the TNR on 1.0mm thin 3D‐FIESTA‐MRI that was co‐registered with 0.7mm thin planning‐CT. Treatment plans were generated in iPlan (BrainLAB) with a 4‐mm diameter cone using 79 arcs with differential‐weighting for Novalis‐TX 6MV‐SRS(1000MU/min) beam and optimized to minimize brainstem dose. Winston‐Lutz test was performed before each treatment delivery with sub‐millimeter isocenter accuracy. Quality assurance of frame placement was maintained by helmet‐bobble‐measurement before simulation‐CT and before patient setup at treatment couch. OBI‐CBCT scan was performed for patient setup verification without applying shifts. On clinical follow up, treatment response was assessed using Barrow Neurological Institute Pain Intensity Score(BNI‐score:I–V).

Results:

26/28 TNR‐patients (16‐males/10‐females) who were treated with following single‐fraction point‐dose to isocenter: 80Gy(n=22),75Gy(n=1),70Gy(n=2) and 60Gy(n=1, re‐treatment) were followed up. Median follow‐up interval was 8.5‐months (ranged:1–48.5months). Median age was 70‐yr (ranged:43–93‐yr). Right/left TNR ratio was 15/11. Delivered total # of average MUs was 19034±1204. Average beam‐on‐time: 19.0±1.3min. Brainstem max‐dose and dose to 0.5cc were 13.3±2.4Gy (ranged:8.1–16.5Gy) and 3.6±0.4Gy (ranged:3.0–4.9Gy). On average, max‐dose to optic‐apparatus was ≤1.2Gy. Mean value of max‐dose to eyes/lens was 0.26Gy/0.11Gy. Overall, 20‐patients (77%) responded to treatment: 5(19%) achieved complete pain relief without medication (BNI score: I); 5(19%) had no‐pain, decreased medication (BNI‐score:II); 2(7.7%) had no‐pain, but, continued medication (BNI‐score:IIIA), and 8(30.8%) had pain that was well controlled by medication (BNI‐score: IIIB). Six‐patients (23.0%) did not respond to treatment (BNI‐score:IV–V). Neither cranial nerve deficit nor radio‐necrosis of temporal lobe was clinically observed.

Conclusion:

Linac‐based SRS for medically/surgically refractory TNR provided an effective treatment option for pain resolution/control with very minimal if any normal tissue toxicity. Longer follow up of these patients is anticipated/needed to confirm our observations.
SU‐F‐T‐648: Sharpening Dose Fall‐Off Via Beam Number Enhancements For Stereotactic Brain Radiosurgery
Authors: Chiu J , Pierce M , Braunstein S , McDermott M , Sneed P , Ma L
Published: July 2016

Purpose:

Sharp dose fall‐off is the hallmark of brain radiosurgery to deliver a high dose of radiation to the target while minimizing dose to normal brain tissue. In this study, we developed a technique for the purpose of enhancing the peripheral dose gradient by magnifying the total number of beams focused toward each isocenter via patient head tilt and simultaneous beam intensity modulations.

Methods:

Computer scripting for the proposed beam number enhancement (BNE) technique was developed. The technique was tested and then implemented on a clinical treatment planning system for a dedicated brain radiosurgical system (GK Perfexion, Elekta Oncology). To study technical feasibility and dosimetric advantages of the technique, we compared treatment planning quality and delivery efficiency for 20 radiosurgical cases previously treated at our institution. These cases included relatively complex treatments such as acoustic schwannoma, meningioma, brain metastasis and mesial temporal lobe epilepsy.

Results:

The BNE treatment plans were found to produce nearly identical target volume coverage (absolute value < 0.5%, P > 0.2) and dose conformity (BNE CI= 1.41±0.15 versus 1.41±0.20, P>0.9) as the original treatment plans. The total beam‐on time for theBNE treatment plans were comparable (within 1.0 min or 1.8%) with those of the original treatment plans for all the cases. However, BNE treatment plans significantly improved the mean gradient index (BNE GI = 2.9±0.3 versus original GI =3.0±0.3 p<0.0001) and low‐level isodose volumes, e.g. 20‐50% prescribed isodose volumes, by 2.0% to 5.0% (p<0.02). Furthermore, with 4 to 5‐fold increase in the total number of beams, the GI decreased by as much as 20% or 0.5 in absolute values.

