bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐538: CyberKnife with MLC for Treatment of Large Volume Tumors: A Feasibility Study
Authors: Bichay T , Mayville A 
Published: July 2016

Purpose:CyberKnife is a well‐documented modality for SRS and SBRT treatments. Typical tumors are small and 1–5 fractions are usually used. We determined the feasibility of using CyberKnife, with an InCise multileaf collimator option, for larger tumors undergoing standard dose and fractionation. The intent was to understand the limitation of using this modality for other external beam radiation treatments.Methods:Five tumors from different anatomical sites with volumes from 127.8 cc to 1,320.5 cc were contoured and planned on a Multiplan V5.1 workstation. The target average diameter ranged from 7 cm to 13 cm. The dose fractionation was 1.8–2.0 Gy/fraction and 25–45 fractions for total doses of 45–81 Gy. The sites planned were: pancreas, head and neck, prostate, anal, and esophagus. The plans were optimized to meet conventional dose constraints based on various RTOG protocols for conventional fractionation.Results:The Multiplan treatment planning system successfully generated clinically acceptable plans for all sites studied. The resulting dose distributions achieved reasonable target coverage, all greater than 95%, and satisfactory normal tissue sparing. Treatment times ranged from 9 minutes to 38 minutes, the longest being a head and neck plan with dual targets receiving different doses and with multiple adjacent critical structures.Conclusion:CyberKnife, with the InCise multileaf collimation option, can achieve acceptable dose distributions in large volume tumors treated with conventional dose and fractionation. Although treatment times are greater than conventional accelerator time; target coverage and dose to critical structures can be kept within a clinically acceptable range. While time limitations exist, when necessary CyberKnife can provide an alternative to traditional treatment modalities for large volume tumors.
SU‐F‐T‐539: Dosimetric Comparison of Volumetric Modulated Arc Therapy and Intensity Modulated Radiation Therapy for Whole Brain Hippocampal Sparing Radiation Therapy Treatments
Authors: Kendall E , Higby C , Algan O , Ahmad S , Hossain S 
Published: July 2016

Purpose:To compare the treatment plan quality and dose gradient near the hippocampus between VMAT (RapidArc) and IMRT delivery techniques for whole brain radiation therapy.Methods:Fifteen patients were evaluated in this retrospective study. All treatments were planned on Varian Eclipse TPS, using 3‐Arc VMAT and 9‐Field IMRT, following NRG Oncology protocol NRG‐CC001 guidelines evaluated by a single radiation oncologist. Prescribed doses in all plans were 30 Gy delivered over 10 fractions normalized to a minimum of 100% of the dose covering 95% of the target volume. Identical contour sets and dose‐volume constraints following protocol guidelines were also applied in all plans. A paired t‐test analysis was used to compare VMAT and IMRT plans.Results:NRG‐CC001 protocol dose‐volume constraints were met for all VMAT and IMRT plans. For the planning target volume (PTV), the average values for D2% and D98% were 6% lower and 4% higher in VMAT than in IMRT, respectively. The average mean and maximum hippocampus doses in Gy for VMAT vs IMRT plans were (11.85±0.81 vs. 12.24±0.56, p=0.10) and (16.27±0.78 vs. 16.59±0.71, p=0.24), respectively. In VMAT, the average mean and maximum chiasm doses were 3% and 1% higher than in IMRT plans, respectively. For the left optic nerve, the average mean and maximum doses were 10% and 5% higher in VMAT than in IMRT plans, respectively. These values were 12% and 3% for the right optic nerve. The average percentage of dose gradient around the hippocampus in the 0–5mm and 5–10mm abutted regions for VMAT vs. IMRT were (4.42%±2.22% /mm vs. 3.95%±2.61% /mm, p=0.43) and (4.54%±1.50% /mm vs. 4.39%±1.28% /mm, p=0.73), respectively.Conclusion:VMAT plans can achieve higher hippocampus sparing with a faster dose fall‐off than IMRT plans. Though statistically insignificant, VMAT offers better PTV coverage with slightly higher doses to OARs.
SU‐F‐T‐541: Impact of VMAT Dose Calculations with Respiratory Movements in Lung
Authors: Komatsu K , Araki F , Ohno T , Shimohigashi Y , Onizuka R 
Published: July 2016

