bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐428: Dosimetric Impact of Multileaf Collimator Leaf Width On Single and multiple Isocenter Stereotactic IMRT Treatment Plans for multiple Brain Tumors
Authors: Giem J , Algan O , Ahmad S , Ali I , Young J , Hossain S 
Published: July 2014

Purpose:To assess the impacts that multileaf collimator (MLC) leaf width has on the dose conformity and normal brain tissue doses of single and multiple isocenter stereotactic IMRT (SRT) plans for multiple intracranial tumors.Methods:Fourteen patients with 2–3 targets were studied retrospectively. Patients treated with multiple isocenter treatment plans using 9 to 12 non‐coplanar beams per lesion underwent repeat planning using single isocenter and 10 to 12 non‐coplanar beams with 2.5mm, 3mm and 5mm MLC leaf widths. Brainlab iPlan treatment planning system for delivery with the 2.5mm MLC served as reference. Identical contour sets and dose‐volume constraints were applied. The prescribed dose to each target was 25 Gy to be delivered over 5 fractions with a minimum of 99% dose to cover ≥ 95% of the target volume.Results:The lesions and normal brains ranged in size from 0.11 to 51.67cc (median, 2.75cc) and 1090 to 1641cc (median, 1401cc), respectively. The Paddick conformity index for single and multiple isocenter (2.5mm vs. 3mm and 5mm MLCs) was (0.79±0.08 vs. 0.79±0.07 and 0.77±0.08) and (0.79±0.09 vs. 0.77±0.09 and 0.76±0.08), respectively. The average normal brain volumes receiving 15 Gy for single and multiple isocenter (2.5mm vs. 3mm and 5mm MLCs) were (3.65% vs. 3.95% and 4.09%) and (2.89% vs. 2.91% and 2.92%), respectively.Conclusion:The average dose conformity observed for the different leaf width for single and multiple isocenter plans were similar, throughout. However, the average normal brain volumes receiving 2.5 to 15 Gy were consistently lower for the 2.5mm MLC leaf width, especially for single isocenter plans. The clinical consequences of these integral normal brain tissue doses are still unknown, but employing the use of the 2.5mm MLC option is desirable at sparing normal brain tissue for both single and multiple isocenter cases.
SU‐E‐T‐429: Uncertainties of Cell Surviving Fractions Derived From Tumor‐Volume Variation Curves
Authors: Chvetsov A 
Published: July 2014

Purpose:To evaluate uncertainties of cell surviving fraction reconstructed from tumor‐volume variation curves during radiation therapy using sensitivity analysis based on linear perturbation theory.Methods:The time dependent tumor‐volume functions V(t) have been calculated using a twolevel cell population model which is based on the separation of entire tumor cell population in two subpopulations: oxygenated viable and lethally damaged cells. The sensitivity function is defined as S(t)=[δV(t)/V(t)]/[δx/x] where δV(t)/V(t) is the time dependent relative variation of the volume V(t) and δx/x is the relative variation of the radiobiological parameter x. The sensitivity analysis was performed using direct perturbation method where the radiobiological parameter x was changed by a certain error and the tumor‐volume was recalculated to evaluate the corresponding tumor‐volume variation. Tumor volume variation curves and sensitivity functions have been computed for different values of cell surviving fractions from the practically important interval S2=0.1‐0.7 using the two‐level cell population model.Results:The sensitivity functions of tumor‐volume to cell surviving fractions achieved a relatively large value of 2.7 for S2=0.7 and then approached zero as S2 is approaching zero Assuming a systematic error of 3‐4% we obtain that the relative error in S2 is less that 20% in the range S2=0.4‐0.7. This Resultis important because the large values of S2 are associated with poor treatment outcome should be measured with relatively small uncertainties. For the very small values of S2<0.3, the relative error can be larger than 20%; however, the absolute error does not increase significantly.Conclusion:Tumor‐volume curves measured during radiotherapy can be used for evaluation of cell surviving fractions usually observed in radiation therapy with conventional fractionation.
SU‐E‐T‐430: Modeling MLC Leaf End in 2D for Sliding Window IMRT and Arc Therapy
Authors: Liang X , Zhu T 
Published: July 2014