Conclusion:

BNE via head tilt and simultaneous beam intensity modulation is an effective and efficient technique that physically sharpens the peripheral dose gradient for brain radiosurgery.
SU‐F‐T‐654: Pacemaker Dose Estimate Using Optically Stimulated Luminescent Dosimeter for Left Breast Intraoperative Radiation Therapy
Authors: Chen Y , Goenka A , Sharma A , Wang L , Cao Y , Jamshidi A
Published: July 2016

Purpose:

To assess and report the in vivo dose for a patient with a pacemaker being treated in left breast intraoperative radiation therapy (IORT). The ZEISS Intrabeam 50 kVp X‐ray beam with a spherical applicator was used.

Methods:

The optically stimulated luminescent dosimeters (OSLDs) (Landauer nanoDots) were employed and calibrated under the conditions of the Intrabeam 50 kVp X‐rays. The nanoDots were placed on the patient at approximately 15 cm away from the lumpectomy cavity both under and above a shield of lead equivalence 0.25 mm (RayShield X‐Drape D‐110) covering the pacemaker area during IORT with a 5 cm spherical applicator.

Results:

The skin surface dose near the pacemaker during the IORT with a prescription of 20 Gy was measured as 4.0±0.8 cGy. The dose behind the shield was 0.06±0.01 Gy, demonstrating more than 98% dose reduction. The in vivo skin surface doses during a typical breast IORT at a 4.5 cm spherical applicator surface were further measured at 5, 10, 15, and 20 cm away to be 159±11 cGy, 15±1 cGy, 6.6±0.5 cGy, and 1.8±0.1 cGy, respectively. A power law fit to the dose versus the distance z from the applicator surface yields the dose fall off at the skin surface following z^‐2.5, which can be used to estimate skin doses in future cases. The comparison to an extrapolation of depth dose in water reveals an underestimate of far field dose using the manufactory provided data.

Conclusion:

The study suggests the appropriateness of OSLD as an in vivo skin dosimeter in IORT using the Intrabeam system in a wide dose range. The pacemaker dose measured during the left breast IORT was within a safe limit.
SU‐F‐T‐661: Dependence of Gold Nano Particles Cluster Morphology On Dose Enhancement of Photon Radiation Therapy Apply for Radiation Biology Effect
Authors: Ahn S , Chung K , Han Y , Park H
Published: July 2016

Purpose:

Injected gold nano particles (GNPs) to a body for dose enhancement are known to form in the tumorcell cluster morphology. We investigated the dependence of dose enhancement on the morphology characteristic with an approximated morphology model by using Monte Carlo simulations.

Methods:

For MC simulation, TOPAS version 2.0P‐03 was used. GNP cluster morphology was approximated as a body center cubic(BCC) model by placing 8 GNPs at the corner and one at the center of cube with length from 2.59 µm to 0.25 µm located in a 4 µm length water filled cube phantom. 4 µm length square shaped beams of poly‐energetic 50, 260 kVp photons were irradiated to the water filled cube phantom with 100 nm diameter GNPs in it. Dose enhancement ratio(DER) was computed as a function of distance from the surface of the GNP at the cube center for 18 cubes geometries. For scoring particles, 10 nm width of concentric shell shaped detector was constructed up to 100 nm from the center. Total dose in a sphere of 100 nm radius of detector were normalized to 2.59 µm length cube morphology. To verified biological effect of BCC model applied to cell survival curve fitting.

Results:

DER increase as the distance of the GNPs reduces. DER was largest for 0.25 µm length cube. Dependence of GNP distance DER increment was 1.73, 1.60 for 50 kVp, 260 kVp photons, respectively. Also, Using BCC model applied to cell survival curve was well prediction.

Conclusion:

DER with GNPs was larger when they are closely packed in the phantom. Therefore, better therapeutic effects can be expected with close‐packed GNPs.

This research was supported by the NRF funded by the Ministry of Science, ICT & Future Planning (2012M3A9B6055201 and 2012R1A1A2042414), Samsung Medical Center grant[GFO1130081]
SU‐F‐T‐663: Cerenkov Radiation Enhanced Radiotherapy with Titanium Dioxide Nanoparticle: A Monte Carlo Study
Authors: Liu B , Ouyang Z , Sajo E , Ngwa W
Published: July 2016

Purpose:

A recent publication has shown that by delivering titanium dioxide nanoparticles (titania) as a photosensitizer into tumors, Cerenkov radiation (CR) produced by radionuclides could be used for substantially boosting damage to cancer cells. The present work compares CR production by various clinically relevant radiation sources including internal radionuclides and external beam radiotherapy (EBRT), and provides preliminarily computational results of CR absorption by titania.