Purpose:To evaluate dose impact due to respiratory movements for volumetric modulated arc therapy (VMAT) in lung, using deformation technique.Methods:The dose impact due to respiratory movements was evaluated for VMAT in lung. VMAT dose distributions were calculated with 4D‐CT images for a 3‐D dynamic lung phantom and seven patients. First, one‐arc VMAT dose distributions were calculated at the reference phase (the maximum of expiratory phase) using the Varian Eclipse (ver.10) treatment planning system. All VMAT were planned with 48Gy for 4 fractions. The VMAT dose distributions were divided into 88 control points (CPs) and were assigned to each one of ten phases divided through one respiratory cycle time. Next, the dose distributions were recalculated at each phase and were deformed at the reference phase using DIRART ver.1.0a and Velocity AI ver.3.1 software. The deformed dose distributions were summed up. Finally, VMAT dose distributions with respiratory movements were evaluated from dose volume histograms (DVHs).Results:VMAT dose distributions deformed by DIRART and the Velocity AI in the phantom study agreed within 2% with that of the reference phase for 95% of GTV (D95). In the patient study, deformed VMAT dose distributions decreased up to 4.15% and 3.46% for DIRART and Velocity AI, respectively. The maximum dose of GTV (Dmax) tended to be higher with increasing tumor movements. In constant, D95 for DVHs decreased with increasing tumor movements. The discrepancy in the VMAT dose distributions deformed by two software depended on specific properties of respective algorithms and parameters.Conclusion:Respiratory movements impact on the dose distributions for GTV. The Dmax may relate with amplitude of tumor movements.
SU‐F‐T‐542: Using Calypso Electromagnetic Beacons to Determine When to Modulate and When Not to Modulate SBRT Treatment Plans When Breathing Motion Is Present
Authors: Saleh H , Howlin T , Pokhrel D 
Published: July 2016

Purpose:To use the Calypso system to conduct a comprehensive study to determine what is the maximum breathing amplitude and length of breathing cycle allowed to accurately deliver IMRT or VMAT plans for liver tumors treated with SBRT when breathing motion is present.Methods:A phantom that simulates breathing motion was constructed using solid water. The phantom contains a 5 cm diameter insert of low density material to simulate a tumor, 3 calypso beacons to track breathing motion and a micro ion chamber for point dose measurements. Radiochromic films were used to measure spatial dose distribution. Gamma 3%, 3 mm metrics were used for plan evaluation. With phantom placed on a respiratory gating platform, 4DCT data sets were acquired for breathing amplitudes of 5, 10, 15, 20, 25, 30, and 40 mm respectively. Breathing cycles of 2, 4, and 6‐seconds‐long were used for each case. Minimum intensity projection (MINIP) datasets were generated for each case. Eclipse treatment planning system was used to generate IMRT and VMAT plans. Calypso system was used to gate all treatment deliveries.Results:Point dose measurement did not show significant difference for different breathing amplitude. This is because the ion chamber is placed at isocenter, and film analysis revealed most dose variations occur on the edges of the tumor. Gamma analysis shows significant reduction in passing rate for plans with motion due to MLC interplay effect and dose blurring. With 15 mm breathing amplitude, gamma passing rate dropped by 10% and 25% for IMRT and VMAT respectively.Conclusion:With a breathing motion management, it is safe to modulate SBRT plans when breathing amplitude is less than 10 mm and 15 mm for IMRT and VMAT respectively. Longer breathing cycles lead to less accurate dose delivery. More analysis is being performed for breathing amplitudes greater than 15 mm.
SU‐F‐T‐543: The Impact of Density Overrides in IMRT and VMAT Planning for Lung Cancer Patients Treated SBRT
Authors: Qin Y , Chetty I 
Published: July 2016

