bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐T‐623: Dosimetric and Radiobiological Comparison of Conventional and Monte Carlo Treatment Plans of Lung Tumors Using SBRT
Authors: Stathakis S , Mavroidis P , Tuazon B , Defoor D , Kirby N , Papanikolaou N
Published: July 2016

Purpose:

This study aims at estimating the dosimetric differences of Pinnacle and Monte Carlo (MC) calculation algorithms in computing the dose distributions in lung cancer SBRT cases. Furthermore, to interpret the dosimetric findings into expected tissue response rates in order to estimate their clinical impact.

Methods:

17 patients were studied and for each one, two treatment plans (one from Pinnacle and one MC) were created. The structures that were used for the optimization were: PTV, ipsilateral and contralateral lungs, spinal cord, heart, esophagus and stomach. The same dosimetric constraints were used for both pairs of plans. These dosimetric indices were used for the comparison of the two calculation modalities. Additionally, the TCP and NTCP values of the different targets and organs at risk (OAR) were calculated and compared together with the complicationfree tumor control probability.

Results:

The proposed plan evaluation shows that the plans by Pinnacle deliver higher doses to the OAR than MC. The same is observed for the PTV (minimum dose and BEUD: 58.3 vs. 55.1Gy, respectively). However, these dosimetric differences are translated to negligible differences in TCP and NTCP.

Conclusion:

The results of this work indicate that for the fractionation scheme of 18Gy in 3 fractions, the treatment plans in Pinnacle and Monte Carlo show minor differences in the doses to the organs at risk (in all the cases the doses by MC were lower than those calculated by Pinnacle). Those doses are predicted to cause 0.0% of side effects. On the other hand, the findings of the analysis indicate that Pinnacle calculation is shown to deliver higher dose to the PTV than MC. However, the dosimetric differences do not appear to have a measurable impact in the expected TCP rates of the targets.
SU‐F‐T‐624: Dose Sparing to Normal Brain Tissue for Stereotactic Radiosurgery Utilizing Negative Margins
Authors: Baker J , Gibb J , Ailawadi S , Hsia A , Han J , Kim J , Xu Z , Ryu S
Published: July 2016

Purpose:

The volume of normal brain tissue exposed to doses above 12 Gy (V12) strongly predicts the risk of radionecrosis. A negative margin MLC aperture results in fields smaller than the PTV. The aim of this study is to investigate the relationship between V12 and the negative margin MLC while keeping adequate PTV coverage with proper dose normalization.

Methods:

Spherical PTVs were contoured with a center of mass in the frontal and left temporal lobe ranging in size from 1 cm to 4 cm in diameter. A field arrangement was determined for each PTV location using five dynamic conformal arcs for the frontal PTV and three dynamic conformal arcs for the left temporal PTV. Treatment plans for each PTV were generated using a MLC aperture with a positive margin of 1 mm and dose normalized so that the prescribed 18 Gy covers 95% of the PTV. New plans were generated with MLC aperture margins reduced in 1 mm increments, until the max point dose reached is greater than 200%. The volume of dose outside the PTV to 12, 9 and 5 Gy was analyzed.

Results:

Depending on the PTV size, the greatest negative margin planned was between −4 mm and −2 mm. Negative margins of −1 mm yielded the lowest significant volumes to all doses. Reductions in V12 in relation to the PTV volumes were between 15% and 31% for PTV sizes of 4 and 1 cm, when compared to the 1 mm positive margin plan.

Conclusion:

Doses to normal tissue were reduced most with margins of −1 and −2 mm for all PTV sizes. In general the −2 mm margin was minimally superior, so a −1 mm margin can be followed in most circumstances to limit maximum PTV dose.
SU‐F‐T‐626: Intracranial SRS Re‐Treatment Without Acquisition of New CT Images
Authors: Wiant D , Manning M , Liu H , Maurer J , Hayes T , Sintay B
Published: July 2016

Purpose:

Linear accelerator based stereotactic radiosurgery (SRS) for multiple intracranial lesions with frequent surveillance is becoming a popular treatment option. This strategy leads to retreatment with SRS as new lesions arise. Currently, each course of treatment uses magnetic resonance (MR) and computed tomography (CT) images for treatment planning. We propose that new MR images, with course 1 CT images, may be used for future treatment plans with negligible loss of dosimetric accuracy.

Methods:

Ten patients that received multiple courses of SRS were retrospectively reviewed. The treatment plans and contours from non‐initial courses were copied to the initial CTs and recalculated. Doses metrics for the plans calculated on the initial CTs and later CTs were compared. All CT scans were acquired on a Philips CT scanner with a 600 mm field of view and 1 mm slice thickness (Philips Healthcare, Andover, MA). All targets were planned to 20 Gy and calculated in Eclipse V. 13.6 (Varian, Palo Alto, CA) using analytic anisotropic algorithm with 1 mm calculation grid.

Results:

Sixteen lesions were evaluated. The mean time between courses was 250 +/− 215 days (range 103–979). The mean target volume was 2.0 +/− 2.9 cc (range 0.1–10.1). The average difference in mean target dose between the two calculations was 0.2 +/− 0.3 Gy (range 0.0 – 1.0). The mean conformity index (CI) was 1.28 +/− 0.14 (range 1.07 – 1.82). The average difference in CI was 0.03 +/− 0.16 (range 0.00 – 0.44). Targets volumes < 0.5 cc showed the largest changes in both metrics.