Methods:

1) Geant4.10.1 was used to simulate ionizing radiation‐induced CR production in a 1cm diameter spherical volume using external radiotherapy sources: Varian Clinac IX 6MV and Eldorado 60Co, both with 10*10 cm2 field size. In each case the volume was placed at the maximum dose depth (1.5cm for 6MV source and 0.5cm for 60Co). In addition, 18F, 192Ir and 60Co were simulated using Geant4 radioactive decay models as internal sources. Dose deposition and CR production spectra in 200nm‐400nm range were calculated as it is the excitation range of titania. 2) Using 6MV external source, the absorption by titania was calculated via the track length of CR in the spherical volume. The nanoparticle concentration was varied from 0.25 to 5µg/g.

Results:

Among different radioactive sources, results showed that 18F induced the highest amount of CR per disintegration, but 60Co had the highest yield per unit dose. When compared with external sources, 6MV source was shown to be the most efficient for the the same delivered dose. Simulations indicated increased absorption for increasing concentrations, with up to 68% absorption of generated CR for 5µg/g titania concentration.

Conclusion:

The results demonstrate that 6MV beam is favored with a higher CR yield, compared to radionuclides, and that the use of higher concentrations of titania may increase photosensitization. From the findings, we propose that if sufficiently potent concentrations of titania are delivered to tumors this could substantially boost EBRT.
SU‐F‐T‐664: The Efficacy of Gold Nanoparticles as Contrast Agents in Mice
Authors: Yuan Y , Zhang Y , Yasmin‐Karim S , Karve A , Sajo E , Ngwa W
Published: July 2016

Purpose:

Micro‐Computed Tomography (micro‐CT) has been widely used as a non‐invasive, high‐resolution imaging modality in preclinical research. However, tumors cannot be well distinguished, since their density are similar to those of surrounding tissues, and the tumors’ natural contrast is very low. The benefits of using Gold Nanoparticles (AuNPs) as a promising high atomic weight contrast agent have been published in recent years. The aim of this study is to investigate the efficacy of AuNPs as contrast agents using different energy x‐rays.

Methods:

The left flank of an immune‐compromised athymic nude mouse was implanted with subcutaneous xenograft model of human lung cancer line, A549 cells (from ATCC). After 14 days, this mouse was imaged with dual energy cone‐beam micro‐CT. The selected energies were 45 kVp and 65 kVp. 10µg AuNPs (200 µg/ml concentration) approximately 12 nm in size were injected subcutaneously into the tumor. The mouse was imaged 0, 3 and 24 hours post‐injection. During scanning, this mouse was anesthetized. All projection raw data have been optimized and then images were reconstructed with the FDK Algorithm.

Results:

Based on images, at 0 hour, AuNPs provided obvious contrast no matter which energy selected, 45 kVp or 65 kVp; and using 45 kVp X‐ray, AuNps showed greater contrast. After 3 hours or evenand longer, AuNPs distributed throughout the whole body of mouse, and they were not shown clearly shown in the images.

Conclusion:

In this study, we investigated the efficacy of AuNPs as image contrast agents at different energies with dual‐energy micro‐CT, using 200µg/mL of AuNPs. Sufficiently high concentrations of AuNPs are needed to be able to track intratumoral distribution. Images showed good contrast immediately following the administration of the agent but results were poor after 3 hours.
SU‐F‐T‐667: Development and Validation of Dose Calculation for An Open‐Source KV Treatment Planning System for Small Animal Radiotherapy
Authors: Prajapati S , Mo X , Bednarz B , Lawless M , Hammer C , Flynn R , Westerly D , Jeraj R , Mackie T
Published: July 2016

Purpose:

An open‐source, convolution/superposition based kV‐treatment planning system(TPS) was developed for small animal radiotherapy from previously existed in‐house MV‐TPS. It is flexible and applicable to both step and shoot and helical tomotherapy treatment delivery. For initial commissioning process, the dose calculation from kV‐TPS was compared with measurements and Monte Carlo(MC) simulations.

Methods:

High resolution, low energy kernels were simulated using EGSnrc user code EDKnrc, which was used as an input in kV‐TPS together with MC‐simulated x‐ray beam spectrum. The Blue Water™ homogeneous phantom (with film inserts) and heterogeneous phantom (with film and TLD inserts) were fabricated. Phantom was placed at 100cm SSD, and was irradiated with 250 kVp beam for 10mins with 1.1cm × 1.1cm open field (at 100cm) created by newly designed binary micro‐MLC assembly positioned at 90cm SSD. Gafchromic™ EBT3 film was calibrated in‐phantom following AAPM TG‐61 guidelines, and were used for measurement at 5 different depths in phantom. Calibrated TLD‐100s were obtained from ADCL. EGS and MNCP5 simulation were used to model experimental irradiation set up calculation of dose in phantom.