Purpose:To evaluate the dosimetric impact of target volume overrides on the quality of IMRT and VMAT lung, SBRT treatment plans.Methods:Ninety one patients previously treated with lung SBRT at our institution were retrospectively studied. IMRT and VMAT plans were created on 5 image sets for each patient: free breathing scans(FB), average scans(AVE), average scan with internal target volume overridden to tumor density(ITVoverride), average scan with planning target volume overridden(PTVoverride), and a hybrid method where the internal target volume was set to tumor density and the set‐up margin was set to an intermediate density between lung and tumor(HBoverride). All plans were optimized with the same constraints as the original clinical plan AVE. Dose fractionation scheme included 12Gyx4, 10Gyx4, 8Gyx4, 12Gyx3, and 9Gyx5. EQD2 was computed for various target metrics (mean, D1%, D99%) and normal lung metrics (V5Gy, V20Gy, mean lung dose). Plan quality was investigated via conformity index (CI) and gradient index (GI).Results:The ITVoverride plans achieved the highest mean target EQD2(0.38±0.69Gy over AVE) and the highest D1% hotspot(0.73±1.17Gy over AVE) in comparison to all other plans. PTVoverride and HBoverride also demonstrated higher mean target EQD2 than AVE, but lower hotspots. Compared to AVE, PTVoverride and HBoverride resulted in lower coldspots of −9.95±3.78Gy and −9.91±3.68Gy respectively. All override plans achieved lower lung metrics than the AVE plans, with the largest reductions in PTVoverride (−0.31±0.30Gy for V20Gy, −0.44±0.44Gy for V5Gy, −0.23±0.18Gy for mean lung dose). Comparing FB (largest CI,GI) to PTVoverride (smallest CI,GI), CI and GI improved from 1.05 to 1.00, and 4.81 to 4.48 respectively. The differences in these metrics did not correlate with tumor motion or target volume.Conclusion:Despite the improvements in CI and GI, density overrides in target volumes for 91 lung SBRT patients showed limited dosimetric advantages over clinical plans on the average CT.
SU‐F‐T‐545: Dosimetric and Radiobiological Evaluation of Dose Calculation Algorithms On Prostate Stereotactic Body Radiotherapy Using Conventional Flattened and Flattening‐Filter‐Free Beam
Authors: Kang S , Chung J , Eom K , Lee J , Suh T 
Published: July 2016

Purpose:The purpose of this study is to evaluate the dosimetric and radiobiological impact of Acuros XB (AXB) and Anisotropic Analytic Algorithm (AAA) dose calculation algorithms on prostate stereotactic body radiation therapy plans with both conventional flattened (FF) and flattening‐filter free (FFF) modes.Methods:For thirteen patients with prostate cancer, SBRT planning was performed using 10‐MV photon beam with FF and FFF modes. The total dose prescribed to the PTV was 42.7 Gy in 7 fractions. All plans were initially calculated using AAA algorithm in Eclipse treatment planning system (11.0.34), and then were re‐calculated using AXB with the same MUs and MLC files. The four types of plans for different algorithms and beam energies were compared in terms of homogeneity and conformity. To evaluate the radiobiological impact, the tumor control probability (TCP) and normal tissue complication probability (NTCP) calculations were performed.Results:For PTV, both calculation algorithms and beam modes lead to comparable homogeneity and conformity. However, the averaged TCP values in AXB plans were always lower than in AAA plans with an average difference of 5.3% and 6.1% for 10‐MV FFF and FF beam, respectively. In addition, the averaged NTCP values for organs at risk (OARs) were comparable.Conclusion:This study showed that prostate SBRT plan were comparable dosimetric results with different dose calculation algorithms as well as delivery beam modes. For biological results, even though NTCP values for both calculation algorithms and beam modes were similar, AXB plans produced slightly lower TCP compared to the AAA plans.
SU‐F‐T‐546: A Radiobiological Comparative Study of Robotic and LINAC‐Based Lung SBRT
Authors: Roth T , Rankine L , Schreiber E , Das S , Mavroidis P 
Published: July 2016