Conclusion:

Continued treatment based on initial CT images is feasible. Dose calculation on the initial CT for future treatments provides reasonable dosimetric accuracy. Changes in dose metrics are largest for small volumes, and are likely dominated by partial volume effects in target definition.
SU‐F‐T‐631: Linear Accelerator‐Based Frameless Extracranial Radiosurgery for Treatment of Occipital Neuralgia for Non‐Surgical Candidates
Authors: Denton T , Howe J , Spalding A
Published: July 2016

Purpose:

Occipital neuralgia is a condition wherein pain is transmitted by the occipital nerves. Non‐invasive therapies generally alleviate symptoms; however, persistent or recurring pain may require invasive procedures. Repeated invasive procedures upon failure are considered higher risk and are often contraindicated due to compounding inherent risk. SRS has not been explored as a treatment option largely due to the extracranial nature of the target (as opposed to the similar, more established trigeminal neuralgia), but advances in linear‐accelerator frameless‐based SRS now present an opportunity to evaluate the novel potential of this modality for this application.

Methods:

Patient presented with severe occipital pain following decompression and fusion of the cervical vertebrae with prior intervention attempted via radiofrequency ablation yielding temporary pain cessation. A 0.6 mm slice spacing CT was obtained for treatment planning, and a cervical spine oriented 1.0 mm slice spacing CT myelogram was obtained for the purpose of defining the targeted C2 occipital dorsal root ganglion (to receive 80 Gy to the isocenter) and spinal cord.

Results:

The spinal cord was most proximally 12.0 mm from the isocenter receiving a maximum dose of 3.36 Gy, and doses to 0.35 and 1.2 cc of 1.84 Gy and 0.79 Gy, respectively. The brain maximum dose was 2.29 Gy. The treatment was successfully performed with a NovalisTX (Varian) equipped with ExacTrac stereoscopic x‐ray image guidance (BrainLAB). Treatment time was 59 minutes for 18,323 MUs. Imaging was performed prior to each arc delivery resulting in twenty‐one imaging sessions (twelve requiring positional corrections with the remaining verified within tolerance). The average deviation magnitude requiring a positional or rotational correction was 0.96±0.25 mm, 0.8±0.41° while the average deviation magnitude deemed within tolerance was 0.41±0.12 mm, 0.57±0.28°.

Conclusion:

Linear accelerator‐based frameless radiosurgery provides an accurate, non‐invasive alternative for treating occipital neuralgia where an invasive procedure is contraindicated.
SU‐F‐T‐633: Cyberknife Boost Versus Conventional Tandem and Ovoid Treatment for Cervical Cancer
Authors: Santoro J , Witten M , Haas J
Published: July 2016

Purpose:

Brachytherapy has been the standard of care for cervical cancer for 100 years. The treatment can be administered using an HDR (high dose rate) remote afterloader with a 192Ir source in an outpatient setting, a PDR afterloader with a 192Ir source, or with LDR manually loaded or a remote afterloader utilizing 192Ir or 137Cs sources in an inpatient setting. The procedure involves the placement of a tandem and ovoid, tandem and ring, or tandem and cylinder applicator in an operating room setting with the patient under general anesthesia. Inaccuracies introduced into the process occurring between placement of the applicator and actual delivery can introduce uncertainty into the actual dose delivered to the tumor and critical organs. In this study we seek to investigate the dosimetric difference between an SBRT‐based radiotherapy boost and conventional Brachytherapy in treating cervical cancer.

Methods:

Five HDR tandem and ovoid patients were planned using the Brachyvision treatment planning system and treated in four fractions using the Varian Varisource afterloader (Varian Medical Systems). For the same cohort, the patient planning CTs were imported into Multiplan (Accuray Inc) and a dose/fractionation‐equivalent CyberKnife SBRT plan was retrospectively generated. Dosimetric quantities such as target/CTV D90, V90, D2cc for rectum, bladder, and bowel were measured and compared between the two modalities.

Results:

The CTV D90 for the tandem and ovoid was 2540cGy (90.7%) and 3009cGy (107.5%) for the CyberKnife plan. The D2cc for the rectum, bladder, and bowel were 1576cGy, 1641cGy, and 996cGy for the tandem and ovoid and 1374cGy, 1564cGy, and 1547cGy for CyberKnife.

Conclusion:

The D2cc doses to critical structures are comparable in both modalities. The CTV coverage is far superior for the CyberKnife plan. The dose distribution for CyberKnife has the advantage of increased conformality and lower maximum CTV dose.
SU‐F‐T‐636: Comprehensive Approach to Motion Assessment for Liver and Pancreas SBRT Patients
Authors: Halvorsen P , Iftimia I , Hunter K
Published: July 2016

Purpose:

Our past practice for liver and pancreas SBRT consisted of free breathing (FB) with gated treatment delivery using a 30‐70% phase window. We have recently adopted an assessment method leading to individualized motion management to minimize target motion. We present our results from 47 patients treated with this new approach.

Methods:

We perform an initial patient coaching and assessment session in our conventional simulator suite to observe the motion of the implanted fiducials with FB anterior and lateral 20‐second cine acquisitions. The physician decides whether to attempt inhale or exhale breath‐hold (BH). The patient is coached while observing with cine to ascertain their ability to achieve the desired BH mode for long periods as needed for treatment delivery. If the patient cannot comply, a FB approach is adopted using gating or simple ITV method (for patients without fiducials). After achieving a patient‐specific motion management mode, we perform CT‐simulation using the Varian RPM system to reproduce the chosen mode and record a reference session for treatment delivery. For pre‐treatment imaging, the fiducials are observed under fluoro while coaching the patient.