Results:

Using the homogeneous phantom, dose difference between film and kV‐TPS was calculated: mean(x)=0.9%; maximum difference(MD)=3.1%; standard deviation(σ)=1.1%. Dose difference between MCNP5 and kV‐TPS was: x=1.5%; MD=4.6%; σ=1.9%. Dose difference between EGS and kV‐TPS was: x=0.8%; MD=1.9%; σ=0.8%. Using the heterogeneous phantom, dose difference between film and kV‐TPS was: x=2.6%; MD=3%; σ=1.1%; and dose difference between TLD and kV‐TPS was: x=2.9%; MD=6.4%; σ=2.5%.

Conclusion:

The inhouse, open‐source kV‐TPS dose calculation system was comparable within 5% of measurements and MC simulations in both homogeneous and heterogeneous phantoms. The dose calculation system of the kV‐TPS is validated as a part of initial commissioning process for small animal radiotherapy. The kV‐TPS has the potential for accurate dose calculation for any kV treatment or imaging modalities.
SU‐F‐T‐676: Measurement of Hydroxyl Radicals in Radiolized Water Systems
Authors: Ouyang Z , Strack G , Sajo E , Ngwa W
Published: July 2016

Purpose:

Hydroxyl radicals can be produced within tissue by radiation therapy, and they are largely responsible for DNA damage and cell killing. Coumarin‐3‐carboxylic acid (3‐CCA) and crystal violet are reported to react with hydroxyl radicals and can be used for fluorescence and absorbance measurements, respectively. This study assesses the ability of hydroxyl measurement for both 3‐CCA and crystal violet in radiolized water systems in order to provide dosimetric information in radiation chemistry and radiation biology experiments.

Methods:

3‐CCA and crystal violet were both dissolved in phosphate buffered saline (PBS, pH 7.4) with final concentrations 0.5 mg/mL and 0.05 mg/mL. 3‐CCA and control solutions (PBS only) were loaded in black bottom 96‐well plates. Crystal violet and control solutions were loaded in clear bottom 96‐well plates. The prepared solutions were irradiated at 2 Gy using a small animal radiation research platform. Fluorescence reading with 360 nm excitation wavelength and 485 nm emission wavelength was done for 3‐CCA, and absorbance reading at wavelength 580 nm was done for crystal violet before and after radiation.

Results:

3‐CCA showed clear difference in fluorescence before and after radiation, which suggested hydroxyl production during radiation. However, crystal violet absorbance at 580 nm was not changed significantly by radiation.

Conclusion:

The overall conclusion is that 3‐CCA can be used for hydroxyl measurement in radiolized water systems, while crystal violet cannot, although crystal violet is reported widely to react with hydroxyl radicals produced in Fenton reactions. Possible reasons could relate to reaction pH.
SU‐F‐T‐680: Radiobiological Analysis of the Impact of Daily Patient Deformation and Setup Variations Through the Use of the Cone Beam CT and Deformable Image Registration in Lung Cancer IMRT
Authors: Jurkovic I , Stathakis S , Markovic M , Papanikolaou N , Mavroidis P
Published: July 2016

Purpose:

To estimate the dose distributions delivered to the patient in each treatment fraction using deformable image registration (DIR) and assess the radiobiological impact of the inter‐fraction variations due to patient deformation and setup.

Methods:

The work is based on the cone beam CT (CBCT) images and treatment plans of two lung cancer patients. Both patients were treated with intensity modulated radiation therapy (IMRT) to 66Gy in 2Gy/fraction. The treatment plans were exported from the treatment planning system (TPS) to the Velocity AI where DIR was performed and the same deformation matrix was used for the deformation of the planned dose distribution and organ contours to each CBCT dataset. A radiobiological analysis was performed based on the radiobiological parameters of the involved organs at risk (OARs) and planning target volume (PTV). Using the complication free tumor control probability (P+) index, differences in P+ were observed between each CBCT as well as between CBCT and planning dose distributions.

Results:

The optimal CBCT P? values ranged from 91.6 % to 94.8 % for patient #1 and from 88.8 % to 90.6 % for patient #2. At the dose level of the clinical prescription, the CBCT P+ values ranged from 80.3% to 80.7% for patient #1 and from 80.7% to 81.0% for the patient #2. The planning CT P+ values were 81.0% and 80.7% for the two patients, respectively. These differences emphasize the significance of using the radiobiological analysis when assessing changes in the dose distribution due to the tumor motion and lung deformations.