Purpose:To expand the dosimetric comparison of CyberKnife and Elekta Versa HD regarding their capability to perform SBRT in lung cases by including radiobiological measures, which can estimate the clinical impact of the observed differences.Methods:This study analyzes treatment data of 10 patients, who were treated with SBRT on Elekta Versa HD and replanned using CyberKnife. The original structure sets from the RayStation treatment plans were transferred to MultiPlan and were used for planning, with the exception of the PTV. Special attention was given to the following structures during optimization in MultiPlan: PTV (expanded off GTV instead of ITV), ipsilateral and contralateral lungs, and chest wall. For each patient, the same dosimetric constraints were applied to both plans. The dose volume histograms (DVH) of the targets and organs at risk (OAR) were computed and used to compare the dosimetric differences between the two modalities. Additionally, the tumor control probability (TCP), normal tissue complication probability (NTCP) and complication‐free tumor control probability (P+) radiobiological indices were calculated and compared.Results:The dosimetric indices show a negligible differences (Versa – CK) for the PTV (mean dose difference of 1.7 Gy and average minimum dose difference of −0.3 Gy). For the OARs, the average differences in mean and maximum doses, which varied between 0.4 to 1.7 Gy and 1.1 to 4.7Gy, respectively. The average differences in the radiobiological indices were also similar TCP = 0.3±0.6%, Composite NTCP = 2.4±2.9%, and P+ = −.1±3.3%, respectively.Conclusion:Both modalities managed to meet the same dosimetric goals equally well. The similarities between the dosimetric and radiobiological indices indicate that the two treatment modalities are comparable. A larger patient cohort involving patients of different complexities would give a better insight for this comparison.
SU‐F‐T‐550: Radiochromic Plastic Thin Sheet Dosimeter: Initial Performance
Authors: Jordan K , Adamovics J 
Published: July 2016

Purpose:Thin sheets, of a high sensitivity formulation of radiochromic dosimeter, Presage were prepared and evaluated for optical readout.Methods:Sheets of radiochromic polyurethane, 12 cm long, 10 cm wide and 0.2 cm thick were prepared with leuco crystal violet as the reporter molecule. Sample transmission was evaluated at a wavelength of 590 nm with in‐house constructed instruments: optical cone beam laser CT scanner, fixed and scanning spot densitometers. Sample sequential irradiations to a total dose of 40 Gy were conducted with a modified, Theratron 60, cobalt radiotherapy machine at dose rates of 1 or 0.25 Gy per minute. Exposure to ambient and readout light was minimized to limit background photochromic signals. Samples were stored at 4°C. Optical activity was assessed from linearly polarized transmission images. Comparison sensitivity measurements with EBT3 film were conducted.Results:Samples were transparent, smooth and pale purple before irradiation. Radiochromic reaction was completed in less than 5 minutes. A linear dose response with a sensitivity of 0.5 cm‐1Gy‐1 was observed. Micrometer measurements found sheet thickness variations up to 20%. Uniform dose, 2 Gy attenuation images, correlated with local sheet thicknesses. Comparable measurements with EBT3 film were 3 times more sensitive at 1 Gy but above 15 Gy, EBT3 film had lower sensitivity than 0.2 cm thick Presage sheet dosimeter due to its non‐linear response.Conclusion:Dose sensitivity provided a 10% decrease in transmission for a 1 Gy dose. Improvements in mold design are expected to allow production of sheets with less than 5% variation in thickness. Above, 10 Gy, Presage sheet dosimeter performance expected to exceed EBT3 film based on linearity, sensitivity, transparency and smoothness of samples.J Adamovics is owner of Heuris Inc
SU‐F‐T‐552: A One‐Year Evaluation of the QABeamChecker+ for Use with the CyberKnife System
Authors: Gersh J 
Published: July 2016

Purpose:By attaching an adapter plate with fiducial markers to the QA BeamChecker+ (Standard Imaging, Inc., Middleton, WI), the output of the CyberKnife can be accurately, efficiently, and consistently evaluated. The adapter plate, known as the Cutting Board, allows for automated alignment of the QABC+ using the CK's stereoscopic kV image‐based treatment localization system (TLS). Described herein is an evaluation of the system following a year of clinical utilization.Methods:Based on a CT scan of the QABC+ and CB, a treatment plan is generated which delivers a beam to each of the 5 plane‐parallel ionization chambers. Following absolute calibration of the CK, the QA plan is delivered, and baseline measurements are acquired (and automatically corrected for temperature and pressure). This test was performed at the beginning of each treatment day for a year. A calibration evaluation (using a water‐equivalent slab and short thimble chamber) is performed every four weeks, or whenever the QABC+ detects a deviation of more than 1.0%.Results:During baseline evaluation, repeat measurements (n=10) were performed, with an average output of 0.25% with an SD of 0.11%. As a test of the reposition of the QABC+ and CB, ten additional measurements were performed where between each acquisition, the entire system was removed and re‐positioned using the TLS. The average output deviation was 0.30% with a SD of 0.13%. During the course of the year, 187 QABC+ measurements and 13 slab‐based measurements were performed. The output measurements of the QABC+ correlated well with slab‐based measurements (R2=0.909).Conclusion:By using the QABC+ and CB, daily output was evaluated accurately, efficiently, and consistently. From setup to break‐down (including analysis), this test required 5 minutes instead of approximately 15 using traditional techniques (collimator‐mounted ionization chambers). Additionally, by automatically saving resultant output deviation to a database, trend analysis was simplified.Spectrum Medical Physics, LLC of Greenville, SC has a consulting contract with Standard Imaging of Middleton, WI
SU‐F‐T‐556: A Potential Real Time AQA for Cyberknife Cones and MLC Based Treatments
Authors: Shang C , Gibbard G , Cole J , Schramm A , Leventouri T , Khanal S 
Published: July 2016