Results:

Of 47 SBRT cases analyzed, 32 were liver and 15 were pancreas. The chosen techniques were: 32 exhale BH (12 with abdominal compression), 7 FB gated, 4 inhale BH, and 4 FB ITV. Maximum fiducial motion amplitude was 5 mm for the FB gated patients, and less than 5 mm for all BH patients with most able to achieve a maximum amplitude of 3 mm.

Conclusion:

This study showed that an individualized motion management approach can reduce the target volume and, therefore, the volume of irradiated healthy tissue from liver or pancreas SBRT. Effective coaching is essential in achieving consistent BH with 3 mm amplitude. The fluoro/cine session is helpful in establishing the right coaching approach for each patient.
SU‐F‐T‐642: Sub Millimeter Accurate Setup of More Than Three Vertebrae in Spinal SBRT with 6D Couch
Authors: Wang X , Zhao Z , Yang J , Yang J , McAleer M , Brown P , Li J , Ghia A
Published: July 2016

Purpose:

To assess the initial setup accuracy in treating more than 3 vertebral body levels in spinal SBRT using a 6D couch.

Methods:

We retrospectively analyzed last 20 spinal SBRT patients (4 cervical, 9 thoracic, 7 lumbar/sacrum) treated in our clinic. These patients in customized immobilization device were treated in 1 or 3 fractions. Initial setup used ExacTrac and Brainlab 6D couch to align target within 1 mm and 1 degree, following by a cone beam CT (CBCT) for verification. Our current standard practice allows treating a maximum of three continuous vertebrae. Here we assess the possibility to achieve sub millimeter setup accuracy for more than three vertebrae by examining the residual error in every slice of CBCT. The CBCT had a range of 17.5 cm, which covered 5 to 9 continuous vertebrae depending on the patient and target location. In the study, CBCT from the 1st fraction treatment was rigidly registered with the planning CT in Pinnacle. The residual setup error of a vertebra was determined by expanding the vertebra contour on the planning CT to be large enough to enclose the corresponding vertebra on CBCT. The margin of the expansion was considered as setup error.

Results:

Out of the 20 patients analyzed, initial setup accuracy can be achieved within 1 mm for a span of 5 or more vertebrae starting from T2 vertebra to inferior vertebra levels. 2 cervical and 2 upper thoracic patients showed the cervical spine was difficult to achieve sub millimeter accuracy for multi levels without a customized immobilization headrest.

Conclusion:

If the curvature of spinal columns can be reproduced in customized immobilization device during treatment as simulation, multiple continuous vertebrae can be setup within 1 mm with the use of a 6D couch.
SU‐F‐T‐644: Reproducibility of Target Position Using Moderate Voluntary Breath‐ Hold During Liver Stereotactic Ablative Radiotherapy
Authors: Cui G , Trakul N , Chang E , Shiu A
Published: July 2016

Purpose:

To evaluate the reproducibility of target position using moderate voluntary breath‐hold during liver stereotactic ablative radiotherapy (SABR).

Methods:

Two patients who underwent liver SABR on a Varian TrueBeam STx linac were used for this study. Fiducial markers were placed in and around the target in the liver as surrogates for the target position and motion. GTVs were contoured by assessing tumor extent on contrast enhanced CT. The PTV was created from the GTV by adding 2 mm margins to account for the residual motion during breath‐holds. A portable biofeedback system was used to facilitate the breath‐hold to a reproducible position. The Varian RPM system was used for gating the linac. Proceeding each treatment, orthogonal kV pairs were taken, and alignment to nearby bony anatomy was performed. Then the breath‐hold CBCT was acquired to align the fiducial markers. On‐line fluoroscopy was used to fine‐tune the breath‐hold gating thresholds to correlate with the positions of the fiducial markers. The inter‐fraction reproducibility of the target was evaluated by the offsets of the daily breath‐hold CBCTs from the paired kV matches as a direct measure of the target position relative to the bony anatomy. The intra‐fraction reproducibility of the target position was assessed by the gated window of the RPM marker block for each fraction.

Results:

The absolute mean offsets between the CBCT and paired kV matches in the vertical, longitudinal, and lateral directions were 0.06 cm, 0.10 cm, and 0.06 cm for patient 1, and 0.37 cm, 0.62 cm, and 0.09 cm for patient 2. The gated window of the RPM marker block for the breath‐hold for each fraction was within 0.63 ± 0.16 cm and 0.59 ± 0.12 cm for patients 1 and 2, respectively.

Conclusion:

Moderate voluntary breath‐hold showed good inter‐ and intra‐fraction reproducibility of target position during liver SABR.
SU‐F‐T‐645: To Test Spatial Anddosimetric Accuracy of Small Cranial Target Irradiation Based On 1.5 T MRIscans Using Static Arcs with MLCDefined Fields
Authors: Brezovich I , Wu X , Popple R , Shen S , Cardan R , Bolding M , Fiveash J , Kraus J , Spencer S
Published: July 2016

Purpose:

To test spatial and dosimetric accuracy of small cranial target irradiation based on 1.5 T MRI scans using static arcs with MLC‐defined fields

Methods:

A plastic (PMMA) phantom simulating a small brain lesion was mounted on a GammaKnife headframe equipped with MRI localizer. The lesion was a 3 mm long, 3.175 mm diameter cylindrical cavity filled with MRI contrast. Radiochromic film passing through the cavity was marked with pin pricks at the cavity center. The cavity was contoured on an MRI image and fused with CT to simulate treatment of a lesion not visible on CT. The transfer of the target to CT involved registering the MRI contrast cannels of the localizer that were visible on both modalities. Treatments were planned to deliver 800 cGy to the cavity center using multiple static arcs with 5.0×2.4 mm MLC‐defined fields. The phantom was aligned on a STx accelerator by registering the conebeam CT with the planning CT. Films from coronal and sagittal planes were scanned and evaluated using ImageJ software

Results:

Geographic errors in treatment based on 1.5 T scans agreed within 0.33, −0.27 and 1.21 mm in the vertical, lateral and longitudinal dimensions, respectively. The doses delivered to the cavity center were 7.2% higher than planned. The dose distributions were similar to those of a GammaKnife.

