bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐487: On‐Site Beam Matching of An Elekta Infinity with Agility MLC with An Elekta Versa HD
Authors: Nelson C , Garcia M , Mason B , Kirsner S 
Published: July 2016

Purpose:Historically, beam matching of similar Linear Accelerators has been accomplished by sending beam data to the manufacturer to match at their factory. The purpose of this work is to demonstrate that fine beam matching can be carried out on‐site as part of the acceptance test, with similar or better results.Methods:Initial scans of a 10 × 10 Percent depth dose (PDD) and a 40 × 40 beam profile at the depth of Dmax, for 6MV and 10 MV were taken to compare with the standard beam data from the Versa. The energy was then adjusted and the beam steered to achieve agreement between the depth dose and the horns of the beam profile. This process was repeated until the best agreement between PDD and profiles was achieved. Upon completion, all other clinical data were measured to verify match. This included PDD, beam profiles, output factors and Wedge factors. For electron beams PDD's were matched and the beam profiles verified for the final beam energy. Confirmatory PDD and beam profiles for clinical field sizes, as well as Output Factors were measured.Results:The average difference in PDD's for 6MV and 10MV were within 0.4% for both wedged and open fields. Beam profile comparisons over the central 80% of the field, at multiple depths, show agreement of 0.8% or less for both wedged and open fields. Average output factor agreement over all field sizes was 0.4% for 6MV and 0.2 % for 10MV. Wedge factors agreement was less than 0.6% for both photon energies over all field sizes. Electron PDD agreed to 0.5mm. Cone ratios agreed to 1% or less.Conclusion:This work indicates that beam matching can be carried out on‐site simply and quickly. The results of this beam matching can achieve similar or better results than factory matching.
SU‐F‐T‐492: The Impact of Water Temperature On Absolute Dose Calibration
Authors: Islam N , Podgorsak M 
Published: July 2016

Purpose:The Task Group 51 (TG 51) protocol prescribes that dose calibration of photon beams be done by irradiating an ionization chamber in a water tank at pre‐defined depths. Methodologies are provided to account for variations in measurement conditions by applying correction factors. However, the protocol does not completely account for the impact of water temperature. It is well established that water temperature will influence the density of air in the ion chamber collecting volume. Water temperature, however, will also influence the size of the collecting volume via thermal expansion of the cavity wall and the density of the water in the tank. In this work the overall effect of water temperature on absolute dosimetry has been investigated.Methods:Dose measurements were made using a Farmer‐type ion chamber for 6 and 23 MV photon beams with water temperatures ranging from 10 to 40°C. A reference ion chamber was used to account for fluctuations in beam output between successive measurements.Results:For the same beam output, the dose determined using TG 51 was dependent on the temperature of the water in the tank. A linear regression of the data suggests that the dependence is statistically significant with p‐values of the slope equal to 0.003 and 0.01 for 6 and 23 MV beams, respectively. For a 10 degree increase in water phantom temperature, the absolute dose determined with TG 51 increased by 0.27% and 0.31% for 6 and 23 MV beams, respectively.Conclusion:There is a measurable effect of water temperature on absolute dose calibration. To account for this effect, a reference temperature can be defined and a correction factor applied to account for deviations from this reference temperature during beam calibration. Such a factor is expected to be of similar magnitude to most of the existing TG 51 correction factors.
SU‐F‐T‐495: Method for Simultaneous Commissioning of Multiple Truebeam (TB) Linacs: Small Field Data and the Choice of Dosimetric Lead Gap (DLG)
Authors: Mihailidis D , Mallah J 
Published: July 2016