Purpose:To develop a 2D geometric model for MLC accounting for leaf end dose leakage for dynamic IMRT and Rapidarc therapy.Methods:Leaf‐end dose leakage is one of the problems for MLC dose calculation and modeling. Dosimetric leaf gap used to model the MLC and to count for leakage in dose calculation, but may not be accurate for smaller leaf gaps. We propose another geometric modeling method to compensate for the MLC round‐shape leaf ends dose leakage, and improve the accuracy of dose calculation and dose verification. A triangular function is used to geometrically model the MLC leaf end leakage in the leaf motion direction, and a step function is used in the perpendicular direction. Dose measurements with different leaf gap, different window width, and different window height were conducted, and the results were used to fit the analytical model to get the model parameters.Results:Analytical models have been obtained for stop‐and‐shoot and dynamic modes for MLC motion. Parameters a=0.4, lw' =5.0 mm for 6X and a=0.54, lw' =4.1 mm for 15x were obtained from the fitting process. The proposed MLC leaf end model improves the dose profile at the two ends of the sliding window opening. This improvement is especially significant for smaller sliding window openings, which are commonly used for highly modulated IMRT plans and arc therapy plans.Conclusion:This work models the MLC round leaf end shape and movement pattern for IMRT dose calculation. The theory, as well as the results in this work provides a useful tool for photon beam IMRT dose calculation and verification.
SU‐E‐T‐431: Vertically‐Oriented Farmer‐Type Chamber for Small‐Field Applications
Authors: Ahmad M , Chu A , Lincoln H , Chen Z , Deng J , Nath R 
Published: July 2014

Purpose:To introduce a non‐conventional measurement setup using Farmer‐type chambers to accommodate several situations of small‐field dose measurements without compromising accuracy. The validation of this technique was demonstrated for photon small‐field output measurements, and electron small‐field percentage depth‐dose (PDD) measurements.Methods:Initial chamber alignment was performed using the conventional (horizontally‐oriented) chamber setup. A PDD was acquired for a 4×4 cm2 field size using this arrangement. This PDD was used as a positional reference for the vertically‐oriented chamber (VOC) configuration. Next, a PDD was acquired for a 4×4 cm2 field size with the VOC. The PDD's were superimposed to find the effective shift of the VOC. Using the shifted VOC setup, photon small‐field output factors were measured and compared to stereotactic diode output factor measurements. Additionally, electron smallfield PDD's were acquired using the VOC setup and results were compared to electron Monte Carlo (eMC) predictions in the Eclipse treatment planning system (TPS).Results:(1) For photon small‐field output factors field‐sizes 2×2 cm2 and larger, the difference between the VOC setup and SFD measurements were less than 0.8%. For field sizes less than 2×2 cm2 discrepancies ranged from 4.0 to 10.6%. (2) PDD's measured by VOC setup show better than 1.6% agreement as compared to eMC for all electron energies measured down to the 80% depth on the 2×2 cm2 PDD curve. Disagreement between the VOC setup measurement and eMC calculations for depths down to the 50% depth on the PDD curve is 3.6% or less.Conclusion:Using the VOC setup, it is possible to use a conventional farmer chamber for small field‐size measurements down to 2×2 cm2 field size without sacrificing the accuracy of measurements.
SU‐E‐T‐432: A Rapid and Comprehensive Procedure for Daily Proton QA
Authors: Zhao T , Sun B , Grantham K , Knutson N , Santanam L , Goddu S , Klein E 
Published: July 2014