Conclusion:

Radiation can be delivered with an accelerator at mm accuracy to small cranial targets based on 1.5 MRI scans fused to CTs using a standard GammaKnife headframe and MRI localizer. MLC‐defined static arcs produce isodose lines very similar to the GammaKnife.
SU‐F‐T‐651: Dosimetric Impact of Patient Setup Rotational Errors for Multi‐Staged Large AVM Gammaknife Radiosurgery
Authors: Ding C , Hrycushko B , Abdulrahman R , Whitworth L , Jiang S , Timmerman R
Published: July 2016

Purpose:

Multi‐staged large AVM (>10 cm3 or diameter > 3 cm) Gammaknife radiosurgery requires setting up the patient based on a pre‐treatment plan over several fractions. Residual rotational errors cannot be compensated by translational repositioning of the patient and may adversely impact the dose distribution on the total AVM target. This study evaluates the effect of residual rotational setup error.

Methods:

The total AVM target was contoured and split into several small sub‐targets. A Gammaknife plan was completed for the whole AVM target to meet the prescription goals. Shots were split and grouped according to the location of each sub‐target to be delivered in separate staged sup‐plans. Rotational errors of ±1‐5° about the three rotational axes along with 5mm random translational errors were used to simulate head frame setup errors on different treatment days. Software was developed to compensate for translational errors to bring the shots back to the position of the original plan. Dose distributions were compared between the original planned dose and that resulting from residual rotational errors.

Results:

The volume of the target having dose differences within 3% is decreased with larger residual rotational errors (98.28%, 84.22% and 68.08% for ±1°, ±3°, and ±5° rotation, respectively). The volume of the target with dose differences within 5% (99.89%, 94.86% and 83.01% for ±1°, ±3°, and ±5° rotation, respectively) indicate that rotation less than ±3° is acceptable for treatment.

Conclusion:

Dosimetric errors increase as rotational errors increase. The dosimetric impact was shown acceptable when rotational errors are less than 3°.
SU‐F‐T‐662: Feasibility Study of Fe3O4/TaOx Nano Particles as a Radiosensitizer for Radiation Therapy
Authors: Ahn S , Lee N , Shin S , Choi C , Han Y , Park H , Choi D , Lim D
Published: July 2016

Purpose:

To investigate the feasibility of using multifunctional Fe3O4/TaOx(core / shell) nano particles developed for CT and MRI contrast agent as dose enhancing radiosensitizers.

Methods:

Firstly, to verify the imaging detectability of Fe3O4/TaOx nano particles, in‐vivo tests were conducted. Approximately 600 mg/kg of 19 nm diameter Fe3O4/TaOx nano particles dispersed in phosphate buffered saline(PBS) were injected to ten nude Balb/c mice through the tail vein. Difference between pre‐ and post‐injection images was analyzed by computing the pixel histogram and correlation coefficient factor using MATLAB in the user defined ROI. Secondly, to quantify the potential therapeutic enhancement with nano materials, DER (Dose Enhancement Ratio) and number of SER (Secondary Electron Ratio) were computed using TOPAS(ver.2.0 P‐03) MC simulation.

Results:

In CT, MRI imaging, the aorta, the blood vessel, and the liver were clearly visualized after intravenous injection of Fe3O4/TaOx nano particles. There was large different between pre and post‐injection images of Histogram data and Coefficients of correlation factor in CT and MR are 0.006, 0.060, respectively. When 70 MeV protons were irradiated for a Gold, Tantalum, TaOx, Fe3O4/TaOx, Fe3O4 nano particle, DER was 2.59, 2.41, 1.68, 1.54 and 1.36 respectively. Similarly, SER increment was 2.31, 2.15, 1.56, 1.46, and 1.27 for Gold, Tantalum, TaOx, Fe3O4/TaOx, Fe3O4 nano particle, respectively.

Conclusion:

Fe3O4/TaOx nano particles have potential as a multifunctional agent which enhances the accuracy in cancer detection through visualization of developed tumor lesion and increases the therapeutic effect in proton therapy. The dose enhancement with Fe3O4/TaOx was estimated as half of the Gold. However, tumor targeting such as combined with magnetic field may overcome the low DER.

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‐665: Confocal Microscopy Imaging of Cell Cycle Distribution in Cells Treated with Pegylated Gold Nanoshells
Authors: Sadetaporn D , Flint D , McFadden C , Asaithamby A , Sawakuchi G
Published: July 2016

Purpose:

To use confocal microscopy to distinguish cells in different phases of the cell cycle before and after treatment with pegylated gold nanoshells (PEG‐AuNSs).