Conclusion:

Daily setup variations yield to differences in the actual dose delivered versus the planned one. The observed differences were rather small when only looking at the dosimetric comparison of the dose distributions, however the radiobiology analysis was able to detect clinically relevant differences among the studied dose distributions.
SU‐G‐BRA‐13: An Advanced Deformable Lung Phantom for Analyzing the Dosimetric Impact of Respiratory Motion
Authors: Shin D , Kang S , Kim D , Kim T , Kim K , Cho M , Suh T
Published: July 2016

Purpose:

The difference between three‐dimensional (3D) and four‐dimensional (4D) dose is affected by factors such as tumor size and motion. To quantitatively analyze the effects of these factors, a phantom that can independently control for each factor is required. The purpose of this study is to develop a deformable lung phantom with the above attributes and evaluate characteristics.

Methods:

A phantom was designed to simulate diaphragm motion with amplitude in the range 1 to 7 cm and various periods of regular breathing. To simulate different size tumors, tumors were produced by pouring liquid silicone into custom molds created by a 3D printer. The accuracy of phantom diaphragm motion was assessed using calipers and protractor. To control tumor motion, tumor trajectories were evaluated using 4D computed tomography (CT), and diaphragm‐tumor correlation curve was calculated by curve fitting method. Three‐dimensional dose and 4D dose were calculated and compared according to tumor motion.

Results:

The accuracy of phantom diaphragm motion was less than 1 mm. Maximum tumor motion amplitudes in the left‐right and anterior‐posterior directions were 0.08 and 0.12 cm, respectively, in a 10 cm3 tumor, and 0.06 and 0.27 cm, respectively, in a 90 cm3 tumor. The diaphragm‐tumor correlation curve showed that tumor motion in the superior‐inferior direction was increased with increasing diaphragm motion. In the 10 cm3 tumor, the tumor motion was larger than the 90 cm3 tumor. According to tumor motion, variation of dose difference between 3D and 4D was identified.

Conclusion:

The developed phantom can independently control factors such as tumor size and motion. In potentially, this phantom can be used to quantitatively analyze the dosimetric impact of respiratory motion according to the factors that influence the difference between 3D and 4D dose.

This research was supported by the Mid‐career Researcher Program through NRF funded by the Ministry of Science, ICT & Future Planning of Korea (NRF‐2014R1A2A1A10050270) and by the Radiation Technology R&D program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning (No. 2013M2A2A7038291)
SU‐G‐206‐01: A Fully Automated CT Tool to Facilitate Phantom Image QA for Quantitative Imaging in Clinical Trials
Authors: Wahi‐Anwar M , Lo P , Kim H , Brown M , McNitt‐Gray M
Published: July 2016

Purpose:

The use of Quantitative Imaging (QI) methods in Clinical Trials requires both verification of adherence to a specified protocol and an assessment of scanner performance under that protocol, which are currently accomplished manually. This work introduces automated phantom identification and image QA measure extraction towards a fully‐automated CT phantom QA system to perform these functions and facilitate the use of Quantitative Imaging methods in clinical trials.

Methods:

This study used a retrospective cohort of CT phantom scans from existing clinical trial protocols ‐ totaling 84 phantoms, across 3 phantom types using various scanners and protocols. The QA system identifies the input phantom scan through an ensemble of threshold‐based classifiers. Each classifier ‐ corresponding to a phantom type ‐ contains a template slice, which is compared to the input scan on a slice‐by‐slice basis, resulting in slice‐wise similarity metric values for each slice compared. Pre‐trained thresholds (established from a training set of phantom images matching the template type) are used to filter the similarity distribution, and the slice with the most optimal local mean similarity, with local neighboring slices meeting the threshold requirement, is chosen as the classifier's matched slice (if it existed). The classifier with the matched slice possessing the most optimal local mean similarity is then chosen as the ensemble's best matching slice. If the best matching slice exists, image QA algorithm and ROIs corresponding to the matching classifier extracted the image QA measures.

Results:

Automated phantom identification performed with 84.5% accuracy and 88.8% sensitivity on 84 phantoms. Automated image quality measurements (following standard protocol) on identified water phantoms (n=35) matched user QA decisions with 100% accuracy.

Conclusion:

We provide a fullyautomated CT phantom QA system consistent with manual QA performance. Further work will include parallel component to automatically verify image acquisition parameters and automated adherence to specifications.

