bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐419: Evaluation of PlanIQ Feasibility DVH as Planning Objectives for Skull Base SBRT Patients
Authors: Jiang W , Wang H , Chi P 
Published: July 2016

Purpose:PlanIQ(Sun Nuclear Corporation) can provide feasibility measures on organs‐at‐risk(OARs) around the target based on depth, local anatomy density and energy of radiation beam used. This study is to test and evaluate PlanIQ feasibility DVHs as optimization objectives in the treatment planning process, and to investigate the potential to use them in routine clinical cases to improve planning efficiency.Methods:Two to three arcs VMAT Treatment plans were generated in Pinnacle based on PlanIQ feasibility DVH for six skull base patients who previously treated with SBRT. The PlanIQ feasibility DVH for each OAR consists of four zones – impossible (at 100% target coverage), difficult, challenging and probable. Constrains to achieve DVH in difficult zone were used to start plan optimization. Further adjustment was made to improve coverage. The plan DVHs were compared to PlanIQ feasibility DVH to assess the dose received by 0%(D0), 5%(D5), 10%(D10) and 50%(D50) of the OAR volumes.Results:A total of 90 OARs were evaluated for 6 patients (mean 15 OARs, range 11–18 OARs). We used >98% PTV coverage as planning goal since it's difficult to achieve 100% target coverage. For the generated plans, 96.7% of the OARs achieved D0 or D5 within difficult zone or impossible zone (ipsilateral OARs 93.5%, contralateral OARs 100%), while 90% and 65.6% of the OARs achieved D10 and D50 within difficult zone, respectively. Seventeen of the contralateral and out of field OARs achieved DVHs in impossible zone. For OARs adjacent or overlapped with target volume, the D0 and D5 are challenging to be optimized into difficult zone. All plans were completed within 2–4 adjustments to improve target coverage and uniformity.Conclusion:PlanIQ feasibility tool has the potential to provide difficult but achievable initial optimization objectives and therefore reduce the planning time to obtain a well optimized plan.
SU‐F‐T‐429: Craniospinal Irradiation by VMAT Technique: Impact of FFF Beam and High Resolution MLC On Plan Quality
Authors: Ganesh T , Sarkar B , Munshi A , Mohanti B 
Published: July 2016

Purpose:Objective of this study was to evaluate the impact of using flattening filter free (FFF) beam with 0.5 cm multileaf collimator (MLC) leaves over conventional flattened beam with 1 cm leaf width MLC on the treatment plan quality in cranio‐spinal irradiation (CSI).Methods:For five medulloblastoma cases (3 males and 2 females), who were previously treated by volumetric modulated arc therapy (VMAT) technique using conventional flattened beam shaped by 1 cm width MLC leaves, four test plans were generated and compared against the delivered plan. These retrospective plans consisted of four different combinations of flattened and FFF beams from Elekta's Agility treatment head with 0.5 cm width MLC leaves. Sparing of organs at risks (OAR) in terms of dose to 5%, 50%, 75% and 90% volumes, mean and maximum dose were evaluated.Results:All plans satisfied the planning objective of covering 95% of PTV by at least 95% of prescription dose. Marginal variation of dose spillage was observed between different VMAT plans at very low dose range (1–5 Gy). Variation in dose statistics for PTVs and OARs were within 1% or 1 Gy. Amongst the five plans, the plan with flattened beam with 1 cm MLC had the highest number of MUs, 2.13 times higher than the plan with Agility MLC with FFF beam that had the least number of MUs. No statistically significant difference (p≥0.05) was observed between the reference plan and the retrospectively generated plans in terms of PTV coverage, cold spot, hot spot and organ at risk doses.Conclusion:In the treatment of CSI cases by VMAT technique, FFF beams and/or finer width MLC did not exhibit advantage over the flattened beams or wider MLC in terms of plan quality except for reduction in MUs.
SU‐F‐T‐438: A Practical Technique to Avoid the Radioactive Otitis Media in Whole Brain Radiotherapy
Authors: Duan J 
Published: July 2016