Methods:

Transfected fibrosarcoma cells (HT1080‐EYFP‐53BP1‐FUCCI) were cultured in T‐25 flasks and seeded in glass bottom dishes. These cells express the fluorescent probe AmCyan during the G2/S phases of the cell cycle, mCherry during the G1 phase, and EYFP tagged to the DNA repair protein 53BP1. After allowing cells 4 h to adhere to dishes, PEG‐AuNS (Nanospectra Biosciences, Houston, TX) at a concentration of 0.15 OD were administered. At time points of 8, 16 and 24 h following treatment, the PEG‐AuNS‐treated and control samples were washed with phosphate buffered saline (PBS) and fixed using 4% paraformaldehyde in PBS. Samples were imaged with an Olympus FV1200 confocal microscope using 473, 543, and 641 nm excitation lasers. We used band‐pass filters to select AmCyan and mCherry fluorescence. Reflection from the 641 nm laser was used to detect PEG‐AuNSs. Z‐stack images were analyzed to assess cell cycle distribution through fluorescent probe expression. Live cells were imaged after PEG‐AuNS treatment using a confocal microscope with a stage top CO2 incubator.

Results:

We were able to obtain high‐resolution images of cells with internalized AuNSs. We were also able to distinguish cells in different phases of the cell cycle.

Conclusion:

This work demonstrates a new assay to investigate the effect of AuNSs on the cell cycle phase in live cells. Future work will employ confocal microscopy and flow cytometry to focus on effects of AuNS treatment on cell cycle distribution.

This research was supported by the Sister Institution Network Fund and the Center for Radiation Oncology Research at The University of Texas MD Anderson Cancer Center and Cancer Prevention and Research Institute of Texas. Gabriel Sawakuchi has research support from Elekta Inc.
SU‐F‐T‐669: Commissioning of An Electronic Brachytherapy System for Targeted Mouse Irradiation
Authors: Culberson W , Carchman E , Micka J
Published: July 2016

Purpose:

The aim of this study was to commission the Xoft Axxent™ electronic brachytherapy (eBT) source and 10 mm diameter surface applicator with NIST traceability for targeted irradiations of mouse anal carcinomas.

Methods:

The Xoft Axxent™ electronic brachytherapy (eBT) and 10 mm diameter surface applicator was chosen by the collaborating physician as a radiation delivery mechanism for mouse anal carcinomas. The target dose was 2 Gy at a depth of 3 mm in tissue to be delivered in a single fraction. To implement an accurate and reliable irradiation plan, the system was commissioned by first determining the eBT source output and corresponding dose rate at a depth of 3 mm in tissue. This was determined through parallel‐plate ion chamber measurements and published conversion factors. Well‐type ionization chamber measurements were used to determine a transfer coefficient, which correlates the measured dose rate at 3 mm to the NIST‐traceable quantity, air‐kerma rate at 50 cm in air, for eBT sources. By correlating these two quantities, daily monitoring in the well chamber becomes an accurate and efficient quality assurance technique. Once the dose‐rate was determined, a treatment recipe was developed and confirmed with chamber measurements to deliver the requested dose. Radiochromic film was used to verify the dose distribution across the field.

Results:

Dose rates at 3 mm depth in tissue were determined for two different Xoft Axxent™ sources and correlated with NIST‐traceable well‐type ionization chamber measurements. Unique transfer coefficients were determined for each source and the treatment recipe was validated by measurements. Film profiles showed a uniform dose distribution across the field.

Conclusion:

A Xoft Axxent™ eBT system was successfully commissioned for use in the irradiation of mouse rectal tumors. Dose rates in tissue were determined as well as other pertinent parameters to ensure accurate delivery of dose to the target region.
SU‐F‐T‐677: Synergistic Effect(s) of Clotrimazole On Radiation Cell Survival of A549 Lung Cancer Cells in Glucose Vs. Galactose Media
Authors: Boss G , Tambasco M , Garakani M
Published: July 2016

Purpose:

In order to determine the synergistic effect of clotrimazole on radiosensitivity of A549 lung cancer cells, and the effect of oxidative pathways on modulating radiosensitivity, we studied how these cells survived under varying amounts of radiation and clotrimazole as well ass when glucose was switched for galactose media.

Methods:

The glucose media was used to determine the presence of any synergistic effect of clotrimazole on radiation using values of radiation and clotrimazole concentrations, varying from 0 – 8 Gy and 0 – 20 µM, respectively. As a galactose diet is known to activate oxidative pathways, which do not rely on hexokinase II (HK2), all trials were repeated using galactose media to determine the extent that HK2 unbinding from the mitochondrial membrane plays a role in modulating the observed radiosensitivity. An apoptosis vs. necrosis assay was implemented to find out the modality by which cell death occurred. An intracellular lactate assay was performed to exhibit the extent of anaerobic glycolysis.

Results:

After running the primary experiments, it was found that in glucose media, the cancer cells showed higher cell kill when clotrimazole was added to the media, followed by the cells being irradiated.

Conclusion:

Given the preliminary results it is validated that under higher concentrations of clotrimazole, in glucose media, A549 lung cancer cells exhibit a lower amount of survival. While all results have not yet been gathered. We anticipate that in galactose media the A549 cells will exhibit this effect to a much smaller degree, if at all.
SU‐F‐T‐679: Monte Carlo Simulation On Surface Dose in Preclinical Irradiation Using Monoenergetic Photon Beams
Authors: Vuong A , Chow J
Published: July 2016

Purpose:

This study investigated the surface dose variation in preclinical irradiation using small animal, when monoenergetic photon beams with energy range from 50 keV to 1.25 MeV were used.