Institutional research agreement, Siemens Healthcare; Past recipient, research grant support, Siemens Healthcare; Consultant, Toshiba America Medical Systems; Consultant, Samsung Electronics; NIH Grant support from: U01 CA181156.
SU‐G‐206‐04: A Method for Realizing Phantom Calibration and Geometry Calibration Accurately Based On a Geometry Evaluation Index
Authors: Yang S , Wu S , Qi H , Xu Y , Zhou L
Published: July 2016

Purpose:

For traditional geometric calibration, the calibration accuracy relies on both accuracy of geometry phantom manufacture and accuracy of ball bearings (BB) location estimation. In this work, we have developed a method to perform phantom calibration and geometry calibration iteratively and accurately in a whole procedure.

Methods:

We have designed and manufactured a geometry phantom with BB and an evaluation phantom of a crystal ball contained in a cubic gel box. Our calibration method consists of five steps: 1) Estimate BB locations using spiral CT image, which are then used to initialize the particles in Particle Swarm Optimization (PSO) algorithm; 2) Perform geometric calibration; 3) Reconstruct the images of the evaluation phantom based on the current geometry calibration; 4) Evaluate the reconstructed images using a geometry evaluate index; 5) Update BB locations in PSO algorithm. Repeat step2)‐5) until our stopping criteria is met. The edge of the crystal ball in the calibration phantom on CBCT images is detected by Hough transform to define two circular rings outside and inside the ball. The evaluation index used in step 4) is defined as the difference of the averaged image intensities of these two circular rings.

Results:

We have demonstrated the feasibility and performance of our method on a benchtop CBCT system. It is observed that inaccurate BB locations lead to severe image distortion and relative small evaluation index. With our method, streak artifacts are reduced and the structure becomes sharper and clearer. The evaluation index increases fast within 10 iterations, and then becomes stable gradually.

Conclusion:

Our method can perform accurate phantom calibration and geometry calibration together in a whole procedure. It helps to mitigate the impact of the geometry phantom manufacture errors on the calibration, which could hence save the cost of the geometry phantom manufacture.
SU‐G‐206‐08: How Should Focal Spot Be Chosen for Optimized CT Imaging with Dose Modulation?
Authors: Bache S , Liu X , Rong J
Published: July 2016

Purpose:

To choose the preferred focal spot for achieving optimized CT image quality with balanced tube heating considerations.

Methods:

An anthropomorphic pelvic phantom was scanned using a GE Discovery CT750 HD at 120 and 140kVp, 0.8s rotation time, and pitch of 0.984. “Smart mA” was enabled to simulate a routine abdomen–pelvis CT scan. Permissible mA values at 120 and 140 kVp were obtained from the Serial Load Rating table (for mimicking a busy CT clinical operation) in the scanner Technical Reference Manual. At each kVp station and two Noise Index levels, the mA Upper Limit was set above/below the permissible mA values. Scanned mA values and focal spot (FS) used were obtained from the DICOM header of each image, and the FS‐mA relationship was analyzed. For visual confirmation beyond recorded FS information, a CatPhan with a fat‐ring attached for mimicking patient size/shape was scanned at 120kVp. A group of radiologists/physicists compared a pair of CatPhan images qualitatively. Lastly, a number of patient cases were evaluated to confirm the FS‐mA relationship.

Results:

When preset Upper Limit values were above the permissible mA values, the Large FS (labeled 1.2) was used in scans, even if the maximum scanned mA values were much lower than the permissible values at both 120 and 140 kVp. Otherwise the Small FS (labeled 0.7) was used. Visual evaluation of the high contrast module of CatPhan and additional analysis of patient cases further confirmed that the preset Upper Limit determines which focal spot is to be used, not the actual maximum mA value to be scanned.

Conclusion:

Specific FS can be selected by setting up appropriate mA Upper Limit in a protocol. CT protocols could be optimized by selecting appropriate FS for improving patient image quality, especially benefiting the small size and pediatric patients.
SU‐G‐206‐14: Individual Dose Alert Thresholds for Abdominal CT Protocols Due to Statistical Independence of Dose Distributions
Authors: Stewart BK
Published: July 2016

Purpose:

To determine whether a single dose management system alert threshold will suffice for the 34 abdomen protocols on our institution's CT scanners, or if these alert thresholds should be set per protocol. Parametric statistical analysis is ideally valid only for distributions demonstrating: (1) normality (2) homogeneity of variance (3) interval scale and (4) independence. Dose distributions are notoriously non‐normal and thus nonparametric statistical analysis is typically required.