Purpose:The objective is to develop a rapid and comprehensive daily QA procedure implemented at the S. Lee Kling Proton Therapy Center at Barnes‐Jewish Hospital.Methods:A scribed phantom with imbedded fiducials is used for checking lasers accuracy followed by couch isocentricity and for X‐ray imaging congruence with isocenter. A Daily QA3 device (Sun Nuclear, FL) was used to check output, range and profiles. Five chambers in the central region possess various build‐ups. After converting the thickness of the inherent build‐ups into water equivalent thickness (WET) for proton, range of any beam can be checked with additional build‐up on the Daily QA3 device. In our procedure, 3 beams from 3 bands (large, small and deep) with nominal range of 20 cm are checked daily. 17cm plastic water with WET of 16.92cm are used as additional build‐up so that four chambers sit on the SOBP plateau at various depths and one sit on the distal fall off. Reading from the five chambers are fitted to an error function that has been parameterized to match the SOBP with the same nominal range. Shifting of the error function to maximize the correlation between measurements and the error function is deemed as the range shift from the nominal value.Results:We have found couch isocentricity maintained over 180 degrees. Imaging system exhibits accuracy in regard to imaging and mechanical isocenters. Ranges are within 1mm accuracy from measurements in water tank, and sensitive to change of sub‐millimeter. Data acquired since the start of operation show outputs, profiles and range stay within 1% or 1mm from baselines. The whole procedure takes about 40 minutes.Conclusion:Taking advantage of the design of Daily QA3 device turns the device originally designed for photon and electron into a comprehensive and rapid tool for proton daily QA.
SU‐E‐T‐433: Calibration Accuracy in Mailed High‐Resolution 3D Dosimetry Service for SRS/SBRT QA
Authors: Maryanski M , Keane J , Zimberg S 
Published: July 2014

Purpose:SRS/SBRT combines hypofractionation with excellent dose distributions. However, extremely steep gradients across the target along with dose escalation, if not administered accurately, may lead to serious complications, recurrences, or even fatalities. Existing commercial QA products either lack adequate spatial resolution or the 3D aspect. By contrast, the new CrystalBall™ mailed high‐resolution 3D dosimetry service removes the above limitations while reducing the overall workload on medical physics staff. The exposed dosimeters, which change optical density in proportion to local dose, are sent back to the manufacturer (MGS Research Inc., Madison, CT) for sub‐millimeter‐resolution laser‐CT scanning and QA data analysis. QA report is returned electronically within 24 hours. The purpose of this study was to evaluate the dose calibration accuracy in this system.Methods:Two spherical CrystalBall™ polymer gel dosimeters from the same batch, 166 mm diameter, with embedded 3D image registration markers, were mounted in a special phantom designed for reproducible positioning. For full end to end testing, the optical guidance array was mounted onto the phantom and a CT was taken. Two separate Rapid Arc SRS plans were designed. Varian Medical Systems optical guidance system was used to position the phantom and the SRS treatment plans were delivered to the two spheres on Varian's Trilogy Accelerator. Exposed dosimeters were mailed back to the manufacturer for laser CT scanning and analysis.Results:For each plan, 3D gamma passing rate was 100% for 2%/2mm distance‐to‐agreement criteria above 50% isodose level. The two calibration curves, generated using volumetric dose and optical density data, showed excellent mutual agreement (max difference 2.2%, median difference 0.75%).Conclusion:The clinical utility of new CrystalBall™ mailed QA service for SRS/SBRT and high accuracy of dose calibration have been validated. The workflow associated with the use of the CrystalBall™ in clinical setting was found to be minimal.The presenting author is the founder of and has an ownership in MGS Research Inc which manufactures the CrystalBall system for 3D dosimetry.
SU‐E‐T‐434: Evaluation of the Machine Performance Check (MPC) Program for Truebeam 2.0
Authors: Chin E , Yu S , Hadsell M , Bush K , Mok E 
Published: July 2014