Methods:

Inhomogeneous, homogeneous and bone‐tissue homogeneous mouse phantom based on the same CT image set were used. The homogeneous and bone‐tissue homogeneous phantom were created with the relative electron density of all and only bone voxels of the mouse overridden to one, respectively. Monte Carlo simulation based on the EGSnrc‐based code was used to calculate the surface dose, when the phantoms were irradiated by a 360° photon arc with energies ranging from 50 keV to 1.25 MeV. The mean surface doses of the three phantoms were calculated. In addition, the surface doses from partial arcs, 45°–315°, 125°–225°, 45°–125° and 225°–315° covering the anterior, posterior, right lateral and left lateral region of the mouse were determined using different photon beam energies.

Results:

When the prescribed dose at the isocenter of the mouse was 2 Gy, the maximum mean surface doses, found at the 50‐keV photon beams, were 0.358 Gy, 0.363 Gy and 0.350 Gy for the inhomogeneous, homogeneous and bone‐tissue homogeneous mouse phantom, respectively. The mean surface dose of the mouse was found decreasing with an increase of the photon beam energy. For surface dose in different orientations, the lateral regions of the mouse were receiving lower dose than the anterior and posterior regions. This may be due to the increase of beam attenuation along the horizontal (left‐right) axis than the vertical (anterior‐posterior) in the mouse.

Conclusion:

It is concluded that consideration of phantom inhomogeneity in the dose calculation resulted in a lower mean surface dose of the mouse. The mean surface dose also decreased with an increase of photon beam energy in the kilovoltage range.
SU‐G‐BRA‐02: Development of a Learning Based Block Matching Algorithm for Ultrasound Tracking in Radiotherapy
Authors: Shepard A , Bednarz B
Published: July 2016

Purpose:

To develop an ultrasound learning‐based tracking algorithm with the potential to provide real‐time motion traces of anatomy‐based fiducials that may aid in the effective delivery of external beam radiation.

Methods:

The algorithm was developed in Matlab R2015a and consists of two main stages: reference frame selection, and localized block matching. Immediately following frame acquisition, a normalized cross‐correlation (NCC) similarity metric is used to determine a reference frame most similar to the current frame from a series of training set images that were acquired during a pretreatment scan. Segmented features in the reference frame provide the basis for the localized block matching to determine the feature locations in the current frame. The boundary points of the reference frame segmentation are used as the initial locations for the block matching and NCC is used to find the most similar block in the current frame. The best matched block locations in the current frame comprise the updated feature boundary. The algorithm was tested using five features from two sets of ultrasound patient data obtained from MICCAI 2014 CLUST. Due to the lack of a training set associated with the image sequences, the first 200 frames of the image sets were considered a valid training set for preliminary testing, and tracking was performed over the remaining frames.

Results:

Tracking of the five vessel features resulted in an average tracking error of 1.21 mm relative to predefined annotations. The average analysis rate was 15.7 FPS with analysis for one of the two patients reaching real‐time speeds. Computations were performed on an i5‐3230M at 2.60 GHz.

Conclusion:

Preliminary tests show tracking errors comparable with similar algorithms at close to real‐time speeds. Extension of the work onto a GPU platform has the potential to achieve real‐time performance, making tracking for therapy applications a feasible option.

This work is partially funded by NIH grant R01CA190298
SU‐G‐BRA‐07: An Innovative Fiducial‐Less Tracking Method for Radiation Treatment of Abdominal Tumors by Diaphragm Disparity Analysis
Authors: Dick D , Wu X , Zhao W
Published: July 2016

Purpose:

To investigate the feasibility of tracking abdominal tumors without the use of gold fiducial markers

Methods:

In this simulation study, an abdominal 4DCT dataset, acquired previously and containing 8 phases of the breathing cycle, was used as the testing data. Two sets of DRR images (45 and 135 degrees) were generated for each phase. Three anatomical points along the lung‐diaphragm interface on each of the Digital Reconstructed Radiograph(DRR) images were identified by cross‐correlation. The gallbladder, which simulates the tumor, was contoured for each phase of the breathing cycle and the corresponding centroid values serve as the measured center of the tumor. A linear model was created to correlate the diaphragm's disparity of the three identified anatomical points with the center of the tumor. To verify the established linear model, we sequentially removed one phase of the data (i.e., 3 anatomical points and the corresponding tumor center) and created new linear models with the remaining 7 phases. Then we substituted the eliminated phase data (disparities of the 3 anatomical points) into the corresponding model to compare model‐generated tumor center and the measured tumor center.

Results:

The maximum difference between the modeled and the measured centroid values across the 8 phases were 0.72, 0.29 and 0.30 pixels in the x, y and z directions respectively, which yielded a maximum mean‐squared‐error value of 0.75 pixels. The outcomes of the verification process, by eliminating each phase, produced mean‐squared‐errors ranging from 0.41 to 1.28 pixels.

Conclusion:

Gold fiducial markers, requiring surgical procedures to be implanted, are conventionally used in radiation therapy. The present work shows the feasibility of a fiducial‐less tracking method for localizing abdominal tumors. Through developed diaphragm disparity analysis, the established linear model was verified with clinically accepted errors. The tracking method in real time under different radiation therapy platforms will be further investigated.
SU‐G‐BRA‐08: Diaphragm Motion Tracking Based On KV CBCT Projections with a Constrained Linear Regression Optimization
Authors: Wei J , Chao M
Published: July 2016

Purpose:

To develop a novel strategy to extract the respiratory motion of the thoracic diaphragm from kilovoltage cone beam computed tomography (CBCT) projections by a constrained linear regression optimization technique.