Methods:

Dose distribution data were collected from a HD750 CT scanner (GE Healthcare) at our institution over the third and fourth quarters of 2015. In total there were 1793 abdomen studies using 34 different protocols. Protocols were selected for statistical analysis (SPSS, IBM Corp.) if the count over the period was ≥ 50 to produce statistically meaningful results. Nine protocols with count ranging from 61‐398 were selected. Protocol dose distributions were statistically analyzed to determine: (1) normality – Shapiro‐Wilk test (2) homogeneity of variance – Levene Statistic (3) similarity of medians – Median test, and (4) similarity of distribution – Kruskal‐Wallis test.

Results:

For the nine abdomen protocols used with exam count ≥ 50, the dose distributions were statistically significantly different from normal for eight protocols (p≤[0.001‐0.035]), homogeneity of variance invalidated for five protocols (p≤[0.001‐0.037]), median values not the same across all protocols (p<0.001), and all dose distributions different from each other (p<0.001).

Conclusion:

That all abdomen protocols with exam count ≥ 50, the distributions were predominantly: (1) non‐normal (2) of unequal variance over the distributions (3) of unequal means and (4) non‐identical distributions indicates that the abdomen protocols in general must be treated independently with non‐parametric statistical analysis and thus the alert thresholds should be calculated and set individually, that is, there cannot be a solitary meaningful alert threshold utilized over all abdominal protocols examined in this study.
SU‐G‐IeP1‐05: Diffusion Kurtosis Imaging for Oropharyngeal Cancer Detection
Authors: Ding Y , Mohamed A , Ma J , Frank S , Wang J , Fuller C
Published: July 2016

Purpose:

Diffusion kurtosis imaging (DKI) is an emerging diffusion MRI technique in cancer diagnosis applications. The objective of this study is to compare DKI with conventional diffusion weighted imaging (DWI) for diagnosis of head and neck cancer.

Methods:

Five male patients with histologically documented phase II/III squamous cell carcinoma of the oropharynx were included in this study. DKI (with 6 b‐values of 0‐2000 s/mm2) and conventional DWI data were acquired at a 3.0 T GE MRI scanner. Monoexponential (calculating apparent diffusion coefficient (ADC) using DWI data) and non‐Gaussian kurtosis (calculating mean diffusion coefficient (MD) and mean kurtosis coefficient (MK) using DKI data) fits were performed on a voxel‐by‐voxel basis in selected regions of interest (primary tumor, metastatic nodes, contralateral region of tumor (tongue muscle), and submandibular glands). The non‐parametric Wilcoxon test of ADC and DKI parameters between primary tumor and tongue muscle in contralateral region of tumor were calculated for comparison.

Results:

Examples of T1 post‐contrast images and diffusion parametric maps (ADC, MD and MK) were illustrated in Figure 1 for an oropharynx cancer patient. MK parameters were significantly higher in the primary tumor than in the contralateral tongue muscle (0.89 ± 0.17 vs 0.68 ± 0.13, respectively; P <.05). MD and ADC in the primary tumor were significantly lower than those in the contralateral tongue muscle (1.20 ± 0.23 vs 2.57 ± 1.01; P <0.02 and 0.88 ± 0.22 vs 1.41 ± 0.18; P <0.01, respectively) (Table 1). Figure 2 showed statistical distribution of DWI and DKI parameters in selected regions of interest (primary tumor, metastatic nodes, tongue muscle, and submandibular glands).

Conclusion:

The preliminary results of this study showed DKI could be a new option for increasing diagnostic confidence of oropharyngeal lesions. We continue to accrue study patients to evaluate the potential correlation between DKI parameters and tumor pathologic factors.
SU‐G‐IeP1‐13: Sub‐Nyquist Dynamic MRI Via Prior Rank, Intensity and Sparsity Model (PRISM)
Authors: Jiang B , Gao H
Published: July 2016

Purpose:

Accelerated dynamic MRI is important for MRI guided radiotherapy. Inspired by compressive sensing (CS), sub‐Nyquist dynamic MRI has been an active research area, i.e., sparse sampling in k‐t space for accelerated dynamic MRI. This work is to investigate sub‐Nyquist dynamic MRI via a previously developed CS model, namely Prior Rank, Intensity and Sparsity Model (PRISM).