Purpose:Radioactive otitis media is a common complication in whole brain radiotherapy. In this study, we present a practical technique to avoid the injury for whole brain radiotherapy patients.Methods:For this study, 10 whole brain radiotherapy patients with planning CT were selected. For the target, 40Gy/20fractions was prescribed. In the treatment planning, two opposing lateral fields were used, from the left and right side of the patient. The MLC (0.5cm width) was used to shape the fields around the brain with a 10 mm margin to allow for the beam penumbra. For 5 patients, six leafs were positioned to block the auris media. For other patients, there were no leafs blocked to auris media according to the routine technique. The target coverage and the mean dose of the auris media were evaluated to assess the new technique in avoiding the radioactive otitis media.Results:The target coverage of new technique decreased by 1.7% (97.6%±1.1% vs. 99.3%±0.5%) compared routine technique. The mean dose of left auris media decreased by 79% (7.92 Gy±0.81Gy vs. 37.82 Gy±2.33Gy). The mean dose of right auris media decreased by 77% (8.8 Gy±0.93Gy vs. 38.4 Gy±2.65Gy). There was no difference for other OARs.Conclusion:An excellent sparing of the auris media is achievable while maintaining high coverage to the target volume. The simple technique to deliver whole brain may avoid the radioactive otitis media prospectively.
SU‐F‐T‐448: Use of Mixed Photon Energy Beam in Volumetric Modulated Arc Therapy (VMAT) Treatment Plan for Prostate Cancer
Authors: Manigandan D , Kumar M , Mohandas P , Puri A , Bhalla N 
Published: July 2016

Purpose:To study the impact of different photon beam combination during VMAT planning and treatment delivery.Methods:Five prostate patients with no nodal involvement were chosen for the study and only prostate was considered as target (7920cGy/44fractions). In each case, three different VMAT plans were generated with two arcs (200°–160°&160°–200°). First plan used only 6MV in both arcs (6X‐6X) and second utilized 6MV&15MV (6X‐15X), whereas third one used 15MV&15MV (15X‐15X). For consistency, all the plans were generated by the same planner using Monaco− treatment planning system (V5.1) for Elekta Synergy− linear accelerator with 1cm leaf‐width. For plan comparison, target mean dose, conformity index (CI)=Planning target volume (PTV) covered by 95% of prescription dose/PTV were analyzed. Mean doses of bladder, rectum, left femur and right femur were analyzed. Integral dose (liter‐Gray) to normal tissue (patient volume minus PTV), total monitor unit (MU) required to deliver a plan and gamma pass rate for each plan was analyzed.Results:The CI for PTV was 0.9937±0.0037, 0.9917±0.0033, and 0.9897±0.0048 for 6X‐6X, 6X‐15X and 15X‐15X, respectively. Mean dose to target slightly increases with the decrease of energy. Mean doses to bladder were 3546.23±692.13cGy, 3487.43±715.53cGy and 3504.40±683.1cGy for 6X‐6X, 6X‐15X and 15X‐15X, respectively. Mean doses to rectum were 4294.60±309.5cGy, 4277.07±279.93cGy and 4290.77±379.07cGy. Mean doses to left femur were 2737.13±545.93cGy, 2668.67±407.12cGy and 2416.77±300.73cGy and mean doses to the right femur were 2682.70±460.81cGy, 2722.58±541.92cGy and 2598.57±481.83cGy. Higher Integral doses to normal tissue observed for 6X‐6X (163.06±24.6 Litre‐Gray) followed by 6X‐15X (154.35±24.74 Litre‐Gray) and 15X‐15X (145.84±26.03 Litre‐Gray). Average MU required to deliver one fraction was 680.75±72.09, 634.81±95.07 and 605.06±114.65. Gamma pass rates were 99.83±0.21, 99.53±0.27 and 99.2±0.20.Conclusion:6X‐15X VMAT plan offer dosimetric advantage compared to 6X‐6X in terms of lesser MU and integral dose without significant compromise in plan quality, where as in 15X‐15X, neutron contamination risk is relatively higher.
SU‐F‐T‐457: A Filmless Method for Measurement of Couch Translation Per Gantry Rotation and Couch Speed for Tomotherapy Using ArcCheck
Authors: Yang B , Wong R , Geng H , Lam W , Cheung K , Yu S 
Published: July 2016