Purpose:Machine Performance Check (MPC) is a software application used to verify that the TrueBeam machine is operating within major specifications prior to treatment. Used in combination with a phantom named Isocal, it verifies beam output, beam uniformity, treatment isocenter size, coincidence of treatment and imaging isocenters, positioning accuracy of kV and MV imaging systems, accuracy of collimator and gantry rotation angle, positioning accuracy of jaws and MLC leafs, and couch positioning. The tests can be performed semi‐automatically and requires approximately 10 minutes of machine time. It is the purpose of this study to report the performance of this program.Methods:A pre‐release version of the MPC tool was installed on a Truebeam linac with 6D couch at our center. Baseline beam output measurements were taken for 5 photon beams (6–15 MV, 6 FFF, 10 FFF) and 5 electron beams (6–20 MeV). Deviations from the baseline output were subsequently recorded for several days and compared against independent measurements from a PTW farmer chamber and our daily QA device (Fluke Biomedical Tracker) as part of an ongoing evaluation.Results:The beam output deviations between the MPC and the PTW chamber measurements were within ±0.7% for photons beams and ±1.0% for electrons beams. This was similar to the tracker performance. There were some isolated incidents where the MPC measurements had unexplained spikes (>3%) that disappeared on a repeat measurement. MPC was also able to detect maximum positioning errors in the jaws (1.12 mm), MLCs (1.14 mm), and couch roll (0.11°).Conclusion:Overall, the ability of the MPC to monitor linac output stability was comparable to that of ionization chamber‐based measurements. MPC also provided fast daily mechanical tests not currently available in the clinic. How best to utilize this previously unavailable data is still under investigation.
SU‐E‐T‐435: Development and Commissioning of a Complete System for In‐Vivo Dosimetry and Range Verification in Proton Therapy
Authors: Samuel D , Testa M , Schneider R , Park Y , Janssens G , Orban de Xivry J , Moteabbed M , Prieels D , Lu H , Bentefour E 
Published: July 2014

Purpose:In‐vivo dose and beam range verification in proton therapy could play significant roles in proton treatment validation and improvements. Invivo beam range verification, in particular, could enable new treatment techniques one of which, for example, could be the use of anterior fields for prostate treatment instead of opposed lateral fields as in current practice. We have developed and commissioned an integrated system with hardware, software and workflow protocols, to provide a complete solution, simultaneously for both in‐vivo dosimetry and range verification for proton therapy.Methods:The system uses a matrix of diodes, up to 12 in total, but separable into three groups for flexibility in application. A special amplifier was developed to capture extremely small signals from very low proton beam current. The software was developed within iMagX, a general platform for image processing in radiation therapy applications. The range determination exploits the inherent relationship between the internal range modulation clock of the proton therapy system and the radiological depth at the point of measurement. The commissioning of the system, for in‐vivo dosimetry and for range verification was separately conducted using anthropomorphic phantom. EBT films and TLDs were used for dose comparisons and range scan of the beam distal fall‐off was used as ground truth for range verification.Results:For in‐vivo dose measurement, the results were in agreement with TLD and EBT films and were within 3% from treatment planning calculations. For range verification, a precision of 0.5mm is achieved in homogeneous phantoms, and a precision of 2mm for anthropomorphic pelvic phantom, except at points with significant range mixing.Conclusion:We completed the commissioning of our system for in‐vivo dosimetry and range verification in proton therapy. The results suggest that the system is ready for clinical trials on patient.
SU‐E‐T‐436: Accelerated Gated IMRT: A Feasibility Study for Lung Cancer Patients
Authors: Gilles M , Fayad H , Boussion N , Pradier O , Visvikis D 
Published: July 2014

Purpose:To evaluate the feasibility of delivering a gated Intensity Modulated Radiotherapy (IMRT) treatment using multiple respiratory phases in order to account for all anatomic changes during free breathing and accelerate the gated treatment without increasing the dose per fraction.Methods:For 7 patients with lung cancer, IMRT treatment plans were generated on a full inspiration (FI) Computed Tomography (CT) and a Mid Intensity Position (MIP) CT. Moreover, in order to achieve an accelerated gated IMRT, multiple respiratory phase plans were calculated: 2‐phase plans including the FI and the full expiration phases, and 3‐phase plans by adding the mid‐inspiration phase. In order to assess the tolerance limits, plans' doses were registered and summed to the FI‐based plan. Mean dose received by Organs at Risk (OARs) and target volumes were used to compare obtained plans.Results:The mean dose differences between the FI plans and the multi‐phase plans never exceeded 0.4 Gy (Fig. 1). Concerning the clinical target volume these differences were even smaller: less than 0.1 Gy for both the 2‐phase and 3‐phase plans. Regarding the MIP treatment plan, higher doses in different healthy structures were observed, with a relative mean increase of 0.4 to 1.5 Gy. Finally, compared to the prescribed dose, the FI as well as the multi‐phase plans were associated with a mean difference of 0.4 Gy, whereas in the case of MIP a higher mean difference of 0.6 Gy was observed.Conclusion:The doses obtained while planning a multi‐phase gated IMRT treatment were within the tolerance limits. Compared to MIP, a better healthy tissue sparing was observed in the case of treatment planning based on one or multiple phases. Future work will consist in testing the multi‐phase treatment delivery while accounting for the multileaf collimator speed constraints.
SU‐E‐T‐437: Dosimetric Assessment of Brass Mesh Bolus for Postmastectomy Chest Wall Irradiation
Authors: Manger R , Paxton A , Cervino L 
Published: July 2014