Purpose:Many times a set of multiple Varian‐Truebeam (TB) linacs are acquired by an institution. Since “beam matching” is an important requirement for many facilities, we developed a strategy to perform a “simultaneous” commissioning between multiple linacs.Methods and Materials: We first commissioned the required photon beam data for eclipse on the 1st TB for all the energy modalities with a beam scanning system, while integrated measurements for output factors, of all field sizes (from 1×1 to 40×40cm2) were conducted on the 2nd TB. Care was exercised during small field dosimetry so the appropriate detectors were used with data taken between two detectors be “linked” to a larger field size (4×4cm2) with the “daisy‐chaining” technique via: OF=[M‐PTW(fs)×(M‐PTW(4×4))‐1]×[MA12s(4×4)×(M‐A12S(10×10))−1]. For all energy modalities, data that span the entire range of field size, was repeated on the next TB linac, for verification. The primarily energy‐dependent dosimetric leaf gap (DLG) which was measured separately on each TB. The modeled data was validated with special measurements conducted on both linacs during commissioning.Results:Our data agreed with the “TB representative beam data” to within 0.5% for all energy modalities and field sizes ≥3×3cm2. Sample depth‐doses and cross‐profiles of a 3×3cm2 between the linacs agreeing to within 1% between linacs. The measured DLGs were quite different with a uniform difference of 1.3% between the two linacs. The measured DLG values are independent of the average dose rate and medium used for the measurements.Conclusion:A comprehensive method of commissioning identical Varian‐TB linacs, outlining the critical issues, especially small field dosimetry and DLG. The dosimetric effect of different DLG values, when it comes to, dynamic delivery and data comparisons will be presented. The dependence of DLG value on the measurement medium (in‐air vs. water) or dose rate used will also be discussed.This work was supported by CAMC Cancer Center and Alliance Oncology
SU‐F‐T‐502: FFF Beams, Jaw‐Tracking and Treatment Techniques: Out of Field Dose Considerations for Pediatric Radiation Therapy Delivery
Authors: Ben Bouchta Y , Bergman A 
Published: July 2016

Purpose:To compare the extended dose profile delivered by 3DCRT and VMAT techniques for flattened and flattening‐filter‐free(FFF) photon beams (6X, 6XFFF,10XFFF), with and without jaw‐tracking (JT) on Varian TrueBeam linac. The goal is to determine which treatment technique/modality will minimize the peripheral photon dose exposure (and ultimately minimize the risk of second malignant neoplasms (SMN)) in pediatric patients.Methods:3DCRT, VMAT, and jaw tracking VMAT (JTVMAT) plans with 6X, 6XFFF and 10XFFF x‐ray beams were created on a 30×60×22.5cm solid water phantom with a 551 cc PTV. The 3DCRT plans consisted of a 4FLD arrangement. The optimization objectives for the single‐arc VMAT plans was V95%Rx=98% to PTV and minimize dose to a 5cm diameter organ at risk (OAR). The OAR to PTV distance varied from 0–30cm along the long axis at 7.5cm depth. The dose to the center of the OAR was measured using a 0.6cc ion chamber.Results:Relative to the 6X flattened beam, the 10XFFF photon beam had the lowest dose in the penumbra and peripheral region (>15 cm) region by up to 20% and 40%, respectively for all modalities (3DCRT, VMAT, JTVMAT). The 6XFFF beams only showed a dose reduction in the peripheral region (by up to 20%). JT did not significantly affect the peripheral dose for all modalities and energies.Conclusion:Treating pediatric patients with a 10XFFF beam is the most effective way to reduce photon scatter dose in both the penumbra and peripheral regions. However, the neutron dose contribution resulting from the 10MV beam still needs to be considered. For all modalities, 6XFFF was the next effective method to reduce peripheral photon doses. 3DCRT beams had the lowest peripheral doses for all energies compared to VMAT and JTVMAT, however previous publications have shown that this comes at the expense of PTV conformity and OAR sparing.
SU‐F‐T‐520: Dosimetric Comparison of Radiation Treatment Plans for Whole Breast Irradiation Between 3D Conformal in Prone and Supine Positions Vs. VMAT and IMRT in Supine Positions
Authors: Bejarano Buele A , Parsai E 
Published: July 2016