Purpose:To develop a filmless methodology based on an ArcCheck for QA measurement of the couch translation per gantry rotation and couch speed of a Tomotherapy unit.Methods:Two test plans recommended by TG148 were chosen for this study. A helical plan with 1 cm field size opened the leaves for 180 degrees at the 2nd, 7th and 12th of total 13 rotations and was used to verify if the couch travelled the expected distance per gantry rotation. The other test plan was a static plan with the gantry at 0°, 1cm field width and constant couch movement speed of 0.5mm/s. It was used for couch speed measurement. The ArcCheck was isocentrically set up and recorded movie files which took a snapshot exposure every 50ms. Due to the spiral pattern of diodes distribution, when one of the diodes of the ArcCheck located at the beam center, the dose profile as measured by the row of diodes which surrounded the center diode should have a symmetrical pattern. We divided the profile into left half A and right half B. Then a shape parameter was defined as S=Σ|(A−B)|/Σ(A+B). By searching the local minimum of S parameter, the beam center at different time could be located. The machine trajectory log data were also collected and analyzed for comparison.Results:The mean value of measured couch translation and couch speed by ArcCheck had less than 0.05% deviation from the planned values. For couch speed measurement, our result showed a mean value of 0.5002 with an uncertainty ±0.0031, which agreed very well with both the plan setting of 0.5 mm/s and the machine log data of 0.5005 mm/s.Conclusion:Couch translation measured using ArcCheck is accurate and comparable to the film‐based measurement. This filmless method also provides a convenient and independent way for measuring couch speed.
SU‐F‐T‐469: A Clinically Observed Discrepancy Between Image‐Based and Log‐ Based MLC Position
Authors: Neal B , Ahmed M , Siebers J 
Published: July 2016

Purpose:To present a clinical case which challenges the base assumption of log‐file based QA, by showing that the actual position of a MLC leaf can suddenly deviate from its programmed and logged position by >1 mm as observed with real‐time imaging.Methods:An EPID‐based exit‐fluence dosimetry system designed to prevent gross delivery errors was used in cine mode to capture portal images during treatment. Visual monitoring identified an anomalous MLC leaf pair gap not otherwise detected by the automatic position verification. The position of the erred leaf was measured on EPID images and log files were analyzed for the treatment in question, the prior day's treatment, and for daily MLC test patterns acquired on those treatment days. Additional standard test patterns were used to quantify the leaf position.Results:Whereas the log file reported no difference between planned and recorded positions, image‐based measurements showed the leaf to be 1.3±0.1 mm medial from the planned position. This offset was confirmed with the test pattern irradiations.Conclusion:It has been clinically observed that log‐file derived leaf positions can differ from their actual positions by >1 mm, and therefore cannot be considered to be the actual leaf positions. This cautions the use of log‐based methods for MLC or patient quality assurance without independent confirmation of log integrity. Frequent verification of MLC positions through independent means is a necessary precondition to trusting log file records. Intra‐treatment EPID imaging provides a method to capture departures from MLC planned positions.Work was supported in part by Varian Medical Systems.
SU‐F‐T‐471: Simulated External Beam Delivery Errors Detection with a Large Area Ion Chamber Transmission Detector
Authors: Hoffman D , Dyer B , Kumaran Nair C , Stern R , Benedict S , Davis UC 
Published: July 2016

Purpose:The Integral Quality Monitor (IQM), developed by iRT Systems GmbH (Koblenz, Germany) is a large‐area, linac‐mounted ion chamber used to monitor photon fluence during patient treatment. Our previous work evaluated the change of the ion chamber's response to deviations from static 1×1 cm2 and 10×10 cm2 photon beams and other characteristics integral to use in external beam detection. The aim of this work is to simulate two external beam radiation delivery errors, quantify the detection of simulated errors and evaluate the reduction in patient harm resulting from detection.Methods:Two well documented radiation oncology delivery errors were selected for simulation. The first error was recreated by modifying a wedged whole breast treatment, removing the physical wedge and calculating the planned dose with Pinnacle TPS (Philips Radiation Oncology Systems, Fitchburg, WI). The second error was recreated by modifying a static‐gantry IMRT pharyngeal tonsil plan to be delivered in 3 unmodulated fractions. A radiation oncologist evaluated the dose for simulated errors and predicted morbidity and mortality commiserate with the original reported toxicity, indicating that reported errors were approximately simulated. The ion chamber signal of unmodified treatments was compared to the simulated error signal and evaluated in Pinnacle TPS again with radiation oncologist prediction of simulated patient harm.Results:Previous work established that transmission detector system measurements are stable within 0.5% standard deviation (SD). Errors causing signal change greater than 20 SD (10%) were considered detected. The whole breast and pharyngeal tonsil IMRT simulated error increased signal by 215% and 969%, respectively, indicating error detection after the first fraction and IMRT segment, respectively.Conclusion:The transmission detector system demonstrated utility in detecting clinically significant errors and reducing patient toxicity/harm in simulated external beam delivery. Future work will evaluate detection of other smaller magnitude delivery errors.
SU‐F‐T‐477: Investigation of DEFGEL Dosimetry Using MRI
Authors: Matrosic C , McMillan A , Holmes J , Bednarz B , Culberson W 
Published: July 2016