Methods:

A parabolic function was identified as the geometric model and was employed to fit the shape of the diaphragm on the CBCT projections. The search was initialized by five manually placed seeds on a pre‐selected projection image. Temporal redundancies, the enabling phenomenology in video compression and encoding techniques, inherent in the dynamic properties of the diaphragm motion together with the geometrical shape of the diaphragm boundary and the associated algebraic constraint that significantly reduced the searching space of viable parabolic parameters was integrated, which can be effectively optimized by a constrained linear regression approach on the subsequent projections. The innovative algebraic constraints stipulating the kinetic range of the motion and the spatial constraint preventing any unphysical deviations was able to obtain the optimal contour of the diaphragm with minimal initialization. The algorithm was assessed by a fluoroscopic movie acquired at anteriorposterior fixed direction and kilovoltage CBCT projection image sets from four lung and two liver patients. The automatic tracing by the proposed algorithm and manual tracking by a human operator were compared in both space and frequency domains.

Results:

The error between the estimated and manual detections for the fluoroscopic movie was 0.54mm with standard deviation (SD) of 0.45mm, while the average error for the CBCT projections was 0.79mm with SD of 0.64mm for all enrolled patients. The submillimeter accuracy outcome exhibits the promise of the proposed constrained linear regression approach to track the diaphragm motion on rotational projection images.

Conclusion:

The new algorithm will provide a potential solution to rendering diaphragm motion and ultimately improving tumor motion management for radiation therapy of cancer patients.
SU‐G‐BRA‐14: Dose in a Rigidly Moving Phantom with Jaw and MLC Compensation
Authors: Chao E , Lucas D
Published: July 2016

Purpose:

To validate dose calculation for a rigidly moving object with jaw motion and MLC shifts to compensate for the motion in a TomoTherapy™ treatment delivery.

Methods:

An off‐line version of the TomoTherapy dose calculator was extended to perform dose calculations for rigidly moving objects. A variety of motion traces were added to treatment delivery plans, along with corresponding jaw compensation and MLC shift compensation profiles. Jaw compensation profiles were calculated by shifting the jaws such that the center of the treatment beam moved by an amount equal to the motion in the longitudinal direction. Similarly, MLC compensation profiles were calculated by shifting the MLC leaves by an amount that most closely matched the motion in the transverse direction. The same jaw and MLC compensation profiles were used during simulated treatment deliveries on a TomoTherapy system, and film measurements were obtained in a rigidly moving phantom.

Results:

The off‐line TomoTherapy dose calculator accurately predicted dose profiles for a rigidly moving phantom along with jaw motion and MLC shifts to compensate for the motion. Calculations matched film measurements to within 2%/1 mm. Jaw and MLC compensation substantially reduced the discrepancy between the delivered dose distribution and the calculated dose with no motion. For axial motion, the compensated dose matched the no‐motion dose within 2%/1mm. For transverse motion, the dose matched within 2%/3mm (approximately half the width of an MLC leaf).

Conclusion:

The off‐line TomoTherapy dose calculator accurately computes dose delivered to a rigidly moving object, and accurately models the impact of moving the jaws and shifting the MLC leaf patterns to compensate for the motion. Jaw tracking and MLC leaf shifting can effectively compensate for the dosimetric impact of motion during a TomoTherapy treatment delivery.
SU‐G‐BRA‐15: Dosimetric Evaluation of Dynamic Tumor Tracking Radiation Therapy Using Digital Phantom: A Study On Margin and Desired Accuracy of Tracking
Authors: Uchida T , Kadoya N , Ichiji K , Nakajima Y , Jingu K , Osanai M , Takeda K , Takai Y , Homma N
Published: July 2016

Purpose:

Dynamic tumor tracking radiation therapy can potentially reduce internal margin without prolongation of irradiation time. However, dynamic tumor tracking technique requires an extra margin (tracking margin, TM) for the uncertainty of tumor localization, prediction, and beam repositioning. The purpose of this study was to evaluate a dosimetric impact caused by TM.

Methods:

We used 4D XCAT to create 9 digital phantom datasets of different tumor size and motion range: tumor diameter TD={1, 3, 5} cm and motion range MR={1, 2, 3} cm. For each dataset, respiratory gating (30%–70% phase) and tumor tracking treatment plans were created using 8‐field 3D‐CRT by 4D dose calculation implemented in RayStation. The dose constraint was based on RTOG0618. For the tracking plan, TMs of {0, 2.5, 5} mm were considered by surrounding a normal setup margin: SM=5 mm. We calculated V20 of normal lung to evaluate the dosimetric impact for each case, and estimated an equivalent TM that affects the same impact on V20 obtained by the gated plan.

Results:

The equivalent TMs for {TD=1 cm, MR=2 cm}, {TD=1 cm, MR=3 cm}, {TD=5 cm, MR=2 cm}, and {TD=5 cm, MR=3 cm} were estimated as 1.47 mm, 3.95 mm, 1.04 mm, and 2.13 mm, respectively. The larger the tumor size, the equivalent TM became smaller. On the other hand, the larger the motion range, the equivalent TM was found to be increased.

Conclusion:

Our results showed the equivalent TM changes depending on tumor size and motion range. The tracking plan with TM less than the equivalent TM achieves a dosimetric impact better than the gated plan in less treatment time.

This study was partially supported by JSPS Kakenhi and Varian Medical Systems.
SU‐G‐BRA‐17: Tracking Multiple Targets with Independent Motion in Real‐Time Using a Multi‐Leaf Collimator
Authors: Ge Y , Keall P , Poulsen P
Published: July 2016

Purpose:

Multiple targets with large intrafraction independent motion are often involved in advanced prostate, lung, abdominal, and head and neck cancer radiotherapy. Current standard of care treats these with the originally planned fields, jeopardizing the treatment outcomes. A real‐time multi‐leaf collimator (MLC) tracking method has been developed to address this problem for the first time. This study evaluates the geometric uncertainty of the multi‐target tracking method.