Purpose:It has been suggested that the use of a brass mesh bolus for chest wall irradiation sufficiently increases surface dose while having little effect on the dose at depth. This work quantified the increase in surface dose when using a brass mesh bolus in postmastectomy chest wall radiotherapy compared to tissue‐equivalent bolus and assessed its effect on dose at depth.Methods:Percent depth doses with brass bolus, 5mm tissue‐equivalent bolus, and no bolus were determined for a 6 MV photon beam in a solid water phantom using a parallel plate ionization chamber. Gafchromic film was used to determine the surface dose for the same three experimental setups. For comparison to a realistic treatment setup, gafchromic film and OSLDs were used to determine the surface dose over the irradiated area of a 6 MV chest wall plan with tangential beams delivered to a heterogeneous thorax phantom. The plan was generated using a CT of the phantom and delivered using brass mesh bolus, 5mm tissue‐equivalent bolus, and no bolus.Results:For the en face beam, the central surface dose increased to 90% of maximum with the tissue‐equivalent bolus, but to only 62% of maximum with the brass mesh. Using tangential beams on the thorax phantom, the surface dose increased from 40–72% to 75–110% of prescribed dose, with the brass mesh, and to 85–109% with the tissue‐equivalent bolus. At depths beyond dmax in the plastic water phantom, the dose with and without brass mesh bolus differed by less than 0.5%.Conclusion:A brass mesh may be considered as a substitute for tissue‐equivalent bolus to increase the superficial dose of 6 MV chest wall tangent plans. The brass mesh does not significantly change the dose at depth, so a non‐bolus plan could be used for bolus and non‐bolus treatments.
SU‐E‐T‐438: Commissioning of An In‐Vivo Quality Assurance Method Using the Electronic Portal Imaging Device
Authors: Morin O , Held M , Pouliot J 
Published: July 2014

Purpose:Patient specific pre‐treatment quality assurance (QA) using arrays of detectors or film have been the standard approach to assure the correct treatment is delivered to the patient. This QA approach is expensive, labor intensive and does not guarantee or document that all remaining fractions were treated properly. The purpose of this abstract is to commission and evaluate the performance of a commercially available in‐vivo QA software using the electronic portal imaging device (EPID) to record the daily treatments.Methods:The platform EPIgray V2.0.2 (Dosisoft), which machine model compares ratios of TMR with EPID signal to predict dose was commissioned for an Artiste (Siemens Oncology Care Systems) and a Truebeam (Varian medical systems) linear accelerator following the given instructions. The systems were then tested on three different phantoms (homogeneous stack of solid water, anthropomorphic head and pelvis) and on a library of patient cases. Simple and complex fields were delivered at different exposures and for different gantry angles. The effects of the table attenuation and the EPID sagging were evaluated. Gamma analysis of the measured dose was compared to the predicted dose for complex clinical IMRT cases.Results:Commissioning of the EPIgray system for two photon energies took 8 hours. The difference between the dose planned and the dose measured with EPIgray was better than 3% for all phantom scenarios tested. Preliminary results on patients demonstrate an accuracy of 5% is achievable in high dose regions for both 3DCRT and IMRT. Large discrepancies (>5%) were observed due to metallic structures or air cavities and in low dose areas. Flat panel sagging was visible and accounted for in the EPIgray model.Conclusion:The accuracy achieved by EPIgray is sufficient to document the safe delivery of complex IMRT treatments. Future work will evaluate EPIgray for VMAT and high dose rate deliveries.This work is supported by Dosisoft, Cachan, France.