Purpose:To investigate the potential use of the Raven™ (LAP of America Laser Applications) for real time AQA of Cyberknife™ with InCise2 MLC (Accuray™ Medical).Methods:At setup, the Raven was rotated 45° on which an Accuray™ AQA cube was positioned. Three different AQA plans for fixed cone, InCise2MLC, and a modified MLC plan were delivered repeatedly ten times. The additional shapes in modified AQA plan enable additional reproducibility checks for all the MLC pairs. During the test, the cube was aligned by imbedded fiducials and irradiated. The two angled radiation beams aimed center tungsten ball of the cube and projected 45° to phosphor screen and registered by a CCD camera of the Raven device. The centricity of the metal ball in the irradiated field was then analyzed using Matlab codes.Results:For AP images, the average offsets of X, Y, and radial directions are 0.24 ± 0.04 mm, 0.25 ± 0.02 mm and 0.35 ±± 0.03 mm respectively for the cone; 0.34 ± 0.02 mm, 0.49 ± 0.04 mm and 0.60 ± 0.04 mm respectively for the MLC. For lateral images, they are 0.63 ± 0.05 mm, 0.11 ± 0.02 mm and 0.64 ± 0.04 mm respectively for the cone, 0.79 ± 0.08 mm, −0.23 ± 0.06 mm and 0.82 ± 0.09 mm respectively for the MLC. No inconsistent MLC shapes were found in the modified AQA group.Conclusion:The results are consistent with clinically acceptable values (≤1mm from baseline). The results suggest the potential of replacement of the standard AQA test with the novel real‐time Raven device for Cyberknife daily QA. The modified MLC based AQA provides a more comprehensive MLC daily QA capability. Further improvements in its resolution and automatic analyzing capability are warranted.
SU‐F‐T‐557: Evaluation of Detector Response in Rectangular Small Field Dosimetry
Authors: Qureshi A , Tanny S , Parsai E , Sperling N 
Published: July 2016

Purpose:As stereotactic treatment modalities grow towards becoming the standard of care, the need for accurate dose computation in small fields is becoming increasingly essential. The purpose of this study is to evaluate the response of different detectors, intended for small field dosimetry, in jaw defined small rectangular fields by analyzing output factors from a stereotactic clinical accelerator.Methods:Two Dosimeters, the Exradin A26 Microionization Chamber (Standard Imaging) and Edge Diode Detector (Sun Nuclear) were used to measure output factors taken on the Varian Edge Stereotactic Linear accelerator. Measurements were taken at 6MV and 6FFF at 10cm depth, 100cm SSD in a 48×48×40cm3 Welhoffer BluePhantom2 (IBA) with X and Y jaws set from 0.6 to 2.0cm. Output factors were normalized to a 5×5cm2 machine‐specific reference field. Measurements were made in the vertical orientation for the A26 and horizontal orientation for both the A26 and Edge. Output factors were measured as: OFFS = MFS/Mref where MFS and Mref are the measured signals for the clinical field and the reference field, respectively. Measured output factors were then analyzed to establish relative responses of the detectors in small fields.Results:At 6MV the Edge detector exhibited a variation in output factors dependent on jaw positioning (X‐by‐Y vs Y‐by‐X) of 5.7% of the 5×5cm reference output and a variation of 3.33% at 6FFF. The A26 exhibited variation of output factor dependent on jaw positioning of upto 7.7% of the 5×5cm reference field at 6MV and upto 5.33% at 6FFF.Conclusion:Both the Edge detector and A26 responded as expected at small fields however a dependence on the jaw positioning was noted. At 6MV and 6FFF the detector response showed an increased dependence on the positioning of the X jaws as compared to the positioning of the Y jaws.