Methods:

Four treatment scenarios are simulated based on a prostate IMAT plan to treat a moving prostate target and static pelvic node target: 1) real‐time multi‐target MLC tracking; 2) real‐time prostate‐only MLC tracking; 3) correcting for prostate interfraction motion at setup only; and 4) no motion correction. The geometric uncertainty of the treatment is assessed by the sum of the erroneously underexposed target area and overexposed healthy tissue areas for each individual target. Two patient‐measured prostate trajectories of average 2 and 5 mm motion magnitude are used for simulations.

Results:

Real‐time multi‐target tracking accumulates the least uncertainty overall. As expected, it covers the static nodes similarly well as no motion correction treatment and covers the moving prostate similarly well as the real‐time prostate‐only tracking. Multi‐target tracking reduces >90% of uncertainty for the static nodal target compared to the real‐time prostate‐only tracking or interfraction motion correction. For prostate target, depending on the motion trajectory which affects the uncertainty due to leaf‐fitting, multi‐target tracking may or may not perform better than correcting for interfraction prostate motion by shifting patient at setup, but it reduces ∼50% of uncertainty compared to no motion correction.

Conclusion:

The developed real‐time multi‐target MLC tracking can adapt for the independently moving targets better than other available treatment adaptations. This will enable PTV margin reduction to minimize health tissue toxicity while remain tumor coverage when treating advanced disease with independently moving targets involved.

The authors acknowledge funding support from the Australian NHMRC Australia Fellowship and NHMRC Project Grant No. APP1042375.
SU‐G‐206‐05: A Comparison of Head Phantoms Used for Dose Determination in Imaging Procedures
Authors: Xiong Z , Vijayan S , Kilian‐Meneghin J , Rudin S , Bednarek D
Published: July 2016

Purpose:

To determine similarities and differences between various head phantoms that might be used for dose measurements in diagnostic imaging procedures.

Methods:

We chose four frequently used anthropomorphic head phantoms (SK‐150, PBU‐50, RS‐240T and Alderson Rando), a computational patient phantom (Zubal) and the CTDI head phantom for comparison in our study. We did a CT scan of the head phantoms using the same protocol and compared their dimensions and CT numbers. The scan data was used to calculate dose values for each of the phantoms using EGSnrc Monte Carlo software. An .egsphant file was constructed to describe these phantoms using a Visual C++ program for DOSXYZnrc/EGSnrc simulation. The lens dose was calculated for a simulated CBCT scan using DOSXYZnrc/EGSnrc and the calculated doses were validated with measurements using Gafchromic film and an ionization chamber. Similar calculations and measurements were made for PA radiography to investigate the attenuation and backscatter differences between these phantoms. We used the Zubal phantom as the standard for comparison since it was developed based on a CT scan of a patient.

Results:

The lens dose for the Alderson Rando phantom is around 9% different than the Zubal phantom, while the lens dose for the PBU‐50 phantom was about 50% higher, possibly because its skull thickness and the density of bone and soft tissue are lower than anthropometric values. The lens dose for the CTDI phantom is about 500% higher because of its totally different structure. The entrance dose profiles are similar for the five anthropomorphic phantoms, while that for the CTDI phantom was distinctly different.

Conclusion:

The CTDI and PBU‐50 head phantoms have substantially larger lens dose estimates in CBCT. The other four head phantoms have similar entrance dose with backscatter hence should be preferred for dose measurement in imaging procedures of the head.

Partial support from NIH Grant R01‐EB002873 and Toshiba Medical Systems Corp.
SU‐G‐206‐11: The Effect of Table Height On CTDIvol and SSDE in CT Scanning: A Phantom Study
Authors: Marsh R , Silosky M
Published: July 2016

Purpose:

Localizer projection radiographs acquired prior to CT scans are used to estimate patient size, affecting the function of Automatic Tube Current Modulation (ATCM) and calculation of the Size Specific Dose Estimate (SSDE). Due to geometric effects, the projected patient size varies with scanner table height and with the orientation of the localizer (AP versus PA). Consequently, variations in scanner table height may affect both CTDIvol and the calculated size‐corrected dose index (SSDE). This study sought to characterize these effects.

Methods:

An anthropomorphic phantom was imaged using an AP localizer, followed by a diagnostic scan using ATCM and our institution's routine abdomen protocol. This was repeated at various scanner table heights, recording the scanner‐reported CTDIvol for each diagnostic scan. The width of the phantom was measured from the localizer and diagnostic images using in‐house software. The measured phantom width and scanner‐reported CTDIvol were used to calculate SSDE. This was repeated using PA localizers followed by diagnostic scans.

Results:

1) The localizer‐based phantom width varied by up to 54% of the nominal phantom width between minimum and maximum table heights. 2) Changing the table height caused a variation in scanner‐reported CTDIvol of a factor greater than 4.6 when using a PA localizer and almost 2 when using an AP localizer. 3) SSDE, calculated from measured phantom size and scanner‐reported CTDIvol, varied by a factor of more than 2.8 when using a PA localizer and almost 1.5 when using an AP localizer.

Conclusion:

Our study demonstrates that off‐center patient positioning affects the efficacy of ATCM, more severely when localizers are acquired in the PA rather than AP projection. Further, patient positioning errors can cause a large variation in the calculated SSDE. This hinders interpretation of SSDE for individual patients and aggregate SSDE data when evaluating CT protocols and clinical practices.