Purpose:The target volume for Whole Breast Irradiation (WBI) is dictated by location of tumor mass, breast tissue distribution, and involvement of lymph nodes. Dose coverage and Organs at Risk (OARs) sparing can be difficult to achieve in patients with unfavorable thoracic geometries. For these cases, inverse‐planned and 3D‐conformal prone treatments can be alternatives to traditional supine 3D‐conformal plans. A dosimetric comparison can determine which of these techniques achieve optimal target coverage while sparing OARs.Methods:This study included simulation datasets for 8 patients, 5 of whom were simulated in both supine and prone positions. Positioning devices included breast boards and Vaclok bags for the supine position, and prone breast boards for the prone position. WBI 3‐D conformal plans were created for patients simulated in both positions. Additional VMAT and IMRT WBI plans were made for all patients in the supine position.Results:Prone and supine 3D conformal plans had comparable PTV coverage. Prone 3D conformal plans received a significant 50% decrease to V20, V10, V5 and V30% for the ipsilateral lung in contrast to the supine plans. The heart also experienced a 10% decrease in maximum dose in the prone position, and V20, V10, V5 and V2 had significantly lower values than the supine plan. Supine IMRT and VMAT breast plans obtained comparable PTV coverage. The heart experienced a 10% decrease in maximum dose with inverse modulated plans when compared to the supine 3D conformal plan, while V20, V10, V5 and V2 showed higher values with inverse modulated plans than with supine 3D conformal plans.Conclusion:Prone 3D‐conformal, and supine inverse planned treatments were generally superior in sparing OARs to supine plans with comparable PTV coverage. IMRT and VMAT plans offer sparing of OARs from high dose regions with an increase of irradiated volume in the low dose regions.
SU‐F‐T‐554: Dark Current Effect On CyberKnife Beam Dosimetry
Authors: Kim H , Chang A 
Published: July 2016

Purpose:All RF linear accelerators produce dark current to varying degrees when an accelerating voltage and RF input is applied in the absence of electron gun injection. This study is to evaluate how dark current from the linear accelerator of CyberKnife affect the dose in the reference dosimetry.Methods:The G4 CyberKnife system with 6MV photon beam was used in this study. Using the ion chamber and the diode detector, the dose was measured in water with varying time delay between acquiring charges and staring beam‐on after applying high‐voltage into the linear accelerator. The dose was measured after the time delay with over the range of 0 to 120 seconds in the accelerating high‐voltage mode without beam‐on, applying 0, 10, 50, 100, and 200 MUs. For the measurements, the collimator of 60 mm was used and the detectors were placed at the depths of 10 cm with the source‐to‐surface distance of 80 cm.Results:The dark current was constant over time regardless of MU. The dose due to the dark current increased over time linearly with the R‐squared value of 0.9983 up to 4.4 cGy for the time 120 seconds. In the dose rate setting of 720 MU/min, the relative dose when applying the accelerating voltage without beam‐on was increased over time up to 0.6% but it was less than the leakage radiation resulted from the accelerated head. As the reference dosimetry condition, when 100 MU was delivered after 10 seconds time delay, the relative dose increased by 0.7% but 6.7% for the low MU (10 MU).Conclusion:In the dosimetry using CyberKnife system, the constant dark current affected to the dose. Although the time delay in the accelerating high‐voltage mode without beam‐on is within 10 seconds, the dose less than 100 cGy can be overestimated more than 1%.
SU‐F‐T‐555: Accurate Stereotactic Cone TMRs Converted from PDDs Scanned with Ray Trace
Authors: Li H , Zhong H , Qin Y , Snyder K , Chetty I , Wen N 
Published: July 2016

Purpose:To investigate whether the accuracy of TMRs for stereotactic cones converted from PDDs scanned with Ray Trace can be improved, when compared against the TMRs converted from the traditional PDDs.Methods:Ray Trace measurement in Sun Nuclear 3D Scanner is for accurate scan of small field PDDs. The system detects the center of field at two depths, for example, at 3 and 20 cm in our study, and then performs scan along the line passing the two centers. With both Ray Trace and the traditional method, PDDs for conical cones of 4, 5, 7.5, 10, 12.5, 15, and 17.5 mm diameter (jaws set to 5×5 cm) were obtained for 6X FFF and 10X FFF energies on a Varian Edge linac, using Edge detectors. The formalism of converting PDD to TMR given in Khan's book (4th Edition, p.161) was applied. Sp values at dmax were obtained by measuring cone Scp and Sc. Continuous direct measurement of TMR by filling/draining water to/from the tank and spot measurement by moving the tank and detector were also performed with the same equipment, using 100 cm SDD.Results:For 6XFFF energy and all the cones, TMRs converted from Ray Trace were very close to the continuous and spot measurement, while TMRs converted from traditional PDDs had larger deviation. Along the central axis beyond dmax, 1.7% of TMR data points calculated from Ray Trace had more 3% deviation from measurement, with maximal deviation of 5.2%. Whereas, 34% of TMR points calculated from traditional PDDs had more than 3% deviation, with maximum of 5.7%. In this initial study, Ray Trace scans for 10XFFF beam were noisy, further measurement is warranted.Conclusion:The Ray Trace could improve the accuracy of PDDs measurement and the calculated TMRs for stereotactic cones, which was within 3% of the measured TMRs.
SU‐F‐T‐562: Validation of EPID‐Based Dosimetry for FSRS Commissioning
Authors: Song Y , Saleh Z , Obcemea C , Chan M , Tang X , Lim S , Lovelock D , Ballangrud A , Mueller B , Zinovoy M , Gelblum D , Mychalczak B , Both S 
Published: July 2016