Purpose:The DEFGEL dosimeter/phantom allows for the measurement of 3D dose distributions while maintaining tissue equivalence and deformability. Although DEFGEL is traditionally read out with optical CT, the use of MRI would permit the measurement of 3D dose distributions in optically interfering configurations, like while embedded in a phantom. To the knowledge of the authors, this work is the first investigation that uses MRI to measure dose distributions in DEFGEL dosimeters.Methods:The DEFGEL (6%T) formula was used to create 1 cm thick, 4.5 cm diameter cylindrical dosimeters. The dosimeters were irradiated using a Varian Clinac 21EX linac. The MRI based transverse relaxation rate (R2) of the gel was measured in a central slice of the dosimeter with a Spin‐Echo (SE) pulse sequence on a 3T GE SIGNA PET/MR scanner. The R2 values were fit to a monoexponential dose response equation using in‐house software (MATLAB).Results:The data was well fit using a monoexponential fit for R2 as a function of absorbed dose (R2 = 0.9997). The fitting parameters of the monoexponential fit resulted in a 0.1229 Gy−1s−1 slope. The data also resulted in an average standard deviation of 1.8% for the R2 values within the evaluated ROI.Conclusion:The close fit for the dose response curve shows that a DEFGEL based dosimeter can be paired with a SE MRI acquisition. The Type A uncertainty of the MRI method shows adequate precision, while the slope of the fit curve is large enough that R2 differences between different gel doses are distinguishable. These results suggest that the gel could potentially be used in configurations where an optical readout is not viable, such as measurements with the gel dosimeter positioned inside larger or optically opaque phantoms.This work is partially funded by NIH grant R01CA190298.
SU‐F‐T‐478: Effect of Deconvolution in Analysis of Mega Voltage Photon Beam Profiles
Authors: Muthukumaran M , Manigandan D , Murali V , Chitra S , Vikraman S , Ganapathy K 
Published: July 2016

Purpose:To study and compare the penumbra of 6 MV and 15 MV photon beam profiles after deconvoluting different volume ionization chambers.Methods:0.125cc Semi‐Flex chamber, Markus Chamber and PTW Farmer chamber were used to measure the in‐plane and cross‐plane profiles at 5 cm depth for 6 MV and 15 MV photons. The profiles were measured for various field sizes starting from 2×2 cm till 30×30 cm. PTW TBA scan software was used for the measurements and the “deconvolution” functionality in the software was used to remove the volume averaging effect due to finite volume of the chamber along lateral and longitudinal directions for all the ionization chambers. The predicted true profile was compared and the change in penumbra before and after deconvolution was studied.Results:After deconvoluting the penumbra decreased by 1 mm for field sizes ranging from 2 × 2 cm till 20 x20 cm. This is observed for along both lateral and longitudinal directions. However for field sizes from 20 × 20 till 30 ×30 cm the difference in penumbra was around 1.2 till 1.8 mm. This was observed for both 6 MV and 15 MV photon beams. The penumbra was always lesser in the deconvoluted profiles for all the ionization chambers involved in the study. The variation in difference in penumbral values were in the order of 0.1 till 0.3 mm between the deconvoluted profile along lateral and longitudinal directions for all the chambers under study. Deconvolution of the profiles along longitudinal direction for Farmer chamber was not good and is not comparable with other deconvoluted profiles.Conclusion:The results of the deconvoluted profiles for 0.125cc and Markus chamber was comparable and the deconvolution functionality can be used to overcome the volume averaging effect.
SU‐F‐T‐480: Evaluation of the Role of Varian Machine Performance Check (MPC) in Our Daily QA Routine
Authors: Juneja B , Gao S , Balter P , Nitsch P 
Published: July 2016