Methods:

The proposed method utilizes PRISM with rank minimization and incoherent sampling patterns for sub‐Nyquist reconstruction. In PRISM, the low‐rank background image, which is automatically calculated by rank minimization, is excluded from the L1 minimization step of the CS reconstruction to further sparsify the residual image, thus allowing for higher acceleration rates. Furthermore, the sampling pattern in k‐t space is made more incoherent by sampling a different set of k‐space points at different temporal frames.

Results:

Reconstruction results from L1‐sparsity method and PRISM method with 30% undersampled data and 15% undersampled data are compared to demonstrate the power of PRISM for dynamic MRI.

Conclusion:

A sub‐ Nyquist MRI reconstruction method based on PRISM is developed with improved image quality from the L1‐sparsity method.
SU‐G‐JeP1‐09: Evaluation of Transperineal Ultrasound Imaging as a Potential Solution for Target Tracking During Ablative Body Radiotherapy for Prostate Cancer
Authors: Najafi M , Han B , Cooper D , Hancock S , Hristov D
Published: July 2016

Purpose:

Prostate SABR is emerging as a clinically viable, potentially cost effective alternative to prostate IMRT but its adoption is contingent on providing solutions for accurate tracking during beam delivery. Our goal is to evaluate the performance of the Clarity Autoscan ultrasound monitoring system for inter‐fractional prostate motion tracking in both phantoms and in‐vivo.

Methods:

In‐vivo evaluation was performed under IRB protocol to allow data collection in prostate patients treated with VMAT whereby prostate was imaged through the acoustic window of the perineum. The probe was placed before KV imaging and real‐time tracking was started and continued until the end of treatment. Initial absolute 3D positions of fiducials were estimated from KV images. Fiducial positions in MV images subsequently acquired during beam delivery were compared with predicted positions based on Clarity estimated motion.

Results:

Phantom studies with motion amplitudes of ±1.5, ±3, ±6 mm in lateral direction and ±2 mm in longitudinal direction resulted in tracking errors of −0.03 ± 0.3, −0.04 ± 0.6, −0.2 ± 0.9 mm, respectively, in lateral direction and −0.05 ± 0.30 mm in longitudinal direction. In phantom, measured and predicted fiducial positions in MV images were within 0.1 ± 0.6 mm. Four patients consented to participate in the study and data was acquired over a total of 140 fractions. MV imaging tracking was possible in about 75% of the time (due to occlusion of fiducials) compared to 100% with Clarity. Overall range of estimated motion by Clarity was 0 to 4.0 mm. In‐vivo fiducial localization error was 1.2 ± 1.0 mm compared to 1.8 ± 1.9 mm if not taking Clarity estimated motion into account.

Conclusion:

Real‐time transperineal ultrasound tracking reduces uncertainty in prostate position due to intrafractional motion.

Research was supported by Elekta.
SU‐G‐IeP3‐04: Effective Dose Measurements in Fast Kvp Switch Dual Energy Computed Tomography
Authors: Raudabaugh J , Nguyen G , Moore B , Lowry C , Nelson R , Yoshizumi T
Published: July 2016

Purpose:

The objective of this study was two‐fold: (a) to test a new approach to approximating organ dose by using the effective energy of the combined 80kV/140kV beam in dual‐energy (DE) computed tomography (CT), and (b) to derive the effective dose (ED) in the abdomen‐pelvis protocol in DECT.

Methods:

A commercial dual energy CT scanner was employed using a fast‐kV switch abdomen/pelvis protocol alternating between 80 kV and 140 kV. MOSFET detectors were used for organ dose measurements. First, an experimental validation of the dose equivalency between MOSFET and ion chamber (as a gold standard) was performed using a CTDI phantom. Second, the ED of DECT scans was measured using MOSFET detectors and an anthropomorphic phantom. For ED calculations, an abdomen/pelvis scan was used using ICRP 103 tissue weighting factors; ED was also computed using the AAPM Dose Length Product (DLP) method and compared to the MOSFET value.

Results:

The effective energy was determined as 42.9 kV under the combined beam from half‐value layer (HVL) measurement. ED for the dual‐energy scan was calculated as 16.49 ± 0.04 mSv by the MOSFET method and 14.62 mSv by the DLP method.

Conclusion:

Tissue dose in the center of the CTDI body phantom was 1.71 ± 0.01 cGy (ion chamber) and 1.71 ± 0.06 (MOSFET) respectively; this validated the use of effective energy method for organ dose estimation. ED from the abdomen‐pelvis scan was calculated as 16.49 ± 0.04 mSv by MOSFET and 14.62 mSv by the DLP method; this suggests that the DLP method provides a reasonable approximation to the ED.