Purpose:The prevailing approach to frameless SRS (fSRS) small field dosimetry is Gafchromic film. Though providing continuous information, its intrinsic uncertainties in fabrication, response, scan, and calibration often make film dosimetry subject to different interpretations. In this study, we explored the feasibility of using EPID portal dosimetry as a viable alternative to film for small field dosimetry.Methods:Plans prescribed a dose of 21 Gy were created on a flat solid water phantom with Eclipse V11 and iPlan for small static square fields (1.0 to 3.0 cm). In addition, two clinical test plans were computed by employing iPlan on a CIRS Kesler head phantom for target dimensions of 1.2cm and 2.0cm. Corresponding portal dosimetry plans were computed using the Eclipse TPS and delivered on a Varian TrueBeam machine. EBT‐XD film dosimetry was performed as a reference. The isocenter doses were measured using EPID, OSLD, stereotactic diode, and CC01 ion chamber.Results:EPID doses at the center of the square field were higher than Eclipse TPS predicted portal doses, with the mean difference being 2.42±0.65%. Doses measured by EBT‐XD film, OSLD, stereotactic diode, and CC01 ion chamber revealed smaller differences (except OSLDs), with mean differences being 0.36±3.11%, 4.12±4.13%, 1.7±2.76%, 1.45±2.37% for Eclipse and −1.36±0.85%, 2.38±4.2%, −0.03±0.50%, −0.27±0.78% for iPlan. The profiles measured by EPID and EBT‐XD film resembled TPS (Eclipse and iPlan) predicted ones within 3.0%. For the two clinical test plans, the EPID mean doses at the center of field were 2.66±0.68% and 2.33±0.32% higher than TPS predicted doses.Conclusion:We found that results obtained with EPID portal dosimetry were slightly higher (∼2%) than those obtained with EBT‐XD film, diode, and CC01 ion chamber with the exception of OSLDs, but well within IROC tolerance (5.0%). Therefore, EPID has the potential to become a viable real‐time alternative method to film dosimetry.
SU‐F‐T‐622: Comparative Analysis of Pencil Beam and Anisotropic Analytical Algorithm (AAA) for Stereotactic Body Radiation Therapy (SBRT) of Thoracic Spine
Authors: Badkul R , Nicolai W , Pokhrel D , Ramanjappa T , Jiang H , Wang F , Lominskac C 
Published: July 2016

Purpose:To compare the impact of Pencil Beam(PB) and Anisotropic Analytic Algorithm(AAA) dose calculation algorithms on OARs and planning target volume (PTV) in thoracic spine stereotactic body radiation therapy (SBRT).Methods:Ten Spine SBRT patients were planned on Brainlab iPlan system using hybrid plan consisting of 1–2 non‐coplanar conformal‐dynamic arcs and few IMRT beams treated on NovalisTx with 6MV photon. Dose prescription varied from 20Gy to 30Gy in 5 fractions depending on the situation of the patient. PB plans were retrospectively recalculated using the Varian Eclipse with AAA algorithm using same MUs, MLC pattern and grid size(3mm).Differences in dose volume parameters for PTV, spinal cord, lung, and esophagus were analyzed and compared for PB and AAA algorithms. OAR constrains were followed per RTOG‐0631.Results:Since patients were treated using PB calculation, we compared all the AAA DVH values with respect to PB plan values as standard, although AAA predicts the dose more accurately than PB. PTV(min), PTV(Max), PTV(mean), PTV(D99%), PTV(D90%) were overestimated with AAA calculation on average by 3.5%, 1.84%, 0.95%, 3.98% and 1.55% respectively as compared to PB. All lung DVH parameters were underestimated with AAA algorithm mean deviation of lung V20, V10, V5, and 1000cc were 42.81%,19.83%, 18.79%, and 18.35% respectively. AAA overestimated Cord(0.35cc) by mean of 17.3%; cord (0.03cc) by 12.19% and cord(max) by 10.5% as compared to PB. Esophagus max dose were overestimated by 4.4% and 5cc by 3.26% for AAA algorithm as compared to PB.Conclusion:AAA overestimated the PTV dose values by up to 4%.The lung DVH had the greatest underestimation of dose by AAA versus PB. Spinal cord dose was overestimated by AAA versus PB. Given the critical importance of accuracy of OAR and PTV dose calculation for SBRT spine, more accurate algorithms and validation of calculated doses in phantom models are indicated.
SU‐F‐T‐628: An Evaluation of Grid Size in Eclipse AcurosXB Dose Calculation Algorithm for SBRT Lung
Authors: Pokharel S , Rana S 
Published: July 2016