Purpose:(A) To assess the role of Varian MPC in our daily QA routine, and (B) evaluate the accuracy and precision of MPC.Methods:The MPC was performed weekly, for five months, on a Varian TrueBeam for five photon (6x, 10x, 15x, 6xFFF, and 10xFFF) and electron (6e, 9e, 12e, 16e, and 20e) energies. Output results were compared to those determined with an ionization chamber (TN30001, PTW‐Freiburg) in plastic and a daily check device (DQA3, Sun Nuclear). Consistency of the Mechanical measurements over five months was analyzed and compared to monthly IsoCal results.Results:The MPC randomly showed large deviations (3–7%) that disappeared upon reacquisition. The MPC output closely matched monthly ion chamber and DQA3 measurements. The maximum and mean absolute difference between monthly and MPC was 1.18% and 0.28±0.21% for all energies. The maximum and mean absolute difference between DQA3 and MPC was 3.26% and 0.85±0.61%. The results suggest the MPC is comparable to the DQA3 for measuring output. The DQA3 provides wedge output, flatness, symmetry, and energy constancy checks, which are missing from the current implementation of the MPC. However, the MPC provides additional mechanical tests, such as size of the radiation isocenter (0.33±0.02 mm) and its coincidence with MV and kV isocenters (0.17±0.05 and 0.21±0.03 mm). It also provides positional accuracy of individual jaws (maximum σ, 0.33mm), all the MLC leaves (0.08mm), gantry (0.05°) and collimator (0.13°) rotation angles, and couch positioning (0.11mm) accuracy. MPC mechanical tests could replace our current daily on‐board imaging QA routine and provide some additional QA not currently performed.Conclusion:MPC has the potential to be a valuable tool that facilitates reliable daily QA including many mechanical tests that are not currently performed. This system can add to our daily QA, but further development would be needed to fully replace our current Daily QA device.
SU‐F‐T‐481: Physics Evaluation of a Newly Released InCise™ Multileaf Collimator for CyberKnife M6™ System
Authors: Wang L , Chin E , Lo A 
Published: July 2016

Purpose:This work reports the results of the physics evaluation of a newly released InCise™2 Multileaf Collimator (MLC) installed in our institution.Methods:Beam property data was measured with unshielded diode and EBT2 films. The measurements included MLC leaf transmission, beam profiles, output factors and tissue‐phantom ratios. MLC performance was evaluated for one month after commissioning. Weekly Garden Fence tests were performed for leaf / bank positioning in standard (A/P) and clinically relevant non‐standard positions, before and after MLC driving exercises of 10+ minutes. Daily Picket Fence test and AQA test, End‐to‐End tests and dosimetric quality assurance were performed to evaluate the overall system performance.Results:All measurements including beam energy, flatness and symmetry, were within manufacture specifications. Leaf transmission was 0.4% <0.5% specification. The values of output factors ranged from 0.825 (7.6 mm × 7.5 mm) to 1.026 (115.0 mm × 100.1 mm). Average beam penumbra at 10 cm depth ranged from 2.7mm/2.7mm(7.6 mm × 7.5 mm) to 6.0 mm/6.2mm(84.6 mm × 84.7 mm). Slight penumbra difference (<10% from average penumbra for fields >20 mm) was observed in the direction perpendicular to leaf motion due to the tilting of the leaf housing. Mean leaf position offsets was −0.08±0.07mm and −0.13 ± 0.08 for X1 and X2 leaf banks in 13 Garden Fence tests. No significant difference on average leaf positioning offsets was observed between different leaf orientations and before/after MLC driving exercises. Six End‐to‐End tests showed 0.43±0.23mm overall targeting accuracy. Picket‐Fence and AQA showed stable performance of MLC during the test period. Dosimetric point dose measurements for test cases agreed with calculation within 3%. All film measurements on relative dose had Gamma (2%, 2mm) passing rate of >95%.Conclusion:The Incise™2 MLC for CyberKnife M6™ was proven to be accurate and reliable, and it is currently in clinical use.Stanford was one of the physics evaluation sites for the newly released InCise 2 MLC for Accuray Inc.