Purpose:purpose of this study is to evaluate the effect of grid size in Eclipse AcurosXB dose calculation algorithm for SBRT lung.Methods:Five cases of SBRT lung previously treated have been chosen for present study. Four of the plans were 5 fields conventional IMRT and one was Rapid Arc plan. All five cases have been calculated with five grid sizes (1, 1.5, 2, 2.5 and 3mm) available for AXB algorithm with same plan normalization. Dosimetric indices relevant to SBRT along with MUs and time have been recorded for different grid sizes. The maximum difference was calculated as a percentage of mean of all five values. All the plans were IMRT QAed with portal dosimetry.Results:The maximum difference of MUs was within 2%. The time increased was as high as 7 times from highest 3mm to lowest 1mm grid size. The largest difference of PTV minimum, maximum and mean dose were 7.7%, 1.5% and 1.6% respectively. The highest D2‐Max difference was 6.1%. The highest difference in ipsilateral lung mean, V5Gy, V10Gy and V20Gy were 2.6%, 2.4%, 1.9% and 3.8% respectively. The maximum difference of heart, cord and esophagus dose were 6.5%, 7.8% and 4.02% respectively. The IMRT Gamma passing rate at 2%/2mm remains within 1.5% with at least 98% points passing with all grid sizes.Conclusion:This work indicates the lowest grid size of 1mm available in AXB is not necessarily required for accurate dose calculation. The IMRT passing rate was insignificant or not observed with the reduction of grid size less than 2mm. Although the maximum percentage difference of some of the dosimetric indices appear large, most of them are clinically insignificant in absolute dose values. So we conclude that 2mm grid size calculation is best compromise in light of dose calculation accuracy and time it takes to calculate dose.
SU‐F‐T‐639: Use of a 6D Couch for Real‐Time Motion Correction During Frameless Stereotactic Radiosurgery
Authors: Liu X , Belcher AH , Wiersma R 
Published: July 2016

Purpose:High precision patient positioning is critical in stereotactic radiosurgery (SRS). A 6 Degree‐of‐freedom (6D) robotic serial couch has the potential to correct both translational and rotational target motion deviations during image‐guided radiosurgery procedures. An inverse kinematics algorithm based on the structure of the couch is presented, and a feedback control algorithm is discussed. The feasibility of motion compensation with a 6D couch is demonstrated by simulation with prerecorded volunteer head motion data.Methods:The proposed 6D couch motion compensation system included a robotic 6D couch, an image tracking system, and a control computer. For the control, the desired couch top plane was computed based on coordinate frames transformation, and the actuator outputs were calculated by 6D couch inverse kinematics algorithm. During the control, the rotation and translation were coupled, leading to undesired coupling motion of the lesion. Although such coupling was eventually cancelled out, it nonetheless represented unnecessary displacements of the target. An optimal decoupling control algorithm was designed to resolve this problem. The lever effect of the distance of between the target and the pivot of 6D couch roll/pitch were also discussed.Results:The pre‐recorded volunteer head motion data was used in a computer‐based motion compensation simulation, by 6D couch motion compensation, the corrected target was within a 0.3 mm of translational errors and 0.1 degree in the rotational errors about 99.5% of time.Conclusion:We presented an optimal decoupling control algorithm for motion compensation by using a robotic 6D couch. The simulation also showed that reducing the distance between the target and the pivot of roll/pitch of the couch can also improve the accuracy of the compensation. The simulation showed that the 6D robotic system can achieve submillimeter/subdegree position accuracies.